)VIESI_] RETURNING MATERIALS: P1ace in book drop to LIBRARIES remove this checkout from .a-Inzyllun. ‘your record. FINES wil1 be charged if book is returned after the date stamped below. EVALUATION AND COMPARISON OF TWO COMMERCIAL ORIENTED STRANDBOARD (OSB) PRODUCTS By Titus Adekanmi Oni AN ABSTRACT OF A THESIS Submitted to Michigan State University in partial fquiIIment of the requirements for the degree of MASTER OF SCIENCE Department of Forestry 1985 ABSTRACT EVALUATION AND COMPARISON OF TWO COMMERCIAL ORIENTED STRANDBOARD (OSB) PRODUCTS By Titus Adekanmi Oni Commercial 058 products were obtained from two prominent manufacturers in the United States: Potlatch Corporation (Minnesota) and Weyerhaeuser Company (Michigan). Both board types had the same thickness, but the Potlatch board consisted of five layers and the Neyerhaeuser of three layers. The two board types were compared in terms of their standard mechanical and physical properties and in terms of the degree of strand orientation on the board surfaces. The surface strand orienta- tion was measured by three different methods while the mechanical and physical properties were determined according to ASTM specification. The results of the orientation measurement were inconclusive. There was little correlation between degree of orientation and mechani- cal properties. Bqth boards showed similar orientation character- istics. In terms of mechanical and physical properties, the Potlatch board appeared to be superior. Part of its superior performance was due to higher board density. Other contributing factors may have been: higher resin content, number and thickness of layers, density dis- tribution, and others which could not be measured in the laboratory. DEDICATION Dedicated to my Lord and Savior, Jesus Christ, who is the author of knowledge and wisdom. ii ACKNOWLEDGMENTS I wish to express my sincere appreciation to my major pro- fessor, Dr. Otto M. Suchsland, whose experience, guidance, assistance, and emotional support helped me get through the hardship of this study. I appreciate the keen interest and cooperation of the other committee members, Dr. Alan Sliker and Dr. Henry Huber. My thanks to Mr. Ivan G. Borton for his encouragement and assistance in cutting the sample boards in the laboratory. I appre- ciate the cooperation of friends for their assistance and encourage- ment. I also thank my wife for her full support and encouragement throughout this study. I am particularly indebted to my country, Nigeria, whose sponsorship was responsible for this graduate work. iii TABLE OF CONTENTS LIST OF TABLES . LIST OF FIGURES Chapter I. INTRODUCTION Objectives and Scope . II. HISTORY OF ORIENTED STRANDBOARD (058) AND PREVIOUS WORK . . Hood Strands . Early Development of OSB Economic Advantage of 058 III. FLAKE ALIGNMENT AND PROPERTIES OF ORIENTED STRANDBOARD (OSB). . . Flake Alignment Mechanical Alignment . . . . . Electrical (Electrostatic) Alignment . Flake Alignment Measurement . Effect of Flake Geometry and Alignment on Proper- ties of 058 . . . . . . . . . . . . Strength Properties Dimensional Stability. . Effect of Other Variables on Properties of 058 Board Density . . . Layering Resin Content IV. EXPERIMENTAL DESIGN AND PROCEDURE Experimental Design Flake Alignment Measurement The Weighted Sum Percent of Alignment iv Page vi vii Chapter Percent of Angles within +20° of the Cardinal Direction of Alignment. . . Degree of Alignment in Terms of Mechanical Property Ratio of MOE Parallel to MOE Perpendicular . . Test Specimen Preparation and Conditioning Test Procedure . . . . Modulus of Elasticity and Rupture . Internal Bond . . Linear Expansion . Water Absorption and Thickness Swelling . V. RESULTS AND ANALYSIS Flake Alignment . Modulus of Elasticity and Rupture Internal Bond . . Linear Expansion . Thickness Swelling and Water Absorption VI. DISCUSSION . VII. CONCLUSION . APPENDIX A. HANKINSON-TYPE FORMULA LITERATURE CITED Page Table 3A. LIST OF TABLES Design of experiment . Summary of flake alignment and mechanical properties of two types of 058 . . . . . Summary of flake alignment and dimensional stability of two types of 053 . . . Summary of mechanical and physical properties including statistical characteristics . . . . . . . Correlation coefficient and regression equation for relationship between mechanical properties and board density . . . . . . . . . . Comparison of physical and mechanical properties of a composite panel, plywood, and oriented strandboard . vi Page 36 65 66 67 68 89 Figure 0501-350.) 10. 11. 12. 13. 14. LIST OF FIGURES Typical oriented strandboard (OSB) . Schematic of a facility for the manufacture of 058 boards by the Bison system The material flow diagram of 058 panel manufacture Surface structure of 058 from Potlatch Corporation Surface structure of 058 from Neyerhaeuser Company Diagram for random selection of particles for degree of orientation test: 4- by 4- foot panel . Diagram for cutting test specimens from 4- by 4- foot 058 panel . . . . - Instron testing machine showing bending strength specimen (b) at test, and (c) at failure . Dimensions of compression shear test specimen for 7/16-inch-thick 058: the shear strip laminated between 3/4-inch-thick particleboard compression strips . . . . . . Compression shear test strength specimen undergoing test. . . . . . . . . Measurement of linear expansion using a dial gage comparator . . . . . . . . . . Measuring jig for thickness measurement of water absorption specimen to the nearest 0.001 inch Flake alignment angles as measured for Potlatch's 058 with 53% alignment (as measured by percent of align- ment): Board # PA . . . . . . . . Flake alignment angles as measured for Potlatch's 058 with 59% alignment (as measured by percent of align- ment): Board # PC . . . . . . . . vii Page 11 13 15 37 39 41 44 46 48 50 53 56 58 59 Figure , Page 15. Flake alignment angles as measured for Potlatch' s OSB with 61% alignment (as measured by percent of align- ment): Board # PE . . . . . . . . . . . . 6O 16. Flake alignment angles as measured for Neyerhaeuser's OSB with 63% alignment (as measured by percent of alignment): Board # MA . . . . . . . . . . 61 17. Flake alignment angles as measured for Meyerhaeuser's OSB with 49% alignment (as measured by percent of alignment). Board # NB . . . . . . . . . . 62 18. Flake alignment angles as measured for Neyerhaeuser's OSB with 62% alignment (as measured by percent of alignment): Board # NC . . . . . . . . . . 63 19. Internal bond as function of board density of 2 types of 058 . . . . . . . . . . . . . . 69 20. MOE (II) in bending as function of board density of 2 types of OSB . . . . . 7O 21. MOE (.1 ) in bending as function of board density of 2 types of OSB . . . . . . . . . . . . . 71 22. MOR (II) in bending as function of board density of 2 types of OSB . . . . 72 23. MOR ( I.) in bending as function of board density of 2 types of OSB . . . . . . . . . . . . . 73 24. Relationship of modulus of elasticity to percent of flake alignment of 2 types of OSB . . . . . . . 75 25. Relationship of modulus of rupture to percent of flake alignment of 2 types of OSB . . . . . . . . 76 26. Relationship of linear expansion (52 to 93%‘ Relative Humidity--RH) to percent of flake alignment of 2 types of OSB . . . . . 77 27. MOE of two types of 058 . . . . . . . . . . 78 28. MOR of two types of OSB . . . . . . . . . . 79 29. Linear expansion (52% to 93% relative humidity) of OSB from Potlatch and Meyerhaeuser . . . . . . . . 