TIr: LSVSCT OF AL-:Y1^3UBJTITUTSiJ PILliG^IC a^hlstvis on thg bo:;dii:g op couglas pip VGiiisi 37 John K. Guihor A Thesis Submitted to the School or Graduate Studies of L-ichigan State College of Agriculture and Aonlied Science in partial fulfillment of tho requirements for the degree of DOCTCa OF PHILOSCrhY Leqartment of Porest Products 1953 J ch n ^ . L h iih cr John K. Guiher The rf: inf0.yf5in o f v r r i m c c nofh oof nine. .fLth. i -cr no .c’. c h y J r i.ivKccvfco'1 f n r . t j — i.oiT’r . dnys eft i ACL-.Cd Jn.jGI_EhTo The author extends his sincere thanks tc Jr. A. J. P'arshin for his ssistance and guidance durin^: the conduct of this investigation. ho "ishes also to e-'orors his amreciation to rroie: scr 1. f. artsuch, — hose guidance in the cher.istry 'hases of the investira.tion as of inestir.able value. Ackncr.viedgr.er.t is gratefully extended to Jr. H. _. Guile \rho nitially r.ade arrangements fcr a ocrtion of the v:ork to be conducted n the lledzie Clerical Laboratory. Th^ v.-riter also desires tc thank nr. ... a. later, fcr invaluable csiscar.cc in the statistical analysis of the data obtained in this o search. In ctdditicn, sincere at reciation is extended to the Graduate cane if cf Lichigsn dtate College for the graduate feilcvship v.iich -vas revised for the 'ast tcc ye:r: ar.d vrhdeh greatly aided the pcssibi.ity f ccmloting this -robler.. Thanhs is extended tc hr. lyvcod V.‘. Sutherland of the United states Corocraticn ana t- lor. 1. ... hall of the Sirnson Legging or an;.’ vrho, together, ra lied the acuglas fir veneer for this grab lee;, ho --alrrat shelf flour used in the areb.-en vrs.s iiir.dly supplied by the chn end Maas Cor.t any through hr. k. E. Goodale, and by the lionsantc lexical Coro;ante through hr. 1. h. harris. I. ii:t u o d u c t i o i -; Tlie use of synthetic resin adliesives for the bonding of wood is relatively recent. Their use in the United ftates dates back to 193b, v:her. a phenol-fornaldehyde resin film adhesive vrns introduced. This period, a total of about 18 years, appears especially short if one considers that the art of gluing wood has been practiced for more than 35 centuries, having had its start in early Egypt. Up to the time of the introduction and use of synthetic resin adhesives for wood bonding, most of the wood glues vrere of animal or vegetable origin. Examples of these are animal glue, wliich is obtained from the hides and bones of animals, starch glue, mainly originating from the roots of the cassava plant, casein glue from the curd of milk, soybean glue, made from soybean meal, and blood albumin from the blood of animals. All of there glues produced acceptable dry wood bonds but were not water resistant. The advent of the synthetic resins as rrood adhesives had a marked effect on commercial wood gluing. extremely water resistant. These adhesives were found to be Urea—formaldehyde adhesives showed some tendency toward hydrolyzing on contact with water, but the phenolic resin adhesives appro ached the point of being waterproof, and vrere not attacked by molds or fungi. This allowed the use of glued—vrood pro­ ducts in vater and under conditions where the bonded construction was exposed to adverse weather. Glued, laminated boats, for example, exposed to fresh or salt water for long periods of time gave highly satisfactory performances. i-any other weather and water resistant wood products can be made with synthetic resin adhesives. For instance, phenolic resins are used in the production of exterior type Douglas fir plywood which gives the plywood an excellent reputation in the building industry. The synthetic resin adhesives that usually are in use for plywood manufacture are the so-called thermosetting resins; these include phenol-formnldehyde, urea-fomaldehyde, melanin e-formaldehyde, and resorcinol—formaldelyde resin types. These resins 'usually are cured by heat and pressure, or by the addition of a catalyst into infusible and insoluble films in the glue line of a bonded vrood construction. The term thermosetting refers then to a resin which becomes irrevers­ ibly infusible and insoluble on application of heat or catalyst. In contrast, the tern thermoplastic refers to a resin, for example poly­ styrene or polyvinyl acetate, which is hard when cool but will soften when heated to particular temperatures, becoming hard again on cooling below its softening point. The investigation herein described lias to do with phenol-formaldehyde and other phenolic type resins. There has been considerable research done on the use of phenol—formaldehyde resins for plywood bonding, particularly with one-sixteentli inch yellow birch. However, most of this research has been conducted 'with phenolic resins for which the rosin production data are net available. Consequently, if in conducting research on synthetic resin adhesives information on composition of the adhesive is desired, the investigator is forced to produce his own resin. In the experiment described in this thesis, the 3. phenolic resin adhesives used — ere made in the laboratory since it v^as desired tc produce alkyl— substituted phenolic resins Tor vniich manu­ facturing conditions vrere Iatra, The formulation and '.so of various ohcnolic resins lias been ex­ amined suite extensively in the case of molding and laminating mater­ ials. To a limited extend adhesive qualities of phenol—formaldehyde rosin and cresol-fomaldelyde resin have also been studied. appears, however, that there is no It published information on the ad­ hesive properties of alkyl— substituted phenolic resins in general. It was proposed, therefore, that four phenolic resins, including phenol-fcrmaldehyde resin be prepared and that these resins be used in the bonding of one— eighth inch Douglas fir veneer into three-ply plyood. h. II. stattl:ii;t of tis ivjoblil: The purpose of this study was to determine the effective bond, strength of Douglas fir plywood as related to different phenol-fomalaehyde resin adhesives. The adhesives were f o m e d by reacting phenolic compounds, that had certain alkyl groups substituted in the r.eta positions of the phenolic rings, r.-uth formaldehyde. These alkyl- suostizuted phenols were obtained from commercial soui’ces and vrere reacted with Fon .aldehyde using a srr.rll m o u n t of ammonia as a cata­ lyst. The ply:,-cod produced using these resin adhesives was then tested for shear strength, using the standard ply rood shear test procedure (Ij.2)• The resins prepared id r tziie study inc-.uded those formed l’ron phcncl and f .m a l e e h y d e , and t’iree aiiyl— substituted resins formed from n-cresol and f .rr.aldehyde, 3,5-dinetIylphenol and f ormalde’ nyde, and n-etiylgdienol and f c m a l d c l y de• These resins were pr.duced in the lab­ oratory tc assure that each of the allyl— substituted phenolic resins was reacted with forr.alaehyde for a length of tine that corresponded tc the length of reaction tire used for the phenol—Tormalrehyde resin. ft was or:posed Further that whereas a portion of each resin would be used in an unmodified w r m , another rocrtion vrruld be used with different percentages of walnut shell flour, tc find how a given quan­ tity of flour would affect bond strength. The use of the flour re­ tards resin flow into the wood and also minimizes squeeze—out of resin from the glue line during the bending operation. It should be mention­ ed that there is an increase in bond strength if a certain amount of 5. adhesive goes into the vrood. Hovrever, it is obvious that if too much adhesive penetrates into the ivood, the amount of adhesive retained in the glue line may be inadequate, resulting in a "starved" glue Joint. The Douglas fir veneer pieces used in the investigation vrere standardized as much as possible. All the pieces of veneer vrere con­ ditioned to the same moisture content before they v.-ere used. The gluing surfaces of the veneer vrere sanded to obtain comparable sur­ faces. The venoer v,ras selected and cut so that the grain direction parallel to the sides of the ^ieces. yjus The specific gravity of each piece of veneer v:as determined and the veneer was divided into four specific gravity groups. This oreliminary processing cf the veneer tended to reduce variability. A theory vras proposed regarding the effect of allyl substitution on the aromatic rings of the phenolic resins as related tc the strength of Doug?..as fir ply/rood bonded v/ith these resins. The theory suggested that phenol-fomaldebyde resin bonded plywood vrculd shov; the highest shear strengths since there are no allyl groups on the phenolic ring to hinder polymerization of this resin. It rras further theorized that ply.Tood strength vrould decrease in the follo-.ving order— n-creso 1-form­ aldehyde resin bonded p.lyvrocd, 3 ,5-dimethylphenol-fcrmaldehyde resin bonded ply/rood, and m-ethylohenol-foimaldohyde resin bonded plywood. This order v.-as suggested because m—ere so 1-formaldehyde resin has only one methyl grouo on the aromatic ring, 3 ,5-dime tlyO.phenol-foiriaideiyde rosin has tv:c separated met’iyl groups, and m-etlylpheno 1-formaldehyde has a tvro-carbon etlyl group vxhich extends farther from the phenolic ring and perhaps r/ould have more effect in hindering good glue bonds. 6. III. JIoCuo^IOi; OF BACKGdCUhiJ TOPICd Phenolic Typo Resins Jeve?-opment of phenolic type resins. In view of the Tact that this thesis deals -with phenolic typo resins it seems Pitting that a brieT Iiictorical and theoretical background be presented concerning the develo'cnent of these resinous products. Only the points -which are per­ tinent to the development of the phenolic resins in general vri.ll be presented. It is of interest to note that the basic raw materials for the production of phenolic resins, namely phenol and formaldehyde, '.rere not 1rno-.vn early in chemical history. Phenol -was identified in 163k by lunge some 38 years before the first published reference to phenolic resins. Formaldehyde -was prepared by Hoffcian in 1668, a scant four years before Baeyer conducted his experiments on the ^reparation of phenolic resins. Previous to 1872, many chemists had discovered that some reac­ tions vrhich they had carried out resulted in a resinous substance as a product. These ne-w substances were not all appreciated since they could not be analysed. not bo crystallized. They had no definite melting points and could Consequently, at that time, they represented undesirable reactions and such products -were discarded -without further thought. The value of resins is definitely recognized today. The first work of any consequence in the study of phenolic resins 7. was conducted by Baeyer (6) in 1872. He produced several colorless rosins and published the results or his investigations. He evidently did not visualize any particular uses Tor the resins he produced, but he did report that his investigations indicated that the reaction between phenol and aldehydes v;as a general reaction. The first research vrork which provided any information of impor­ tance on the way the phenol—formaldehyde condensation reaction took place was conducted by Lederer (33) and Lianas ce (3U). These two investigators, working separately, isolated ortho-hydrojybenzyl alco­ hol and para-hydroxybenzyl alcohol, the former being known as saligenin. These phenol alcohols v.rere shown to be the simplest pro­ ducts formed in the phono 1-foimaldehyde resin reaction. The work of these two men was the basis for all later investigations involving the resinification of phenol with formaldehyde. It is recognized today that phenol alcohols are probably the first products formed in the phenol-fomaldehyde reaction. Up to 1900, research on phenolic resins consisted mainly in pre­ paring the resinous products or in the examination of the initial pro­ ducts of the phenol—formaldehyde condensation reaction. In 1900, research began which had as its purpose an examination of the resins obtained in the jjhenol-formaldehyde reaction to see what could be done with them. In the same year phenolic resins were proposed as an elec­ trical insulating material. Phenolic resins as a substitute for shelllac were also suggested and work was actually done toward this goal in 1902 to 190U. Also at this tine, in 1901, the first suggested uses 8. of phenolic resins as an adhesive for bonding wood appeared in a British potent issued to Societe Deropas Frferes (50). There is no evidence that a successful adhesive resin vras actually developed in that year. Baekeland (U) introduced a theory of resin formation. Ke con­ sidered the reaction of phenol and formaldehyde as a condensationpolymerization reaction having three steps or stages. In the first part or A stage of the reaction, the resin, called a resol, was formed. It vras considered to be of lovr molecular’ weight, having the form of a liquid, solid, or semisolid. During this stage the resin vras soluble in acetone, alcohol, or toluene. In the second part of the reaction or B stage, the resin, called a resitol, was formed. This resin vras considered to bo a solid insoluble in acetone but swollen by this sol­ vent. The resin could be softened by heating a limited number of times bcfoi’e it vras converted to the final stage. The final stage or G stage produced an insoluble, infusible substance called a recite. These stages are recognized today. Baekeland c: ~ r ° X ^ > 'f 0- ' < d > ' d d L* ™ 0 *— L/ H TJ This reaction, through phenolic hydrosyl groups, is not recognized today. Baekeland also reacted phenol vrilth formaldehyde using a small quantity of hydrochloric acid as a catalyst. fusible resinous mass. phenol. The product was a soluble The reaction v/as carried out using an excess of His third resinification reaction showed that in the presence 10 . or an alkalino catalyst, the reaction gave an insoluble, infusible pro­ duct even with an excess of phenol. Raschig (H5) uid not like Baekeland's ether linkage and suggested that phenol alcohols could react in two ways. The alcohols could react either with nore phenol to produce diphenoloIne thanes or could react with themselves to form, alcohols of diphenylolmethanes. oil Oil OH X \ tCImOH OH - OH OH GHoOI! ch2 - --------- >» + OH Giio01I ;k 2 ntt r,Tj wx 4 - non Raschig1s reaction scheme for the formation of phenol-fomaldehyde resins was then either the first initial reaction, alcohols reacting with more phenol, or phenol alcohols reacting with themselves to form an insoluble, infusible resin product. Rasehig, in considering his data, pointed out that in phonol-foinaldehyde resin reactions, soluble fusible resin products are obtained v/hen one, or less than one, mole of formaldehyde is reacted with one m.cle of phenol. t.hen the molar portion of form.aldehyde is greater than 11. one mole, the nolar nortion of ohenol being one, Insoluble products are obtained. According to liuschig, v.'here less than one nole or rorm«ilde­ lude reacted ~..'ith one mole or aliencl cUnhonololriothrnes are favored, v.'hereas vrith excess formaldehyde, products of early stages or the reaction are phenol alcohols and diarylr.etliancs. U n a l products in the latter case arc referred to as resinous mixtures having great complex­ ity . Thirteen yen's later, Baekeland and Bender (5), reviewed oast theories, anal alter sor.o cxoer ir.’ .ontn 1 work developed a nev; hypothesis .diich still retained the idea of the ether linkage. Three chemical ste :s in the condensation l’or.ction '..'ere recognised. The fclfovbng e ana tions represent those three steps. In the r.lrst steo, tv:c molecular ocrticnc cf ohenol corbine v.lth one molecular oortion of f orrsalueliyde to give an unsomn.etrical ether, ->-hydro3$r->!xenylphcno:q/nct:'.anc. It v;as stated tiia.t this c o m o u n d v;as the insert ant cri.soncnt of the initial, or the A stage resin. dih-0 + A c6% c n -u- CH \ y OK In the B stage it ’..as thought that another molecule cf f o m a l d e — 12. horde condensed with the ether to form unsaturated compounds. II L> — ii II + CKo0 I H ''c 6h u c h ,c 6 h u o h o ■ C^OI-I N / OH The final C stage vras thought to be brought about gradually by addition polymerisation. II , uc6% / C / II = G \ c 6h u o h G I H - G - c 6 iiu o h n II C6\0U / \ G / II = G \ TT c6nhon 1 1 G - G — 1 1 n g 6 h U0H i 1 T T 13. Up to about 1930 both the theories or Baekeland and Raschig were accepted. However, during the 1930’s the condensation polymerization reaction between phenol and formaldehyde was reviewed by several researchers and the hypothesis of Iiaschig vras declared essentially valid. Robitschek and Lewin (U7) considered that this point in the advancement of knowledge concerning the phenol-fonnaldeliyde resins brought the development tc present-day thinlcing. Present concepts of pheno 1-formaldeliyde resin reaction. The review of present— day thinlcing on the concept of the phenol—formalde­ hyde resin reaction will include only the more important general ideas concerning this reaction. It must be emphasized that the ideas presen­ ted will be general in nature since pheno1-formaldehyde reactions can assume all manner of variations due to variation of reaction conditions, which are especially important when phenolic compounds arc reacted with formaldehyde. Changes in temperature conditions, in the type and amount of catalyst, in the phenol—formaldehyde ratio, and in the manner of dehydration of the resin are a few of the variables which have a narked effect on the type of resin produced. The phenol—formaldehyde reaction appears to be more sensitive to minor changes than many other chemical reactions^ this fact accounts for considerable lack of agree­ ment in the data produced by different investigators. These facts must be borne in mind when the phenol—formaldehyde reaction is under discus­ sion. One of the classical concepts of organic chemistry which has been llw ’mov.Ti and accented Tor inany years ic that a hydro:it.:adde’ .vyde and id the H'-'dmr-^y-l frou.i is a.cctylated or methylated, the reaction between the ■.-liono.'ic con.vaunt and f e m a idoh'dc takes olace '.cith great cLLL’iicnjlty. This concent of reactive none ring loads to the theory of .linnet lorn.I it;/ Ter or;it ions on the ben— .honolic coracunis. .Is indi.ee ted in Table 1, ohenolic cor. >cunds can be divided into trii’unctionr.l, b ifunctions. I , and nonofunctional tygcs. As can be seen, the functionality oi* the phenolic cor;round is determined by the number r'i a.vailablc re .active •coitions an the bensene ring. funcbicnai end can tints roar.: bridges between r’oir.a doliyde is bi- ineno.de nuclei. In vicvr ox th.is a triTunction.nl hnonel ic cc:: round vault be e:c >ectcd to Terr, cross-linhcd nacror.olocu.lcr, r bifunctiorr 1 "honelie c or..->ound vr uld be evoected t ‘ form and” linear chain nolecu"' os, an.. a mono Tunc tional Phe­ nolic c~me -uni would n't f •it*, large molecules acted with fc n.’ .alr’ehydc. been found. 'hen the compounds are re­ lb:cc >tions to the theory 01 functionality ha.vo A notab?