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\ No. 1121906 ) I VISCOSE-RAYON PULPS FROM HARDWOODS COIGUE, TIEPA, AND IJIMO September 1951 \laR.44) MAR 10 1952 UNITED STATES LEPARTMENT OF AGRICULTURE ,\EOREST SERVICE iFORESTPRODUCTS LABORATORY Madison 5, Wisconsin In Cooperation with the University of Wisconsin

VISCOSE-RAYON PULPS FROM HARDWOODS COIGUE, TIEPA, …

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Page 1: VISCOSE-RAYON PULPS FROM HARDWOODS COIGUE, TIEPA, …

\ No. 1121906 )

I

VISCOSE-RAYON PULPS FROMHARDWOODS COIGUE, TIEPA, AND IJIMO

September 1951

\laR.44)

MAR 10 1952

UNITED STATES LEPARTMENT OF AGRICULTURE,\EOREST SERVICE

iFOREST—PRODUCTS LABORATORYMadison 5, Wisconsin

In Cooperation with the University of Wisconsin

Page 2: VISCOSE-RAYON PULPS FROM HARDWOODS COIGUE, TIEPA, …

VISCOSE-RAYON PULPS FROM CHILEAN HARDWOODS

COIGUE, TEPA, AND ULM61/g

By

F. A. SIMMONDS,2 Chemistand

R. M. KINGSBURY, Chemist

Forest Products Laboratoryi4 Forest ServiceU. S. Department of Agriculture

n•n ••••n

Abstract

A study was made of the possibility of producing pulp of viscose rayon gradefrom three Chilean hardwoods, coigue,tepa, and ulmo. Unbleached pulps weremade from the three woods by (1) the neutral sulfite semichemical processwith and without steam prehydrolysis, (2) a water prehydrolysis-sulfateprocess, and (3) the sulfite process. These pulps were purified by meansof the conventional sequence of chlorination, alkaline extraction, oxidation,and acidic extraction. Yields of purified pulps, which contained from 2 to7.5 percent of pentosans, ranged from 38 to 1i5 percent of the woods. Resultsof filtrability tests of viscose solutions. from two of the pulps, of spinningtrials on four of the pulps, and the general similarity of all of the pulpsin chemical composition indicated that pulps acceptable for continuous-threadviscose rayon can be produced from the three woods by any of the processesinvestigated.

-To be presented at the 5th meeting of the Technical Committee on WoodChemistry of the Food and Agriculture Organization of the United Nations,Appleton, Wis., September 17-18, 1951.

-In cooperation with the Chilean Development Corporation.

-Acknowledgment is made to the following members of the Forest Products Labo-ratory staff: J. N. McGovern, J. S. Martin, and E. L. Keller for theproduction of the unbleached pulps and constructive suggestions; to E. S.Lewis for assistance in the analytical and purification work; and to G. H.Chidester for his encouragement and guidance. Further acknowledgment ismade to the Standards Department of the American Viscose Corporation wherethe spinning trials were held; to E. I. Du Pont De Nemours & Company, Inc.,Rayon Dept., Technical Div., Viscose Research Laboratory, Richmond, Va.,where the filtrability tests were made.

Maintained at Madison, Wis., in cooperation with the University of Wisconsin.

Rept. No. 81906 -1- Agriculture-Madison

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centipoises;percent;

per million;per million;per million;

11.6.09

10.3.

.5

Introduction

The Forest Products Laboratory, in cooperation with the Chilean DevelopmentCorporation, has investigated the possibility of producing pulps from threeChilean hardwoods, coigue (Nothofagus dombeyi), tepa (Laurelia serrata), andulmo (Eucryphia cordifolia) that would be acceptable for continuous-threadtextile rayon.