83 viii Figure 30. Water absorption by weight change and thickness (volume) change of OSB from Potlatch and Weyerhaeuser (24-hour soak) . . . . . . . . . ix Page 84 CHAPTER I INTRODUCTION Oriented strand board (OSB), also known as oriented structural board, is a built-up panel, made of oriented 'strands' which are flakes having a certain length-to-width ratio. While no accurate definitioncfiithis ratio is given, probably a flake having a length-to- width proportion of about two-to-one, or more, may be said to be a 'strand:' These strands are purposefully formed into alignment or orien- tation either in only one direction to form a one-layer board or in layers perpendicular to each other to form a multi-layer board. The most common multi-layer board is composed of three layers with the two face layers oriented perpendicular to the core layer. Thus, OSB requires long, narrow strands, which rely on orientation for the vital board properties. A wood particleboard is composed of essentially small, dry wooden elements or particles randomly distributed and oriented, arranged in layers and glued together to form a composite board. The properties of particleboard are functions of material and process variables. Commercial standards have been adopted that specify maximum and minimum values for these pr0perties, regardless of the raw material or process used. OSB, however, is a new durable flakeboard product emerging in the composite panel business, with superior strength properties and should be considered outside the existing standards for conventional particleboard. Its end use is directed mainly at the building industry as a sheathing type material; the most obvious applications are roof- and floor-decking, but it is also used for interior and exterior wall paneling. It is also in demand for such applications as car- and container-lining, mobile home decking, agricultural buildings, such as silos, bins, barns, etc. This cross-oriented structural strandboard consequently has superior properties to standard particleboard. Depending on layer construction, same properties in length and cross direction can be obtained. When sanded, thin decorative veneers, vinyl, and other films can be pressed on, but also the strand surface structure, itself, when lacquered, can be used as decorative finish as well. The achievable strength properties of OSB depend on the wood species, resin quantity, the bulk density-ratio of the individual oriented layers, the number of layers, and the density of the panel. OSB, beinga structural board, must retain its strength characteristics and durability under exposure to weather conditions or to varying humidity conditions. The incentive for the development of OSB can thus be considered as the limit in the application of particleboard for structural purposes. Certainly the ever-decreasing supply of sawmill and peeler logs, concomitant with rapidly increasing prices, has been the major economic factor responsible for more serious attention being given to the production of engineered wood composition products and structural elements. The rationale for reconstituted or composite structural wood panels is the more efficient utilization of our forest resources. Composite plywood, waferboards, and multi-layer strandboards fulfill this objective, each according to its unique logistics of wood supply, residue volumes, conversion efficiencies, and marketability. The targets are panel products, which will serve the same functions as construction grade plywood for which the markets are mature and per- formance factors, are well known (30). OSB provides a relatively tested method of achieving a dramatic improvement in strength and stiffness properties, at little or no extra manufacturing cost, while arriving at a product having similar strength and stability characteristics to commercial softwood plywood of the same thickness and can be regarded as a good alternative for it. Objectives and Scope For this study, two types of OSB were obtained from two promi- nent Midwest companies in the United States: Potlatch Corporation, Minnesota, and Meyerhaeuser Company, Michigan. The boards from the former are of a five-layer type, while boards from the latter are of a three-layer type, both having same thickness of 7/16-inch. Specifically, the objectives of this study are (1) to examine these two readily available OSB, from two renowned industries, which are used interchangeably and produced in large quantities, and make a technical comparison of their various properties; and (2) to make evaluation of the surface orientation and its effect on their mechanical properties and dimensional stability; hence determining the effect of flake/strand alignment on the pr0perties of the OSB thus evaluated. CHAPTER II HISTORY OF ORIENTED STRANDBOARD (OSB) AND PREVIOUS WORK Nood Strands 'Nood strands' are defined as slender, flat elements, about 1/2 in. to 6 in. long, but no wider than about one-third of their length (61). Generally, these strands are envisioned as being knife- cut by some type of flaking machine so that the thickness is reason- ably uniform and the wide surfaces are fairly smooth. Various views have also been expressed by some early researchers as to what is to be the ideal flake geometry (dimension) of a 'strand'. Vajda (80) had a preference for a strand length of 2 to 3 in. (51 to 76 nmL)and a width of 1/4 to 1/2 in. (6.4 to 12.7 mn.). The Bison-Herke OSB plant of Western Germany made its own board with strands of 0.012 to 0.024 in. (0.3 to 0.6 mm.) thick, 0.2 to 0.4 in. (5 to 10 mm.) wide and 1.5 to 2.8 in. (40 to 70 mn.) long. In his own paper, Brinkmann (2) described the particle geometry of a strand as being 0.4 to 0.6 mm. thick, 5 to 12 mm wide, and 60 to 90 mm. long. Strands thus require very long length with narrow widths. They must be quite thin--especially if high density species are used-- and they require minimum fine content. Early Development of OSB It was recognized early by pioneer particleboard researchers that mechanical properties were closely related to particle shape. Particles in the form of flakes, ribbons, and strands--with smooth-cut faces parallel to the grain direction and having high lengthzthick- ness ratio--were described by Elmendorf in 1949 (‘7) and in 1950 (:8). He envisioned strandboards that would be superior to excelsior boards in moderate to low density categories. He also recognized that inorganic binders could be used to reduce cost and to provide boards resistant to fire and flamespread. In his comprehensive research on particle geometry in 1954, Turner (76) demonstrated the superior pr0perties afforded by specially generated wood strands and flat flakes. Turner's basic purpose was to define potential product capabilities nearing those of lumber and ply- wood because commercial particleboards at; that early time, with a few possible exceptions, had a low order of strength primarily because of what they were made of. The common concern of the previously mentioned studies was the ultimate development of useful and superior products from so-called waste materials, which obviously had to be bulky enough to permit the cutting of the special elements specified. In the early 1950's, German scientists showed their concern about using wood more effectively by reconstitution processes. Klauditz and his associates in 1960 (37) and 1965 (38) published a significant summary of