A STUDY OF THE. PROGRESSIVE OXIDATION OF CELLULOSE Thtsls for the Degree of Ni S. MICHIGAN STATE COLLEGE ’ 0131'; D. Beimleson 1939 . . , yo 1‘? .. \..u\ hia.‘1¢t.curru . . - It'l‘n‘...- . . ‘....II‘ E” .9 ’.n Ody... .. . K .Jh.oh ‘ . . . .I . ' v .. ,V-h-.~..‘......rr§ -. . ...l.5. . ..-.~..v.rA. Cl , _ f. ,. . H. d: ’T.‘ ll .A STUDY OF THE PROGRESSIVE OXIDATION OF CELLULOSE A.Dlelertetion Submitted to the Faculty of Michigan State College of Agriculture and Applied Science In partial fulfillment of the Requirements for the degree or Master of Science by John David Bartleaon 1939 ACKNOWLEDGMENT To Prof. B. Eu Hartcuch, the writer wishes to acknowledge his appreciation for the guidance and helpful suggestions which have made possible com- pletion or this wont. 121501 Contents Page- Introduction A. Purpose of the work ................... 1 B. Nature Of the “Pk ............. O O O - o o a Historical - - ------ - ....... - .......... 10 Present work A. Study of the Progressive Oxidation of Cellulose - - - - 19 B. The Nature of the Oxidized Cellulose ---------- 21 Laboratory Procedures a. Oxidation Part I ............... - - - - - 27 B. Oxidation Part II .................. - - 29 0. Analysis of Residues ....... - - - - - - ..... 33 Data A. Tables ......................... 38 B. Graphs ......................... 44 Discussion of Data A. Neutral Oxidation ------ ~ - - ----- - - - - - - — 53 B. Acid Oxidation .................... - 56 0. Alkaline Oxidation - - - - - - - - , - - ------ - - 57 Dc00mpar180Dl--o----—--------------- 59 ............ --------------66 Introduction l§;=?urpose of the worg In spite of the enormous amount of research which has been devoted to cellulose, many of its chemical reactions are not under- stood. very little is known of its degradation, either hydrolytic or oxidative. much.of the study of cellulose has'been carried out in the field of textiles. rhe greater*part of this work has been done in a qualitative manner and its object has been to find simple tests which could be used to differentiate among the various modifications of cel- lulose. various tests have been deve10ped.vhich.show the difference between normal cellulose and oxidized cellulose. Since these tests have been intended solely for application to commercial materials a great part of the research work has been¢ione from the industrial rather than from the scientific viewpoint. In the last few'years some of these gialitative tests have been refined and deve10ped into quantitative measurements and there have been several investigations in which these quantitative measurements have been used to follow the chemical degradation of cellulose. Their object has been the attainment of a better understanding of the chemical nature of cellulose. Unfortunately a large amount of this study has been poorly organized and has not been carried out along scientific lines. In many instances the workers have failed to state the conditions under which their research has been done and their procedures often lack many details which are necessary for a thorough understanding of their work. In these cases the results are meaningless. The study of the oxidation of cellulose has had a gradual evolu- tion beginning with the preparation of oxycelluloses. These oxycellulose preparations were thought to be chemical compounds by the pioneers of cellulose chemistry, each worker having his own oxycellulose and each oxycellulose having its own molecular formula. With a setter understanding of the nature of oxycellulose came the realization that the oxidation of cellulose is a gradual process and that no single, isolatable oxycellulose is formed during this process. In recent years several studies have been made on the progressive oxidation of cellulose. These studies havediffer- ed in the care with.which the conditions have been controlled and in the variables which have been used during the oxidations. some of the pos- sible variables are the nature of the oxidant employed, the strength of the oxidizing solution, the pH of this solution and the temperature at which the oxidations are carried out. T.e present work.differs from previous work in the variable which was chosen; in the present work time is the variable. The purpose of the present work is to make a study of the progressive oxidation of purified cotton cellulose under carefully controlled conditions and to analyze the oxidized cotton residues. B. Nature of the work The structure of cellulose has been the subject of much contro- versy since Tollens postulated the first hypothetical formula in 1895. In the last fifty years many formulas for cellulose have been preposed, accepted and later-discarded. At the present time cellulose is regarded as a chain in which.a large number of cellobiose units are linked together through the one and four positions by glucosidal linkages. It is assumed that the chain is Open, which means that there is no linking between the two terminal units, the first unit having a free hydroxyl in the four- position and the end unit a free hydroxyl in the one—position. The accepted formula is: — P r—— F— l_— f__‘ //0- C—x/ —— g—y —— (IL—fl — cl —// H-é-w/ fl-Cl-dfl Ive-o” H-g-OH flo-C'-// x/a-ci-xx , yous—y H0 g—H H-C'-——""“ #00 #g—o //-§-0// | I l _ _ ___J H—C—O— #g-o H-e-o 6’ § 0 l/fil-a/z’ sea/x Has-0H ”OOH £7 L H // —/v '9’ The molecular weight of cellulose is not definitely settled. Several molecular weights have been suggested depending upon the method used and the past history of the cellulose preparation used. Haworth and Machemer (I), using chemical methods, have calculated it to consist of not fewer than 100 and not more than 200 glucose units, and they regard this size to be the average lower limit of the cellulose molecule; the corresponding molecular weight of the cellulose would be between 20,000 and 40,000. The osmotic pressure method, a physicochemical method, indicates molecular weights which range between 25,000 and 100,000 (between 155 and 600 glucose units), depending upon the degree of depolymerization through which the various preparations have passed. The most recent and most accepted method is the Svedberg ultra centrifugal method which has proved so valuable in protein chemistry. It is based upon photographic Observations and records of equilibrium or velocity of sedimentation in a strong centrifugal field. The values found are much higher than those obtained with the other methods. The following figures are given: 570,000 for native cellulose (corresponding to 3,600 glucose units}; 150,000 to 500,000 for purified cellulose and 50,000 to 120,003 for re- generated cellulose. Xpray analysis has furnished definite proof of the crystalline nature of cellulose. The lattice on which the cellulose crystal is built is of the monoclinic system and there is one cellobiose unit (correspond- ing to two glucose units) in.the unit cell. The constituent units are arranged in continuous chains which run parallel to the fiber axis through the unit cell. The glucose to glucose horizontal linkages are held together by primary valence forces while the position of the chains with respect to each