Analytical values typical of commercial pulps used for this grade of rayonwere obtained from rayon producers. These values were:

Alpha cellulose percent; 91.81Beta cellulose percent; 4.26Gamma cellulose.. percent; 4.33

hydroxide solutionDispersed viscosity (pulp at 0.5 percent

concentration in cupri-ethylenediamine)

Ash Iron partsCopper partsManganese parts

Several pulping processes were applied to the three woods in order to determinethe effect the pulping treatment had on the yield and quality of the purifiedpulp. All , of the purified pulps were evaluated by conventional tests and:incertain instances, by filtrability tests of viscose solutions and by spinningtrials.

Use of Hardwoods for Viscose Puips

The problem of producing a pulp from which a commercial, filtrable, viscose Solu-tion can be made is common to all cellulosic source materials used for thispurpose. As mentioned in a recent interpretive review on cellulose and woodpulp research (5)y2 the literature reveals much work directed toward identifi-cation of those characteristics of pulps which relate to unsatisfactory fil-trability. These studies have dealt with the molecular properties of cellulose,the cell and so-called chemical composition of rood pulps, and the structure ofthe cells. The hypothesis that high-polymer fractions must be of abnormalcomposition (cross-bonded) to cause poor filtrability has also been proposed(1). Another hypothesis has been advanced concerning an interaction of hemi-celluloses under the conditions of sulfate pulping. It is based on the assump-tion that upon the rupture of lignin•hemicellulose bonds, the released hemi-celluloses cross-link and form stable anhydro hemicelluloses that may have anadverse effect on the filtrability of a viscose solution (14).

1.1riderlined numbers in parentheses refer to Literature Cited at end of report.

Solubility in 7.14 percent sodium percent; 13.9

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In another investigation, insoluble residues of viscose solutions were foundto be higher in methoxyl content than the original pulps. This was inter-preted as indicative of the presence of nonglucosidic groups in the cellulosechains (10). Another has concluded that the nresinr component of pulp has adirect and favorable effect on the xanthation reaction, and that consequently,if too little resin is present, poor filtrability will result (27).

Although a rational system for predicting the filtrability of viscose obtain-able from a pulp has not appeared in the literature, an empirical stainingtechnique using malachite green has been developed for this purpose (35).Its originator was able to classify pulps into five groups which rould giveviscose solutions ranging from nonfiltrable to readily filtrable.

The manufacture of viscose rayon from hardwood involves two problems peculiarto hardwoods. One is the high content of pentosan hemicellulose that must beremoved; the other results from the short fibers and tracheids and the amount ofparenchyma cells. Possibly neither of these is related to filtrability.

Because of the short fibers and tracheids and the high content of parenchymacells, sheets of purified hardwood pulp are especially weak when in contactwith a strong solution of sodium hydroxide. Difficulties encountered inindustrial use because of this low strength include the breaking away offibers from the sheets while they are steeping, the rupture of sheets whilebeing pressed, and breakage of sheets as they are removed from the press.

The beating of purified pulp has been proposed as a means of increasing sheetstrength sufficiently for conventional viscose preparation (22). The authorshave been informed by a European manufacturer of hardwood viscose pulp thatsufficient strength can be obtained by compressing the sheet in calendering toa density of approximately 1 gram per cubic centimeter. Slurry steeping,characteristic of the continuous process for preparing viscose, avoids theproblem of low sheet strength. This technique was considered of considerable

bimportance in the development of purified hardwood pulp in Germany (28), and itsias also been reported in the United states (4).

It has been concluded that the parenchyma fraction of European beech sulfitepulp of viscose grade (about 15 percent) has no harmful chemical effects (9).A screen fraction containing about 80 percent of parenchyma cells underwentxanthation more rapidly than did the remaining fraction of the pulp, whichcontained mostly fibers and tracheids, Any filtration difficulties were saidto arise from the coarser of the two fractions. The finer fraction was aboutL percent lower in alpha cellulose, and its degree of polymerization was 520as compared to 850 for the coarser fraction. This variation of cells in degreeof polymerization was observed in the case of a bleached sulfate eucalyptuspulp (16).