research directed at that purpose done at the Braunschweig Technical Institute. Experiments definitely were performed with oriented woodchips and a "semi-commercial" effort was also made in 1956-57 when small beams of oriented flakes were made in the laboratory. Experiments recognizing that orientation can be caused by electrical means were also said to have been performed in 1954 with the assistance of other specialists at Braunschweig Technical University. The German scientists definitely were interested in under- standing what the full potentials might be for creating structural wood-base materials from "woodchip" particles (i.e., flakes). There seemed to be great concern for utilization of hardwood, such as beech, and for the "efficiency" of reconstitution procedures. The early studies in Germany in the 50's soon led to a series of research works carried out in Czechoslovakia at the State Research Institute, Bratislava. The result of these studies were published in 1962 by Stofko (64). The research included studies of boards of oriented wood strand elements, i.e., "woodchips." The scientists involved developed much good basic data comparing boards of oriented to nonoriented furnish and relationships of properties to density. In 1965, Stofko (65) published on orientation by electrical means as compared to mechanical methods. In 1970, he also summarized much of the earlier Czechoslovakian work and briefly described a small commer- cial plant established in that country to practice the research findings (66). In North America a few research workers have been active and from time to time have released papers about flakeboard. Representative discussion can be found in some early proceedings of Washington State University Symposium (N1 Particle board (52, 84) and in various issues of the Forest Products Journal. One perti- nent United States study of record was done by Brumbaugh (4 ) in 1969. His study was designed to explore the possible formation of high—strength boards of relatively low density by including orienta- tion (done by mechanical means) of rather long (5 in.), narrow flakes of Ponderosa pine. This study clearly showed the benefits of orientation related to degree of alignment in terms of relationships to board properties. There were a series of reports of advancements being made in the field of OSB at the various proceedings of particleboard symposium. In 1973, Snodgrass (61) gave a talk on oriented structural board and reported on the experiments conducted by Elmendorf Research and Potlatch. He also outlined the market potential of this structural panel. In 1976, Impellizzeri (27') of Elmendorf Research announced that "Strandboard" or oriented strandboard (OSB) was a product whose time had finally come. Also in 1978, the United States Forest Service held a meeting in Kansas City, Missouri. The meeting dealt with struc- tural flakeboard from forest residues, presenting research work carried out by the Forest Service in this regard in 1976/78 period (78). Vajda (80) mentioned that as of 1980, there were two structural-type reconstituted wood panel products proposed: (1) the well-known waferboard product, manufactured mainly in Canada, but sold in the United States markets as well, and (2) the newer OSB products, which is said to have improved strength properties at little or no extra manufacturing cost. From the above-mentioned history and early developmental studies in OSB, it became evident that the wood products industry is to be constantly faced with the need to modify manufacturing processes to c0pe with changing wood resources. These dynamic situa- tions of resource availabiliy must be reacted to with appropriate application of technology. Therefore, product changes are not only reasonable, they are necessary and inevitable. One of the major companies in the United States that had given an early consideration of this major manufacturing change was Potlatch Corporation at Lewiston, Idaho. In early 1969, interest was aroused among research staff members in oriented wood strand technol- ogy. Basic concepts of this technique were described many years ago ( 8, 9,37), as earlier reviewed. There was an awareness that through the orientation procedure, good quality structural panels could be produced from low quality logs, forest residues, and similar solid wood resources. By the end of June, 1969, with complete back- ing of company management, a major development project was launched. The principal objective of the new project was to produce a panel with structural properties and physical characteristics close to those of plywood (48). In Western Germany, Bison-Nerke Company gave a thought to the establishment of an OSB plant as early as 1976 when research work 10 started in that direction. They were convinced that the time was right to work out the technical and equipment problems necessary to design a plant to produce (1) reconstituted ply-core (oriented struc- tural panels) using multiple layer, two-directional flake orienta- tion (Figure 1), and (2) lumber products using single directional flake orientation ( 5). In 1978 the decision was taken by the com- pany to construct its own OSB plant in Bevern, West Germany. The Bison OSB plant started operations in April, 1979, to become the first European plant for the manufacture of OSB on an industrial scale. The detailed process description was given by Bucking et al. ( 5) and the schematic diagram of the processing is as in Figure 2. The material flow diagram for OSB panel manufacture is shown in Figure 3. Economic Advantage of OSB Orientation provides an economical means of making better use of the wood resource base, increasing plant efficiency, and providing product design and manufacture flexibility. Random panels have made the first step for composite products into the structural- use marketplace; however, orientation is needed to supplement markets where plywood has traditionally been used because of its high strength/stiffness-to-weight ratio. The key element for meeting these objectives is an efficient process of orientation which, in turn, results in potential savings. The better the alignment, the closera structural composite can resemble that of the highly aligned fiber manufactured by 11 Figure 1. Typical oriented strandboard (OSB). 12 13 Figure 2. Schematic of a facility for the manufacture of OSB boards by the Bison system. Source: Brinkmann, E. (2). 14 muw>mo mcwxuoum .mH .mmmu m:_umo_:= .wH .mmmcaiacwcmaoimpawp_zz .NH .mmmu mcwumOJ .oH .umom .mH .3mm wwo-u:u .¢H .cowpmum mewscodummo .mH .muw>mo mcwummd uca-mcwx_z a=_u .NH .Lmecm_m .HH .cwm mc_emma .ofl .CCm-S_mm .m .cmmcum .m .prz cameum .5 .memwmmwpu L_< .m .mecoiwneou .m .P—wz Lassa: .e .cmmcum .m .cwm .N .mem_u Sago mmwcg .H m. mmwmmm S t S \III'J -_J . ‘E 15 Figure 3. The material flow diagram of OSB panel manufacture. Source: Silvis and Koenigshof (60). 16 mmo omImHsz . swam oe empo.11. sz<fl ozmo 1“ szmo ”a 1 xwo mgqse swam op * zmmmo .umHz a xm oz<~¥mHe coHHmeoaeou :OHmHuoe gaze oHee Hmmov ueaonecaeem umecmeeo HHV Hmmu conzmaxm emmcHH .uemoa ema HHmmp emom e36: «NV memeHomam Hump comuaeomnm ecu mcHHHozm mmmcquse .uemon ewe mcmeHumam econ Hmcemch wadv nemoa emu mewswuoqm H HHQ .uemon emu H HHV memEHumnm Hmmp newccwm uemon some Eoem mcmewumam Ho mpmm mo emnE:z uemon eon :owumcweemumu pcmscmHHm wummeam eow emezmmms mmmee mo eonszz cmpomHmm HHEoucme mnemom mo emnE:z cowuuaeumcoo venom mueaom mmmcxumgp HmcHEo: mmmem>< waxy venom .HH .m .m .e .m .N .H HamEHemaxm eo :mHmmo .H mHamh 37 Figure 4. Surface structure of OSB from Potlatch Corporation. "bl! "all 39 Figure 5. Surface structure Of OSB from Weyerhaeuser Company. 