other is stabilized by secondary valence forces. The cellulose crystallite or micelle, the smallest visible microscOpic unit, is made up ofia few chains gathered into a long, thin bundle. A.micelle contains approximately 2,000 glucose units and assuming the chain to contain 200 glucose units, one micelle would comprise ten chains. The micelles are oriented parallel to the fiber axis, and in cotton are turned spirally around the axis. This orientation is directly related to the strength of the fibers. These micelles are held together by tertiary, miceller or "supermolecular" forces. This structure explains a number of the physical phenomena exhib- ited by cellulose. It accounts, for instance, for the swelling in water or in other liquids not attacking the cellulose chemically. This swelling is small in the longitudinal direction.of the chains since there is apparently no opportunity for the molecules of these liquids to penetrate between the single units of the chain. In the lateral direction, however, molecules of the liquid find sufficient space to enter and in so doing widen the space still further. This theory is in agreement with the g-ray pattern of swollen imercerized) cellulose. (The author is indebted to "Organic Chemistry: by Gilman, Volume II (1534-1595) for parts of this section; a much more thorough discussion, together with complete references, may be found there.) These structunal principles are important in the present work, in which all of the oxidation reactions were carried out in.a two-phase system (liquid, solid); i.e., oxidizing solution and solid cellulose. The oxidizing solution could penetrate between the chains but not between the single units of the chains. Another method of attack for this problem would have been to dissolve the cellulose in some medium such as cupric ammonium hydroxide solution, and thus the cellulose would have been attacked in a homogeneous one-phase system; however, in this system the micellar orientation is lost and true cellulose is no longer present. Proof of this loss in miceller orientation is found in the regeneration of cellulose frouithe cupric ammonium hydroxide solution. The regenerated product is similar to cellulose in many respects, but has a decreased tensile strength and a lower average molecular weight. Cellulose undergoes two types of chemical degradation; namely, hydrolytic and oxidative. Hydrolytic degradation is brought about by the action of acids while oxidizing agents are responsible for the oxidative type. The products formed by hydrolytic degradation are usually referred to as "hydrocellulose", and the products of oxidation are termed "oxycsllulcse"; these are general names and their meaning is not well defined. The first stages in any degradation of cellulose or its derivatives consists in the weakening of the supermolecular forces which hold the micelles together and in the further breakdown of the secondary valence bonds converting the micelles to their constituent chains of cellobiose molecules. It can be seen from the foregoing why in the initial stages of the formation of oxy- and hydrocelluloses, the products obtained are similar in properties; at the same time it must be realized that such a procedure must of necessity give rise to a mixture of degradation products. Thomas (2) believes that it is the end groups of these chains which are of primary importance in determining the prOperties of the degradation products, and he states that it is there that the difference between oxy- and hydrocellulose is to be found. The next stage in the formation of oxycelluloses and hydrocelluloses will therefore be an attack on the and glucose units of the chain. Thomas considers that it is possible that in the formation of hydrocellu- loses the six membered rings of the end glucose units are Opened to give the active reducing aldehyde form, while in the formation of oxycellu- loses some or all of the exposed aldehyde groups are oxidized to carboxyl groups. It is also probable that the GH20H group at position number six in the glucose molecule is oxidized to an aldehyde or carboxyl group. since there are many of these OHBOH groups in the molecular chain, there is considerable Opportunity for the formation of these groups. wring degradation further "cracking" may also occur, thus yielding shorter chains and exposing more terminal glucose units with their oxidizable aldehyde groups. Therefore it is considered that material produced by treatment of cellulose with acid contains free aldehyde groups in its structure and corresponds to the sO-called hydrocellulose, while that prepared by a mild oxidation using'either'an acid or alkaline oxidizing agent contains both carboxylsnd aldehyde groups, the carboxyl groups most probably being'at the terminal position in the chain of glucose units, and corresponds to the sO-called "oxycellulose." A.chenical investi- gation of these materials is dependent upon the presence and relative amounts of these aldehyde and carboxyl groups in the molecules of the degraded cellulose. However carefully the conditions are controlled during the preparation of these materials, it cannot be conceived that the macromolecules will break down into molecular chains which are exactly equal in length. The properties of oxy- and hydrocellulose, which are very similar are in agreement with the structural facts which have just been discussed. As a result of‘the miceller breakdown the degraded cellulose has a lower tensile strength than the unmodified material. It also has a decreased viscosity in cuprammonium solution, this being’ascribed to its lower average molecular weight. Many workers in this field believe the vis- cosity of a cellulosic product in cuprammonium solution to be prOpertion- al to its molecular weight. Two other prOperties which differentiate both types of degraded cellulose from the unmodified material are a marked solubility in dilute alkali and a strong reducing'power, the latter prOperty being attributed to the action of aldehyde groups. The one property which distinguishes oxidized cellulose from acid degraded cellulose is the greater affinity of the former for'basic dyestuffs. Because of the similarity in prOperties of oxy- and hydrocellu- lose the literature is often.confusing in its references to them. Thomas (2) realised the need for a better definition of the properties of these products and for a more apprOpriate nomenclature. Since both oxycellulose and hydrocellulose are degradation products of cellulose, in other words cellodextrin derivatives, Thomas classified them under the general name of "cotton dextrin products." As a result of his study, vhich.showed clearly that hydrocellulose is a cellodextrin product containing free aldehyde groups and that oxy- cellulose is a cellodextrin product containing both free aldehyde and carboxyl groups, he proposed the new terminology "aldehydic cotton dextrin“ to be applied to hydrocellulose and “carboxylic cotton dextrin" for oxycellulose. To get a clear picture of what happens when cotton cloth is subjected to the action of various chemical agents it must be remember- ed that the agents