_c enceetion is that both ortho .and earn cresols, A convenient diagram of th.e bonsone ring to show its nomenclature is os follows (17)5 Oil ortho ortho nota neta para 15. TABLE I. TIE FUNCTIONALITY OS* PHENOLIC COMPOUNDS Trifunctional Phenols OH Bifunctional Phenols lionofunctional Phenols OH oh ch 3 o—cresol phenol OH OH gh3 / \ ch3 2, 6-dijiethylphonol OH CH3 ch 3 CH3 n —eresol OH C H s^ Jc H s p—eresol CH3 2 ,U- din c thylphenol OH VCH3 CH3 3 »5-dJu.ictiijrl")henol 3 ,U-dinc thylpheno 1 OH — reactive position n— otljylphenol although being classed as bifuncticnal vd.ll, ij? reacted lor a long enough period of* time with formaldehyde, form insoluble and infusible resinous material. A bifunctional phenolic cor.nound u.wually would be o;.pectcd to form. only soluble and fusible resins. Thus these two compounds when reacted with f rmaldehyde act some-/,'hat like trifunc­ tional compounds -which give rise to insoluble and infusible resins. The nonofunctional compounds do not 1 c m resins. It is now generally believed that the first products formed in the phone 1-f orr.aldeliyde reaction are phenol alcohols. As indicated pre­ viously these are simple compounds which have been isolated in crystal for.cg they are -water soluble, alcohols, fhose alcohols nay be mono— or dihydric fhe scheme of their formation may be represented by the following equations: Oil CH GHo0Ii + \ / 2CHo0 n / c h 2o h J 17. In addition to mono— and diliydric alcohols it has been suggested that trihydric alcohols are also formed (20)(22). Their formation may be s’ no'.vn by the foHerring reaction scheme: OH OH / \ h o h 2c / \ GH,,0H 3CIIoO \ y c h 2o h The grovrth of the phenol—formaldehyde molecule can take place from the alcohol stage in two ways; either by the elimination of a molecule of rater, formed by the uniting of a molecule of phenol alcohol and a molecule cf phenol betvoon rdiich a methylene bridge is formed as in the following equation, OH . v> M , ■ A fvr i CIIoOH OH vj OH \ + HOE y or by elir.ination of a molecule of "rater when two molecules of phenol alcohol unite to form a methylene ether bridge. 18 Oil / \ OH Cll OH — CH2—O—’dig” HDHgC HCH c h 2o Two points should be made concerning the last tyro equations. In the first place these equations nust be considered general in nature since usually either acid or alkaline catalysts are used which vrill determine the type reaction that will occur. In trie second place these equations represent a condensation polymerization reaction in which some sinole confound such as water or alcohol is eliminated in the reaction. This is in contrast to addition polymerization in vrhich the reaction takes y.Lace through the unsaturation caused by double or triple bonds in a chemical compound. There are no eliminated compounds in the addition polymerization reaction. In connection vith the use of catalysts, the phenol—fomaldehyde ratio r.rust bo considered. It is accepted that yfnen the r^henol to Ton'.aldehyde ratio is below one, that is, when the number of moles of phenol in a reaction are fewer than the number of moles of fc.imaidchyue, an insoluble and infusible resin can result. On the other hand, when the number of moles of phenol exceeds the number of moles of formalde­ hyde, or -when the phenol—formaldelyde ratio is greater than one, a permanently soluble and fusible resin re::ults. This is a basic concept 19. and an important factor underlying the use of catalysts. In order to obtain a hardenable rosin it is necessary that the reaction mixture contains a greater number of moles of form.aldehyde at the start of the reaction* or else an additional quantity of formaldehyde must be add­ ed after the reaction has proceeded to some extent. The addition of more formaldehyde can take place at the time the resin soj.ution is used for some operation such as fcr molding or as an adhesive. In the presence of an acid catalyst, if the phenol—formaldehyde ratio is greater than one, only permanently soluble and fusible resins can be obtained. However, if the formulation is such that the phenol- Jor.-'.aldehyde ratio is changed to a ratio which is less than one, the resin obtained v.ill be capable of hardening into an insoluble resin, this is the effect obtained '..hen an acid catalyst is used in the pre­ paration of a phenol—fox’;..aldehyde resin used as an adhesive. •..ith an acid catalyst it is belived that chain molecules are formed in v.iiich phenolic rings are joined by methylene bridges. product of such reaction is represented by A in figure 1. frmaidehyde is added later, a hardened resin is produced. The If more this resin may be represented by formula B in figure 1. jhen an alkaline catalyst is used under the usual conditions of a less-than-one phono1-formaldehyde ratio, a resin capable of being hardened is formed. In the initial stages of the reaction, polyliydric alcohols are formed; these alcohols vd.ll form oven if the phenol-fcimaldelyde ratio is greater than one, in vmich case a quantity of phenol remains unreacted. If the imreacted phenol along vrith the v/ater intro— 20. duced with the formaldehyde is removed by distillation, the regaining solution consists mainly of polyliydric alcohols having sufficient f rmalochyde groups for subsequent cross-linking into an insoluble and infusible resin. On the other hand, if the free phenol is allowed to rer oin in the solution and if the phenol-fornal^eliyde ratio is greater than one, a permanently fusible and soluble resin can be Termed. The phenol reacts with the polyalcohols present. tith an alkaline catalyst, both r.etliylene bridges, as f<:rued with an acid catalyst, and methylene— ether bridges are d o m e d . A branched chain molecule, as shown in A of figure 2, results due to the grov.th of the molecule from jolyliydric alcohols. It is believed that both typos of bridges are formed up to a ter pcraturc of 160° C. The meth­ ylene-other bridge is unstable at higher temperatures, and between 130° G. and 200° C. the methylone-ethcr bridge is transformed into a net'uylenc bridge as represented by equation B in figure 2. At tem­ peratures bctv.'cen 170° C. and 220° C., the nethyiene-ether bridge is tra.ncforr-.ed into the quinone methide. Chc.pm.an. (lh) suggested that the quinone methide monomer may be formed from a phenol alcchol with the elimination of a molecule of mater. The transforotation of a. phenol alcohol structure is shovm in A of Figure 3» The transfomation of a molecule of dihydro:emitting molecular orientation and polar adjustments. however, Jelmonte suggested that after the adhe­ sive is spread and has accomplished its rurpcse, the faster the sol­ vent is removed the better will be the results of bonding. In porous materials such as vrood the removal of the solvent is thought to take place in part by diffusion of the solvent into the material by means of capillary action, and in onrt by evaporation into the air. The removal of solvent nay be speeded up by using an open assembly period. Other references have indicated what deleterious effects may be caused by the retention of solvent in the glue line. Hockstra and iritzius (23) have pointed cut that when an adhesive is brought into 36. contact with a surface, that surface is 'vetted by the solvent. The solvent molecules thus take up the most favorable polar positions toward the surface, allowing only a limited number of the adhesive molecules such preferred positions. If the solvent is not removed the adhesive molecules ivhich have not obtained these favorable positions will not orient themselves, that is, they wi-Ll not turn their most active joints toward the surface. Eventually, when the solvent is eliminated duo to diffusion or evaporation the adhesive will become viscous, '.vliich will nrevent orientation of the :>articles and a good Clue bond c a m c t be obtained. In the case of the synthetic resins, the adhesive, when used in hot prossinp, nay be quite viscous when the wood assembly is p?_aced in the hot presses, ta.it loses some of its viscosity due to the heat, for a short period of tine the adhesive may be able to orient its molecules while solvent is beimp forced out of the glue line by the pressure a -plied to the assembly/. tively short. This period is rela­ After that the adhesive becomes more vise us during the hardenin': phase and finally it solidifies. Under the conditions just mentioned, if pressure is not adequate during the bonding operation air bubbles nay be trap n d in the glue line, thus oroducing a weak bond (36). btrong acids and alkalies are considered detrimental to the adhe­ sive bond and this effect is known tc be very narked if the material being bonded Is affected by strong acids or alkalies, delmonte (lo) indicates that a pH value of an adhesive lowerthan 2.5> is considered detrimental to wood bonds. The effect of acids and alkalies on the strength of birch plywood has been investigated by 1l i n e , lieinhart, 37. iidnker and Delollis (29). -Results of these investigations have indica­ ted that the glue bond is reduced in strength by the action of strong acids and bases. It was round that for phenolic resins a pH value of 3.5 cr lower is detrimental to the strength of the glue bond and that strength begins tc decrease at a pH value cf about 8. I£>:periments conducted at the United dtates Forest Products Laboratory by Blonquist (10) on the effect of strong alkali on phenol-formaldehyde and resor— cinol-iorr.aldehyde resin adhesives have substantiated results obtained by the previously mentioned investigators. The recorded molecular weight of a synthetic resin adhesive is not considered to apply to each molecule in the adhesive since molecules in a resin vary in molecular weight; but the given molecular weight is an average of the ’.veights of large, medium and small molecules. There must be, therefore, a combination of molecular a/eights that give the best adhesive bonds. Delmonte (le) suggested that snail molecules of rosin are required tc make contact with bonding surfaces and act as a bridge between these surfaces and the large molecules of the resin, inall molecules would be required for adhesion, and the large molecules would supply the required cohesion when the resin idhecive is cured. Links two and tlircc, as indicated in Figure probably can be con­ sidered to be the most mysterious parts of the glue b m d . However, certain factors are lcnov.n to have an influence on the glue bond. For ezcamplo, it has been stated that a satisfactoiy glue bond is directly related, in part, to the wetting characteristics that a. liquid adhesive exhibits toward the surfaces which are to be bonded together (18). f l 39. cd rue':: a condition is a drop of r.erc’u y on a r.etcl surf ace; the aerr u y ices net adhere to the surdace. The cor.plete vetting cf a solid bp* a liquid is re oreseracd by a contact angle cd aero. bat isd acts iy --eating is iniicatei by c :replete S"reading ci the liquid over a S'urface •,itrout a tendency for droplets to be d o m e d . lo'.: surdace tension der a liquid adhesive is a dactcr davorable dor the spreading od the liquid over a surdace; and it also aids in the -.vetting od the adherent noro'aoe \22,• Viscosity indluences the so reading cd a iiquiu ever a so 111 in thou id viscosity is great it retards the ocver.er.t od she lionid and in c -nseouer.ee the _iguia vill not syreo.d drcely. In the esse od th.e ••ottir.g cd a solid surdsce by a liquid the oclarity od th.e liquid ana the solid should bo considered. Ironically, iiddcrer.t rioorscec can be broadly grouped into aciar and non-pclar substances, vith scr.e substances being included beto-ccr. these uvo orarer.es. -overran n-/ points -ut that a r.olecule r.ay be cor.gletely r.on-orlar, contain cnly active negative vc lariat*. contain snip' acsitive poloria.v, or have both nag naive end c oitivo active oudaoes. substrates ao'C aloo so v.bici hove t oh negative an., — Coos. iclar ositlve active sur— _ o ar n o _ e c u -as too— — attract one anc ^ocr• In the bending od -..*00 1 -.vith on adhesive, strcng Joints caoo never be r.ado bct.eer. :-o1.or cor'd rocs vith ncn— polar adi.esives nor can she con­ verse be true, doc d one. derivatives cd cellulose ao'e pci ar not erioi s and id a r evict is r.ade cd the outstanding adhesives used dor bonding no: it ill b e dound that they are characterised bp.* strong "roue s (11/. The I11 grouts in :clar Irene lie spare I ho. reclns make these resins polar and the same groups In vrood and cellu­ lose make these materials polar also. It is known that p henc.1-f o m a l - dehyde resin adhesive is definitely a satisfactory adhesive for bonding; Y.'OOd . It has been suggested by linker and hline (U6) that the mechanism for the bond between vrood and phenolic resins is probably hydrogen bridging accomplished through the hydroxyl groups of the resin adhesive and the vrood surface, lieactivity of the hydroxyl groups in the phe­ nolic resin adhesive is shown by the fact that a water-insoluble phenol—formaldehyde resin is dissolved readily in sodium hydroxide solutions of relatively mild concentration, and that even a cured resin is attached by strong alkaline solutions. kudkin (LC) has demonstrated that hydroxyl groups in vrood play a part in adhesion between adlicsive and wood. i.orbing v.ith urea—foimai— dehyde, it was found that if hydroxyl grow is of -wood were acetylated prior tc gluing, a merited reduction in glue bond strength- was observed. This work, although it did not indicate what kind of forces ettisied between vrood and adlicsive in glue joints, did shew the importance cf the hydrottyl groups in wood as related tc vrood bonding. In ail proba­ bility the hydroxyl groups in vrood and the amine and imino groups in urea resin adhesives contribute tc the strength of th.e wood glue joint, reactivation of hydroxyl greuns in wood would undoubtedly reduce the glue bond strength if phono 1-forc.aIclehyde resins were used. The final links in the wood glue bond, link's four and five, as shovm in Figure i;, re present the materials being bonded. J la. The surface cf v/cod can be modified to an ap preciable extent to in. rove its adhesive Topcrties. ..ocd surfrces should be machined smooth, even and flat for best results in gluing their, together. Truce: (55) referred, to a planed surface as being the ideal surface for the bonding of 7:0 ,0 . lie indicated; that numerous comparative strength tests conducted by the United States Forest Products Laboratory had definitely failed to shovr any advantage obtained by roughening vcood surfaces -rior to gluing. In recent years, it has been restated by Lnauss and oelbc ( 3 0 that a smooth planed surface is considered ideal for v.-cod glue joints. ul sr.ooth planed surface obviously is out of the cuestion -with voneer vchicl is tc be made into plywood. haufert (26) has shown by an investigation carried out at the United Itates Forest Products Labora­ tory that the clue bond betv.een veneers can be improved by light sand­ ing to restore surface attraction. IV. DEVELOPLiKiT CF HiKi.'ClIC TYPE iiEDIi: ADHDDIVDD AIID THEIR UDE FuR DCUDIfG DOUGLAD FIR IIX'/COD Development of Phenolic .Liesin Adlicsives There has been a substantial amount of research into the uses of nhenolic type resins, mainly of the phenol-fornaldel'yde type, for the bonding of vrood. Undoubtedly there has been considerable research into the specific problem of bonding Douglas fir veneers vrith phenolic type resins; ho..ever, the literature is not rich in the details of such re­ search. In respect to the phenolic resin adhesives available, commercial competition compels resin adhesive nanufacturers to guard their pro­ ducts by not aliov.ing free circulation of inTornation on nanufacturing ;rocesses. It is true that phenol—forualdeiyde resins are described in pa.tor.ts but there is no v;oy of linking the information in the patent v.ith the manufactured product. Consequently the fo H o m i n g discussion cannot ore sent an exhaustive account of research in tliis field. The first attempt to use phenolic resins as adhesives in the pro­ duction of nlyv:cod is recorded in a British patent issued in 1901 to Docietve Derep as Frcres (50). v/hich covered the m e of plymood. In 191G a french patent (22) vras issued of phenolic resins as adhesives for the production In 1912 the use of phenolic rosins as adiiesives for the vraicroroof bonding of plyaood v;as suggested in a patent issued to Eaeheland (3). Three years later, in 1915, another patent %vas issued Uh. An .adhesive suitable for one surface nay not be suitable lor another eurfs.ee. The third reason eras a lack or expensive hot cresses requir­ ed dor bonding '.rood vrith phenol-fernaldebyde resins. hie in (fC) states that activity in the phenolic resin adhesive field did not appeal’ until the late 1920’s vrhen some uevelopr.ent vrorl: vras started in this direction. Cnee again, phenol-f orr.aluebyde resin s lids dispersed in cd.cch i became available for the bending of vrood. ene com cany manufactured and sold nhcnolic resin solids in vrater solu­ tion. hovrcvcr, the rosins could not be used vrith satisfaction mainly hocauae the control of the reread v;as difficult and it vras almost ir.i— '■’ >0 c s i b l o in p . t o r d j ' u s t th.o m o i s t u r e c n t o n t o f t h v ’‘o o d a t t h e t i m e o f ,glu— . o r o n s o n and h l c i r . ( i d ) in d ic a te d t a t a v e ry in v r t a n t p iu b le n e n c o u n t e r e d a t t h i s t i r e vras t h e l a c k c f c m e t r o l o f th.o f lerrr o f t h e rc :.in a d h e siv e th e re sin d u r in " th e p r e s s in g c n e rc .tio n . so lu tio n s in v o le t Me so lv e n ts, re s in s in uuc t o th e f a i l u r e of some m a n u f a c t u r e r s p r o d u c e d e rr v d e r f o r m a n d a f.se r o s i n s i n m a'ocr s o l u t i o n c a l l e d c o l l o i d ­ a l re sin s, h lo in ( 2 c ) s a i d t h e p c u b .c r s vrcro u se d , b y a; r I n k l i n g t h e n on t h e v'-vod t<" b e l*c>ndcu. f h e p o v rd cr vras t h e n m o i s t e n e d v r i t h v r a t e r a n d she *.:ec d a s : c . .b l y p r e s s e d , f 'r*. .-.Idckvc.o r e s i n a s m ’. . e i t h e r o f t h e s e a .tt e . , : t s t o u s e p h e n o l — a c .h e e i v e f o r vrocd vras s u c c e s s f u l . In the year 1127 the first resin flues for ..nod vrcrc ->r: duced in .nmo. '..opnor (;>f ), as a con suit inf en fine or for the Juropean firm introducin; the rosins, vrorked on the ; r bier: of the best f:rr. for the rosin adhesive for oi. f.ic result of the '.or’-; n.t tnat plait vras tlie introduction of resin adliesives for *.rcod in the term of a dry fill.:. U5Ulein (28) indicated that in 1932 phenolic dry film Tor bonding wood was intoduced int-- the United btatcs. film -.'or production of phenolic resin ood bonding war. started in the United fitat os in 193U. i’he vide acceptance of this iiln was hampered at i'irst by the Tact that in the United .States there v;ere less than a dozen hot presses for vrood bonding. Uovrever, by 1981 there were sore 150 hot presses in operation. between the yeans 1938 and 1937, the resin film v/as probably the only satisi-actory t;,pc of phenolic rosin adhesives available. in the latter years, improved phenolic resin solutions and phenolic resin ad­ hesives in powder foro. arere in the experimental stage, alth.ough some ol these adhesives were already used to a limited extent lor bending vrood, inc'!Aiding rjouglas i‘ir veneer (31). In 19hO improved phenolic resin adhesive solutions and trie powder adhesives were accepted for vrood bonding (28). since the introduction of resins in 1980, the trend has been to improve ohcnolic type resin adhesives and modify then for particular our rose s. Phenolic Tyge hosins Used With Douglas Fir Veneer ihenc 1-dorr.alo.ehyde rosin bended Douglas dir plyvrocd, or eicterior ty:9 "'ly.vood, did net becor.e cor::.ere ielly important until the years 1339—I?u0. The advent cd e:rtericr type Douglas dir ply.vood paralleled closed;." the introduction od on accepted improved liquid resin adhesive and sprayed dried phenol—dorr.aldehyde resin adhesive in 'order dorr.. The resin dilr. -.rliich had been introduced in 113*- '.