40 4.29 aNmNiiN. 66¢ $325 NVer 41 CROSS-FLAKE DIRECTION I 2 A 1234567 18 91011121314 2.“ O r: 15 15 17 18 19 20 21 {'3 e; D 22 23 24 25 26 27 28 L2.122 5 “L 29 3o 31 32 33 34 35 335 37 38 39 4o 41 42 43 44 45 46 47 43 49 4 Figure 6. Diagram for random selection of particles for degree Of orientation test: 4- by 4- foot panel. 42 formula which can be used to approximate strength properties (in this case, MOE) in directions ranging from parallel to perpendicular to the flakes (79). The weighted sum for each board was computed from the graph of percent frequency of surface flake alignment angles (Figures 13-18). The weighted sum was obtained from the relation: S ;:E:: % Frequency of Observed x Orientation index Weighted Sum flake angles (N) An explanation of the equation may be found in Appendix I. The sum of the weighted values for each board was used to compare flake alignment of boards from the same manufacturer or those from different manufacturers. Boards with the greatest weighted sum were considered the best. Other methods as reviewed in the literature were also used for comparison. Percent Of Alignment The average of the angles measured in the weighted method, without regard to sign, was defined as e, and Percent alignment = 454; e (100) Here, the random board was considered as having 0 percent alignment. 43 Percent of Angles within :20° of the Cardinal Direction Of Alignment Results of this alignment test are shown in Table 2. Degree of Alignment in Terms of Mechanical Property Ratio of MOE Parallel to MOE Perpendicular The result of this alignment test is shown in Table 2. Test Specimen Preparation and Conditioning The 4-by-4 foot board sections were sawn into test specimens according to the design shown in Figure 7. Because bending properties (MOE and MOR) are directional, two sets Of ten 3-inch by 14-inch specimens were cut in both board directions from each 4-by-4 foot section Of panel. For the same reason, two sets of two 11-inch by 12-inch linear expansion speciems were cut in both board directions from each board. For the internal turn! test, two 3/4-inch by 12-inch strips, each yielding six test specimens, were cut from each board. Two water absorption specimens of 6-inch by 6-inch were also obtained from each board section. Special care was used to insure precise dimensions. The boards were kept in a controlled room at 65°F and 50 per- cent relative humidity before cutting them into specimens. After cutting, all test specimens were further conditioned for about two weeks. 4 .5 CENTER LINE SECTION 1 SECTION 2 '3 N 0’ I I III, )[l’l ”/I _i .— ”/ ’ ’Illt ’Il” 7 //////J DIRECTION OF ORIENTATION OF STRANDS Figure 7. Diagram for cutting test specimens from 4- by 4- foot OSB panel. SE§§§ Bending (mop & MOE ) 3" x 14" Internal Bond Strips 3/4“ x 12" ”’I . 0”, Water Absorpt1on 6" x 6" III]; Linear Expansion 11" x 12" 45 TestingpProcedure All the strength and dimensional stability tests were conducted according to ASTM D 1037-78 (1 ), except the internal bond test. Modulus of Elasticity and Rupture The static bending tests, MOE and MOR, were carried out on an Instron Testing Machine (Figure 8) 'N1 accordance with ASTM standard (1 ). The bending tests were performed on the specimens with the tension side being the surface on which the flake alignment was measured. The specimens were simply supported at the two ends with a span Of 11 inches and with a single point loading at the center of the span (Figure 8). The rate of loading (cross-head speed) was 0.20 inch per minute. The head versus deflection curves were recorded automatically by the testing machine. Internal Bond The internal bond (tensile strength perpendicular to the board surface) test was performed by compression shear test as described by Suchsland (69). The method involved lamination of the shear strip specimen of 3/4-inch by 12-inch between two boards and cutting the laminate to yield six compression shear test specimens, each of 1-inch by 4 7/16-inch and 3/4-inch thick (Figure 9). The specimen was tested in compression at a ccosshead speed (rate of loading) Of 0.02 inch per minute until it failed in shear (Figure 10). The shear strength is calculated as: 46 Figure 8. Instron testing machine showing bending strength specimen (b) at test, and (c) at failure. 47 48 Figure 9. Dimensions of compression shear test specimen for 7/16-inch-thick OSB: the shear strip laminated between 3/4-inch-thick particleboard compression strips. 1.5" 71' 2. 5" F COMPRESSION STRIP 49 “st I F \ l0 “ \\‘ \‘\\\\“ Q} = § \ '- \\ \\§ \\ \ § ‘\Q ‘x\“\ \\ $§ Q \ \\ \\\A\\\\ \\\\ \ 2. 5|. ' me". 1.,— 1-5“ ,HIHIII SHEAR STRIP 5O . ) Figure 10.--Compression shear test strength specimen undergoing test. 52 -_P_ Tmax ' 2A where: Tmax = shear stress at failure P = axial load A = cross-sectional area of column The value of internal bond was obtained by the relation: I8 = Shear stress x 0.208 Planes parallel to the center plane Of the specimen will thus become planes of maximal shear stresses. Correlation between compression shear test and the standard 18 test for most composition board is very high (r = .917) (69). Linear Expansion The test specimens were first brought to equilibrium in the conditioning room at 52 percent relative humidity and 65°F. The length was measured to the nearest 0.001 inch, using a dial gage comparator (Figure 11), and the weight measurement taken to Unanearest 0.01 gm. The test specimens were then placed in a controlled chamber, over saturated salt solution, at 93 percent relative humidity and 65°F until practical equilibriuniwasreached. At the end of this period, the specimens were again measured and weighed. The percent change in length with change in moisture content, based on the dimension at the first measurement, was then calculated. 53 Figure 11. Measurement Of linear expansion using a dial gage comparator. 55 Water Absorption and Thickness Swellipg The test specimens were measured for thickness to the nearest 0.001 inch by averaging four measurements taken at midway along each side 1 inch in from the edge Of the specimen (Figure 12). Specimens were placed horizontally under 1 inch of distilled water for 24 hours after which they were removed from the water, allowed to drain, and wiped with paper towels. They were then weighed and measured again. Specimens were afterwards oven-dried and weighed. The moisture content, water absorption in percent by weight and percent by volume, and the thickness swelling in percent of original thickness were then calcu- lated for the 24-hour soak test. Figure 12. 56 Measuring jig for thickness measurement Of water absorption specimen to the nearest 0.001 inch. Specimen was measured 1 inch in from the edge of midway along each side. 58 4O 1L____, 30 ' g _1 >- 22 20 ‘ LLJ D a: __. E 10‘- I 0 1 I l 1 0 IO 20 30 4O 50 60 70 BO 90 FLAKE ANGLES (DEGREE) Figure 13. Flake alignment angles as measured for Potlatch's OSB with 53% alignment (as measured by percent Of align- ment): Board # PA. 59 4o AFT 30 - Z 9. 1 . g 20 - CI :2 LI. 11—1 10 - 1,.