attack the fiber (the basic unit of the fabric) in a two-phase system and that the reactions take place only at the surface of the fiber. There‘are an infinite number of stages in this process, as the point Of chemical attack works its way inward from the surface of the fiber. There are several visible signs of this gradual attack. In the initial stages of degradation the modification may be detected only by certain.qualitative laboratory tests. As the surface becomes more degraded the dyeing properties of the fabric are changed and it becomes partially soluble in water and alkail. When a fabric has reached an intermediate stage of degradation its strength is appreci- ably decreased and it is no longer of any value for textile purposes. Upon washing>such a fabric there is a noticeable loss in weight, and when this same material is boiled in alkali there is an even greater loss in weight and a yellow—colored solution, similar to that pro- duced by boiling alkaline solutions of sugars, results. The modified cellulose produced in the final stages of the degradation of cotton fabric crumbles at the slightest touch, changing to a powdery, homo- geneous mass which in no way resembles the original material. 10 Historical The study of the progressive oxidation of cellulose has not had the logical step-by-step develOpment that is characteristic of scientific research. The workers have not made good use of the literature,and as a result some of the more recent study has been a repetition of previous research. The lack of a single outstanding contributor or group of contributors is probably responsible for the existing state of confusion. As a result of this lack of leadership the conditions and methods of the previous studies of cellulosic oxidation have not been standardized, thus making comparative inter- pretations of results very hazardous. Because of the poor continuity in the previous study of the progressive Oxidation of cellulose the historical references will be listed chronolOgically and discussed individually. 11 1. in 1893 Cross, Bwan and Beadle (5) oxidized cellulose at room temperature using chromic acid as the oxidant. They found that the modified cellulose lost weight as the extent of oxidation was increased. 2. In 1922 Knecht and Thompson (4) oxidized cellulose progres- sively using an acid solution of potassium permanganate. using methods which are applied to cellulosic materials they analyzed the Oxidized residues for aldehydic and acidic prOperties and submitted the residues to various chemical reactions. They found that the increase in the reducing power of the oxidized cellulose was preportion- al to the amount of oxidant used up until a half atomic portion of Oxygen per 66H1005 unit had been supplied, and that further oxida- tion caused no increase in reducing power. from this study they concluded that in the initial stages of oxidation the action is mainly to produce or liberate aldehyde or ketone groups and that the later stages involve more complicated chemical processes. from results obtained from acylating degraded cellulose they concluded that the Oxidation process results in a suppression of the hydroxyl activity of these degradation products. 3. In 1923 Knecht and mgan (5) oxidized cellulose using solu- tions of sodium hypochlorite and hypochlorous acid Of varying’oxidiz— ing strength. measurements of the reducing power and tensile strength were made on the cotton residues. no conclusions were drawn. 4. In 1924 n. J. Lewis (6) made a study of the fluorescent properties of cellulosic products. His experimental work showed that the fluorescence of a degraded cellulose increases with a correspond- ing increase in.alkali solubility (indicative of acid properties), but no indication of a connection between reducing properties and fluores- 12 cent power was found. he concluded that the form and dimensions of the fluorescent curve are an expression of‘the chemical constitution of the substance. 5. In 1925 Hibbert and rarsons (7) carried out a comprehensive and well-organized study Of the Oxidation of celluloSe. They oxidized cotton cellulose prOgressively at room temperature (22°- 26°) over the oxidizing range 0.01 - 2.00 atomic portions of oxygen per 06H1005 unit. Potassium, magnesium and barium permanganate in neutral and slightly alkaline solutions, and chromic acid in 90h acetic acid were the Oxidiz- ing solutions. Their work included a complete analysis of the oxidized residues and a microscOpic study of the fibrous structure of the residues. home of the conclusions drawn from this important contribu- tion were: 1. The Oxidation reaction is typical of'a heterogeneous system in which there is a progressive degradation of the fibres. 2. The degree of disintegration of the fibres is more pronounced in neutral, or slightly alkaline, solutions, a fine powder being obtained when the maximum amount (2.00 atomic portions of oxygen) of oxidant is employed. A marked disintegration does not appear until Over 0.10 atomic portion of oxygen is consumed, although a deteri- oration in strength is noticeable. 3. The fibre losses are greater in neutral and slightly alkaline media, and the reaction is more rapid, than in acid solution. The losses always increase wdth increas- ing amount of oxidant used. With the permanganates, the 13 losses are practically independent Of the nature of the metallic radical (K, Mg or Ba), and do not vary materdally when the concentration of the solution is changed within a small range. 4. Carbon dioxide is one of the chief products of the Oxidation. 5. Cotton cellulose when oxidized in acid solutions contains a larger'amount Of oxidized material than when oxidized in either neutral or alkaline solution. The ash, OOpper number (a measure Of the reducing power), alkali-solubility, pentosan and glycurone constituents have higher values in the case of cellu- lose oxidized in acid solution, and the percentage yields are greater. 6. Acetylation tests indicate that for the oxidizing range studied, the number of alcoholic groups in oxidized cellulose decreases from three to nearly two for 0631005 unit. 7. The solubility of oxidized cellulose in alkali is regarded as due not only to salt formation and to re- actions involving the aldehyde group, but also to a peptisation of a portion.of the unattacked cellulose. 8. The viscosities of the cuprammonium hydroxide solutions of the various oxidized celluloses are much lower than those of the original cotton. The con- sumption of an amount of oxidant represented by only 0.01 atomic portion Of oxygen per 0631005 unit pro- 14 duces a very marked decrease in viscosity. This fact, tOgether with the alkali—solubility determin- ations, suggests that a portion of the unattacked cellulose .- probably the layer adjacent to the oxidized portion of the fiber - is changed in some profound manner, probably the result of a depoly- merization process. 9. The oxidation is accelerated by alkalis, and re- tarded by dilute acids, because the former act on the initially oxidized cellulose so as to give a much larger concentration of the oxidizabls components. These latter are more readily oxidized, under the conditions, than cellulose itself. 