-c.s od little use to the Douglas dir :>ly.rood industry dor three reasons: l) the phenolic dilr. vras rueh too expensive dor use in producing the relatively cheap nly.vood "reduct, 1) the dilr could not be adapted to the r/.ass produc­ tion Indus tin", v.hich the Doug; as dir 'b’-.od industry had becor.e in 1933, and 3} the resin dilr. v:rc not suited dor the bending od the rough veneers used in the Douglas dir ply.vood industry’' or dor bonding '.rood ‘ .laving as '.ride a variability in density as Douglas .dir veneer. true, as It is .ointed our by davyer, Hodlcins and del er (ip), that cone phenol—dorr.aldehyde resin bonded DcugT a.s dir ply.vood '..'as produced bet”,"eon IS?31; end 1333 • However, this plywood. '..as bonded using the old unir.nrcved resin adhesive so nitons od ohcnol—dormaldehyde resin solids dissolved in alcohol (1). The introduction od improved phenolic resins narked the real beginning od the production od e:rterior Douglas dir ply.vood (1). Although not used today, at least up to 1933 tve excellent resins were used by the Douglas dir plywood industry. One adhesive vras used in U7. aqueous form. without extenders to give plywood of the highest exterior durability. F. The press temperatures used vrere between 2u0° F. and 300° A second phenol-formaldehyde resin was used v.ith a soluble dried blood e:ctender. With the latter, good bo 12-proof glue bonds were obtained at pressing temperatures of from 2l|0° F. to 260° F. The use of b2-Ood extenders undoubtedly resulted in very economical glue line costs. It was indicated by sawyer, Hodkins and Zeller (li9) that blood extended ehenol—formaldehyde resins were not used extensively in the Douglas fir plywood industry. hood and Linn (oO) described "an excellent" adhesive for bonding Douglas fir olyvood, which probably was tried at the time the Douglas fir pJy.Tood industry was beginning the production of exterior type ply­ wood. The adhesive as prepared by the reaction of laeta cresylic acid and fomaldehyde in the presence of sodium hydroxide. Tlie adliesive was so2.uble in water and vras used under press temperatures of 320° F. to 3h0° F. and a pressure of 175 rounds per square inch. Tlie high temper­ ature requirements for this adliesive indicated that the resin had slow curing charactoristic s . Beaty (7) studied the production of Douglas fir plywood relative t the factors that affected its quality. wood shear test strength data. He based his results on ply­ In all cases, shear specimens were boiled in water for four hours, given a 20-hour drying period at ji;5° F., and then given a second four-hour boil treatment. The tests were con­ ducted immediately after the second four-hour boil period. In all cases phonol-fomaldehyde resin a.dhesivcs were the typo used and test U8. specimens were obtained by sampling plywood panels that vrcre bended in the course of regular plywood production. rre-cure of the adliesive, 'which term refers to curing an adliesive on a wood assembly before pressure is applied, was considered bp Beaty. Tliir. is an important factor in any gluing operation and it must be con­ trolled rigidly in production processes. Beaty reaffirmed that a phenolic resin adhesive v.ill pre-cure if brought in contact with tlie heated press and allowed to become heated before pressure is ap iied. The effect of variations in torture and grain of the veneer used in the production of Douglas fir ply.rood v.•.s also eorarined by Beaty, reg.ortant factors were slope of grain or grain orientation in the core plies of -'lywood, number of growth rings per inch measured in a radial direction, sr.ootlmc; s if veneer, and veneer density. In considering these factors, Beaty pointed cut that the variation found in Douglas fir veneer usually -..'as attributed to two factors. Tlie first concerned the large diameters of the peeler logs used in veneer production. charscteristies Tlie of the v;cod at the center of these logs cere observed to be very much different then the wood at the outside of the log. secondly, the trees grow in many and various sites from lev swampy areas to higher ivc’y bluffs, the various sites having effect 0:1 the character of the wood. As a part of his investigation, Beaty classified plywood shear specimens into three groups related to the orientation of growth rings in the core w-lies. Figure 5 shows plywood shear specimen diagrams in which the tlirco t;~cs of growth ring orientation in the core are inui- U9. S TANDARD SHEAR SPECIMEN sr RADIAL DI RE CTI ON OF G R O W T H RINGS IN T H E C O R E PLY B r /5 \ / < RADIAL DIRECTION OF G R O W T H R I N G S IN T H E C O R E PLY CORE PLY \ \ ,5 D Figure J l. A. Jir.erisions of the standard plywood she nr soc c inen. B, G and D indicate the variation in the orientation of crorrth rin.ja in the core ply of doubles fir ply— vrood shear specimens as described by Beaty (7). .-‘.c vc/.i'cr I 51. reports that variation in density did have an effect on the strength of the 'ply.vood, in tliat light veneers tended to be v;eal:er than heavier veneers and sho-.ved greater vrcod failure percent than the ply.vood node ci the heavier veneers. 52 V. xd _. a cAl U o Ai.u .a b U n e H Statistical Design od the Ibcperir.eent In an:,' c;: .erircntal endeavor that involves a statistical analysis, it is ir.portart tc develop a design dcr the erpc riser,t s' that the data obtained r.ay be easily' analysed. In. e;:o eriner.tal design vras developed for the probler described in this thesis bed. .re actual investigation ■ c c u ni' l/0ci • T’lis expcriroent v s designed for statistical analysis od variance procedures. Four variable dactors .ere involved, balanced ,.esipn is shorn in Figure 6. hn outline od the The synbols in Figure 6 are iedined in Table II. As s h a m in Figure 6 dour adhesive resins vrere used tc bond boug­ ies dir veneer into vlyvood - a n d s. v;o:d anels v.-as vidual resin. loL, The total r.ur.bcr od three-ply ply- sc that 1?2 panels v.-ere reduced usin ; each, indi­ Tice veneer used dcr each resin v.t.s divided into dour specidic gravity grouos and plyvocd od cac'c s' ecidic gravity group.. .anels vere dabricatod vrith veneer For each resin let :iy..v'cd panels rep­ resented each specidic gravity group. The nurdoor od :■ yvrood ".anels drr each specidic gravity group v:ithin each resin vras divided by dour tc give 12 -anels that represen­ ted each od dour ■•ralnut shell dlour groupings dcr each, specidic gravity group. The dour tire doctors c npleted the balanced design. For the 53. Specific Gravity (groups) 1 2 3 a Y/alnut Shell Flour liesins I Time (days) 0 10 20 30 0 10 20 30 0 10 20 30 5 9 12 16 II 5 9 12 16 l?I 5 o s 12 16 IV 5 9 12 16 Figure 6. Outline of the experimental design for tlie investigation. 0 10 20 30 5U. TABLE II. Design Factor I 11 III IV DE SIG1TATION OF EYL30LD FOR FIGURE 6 Designation phenol-f omaldehyde n—eresol-formaldehyde 3 9 5—dime tliylpheno l-f ormaldebyde m-ethylohenol-formaldehyd© 1 Specific gravity group (0.39 - 0.U6) 2 Specific gravity group (0.U7 - 0.5U) 3 Specific gravity group (0.59 - 0.62) U Specific gravity group (0.63 - 0.70) 0 Walnut shell flour - Op & 10 Walnut shell flour - 105 20 Walnut shell f3.our - 205 30 Walnut shell flour - 305 ^ 5 3 days olus US hours soak after oreosing 9 7 days plus Uo hours soak after pressing 12 10 days olus 1;8 hours soak after pressing 16 1 )4.days plus ]j.8 hours scale after oreosing Based on resin solids content. 55. entire experiment, each time factor vras represented by 1^2 ply.rood panels or Ue panels for each individual resin. It is noted that for each individual condition of the experiment, for exxrmple, for liosin I, Specific Gravity 1, and a Time of five days, there v;ere tliree n ly.rood oancis. Furthemore, four p l y rood shear test specimens vrere obtained from each olyrood panel. The balanced statistical design v:as used as the basis for the entire thesis experiment. 56. i reparation of Douglas Pir Veneer for tlie .fcperiricnt Tlie vcnccr used in this exocrir.ent vras one-eighth inch Douglas fir ^ 1 seudotsnga taniTolia (loir. ) BrittIJ veneer. Douglas fir veneer v:as selected because of the investigator's varticular interest in Jcuglcs rir veneer and oly.vood. Airthcznorc, Douglas fir ..'vt.voou is considered tc be an entrcwely ir. ortant nroduct Tor which nany uses arc hnov.n. noir;..:.ns xir qjywcod is used for reeling, sheathing, sub—flooring and panering in the construct:!.on of houses, schools, churches and com.icr— cial buildings. It is used i‘or concrete Tonus with tie advantage of sr.oobh concrete surfaces. Phenei-fonnaidehvdc resin bonded Doug_as fir ply/:; od, or eaterior type "lyood, is used as e::torior \>ane. .ing Tor buiruings including prefabricated constructions, aircraft hangers and lev; cost houses. The actual veneer used vras obtained fror. two m e if tc northwest r.anuf ncturcrs oC Douglas fir vcnccr. The shiper.cnt consisted of tv:o vachv.gcs; one occhage contained air;.roodc.:ately COO square feet of u. terial in the fcrr. of two by eight foot shoots, and the second paclage con­ tained about th.o sane t~tal nuuber of square foot but in the for. of seven by 36 inch vicces. the "robier:: but it The veneer was not siocificalDy se. ected Tor s believed that inis offered no particular harci— s'lio in findlrw the desired nieces of veneer. hovrever, the J.arge 57. sheets of veneer vrerc heavier, tighter cut-*'*, .and had snoothcr surfaces thnn the smaller pieces which wero loss tightly cut, v/ere of lev specif­ ic gravity, and had rougher surfaces. The entire amount of veneer shewed all manner of growth ring orientation and growth ring widths .as viewed on the end grain of the sheets. Tliis situation '.vas expected and rc orcscntod the actual tyoe of veneer used by tlie industry to bend into Douglas fir plywood. Tlie initial step in processing the veneer consisted in conditioning it tc a seven percent moisture content, the percentage referring to the lorcontago of moisture in a piece of wood based on the moisture free vreight of the vjcod. seven percent moisture content v/c s selected be­ cause it was considered to bo an intermediate value for the gluing of wood and was a figure which could be maintained easily during the course of the study. The actual, conditioning vras accomplished in a standard Dry Kiln designed for the particular purpose of drying or con­ ditioning -wood t a desired moisture content. The veneer was stacked in tlie clry kiln using stickers to sep/rate the sheets so that air cir­ culated through the pile of veneer during the conditioning period. The control mechanism of the kiln was set tv attain equilibrium moisture content of seven percent in the veneer. oince the veneer did not con­ stitute a full kiln load it was necessary to adjust the Iziln control *- In the cutting of veneer by the rotary method, checks or cracks are developed on the under or concave surface. The depth of the cracks depends on the adjustment of the pressure bar of the vcnccr lathe and on the sharonecs of veneer knives. Tight cut veneer is indicated by siio.llow checks, and loose cut veneer is indicated by deep cracks. 58. ncchanisrr. during the conditioning; this adjustment ores based on the moisture content of kiln samples. '.Then the veneer oras pieced in the leLIn, sr.all nieces of it rrere (distributed tlirougliout the nile. sarnies. These ss.al pieces v;ere used as kiln Tlie average moisture content cf these samples eras taken as tlie average moisture content of the veneer at a particular time of testing. The moisture content of the veneer ale vms fcllcv.-ed from day to day until the samples indicated that the veneer vras at the desired value, after v.iiich time tr.ro days vrere allovred tc elapse in order to take care of any lag in moisture content change in the veneer sheets due to their large sizes. It eras decided tc use four by five inch pieces of veneer to pro­ duce four by five inch, ipx'.d three factors: .one-s. This decision eras based upon 1} the hot cress to be used in the bonding of tlie panels had sin by si:: inch plates, 2) from each panel it vras desired tc obtain four slyrrooc tost spccir.ens, and 3) only a limited amount of r e d n adliesive could be pre-ared, which required that the smallest usable plyvrccd ianels bo oroduced in order not tc vraste adliesive. Con­ sequently the nccrt ©aeration consisted in sawing the vcnccr into four by five inch sheets. These vrere then returnee, to tlie dry kiln vrhere they were "laced into specially built recks th.at kept the indivloual pieces separated tc aider: circulation cf liiln air. ..hen a substantial number cf sheets of veneer irere savred, a. tvro— day ceriod v.ws alic.red to elapse t stabilize tne nieces. tc.er. determined. The srecific gravity cf each sheet eras 59. Approximately U,000 of those small sheets of veneer were cut. One- third of the sheets were core plies in v/hich the grain direction of the sheet vras oriented parallel to the longer five inch dimension, and tvcthirds of the pieces vrere face plies in which the grain direction vras oriented parallel to the shorter four inch dimension. It is noted that a core ply inserted between two face plies forms a three—ply plywood panel. deveral points should be mentioned in regard to the determination of the specific gravity of the veneer sheets. It is ’veil knovm that wood is subject to shrinkage and swelling -when it dries or takes on moisture due to its hygroscopic character. In deteimining the specific gravity of -weed a particular moisture content must be selected. Usually the cwccific gravity of wood is evaluated cn the basis of oven dry ".."eight or moisture free -wood, and on volume in a green condition or at the ooint of fiber saturation. The fiber saturation point refers to the point when "wood has taken up tlie maximum amount c.f moisture but the cell cavities of the wood are not filled -with -water. This is a theo­ retical point at -which tlie -wood is s-wolien as much as it possibly can be, and any additional moisture -will not cause a change in its dimen­ sions. If a niece of -weed is accurate.y saved ■..lien at the fiber satur­ ation ooint the dimensions of the oiecc of wood will not change so long as this condition is maintained. It follows that if a particular mois­ ture content for wood below the fiber saturation point is selected and that -wood is sawed accurately to specific dimensions, these dimensions con be maintained as long as tlie particular moisture content remains 60. constant. Obviously the v.uight of the siece will remain the sane at a particular noisture content. In tliis investigation a noisture content of seven percent was selected as a basis for determining constant weight and constant dimen­ sions for the Douglas fir veneer. A common method for determining the specific gravity of mood is the volumetric method in which the wood must be sealed vrith paraffin so that it may be dipped into water to find the weight of water equal to the volume of the vrood. It is obvious that if vrood is to be glued lator it would not be advantageous tc cover it vrith paraffin. The dimensional method for specific gravity determination was used in this investigation. In this method, the in length, vridth and thie!mors. is calculated. lece of vrood is measured accurately The weight of an equal volume of water The soccific gravity can, then, be found by dividing the '.eight of oven dry wood by the weight cf water c orre so ending to the ved/ume of vrood at a particular moisture content. In order to determine the specific gravity of such a large number of veneer sheets, a sample of 310 sheets was selected at random. The dimensions of these sheets wore accurately i.ersured end then the sheets '..ere weighed ct seven percent moisture content. For all 310 sheets, the oven dry weight of e:ch sheet was calculated, using the following re la ti on sliip: ., weight at seven ocrcent moisture content oven ray v.'engnt “ --- -------— — -— ■*-------------- ----------0.07 + l.oi Using the measured volume cf the vcnccr sheet, the weight of an equal. volume oT .rater vras cc.lculr-t.cd. Spec IT ic gravity vras detciTnincd by dividing the even Cry •..•eight od the veneer sheet by the vreight od a volume ol •.■■■s.ter corresponding to the volume od the veneer sheet ct c. moisture content od seven percent, 'dho svccidic gravities calculated, vrere used in conjunction v.dtli the '..‘eight od vcnccr sheets at seven per­ cent moisture content to construct a graph od cnecidic gravity over ..eight od dour-inch by dive-inch pieces od vcnccr ct that moisture con­ tent. In this graph the cruinate represents cpecidic gravity end the abscissa, re -.resents -..-eight cd the dcur-inch by dive— Inch, sheets od veneer. This graph is reproduced in Figure 7» Three hundred and eighty points vrere plotted and by the method od least squares a straight hinc -.as dittod to the plotted points. Thus dcr the lot od veneer under consideration, id the -.•eight of a dour by dive veneer sheet vrere h e m , dron the granh. the cpecidic gravity od the sheet could be determined It should be stressed again that during the -weighing ooriration tlie vcnccr sheets -ere maintained at the seven percent mois­ ture content by removing sheets dron the dry Id.In, v'oighing them, and immediately returning the sheets t the Id.in. Adter determining the cpecidic gravities od tlie veneer sheets, dour coccific gravity groups -./ere selected. The specidic gravity groups chosen vrere A) 0.39 tc 0.1;6, 13) 0.U7 tc- u.3U, C) 0.99 to 0.62, and .j) 0.63 to 0.70. There vrere suddicient pieces od veneer in each od those groups to carry out the investigation. The veneer sheets vrere sorted to condo its to the emocrimental design od the irob.em into lots od dC veneer sheets, 16 core sheets GRAVITY SPECIFIC 16 18 20 22 24 26 28 30 32 ORAM WEIGHT OF VENEER - 7 PERCENT MOISTURE CONTENT Figure 7* relationship between specific gravity of veneer and veneer weight at seven oorcent noisture content. On ro 63. and 32 race sheets. gravity proup. dach lot was made up of sheets fror.: one specific There were 16 such ->acl:s Tor each of four adhesives. dach prouo of veneer vras wrap.ed in wan paper, and the vu-apped 'pacha.pe sealed vrith oaraffin. Tvro such lots vrere disced in moisture— "-roof 0 0 lyethylene food baps vrhic; vrere then sealed. v.tco ed in this manner were stored for later use. The veneer sheets 6U. drepe-re.tion or Ihcnolic I^pc h esin Adhesives The determination of fo n r,aI do liyde. The alkaline peroxide method as described by calker (57) v;cs used to determine the oercentupe of Ton.vaidehyac in a fcuTialin solution. The alkaline ocroxide method Tor the determination of formaldehyde is based on the oxiuc tion el* forms Idehyde by hydrogen presence cl a measured excess of all:all. .eroid.de in the The aldoliyde is converted to formic ccid which is neutralised immediately by the sodium hyuroxide. The amount of sodium hydroxide that re-cts vrith the f s m i c acid is determined by titrating tlie unreactod sodium liydroxide with hydrochlo­ ric acid. The first step of formaldehyde determination consisted in placing into a flash 50 i.a. . of normal sodium hydroxide and 25 nr. of six or seven vcrcent hydrogen oeroxidc. prepared by diluting 30 The l^rdror;en -'croxide solution was percent hydrogen «ix>xidc with distilled water. A carefully weighed sample of formalin to be analyzed was added tc the flash. This mixture w,s agitated for- about a minute and then the flesh -was vlaced in a water bath at a tes.iperrturo cf remain for five minutes. 60° C. one allow-ed to Tlie flash was allowed tc remain in the bath without heatin" for another five minutes: after that the mixture was allowed to cool to room ten;lor-turc and titrated with normal hydrochlo­ ric acid. in! ice tor. fix drops of broncthymol blue solution were used as the Tlie end loint was taken when the color of the solution 65. chanced from blue bo green. A blank titration vras made vrith 50 mm. of the normal alkali and 25 vx.. oi the dilute •>eroxide. The percentage ol' formaldehyde in the formalin '.vac calculated by the following equation: 5 dorr.;aliehyde _ (blank titration - sample titration) normality of acid x 3.002 ___ vreight of formalin sonnle Thic procedure vras carried out each tine a nevr solution of formalin vras used. Initial preliminary investigations. Preliminary invc:ligations ..ore conducted to determine acceptable c-.nstont factors, f .r the resins that vrere used in the princior.e part of the e:rerir.ent. This, research invc Ivcd the orconr-tion of resin in less than Iff gran batches which ■ere used to examine the factors. The ahenolic compounds used in the investigation inc udcd phenol, n —eresol, 3j5-dinothylphenol and 1. 