___1, l T I j O 10 20 30 4O 50 60 7O 80 9O FLAKE ANGLES (DEGREE) Figure 14. Flake.alignment angles as measured for Potlatch's OSB with 59% alignment (as measured by percent of align- ment): Board # PC. 4o- 30 - 20‘- FREOUENCY (%) IO ' 60 O 10 20 3O 4O 50 60 7O 80 90 Figure 15 FLAKE ANGLES (DEGREE) . Flake alignment angles as measured for Potlatch's OSB with 61% alignment (as measured by percent Of align- ment): Board # PE. 61 ‘— 40- .__e1 30— g is 5 20.. D 8 E 10. ____. 0 l l 1 I 1 fl O 10 20 3O 4O 50 6O 7O 80 9O FLAKE ANGLES (DEGREE) Flake alignment angles as measured for Ueyerhaeuser's OSB with 63% alignment (as measured by percent of alignment): Board # NA. Figure 16. 62 4O " I—. 30 - E >. :‘e’ 20 a 3 8 a: —. u. ,_____. 10 "" 1—. o . 1 l I O 10 20 30 4O 50 60 7O 80 9O FLAKE ANGLES (DEGREE) Figure 17. Flake alignment angles as measured for Meyerhaeuser's OSB with 49% alignment (as measured by percent of alignment): Board # MB. 63 4o- 30 ' g; .......l 5 20- Z “J D c, g u. ""— 10‘- 0 I 1 T 1 *1 O 10 20 3O 4O 50 60 7O 80 9O FLAKE ANGLES (DEGREE) Figure 18. Flake alignment angles as measured for Meyerhaeuser's OSB with 62% alignment (as measured by percent of alignment): Board # NC. CHAPTER V RESULTS AND ANALYSIS Table 2 shows the summary of Flake alignment and mechanical properties while Table 3 shows the summary of flake alignment and dimensional stability properties of the OSB from the two sources. Table 3A shows the summary of mechanical and physical properties including statistical characteristics. The sample correlation coeffi- cient, r, was calculated for relationship between board density and the mechanical properties--MOE and MOR in both directions, and 18. The linear regression equations were also developed for these mechani- cal properties Over board density for all sample boards. Table 4 gives the summary Of the correlation coefficients, r, and the regres- sion equations. These relationships are also represented in Figures 19-23. Flake Alignment From the results Obtained from the flake alignment measure- ment performed on both face and back surfaces, it was discovered that the back surface had greater orientation and better correlation with the mechanical properties of the boards. The back surface was thus considered for flake alignment measurement. For the same reason, the bending test was carried out with the back surface being the tension side. 64 65 Table 2. Summary Of flake alignment and mechanical properties Of two types Of 058* Flake Alignment Static Bending Internal Bond .5 ‘2 E a a a E .. VH5 13 u- to- 00 1.1.1 ‘3' 1 l .5 mtg g2 v o: o 3: pg 3, 1105(11) 1405(1) MOR(ll) 1102(1) 6 ‘36: a: Q) 02 H 0" D HQ) 2 0 2 cm: .— E 51 35» 33; 3: 1 3 . 3 . g 1;, 3: 3 g: :33 (9/cm ) (1.000 p51) (psi) (g/cm ) (951) D 3 ad Q03 cc}: Potlatch (S-Iayer) . PA-l .72 2 1.802 2 676 8.163 4.197 .69 107 .499 52.60 61.22 2.57 (.69) (1,609) (625) (7,033) (3,748) (.72) (121) 2 .66 1.416 573 6.003 3,298 .75 135 PC-l .71 1.646 777 6.789 4,219 .67 120 .513 58.76 61.22 2.45 (.70) (1,656) (689) (6,979) (3.828) (.70) (115) 2 .69 1,665 600 7.168 3.436 .73 110 PE-l .75 1,701 714 7,539 4,727 .77 145 .503 61.18 73.47 2.34 (.73) (1.700) (725) (7,605) (4,555) (.72) (134) 2 .71 1.698 736 7.670 4.382 .67 122 Avg. .505 57.51 65.30 2.45 .71 1.655 679 7.222 4.043 .71 123 Weyerhaeuser (3-layer) HA-l .65 1,697 537 7,825 3.494 .65 86 .585 62.62 81.63 2.89 (.65) (1.647) (573) (7.630) (3,779) (.64) (83) 2 .65 1.596 609 7,434 , 4 .63 79 WB-l .63 1.362 532 5.729 3.742 .65 97 .464 49.0 55.10 2.53 (.635) (1,403) (556) (6.022) (3.698) (.625) (91) .64 1,444 580 . 5 , 4 .60 85 WC-l .64 1.510 578 6.506 3,670 .64 81 .590 62.24 69.39 2.67 (.65) (1.585) (594) (7.022) (3,767) (.60) (75) .66 1.659 609 7,537 3,864 .55 68 Avg. .546 57.95 68.71 2.70 .65 1.545 574 6,891 3,748 .62 83 1(ll) - parallel (flake direction), 1_- perpendicular (cross-flake direction) 2 *All tests were performed at 7.3 percent moisture content. Figure in parenthesis is the mean value for each board sample. 66 Table 3. Sunnmry of flake alignment and dimensional stability properties of two types of 058 f : Flake Alignment Dimensional Stability1 O 8 e Linear Water V’“’ g o 2? Expansion Absorption 1’? m u- u- o -.- 5;? ca 0 N m an He '0 C +l S—\ I: 0101 A L E 3 :3 210: 02A 8 ”2 12 35 g 8 0 g 9% “W'P 0—0— 3 4 J'- O I: o .— 13... 8'35 ‘51:: 3 "Pi-H HA-V .2"; '7‘ ‘1": ““ a a: as; gee (Si/cm) (2') :53. e. 2: Potlatch (5-layer) pA_1 .72 .07 5 .13 24.68 17.85 12.22 6.84 33.21 .499 52.60 61.22 2.57 ( 69)5 (.065) (.125) (26.45) (18.96) (11.68) (6.93) (35 27) 2 .66 .06 .12 28.22 20.07 11.14 7.11 37.33 PC-I .71 .07 .12 23.95 15.99 9.00 6.84 32.43 .513 58.76 61.22 2.45 (.70) (.06) (.135) (22.47) (15.95) (10.25) (6.86) (30.87) .69 .05 .15 20.98 15.91 11.50 6.88 29.30 PE-l .75 .06 .13 19.17 15.19 7.89 6.80 27.28 .503 61.18 73.47 2.34 (.73) (.07) (.105) (27.48) (19.80) (12.18) (7.05) (36.49) .71 .08 .08 35.79 24.40 16.46 7.29 (45.49) Avg. .505 57.51 65.30 2.45 .71 .07 .12 25.47 18.36 11.37 6.96 34.21 Heyerhaeuser (3-layep) WA-I .65 .08 .16 38.94 25.67 17.62 7.80 49.78 .585 62.62 81.63 2.89 (.65) (.09) (.145) (42.23) (27.30) (18.03) (7.82) (53.35) 2 .65 .10 .13 45.52 28.93 18.43 7.83 56.91 WB-l .63 .08 .14 50.40 30.62 17.72 7.99 62.41 .464 49.0 55.10 2.53 (.635) (.07) (.14) (52.53) (31.42) (18.68) (7.97) (64.68) .64 .09 .14 54.66 32.21 19.64 7.95 66.94 WC-I .64 .08 .18 39.49 26.39 19.60 7.74 50.29 .590 62.24 69.39 2.67 (.65) (.08) (.155) (39.91) (28.45) (17.82) (7.70) (50.68) .66 .08 .13 40.33 26.50 16.04 7.65 51.07 Avg. .546 57.95 68.71 2.70 .65 .09 .15 44.89 28.39 18.18 7.83 56.23 1All figures in percent based on original oven-dry condition 2ll - parallel (flake direction), l - perpendicular (cross-flake direction) 3Rater absorption by weight change (24-hour soak) Water absorption by thickness (volume) change (24-hour soak) 5Figure in parenthesis is the mean value for each board sample 'All tests were performed at 7.3 percent moisture content. 67 Table 3A. Summary of mechanical and physical properties including statistical characteristics MOE MOR 18 LE Board Statistical Density Number Characteristics II 1. II 1. II 1 (9/cm (1.000psi) (psi) (1151') (‘4‘) Potlatch (5-layer) PA Average .69 1609 625 7083 3748 120 .07 .13 Std. Deviation .04 240 77 1259 681 I9 .01 .01 N* 20 10 10 10 10 12 2 2 PC Average .70 1656 689 6979 3828 115 .06 .14 Std. Deviation .03 123 107 1162 721 23 .01 .02 N 20 10 10 10 10 12 2 2 PE Average .73 1700 725 7605 4555 133 .07 .11 Std. Deviation .03 195 53 1195 415 22 .01 .04 N 20 10 10 10 IO 12 2 2 Board Average .71 1655 680 7222 4044 123 .07 .13 Average Std. Deviation .03 192 82 1206 620 21 .01 .03 N 60 30 30 3O 30 36 6 6 Weyerhaeuser (3-layer) NA Average .65 1646 573 7629 3779 83 .09 .15 Std. Deviation .02 131 44 634 397 11 .01 .02 N 20 10 10 10 10 12 2 2 W8 Average .63 1403 556 6022 3698 92 .09 .14 Std. Deviation .02 177 64 794 502 12 .01 0 N 10 10 10 10 10 12 2 2 WC Average .65 1585 593 7021 3767 74 .08 .16 Std. Deviation .03 179 S 997 566 16 .0 .04 N 20 10 10 10 10 12 2 2 Board Average .64 1545 S74 6891 3748 83 .09 .15 Average Std. Deviation .02 I64 68 822 493 13 .0 .01 N 60 30 30 30 30 36 6 6 'N - Number of Observations. 68 Table 4. Correlation coefficient and regression equation for relationship between mechanical properties and board density No. Of Correlation Observa- coefficient Regression Equation tions 'r' Potlatch 6 0.7766 005(11)a = -691.9+3320.6 0C 058 6 0.6902 MOE(.1)b = -607.7+1821.3 0 6 0.7383 MOR(11) = -5890.8+18555.9 D 6 0.9307 MORLL) = -8161.4+17270.6 D 6 0.6472 18 = -34.3+220.8 O Weyerhaeuser 6 0.9068 MOR(11) = -5667.6+11181.8 D OSB 6 0.6220 MOELl) - =710.0+1990.9 D 6 0.9070 MOR(11) = -39207.9+71472.7 D 6 0.2913 MORL1) = 229.8+5454.5 D 6 0.7757 18 = -34.8+189.5 D a(11) = parallel bLl) = perpendicular cD = density 69 P = Potlatch W = Weyerhaeuser 140 ‘ x. E? l 8 i as .'