10. Oxidized cellulose, as prepared in this inves- tigation, is regarded as a mixture of a large amount of unattacked cellulose (which may exist in different degrees of'polymerization or association) with rela- tively snall quantities of degraded Cellulose in the form of complex oxidation products, aldehydic and acidic in nature. The amounts of these substances formed depend on the conditions of the oxidation. I.In 1927 Ludwig Kalb and Friedrich V. Falkenhausen (8) carried out a one-phase progressive oxidation of cellulose. They dissolved cotton cellulose in cupric oxide - ammonium hydroxide solution and oxidized it with increasing amounts of potassium permanganate. The oxidized residues were obtained by acidifying the cuprammonium solutions and were compared with the precipitates resulting from 15 acidification of similar non-Oxidized cuprammonium solutions. From an analysis of the Oxidized residues they found that their reducing power increased regularly with the degree of oxidation, but their acidity increased only in the later stages of Oxidat ion. from these results they concluded that the first step in the oxidation is a conversion of primary alcohol groups to aldehyde groups and the second step is a conversion of the aldehyde groups to carboxyl groups. Some of the water soluble, oxidized residue obtained by supply- ing 2 atomic portions of oxygen per Ctéliloo5 unit was dialyzed until free of sulphate, cupric and manganous ions. The contents of the dialyzing thimble were found to be largely glucuronic acid and it was actually isolated in the form of its cinchonine salt. They suggested that the fact that the glucoronic acid did not dialyze away indicated that it was originally present in some chemical or adsorptive combin- ation and was liberated only in the manipulations involved in prepar- ing the salt. 7. In 1927 Hibbert and Hassan (9) made a study of the Oxidat ion and hydrolysis of cotton cellulose. In one series of experiments they treated cellulose samples with constant amounts of chromic oxide dissolved in solutions of varying acid concentration, and in a second series they used varying amounts of chromic oxide dissolved in solu- tions of constant acid concentration. 0n the resultant residues they determined the reducing power, percent carbon dioxide and percent furfursldehyde. Glucose, methyl glucoside and lactose were treated in a similar manner. No conclusions applicable to the present work were drawn. 8. In the same year Miss Elaine alvord (10), working in this 16 laboratory, began the study of the progressive oxidation of cellulose using time as the variable. Calcium hypochlorits (bleach liquor) was the oxidant used. Two years later Miss Louise Drake (11}, also in this laboratory, made a similar study except that she used buffered solutions of potassium permanganate. Miss Drake found that the rate of oxidation increased as the hydrogen ion concentration of the potassium permanganate solution increased, and that oxidati on con- tinued until all of the manganese had reached the bivalent form. 9. In 1930 Murray, btaud and Gray (12) made a study of the oxidation and hydrolysis of cellulose. In their oxidation experi- ments they used potassium permanganate and potassium dichromate and in their hydrolysis experiments they used hydrochloric, sulphuric and phosphoric acid. The work was done primarily to determine the alkali solubility and Optical properties of the modified cellulosic residues. 10. In 1931 Somr and Markert (l3) searched for a test that would distinguish between the two degradation products of cellulose and show the extent of degradation. Upon examining their materials under the mercury vapor lamp they found that normally bleached cotton showed a feeble white fluorescence with a violet tinge. The fluores- cence was sligztly duller and had a deeper violet color when the cellulose had undergone oxidativs degradation, while acid degraded cellulose showed a brilliant white fluorescence. They also found that methylene blue is an excellent indicator for showing degree of alteration, but does not differentiate clearly among hydrocellulose, oxycellulose and pectic products. 11. In 1953 Doree and nealey (14) made one of the more 17 important studies of the progressive oxidation of cellulose. Their investigation consisted of a series of experiments in which measure- ments were made of (a) the time necessary to decompose a fixed amount of potassium permanganate, in solutions of graded pH values, by a fixed weight of cellulose, (b) the modifications produced in the prOperties of cellulose by treatment with potassium permanganate solutions of graded pH value in definite times, (0) the properties of oxycelluloses prepared in solutions of extreme acidity and alkalinity. Some of their more important findings were: I. The reaction of potassium permanganate with cellu- lose is at a minimum at a pH of 9. The measurable qualities produced have here the lowest values and they increase at the slowest rate with progressive treatment. The activity of potassium permanganate in strongly acid and alkaline solutions is high. The extreme activity in sodium carbonate solution (pH 11.2) is noteworthy. 2. The value of pH 9 differentiates the products formed. On the acid side, oxycelluloses of the reducing'type are produced; on the alkaline side they are of the high methyline blue absorption type, resembling those produced with alkaline hypobromite solution. 12. In 1937 T. Brissaud (15) made the most recent study of the progressive oxidation.of‘cellulose that is recorded in the literature. He oxidized cellulose in the dark with a neutral solution of sodium 18 hypochlorite, and obtained five samples which were oxidized progres- sively. Analysis of these samples showed that their reducing power and methylene blue absorption increased with the extent of oxidation. An x-ray examination of'the dyed oxycellulcse showed that the diagram wasps superposition of the methylene blue on the diagram of the original cellulose, indicating that it was an absorption phenomenon. 19 Present Iork ‘5. Stugy*of the Preggessive Oxidation of Cellulose The present work is an application of quantitative methods to a study of the progressive oxidation of cellulose. Weighed amounts of pure cotton.csllulose were oxidized for definite periods of time by standard permanganate solutions of different pH, one being neutral, one acid and one alkaline. Certain measurements were made as the oxidations were carried out. The amount of oxygen used and the change in hydrogen ion concentration during each oxidation were accurately -measured. The loss in weight of the cellulose during oxidatflan was also determined. The reduction of potassium permanganate involves more than one chemical reaction. In acid solution the oxidation of cotton by per- manganate is the result of at least two reactions acconiing to Birtwell, Clibbens and Ridge (16). The two reactions are: l. The reduction of permanganate to manganous sulphate (sulphuric acid solutions of permanganate were used in the present work). 