1—ethylohoncl. The foimulas for tncsc corvoounds arc shorn in figure G . As a start in these investigations, small batches of phonol-fcrnaldclyde resin vrere arena rod. The ohenol to forma ldehydc ratio wac one mole of phenol to 1.1 moles of forma, dchyde and the final adjusted solids content was ph percent. The catalyst vras concentrated asmonium hydroxide used in tlie amount of nine percent of the ..•eight of tlie whenol. This amount of catalyst oroduced a slow reaction between phenol and formaldehyde and vras considered suitable for the resin reaction. 66. OH phenol hydroxybenzene iolecular height, S'H.Ill OH _u C H j m—eresol 1 hydroxy 3 r.ethylbenzene 3 nethylphenol loleculrr height 10G.13 OH CH CH 3 s5-Girae oliylphenol 3,5-^ylenol 1 hydroxy 3 3 3-dix.otIiylbcnzene hoiecular height 1 2 2 . 1 6 OH ch2 ch3 "igure G . r.:-cthylphenol 1 hydroxy 3 etiylbenzene L'.olecular height If:2 .16 id:cno lie cor.poiinds usoii in the product,.!on ol phenolic type resin adhesives lor bonding Jouglas fir veneer. 67 tie: batches of phenol-iolTraldehyde resin with f’O percent resin soli 's vrere pro-nred. cC, and i.eaction tiroes lor the resins vrere 1;G, pO, 60, rrir.utes. lor each resin the relative viscosity vras ever..-inch. -r.ch of tire sir: resin solutions vras used to bond Jouplas sir veneer into three-ply p.Iyvcoc' p m e l s that vrere tested for strength, due ply.vood panels vrere prepared and tested in tire r armor that trill be described later. due relative viscosities end tire results of the plv- vr?o i rhr-myth tests -re resented *.eactic:r dirvc ....... . . .— in tire follcvrins ta'ule: uly.vood Giron,-th*...... .V. . ■ ^ •) u ^toC/n 31u G79 •_---_p .u te s .u te s ,.► -,-X Wv^..u te s Lutes 'U te s ..elative Viscosit”*■ .:• r*» -» _1• W >• X• c*• n—• *• p . c*• *— •• C •* r- • — —• 1 . JO 1.1 ;y —• I-'-A c • t ’'✓ —• i"y — 2 <“kd — irt ply.voo d t e s t -» • . .rv • *? r . : \v ~ JC sp o c ir:;en s* w Li ^O'.i u. iir u L/. _ ’*y " ", y ''■ d o r tw o r : : r : c r . c . non tire rrc'er• s c u c r .c uu./w — " s'h > r c d 4O •_. *-v • 11# rtre:r"ti: data. - T-. -- c o t t e r TiUd".c c t v c c ■uuv . c t c r i . s t i e s t., 5 the -2.no l i n e - . .• ^ t h e _■ly ^ raild. irsv e t o ^ ^ .> . re o r c o n t s ' l i d s a.a „.U". H..C/ .. i_. Is n o t e f s u d f i c - v i s c o s i t ; ' to n r c v o n t e x c e s s i v e p - n e i r a .G i o n i n t o on H r • : .-eratio n • .d rs t, C t h e -.rood d u r i r y A c o r . s i d c r able rec o u n t of r e s i n vrr.s s p r o c e e d od tir e '- l y . . c -d n u n c i b e c a u s e cf t h e p r e s s u r e :>~ -■n b o n d i n '* , a n d rj.se- ,ue t e a t c : o o r r r r re d u c tio n in r e s in v i: 6C • cocity caused by the heat applied to cure the resin. becond, the glyc- erol oath used in tne preparation of the rosins v;as not heated to a starting temperature o f 1.15° G. before the reaction flock that con­ tained 2^henol, for.aaluchydo, and amoniur: lydrouide v'as immersed into at. inch a. procedure contributed a large m o u n t of variation in resin orepnrations created bp unequal heating rates and unequal reaction tines. 'fie description of the procedures for resin reactions and dc— iterations final.lv used in the onperii.ient vd.ll clarify the procedure used for preparation of the phono1-formaldol^ / d o resins of >0 percent rosin solids content. 1 rocodure for rosin preparations. for additional prcli: inary in­ vestigations and for final resin preparations, the procedures used for resin reactions, resin deb/drations, ant viscosity ccteminationc on the rosins vroro tine sane. The preparation of the resin consisted, of tvro operations. The first operation *.vas conducted using the apparatus chovm in figure 9. he this operation the required weight in grar.c of the phenolic com­ pound end the .ton. aldehyde vac placed into the resin flash. flask consisted of t v parts as shovm in figure lb. joined by means of ground glass flange s. The resin The tvro parts vrere the flack -.rith the reactants was placed into the onenin.q of the adjustable plati’o m of the glycerol bath which had been heated previously to a temperature of 115° C.-*. stirring rotor with a stirring rod, a v;ater— cooled condenser and a In the initial preliminary investigations the glycerol bath was r.ot heated before the resin flask vras irinersed into the bath. A F2 — S T I R R I N G MOTOR WATER C O O L E D ' C O NDE NS E R THERMOMETERS ADJUSTABLE PLATFORM S T I R R I N G ROD RESI N F LAS K OIL BA T H RING Figure 9 BURNER D i a - r m of the a ;cratuc used for the resin reaction. GROUND GLASS ^ FLANGE RESIN FLASK GLYCEROL BATH yijjurc 10. Details of the clycorol both and the resin flask used in the resin reaction. 71 wnoneter, vras adjusted to the resin flask. The a n oniur. hjrdrod.de ertalrst ir. the m o u n t of nine percent c: the rreirrht cf ;henol rev.. nr'.-; rir.sk. i..£ resan ^aask. warrant nctcr o oer, rti: i are;*. ;h._ orscd into the ~Ip'cerol bath. -ire of the recction -;ns noted. a.octree a on *tr ca aarc .re 9$° in about 15 don. The reaction v;ac carried out Tor the at -..-as "corci o,'L.i causcc At tiias point the starting .so ncuec that the 115° termer aturo ire ter. rorr.ture inside tire Tic.; nut cs ana t; tarn era ture ra se to mtaanec. ercent. panels. The adjusted Tliesc resins vrere used tc bond plywood The viscosity was detemined for all phenol-forra_dcliyde resins and r.-cresol-forrr.aldehyde resins. si’ , v.n in Table IV. The results of the tests are The 50 Minute ihena 1-forrwtldcbydo resin and the 1|D minute r.—cresol-fom aldehyde resin a ■ car to pive the best results. In pre >arinp the cresci resins, sor.evrhat larror quantities were prepared in order to invostir;ate several factors. iortions cf the 15, 10, a5 and 30 minute n-crosol-fori.rldclyde resins v;ere adjusted to various solids content and then used to bond plyvrood panels. Tlie panels were tested for plywood strenqth. The results shown in the fol crsinp table were obtained: deaction Tine 5o5 15 20 25 30 315* 301;;310-;319* Solisc Content 6o5 55/j 313*30k* 297* 303*- 2b;r>'271* -O'-"316-;;- 655 320332* 331:* 338* Yveraqc of seven plywood t e st so ec in en s in p.s.i from these results, it apoeared that a 65 percent- solids content should be used in the e:coerir.ent. The results for the resin of 65 per- 76. cent solias content seemed to be generally sonevhat higher than data i'r tlie other solids contents. It --as decided to use an adhesive spread of UO counds ;>cr 1,0•.-0 sqm rc loot in bending *.-lyvood. In order to see id this spread could be reduced, plyvocd v.ts bonded v.'ith various resin spreads. A 30 minute -•-eresol-iom: ddohyde resin vu.s used Tor tiiis investigation. ■ m e I s vrere bended and t e s t e d i'r each different spread. iVo Information shorn in Table III w.s obtained. Those rcs-.dlts suggcsted that a spread cf Lo vcunos per 1,0.0 square feet w.s a satisfa.ctory spread. Hie rolaticnsh-ip bctvrecr. the molecular v-eight of a phenolic ccn1--aund and the number of phene lie rings in a rosin s'prer.d vras then investigated. A phenol—fcm.sldehyde resin of 6f percent solids con­ tent, spread in the m o u n t of 1.5 grans ->er 20 square inch glue line area, w.s considered tc su mIp a certain nurber of phenolic rings. due to a greater molecular a*eight cf n.-croscl, caused by a methyl group side chain, C'ual -.'eights of ph.er.c2-ferr .a dch.ydc resin £ r.d n—eresol— ferr..:...dchydc resin vrould have a different nur.ber of phenolic rings. It '.’-c theorised that the n-cresol-fomrfdehydc resin in this c- se had a fc-.ocr number cf phenolic rings in the rosin spread anc therefore va s unable to f c m as r.any crc ss_dnl:s bct.vcen rolecuies as v.'as -.cssiblc for the pher.ol-forr.aldehyde resin. It -..vs farther thought that if the num­ ber of phenolic rings in the r.-cresol-fom.a delyce resin vac increased by using a greater solids content cf resin, the m-crecol-fcma. dehyde resin %could possibly produce plywood of greater strength than shev.n in Table IV. The follcv.-ing caJ.cula.tion a.as performed to dctexninc the 77 TA2LE III -jata c :: api*k a j k )a tidhcty liikuts ei— (A_0fOL-A'ilLALJf Hi Jh icJi?Il.: AJHAoIVl or>reaa .6 g r a m llyvfood Strength*- -»cr glue line 320 p.s.i. (25,v / 1,000 sq. ft. .9 grar.s oer glue line 329 p.e.i. (30,,-- / 1,000 SC. ft.) .2 g r a m nor glue line (35; / l , m •f-t- > Xu*/ ,5 g r a m per glue line 339 e.s.i. (U0,r / 1,000 sc. ft.) Average of eight olyn’oof tost aaecinens, 78. t a l l :; rv LATA Cl.* a.IALL BATCHDo CF PHBBCL- AND r.-CR3SOL-FO;-OCAlU3!:rj:2 ICSiSCIis Reaction Time Resin p he nol-f o rmal dehyde n-cre so 1-f oroaldehyde 50 minutes 60 minutes 70 minutes 80 minutes 90 minute s ^h ;1CO minutes 15 20 25 30 35 iiO minutes minutes minutes minutes minutes minute s*-- Ply-.Tood dtrength-»- Relative Viscosity 337 327 3u 5 355 368 366 p.s.i. "'.s.i. p.s.i. p.s.i. p.s.i. p.s.i. 1.8U 320 332 33U 338 3ho 351 o.c.i. p.s.i. p.s.i. p.s.i. p.s.i. ;.s.i. 2.26 1.67 2.00 2.03 2.21 2.38 2.27 2.28 2.30 2.32 2.35 -* Average of seven shear specimens. Apparent best resin to use. TABLL V DATA CL BL1ALL BATGI-lDS OF 3,5-j L A i 1B lL P I IBKGLAND m- ET;IYLFHNNOL—PCI22ALJDIIxDB hSoII'15 Resin 3,5-dimethylphenolf0 rmal dehyde m- ethylpheno 1f cmaldehyde iteaction Time Fly/rood dtrength*- U0 U5 50 55 minutes minutes*-* minutes minutes 297 325 317 20U p.s.i o.s.i p.s.i n.s.i 50 55 60 70 minutes minutes minutes minute s*-* 296 293 307 311 n.s.i p.s.i o.s.i o.s.i Average of seven test specimens. An 0 ?rent best resin. Relative Viscosity 2.1U 2.18 2.21 2.26 2.15 2.18 2.22 2.30 79. required solids corrbcrvt for the m —cresol—formaldehyde resin: 9U.11 / 103.13 = 0.65 / x x = 0.7U7 cr 755 solids Two plywood panels each vrere bonded with the 15 minute, 20 minute, 25 minute and the UC minute n-cresol-fomalaehyde resin. •Tore tested fcr plywood strength. These panels The results of these strength tests indicated that there was no basic for strength differences due to the possibility of a greater nuiu.ber of phenolic rings in one resin spread as compared vrith another. JAirthemore, the 75 percent resin solids solutions vrere extremely difficult to spread because of their high viscosities. ifciall batches of 3j5—dincthylphenol—formaldehyde resin and m — etliylphencl-fomaldchyde resin vrere prepared and these resins vrere used to bond ply.vcod panels. Tlie nlywood panels vrere tested for strength. The results of these tests arc shov.n in Table V. The snail batches of all resins had been prepared and these resins had been used to bond olyvroou panels that had been tested for strength. It had been decided initially that the highest ply.vocd strength value shov.n by any resin batch for any one of the rosins vrould indicate which reaction times vrere most suitable tc use in the experiment. However, --t upp er red that this particular orccedure -.vs sort cf a try this, try that affair. Consequently, it w s decided to find some other way for detcmiining comparable reaction times for the resins. It iiad been noted during resin prcpara.tions that each of the resins became turbid. at particular tines; the phenol—formaldehyde resin eo turbiJitv in abou ^ .cr' Oy nLXi-oE, m e tt— c t c cc J_—2 omr..-de:v rde resir. tv.rbiiitv in about ii r.inutee, tbe 3,5—cli; :.c.”.u.e rc:_~ fcoc.e.e - ,V - about sever. rbLnutcc, 1- 1*:ir.£idcrr”do “3 ^ N-A. >•/ . J i _ i-/ .• L» / g cl b " "CVICV.S ca; ter - . • A .1 W < 0 w> • • I __ . _ecs :on a; 'J ^ 1 ^GClLGL trO 1 Gl. Figure 12. The potentiometer used in the experiment for the determina­ tion oi' temperatures. fl't O * ar. -— tc t h e s t i r r i n * re d and t h e t i r e r c c c h t h e p a i n t oV t u r b i d i t y -.ras r e c o r d e d . :ac c r . m c ; : or. C-sl W. s t i r r bnp r o d . t h e tirr.c v;; r,>.C'^OC, reco rd ed . :n it Vhc r e ­ ■c oV h a r d e n i r . p u r .t i d t h e : • i s c c e e c n a n m t o ••:nn.„ up 0:1 f. 'v. v:r> r ru rir.p t h e r e a r 'in n* At i b i s p o in t t i n V his p o i n t v a s d e s i p — a *e oV h . i r d o n i n • a n d v;as c . n s i d c r e d t o b e r o c o n r rer.c.'.c:. c~ua. _r.e a v e r a p e o_ v and *c. r u c .iy s .e r e eon o/d XAcoca. p o i n t Y, ^ ■ ; r n 1:07 b:e c : o r 0 p n o n e 0 -1 ■ciioee a .v e ra p e o n .c 1 H . b l e V I, t h e v _::ce so t o e s . cCCG C.lv'Vill Ull ..^lC-lC Vx* score p r o c e d u r e ".roe c a r e ^iC 5.101iTl ; o u t 0:1 t h e o t h e r r e c o n e rod i n t h e c i p c e i . c n t . **c c 1 5 *5 "'ci* t/^c 1ic^ c " o.iC ‘ ,..e : c a t. s a o r e o a c c a r ■_or. .a. arvoo-.. ’CCU. ;o. _no r e a c o o : n. u_n.e _ o r t n o s r c s o r v.-ac ? 0 r . d v o t e c , A'. Vue d i i i ' o r e n c c b e t . ; o e n t u r b o 'd tp t h e 01 .i o n t i c .e o f ? 0 j i i n u t e s v a c 1 r.in u to s . ■a a■">1e c t - a s sbevm i n Vo.bio ’1 >0m-^..s e n d t h e rcac— <■» to_j-.e ,-■>'e Vor t h e o h .e n o l—I'orrr— d >;T.” ;e r e s i n r e a c t i o n t o r e a c h r> o in t Y .;ac r e c o r d e d a s l i d .2 r . i r . u t c s , -iv ic h -a v o 0 t h e ' • •* v e •» 1 -f* r* rs oV I t . 2 : i n t o a bct-vc-m. t h e o v e r a p e t u r b i d i t y t h e i..o U ..v_' - tI-' e r . t c d a p o r c o n t a p c 00 or l i d . 2 :._Lnutns. T hen 21 d i v i d e d oy - o r e p r o - c r cacticn tire Vror. turbidity to point Y Tor : icnel-V orr.'.r 1 > h v i c r o s i n . 00.c.orcr.cc 00 nos nereenoo 'e v.'ot then m a i l e d to tlie a..cor. turbidity tirr.c and Y tire Vor the other resins. Vhc oronco jo1y ,-ccr. turbidit-- tii.e Vor the m-crecol-oorr.alderyde resin I 83 TABLE VI RE oilJIEICATION AND HARDENING DATA Average Turbidity Time (minutes) Time to Reach Stage Y (minutes) Time Difference (minutes) pheno 1-f 0 rmaldehyde 6 9 .0 115.2 U6 . 2 n-c re sol-formaldehyde 12.3 6U . 1 5 1.8 3 > 5-dimethylphenolformaldehyde 6.9 86.1 79.2 m-cthylohenolfomaldehyde 5.8 llU. 8 109.0 Resin Calculations for Reaction Times 90 minutes • Reaction tine for phenol-formaldehyde resin. 90-69 ** 21.0 Minutes between tine for turbidity and reaction time for pheno 1-fo m a0 dehyde re sin. 51.8/U6.2 = 1.12 Ratio difference of m-c re sol-formaldehyde resin and phenol-formaldehyde resin. 1.12 x 21.0 = 23*5 Reaction time after turbidity for m-cresol-formaldehyde resin. 23.5 + 12.3 = 35.8 Reaction time for m-cresol-formaldehyde resin. Calculations for 3 *5-dinethylpheno 1-formaldehyde Resin _______ and for n-ethylphenol-fornaldehyde Resin_______ 79.2/U6.2 = 1.71? 1.71 x 2 1 . 0 = 35.7 35.7 + 6.9 = U2.6 or h3 Minutes reaction tine for 3>5-dimethylphenolfomaldehyde resin. 109.0/U6.2 = 2 . 3 6 5 2 . 3 6 x 2 1 . 0 = U9.56 U9.6 + 5.5 = 55.1 or 55 Minutes reaction time for m-ethyloheno 1-for­ maldehyde resin. Glu one point Y Tor this resin ras pl.C minutes. The fraction 21 divided oy H6 tires 3l.C [;ave a period of 23*5 minutes for the rc—crcsol—form— aldeliyde resin to be reacted after turbidity. dince the turbidity time for the rc— crescl—fon..aldokyc;o resin was 12.3 minutes, the reaction tirr.c tc produce a comparable resin vrac 23.3 plus 12.3 or 36 minutes. Tlie m-cresol-fornaldehydo rosin for the final q-!.uinp problem was reacted for 36 minutes. The other resins vrere treated the same v:ay to qive a reaction time of !;3 minutes for the 3 >: J— dimetliylphenol—foxmaldciiyde resin, and ninutes fox* tlie n-eth.ylph.enol-forrr.aldel^/’do resin, fliis procedure vras based on the assumption tliat when the resins had reach­ es point Y they had a ;oroni.iatelv the sane viscosity. is in;: the calculated reaction tines as indicated above, the final resins vrere prep or od. he sin adhesives for the main part of tlie e::pori.ient. The r'csin alhesivcs fox' tlie rain nart of the e::nerinent vrere prepared in the sane 1'.anner as tlxat used for the rosins, cf 13 percent rosin s lids con­ tent in tlie orc~b '.inary invcstipatiens. scribed. fliis procedure has been de­ dacii final resin '.ras ;,ro .orod in Your batch lots of about ypu pi-ar.c of resin per lot. The came procedure vras used tc prepare each lot of a narticuiar l'csin and the lots were i.uscee. to proaucc a final re sir. quantity of about 1,CG0 ;trail s of resin for each resin used in the e:sver:imcnt. by prcoarin;: four batches ox cac.i l’csin, an avcrape solution rc suited for each type used in the e:rvex*ament. Thus particu­ lar oroecdurc pi’cvided a resin in each ca.se tnat coula be reproaucod satisfactorily. It also provided the means of producing 1,C00 praxis of >-3. resin r.ore es saly tnan 'would lu vc been tlie case if tlie entire ouantity of resin hud been nr educed at one tine. Tlie resin flasks avai_abie vrere net considered, of sufficiert sise to produce 1,1.00 qrans cT resin ss.ti sf acto r ily. The follovainq conditions Tor resin nanui'acture, as determine d in the preliminary investiqations, -..'ore adhered to in the r.ain part of tlie c rio d . I n o r d e r to t e s t t h e v a l i d i t y of th e th e o ry , a b o u t 100 g r a n s o f d e h y d r a t e d p h e n o l —f o r m 1 d e h y d e r e s i n v rere r e m o v e d f r o m t h e r e s i n f l a s h shon th e f i r s t b a tc h c f t h i s r ^ s in vac p re p a red f o r th e f i n a l c x p o ri- m c n t r l phf. c o s o f t h e p r i n c i p l e i n v e s t i g a t i o n . '.e r e a d ,ju s te d t o ic lu c re The 100 g r a m s o f r e s i n 69 T' e r c e n t s o l i d s c o n t e n t u s i n g a 9 0 - 1 0 m e t h y l a l c o h o l ­ so lv e n t s o lu tio n . Tlie r e s i n v:as t h e n u s e d t o D o u g l a s f i r v e n e e r t o m.aho e i g h t o ly .v o o d p a n e l s . panel v. t .s su b je c te d to a c lif f o r e n t o p e n a s . e m b ly s p re a d enough Tlie v e n e e r f o r e a c h u irio d . These p e r io d s r a n g e d f r o m f o u r h o u r’s t c 3d h o u r s a t i n t e r v a l s o f f o u r h o u r s . t i n e p e r i o d . c ? .e p e e d t h e o a n e l vrac b o n d e d , t h e n p l a c e d i n h o u r s tc- a s s u i 'e cos. i l o t e c u r e o f t h e r e s i n . c n o v e n f o r t il At th e end o f th e r e q u i r e d t i m e p e r i o d i n t h e o v e n , e a c h p a n e l sras s a w e d i n t o t h e r - > e c in e n c v .c r e t e s t e d . As e a c h s h e a r sp e c im e n s and Tlie r e s u l t s o f t h o s e t e s t s m e re c o m p a re d r l t h r e s u l t s o b t a i n e d 1y u s i n g s. s i / i j a r 'r o c e d u r e b u t s u b s t i t u t i n g e th y l a lc o h o l a s th e a lc o h o l com eonent o f th e .o.' r o m i n a t c l y t h e came c l p n o d so lv e n t s o lu tio n . s t r e n g t h s ..'ere o b s e i v o u i n D o th c a s e s , T he o r on a s s e m b l y p e r i o d , r e f e r s i : t h e t i m e b e tv .'o e n s p r e a d i n g a n a d h e s i v e o n n i e c e s c f vrood -are b o n d i n '; t h e s e p i e c e s o f v.o ad, d u r i n g w h i c h t i n e t h e s p r e a d v.'ood s u r f a c e s a r e allo-..re d t o l’ e n a l n s p r e a d s u r ­ f a c e up to th e s u rro u n d in g a tm o sp h e re . 87. i n s i c s t i n g t h a t r e t l i y l a lc o h o l and e t h y l a lc o h o l c o u ld be in te r c h a n g e d b u t n e a t i c r one n o r th e o t h e r meclo a n y a p r c c i a b l e d i T T c r e n c e i n t h e coen a sse m b ly p e r io d r e p a i r e d T o r b o n d in g ;ly v :o o d i n t h i s c ro e ri:. c n t . Tlie s e c o n d s u : p l o m e n t a l i n v e s t i g a t i o n v:as c a r r i e d o u t b y p r e p a r i n g t v o b a t c h e s cT c - c r e s o l - r o i r a i d e h y d e r e s i n . One od t li e r e s i n b a t c l i o s vrac r o a c t o d T o r a p e r i o d o i 1 t'.vo h o u r s a n d t h e n d e h y d r a t e d . The s e c o n d b a t c h v:ac r e a c t e d d o r t.vo a n d o n e —h a l T h o u r s a n d t h e n d e h y d r a t e d . Xn b o t h c a s e s t h e d e h y d r a t e d r e s i n s h a d v e r y lov. v i s c o s i t i e s a n d g a v e o f f v e r y s t r o n g f o m a 1d e h y d e r u n e s . The l a t t e r c h a r a c t e r i s t i c t h a t a l a r g e p r o p o r t i o n oT T o r.;s d .d e h y d e h a d n o t r e a c t e d . c o u _ d n e t b e u s e d t o b o n d n ly.vcocl. in d ie a te d The r e s i n s I t rras a s s u r e d t h a t p - c r e s o l - T o m - a.ddehyde r o s i n v aculd a c t t l i e son e a s t l i e c —c r e s o l - T o i r a l d e h y d e r e s i n a n d n - c r o s o l - f o m a l c e h y d e r e s i n s v aere n o t p r o p a r e d . 