_l 55 E? >4 Le) x .— Z *‘ 100 - To // ° / ° W 80.. ’,,”' '0 0' 3’ ’r"' ‘r' 60' V I r 1 55 60 .65 .70 .75 DENSITY--G/CM3 Figure 19. Internal bond as function of board density of 2 types of OSB. 2000 1800 m 53 X E I .L. 1600 >. 1.. E3 5 1400 :1 LL. 0 W 2 —J B 53‘ 1200 1000 7O x P = Potlatch H = Heyerhaeuser I I I I ‘1 0.60 0.65 0.70 0.75 0.80 DENSITY G/CM3 Figure 20. MOE(//) in bending as function of board density of 2 types of 0S8. 71 800 '- X >< 7OO 1- E .4 : 600 "' Potlatch C 0 S l/ W = Weyerhaeuser '6': / a :5 2'.» “J 4' g; 500 ‘- W :3 .J D D E 400 1 I 1 T? 0.60 0.65 0.70 0.75 0.80 DENSITY--G/CM3 Figure 21. MOE ( j.) in bending as function of board density Of 2 types of OSB. 72 9000 . t’.’ 3000 .. 1 P I E? E 7000 .. 1‘5 9 I - g 6000 q I x P - Potlatch A. W = Weyerhaeuser I 5000 1 1 I 1 0.60 0.65 0.70 0.75 0.80 DENSITY--G/CM3 Figure 22. MOR (II) in bending as function of board density Of 2 types of 0S8 73 5000 -' p 4000 - " P = Potlatch l-‘KIDULUS 0F RUPTURE ( l ) - PSI 3000'" H = Weyerhaeuser 2000 l I I fi 0.60 0.65 0.70 0.75 0.80 DENSITY -- e/cn3 Figure 23. MOR ( 1.) in bending as function of board density of 2 types of OSB. 74 The different methods used in determining the alignment of flakes were as shown in Tables 2 and 3. All three methods of measur- ing flake alignment showed some inconsistencies, but did show some correlation to MOE II/MOE I. There is no basis for conclusion state- ment in that regard because the MOE ratio is very significantly affected by density ratios, face:core thickness ratios, resin content, and other factors, none of which could be assessed in this study. Figures 24 and 25 also show the relationship of both MOE and MOR to percent of flake alignment of the two types of OSB, showing Potlatch boards as having higher strength properties. Even though with a little less percent Of alignment than Weyerhaeuser boards, the Potlatch boards still have a slightly higher strength properties (Figures 27 and 28). The relationship of LE to percent of flake alignment of both Potlatch and Weyerhaeuser is shown in Figure 26. The summary results show that there was no consistency in the effect Of flake alignment on internal bond and dimensional stability. The linear expansion in the perpendicular direction Of alignment was, however, almost twice greater than that in the parallel directions. Modulus of Elasticity and Rupture Modulus Of elasticity (MOE) and modulus Of rupture (MOR) are two important properties particularly for structural applications. It is well documented in the literature that both properties increase with board density. In this study, MOE and MOR increased in both parallel and perpendicular directions as board density increased (Figure 20 to 23). 75 2.0 - 1? S 2: 1.6 " IE .E «5 1.2'- O. ‘7 I >. t 23 E '68 ‘ d n. O U) 3 3 £3 .4 - 0 Figure 24. POTLATCH MEYERHAEUSER m = Perpendicular [W = Parallel WIT "‘6'." j 5.; I}. {9: .EEZI ’ 1 :1 .5? ::E I 1“ } :':' I l 3" ‘ .6 49.0 BOARD CONFIGURATION --(% ALIGNMENT) Relationship of modulus of elasticity to percent of flake alignment of 2 types Of OSB. 76 in thousands) MODULUS 0F RUPTURE-(P.S.I. Figure 25. POTLATCH 58.8 61.2 HEYERHAEUSER = Perpendicular “mm" = Parallel ] Co O. O 0.. L BOARD CONFIGURATION (Z ALIGNHENT) o D O O O .0 O. O Relationship of modulus of rupture to percent of flake alignment of 2 types of OSB. LINEAR EXPANSION (52%RH to 93%RH)-(%) Figure 26. .20- .15- .10- .05- 77 Rela Rela alig POTLATCH HEYERHAEUSER 61.2 49.0 62.2 BOARD CONFIGURATION (% ALIGNMENT) tionship of linear expansion (52 to 93% tive Humidity--RH) to percent of flake nment of 2 types of OSB. = Perpendicular flflIflIfl = Parallel :1... Z. .0: 0:. :‘ 78 r ) ll [—1 II x 1500‘ O3 '2 x 1000... 27; 1 °" * T .I. E"; 500 .. '--7 0 POTLATCH HEYERHAEUSER '(57.5% alignment) (58.0% alignment) ll = Parallel (flake direction) 1_= Perpendicular (Cross-flake direction) Figure 27. MOE of two types of OSB. 79 II II fir .— 6000 " u. l ‘1- 4000 __ _.1, J- 2000 ,H 0 POTLATCH HEYERHAEUSER (57.5% alignment)‘ (58.0% alignment) ll = Parallel (Flake direction) l.= Perpendicular (Cross-flake direction) Figure 28. HOR of two types of OSB. 80 MOE values range from 1,416,000 psi to 1,802,000 psi, with an average of 1,655,000 psi, in the parallel direction and from 573,000 psi to 777,000 psi, with an average of 679,000 psi, in the perpendicu- lar direction for the Potlatch boards, while they range from 1,362,000 psi to 1,697,000 psi, with an average of 1,545,000 psi, in the parallel direction and from 532,000 psi to 609,000 psi, with an average of 574,000 psi, in the perpendicular direction for the Weyerhaeuser boards. The values shown are averages of five tests. MOR values range from 6,003 psi to 8,163 psi, with an average of 7,222 psi, in the parallel direction and from 3,298 psi to 4,727 psi, with an average of 4,043 psi, in the perpendicular direction for the Potlatch boards, while they range from 5,729 psi to 7,825 psi, with an average of 6,891 psi, in the parallel direction and from 3,494 psi to 4,064 psi, with an average of 3,748 psi, in the perpendicular direction for the Weyerhaeuser boards. The values shown are also averages of five tests. There was a positive correlation between the bending properties and board density for boards from both sources (Figures 20 to 23). Linear regression equations were also developed for MOE and MOR, in both directions, over board density for both board types (Table 4). Weyerhaeuser board has a higher correlation coefficient, r, for rela- tionship between both MOE and MOR in the parallel directions and board density, while Potlach board has a higher correlation coeffi- cient, r, for both properties in the perpendicular direction. From Table 2, it was clearly shown that the bending properties in the parallel direction were significantly higher than in the perpendicular 81 direction for both board types. Practically, the Potlatch board has a higher bending strength properties than the Weyerhaeuser board. Internal Bond The internal bond (18), tensile strength perpendicular to the board surface, is a widely determined property and a very controversial one in terms of the analysis of results, as is well documented in the literature. In this particular study, looking at the overall results in general, there is a tendency of internal bond to increase with increasing board density for both board types (Figure 17). 18 values range from 110 psi to 145 psi, with an average of 123 psi, for the Potlatch boards, while they range from 68 psi to 97 psi, with an average of 83 psi, for the Weyerhaeuser boards (Table 2). The values shown are averages of six tests. There was a positive correlation between the internal bond and board density for both board types (Figure 17). Weyerhaeuser board has a higher correlation coefficient,r, than the Potlatch board, but it was practically shown from Table 2 and Figure 17 that Potlatch board has a higher internal bond strength property. Linear Expansion Linear expansion (LE), like MOR and MOE, is a very important property when panels are used for structural purposes. Some scientists have found LE to increase along with increasing board density, while others have found no clear relationship. In this study, no clear relationship between LE and density exists for both board types (Table 3). 