The facts that in this country a purified hardwood sulfite pulp has been usedfor a number of years and that a purified hardwood sulfate pulp has come intouse recently are sufficient evidence that this type of pulp is chemicallysuitable and can be adapted to the mechanical requirements of the viscoseprocess.

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The extensive literature on the removal of hemicelluloses by pulping and sub-sequent purification and the associated effects, especially with reference topentosans, has been summarized comparatively recently (14, 15, 16, 17, 31) toprovide a thorough correlative digest.

The desirability of a low proportion of pentosans in pulp for chemical conver-sion is widely emphasized, Hemicelluloses are converted to viscose as readilyas is cellulose (5), and when converted are considered to have injuriouseffects on the properties of the regenerated fibers (3). Yet one "specifica-tion" would permit up to 4 percent of pentosans in viscose pulp, although withthe qualifying recommendation that material with a degree of polymerizationunder 150 should be at a minimum (12),

It has been pointed out (29) that in the German staple-fiber industryit had been concluded fro experiments that material of low degree ofpolymerization in pulps was harmful to the quality of the fiber, especiallyits strength when wet, and that material with a degree of polymerization ofabove 600 caused difficulties in operation associated with high solutionviscosity. In a study (2) of the influence of polymolecularity of viscoserayons and of the corresponding cotton and wood pulps on certain mechanicalproperties of the rayons, a high degree of correlation was found between theamounts of material of low degree of polymerization in the pulps and corres-ponding rayons, somewhat less between the ratio of weight to average degreeof polymerization of the rayons and tenacity, and a fair degree between theamount of material of low degree of polymerization in the rayons and resistanceto fatigue. It was concluded that the ratio of weight to average degree ofpolymerization and the amount of material of low degree of polymerizationinfluence fatigue resistance of rayon to about the same degree. It was

further suggested as fairly probable that most of the material low indegree of polymerization is removed from the pulp during the conventionalsteeping treatment and that the material low in degree of polymerization isproduced during aging of the alkali cellulose. If this is true, and fromthe correlations cited, it would follow that the amount of material of lowdegree polymerization should be kept as low as possible and that the durationof aging of the alkali cellulose should be as short as possible,

Chain length distribution curves showing the changes occurring in the celluloseduring the production of sulfite viscose pulp and tire cord from pine grown inthe southern States, resulted in the theory that wood cellulose is comprisedof only two fractions, namely, gamma (hemicelluloses), and alpha, and that thebeta cellulose of a wood pulp is not a hemicellulose of wood, but rather aresult of degradation of the alpha fraction during pulping and purification (18).Unpublished data of the present authors appear to support this theory. Conven-tional beta and gamma cellulose values were obtained for holocellulose isolatedfrom southern pine wood and from southern pine pulp prepared by a prehydrolysis-sulfate process. The beta values, based on the wood, increased from 0,5 percentfor the wood to about 2 percent for the purified pulp. The gamma values de-creased from 19 percent for the wood to 0.9 percent for the purified pulp.

Available data indicate that beta cellulose and hemicaluloses are relativelylow in molecular weight. The degree of polymerization values reported forbeta cellulose range from 10 to 150 (11, 30), The fractions of Europeanbeech and spruce extracted in an 8 pe77enTsolution of sodium hydroxide and

-4-Rept. No. 81906

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then purified, were found to have degree of polymerization values of 150 and160 (7). These purified fractions were considered to be xylan and mannan.A crystalline xylan from American paper birch had a degree of polymerizationvalue of 35 (36).

It is of interest to summarize the values for southern pine sulfite pulp whichhave been reported for viscose rayon of tire cord grade. Proportions of alpha,beta, and gamma celluloses and pentosans were, respectively, 95.00, 2.50, and1.98 percent (19). It appears from a chain-length distribution curve for thiskind of pulp (TB) that the fraction with a degree of polymerization value of 150or less amounted to only about 4 percent, and the fraction with a value of 500or less, about 7 percent. If this interpretation is correct, it appears thatthe gamma and pentosan values are actually related to the same fraction unlessit is assumed that the pentosans were all in the alpha cellulose, which is doubt-ful for pulp made from softwood. It has been suggested that gamma cellulose isa mixture of pentosans and a constituent which absorbs chlorine (25).