88. Fabrication or Jouglas Fir Plywood The r e s i n a d h e s iv e s w ere s to r e d u n d e r r e f r i g e r a t e d c o n d itio n s u n t i l v e n e e r had been o ro c e c se d f o r b o n d in g , at a tire h e s i n s w e r e p r e p a r e d o ne a n d o n l y t h e v e n e e r r e q u i r e d t o g l u e t h e n e c e s s a r y n u r.b e r o f o ly v o o d p a n e ls i n r e l a t i o n tc one r e s i n w as p r e p a r e d f o r b o n d in g . Tlie t i n e b e t w e e n 'U 'e p r r i n g t h e r r s i n an d u s i n g i t f o r b o n d i n g v e n e e r w a s 96 h o u r s f o r t h e i n d i v i d u a l r e s i n s , t h i s am o u n t o f t i r e b e i n g r e q u i r e d t o d e t e r m i n e t h e o p e n a s s e m b l y t i m e t c u s e i n b o n d i n g t h e p ly w o o d a n a t o p r e p a r e th.c v e n e e r . The o ptim u m o p e n a s s e m b l y p e r i o d -.ras d e t e m i n e d f o r e a c h r e s i n used in th e e z m e rim e n t. Ac an e n a n p l c c f t h e m e th o d u s e d f o r a l l r e s i n : , t h e n r c c e d u r e f o . .low ed i n t h e es.se o f p hon o 1 - f orr.c.ldoliyde r e s i n w ill b e p re se n te d • f i v e o p e n a s s e m b l y t i m e s v rere c o n s i d e r e d . 16 h o u r s a n d 2h h o u r s . ■. e r e two h o u r s , f o u r h o u r 's , e i g h t h o u r s , These Two .l y v o c d o a n e l s , r c u r e s o r t i n g e i g h t plywood t e s t s p e c i m e n s , for e; c h p e r i o d v rere t e s t e d f o r s t r e n g t h . The a v e r a g e p ly w o o d s t r e n g t h r e s u l t s •.vere f o u n d t ; b e a s f o l l o w s : no o. s.i 2 hour period *-> h hour period 1.J. ■?/; p.s.i y r t- ■ hour period 333 16 hour period 326 i.. ,.i hour period 369 ) • ' 5 X • 9 G •i • s.i Tne r e s u l t s o b t a i n e d i n t i i i s i n v e s t i g a t i o n i n d i c a t e d t h a t a. Li; 39 hour open assembly should be used dor the ohone 1-foxr.cl dciiyde resin. iim.ilax' results vrere obtained dor the ether resins. :::ur r'cr. assembly w e Ccnceguently, a 21; used dor all resins. The veneer to be glued vas dirst x’amoved drcr. its protective .Tap­ pings. The veneer sheets vere hand sanded lightly, using 3/0 oven coat garnet dini shine paper, ’ due amount od sending -.as controlled by using 10 sending strches on each sheet. The ourpooe od the sanding was to remove oily, '.racy, or gurry substances dree: the sheets, to freshen the surface, and to reduce grain ridges on the sheet sux’daces. iince sanding tended to occlude the openings in the vro od surdaces, compx'essed air was used to remove loose v od-dust and v.ocd particles. The sheets vere then placed into three-pay assemblies in such a vay that lathe chechs in the core vcx’e oriented ■•t o coi'ly. Lathe chechs are dine chechc ox- crachs on the under suxnh.ee od veneer, deveio :ed by the rotary lathe hnide as It cuts the veneer. a;a'■crimentad evidence has shov.n the t the strength, od ~ lv.rood is affected by the orientation od la the chechs in the core ply. f o u n d b v b e t h e l a n d H uffm an tasted in tve -.rays: (9) that nly.vood shear specimens could be l) specimens could be pulmcd on on, which would open lathe chechc, or 2) specimens couid be pulled closed ..hiea would tend to close lathe chechs. i'i.pure 13 shears how orientation cd lath.c chechs in relation tc oly.rood shear suecim.en notch.es vrill cause lathe chechc cither to bo opened cr to be close., during piy.vood shear tests. ..her. shear soecir.ens arc pulled open, the pxhnclpie component od force, pulling the specimen apart, acts at right angles to tlie lathe I 90 t A. SPECIMEN PULLED CLOSED FORCE PARALLEL TO LATHE CHECKS LATHE CHECK FORCE PERPENDICULAR TO LATHE CHECKS B. SPECIMEN PULLED OPEN I'ypos oh pull in plywood shear test cnee in:one as related to lathe chcch orientation. A. Uotchos in the snecincn oriented so that lathe chechs rcr.ain closed during the shear test. 12. hotchec in the specimen oriented sc; that lathe Cheches are nulled open during the shear test. , Gluing area ■ 1 5 = 20 square inches ana 20 / llj.li. = 0.139 square feet Then 1 / lo.lh - 0.139 / X X — 2.5 grans per gluing area. i’or parts cl the 'robler. thet did not require theaddition of iLnut shell ilour, the S'oroad por f cc veneer s’ neet .as 2.5 pr-as cl' )sin solution. f’or th.c e:c 'erir.:cntal phases of the problc:. tho.t required the ndu .on of -Tlnut shell .h.our to the resin, the nunber of gr"... oi' resin lution -tor Tree veneer -..as calculated rs icllc .c: i’or the addition of 10 n'U’cent '. alnv t she...:. H o u r . 2.5 grans :: 0.65 = 1.63 gr.'sis el rosin solius in the un.aodified resin spread j_.o3 i*ri-u.-s r ....lO “ u.lo pu..c o_ ..1.1nuu s*j.e.^-i_i.^.uur added H r the spread on eachlace veneer 2.50 4- *J.l6 — 2.66 grar.s ol resin solution ’ percent vralnut shell H o u r spread vith 10 :cr face veneer. lor th.c addition ol 20 percent walnut she.l 1 il.our. 2.5 g r r j .s 0.65 = 1.65 g r a n s 1.63 grans :c 0.20 = 0.33 grans 2.50 4- 0.35 = 2.f3 gra’.:s of resin solution vrith 20 oerccnt vralnut shell5 flour s read per 1 cc veneer. i’or the addition of 30 nercent walnut shell Ho u r . 2.5'J 4- C.up = 2.95 grrx.s cl resin solution spread per face veneer. It is noted that the percentage ol vralnut shell flour added to t os in solution .r;..s based on the resin solid.c content of the solution. ie increased soread lor resins to which vrainut shell flour had been 93. ao.ded nad as its purpose trie i.aintenance of c on strait resin solids and constant solvent oroportions. Tills technic per .itted onl/ variation in tnc quuutity ol m l n u t shell llour, v.iilch -.7as the desired effect. Zt '.ras notco. that the moisture content ol the veneer d r o m c d from seven percent to five percent during open a ■serbly, '..hich is considered to be a more desirable moisture content for bonding rood v;ith ohcnoiic typo r o sin adh e siv c s . The actual bonding of the veneer mas accomplished by using a Carver Laboratoipy Press v.-ith electrically heated hot tiiis arose is shorm in figure I);. ;Iatc platens, The to:.. >orature, ..viicli ivas 320° 1., ;as controlled by thermostats inserted in the pistes ol the ircsc. ll.is temperature cou„d be controlled to plus or minus five deyrcos, v;hich mas much closer control than •..•culm be found in a commercial ply— v:or.d oross. Tom erabure ol the nlrtes v. t s monitored by the 3rcvm c3.ec— tronib ootentiomoter shovm in figure 12. The pressure used on bonding panels '.ras 173 pounds per square inch. Trccciny time as 13 minutes. After a panel had been removed from the oross it ;;as olaccd. in an electric oven 'vhich had a controlled tempera— turc ol 73'° C. in order to ccnnlctcly cure the resin adhesive. Preliminary bonding tests of ply/rood indicated that lb nxnates in the nrcss v.ns not sulf icient time to com \Lotcly cure any ol the resins. These tests invo3.ved an empirical procedure hi a;mch tv:o ply. rood ranej.G .err: bonded lor each o_ sine bonding times. II, 21, 2u and 3'j rinutns. Bonding trace mere Id, 13, Plymocd shear specimens Iron these panels ..-ere saved, soared in vratcr for hi hours, and tested. The tests shoved 9k. Figure lk. The hot ore os used in the exeerixient Tor bonding ply,rood panels. 95. that bonding tiros from 12 to 30 minutes caused an increase strenptn,■sue 30 n m u l e inulywood bondin’ tir.e pivinp the higheststrength. The results or tnese tes'os are shown in the f olIov:in;3 table: Curing Tine*(minutos) lly.vood shear Jtrenpth*--(n.s.i.) 12 15 18 130 213 225 2h6 21 285 2h 30 29U --- Minutes in a 'not -.rocs at 320° 1. ----- hvera.no cf eipht plywood shear soecirenc. In view of the la.rpe number o_* panels bended in this investiga­ tion, r 30 or acre minute bon. liny tiro v. ".s rot convenient, rtu’t h o m c r e the tort values obtained indicated tint the rosin res not cornletoly cured. Jonse'-uently additicna. tests were ccrelucted to deter.ine .viiat j.cn.rbli ol tiro in on e cclric oven at 75° 0. would be necessar/, after a 15 rinv.tc press tire, to co;:. >letely cur'.'; the ai.esive in the slue b:ncl. fl.o results of the tests indicated that the length of tire the eanels should rcr.ain in the oven varied: -with the resin used., he the basis for the d~termination of oven tir.e, phenoi-fema dehyde resin was used tr. bond fywood. The d.. ta obtained from shear specimens prepared fro::, this "ays;’cod are shown in the f o ’lowin'; table: I 96 during Vine^ Ply.vood dhear strength ^ (hours) (p.s.i.) 6 270 10 295 lh 320 16 2k U8 33U 351 3U6 / Tire period in an cucctric oven at 75° C. alter 15 minutes crossing tine in a hot press at 320° P. fi Average of eight ply.vocd shear c'>ecir.iens* The data Torthe .ohcno 1-1 orr.aIdehydo re sinbonded olyivood ted chat2h hours in the ovenafter a aouarent besttime. Tor the resins. 15 minute 4’occ ti.e was the In order todetermine oven three rosins,stroke cure tests--- vrere indica­ tinesTor the other conductedto determine cure time Cure ratios -..'ere calculated Tor tiireo resins, using the strode cure tine and host oven ti'o Tor ;>honcl—Torrr.odehydc resin as a basis. The ratios v«erc used t. determine even cure tine. oven tine Tor n-crcso1—T o m •.•dolr/de rosin -.;as determined as Toliov:s: Stroke cure tire Tor stroke ’henol-Torsr^elipdo resin, 105.0 seconds; cure tine Tor m-crcsc 1—Torrnalde'vdc resin, 12k.kseconds. Cure ratio - 122.9 / 105.0 - 1.17 Cven tir.ie ™ 1.17 Stroke 2k — 2t ,0o or 26.1 hours cure tii; e, curing ratio, and cven tir.e Tor al.l resins are shoun in the follov/dns table: * The stroke cure test involves the curing oT a small! v.eighed quan­ tity oT resin on a hot ‘Arte at a particular temperature. The resin i: stroked -;ith a cnatula in a two and one—half inch square area until cured. IT constant conditions of a eight 1' resin ~-* (hours) pheno 1-1 o rr.aldehyde 105.0 1.00 2I4 .O n— cresol-1 errnaldehyde 122-9 1.17 2c *1 3 ,5- diir.ethylph eno 11'o ms. Id ehyde 1U0.2 1.3U 32.2 n— et:ryloheno1— lo nna Idolryde 156.8 1.H9 35.8 Resins cured on r hot pinto regulated to320° F. Stroke cure tir.e of ohcnc1-f orr.isldchydo resin divided into the stroke cure ti..e for ctlier resins. -U'TT-i:- Curing ratio ol resins r.ultipliod by 2bhours to give required curing tir.e in the oven at 75° C. As indicated in the above table, 2l; hours v;orc required to cure the glue bond in -anol.s bonded. u-ith "hcno 1!-Ton.in1denydo resin, 2C hours v:crc used dor the r—ere sol—loiaIdeliydc resin bonced panels, 32 hours '"as the tii c to cure the glue in panels bonded uith 3, 5-din otliylphono 1xorrialdehr/de resin, and the oanclr bonded vs.th n-cthylphonol-fom.aldehydo resin required a period 36 hours. It v;as necessary to be certain that aid resins v/ere completely cured. Tor tv;o ressens. First, the plyvrood test soecis.ens viere to be given a Ho hour seal: in cold viator before testing to reduce variability in )ly..rood test results. second, the objective ol using the tine fac­ tor v;.vs to try to determine v.hethcr er not the strength cl the com­ pletely cured glue bond increased v.ith tir.e, since an increase might indicate ib-at a conditioning >criod v:as required lor glued oly.Tood to alloc; additional adhesion botvrcen the glue and the uood. 98. After the curing period in the oven, the xLy.vood panels v.-cre stacked v.ithout special means being used to control moisture content since each olyv/ood test s ^ecir.:en would be soaked for the I48 hour period in vaster. In order to examine some ohysical choracteristics such as hard­ ness, toughness, and crazing of the resins, resin films for each resin v:ere cured on glass plates. Both unmodified and vralnut shell flour fi.lled resin films v:ere examined. Characteristics observed for resin films vn.ll be referred to later in this thesis. 99 hreparation and Testing or Plywood ah ear Specimens The ply.,'ood panels v.-crc sawed vrith a sueciol veneer and nlyvood sav; into test s )ecinens one inch vn.de and three and long. 021e—quarter inches Two notches vrcre cut into the specimen, one on either side, so that a one square inch sheen area remained in the center of the test specimen. viguz’c 15 indicates the procedure used in bonding; and sawing ply— vrood panels into test specimens. At the ten of the figure is shov.n throe nieces ol veneer with the grain direction of the f v . e e plies at right angles to tlio grain direction o f the c re—p?.y. These veneer are bended together into a three—p3y plywood vancl. uly.vood panel four plywood test s .>ecimens are sa*wcd. :icccs of from this The test speci­ mens shov: t’ ne position of the notches and the one square inch of shear area. There mere 192 canals for each rosin adhesive, from v.iiich 760 test specimens mere obtained. The >anels './ere numbered from one tc 192. ha.ch panel, and subsequently each test specimen, vfacalso narked vrith the letter r, C, A or d to indicate that it was bonded withphono 1- formaldehyde, n —cresol—formal delude, 3,9— cincblyiphcnol-f ormaldeliyde or n-ethylnhono 3—fonraldc: lyde re sin , re a 2ec t ively. .'sfter saving and ma.rhinp th.o test s >ecir.cns they vere pieced in a wire basket, and the basket was suspended in cold water for Ho hours. .ifter this, the s c c i ’ens were tested with a xiiohlc Ply/nod Testing; loo. * H * ’ PL* » o o o / TTT7 zzzzz ^CU t’q ^ n o o ^ 1 °*' v Pn„ ^ Q e t tO ^+J '^CQr.-. fc°^t “ i-fOj- *, °-,eoi a o n . ,e 101. ...c.cn_nc j The u — vtcX'Xwtccl JLii 'lyne-d testin': mac-line n.^T.tz'0 ha;. a cr -acity cl 1,0:,.: younds and Icr.v.c a ”!-L.y.."aod tost c ^ecir.cn at the lv.ic cl 6ca •••otuv:s cr minute by morns ex' rn electric motor uliich actc, t;iroir;h a ecrc.v, to advance a ye ice ridiu;: on the boon ol trie machine. The boa::, cl the machine bal­ ancer on ’rrifo eclr*cs v'hioh arc located V,> vc the u o >or yri i 'in • liead. 1 rod and balance weight arc al-tachcd to lie bona ol the machine. terti'i” -X’ccecairc includes the lo cv.hLnd onorati* ■ns; in l a c e d in the cyecial vro•>d ;rio .iny heads• The The The teat s '.•ccim.on -oisc *..rhich rider ...n the Lea; is "djuctod to the ri :ht ride ol the boa- re that the indica­ tor cn the bor; coincides \;ith the aero ;:nrh on the oca 1c on the bor. The boon io a H o m e d to balance and, 11 out el ba„ancc, the balancing oV'ht io novel unti? balance io obtained .end., then ic titlvtened on the rod. The her: is than io 'ored on f ie ri on. s H e . The yxi . ;lnj jairs aro ti ytcned on the test s eci.on -.-hieh 'no boon inserted into the heads. The 2a or ;;rh adjusting han.tvrheel at the attorn i.l the machine is turned anti’ a very cli,":hb t e n d o n h- s been i..> died -,n the suecincn. lie lever on the noise ic nnved Irom the no f o.: a. 7gs th.e ••oiso m d the a.oadiny ocrcu. the d m r 'ocitlon v/hlch The be sc: is ,;rs.dually unbal— snc ot. bra the movement ■ .d ’ f ie ;eisc unti.l the levcra/ ;o created by the lea;' breads th.e s-ecbren. h c dutch automat Lcally etc acre.; and the sirenytli in total ool; e, nointind f e the lcadiny >ounds is shnvn by the indicator on the th.e scale on the; bear;. lor yiyv.-ocu r.uea.r s ecir.ens h.a.vin.: a one inch shear area, the f tal load :.c read in oeunac ,.cr cr.uaro inch. In unhind -'ly-Tood shear tests certcd.ii lac tors v.'ere considered in 102 16 . ^ J- e:r * >~> * . t.■ >i rL i ■• —• *-, » *.r* w **^ine 103. I i o U. the c;X2cir.cn res increased up tc a :oint .'here the c )oci:r.onc had a r.ioirturc content od about 12 norccnt. recnZ.tr henan to cocrcrec. beyond t-iet oint bhe strength 1 -“ DO•> o u o ::'! o\y "arm pp nT.’ o v a . , U O ' i ’-o A O T 'S o n ~ ~ ■rancan o air onon •-aoa <.o ..a s o; or ' ..o GnOC . ... v t'T l'[o 'o a r o .;;oT 3T .:.r;o ono.r :o:.oC —TOO'- su o ix r o o c fc j 3.V 3 O.TO " 070 ■'.UO' ■ vo I JI . j j/X •p a rn rn o v o p T.TOT! !OTq.’;tr"Tr“ o T :o _ ;ir or o n o .v . voTO Touoo • O ' o u c t i ~ ' o.;;o o nop paar. -q o^ a nr: n novo .ic : o n o j .\ c p /p isa n m nop o a t .t t c .v t o ir u otjtoolo; tout a ; oo ■•a a n out oa Aovnco: t: t nXV.'y ‘ j p : ; o .i j~ jv o p a •v : . o i v up. Jv on pa . v o p : p .o.._pr. anr ;a a or ~ o n ;or LITC o n prauooro; 'at: O 'a C v O ' ‘o v o r - o ; . r v rr j t \Of' .t : ' o ; v U~S 3vC a n or. :oo puc i ■)OG.'A q.ou r norp. :p-x.o. W or on ; o a . r ; ^ ;p: u o n n a n o o r s P 'O ." u .r .0 7 7 on :o : tv ,-fsO o on r ,.' O j vout 70- 7 onouLa no rno; nvox.;a nop poirreq.t^u non-op upvr jo n o p p o proron • pr •£0T • a f oar r.;::o n p ‘ u o p a - . u t . o ‘popuo runa.,:-:a pcnppA ppvr: ’/ o v a n o x p .'.TU s t nuv: U ' ■r.o or. o .'.n n o c op .rvoTT m o n l. .'>rTAV.XJ oil. pu xi O ouorruoov n ■OO'O. avarra.v. p u o o n o - on oz o vp nop ono :p r or -vnc' 106 TABLE VII FLTXGiJ JTicSIJuTH AOJ Wuyju KAILUItK JATA FCA FIU:i:OL-FOAilALOEIIYDS R0GHJ Specific Gravity (Groups) Time 20 250 100 251 100 258 100 v\ cCsl 12 0 10 ) 2hh 255 100 99 263 260 100 100 256 259 100 100 'iValnut Ghell Flour (Percent) 30 0 10 20 30 0 10 250 350 352 265 285 303 100 10 0 97 100 100 72 97 281 315 280 253 338 353 271 100 loo 98 100 100 77 97 266 295 305 285 259 353 350 100 100 97 100 ICO 73 100 257 256 255 271 100 100 100 100 295 317 280 251 100 100 100 100 257 296 2 5 c 100 IOC 100 2 3 9 291 237 100 100 100 287 268 3 2 1 28? 