82 LE values range from .05 percent to .08 percent, with an aver- age of .07 percent in the parallel direction and from .08 percent to .15 percent, with an average of .12 percent, in the perpendicular direction for the Potlatch boards, while they range from .08 percent to .10 percent, with an average of .09 percent, in the parallel direc- tion and from .13 percent to .18 percent, with an average of .15 per- cent, in the perpendicular direction for the Weyerhaeuser boards. From Table 3 and Figure 29, it was shown that the LE in the parallel directioncn alignment was less than in the perpendicular direction; about half. It was also shown that Potlatch board expanded to a less extent than Weyerhaeuser board under the same condition of relative humidity. Thickness Swelling,and Water Absorption Thickness swelling is another very important property when considering most of the uses of composition boards. Thickness swelling values range from 9.00 percent to 16.46 percent, with an average of 11.37 percent, for the Potlatch boards, while they range from 16.04 percent to 19.64 percent for the Weyerhaeuser boards. The average water absorption by weight change was 25.47 percent for Potlatch and 44.89 percent for Weyerhaeuser, while the average water absorption by thickness (volume) change was 18.36 percent for Potlatch and 28.39 percent for Weyerhaeuser. From Table 3 and Figure 30, it was shown that Potlatch board absorbed less water both by weight change and thickness (volume) change, than the Weyerhaeuser board. 83 0.15 -‘ ‘F""fi' 0.10“ H LINEAR EXPANSION (%) l POTLATCH NEYERHAEUSER ll = Parallel (flake direction) _J_ = Perpendicular (cross flake direction) Figure 29. Linear expansion (52% to 93% relative humidity) of 058 from Potlatch and Weyerhaeuser. 84 50 H = Height change w ..____1. T = Thickness change 40.— E E3 30.. T E3 ---w a. N ‘3‘: 22 < 0!. if 20.. T § I)——T 10.. 0 POTLATCH NEYERHAEUSER Figure 30. Hater absorption by weight change and thickness (volume) chan e of OSB from Potlatch and Weyerhaeuser (24-hour soak) 85 The summary of mechanical and physical properties including statistical characteristics, as shown in Table 3A, indicates that there is a greater variation in properties within the Potlatch board than within the Weyerhaeuser board. CHAPTER VI DISCUSSION The results obtained from the evaluation of the various proper- ties of the two oriented strandboard (OSB) types and the analysis of the data did indicate that these properties were affected, not only by flake geometry and alignment, but also by other processing variables such as board density, layering, and resin content. The different methods used in determining the degree of flake/ strand alignment seemed to show an indication of increase in the Overall prOperties of the boards as the flake alignment increased. The results from three of the methods--percent of alignment, percent of angles within i20° of the cardinal direction of alignment, and mechanical property ratios of MOE in both parallel and perpendicular direction of alignment--were, to a reasonable extent, in agreement with the previous works of Geimer (14,15) and other researchers (30,61). Though the simple method used might not have yielded a very satisfactory result, better results could be obtained by means of a more sophisticated device. The flake alignment measurement was performed on the back surface of the boards because it showed a greater orientation and a better correlation with the mechanical properties. This greater orientation of the back surface of the board may have to do with the 86 87 forming of the flake layer; the back surface having the first series of layers falling on it with possible better alignment of these flakes. Though the visual assessment of the two board types gave no great contrast in degree of orientation, there was, however, a great contrast in mechanical properties between parallel and perpendicular directions. Hence, it might be misleading to assess the properties by means of visual inspection of the degree of orientation. The effect of the degree of flake orientation on the mechani- cal properties--MOE and MOR--of both types of boards was evident though, but to a less significant extent within boards of the same type, as shown in Figures 25 and 26. It was, however, shown that the properties in the parallel direction were about twice that in the per- pendicular direction. This result agreed with the fact that the increase in properties in the parallel direction is made at the expense of those in the perpendicular direction, as pointed out in early research works (19,56). Though Weyerhaeuser board appeared to have a slightly higher degree of flake alignment, its mechanical properties were lower than the values for the Potlatch board. The cause for this could be traced to the effect of board density on these properties. Potlatch board was of higher density than that of Weyerhaeuser,hence the higher mechanical properties of the Potlatch board. Within each board type, however, there was substantial increase in the strength properties as board density increased. It was well documented in the 88 literature that increasing board density improves all the physical strength and stiffness properties and this was confirmed by Hse (24, 25) and Heebink (23). Increasing resin content has also been found to improve all of the physical properties of boards (43,44,45,54,58) and this is a possibility for the Potlatch board's case. The effect of 'layering' might have come to play in the results of the physical properties of both types of boards. Potlatch (five-layer) appeared to be a better OSB than Weyerhaeuser (three-layer) because the five-layer structure, where the face is length oriented, the middle layer is cross-oriented, and the core consists of random-oriented finer material, makes it pos- sible to have substantially improved control over panel length versus cross panel strength properties (80). When compared with a 7/16-inch three-layer construction composite panel and a 1/2-inch plywood four-ply CDX, both Potlatch and Weyerhaeuser boards showed very high mechanical and dimensional stability properties (Table 5). The highly significant difference in properties attained by both Potlatch and Weyerhaeuser OSB may be'due to differences in board density, layer construction, and other proces- sing variables in the three types of boards. As previously mentioned by Geimer (14), it was found that the internal bond strength was not affected by strand alignment. Most researchers, however, have found higher IB values with increasing board density, resin content, and press time and temperature (22,24. 44,49). At all densities, 18 strength of the Potlatch board was well .Anev .Pm “a ..m .: .cmmxuz ”auasom .umumape>m mcwmn mam gown; cmmamezcmxuz use goumppoa seem mmOm mcmmcm> H aaocu gucw-w\fi we apaucaoe ugeucmumm .covuuacamcou emxmp-mmesu ..m.w .meou ucmcuquooz-umucmwco cm>o :ucmp\cwm-mmpmaoo mo xpa emmcm> cmuao mcoH 89 mH.mH Am.HH ~.m m.m ARV xaom taos-e~ .Fpazm mmacxu_ee mm.¢e me.mm “.mm m.mm ARV mczo; em cw cowpacomnm cope: mH. NH. mo. «H. Axv capsuwucmaema .cowmcmaxm cmmcm4 mo. so. mo. oH. Agv Puppmcma .cowmcmaxm cmmcwb any—waepm Pocowmcmswa mm mNH mm“ mm Atmav econ PecaaucH mem.m meo.e omo.e omm.~ Acmav ee_=u?u=aaeaa .moz Ham.m NNN.N om~.m owm.m Awmn coo.Hv _a__meaa .moz «Am mew “mm mum Acme coo.Hv ee_=aeu=aacaa .moz mem.H mmo.H mem.a mm~.H Asma coo.Hv FaP_eema .moz pmumcmnumz me. HA. mm. Hm. Angu\mv .sawmeao QH\N efi\n N\H mfi\u A.