When pulping is done under acidic conditions, the removal of hemicellulose isnot generally a problem, even in the case of hardwoods (23), and it might alsobe inferred, from a lack of evidence to the contrary, that filtrability is nota problem. It is well known, however, that both the removal of hemicelluloseand filtrability become problems when nearly neutral or definitely alkaline con-ditions are used for pulping. For an unbleached pulp having a high proportion •

of hemicelluloses the preferred hot alkaline process is not adequate, and therequired cold process is not generally attractive economically. These twoprocesses have been reviewed comprehensively in recent years (15, 16).

The possibility of producing viscose pulps by an alkaline pulping process hasbeen studied because it is suitable for any kind of wood (8, 20). Prehydroly-sis was developed as an adjunct for the removal of hemicelluloses (24, 26). Apossibly unforeseen but important result of the prehydrolysis-alkaline pulpingsequence (specifically, prehydrolysis-sulfate) is the high quality of viscoserayon obtainable from this kind of pulp (32). An additional benefit attributedto prehydrolysis is an improvement in the behavior ("reactivity") of sulfatepulp in conversion to viscose yarn (28, 34). Although a pine sulfate pulp,prepared by the cold alkaline extraction of bleached pulp, was used for a timein Germany for the production of viscose rayon tire cord, the prehydrolysis-sulfate type was preferred when it became available (6). The only informationgenerally available on the commercial production and use of sulfate viscosepulps deals with German practice (6, 13, 28, 3L).

By applying a prehydrolysis-sulfate process and a conventional 3-stage bleach-ing treatment to Australian eucalyptus, purified pulps were obtained which con-tained less than 2 percent of pentosans and up to 95.5 percent of alpha cellu-lose (17).

The possibilities of producing a viscose grade of pulp by acidic hydroly-sis of sulfate pulp prepared from sugar maple have been investigated (31),but the process does not appear to be economically feasible. An acidictreatment of pulp that utilizes the acid formed in a chlorination stage,has been patented as a procedure in the purification of pulp for viscose(21). The preferred temperature is L0° C., and the maximum is100° C. for a period of from 10 to 200 minutes. It is said

Rept. No. R1906 -5-

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that this procedure removes pentosans, and that lowering of the viscositycan be controlled more closely and with less harm to the alpha fractionthan when oxidation is used for this purpose.

The same principle is found in a patented procedure in the production ofbamboo pulp, the treatment in this instance consists of heating for 1 hourin the temperature range of 90° to 150° C. and a pH of 2. The proportion ofalpha cellulose was high in pulps made by this procedure (33).

Woods Used in the Present Study

Results of the tests applied to the samples of Chilean coigue, tepa, and ulmoused in the present study are given in table 1. These test methods, as wellas those applied to the pulps, are identified in the Appendix.

The coigue and tepa were of medium density and in that respect were comparableto North American hardwoods, such as American elm, water tupelo, and sweetgum.The ulmo was much higher in density than the coigue and tepa, being comparableto the North American maples, birches, and some of the oaks.

In chemical composition, the three woods were typical of hardwoods in general.The alpha cellulose contents, however, were at the relatively high level ofapproximately 148 percent, and the pentosan contents of the tepa and ulmo werein the low range. Although the pentosan content of the tepa was only 13.7percent, an earlier sample contained 1707 percent pentosans. The amount ofether-extractable material in the three woods was in the low range for hard-woods, but the coigue contained twice as much as either the tepa or ulmo, adifference that was reflected in the purified pulps.