1 0 0 100 IOC 100 256 100 258 100 253 301 255 2 5 1 lOo 100 100 97 2);6 293 250 252 100 100 1 0 0 luu 219 273 318 275 100 95 100 100 2 C0 271 315 295 100 100 100 255 258 1 0 0 100 287 262 310 271 267 28 U 91 100 269 285 100 100 270 255 259 10 0 ICO 280 253 255 100 100 100 100 259 282 252 253 100 100 100 1 0 c 16 286 275 318 295 95 1 0 0 10 j 100 253 288 255 IOC IOO 100 239 277 256 100 99 100 2li3 100 235 100 98 IOC 100 100 287 258 313 271 100 100 100 1 0 c 289 256 3 1 1 100 100 100 205 258 312 99 100 100 271 100 270 100 r-/■ 257 100 289 272 100 IOC) 100 100 258 lOv 278 100 100 100 100 269 255 306 276 100 1 0 0 100 100 269 2 5 0 253 100 100 100 219 2 5 1 259 100 100 10 0 288 280 253 308 266 262 296 270 100 100 100 100 20 356 100 356 95 357 loo 30 315 76 316 93 310 97 339 353 353 316 85 82 90 97 0 358 69 363 91 359 91 368 86 350 355 82 92 358 35o 83 07 352 355 93 03 355 35o 100 J l 353 360 512 376 77 68 92 98 352 362 503 378 85 73 80 97 358 310 5o6 377 CO 81 95 96 357 369 5o6 370 75 93 96 9 8 351 97 351 90 335 100 350 100 355 3 0 ^ 100 100 362 353 100 _91_ 356 365 365 355 83 95 100' 100 353 363 368 356 72 98 100 loo ^zJ 355 350 371 3<-o 10 20 361 385 97 87 360 393 100 93 361 396 100 93 363 38 C 95 90 80 95 100 100 357 369 38c 350 82 95 100 100 358 395 510 90 97 100 353 390 5 16 75 98 100 3 6 0 390 506 75 97 100 358 386 517 73 97 98 370 35 1 90 97 360 376 90 97 372 356 97 97 361 360 90 100 368 376 105 90 100 98 363 360 521 72 100 _95 36 2 365 515 66 100 93 361 380 515 65 97 92 395 365 100 98 388 356 10^ 97 38; 3o9 98 100 395 365 95 97 30 320 93 320 82 327 80 313 82 3 60 97 377 96 376 93 369 99 3^4 r> OO 395 95 396 87 398 97 107. TABLE VIII PLY.i'OC'D oTiu'uiaTII AK.j ',ivOJ FAILURE JATA FOR m-CREoOL-FCR] AIJJEIIYDE RESIN Specific Gravity (Groups) 1 2 3 ’.Valnut Shell Flour (1 ercent) Time 0 10 20 30 2^2 25U 265 25U 100 100 87 100 265 2U8 251i 2U6 90 10 0 87 100 266 255 268 2U6 100 1 0 0 96 100 257 257 258 2U6 97 100 97 100 265 270 262 257 100 100 100 100 273 266 268 257 100 100 ICC 100 270 265 270 2h3 100 100 100 100 273 267 253 252 99 1 0 0 100 100 o— tr' c' 263 Rw6 271 < >> 100 100 100 100 1O 10 20 30 21k 308 300 268 100 91 10 c 97 268 303 292 280 90 100 90 99 280 301 296 262 90 96 99 2.00 282 3Hi 297 262 100 98 98 97 317 98 317 99 317 97 316 97 328 93 330 9h 3<-e 98 273 100 275 10c: 286 100 295 100 277 296 100 100 323 277 280 93 100 100 0 10 20 3h6 3k3 351 80 68 97 326 33k 335 75 81 100 3k 3 337 33^ 91 96 76 330 3kk 352 93 66 86 36 6 351 366 91 97 98 359 359 371 9 6 77 9k 371 377 376 90 9U 93 370 3iiS 360 86 100 96 30 373 96 372 98 367 98 37U 99 380 82 368 85 359 68 377 73 0 10 20 30 367 kl2 367 389 91 90 100 92 357 a o 5 380 393 93 93 100 93 356 U io 375 393 90 93 93 92 3k2 UoU 370 U02 100 82 100 97 369 383 379 82 92 96 367 380 360 91 77 90 370 385 3CU 95 85 96 376 377 363 90 86 83 100 100 100 100 290 310 260 307 97 100 97 10c 292 315 2 60 295 100 85 97 95 312 325 272 303 92 50 100 96 317 322 26 U 296 95 100 91 99 357 372 363 397 86 8 i 65 85 367 362 377 397 90 100 96 90 367 350 367 a o 6 93 100 Oo 96 3kk 358 387 391 66 85 76 91 361 387 86 91 353 385 82 83 357 361 70 66 357 366 50 97 290 279 2il6 100 97 100 267 279 257 95 100 100 303 33k 282 76 100 100 301 325 266 86 96 100 353 373 37U 71 91 86 361| 377 370 80 96 85 365 372 370 82 98 90 368 380 369 s o 90 65 orc' 371 k l 6 70 100 93 310 367 ho 2 71 97 93 361 369 U76 67 97 92 370 382 a e i 70 93 90 267 257 260 262 100 100 100 100 276 256 252 269 100 100 100 100 268 250 257 266 16 0 279 60 266 100 27U 100 275 100 275 257 270 100 100 100 265 260 279 100 100 10 c 297 100 305 100 295 321l 289 306 93 loo 100 97 297 336 28 u 301 100 93 ICO 100 373 86 388 81 387 78 379 81 387 80 396 63 383 63 395 75 393 a i 2 98 93 382 k01 86 90 382 h06 92 92 387 Uo7 9U 95 385 85 396 90 393 82 393 88 1 106. TABLE IX rLxiKOJ oTIJSiJGTH ALL ..GOB FAILUIiE OATA FOR 3 j5~ BIL.rIV]-IYLi--nM'ICIJ-rX',Il^^DEHY-JE iiTISHJ So oc if i c Gravi ty (Gr ouos) Time (Cay 0 171 5o 16U 80 155 100 163 60 10 20 19 0 2U2 u^: 73 183 2U3 95 73 185 257 83 SO 188 239 76 53 rs ^ 186 203 57 100 175 200 Uo 100 178 203 53 100 Y*ralnut Shell Flour (F ere errb) 30 0 10 20 30 0 10 253 179 207 198 213 207 270 97 30 57 53 67 90 77 252 172 199 196 211 213 267 95 57 65 57 77 27 63 2U6 173 205 202 209 223 op .o 97 53 70 75 60 27 50 259 162 218 199 210 210 275 70 65 57 95 33 67 C . O L 203 251 87 60 197 258 100 60 197 251 ICO 60 1 80 1 99 195 237 2u 62 97 53 12 257 cs 253 67 239 76 25 j 87 35c 387 88 82 335 388 88 63 350 379 92 73 338 372 87 60 20 30 257 357 325 295 22 90 57 65 253 352 320 303 50 87 68 75 253 357 325 3 0 0 23 82 70 77 257 355 328 293 53 65 67 32 351 362 AT. 72 70 237 35 3 3 6 6 53 J l 67 225 352 289 53 73 77 232 335 377 53 83 77 209 322 338 325 199 223 231 221 69 75 77 70 20U 217 227 239 90 80 60 53 161 235 239 235 20 63 30 53 162 229 239 235 8 50 23 67 186 319 357 331 20 50 63 65 185 315 359 3 2 6 17 50 7C 77 19 U 217 231 233 70 85 63 98 199 217 229 70 100 08 83 167 237 236 236 17 50 27 73 163 225 250 227 20 57 _§0 67 187 317 359 330 30 63 67 1 0 0 185 315 356 321 17 5o 57 08 1 10 77 67 259 357 350 310 33 73 70 53 235 352 351 331 37 60 80 57 255 356 365 329 37 65 83 57 207 255 228 237 77 53 57 80 197 251 OOO 239 50 67 67 67 212 253 226 252 37 73 5o 63 /■S /■* 0 325 338 373 53 37 87 60 223 328 338 367 65 68 90 93 225 330 336 370 50 70 98 93 235 325 353 376 0c 63 .21 _90 O O P , c. 363 351 90 70 227 333 360 333 73 83 87 60 225 330 393 3!j5 53 92 97 60 233 322 386 335 57 65 93 37 *7 217 255 233 236 27 78 70 50 30 210 213 23c: -3o 77 87 90 53 216 20U 228 237 87 77 67 57 212 206 225 230 100 82 o7 57 205 213 226 235 67 100 70 57 A 16 172 239 235 27 87 80 160 228 230 30 73 60 169 222 235 27 80 73 166 231 233 27 80 63 20 227 325 57 9 0 228 355 360 320 5o 228 63 330 52 327 77 322 70 319 52 15 53 50 57 18c 321 337 311 13 5o 70 80 185 322 335 320 17 57 52 57 186 320 355 315 7 50 90 75 109. TABLE X PLYWOOD STriEIIGTH ALB 1/OOJ PAIHLvE BATA FOR n —ijT.IXLPIlti.LL i r-FOiiA'ii BEHT.JE RESIN SpeciTic Gravity (Grouos) 2 Tine 0 10 20 o 238 97 259 97 236 100 272 100 .iainut Shell Eiour (Percent) 30 0 10 20 30 0 10 260 2 7 6 265 269 237 312 290 lOv. 10 c 100 96 100 57 92 237 271 267 270 250 336 287 100 96 98 95 100 75 82 260 261 260 271 251 328 283 1 0 c 100 100 70 87 67 77 236 267 2 7 3 269 237 336 295 1 0 c 100 IOC1 93 100 77 93 230 263 100 100 339 355 97 93 355 352 97 97 352 353 90 92 353 356 00 93 OO 100 297 301 291 277 100 3.00 93 100 opr; 273 282 265 c.C^ 97 100 83 100 338 376 3 6 0 Jo 97 67 333 360 38 0 90 87 73 -<71^ 386 336 S 87 100 73 271 362 85 363 90 363 80 366 75 335 73 336 77 337 83 331 60 277 272 269 287 100 100 60 90 277 272 i.Cu 29 70 10 0 99 100 100 368 331 393 93 99 67 387 337 365 88 70 85 391 330 88 100 91 385 3 5 1 363 O 72 72 ✓ 03.16 The total sur. ol c- usres, vrithout th.e decanal, is entered in Table — -l. The nur.ter of decrees ol Ire odor, lor this analysis is always (n-1), v:'.;ere n reprosonIs the nunber cl iters In a sarnie cr subsen ‘ic. - a o...— . ..e, w.vo t ^c — mil .bar ..,.s .....nr, unto one *_*o en ure s lor the sir>ar strength values el Table 7II H loo. sur. o_l The decrees cl Iroodoi.: lor the totr.1 cur. ol squares in Table ..I is -55. The sur,-. ol squares cIvAvn in Table II ler tine, specilic qravity and walnut chcl' H o u r as von. as sur cl squares ler the lirst orc er inter actions^-- (tine s -ceilic qrcvity), arid (specilic qravity tv,'o— ray Tables H I , tion'-;: (ti::o (ti.ee n .:alr.ut she .1 Ho u r ) , v.vlrrut she'.. H o u r ; cvcrc dcie mines. 1 rci: the 1.1/ :nd .//I. The sur: ol squares lor the interac­ s ecilic qra.vity x walnut chc_l H o u r ; was obtained Iror: Th.e ten.. M to indicate tie di sere o m c y be tv:con era v-rir.entai treat: icr.ts. A non— siqnilicant .ivnilleant ir.terection reveals only o:rporinental error. interaction ***“ locts t ’n at or. ir.crer.ent ol a certain treat:..out ir..vsed treatr.ont ..ill n o t cr.luce tc.e sa. .0 eilect every tire, but ■-•-a . vO0 r.»u ire ''* ' c" h.o co. 1 A n e 1 c l lect e._ th.e tvs treats e.'.re. lirst .rder inters.cti n invoIvc s tv -o tro a t :c: t s . A second cr.hr inters cti on ir.vc.-Ves t.vree tract: onts. 1 113. TABLE X I ANALYSIS OF VARIANCE of 1-LXkYOOD sTTiELGTH u ATA FOR PiXXCGD BOLDED Y/ITH FIHU G L-FOPi ALDENYDE RESIN ADHESIVE /analysis of Variance Source Total 3uui of Degrees of Freeden Sou arcs — !■ . , he an Square 255 717,663 Tir.e 3 7,320 Specific gravity 3 6l 6,662 Yfalnut shell flour 3 20,2U3 6,7US-:h ;- Tine x specific gravity 9 13,056 l , U 5l Tine x .valnut shell flour o ✓ o,5^3 732 L'ain Effects 2,lUiO^- 205,55U*-- Interactions Specific gravity x Yfalnut shell flour Tine x s pacific gravity x vralnut shell flour-"-::-:;Error F to be significant 27,U5l 3,050^ 27 21,61h 0O1 192 U,733 25 5:5 1 % For 27 and 3 degrees of freedom 2.96 U.oO For 27 and 9 degrees of freedom .25 3.m Calculated least significant difference = 10.25 -«■ Signifies significance. Signifies high significance. Prooer error tern to use. i lll-U the three-ray Table To/III. The tvro--.;ny Tr.ble /Tl'I cone croc the Teeters c .cciTic brevity and v.s.lnut cholli H o u r . The tiro Teeter is iynorcd in this table. I r- -I v*i T the sheer str enr;bh value l.-r^ vs.hues in the table r.rc the cvu. s u.:o c -. .urn s oT To.b. e Vj._i • .. r;;or Ti"ur :s. The si:allor i'iy.ircc ore the averages <;i' th.e Th.e To..ler.."in ; c r v.t? tions Ter s cciTic The okc this clear. ;revity 'jrcue 1 on.; sere _;orcer.t -.rolnut shell. Tlour. be.; ■+ ho 3 + b n e + .......... + i.3.' + h l j 4- l o r = r ,T T b j f)u‘ / _ 'f T o r s i c c i T i c ; ;r v i t y r r c u ;>H m d 31 , ' c r c c n t 3 so + 3b-• + 3 , b it. / 3b i + ..... 4 •.. l n u t sh e. 1 12.c u r . j.i; 4- 3 T o + 32a.. « 3 , os;.l i o » 3.1 Is analysis sT vrrlrocc -r .rl. .h e m o by s i c i r. s h -a n i n T ab. o IT.:. I . out T r The 1 t:\ in Telle .11' . 'The c; _.cu. - c l . n s .1 f . .o s r s <_.T : o'i'CE arc as Te.a.o.vs: x c t ' 1 ------- = ( ..,T 1 T' 4 .............. + 1 . ’ l l ) ^ / = ...... ■ O ^ 3 s . _ — -1 J I e l s u r - ( T j l l T - + .......... + ~ ...I. j O r. = (1 1 ,1 :1 = to ,a I • - !r - + )C . ~ 1. l our -W' • • 1 :: ._>) * -_rr . ; — — o n ; j ./.I.. + *h / .'“J /' O'-.;, O •h ( ( 11, 6 / 3 )41 / 61 - c o r r e c t i o n • b ~ ■ J- ) h 1.' , 3 Is - c o rre c tio n j i'--. / • s . 1 —4 .0 , ...:,o • *-’0 u l,w l f I .i '*1• . i!. + S.. J*/ 61 - c o r r e c t i o n —O i o , OOJ..UC ‘ ' “ 1 7 ,1 3 0 .7 3 T h o se cur' c eT seu.r-.ro s i t . i G u t t i i c s . r i r s c t i c n . ' .. v r .sues s i c s n o . n i J TABLE XII SU1.IS a n d 12EANS OF rir.'/OCD STRENGTH DATA FOR SPECIFIC GRAVITY AND Y/ALNUT SHELL FLOUR FOR DOUGLAS FIR PLY.7UCD BONDED LTTH P K S 1 I C 111ALDEHYDE RESET ADHESIVE Specific Gravity 0 Y/alnut shell flour* 10 20 (percent) 30 Total Liean 1 2 3 u Total 3,998 25o U,557 285 5,59U 350 5,7U 359 19,890 U,U 60 279 U,392 275 5,607 355 5,990 37U 20,529 -v --*^ s> -J-y 2U5 U,8U3 303 5,573 367 6,5o6 hO't 21,liil U,oUi 253 lj.,336 271 5,U73 3U2 5,82a 19,693 18,130 22,627 2U,07l 283.3 333.5 376.2 16, )tie 256.5 310.3 320.8 330.3 365 307.7 81,253 t ;J3l b x i i i ANALYSIS OF VARIANCE OF SURE CF PLYWOOD s h e a r s t r e n g t h d a t a fi^ n t a b l e x i i Source Degrees of Freedom Lean Sum of Squares Total 15 66U,355 Flour 3 20,2U3 Specific Gravity 3 6l6,661 Specific Gravity x Flour 9 27,U50 317. h f cooAqouo oqq oao::. c j q o q . i n o c ? o s a - . axaJl'Z^J ^V-U, *:.7J2r a* UT U.V-C ;S fJT T/A' O .Cr’J. .iC CoUr.-'A Oqq A ,7 GOTTJqOA'A .70 STCAX-Uw' °’ L'uI. I : l '• - :-.k' + 9 6f + - ..... + 99 e + ......+ oA;+ • ° o' rrq r-qq quo- .mox.T ct + •?•;'• + a 92 7 cq:; qnirqA . q.T.;or,.T'/. c C T;7o '< = 9 A + QifC + ..............+ O'lc + ............... * • ( 9 ’ + ............. • rjjC?T; ja tj' o' 7 ■/ ; o. .’ " . ' 7( 07. j< q tu r; a a •o o 'A7-2::d oo c o t a t a 7;q f '::o 7:q :r •oo!'AtoAo jqoqa w..ro :;ao-• 'V 9 i. o::q { ~;/\ry- o a t . - ; o j'.q q q *t .•q-q.-qj tgia'..--- ooir .-t.to'a 9 ................ 77 •1'; r>7: j + 9'9 [ + .n q ;T o 'q r q 9H o :q i .7 T j o r t . . ? / . q q .: u o . r q o oqq ‘.‘■v.o y q q A A j v * o q tx iq :;q i;q o tjto o iis .1 0 9 + 097 + 99;: + 997 . 't.OvZ. .q ^\ . -- - «J’ .A jj.' *---S ■in. kj o q j q n o ,.o -• »*. 1 ;-r jc£ o v jx o o i-.s ’’O.. .uwu..^ ’*'.To -j>i x 92 + ' r.;v r. :9'.':f 9 - TA2 + 292 + 9 9 ’ + .......... u o * ; q 7": T .o cu.togugo tajx o qoj. o"q-.:; :ctVi";A i;oqq7 :aa qq. uo.oqo aggao 9"q .1 = •\:>o^ou;.x -ZqqA'AT.. :• trx CT.'."AU J cqo .7 9 q qq 7 ” 077 :"7 .o :o ::-;rr 912*9 • x o lr j a o t u :: o q q ;;.7 v.oqq'A ' 7 i : w\aq •iocoo .'7 Q'9 ; ' A'- .:vms oqq oj;-.- :g.ta q,- ol .1 q oqj, O-c.TToo. r: 1q q.v. eo'.:qq c .io z ot’q A q .r-'oqo o'o.: ot ; o r q 7 ~,o: cy<- + c;-3 + •{•is '077 .r tiv /'j 7 v.v. ^ 0 9 uwi.C .1.} » i. v . jjo i ;.: : ; 0 0 :A [.. . 0 j . rac u x j o aq q o A o u ;-: o o a ~ o a u t /.r q jq .T r .o q q o ; q^T q -o iq o J9 : ; . ' - o . " . q v, ' .j qoq -ta a " ? - oxq, 117. TABLE XIV UL:J AITD LEAKS OF tr'LY.7GGJ oTriEUGTH LATA FOil SPECIFIC GlLiVITY AI..J TILE FOA LGUGLAo LI*.; LLY. iG C l 3 C E l E j KITH PHEZ :OL-FLdiI.JtLJEHYDE ItSSBT AJHSoTVE Specific Gravity r* 9 Tii;ie (days) 12 16 Total Lean 1 2 3 U U,io5 U,527 9, ho 6 283 338 5,725 358 19,763 257 U,no 257 U,6k5 5,529 3U6 6 ,0 1 1 20,295 U,l52 U,5io 5,765 6,127 260 282 360 383 U,o5i 253 H>Ui4.8 5,927 370 6,215 278 l6 ,Ul8 1 8,130 22,627 2U,078 256.5 283.2 353.6 376.2 2 9 0 Total 308.8 376 317.1 20,55U 321.2 20,6Ui 382 322.5 81,253 317 .a TABLE XV AILTLYBIS CE V ALIAECE OF BULB OF I-LY.VOCL SffilLi BTiGLGTK LATA FULL TABLE XIV Source Total Lean decrees °£ Freedom Sum of Squares 15 637 ,037 Time 3 7,320 Specific Gravity 3 6 l6 ,6 6 l Time x Specific Gravity 9 13,055 TABLE XVI ' ■^ “? Xw • '* ' "T* * '•* B *•*■ r IT «»—> ^ * IE 7 V \ j7~> AT a—X 11w i -,’T» v.r,T "* rriT T am* *_/ o X * u « 1 •JX I* *^ivl ± ~; ■- ' Tm ~w^I• .i>1.11-»L/ X •-■»- L FLGUFv, AID T U B FOR JOUaLAS FIE FLr.YLOJ b c i b e j ..-i t h PHEi:cL-Fc:-i:xLEEimDE e e s i i : a d h e s i v e Aalnut Shell Flour (percentage) 0 5 20 30 Total I;,951 309 5,123 320 5,072 317 U,617 2o9 19,763 U,9lU 307 U ,io£ 319 5,2c? 331 U,9Sh 312 20,295 12 5,023 3lU 5,19U 325 5,376 336 >1,961 310 2 0 ,35U 16 5, Ge2 313 5,loU 319 5,lBU 330 5,131 321 20,61a 19,£90 20,529 21,lla 19,693 cl,253 310. c 320.6 330.3 307.7 9 Tine (dpys) 10 Total Lean 306.8 317.1 317. U IT ' wF v a r i a n c e OF JULS ^** o li4>"n pm -ID.■TT1IT *»Tt- h v i i* . — A.1* l~ wl. . , -- n ~ i >- — a -* "A i. a. Degrees of Freedon Sun of Squares 15 3u,liiS Tine 3 7,320 Flour 3 20,2u3 (Tir.c ;: Fleur) 9 6,5 CL Source Total ‘“NOP _ ?2-L. c 322.5 Tj.n i..Ui -**t-J—L , Lean 119. yroconted. Uy to this ooint in the crrelanntion of analyses of variance oroc c l s u 'o c , "i.. n i ’ .G oi squaroc in Table XI h;:.vc boon dote m i n e d except for tiiG second oruer interr.ction (time x crocific jravity x v:a_nut shol r 'our) and ibr the error term. The sum oi squares dor the inter, cticn (tine :: s -jecific * ~ravitv *• x —* v x ..nlnut shell flour) ore leoor? ibne< l iron the duilo of Table analysis of variance oi Tab/.e hlh. and the The sum:, ation vrluos oi fab.c 1/ III '. ’cr'- squared am' th.eir cur. ' a c Timtou to- yive the total cu.. ■-£ squares. ihe sure oi squares dor ti: .o, s 'ocific gravity, *.rnlnut she .1 flour an:; i-..r the iiret crier inter, ctic-ns (til:-c :: e 'eciiic yrsvity), (tie ° x -oalnut shell flour), 1’1'ur) on (sreciiic ,qr.- vit./ :: oalnut shell .ere adoed on, t h i s value ‘ u.s subtracted .iron she total su:.. of c-':ua.ros to rive the second oioer ini.eraction sun of squares. The sun of s n a r e s for error in Table hi v;ac calculated by sub­ tree tin • the su:. t>f 11o s u .s of cc;uaroG <:i the tror t: .cots and interac­ tions fro:.: the t Lr.t sui of squares • The mean S'.iuai'c valuec in Table hi v.ere obtained by dividing the rrx . of cqu.are va.lues by the number of deqrees cf free dor: assc-ci' tod •-it!: the sec: of squares*-. Tlio significance or non-siqnif icrnc e of tro.-.t:rents r;:l interactions eras determined by dividing near, square values :rr the rrean souarc value x*<-i* the scc-vnd sruer interaction (tine .b-P ■a- Tiie nu_.bor of 'deyrees of freedcn for as; inter; ciron is ueteia.sLncc r r.mlti lying the nuribor of deyrees of freod.cr. oi the individual rest: .ents involved: in the inters ction• 120 TABLE X V I H SUL 2 AIID LEAH VALUES OF PLYWOOD ETiiENGTII DATA FOR WALNUT SHELL FLOUR, TILE AIID SPECIFIC GRAVITY FOR D.UGLAS FIR PLYWOOD BOLDED Y.TTI! PIISLCJ^FCELAIDELYDS iSJSIL ADHESIVE Y/alnut Shell Flour (percentage) Tine Specific Gravity 0 10 20 2° Total Lean (days) 1 O <_ 3 6 1 2 3 6 1,000 250 1,153 268 1,360 360 1,638 360 977 266 1,132 263 1,385 366 1 ,6.20 355 1 1,0 6 1 2 265 1,167 12 267 3 6 1 1,306 367 1,629 357 960 260 2 16 3 1,125 261 1,663 352 1,665 361 1,003 251 1,125 381 1,382 366 1,562 391 1,186 297 1,092 273 1,369 362 970 263 1,271 318 1,619 355 1,661 1, 6 2 9 365 607 1,131 283 1,036 259 1,668 367 l,56l 390 975 266 985 1,266 1,083 271 1,605 351 5,376 1,686 6,961 258 1,260 310 1,608 1,113 278 1,026 257 1 ,6 62 1,656 361 1,523 366 381 366 6 1,030 312 1,506 377 1,66 9 1,072 268 1,009 252 6,951 309. 6 5,123 320.2 1,256 316 l,28o 320 5,072 977 6,916 317.0 6,617 286.6 307.1 266 i,l5o 5,108 288 1,356 339 1,501 375 319.3 5,28 9 330.6 6,986 311.5 5,023 313.9 266 612 372 971 263 1,201 300 1,566 392 1,666 617 1,007 252 1,096 276 1,656 5,196 326.6 336.0 310.1 5,002 312.6 5,106 319.0 5,606 337.8 366 1,572 393 5,131 320.7 TABLE XIX AXAiYSIS OF VAItlALCE OF THE SUL1S OF PLY.VCCD SHEAR STISI.'GTH JATA FilOi TABLE XVIII Analysis of Variance oource Total Degrees of* Freedom Sum oi Squares 63 712,92? 3 7,320 Lain Effects Tir.e 20,2u3 iypecif ic gravity 616,661 Walnut shell Ilour Interactions Tine x specific gravity 9 6,56U Time x v/alnut shell flour 9 13,055 Specific gravity x vralnut shell flour 9 27,550 Tine x specific gravity x '.ralnut shell flour 27 21,613 122. G -ecil ic ^ravit:,’ 2C oralnut shc_i f ._our j vrliich vas used as the error tor:' in the ana.iysis. The quotients obtained v/ore r values that v.cre cornered to a statistical table oi a' values. The f vu..ucc i'cr signifi car.cc at the live and. the one gorecut levels cl significance arc indi— c: ted in Table XI. It is err'hr sired that the interaction (tine specific gravity :: valnut shell flour) •:ac used as th.c error terra in the analysis. Using the actual error terra rroducccl high significance far a.12. r.rean square values. The actual e r r r toiv. uas considered to rcfioct only sangling crrar end the inter; c tion ton:, a.as considered to be the use as the error ton... ro;or one to This situation is the s.?;.:o for all resins used in the orc'crir.ont. ulnce significsnco v.a s Ind.* crtod fa r treats.ents, it ,;as necessary that the t tost be used t' do to m i n e the .cast si gnif leant r.cen differ­ ence*-. This :iff^ronen v.v s caj.cuju.tc. as fo j.ov.'s: standard deviation of the i.ean .-fsrueru error f t ic u f .'orcnce — VoOI —— - v Lb t (at level) - :..0i (t'lrcn fro,, "t" in' ..o far ;-.V degrees of fro odor:) ..'non th.e difference bet'.;con tec r.e.ans cuecods th.c va .no of the lea ct s.i/Tf. "leant uorei .iterance, the t.:o . • oans arc said to be.'.ong are considered to be significa.rtly "oo a n j.o re no ;C"CJ-’t:'.'v:: d.i.ffercnt. 123. Difference to be significant: :y — xy = t :: 3 = . .ui x 5 " 1 0 . 2 3 (least signif leant near. 0 S is , ton ■ Oi O " r............ .. o> Ol i 5Xm\\\\\\\WWWT X^WWWWWWXWWW■s vWWWWWWWWKWW2 m \\\\\\\\\\m \\v \\ g § r n M c < 9 ,, J C/5- 4 “3 w O A 3 g £ f o 8 u in u n i/i/r n m iii T n n iiu iiiiL iiiin h T rm in n ii/n rm m rT TiTiniiiiiiirTTnm . oi 400 h PLYWOOD SHEAR STRENGTH (RS I.) 126. ordinate (time) calibrated in the sane size units vrith a straight line dr arm having a slope of one. increase of specific gravity. An increase of tine mould give an equal It is rare in most experimental v.'ork to have an ideal additive effect botveen treatments. Hovrover, there can be scne variation from the ideal non— significant situation before sig­ nificant differential effects are evident. The evidence of significant differential effects nay appear in an analysis of variance calculation as vras the case in this investigation. Figures 1C, 19 and 20 shov: graphs of interaction trends. The basis for these graphs are the average shear strength values vrithin Tables XII, XIV and XVI. Graphs of Figure It originated from Table .■HI, graphs in Figure 19 came from Table XIV, and graphs in Figure 20 mere obtained from Table XVI. In Figure 18, graph A shov;s the effect of v.-alnut sholl flour increments on specific gravity groups, and graph B indicates the influence of increments of specific gravity on -v.-alnut shell flour -'ercentages. These graphs vrere constructed by plotting the average shear values for the s jecific gravity groups against vralnut shell flour percentages in graph A, and average shear values for the v.-alnut shell flour pereentages against s >ecific gravity groups in graph B. A similar procedure vras follovred in [lotting the graphs in Figures 19 and 20. In Figure lc, graph A, for the interaction (specific grav­ ity x v.'alnut shell flour), indicates that increments of one treatment did not produce similar effects in the other treatment, the variations being great enough to be significant. variations. Graph B also shov.rs significant Graphs in Figures19 and 20 do not indicate variations ^ 4 0 0 co tL, SPECIFIC GRAVllTY (GROUPS) X 127. s : \ \ N CD 5u. 3 5 0 H CO ac «c ^ 300 O o o 250 0 10 20 30 WALNUT SHELL FLOUR (PERCENT) .4 0 0 WALNUT SHELL FLOUR c/i (PERCENT) a*. E CD 350 CO s s 1 ac X 300 CO 0 250 I [Tare 16. 2 3 SPECIFIC GRAVITY (GROUPS) Graphs oi* interaction trends Tor plywood bonded with •ohenol—formaldehyde resin. A. The effect of incre­ ments of -walnut shelj. flour .ercent on specific gravity groups. B. The effect of increments of spe­ cific gravity groups on \alnut shell flour percent. PLYWOOD SHEAR STRENGTH (P&l) 4 0 0 SPEC 1F1G GRAVI n r (1GROUPS) ^ 350 300 - — _ 9 12 TIME (OAYS) A. 400 2 ' — -— 250 5 PLYWOOO SHEAR STRENGTH (PS.I) 4 3 16 TIME (DAYS) / /. / ✓ / 12 16 9 5 /^ — 350 x 1 .... . /A s / S / /s / 300 /At */ / 9 250 2 B. Figure 19. SPECIFIC 3 GRAVITY 4 (GROUPS) Crraohs of 5_nteraction trends for plywood bonded vi_th phenol-formaldelude resin. A. The effect of increments of time (days) on specific gravity groups. B. The effect of increments of specific gravity groups on time (days). PLYWOOO SHEAR STRENGTH (PS.I.) 4 0 0 WAL NUT SHELl . FLOUR (PERCENl ) 350 ^— ^==r 300 m 20 30 10 0 250 A. PLYWOOO SHEAR STRENGTH (PSl) 129. 