21012104 + 3H3804 + Cellulose ---s 3111804 + Oxidation Products 4- K2804 of Cellulose 2. Its reduction to hydrated manganese dioxide by the manganous sulphate formed in.the first reaction. ZKMnO4 + 2.1120 + M04 ---s K2504 + 2112804 + 5Mn02 sq.- In general these two reactions proceed simultaneously and result in the formation of an oxycellulose on which hydrated manganese dioxide has been precipitated. In the presence of only small amounts of per- manganate the rate of the first reaction is determined chiefly by the rate of oxidation of non-cellulose impurities in the cotton (true 20 bleaching effect) which is rapid compared with the oxidation of cellulose or with.the reduction of permanganate by manganous salts and no precipitation of unoz then occurs. The second reaction formulated above may be retarded by increas- ing the concentration of acid in the solution, but it is only in the presence of acid concentrations dangerous from.the point of view of cellulose hydrolysis that the precipitation of Mnoz is entirely pre- vented. A.further factor of some importance in.this work is that hydrated Mno itself oxidizes cotton cellulose, slowly compared with 2 permanganate, but at a rate which increases rapidly with the acidity of the solution. The reaction of the permanganate is more simple in neutral and alkaline media. In these solutions the reduction of the permanynate stOps at the manganese dioxide stage and large amounts of the hydrated manganese dioxide are precipitated on the surface of the fabric or in the solution. 2Kln04 4 H20 + Cellulose -——+ 2Mn02 + axon + Oxidation Products of Cellulose Since the hydrated manganese dioxide as well as the permanganate has an oxidizing effect on the cellulose, a separate study was made of the progressive oxidation in order to determine the relative effects of the two oxidi sing agents. In this study weighed samples of pure cellulose were oxidized for definite periods of time and a quantitative measurement was mde of the amounts of permanganate and nanganese dioxide present in the oxidizing bath at the completion of each Oxidfiti 0n. 21 B._T_l_re Nature of the Ogidi&0ellulose The structure of the anhydroglucose molecule (basic chemical grouping in the cellulose molecule) readily shows the points of oxi— dative attack. Besides weakening supermolscular forces and breaking down the micellar structure the oxidizing agent is believed to attack certain chemical groups within the anhydroglucose molecule. H l H-(Izj-OH x/o-e—H H.€..0_J\_...... . . . . . . - l lei-e -0— fl-e-OH x/ as has already been stated, the terminal units of the long chain contain certain exposed groups that are not found in the other units of the chain. These are, namely, an exposed aldehyde group in the number one position of the anhydro glucose unit and, at the Opposite end of the chain, a secondary alcohol group in the number four position. Upon breakdown of the long chain into shorter chains, more and more terminal units are exposed. In addition to these terminal units and their vulnerable groups, each anhydroglucose unit on the interior of the chain has certain chemical groups which are susceptible to an oxidizing attack. The most accessible of these is the primary alcohol group in the number six position. In a two-phase oxidizing system this primary alcohol group is more exposed to the chemical agents than tm other two points of attack, the secondary alcohol groups in 23 positions two and three. The primary alcohol group is oxidized to an aldehyde group and then to the carboxyl gnyup. The secondary alcohol groups are oxidized to ketones with further degradation resulting in fission. an analysis of oxidized cellulose is based on the relative amounts of these characteristic groupings which are present in.a given sample. In the present work three of the most common analytical determinations which are applied to cellulosic products were carried out on the oxi- dized residues. whey are: l. COpper number 2. Methylene blue number 3. Alkali solubility The cOpper number determination is a measure of reducing power and is very similar to the common.Munson and walker sugar determination. It is defined as the number of grams of cOpper reduced from the cupric to the cuprous state under standardized conditions by one hundred grams of the sample. The reduction of cupric cOpper to cuprous oxide is a recognized test for the presence of "modified cellulose“ in cellulosic products because both hydrolysis and oxidation of cellulose produce the aldehyde groups which are responsible for this reduction. under the conditions of the determination, pure or unmodified cellulose has little or no reducing action. The estimation of copper number (17) is purely empirical, and the value obtained is seriously affected by slight variations in the experi- mental method used. As several methods are in use the results obtained by different workers are confusing because they are not often comparable, 23 and the value of the test is greatly diminished by this circumstance. Due to the small amount of sample which was available, the micro- method of Hayes (18) was used in the present work. The cOpper number is a valuable laboratory test for the presence of oxycellulose. it is capable of detecting the very slight changes that occur during the initial oxidation process even before the actual structural disintegration has begun. However Birtwell, Clibbens and Ridge (16) point out certain facts that should be considered when interpreting data obtained from cOpper number determinations. They found that when an oxycellulose is boiled with dilute alkali its OOpper number is reduced and may reach as low a value as that of normal unmodified cellulose; vhen, therefore, cotton is boiled with alkali subsequent to the injurious oxidizing treatment, measurement of cOpper number may not be capable of revealing the presence or extent of the oxidizing attack. Even in cases where the possibility of an alkali boil subsequent to oxidation had been excluded, they found that the determination of coPper number alone could not be a quantitative basis for the measurement of the extent of oxidizing attack. This last con- clusion was based on data which showed that different oxidizing agents or the same oxidizing agent used in solutions of different hydrogen ion concentration produce oxycelluloses whose cepper numbers vary over a considerable range even thong: the extent of Oxidation as measured by the consumption of available oxygen was the same. The determination of the amount of methylene blue which a cellulosic material will absorb from a solution of the dye has long been used in the laboratory control of bleaching processes. Unbleached cotton ab- sorbs much greater quantities of methylene-blue than bleached cotton, 24 a property which is due chiefly to'non-cellulosic organic constituents of the raw material such as protein and pectic matter. The progres- sive elimination of these impurities in the bleaching process is ac- oompnied by a gradual decrease in the absorption of methylene blue by the cotton and it is supposed that an ideal "pure cotton" from which all such impurities have been removed would show a