=FV .mmacxuwep _ecvsoz mezmmgemxmz zuumpuoa xoo xpaue Pmcma Ncoozzpa muwmoaeou muemonncmcum umpcmweo venoaucmgum umucmwgo use .uoozxpn .chma muwmoaeou m we mmwpemaoen Pmomcmzums ucm pmuwmaga mo cochmaeou .m mpnmh 90 above that of the Weyerhaeuser board (Figure 19). The high 18 values for Potlatch might have also been due to increased resin content. The result as shown in Table 3 shows that the differences in dimensional stability properties are very practically significant between the Potlatch and Weyerhaeuser boards and as such may not need any further statistical analysis. Geimer (14,18) and Talbott (71) found that flake alignment had little effect on thickness swell- ing, but was the major variable controlling linear expansion. Geimer concluded that orientation afforded a substantial improvement in dimen- sional stability in the aligned direction and a corresponding loss in the cross direction. It was shown from Table 3 and Figure 29 that with both board types, the linear expansion (LE) in the cross direction of alignment was greater than in the aligned direction. This was in agreement with the findings of Geimer (14,18), among other researchers. While some scientists have found LE to increase with board density (13,63,85), others have found no clear relationship (21,43,68,70). In this study, however, no clear relationship between LE and board density existed for both board types. Since LE is less sensitive to surface properties than NOE and MOR, it is less sensitive to the degree of face orientation. The lower LE coefficient of Potlatch board (Figure 29) may, however, be due to its five-layer structure since variation within LE in the parallel and perpendicular directions depends on the thickness of the layers; i.e., thickness ratio of core to face layers. 91 Geimer (18) found that flake alignment had little effect on thickness swelling, and Talbott (72) also discovered that orientation made no significant change in weight increase (water absorption) and thickness increase. These findings are similar to the results obtained from this study as shown in Table 3. It is, however, well documented in the literature that board density affects the rate of thickness swelling by controlling the rate of water absorption (44, 57,81). The results in Table 3 and Figure 30 showed that the Weyer- haeuser board absorbed more water by weight and thickness change than the Potlatch board. This significant difference makes Potlatch a superior board, more so that the lower values correspond to higher density. while the Potlatch board may be more considered for external use where it is exposed to water absorption, the Weyerhaeuser board may not be favored since it may be losing much of its properties after exposure to moisture content. Other possible reasons for the results obtained for thickness swelling might be due to the effect of flake length/thickness ratio (slenderness ratio) and flake thickness (3,44,52,54). CHAPTER VII CONCLUSION It is highly desirable for any manufacturer of structural boards, such as particleboard, oriented strandboard, etc., to evaluate the relationship of raw material and process variables on the proper- ties of the board. This enables him to manufacture board with a range of desirable properties or make adjustments in the processing vari- ables, such as glue content, press cycle, press temperature, resin content and quality, flake length and thickness, and density. The mechanical and physical properties of oriented strandboard (OSB) depend greatly on all these variables. This study was a comparison of two commercial OSB products which were represented by small number of boards produced by the individual manufacturer. This comparison has two components: (1) a comparison of board properties as indicated by the strength proper- ties, and (2) an analysis of the degree of orientation of face flakes. These two boards were manufactured with different processing procedures and variables which might have affected the evaluated properties of the boards differently to a large extent. From the results of the various tests performed, it was evidently shown that the Potlatch OSB is of higher properties than the Weyerhaeuser OSB, both in the mechanical and physical properties. 92 93 These differences in properties could well be offset by cost dif- ferences. It may reflect conversion adjustment of these properties by the manufacturer to attain some cost objectives. It must be realized that these boards were also made at different property level. Orientation of flakes could only be measured at the surface of the board. There is no compelling reason to believe that the orien- tation remains same throughout the layers of the board. The most that can be said of orientation measurement is that the result varies to a little extent over the two board types. One method appears to be more suitable than any of the other two methods. The important thing is to realize that while orientation is a very important variable as far as mechanical properties are concerned, these properties are also very strongly affected by layer thickness ratio, density ratio, and others which could not be assessed. It appears that whatever methods were used in both processes, they achieved same results. Possible improvement in degree of flake orien- tation may translate into very marginal improvement of practical significance. The appearance of mechanical prOperties of both Potlatch and Weyerhaeuser 058 products were not so different to such a signifi— cant extent. The better performance of the five-layer Potlatch 058 was, however, more pronounced in the physical properties, but it is difficult to conclude that this was due to the layering. The increased density of this board type may be said to be of much 94 significance in this respect. Also, for exterior application pur- poses, the Potlatch may be considered to be a better board because of its low thickness swelling and water absorption. If both the Potlatch and Weyerhaeuser OSB were available at the same price, the Potlatch board would definitely be chosen because of its greater bending strength (MOE and MOR) and tensile strength (IB) properties. less linear expansion (LE) on exposure to moisture, and less rate of water absorption and thickness swelling. APPENDIX 95 APPENDIX A HANKINSON-TYPE FORMULA The Hankinson-type formula is as follows: N = . PQ Psm"e + Qcosn 6 where N = the strength property at an angle 6 from the fiber direction 0 = the strength across the grain P = the strength parallel to the grain n = an empirically determined constant Here, n = 2 for modulus of elasticity Q/P = .04 - 0.12 a° e (midpoint of of), N (orientation index) 0-10 5 0.874 10-20 15 0.440 20-30 25 0.228 30-40 35 0.138 40-50 45 0.095 50-60 55 0.073 60-70 65 0.060 70-80 75 0.053 80-90 85 0.050 96 LITERATURE CITED 97 10. 1'6'4",'511. LITERATURE CITED American Society for Testing and Materials. 1979. Standard methods of evaluating the properties of wood-base fiber and particle panel materials. ASTMD 1037-78, Philadelphia, PA. Brinkmann, E. 1979. [Oriented structural boards (OSB), their properties, application, and manufacture.] OSB-Flatten, ihre Eigenschaften, Verwendung und Herstellungstechnologie. Holz als Roh-undWerkstaff (1979) 37(4): 139-142. Brumbaugh, J. I. 1960. Effect of flake dimensions on properties of particleboard. For. Prod. 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