400 9 12 TIME (DAYS) 16 TIM 350 300 250 30 WALNUT SHELL FLOUR (PERCENT) 20 & .gure 20* Graphs of interaction trends for ply.vood shear strengths for ;lyv:ood bonded vrith phenol—fornr ldehyde resin. A. Tlie effect of increments of time (days) on v.-alnut shell flour percent. B. Tlie effect cf increments of vralnut shell flour percent on time (days;. 130. great enough to be significant. The significance of interactions does not detract from the main effects of the analysis of variance for the shear strength values of alyv.ood bonded vrith ohenol—formaldehyde resin. The large neon square value for specific gravity in Table hi indi­ cates that this factor has a considerable influence on the strength of phcnol-fomaldehyde bonded Douglas fir plywood. Tables XII and XIV show that the nean values for specific gravity increase from low to 'nigh specific gravity and differ fror. one another by a considerable amount. Tlie difference exceeds the value of the last significant mean difference of 10.23*• It aipears evident that for the conditions of this experiment, increasing specific gravity for '.veil-bonded Douglas fir ply.vood results in higher strength. Tliis coincides with the con­ cept that the strength of wood, in general, is directly related to specific gravity. The specific gravity of solid dry wood substance is about 1.5• hood has a certain volume of cell cavity space and other open space so that the specific gravity of normal wood is much less than 1.5. A higher specific gravity for w o o d signifies more wood per unit volume which logically gives greater strength. Tlie evidence in the care of ehenol—formaldehyde resin bonded plywood appears to indicate that more v.ocd -:or unit volume in Douglas fir veneer gives greater ply.vood strength if the glue bend is adequate. It is suggested that an ade­ quate glue bond implies that the adhesive nay be considered an integral nart of the 'wood. The relatively' high values cf v:ood failure percent— ■M- This value has been calculated previously on pages 1^2 and 123* 131. ages given in Table VII imply that, an adequate bend was obtained in o_yvrcod bonded vrith the phenol—formaldehyde resin adhesive. The norms for walnut shell flour in Tables XII anti XVI shov; tliat <.0 percent vralnut shell flour is significantly better than either zero percent or 30 percent. It appears that 20 percent vralnut shell flour ad^ed to the vhenol-formaldeiiyde resin gives a satisfactory plywood glue bond. Since 10 percent vralnut shell flour is not significantly v.'crse than 20 percent vralnut shell flour, it can be concluded that slightly under 10 and sonervrhnt no re than 20 percent vralnut shell flour filler is satisfactory for the vhenc1-fcnraldclyde resin. It is knovrn that •valnut shell flour, vrhen coded to phenol-fomaldehyde adhesives, retards the flovr of the rosin adhesive during that part of the curing period ..hen the resin decreases in viscosity. At this point in curing, the resin tends to flovr considerably, penetrating the vrood excessively and flowing froir. between the veneer layers as squeeze-out. The flour tends to retain the adhesive in the glue line until the resin begins to solidify. At the sane tine, a certain amount of resin -.enetrates the vrood tc some extent, vrhich is desirable. Tables XIV and XVI shovr the mean values for tine. Time 'periods of 12 days and 16 days belong to the same population since they arc not significantly different. However, these tvro time periods are both sig­ nificantly better than a time oeriod of five days. A time period of nine days arr ears to be an intermediate mean that could belong to the same statistical copulation as the time period of five days or to the copulation that includes the time periods of 12 and lo days. The nine 132. day tine period cannot be safely included in the discussion of the con­ clusions for the tine factors. This situation suggests that there is a significant increase in olywood strength betv;een nine and 12 days after bending Douglas fir venc-er vith phonol-fornaldehyde resin adhesive under the conditions of the experiment. This suggests further that since the resin bonded vly.vood was treated to fully cure the resin be­ fore strength tests -were conducted, both non bonds or stronger bends between vrood and adhesive must be formed over the nine to 12 day period. The analysis of variance of shear values of n— ere sol—formaldehyde resin bonded plywood appears in Table XX. The least significant mean difference, calculated in the same way as the least significant mean difference for tie phene 1-fcrma.ldeh.yde resin bonded rlywood, is 12.7* Tables XXI and XXII shoo the mean values for the s ecific gravity treatments. Each of these treatments is significantly different from other specific gravity treatments, vith s. definite increase in plywood strength associated with an increase in specific gravity. ted The sugges­ reason for increased strength related to increased specific grav­ ity has been given in the discussion for the results of shear strength analysis for ohcnol—fom a l d e h y d e resin bonded ply.vood. This reason also apolies for the n— cresol— forr.aldehyde resin bonded ply.vood. Tables XXII and XXIII show that a time period of 16 days gives significantly greater plywood strength than a time period of five days, jxr.c '"■eriods of nine days and 12 days are not signal icantly diff eront than either a meriod of five days or a. -ericd of 16 days. tion suggests that a marled increase m This situa­ strength. tales ^.lace in from 1^ 133. TABLE XX ANALYSIS OF VAP1A..CX CF PLYWOOD STiSSXGTH LATA FOli PLY. C C D BONDED vnn: n- CitE30 L-FCXI.lAuDEIITLE ILLGUI ADHESIVE Analysis of Variance Source Total Degrees of Freedom Stan of Squares 255 738,857 Uean Square Lain Effects Tine 3 11,055 Specific gravity 3 636,712 '..alrrut shell flour 3 u,l65 1,388 Tine x specific gravity 9 U,711 523 Tine x v.-alnut shell flour 9 7,726 858 Specific gravity x vralnut shelH flour 9 3a,58 9 3 ,82^3* Tine x specific gravity x vralnut shell flour 27 3 3 ,a 5 o 1 ,2 3 9 192 5 ,9 5 8 31 3,685* 212,237*' Interactions Error See Table XI for the significance of F. Calculated least significant difference = 12.7 ■* Signifies significance. Signifies high significance. 13U. TABLE XXI SUES AID LEAHS OF FLY.YOGD SEAI. TESTS FOR SPECIFIC GRAVITY AID Y/ALNUT SHELL FLOUR FOR DOUGLAS FIR i LY./CCD BOLDED YiTTII ra-CRESCL-FCILJEDEIIYDE IE SHI SpeciTic Gravity 0 ..'nl rrnt shell riour (percent) 1C 20 30 Total Lean 1 2 3 k h,3k7 U,Coc 20,633 300 5,698 356 5,707 357 5,861; 5,760 272 362 6 ,1 8 6 2 1 ,21*0 U ,2 2 0 26U U,152 260 U,lS6 260 16,175 263.7 5,127 320 6,109 337 6,U77 U05 6,337 293 362 396 19,092 29C.3 23,398 365. 6 21;,760 u,acu 280 U,S8l 260 Total Lean 322.1 331.! 20.997 3 2 8 .: 2 1 ,2 6 3 332.! 6U,153 3 2 8 .' 367.3 mX./vX— t-'YV .kAXJ. - TT 1 i..T1 —9 I.E.i-T* iESx.1> ,,-V*- •R•ECIFIC wE Bo *'i- 1l‘ GRAVITY ADD t h e : FI x. DCS Gi_^u. ^ * ^1• ‘ u .DE:rYDE a i t :: r.-c;L S : i . - E . L SpeciTic Gravity 5 1 2 3 k U,093 U , 6 U6 r ^63 6 ,1 2 2 296 It,639 3k9 5 , 65 o 363 302 366 6 ,0C8 256 9 m _* _ ^ j.—r.e 12 (days) 16 Total Lean 1;,203 263 U,197 U,7Uo 262 296 1i,382 27U U,865 301* 376 5,957 372 16,875 263.7 19,092 296.3 23,398 365.6 6,09k Total Lean 2 0 ,u*6 319.5 2 0 ,9 0 6 327.9 301 6,115 38U 6,827 U02 21,090 21*,786 367.3 81;,153 329.5 2 1 ,6 3 1 337.9 326.7 135 TABLE XXIII suns AID LEANS OF PLYWOOD SKSAR TESTS FCIi ..ALMUT SHELL FLOUR AID- TILE FOR DOUGLAS FIR PET..'CCD BONDED ViTTK m- CXCSCL-FCi ODVLDEi IYDE liESIK Y.'alnut Shell Flour (percentage) 0 9 Tine (days) 12 16 Total Lean 10 20 30 Total U,933 308 5,230 327 5,09U 318 5,169 321* 20,UU6 5,298 331 5,309 332 5,176 32L 5,203 325 20,986 5,156 322 5,273 330 5,166 323 5,U95 3U3 21,090 5,2h6 326 5,ue 339 5,56l 3U8 5,396 337 21,631 20,633 21, 2li0 20,997 21,263 6U,153 3 2 2 .h 331.9 328.1 332.5 Lean 315.5 327.5 329.5 337.9 328.7 136. to 16 days after bonding Douglas fir veneer with m-cresol-f onnaldehyde resin. This increase is evident even though the plywood was heat- treated to assure cure of the resin in the glue bond before nlywood shear tests were made. The formation of new bonds or stronger bonds is suggested as the reason for tliis increase of plywood strength. The mean values for the different vralnut shell flour percentages belong to the same statistical population since none of the values differs from one another by as much as 12.7* This situation v.ill be discussed later. The trends of the effects of the treatments— specific gravity, ..'alnut shell flour and time— are shown in Figure 21. The significance of the first order interaction (specific gravity ;c vralnut shell flour), indicated in Table XX, has the same meaning as the corresponding first order interaction that vras considered in the discussion of the results for the shear strength values cf ohenol-formaldehyde resin bonded olyvrood. Table XXIV, the analysis of variance of the average shear strengths of plywood bonded -.vith 3 dinethylrhenol-formuldehyue rosin, shows specific gravity and vralnut shell H o u r to be iiighly significant factors. Time is also significant. The least significant mean square vas calculated to be 13•!. Specific gravity influences the strength 01. the vlyvrcoa bended vrith the 3 ,£-dimethylohenol-f ornaudehyde resin. However, the erratic increase of plywood strength in relation to specific gravity suggests that some other factor is retarding the full effect of specific gravity. Lu m r m iiiiim m iin OCO .5_]0: Hz TTTTTTnnniiiuiiiun .; 8 2 j o w L7 / / / / / / / / / / / / / / / / / / / / / / / 777777777////////////// O JrJ JCC o ^ Lu tl 3 ^ 8 N i i g WO.S2. w w w w w w w w w w w w w <0 __ \ ^WWWWWWWWWWW m- 1u 5w VvWWWWWWWWWWW o H-fi W T \-\\\\\\\\\\\\\\\\\V in i 8 O i n CO o o (0 i o i n CM (TSa) H19N3VJ1S WV3HS OOOMAId i 8CM 130. TABLE XXIV ANALYSIS OF VARIANCE OF FLY.70CD STRENGTH BATA FOR PLY1700D BONDED Y/ITH 3,5-D!niimim3HNN0;L^F0IliUX>EHYD2 REBUT Analysis of Variance Degrees of Freedom Sum of Squares 255 l,06l,3U3 Time 3 Hi,507 Specific gravity 3 565,335 108,1*62*-* Nalnut shell flour 3 315,583 105,19U«* Time x specific gravity 9 10,271 1,1U1 Time x vralnut shell flour 9 12,213 1,357 Specific gravity x vralnut shell flour 9 103,112 Time x specific gravity x vralnut shell flour 27 35,63k 1,320 192 li,638 2h Source Total liean Square llnin Effects U>836* Interactions Error See Table XI for the significance of F. Calculated least significant difference = 13.1 * Signifies significance. Signifies high significance. 11,1*57*-* 139. Tliis su'^cction us substantiated by the relatively low v^luec for v.rood * allure? shown in Table Hi. cause. The quality oi' the resin is evidently the Subsequent discussion vd.ll clarify this situation. ..alnut shell H o u r influcncoc the shear strength values of the nlyv.ocu bonsccl wuun 3 ,3— diirieiiiylphoncl—fcrrialdchydc resin in a manner si: liar to the two previously mentioned resin adhesives. however, the relatively higher near. square value, as shown in Table XIV, for walnut shell riour shews that its influence is somewhat greater. Tables XXV and XXVII show that th.c mean values far vralnut shell flour from aero percent to 20 percent increase considerably, 10 percent being signifi­ cant!;' better than aero percent and 20 percent being significantly better than 10 percent. This increase suggests that the quality of the unfilled rosin is not iJLgh. The quality cf lac rosin was definitely iv. -sroved with a 20 percent addition of finer. A 30 percent addition of v.-alnut sh-cll flour d:cs not seer: to produce a significant decrease in plywood strength in relation to a 20 percent addition. sug 'cats thr-.t while the vralnut si:ell flcur re'gularod rosin f_ovr auiin; the bonding operation, it also ir.vrovci. th.c qua_ity if the resin by acting as a binder between molecules cf the resin. evidently produces a. stronger rosin adhesive. arwlify this This binding effect Later discussion will 'oir.t. The r:e'ns for tine in Tables XXV ana XXV i. slicw wino a sugniiucant increase in 'ly.vcod strength ic indicr.ted after aba ut Is days. no*’#— ever, in .about 16 days after bonding the strength of the plywood decreased significantly iron tlie highest strength readied in 12 days. lilO. TABLE XXV SULLS AND I.JEANS OF PLYWOOD SHEAR TESTS FOR SPECIFIC GRAVITY AND V/ALNUT SHELL FLCUR FOR DOUGLAS FIR PLYWOOD BONDED WITH 3,5-DLR3THYLPIIENGLFORLALDEIIYDE RESIN Specific Gravity 0 Walnut shell flour (percent 10 20 30 Total Liean 1 2 3 U Total 3,013 188 3 ,2 6 1 20h 3,590 22U 3,797 237 2,859 179 3,657 229 3,597 225 3,699 231 3,ia7 211* U,977 311 5,671 3Sh 5,672 35U 3 ,6 2 8 227 5,1*75 31*2 5 ,6 1 2 351 5,ol*7 315 12,917 1 3 ,6 6 1 213.5 1 3 ,8 1 2 2 1 5 .8 19,737 308. U 19,762 3 0 8 .8 Lean 2 0 1 .8 17,370 271.U 1 8 ,1*70 2 8 0 .6 18,215 281*.6 66,972 2 6 1 .6 TAILS XXVI u p s a n d : SANS CF PLYWOOD SHEAR TEST 0 FOR c^RRoIi? IC GPJWTTY Ai "D T L .E FOR DOUGLAS FIR ILYWGGD BONDED ..XT:: 3 ,5-DE.23Tir£LFKEH0u—F0.1 ALDEITYjE iPiisHI SpecifI c Gravity 5 9 Tine (clays ) 12 16 Total Lean 1 2 3 1* Total 3,350 209 3,285 205 3,527 220 3,1*99 219 3,173 198 3,1*91 218 3 ,6 8 6 230 3 ,1*62 216 1*,826 302 5,059 316 16,237 320 1*,737 296 U,C88 306 5,082 318 5,115 320 U,677 292 1 3 ,6 6 1 1 3 ,8 1 2 215.8 19,737 3 0 8 .1; 19,762 3 0 8 .8 213.5 5,n5 Lean 253.7 16,917 261*. 3 17,10*3 272.5 16,375 255.9 66,972 2 6 1 .6 llil. TABLE XXVII SUL1C AI'ID LiEAITS OF FLr.VCOD c5ESAH TESTS FOR YiALIRJT SHULL FLOUR AMD TIME FOR DOUGLAS FIR PLYACCD BOLDED WITH 3,5-DB.::-rrHYLPKEHOI^FORllAiJDE:-IYDE RESIN Walnut Shell Flour (percentage) 5 5 Tine (d a y s ) 12 16 Total llean 30 0 10 3 ,1 9 2 200 U ,085 256 U,lEL7 a , 535 2 sa 1 6 ,2 3 7 276 3 ,2 5 6 20U a ,a a i 270 U,5o5 202 a , 715 255 1 6 ,5 1 7 3 ,5 0 5 215 U,U50 261 U ,501 306 a ,5 a 3 zo a i7 ,a a 3 2 ,5 6 0 165 a , 350 272 U,6U7 250 a ,a io 27 6 1 6 ,3 7 5 1 2 ,5 1 7 1 7 ,3 7 0 1C,U70 1 0 ,2 1 5 6 6 ,5 7 2 2CC.6 2 S a .6 2 0 1 .8 271. U 20 Total Liean 2 5 3 .7 26a . 3 2 7 2 .5 2 5 5 .5 261.6 112. "S '■-G—•''o r.~ r\ c..e D m d i n g u ses n o t " to v ic g e f s cct o i t n o ~..t 1 nv.h c h c ] l f ic u r is 'cne r.e c e s c a r p * r e - a u i r er.cnt f o r r s _ c in g t h e - ,jr- G u n e a h y - . rhono l - f e r r . r . i d e h y d e r e s i n a n acceptable adhesive o 'e r b o r .d - - :t l b c u g l a s l o r v e n e e r i n t o The o c s s i b l e 'p o ;::d . reaso n s T or t h i s c o n ;n tic n v u ^ l be c o n s id e re d l a t e r i n th e d is c u s s io n . -h e e f f - c t s o f eh The t r e n d of* treat: .arts— s .ecafic gravity, .;' Inut shc-11 flour and t i r o — a r c sh'V T . i n f i .ue si grificsr.ee of th.e first era or inter-,cticn (see eifdeO V -'; t-’ l--------..U s - s. V_ U U . . C - __ ___ -error— :.G:;;u e ar.c. :a— croscl—f errs lolohyde resins. The analysis of vrriar.ee for a-eti^l hen:l-ferraldeh;'h r r a h bended lorood a e cars in Table if/III. Too least si gnif icar.t r.ean difference uras calculated tc be I f . 9. The high significance for specific gravh-y is th.e sane as for ail ■'.her resins and its meaning has been discussed. Th.e means f r vrainut sh.eil. flour in Tables lit111 and — H suggest that betrreen 10 and 20 percent -valnut shell flour i m m v o : uhe flc*.v ch.aracteristicc of the resin far adhesive urposes. Tr.e flour filler increases the strength af jJouslas fir :ly. n c d ban dad vith. n-ethyl'drenclformaldehyde rosin .vhen the filler is ad. ed in the orcentage quanti­ ties suggested above. Tir.e is highly significant for shear values cf iyvood bonded vrith the r-cthylah.enol-f ormnldehyde resin. stantially. Tire iru'luences this resin sub­ The means for time an Taoacs increase cf olv.-ccd strength in 16 days. . a.ne. -uull sr.cr.. a u a uni ->e This evidence suggests that i Hi3. STRENGTH (PS.I.) 400 PLYWOOD SHEAR 350 300 250 200 5 9 12 16 TIME (DAYS) 12 3 4 0 10 20 30 SPECIFIC GRAVITY (GROUPS) WALNUT SHELL FLOUR (PERCENT) mu. TABLE XXVIII .'ALYSIS C:F VAi'ilAECS OF PLYWOOD STidlXlTH LATA FOii PLY..OCD B C I U U YflTH m — .JTKYLP Hill0L-FC1i.j\LJEIIYDE i-iELU-I Analysis oF Variance Source Total Degrees of Freedom Sum oF Squares Lean Square 255 792,066 Time 3 23,U95 7,832*-* SpeciFic gravity 3 6U7,956 215,985-** V.'alnut shell Flour 3 .,koh Llain XFFects U,G0i* Interactions Tine x saeciFic gravity 9 5,730 637 Tine x v.'alnut shell Flour 9 20,129 2,237 SpeciFic gravity x vralnut shell Flour 9 37,105 I;,123* Tine x SpeciFic gravity x vralnut shell Flour 27 UO,U23 1,U97 192 2,G2U 15 Error See Table XI For the signiFicance cF F. Calculated least signiFicant diFFerence - 13.9 * SigniFies signiFxcance. ->:• SigniFies high signiFicance. 165 TABLE XXIX llo AXJ llSAi:5 OF PLiiXCD 3HXAX TESTS FOX SPECIF: G.IAVITY Ai:D WALNUT SHELL FLCUX FOX hCUSLAS FIX PLYAuC J BOSSES WITH n-ETHYLPIC210LFGXLALDEIIYDE XXSHI Specific Gravity 0 Walnut shell flour (percent 10 20 3C Total Lean 1 £ 3 u 3,367 262 6,392 275 3,770 236 6,267 265 6,303 26? 5,970 373 6,152 385 6,31*0 396 5,636 352 19,236 6,1*13 276 6,31? 270 5,096 318 5,50? 366 5,335 365 5,563 363 16,276 256.3 17,33? 271.7 oo o ' 0 1,-5 P 21:,0 9 c 79,761 6,356 272 Total Liean 300.5 20,1*07 318.9 20,356 318.1 1?,765 3 0 C •8 311.6 376.5 TA. -i1—< .1 TLr —»Xx -r ->0 J 1-A.w FC-l JTO-" .*-*_J —A.1XE2 2F FLT»k '.'J SL— -44LA* GXAVITY .0 :o Tr.F F- it DCU GLfkb T’ih. ]rLY»i1L1_; XGi .ax:-: n— ET iYLP rIF X L-FC; * -.■ *•-?-/■ -r ;.xsi:; Sbecific Gravity c* 9 Tir-e (lays) 12 16 Total Lean 3,857 21*1 i*,067 251* u,055 253 6,297 26? 2 3 1, ** I,,< OTt —1— rT -3- 0 ^ 332 5,317 332 5,501 31*1* 5,870 367 0 ,v3a 371 6,009 376 5,267 365 6,310 39 k 22,001 3i*3.6 2:1*,09£ 376.5 263 6, 28 2 26c l*,l*ll* 276 6,678 280 16,276 17,38? 25U. 3 271.7 Total Lean 19,317 301.6 19,675 307.1* 19,817 309.6 20,955 327.6 75,766 311.6 lU6. TABLE XXXI aJl.IL AND LEANS OF rLYLOOD SHEAR TEoTS FOE .lALNUT SHELL FLGUR AND TELE FOR DOUGLAS Fill PLY-OGD IGUIDED >*ITH m-ETBYLPin7iT0Lr-F0ia!ALD3rYDE ELGIN Walnut Shell Flour (percentage) 5 0 10 20 2i,798 U,677 292 h,9h2 309 U,900 306 19,317 li,90C 307 5,125 5,008 313 U ,6 3 I; 290 19,675 320 U,592 267 5,o59 316 5,078 317 5,088 318 19,817 h,936 309 5,5U6 3U7 5,33 0 333 5,12*3 321 20,955 19,23k 20,k07 20,358 19,765 79,761; 300.5 318.9 318.1 3 08 .8 300 9 Tine (days) 12 16 Total liean 30 Total llean 301.8 307. h 309.6 327. h 311.6 11*7 . Dougins fur veneer bondca v'ith m— ethylphenol—f orrr.idehyde resin requires a longer tir.e for adhesion bends to develop bev.veen glue and v.'ood to give strong oly.’c o d . The trends of the effect of the treatment— specific gravity, v.-alnut shell flour and tir.e— are shown in Figure 23 • significance is indicated bet-.'een a tir.e of five days and a tire °f 11 days, and between the tir.e of five days and a tir.e of 16 days at both the five and one percent levels of probability. bixteen days is significantly better than nine days at the one percent level. This indicates that the exoerirr.entally bended Douglas fir oly.vood should not be used for at least nine days and that 1 6 days is a better v'a.iting period for best strength. These results also seer, to suggest that additional adhesive bends are forred with the passage of tire after banding. specific gravity follov.'s the fariliar pattern of higher specific gravity giving greater strength. In Table 1C-Z1III it can be seen that all r.err.s for specific gravity are significantly different frcn one another. The reason for this has been indicated previously. The r.erns for v/alnut shel 1 flour for all resins indicate that between 10 and 20 oercent of th«* flour gives the best bond strength. Table .Ld-IIV shcrrs that 10 oercent v.'alnut shell flour is not signifi­ cantly different fror. 2 ‘« percent .valnut ahol. flour. However, both 10 oercont aid 20 ^erccnt -valnut shel?. flour are signif icantly better than zero percent and. 30 percent valnut sb.cl? flour. Discussion ofres u l t s obtained -vith different resins. The nethod m e. 400 co QJ O 350 cc I— CO a: 3 0 0 S x: co §250 i 200 5 Figure 23. 