minimum absorption characteristic of cotton cellulose it self. If the pure cotton cellu- lose is subjected to continued bleaching (oxidation), the absorption of methylene blue is agin apparent and is believed to increase with the extent of oxidation. In 1923 Birtwell, Clibbens and Ridge (19) made a study, the purpose of which was to determine the quantitative relationship between the extent of oxidation of cotton cellulose and its absorption of methylene blue. They did not find the cause of the methylene blue absorption in oxycelluloss, but they did discover several important facts. Their experimental data showed conclusively that an increase in the ash content, or more strictly, the ash alkalinity cf bleached cotton, results in an increased methylene blue absorption when all other factors are the same. Since the ash alkalinity is chiefly con- trolled by the nature and efficiency of washing processes, they stated that the methylene blue absorption of a material had no quantitative meaning until the disturbing effect of variations in ash alkalinity was elimimted by the careful washing of all samples with acid before examimti on. They also found that calendaring and mercerising, which alter the surface prOperties or degree of dispersion of cotton cellulose, have no effect upon the absorption. This indicates that the absorption 25 of methylene blue is not a surface phenomenon, but is the result of some chemical combination. The methylene blue absorption is usually expressed as the number of millimoles of methylene blue which are absorbed by one hundred grams of dry cellulosic material. There are two methods, the colorimetric and the titrimetric, which may be used in the methylene blue determin- ation. In the present work the titrimetric method of Pelet-Jolivet (20) was used. In both methods a weighed amount of cellulosic material is allowed to stand in a definite volume of methylene blue solution of known concentration for a standard period of time. men this time has elapsed the supernatant solution is filtered off and the excess methylene blue is determined. The titrimetric method is based upon the simple stoichiometric ratio existing between methylene blue hydrochloride, a basic dye, and naphthol yellow-S, an acid dye, one mole of the latter being equivalent to two moles of the former. The exact cause of methylene blue absorption of an oxidized cellulose is not known, but it is the accepted belief that carboxyl groups are responsible for it to a great extmt. Recently Neale and Stringfellow (21) deveIOped a method for actually titrating the carboxyl groups present in oxycellulo see. Their method is a great improvement over the methylene blue absorption and should become the accepted method for the determination of acidic groups in oxidized cellulose. The determination of alkali solubility is one of the standard methods of analysis vhich are applied to degraded cellulose. It is a gravimetrio determirmtion of the percent solubility of a cellulosic 26 material in an alkaline solution when treated under a carefully con- trolled set of standard coniitions. This determination may be used as a substitute for the measure- ment of capper number because the value of'the result is affected by exactly the same considerations which affect the value of the results Obtained by the latter determination. However, it is not nearly as accurate as the cepper’numberg especially when the extent of the oxi— dizing attack is slight. Naturally, no indication of oxidizing attack can be obtained by this method from material which has already been subjected to strong alkaline treatment, and even when this has not occurred, serious damage may escape detection if sole reliance is placed on this test. 27 Laboratory Procedures and Calculations The material used in the present work was 100 Berkeley cambric. Before being used it was boiled several times in distilled water and rinsed thoroughly in order to remove the sizing. It was then cut into one-quarter inch squares and allowed to come to moisture equilibrium by standing in a desiccator over calcium chloride for at least 2.4 hours. ‘3 Olidation O Part I In part I of the present work samples of this purified cellulose were oxidized by an acid, an alkaline and a neutral solution of 0.3Mn04 and the resulting oxycellulose residues were analyzed. The alkaline permanganate solution was one tenth normal with respect to laHCOa and the acid solution was one tenth normal with respect to H2804, while the neutral solution was not buffered. The same proced- ure was used for each oxidant. Eiglt 2.5000 gram samples of the purified cellulose were weighed out into 500 ml Erlenmeyer flasks for each series of oxidations. Two. hundred milliliters of 0.3m standard 10an was pipetted into each flask, 4 which was then immediately transferred to a constant temperature bath which was maintained at 50°C. The flasks were steppered with corks wrapped in lead foil to prevent evaporation, and were shaken every 15 minutes. Their time of entry into the bath was accurately recorded arri at the end of exactly one hour intervals the flasks were removed from the bath. The period of oxidation varied from one to eight hours and was measured accurately (within 15 seconds). 28 Upon removal of a sample from the bath approximately 50 m]. of the supernatant liquid were poured off, and to the remainder of the solution a measured volume of .7464 N oxalic acid, sufficient to re- duce all manganese present to the colorless divalent form.and to provide an excess, was added (pipette) immediately so that the oxidatiln process might be stapped at that time. rifteen ml. of 6.0 NHZSO4 was added to the oxalic acid - permanganate - Mnoz - mixture and.it was heated gently in order to hasten the reaction because the Mnoz which is precipitated on the fabric is very stubbornly held and is reduced with difficulty. The 30 ml. portion of'the oxidizing solution was used for-the determination of pH and was then transferred quantitatively to the oxalic acid - oxidizing solution mixture. ‘A Beckmann pH meter was used for the pH measurements. .As soon.as the oxalic acid had reduced all of the KMnO4 and.Mn02, the solution was cooled to 60°C and filtered through a weighed, modified Gooch crucible. The solid cellulose residuevas transferred quantitatively to the crucible and was washed thoroughly, first with dilute H2804 and then several times with distilled water. The crucible was then dried at 60°C in a vacuum oven and weighed and then redried and reweighed until a constant weight was obtained. beveral weighings were required because oxidized cellulose is slightly hygroscopic. The vacuum oven was used for drying because the modified cellulose tends to char and decompose when heated in an ordinary 110°C oven. From the difference between the final weight of the oxidized residue and the original 2.5000 gms. the percent loss in weight was calculated. These dried residues were the samples which were used for the analytical determinations. 