Preparation of the Unbleached Pulps

The processes used to make unbleached pulps from each of the three hardwoodswere (1) neutral sulfite semichemical, with and without prehydrolysis, (2)prehydrolysis-sulfate, and (3) the acid siflfite. Stainless-steel, steam-jacketed, tumbling digesters were used. Pulping conditions are given intable 2.

Semichemical Pulping

Previous experience had indicated that the optimum lignin content for semi-chemical pulps to be bleached was about 10 percent. Thus conditions wereestablished in the preliminary neutral sulfite semichemical digestions toproduce semichemical pulps of approximately this lignin content both with andwithout a steam prehydrolysis of the chips. As previously mentioned, the pur-pose of the prehydrolysis step is to remove the hemicelluloses, which in hard-woods are chiefly pentosans.

Rept, No. R1906 -6-

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The three woods responded differently to semichemical pulping. The ulmo wasthe most responsive, requiring the least chemical and shortest time. Thecoigue was somewhat less responsive, as shown by the higher chemical consump-tion and longer pulping time required. The tepa was considerably moreresistant than the other two, and required a very large amount of chemicaland, proportionately, a much longer equivalent cooking time. A digestiontemperature of 180° C. was required in order to complete pulping in a reason-able time instead-of the 170° C. needed for the others.

The steam prehydrolysis of the chips significantly decreased the time requiredfor digestion but had essentially no effect on the amount of chemical required.It had, however, the effect of lowering the yield of unbleached pulp, due tothe removal of hemicelluloses.

Only the prehydrolysis-semichemical pulp made from ulmo was purified becauseit was believed the results obtained on coigue and tepa afforded sufficientcomparison between semichemical pulps made with and without prehydrolysis.

Sulfite Pulping

An ammonia-base sulfite liquor was used for pulping coigue and tepa becauseprevious experience had shown those species to be incompletely pulped withconventional calcium base liquor, Use of the ammonia base was also expectedto result in lower amounts of mineral matter and ether extractables in thepulps. Previous experience had also indicated that tepa is incompletelypulped with normal amounts of chemical, so a higher bisulfite content wasused in the liquor for pulping that wood than for the coigue.

The coigue was pulped quite satisfactorily under the conditions used. Acalcium-base sulfite liquor was found satisfactory for pulping ulmo under theconditions given in table 2.

Preh7drolysis,sulfate Pulping

The results indicate that the three hardwoods can be pulped readily with theprehydrolysis-sulfate process. Acids generated during prehydrolysis loweredthe pH value to 4. Although the conventional sulfate process was not appliedto the woods, it can be said from experience with other hardwoods and withChilean insignis pine that the prehydrolysis step lowers the amount of chemi-cals required to produce pulps of approximately the same lignin contents.In addition, the combination of prehydrolysis and sulfate pulping removesthe hemicelluloses of hardwoods to an extent which permits the use of thehot extraction process with its attendant low requirement of sodium hydroxide.The descending order of ease of pulping by the prehydrolysis-sulfate processappears to be ulmo, coigue, and tepa, which was essentially the order for thesemichemical and sulfite processes.

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Yield and Analytical. Values for the Unbleached Pulps

The yield values for the unbleached pulps given in table 3 show that those forthe semichemical pulps ranged from 54 to 67 percent and those for the chemicalpulps from about 39 to 48 percent. A high yield is a characteristic of theconventional semichemical process, and the pulp obtained contains a consider-able amount of lignin and hemicelluloses which have to be removed during thepurification treatment.

`With respect to yields of unbleached semichemical pulps made without pre-hydrolysis, the-yield of tepa was very low in comparison with those for semi-chemical pulps of the same lignin content obtained from North American hard-woods, but the yields from coigue and ulmo were about the same. The yieldsof the unbleached pulps made with the prehydrolysis were lower than those ofthe corresponding pulps made without prehydrolysis, due to differences in theamounts of hemicellulose removed:

The alpha cellulose contents of the three hardwoods were all close to 48 per-cent (table 1). Losses of alpha cellulose in pulping can be determined by acomparison of that value with those for the unbleached pulps given in table 3.The comparison indicates that the semichemical process destroys less cellulosethan the other two processes and that some destruction is to be expected byprehydrolysis. In general, the yields of alpha cellulose reported are con-sidered to be good.