9 12 16 T IM E (DAYS) 1 2 3 4 SPECIFIC GRAVITY (GROUPS) 0 10 2 0 3 0 WALNUT SHELL FLOUR (PERCENT) Trends of mean shear strength values of plywood bonded with rc-ethylpheno1-fome3d ebyde resin for tir.e (days), specific gravity grouos, and walnut shell flour percent. U*9 TABLE X X X H ANALYSIS OF VARIANCE CF DOUGLAS Fix: PLr.VCCJ ST.tEIIGTH DATA FOR ALL xiESIN ADHESIVES Analysis of Variance Degrees of Freedom Source Total Sum of Squares 1,023 3,986,093 3 3 3 3 676,1*13 Llean Square Llain Effects Resin Tine Specific gravity Flour 32,808 2,1*29,829 152 ,01*1 225,1*71** 10,936** 809,91*3-** 5 0 ,6 8 0 ** Interactions Resin x tine Resin x specific gravity Resin x flour Specific gravity x tine Flour x tine Specific gravity x flour liesin x specific gravity x tine Resin x flour x tine Resin x specific gravity x flour Specific gravity x flour x tine Piesin x tine x specific gravity x flour 9 9 9 9 9 9 Error F to be significant 23,32 0 36,636 202,107 5,335 15,878 1 0 I*, 25 o 27 27 28,602 1,062 31,023 1,1 U9 27 93,255 3,639** 27 38,051 1,1*09 81 92,812 1 ,11*6 768 18,653 53 13 3 degrees of freedom 9 degrees of freedom 2.72 1.99 8l and 27 degrees of freedom 1.62 U.ol* 2.61* 1.98 8 l and 8 l and * Signifies significance. Signifies high significance. 2,591* 1*,071** 22 ,1*56** 593 1,761* 1 1 ,5 8 3 *-* 21* 150 TABLE XXXIII m i S AND MEANS OF PLYWOOD STiiENGTH DATA SHOWING THE RELATIONSHIP OF RESIN AND TIME Resin I 5 9 Time (days) 12 19,763 309 20,295 317 20,554 Total Mean in IV 20,446 320 20,986 16,237 254 16,917 264 17,443 273 16,375 256 19,317 302 19,675 307 19,817 310 20,955 327 66,972 79,76U 311.6 328 20 ,641 323 21,090 330 21,631 33 3 81,253 317.1; 8U,153 328.7 321 16 II 261.6 Total Mean 75,763 295.9 77,873 301;. 2 73,901; 308.2 79,602 310.9 312,1U2 301;. 8 TABLE XXXIV SU1.1S AND MEANS OF FLY.TOCD STRENGTH DATA SHOWING THE RELATI ON SIU P OF RE SHI AMD SFECIFIG GliAVITY Resin I 1 Specific Gravity 2 3 (Groups) 4 Total Mean 1 6 ,U18 266 18,130 283 22,627 3 3k 21;,078 376 81,253 317. 4 II III IV 16,875 264 19,092 298 23,398 16,276 251; 17,389 24,768 337 13,661 211; 13,812 216 19,737 308 19,762 309 84,153 328.7 66,972 261.6 79,764 311.6 366 272 2 2 , 00 1 3U; 24,098 377 Total Moan 63,230 247.0 68,423 267.3 87,763 342.8 92,726 362.2 312,142 304.8 151 TABLE XXXV SUUS AND MEANS CF PLYWOOD STRENGTH DATA SHOWING THE RELATIONSHIP OF RESIN AND WALNUT SHELL FLOUR Resin 0 Walnut shell Tlour 10 20 (percent.) 30 Total Liean I II HI IV 19,890 311 20,52? 321 21,ll*l 330 19,693 308 20,633 322 21,21*0 332 20,997 328 21,283 333 12,917 202 17,370 271 18,1*70 289 18,215 285 19,231* 301 20,U07 319 20,358 318 19,765 309 81,253 317. 1* 81*,l53 328.7 66,972 79,761* 311.6 261.6 Total Mean 72,671* 283.9 79,51*6 310.7 80,966 316.3 78,956 308.1* 312,11*2 301*. 8 TABLE XXXVI SUMS Ai:D MEANS of plywood strength t i e : RELATIONSHIP OF SPECIFIC g r a v i t y a n d t h e data showing 3pecific Gravity 1 5 Time (days) 9 12 16 Total Mean 2 3 21,120 330 U Total 75,7 63 312,11*2 15,1*05 21*1 15,663 21*5 15,931 21*9 16,229 251* 16,563 259 17,257 270 17,350 271 17,253 270 21,755 31*0 22,389 350 22,1*91 351 22,667 351* 23,196 362 23,231* 363 23,629 369 63,230 21*7.0 68,1*23 267.3 87,763 31*2.8 92,726 362.2 Mean 295.9 77,873 301*.2 78,901* 308.2 79,602 310.9 30l*.8 152. TABLE XXXVII 3JILS AID LEANS CF PLYWOOD STitENGTH DATA SIICViTNG TILS RELATIONSHIP OF WALNUT SHELL FLOUR AID TH!E Vi'alnut Shell Flour (percentage) 0 5 Tine (days) 9 12 16 Total Lean 10 20 30 17,870 279 18,376 287 18,280 286 18,HU; 280 19,119 299 19,983 312 20,016 313 20,028 319 19,525 305 19,978 312 20,521 321 20,902 327 19,205 301 19,536 305 20,087 310 2 0 ,0 8 8 310 72,670 283.9 79,506 310.7 80,966 316.3 78,956 308.0 Total Loan 75,763 259.9 77,873 300.2 78,900 3 0 8 .2 79,602 310.9 312,102 300.8 TABLE XXEVIII SULS AID L E A IS CF PLYWOOD STiiHIGTH DATA SHOWING THE RELATIONSHIP OF SPECIFIC GRAVITY AID "WALNUT SHELL FLOUR Specific Gravity 1 0 Walnut shell xlour (percent) 10 20 30 Total Lean O c. 3 0 15,225 238 16,333 255 15,031 201 16,201 250 16,519 258 17,530 270 17,337 271 17,037 266 19,803 309 21,880 302 23,263 360 22,817 357 21,127 330 23,803 372 20,935 390 22,861 357 6 3 ,2 3 0 207.0 68,023 267.3 87,763 302.8 92,726 362.2 Total Lean 72,670 283.9 79,506 310.7 80,966 316.3 7Q,9$6 308.0 312,102 300.8 153. used for calculating the analysis of variance for the entire experiment was simply an extension of the nrocedure used for computing the analy­ ses of variance for shear strengths of ohenol-formaldehyde resin bonded plywood. The sum of square values in Table XXXII for resin, time, spe­ cific gravity and -.valnut shell flour were determined from two—way Tables XXXIIx, XXXIV, XXXV, XXXVI, XXXVII and XXXVIII. These same two- way tables v.'ere used to cornute the 3ur.i of square values for the first order Interactions (interactions involving two factors). Three-way tables sup >lie cl information for calculating the sum of square values for the second order interactions and a four-way table aided in the determination of the third order interaction. As before, the mean square values were obtained by dividing the sums of squares by the associated degrees of freedom. The value for F in every case was found by dividing the mean square by the mean square for the third order interaction. Thus any mean square value divided by l,lHo gave the F value for tin factor or interaction involved. The value of F -.vac used to determine the non-cignificance or significance of a factor or interaction. In an analysis of variance in wiiich the F test indicates signifi­ cance, the t test is used to determine the least significant mean dif­ ference between the averages of the treatments used in the experiment. In this case the significant difference between the means of the resins, the times, the specific gravities, and the walnut shell flour treat­ ments, as ,,iven in the two-way Tables XXXIII, XXXIV, XXXV, XXXVI, XXXVII and XXXVIII, -was determined. The least significant mean difference at 10U. the five percent level of probability is 0.9 and at the one percent level of probability is 7.9. For the analyses of individual resins only the five oercent level v.as examined. hesins I, II, III and IV represent shear strength values of oly’■'ood bonded vath phenol-formaldehyde, m-cresol-fcmsIdehyde, 3,0-dimctlTylphonol-formaldehyde and m-et}jylpheno 1-formaldehyde resins, respec tively. Tables XXXIII, XXXJV and XXXV Give the means for the resin treatments. These means show resin II as signif ic antly better than the other resins both at the five and one percent levels of significans e. hesins I and IV do not show significant differences in plywood strength we sin III is signif icantly -worse tlian the ether resins. An examination of cured resin films for all rosins, and seme chemical and ehysical aspects concerning the resins, may help to explain the differences in plywood strength among the resins. In order to observe visually nhysical differences between the resins, equal 'weights of the different resin solutions were placed on glass plates, then cured into resin films. inspected. The films were cooled and Films for unfilled and filled resins were produced. The unfilled n-cresol- teristics of a tough resin. formaldehyde resin film had all the charac­ That is, the n-c r e s o l - f o r m a l delude resin film could not be chipped easily with the fingernail. handled -without breaking. crazing. The film did not craze over a oeriod of two remained a solid film. istics. It showed no minute cracks It c wild be or flaws due to months but Filled resin films exhibited similar character­ 155. The pheno1-forrnaIdehyde resin film shovred characteristics similar to those observed Tor the n—eresol—formaldehyde resin film v.ith the exception tlrnt tliis film could be chipped '.ith the fingernail, suggest­ ing a less tough resin film. The filled resin films vrere somewhat tougher tlian the unfilled film. The m-ethylohenol-forrcaldehyde rosin film v;as almost identical v,i.th the phenol-fomoidelyde resin film but seemed to chip easier with the fingernail. The filled resin film seemed to be somewhat stronger than the unfilled film. The cured unfilled film for 3,5"dimethylohenol-fomnIdehyde resin sho-.red immediate crazing or showed what might be termed "delayed craz­ ing" in that the minute cracks or flaws ap -eared after 2h or 36 hours. After crazing had occurred, the film crumpled and fell apart 'when handled. The filled 3,5-dimethylohcnol-formaldehyde resin film ap eared to be tougher than the unfilled film. However, there v:as some indication of fiav.rs even in the filled resin film. The apoarent weakness of the 3,5-dimetl;ylphenol-f ornaldehyde resin film is explainable if the phenomenon of steric hindrance is considered. Jtcric hindrance, as explained by Conant (16), refers to a theory that has been advanced to explain why some chemical reactions take place with difficulty. The explanation involves a consideration of the soa- tial interference to a chemical reaction by substituent chemical grouos, as for example, groups on a benzene ring. Substituent groups nay occur on a benzene ring in such a ivay as to liinder, by therr con­ figuration, a reaction on the ring by keeping a reacting substance away 156. from certain positions on the ring. The ohenolic compound, 3*5—di— nethylphenol, is made up of a benzene ring having an OH group in the number one position, and a methyl group in both neta positions, posi­ tions three and five. There are chemical groups in positions one, three and five, leaving the active positions, two, four and six, open. It can be understood that the methyl— grouns could veiy well orevent other chemical groups from reacting with the ring by blocking reaction posi­ tions. In fact, Sllis (20) has stated that steric hindrance is the phenomenon which prevents 3 ,5-dime thylohcnol from reacting fully vrith fcrraldeVyde or from reacting with metiylol groups on other rings in spite of the trifunctional nature of 3,5—dimethylphonol. In view of v.'hat lias been said, when 3*5—dimethyls hone 1 is reacted ■■.'ith formaldehyde, the cured resin v;ii.i_ not Iiave as many crosslinks between molecules as the other resins used in this experiment. It should, therefore, be expected tiiat lines of weakness will appear in the cured rosin. ouch flaws are verified by the craze effect found in the 3,5—' d imethylphenol—formaldehyde resin film. The means of the four re3ins given in Tables XXXIII, XXXIV and .XXV suggest that the ethyl group on the ring of m-ethylphcncl-formaldehydo resin does not cause steric hindrance. The above discussion offers an explanation for the effects of seme factors within resins, which vrere not fully explained in the previous section. These effects should be clarified. In Table XX of the previous section walnut shell flour was found not to be significant for the average shear strength values of plywood 157. bonded vith in—cresol-formaldehyde resin. resins sho.v this fact-or to be significant* The analyses of all other Cne possible explanation for thas is tnat the more extensive solyncrization of n—cresol—formal­ dehyde resin may produce a sufficient percentage of large molecules relatively early in the process of curing 30 that excessive penetra­ tion into the wood is prevented. In this case walnut shell flour is not necessary to retain the adhesive in the glue line. The effect of specific gravity, walnut shell flour, and time in relation to the 3*^—dinethyloheno1-formaldehyde resin bonded plywood should be explained. The effects of these factors appear in Tables XXV, XXVI and X X V H . Y/hile some effect is shorn by specific gravity, the full effect of specific gravity C-uld not be realized due to the extreme vrealniecs of the rosin film in the plywood. v.'alnut shell flour gave a significant increase in The addition of >ly.vood strength because it reduced the effect of crazing in this r e i n . However, the significant decrease in average olyvocd strength for a time of 16 days suggests that the v.'alnut shell flour did not prevent crazing entirely. The strength of 3 jr-dine11lylohen ■1-f orroaIdeliyde resin bonded plywood decreased because of the crazing effect. lie results of average shear strength of plywood bonded v,ith the different rosins are shown in Tables X X I sj., X.XJ.V and X X V . These data indicate that plywood strength decreased in the order m-crcsolformaldehyde resin bonded olywood, pheno 1-forrnldehydo rosin bonded plywood, m— ethylnhenol—formaldehyde resin bonded oly.vood, and 3*5— di— retiiylohonol—formaldehyde resin bonded plywood. The reasons for this 158. order of strength have boon given. It is noted that the order of strength invalidates the theory postulated in the Statement of the Prob— Ion. This theory suggested that the order of plywood strength as rela­ ted to the phenolic rosins would be phenol—formaldehyde resin bonded plywood, m —cresol—formaldehyde resin bonded plywood, 3,5—dine tly1— phenol—formaldehyde resin bonded /Jywood, and r.i—ethylphcnol—formalde­ hyde rosin bonded plywood. This theory v;ac based on the possible effect of alhyl groups on the phenolic rings of the resins. However, th.e results of this investigation suggest that the strength of the resin .adhesive itself determined the strength of the resin bonded olyv.'ood. 'Hie ally! groups on the phenolic rings did not appear to affect the adhesion between w od and adhesive. The effects of tir.e, specific gravity, rnd walnut shell flour for th.e entire errperir.ent are shewn in Tables ICI'III, 11H i / , llwZV, JiuCVI, 1111/II and 111CVIH. These effects can be observed opiichly in Figure Zh» Table liillH shews that a significant increase in plywood strength is associated with a tir.e of about nine days. EZZZZZZZZZZZZZZ CO CM o CM lAWWWYAWWTW O' ATWWWWWWW tO TIME (DAYS) [WWWWWWWVv WALNUT SHELL FLOUR (PERCENT) co O SPECIFIC GRAVITY (GROUPS) zzzzzzzzzzzzzzzzz o 77777/77/7///7777Z CM 7zzzzzzzzzzzzzzzzz; 7 77/t rn~njnnri0 v// // 7/ nn 0 7 // // // // // // 777/ // // // // u // // ///nnr 400 pi o o CO _L O to CM (TSd) H19N3«iS WV3HS QOOMXld CM RESIN ■ 160. VII. C U H A H Aiiij CCllCLUoxoi'io Summary The statistical analyses lor the individual resins charred that sieciTic gravity of the '.rood had a significant influence cn the strength of Douglas fir plywood. Higher specific gravity of veneer gave higher plywood shear strength, when the glue bonds were adequate, as indicated by wcod failure of about 75 oercont or greater, specific gravity of the wood could be considered as exerting its full effect. In the case of the 3 ,5-direthylnhcnol-fornaldeliyde resin body, steric hindrance prevented full polymerisation of the rosin. wue to a fewer nunber of crosslinks than functionally possible in the cured resin, the 3,5-din ethylphenol-fomaldehyde resin sxiowed a large amount of craze which reduced the full effect of soecific gravity. 'walnut shell flour added to three of the resins increased the bonding strength of the resin when tine flour was added in the amount of 1C to 20 percent of the resin solids. The sheer strength of ilyvcod bonded vrith ir.—cresol-f ~rr.aldehyde resin showed no signif icant increase due to the addition of flour. It is suggested that txiis resin formed large molecules early in the curing stage which prevented excessive penetration of the ravin into the wood. The effect of tine for individual rosins was somewhat varied, then shone1—foinaldehydc resin was vised, a -.eriod of from nine to 12 161. days after bonding shovred a signifleant increase in the strength of the p_y.vooc. bonded ,;ith this resin. The n—cresol—formaldehyde resin bonded Douglas fir olyv.-ood coined significantly in strength after a period of from 12 to lo days had elapsed between crossing and testing. The n-ethylphennl-fornaldelyde resin bond gave increased ely.voou strength after 16 days. The 3>f^dimethylchenol—formaldehyde resin bend gave increased plywood strength in 12 days. in strength appeared in 16 days. I'errever, a significant decrease This observation suggested the in­ fluence of lines cf vreahnecs in the rosin -which developed bet.veen 12 and 16 days after bonding Douglas fir plywood. The m-cresol-formaldehyde resin adhesive gave uhe liighest plywood ctTcn^-th because of its more complete polymerisation. The 3,5-cli- nothylnhencl-fcrmalderyde resin gave the lamest plywood strength values due to its characteristic lo*. — oolymerication because of steric hin­ drance. Phenol-fomcldehyde and m— ethylohenol-forna.ldeiyde resin bonds shewed acceptable intenaediate plywood strength since neither of these resins a--eared to xolynerise as extensively as r.-cre so 1-forma Id cry de rosin, nor did. they amp ear to be affected by steric hindrance. The analysis of variance for the entire cxpcrim.cnt shov/cd that Douglas fir olywood of high specific gravity v.ras stronger than tliat of lorn specific gravity, ‘..’alnut shell flour added to the resins in quan­ tities of 10 to 20 percent cf the resin solids gave increased olywood strength. The means of time treatments shoned that plywood stored for a oeriod of nine to 1 6 days after bonding increased in strength. Conclusions The strength of Douclas fir plyvrood varied with the phenolic tyre resins used in this investigation• for pl;a ocd -.-as as follows: The order of decreasing strength 1) n—cresol—formaldehyde re sir. bonded oly— weed, 2) ohenr 1-f orr.aldehyde resin bonded plywood, 3) n-etiylphenclecrnaldenyue resin bonded olywocd, and ii) 3 jh—dine thylphenol-formalde­ hyde resin bonded olyvood. All phenolic tyre resins used in the investigation ap.eared to give saticfrctcry adhesion between the resin and Douglas fir veneer. Dver. 3 ,3-dinetly loheno 1-formaIdehyde resin ap reared to adhere to the Douglas fir veneer. The assumption that allyl groups on the rings of the phenolic com­ pounds would hinder adhesion between the "'henclic resin adhesives and Douglas fir veneer dees not hold. The a l y l grou~s raocrrod to have no influence in this respect. Cohesive strength in the resin glue line cf Douglas fir plywood a:; eared to be very in sort ant for plywood strength. It is suggested that this nay be the important consideration v:hen bending Douglas fir v.ith any allyl-substituted phenolic tyre resin. The strength of Jourias fir plywood bonded with y.henol-fornaldehyde, n-cresol-f onr.ride'.ydc, or n-etlyl henol-f ormaldehyde resin will increase if stored for a period cf nine to 1 6 days after bonding. Douglas fir plywood bonded with. 3,3-dinethylohenol-fomaidehyde resin ■vri.ll gain strength if stored for 12 days but loses strength after this length of t i me. The specific gravity of the Douglas fir veneer used to make the olyvTood has a definite effect on the strength of the plyvrood. Higher specific gravity gives greater oly.vood strength if the glue bond is adequate. The addition of vralnut shell flour in amounts of 10 to 20 percent of the resin solids, to the phenolic resin adhesives used in the inves­ tigation, vrith the exception of n— crcsol-f ormaldehyde resin, increased the strength of Douglas fir oly.vood bonded vrith these resins. BIBLIOGrAPHY 1. "Anon.": 1953. He sin Bonded Plywood, Plastics Catalog, m . 2. Aylesv/crth, J.: 3. Baekeland, L. II.: 711-723, United States patent 1,139,I*7C, 1915. United States oatent 1,019,503, 1912. _____________ j The Synthesis, Constitution, end Uses of Bake lit e, Ind. Eng. Cher.:., 1: 159, 1909. _, and E. L. Bender, Phenol hesine and kesinoids, Ind. Eng. Chen., 17: 225-237, 1525. Baever, A., Ueber die Verbindungen der Aldehyde nit den Fhenolen, Ber., 5: 25, 2 0, 1,095, 1C72. Beaty, J. J . , Production Factors Affecting the Bonding of Jcuglas H r Plywood -with Synthetic licsin Adhesives, lest Coast Lunbeman, 73: IIo. 1, 90-91; ho. 2, 109-110, 113, 115; ho. 3, o2; ho. 5, 151-102i ho. 5, 92-95; ho. 6, 17, 15, 91-92; 1956. Bensend, J. .V., and k. J. Preston, Some Causes cl Variability in the kesults of Plywood Shear Tests, United States Forest Products Laboratory, Forest Service, Hepc-rt 1615, Ladiscn, 1956. o Bethel, Janes S., and Jacob B. 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