29 To the above filtrate was added 10 ml. of cone. 32504. It was then heated to boiling and the excess oxalic acid was backtitrated with a standard 0.3N Klino4 solut ion. By subtracting the number of milli— equivalents of mm; which were used in the backt itration from the number of milliequivalents of oxalic acid which were added, the number of milliequivalents of W04 which were left after the oxidation of the cellulose was obtained. By subtracting this value from the number of milliequivalents of Kian‘ which were present originally, the number of milliequivalents of KMnO4 which disappeared during the oxidation was obtained. This figure takes into account the fact that the KMn04 may be reduced to either lino or divalent manganese and represents the 2 amount of oxygen which disappmred during the oxidation process. In part A of this work the milliequivalents of oxygen which disappeared during the oxidation was multiplied by .008, thus converting the result to grams of oxygen used up during the preparation of each modified cellulose sample. This value was then used in calculating the number of atomic portions (16 grams is one atomic portion or gram atom) of oxygen which were furnished for every 0631005 unit (equivalent to 162 grams of cellulose). Londation - Part 11 In part II of the present work, samples of the purified cellu- lose were oxidized by an acid, an alkaline and a neutral solution of 0.3N mo and quantitative measurements were made of the amounts of 4 Klino4 and Mnoz present in the oxidising mixture at the end of each oxi dation period. The preparation of the samples, their altry into the constant 3O temperature bath and time of removal from the bath were exactly the same Operations that were carried out in part I of this work. It was in the treatment of the contents of the flasks after their removal from the bath that the two experiments differed. In this experiment a sample, upon removal from the bath, was placed in ice water for exactly five minutes so that it would be cooled to room temperature. Then 25 ml. of the solution was drawn up into a pipette through a piece of glass tubing packed with glass wool. The purpose of the glass wool was to filter out all of the smog which was carried up with the solution. This 25 m1. of LinOZ-free Klin04 solution was transferred to a 200 m1. Erlenmeyer flask and 10 ml. of .7830N oxalic acid (an excess) and 20 ml. of 4.0N 32804 were added to it. The pipette and glass tube were then washed thoroughly and their washings allovad to drain into the original flask. Then 100 ml. of .7830N oxalic acid (an excess) and 25 m1. of 4.0N H SO 2 d flask, and it was heated gently to accelerate the reduction of the were added to the original 111102 which was precipitated on the oxidized residues. The contents of the 200 ml. Erlenmeyer flask were then heated to boiling and the excess oxalic acid was backti trated by .lN Klin04. The original flask was then cooled to room temperature and filter- ed through an asbestos-matted Gooch crucible. The flask and residue were washed several times with distilled vater and the filtrate was then carefully transferred to a 503 ml. volumetric flask, and made up to volume. v In the oxalic acid - Klin04 titrations in part I the endpoints were evanescent due to the soluble degradation products of cellulose. In 31 order to avoid the troublesome endpoint in this second experiment, a combination of gravimetrio and volumetric methods was used to determine the excess oxalic acid. A 25 ml. aliquot portion was removed from the volumetric flask by a pipette and transferred to a 400 ml. beaker. Then 25 ml. of distilled water was added and the solution was heated to boil- ing. Then 15 dr0ps of phenol red and 25 ml. of 1.0M C8012 were added to the hot solution and fimlly 0.5N NH4OH was added slowly with con- stant stirring until the red color had changed to a faint purple (pH- 8). (If the pH of the solution goes above 8, the manganous ions are oxidiz- ed by the air to lino2 which precipitates out. The M1102 oxidizes some of the oxalate and sakes the determination worthless.) The beaker was then set aside for at least 24 hours to allow the precipitation of calcium oxalate to be completed. After standing for this period of time the calcium oxalate was filtered off and the filtrate discarded. The beaker was rinsed with 50 ml. of 4.0}! 32804 which was then poured over the precipitate and the solution collected in a 500 ml. Erlenmeyer. The beaker and filter paper were then washed with hot 0.2N H2804 until no test for chlorides was obtained from the washings. To the filtrate which contained approximately 500 ml. was added 5 ml. of cone. H2804. It was then heated to boiling and titrated with 0.1N 2311104. The results from the tit rat ion of the 2.5 m1. sample which was withdrawn from the original oxidizing solution gave a measure of the Klino4 which was present in the solution. By subtracting the number of milliequivalents of Kline4 which were used in the backtitration from. the number of milliequivalents of oxalic acid which were added to the 25 ml. sample, the minor of mill iequivalents of KMnO4 actually 33 present in the 25 m1. sample was obtained. When this figure was multiplied by eiglt the number of milliequivalents of Klin04 present in the entire 200 m1. of oxidizing solution was obtained. The analysis of the solution in the volumetric flask gave a measure of the total oxidizing power (both mo and linoz) which was 4. present in the original oxidizing solution when it was removed from the water bath. By multiplying the number of milliequivalents of KlinO4 which were used in the titration of the filtrate, obtained by dissolving the calcium oxalate, by twenty the number of milliequival- ents of KMnO4 which would have been necessary to titrate the oxalic acid present in the entire 500 milliliters was obtained. men this value was subtracted from the number of milliequivalents 0f oxalic acid which were added to the 175 ml. of oxidizing solution, the number of milliequivalents of active oxygen (KMn04t linoz) present in the 175 ml. of solution was found. When this last value was added to the nu'nber of milliequivalents of Klino‘1 which were present in the 25 ml. sample that was removed at the close of oxidation, the total number of milliequivalents of active oxygen (KMnO4 s linoz) present in the flask was obtained. This value was used in two calculations: first by sub- tracting it from the number of milliequivalents of KMnO4 (or active oxygen) which were added to the flask originally, the loss in oxidisirg power (expressed in milliequivalents of oxygen) which resulted from oxidation of the cellulose was found, and second, by subtracting the number of milliequivalents of Klino4 which were present in the entire flask at the close of oxidation from the number of milliequivalents of active oxygen (KlinO4 4 linOz) vilich were present in the entire flask 33 1’ when oxidation was stopped, the number of milliequivalents of active oxygen which were present as iinOz was obtained. The number of milli- equivalents of active oxygen which were present as Mnoz had resulted from a valence change in the manganese from seven to four. The differ- ence between this value and the total number of milliequivalmts of oxygen which disappeared during the oxidation had evidently been lost in a valence change of manganese from seven to two. B. is of Residues The methods of analysis mich were used in the present work are empirical, and the relative value of the results depended on a strict adherence to the procedures which were used. . l. Alkali solubility In the determination of alkali solubility 0.5000 gram samples of the oval—dried oxidized residues were used. The sample was placed in a 200 cc. Erlenmeyer flask which was then connected to a short reflux condenser. r‘ifty ml. of 3% (.75N) NaOH was pipetted into the flask and a strong Bunsen flame was immediately placed under the flask. As soon as the solution came to a boil the flame was adjusted so that it would reflux gently. The residue was subjected to this alkaline treatment for exactly one hour starting from the time that the flame was placed under the flask. at the end of the hour the hot, alkaline solution was filtered through a weighed, modified Gooch crucible. The residue was washed with water, then with dilute tiOl and finally with water again. The crucible was then dried in a 105°C oven and weighed,and this was repeated until a constant weight was obtained. The final weight times one hundred divided by the origiml sample weight was the alkali solubility. 2. Dapper number In the determination of cOpper number the micro-method of Hayes (18) was followed very closely. The samples of air-dried oxidized residue weighed 0.25 gs. and were placed in a 6" x 5/8" test tube. Into a similar tube were placed 0.5 ml. of a cOpper sulphate solution (100 grams CuSO4 per liter) and 9.5 m1. of an alkaline solution (160 grams anhydrous Nazooa and 50 grams 161811003 per liter). These two solutions were mixed thoroughly and were then placed in a boiling water bath. As soon as the solution reached the temperature of the bath it was removed and poured over the oxycellulose sample. The tube contain- ing the sample was then steppered with a loose-fitting glass st0pper and placed in the boiling water bath where it was left for exactly three hours. When the three hours had elapsed the tube and its contents were cooled to room temperature and filtered through a modified Gooch crucible. Two ml. of distilled water were used to rinse out the tube and to wash the solid residue in the crucible. Then the crucible was placed in a rubber diaphragm which fitted the t0p Of a short-stemmed 2" funnel, which in turn was connected to a 50 ml. suction flask by a rubber stOpper. The original test tube was then rinsed with 3 m1. of a ferric sulphate solution (40 gn. Fe2(804')3 e 100 ml. conc. H2804 per liter) and then this rinse solution was poured over the contents of the crucible. The ferric sulphate solution was allowed to react with the I Guzo in the crucible“lfor three minutes and was then drawn through the 35 crucible by applying suction. This treatment was then repeated with 2 ml. of ferric sulphate solution. During this treatment the red Cuzo which was precipitated on the surface of the mbric during the three hour digestion period was dissolved by the ferric sulphate solution and a light green solution resulted, the cOpper being oxidized from the cuprous to the cupric state and an equivalent amount of iron being reduced from the ferric to the ferrous state. The test tube and crucible were then washed three times, using 2 ml. of distilled water for each wash. The filtrate in the suction flask was then titrated by a 0.0410N KMn04 solution. A microburette which was calibrated to read to .001 ml. was used for the titration. The endpoint of the titration was a change from a pale green solution to a colorless one and was easily discernible. The blank correction for the titration, as determin- ed in the laboratory, was 0.030 ml. of the 1011104 solution. In calculating the cepper number the blank correction was sub- tracted from the number of milliliters of mm used in the titration, 4 and tin remainder converted to its equivalent in grams of capper. since this weight of copper was reduced by .25 grams or sample, it was multi- plied by 400 so that it would represent 100 grams of sample. 3. Methylene blue number The method of Clibbens and Geeks (22) which involves the use of a buffered solution of methylene blue was used in the determination of the methylene blue number. In this method the methylene blue solution is buffered with KHZPO4 and NaOH. The purpose of the buffer is to stabilize the hydrogen ion concentration and neutralize the effect of traces of 36 acid or alkali which may be introduced with the cellulosic residue. 1. .5 gram sample of the oxidized cellulose was used in this detennination. The sample was placed in a thick-walled pyrex test tube of 1' diameter and.50 ml. capacity. At one-third of the distance from the tap of the tube there was a constriction.which was designed to prevent the passage of the cellulosic residue when the tube was inverted and centrifuged. The sample was pushed down through the con- striction into the lower part of the tube and 15 ml. of buffered methylene blue solution, containing 4.00 millimoles per liter, was pipetted into the tube. Another heavy-walled pyrex test tube of slightly larger diameter-was then fitted over the original tube to prevent evaporation. The residue was then left in the methylene blue solution for eighteen hours. When the time had elapsed the two tubes were inverted and centrifuged, thus driving 13 or 14 m1. of the orig- inal 15 down into the outside tibe and.leaving'the residue in the con- striction. Ten ml. were then removed from the outside tube by a pipette and placed in.a similar tube. The methylene blue in this 10 ml. sample was then titrated by'a solution of‘naphthol yellowbs con- taining 2.24 millimoles per liter (.9 gms. per liter). The naphthol yellow; when.run into the methylene blue solution, produces at first a reddish-brown precipitate, the color of the solution becoming at the same time less and less blue until it finally changes to yellow. This gradual change is largely obscured by the precipitate, which does not settle readily. The approach of the endpoint was detected by observing a dr0p of the liquid suspended from‘a glass red, and when the end point was nearly reached, the tube was centrifuged for thirty seconds. This separates the precipitate, and the color of the supernatant liquid is 37 clearly seen. The endpoint is a change from a light blue to a green, and is not difficult to see. The results were calculated by multi- plying the nunber of ml. of naphthol yellow - S used in the titration by 1.5 and subtracting the value of this volume of naphthol yellow - S eXpressed in millimoles of methylene blue from the number of millimoles 0f methylene blue which were originally added to the sample. This value was then converted to mill imoles of methylene blue absorbed by 100 gms. of sample. AJJ mammv ¢IH madam no haamowzmwnw emmmmnmxm mam mpHSmen omega no.oa " ua.m " mm.am “ moHH.H m ma.mm m meem. m mo.aa w 4m.a m m n w u e Ha.oa w w~.m W om.mm w afiwo.a M am.mm m anew. M No.5H m mm.a m a H a u a mm.m w ma.m m mm.Hm W mmam. M No.0m M haem. 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