There was a tendency torard more destruction of cellulose by the prehydrolysis-sulfate process than by the sulfite process. The markedly higher viscosityvalues of the unbleached sulfate pulps accords with the relative severity ofhydrolysis of the two processes. Although the high amount of lignin in thesemichemical pulps prevented complete dispersion for the determination ofviscosity, they may have been higher in degree of polymerization than any ofthe others because of the very mild pulping treatment, The chemical pulpsdiffered in viscosity over a range of about 11 to 70 centipoises.

A comparison of the total pentosans present in the woods, and in the pulpsmade with the prehydrolysis step without added acid, shows that even verymild hydrolytic treatment is highly effective in the removal of pentosan hemi-celluloses from hardwoods.

Owing to the generally small amount of pentosans removed in the subsequentpurification of these pulps, it is likely that a greater degree of removal ofpentosans in the pulping would have been advantageous to the quality of thepurified pulps. More recent experience with aspen shows that a pentosan con-tent as low as 3 percent in the unbleached pulp results from a slightly in-creased period of hydrolysis at maximum temperature.

A comparison of ether-solubility values suggests that prehydrolysis was advan-tageous in the removal of ether extractables.

It is of interest to compare the coigue prehydrolysis-sulfate pulp with theAustralian eucalyptus (Eucalyptus repans) previously referred to (34)

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because of the similarity of the two raw materials and the differences in thepulping treatments. In the Australian work, the water prehydrolysis was donewithout added acid, as in the present study, but a higher temperature and alonger time were used. In the sulfate pulping, the maximum temperature waslower but a little more chemical and a longer time were used. For theeucalyptus pulp, the yield, alpha, and pentosan values were 32.5, 95.5, and1.4 percent and, correspondingly, for the coigue pulp, 39.3, 94.3, and 7 per-cent. If one adjusts the yield value of the coigue pulp, in accordance withthe lower pentosan content of the eucalyptus pulp and also allows for someadditional loss, however, one may conclude reasonably that essentially thesame character of viscose pulp and about the same yield is obtainable fromChilean coigue and Australian eucalyptus. On the same basis, it would beconcluded that the yield of the very low pentosan type of pulp obtainablefrom the Chilean ulmo would be definitely higher than that from coigue.

Purification of the Unbleached Pulps

The conditions used for the purification of the unbleached pulps are given intable 4. A comparison of the total chlorine requirements of the pulps showsthose of the semichemical pulps were much the highest, which accords with thehigh lignin contents of those pulps. Their chlorine requirements were in therange observed for neutral sulfite semichemical pulps of the same lignin con-tents made from North American hardwoods.

The high amount of hemicelluloses, chiefly pentosans in the semichemical pulpsmade without the prehydrolysis step, made it necessary to use the cold extrac-tion process, following chlorination, in order to remove the required amountof hemicelluloses. For the coigue, the amount of alkali required in the coldextraction of the semichemical pulp was 13 times more than the amount requiredfor the corresponding prehydrolysis-semichemical pulp, and similarly, for thetepa semichemical pulp, it was a little over three times. Although the hotalkaline extraction process was adequate for all of the other pulps, the tepaand ulmo semichemical pulps required from 2 to 3 times more alkali th,F1 didthe others in this group which were quite similar in their requirements.

A final steeping in acidic solution was applied to the pulps as described intable 4 to lower iron content. These treatments had only a slight effect ondispersed viscosity. The iron was a result of contamination rather than fromthe woods from which the pulps were made.

As previously mentioned, the unbleached pulps differed a great deal inviscosity. Because of this, they were not processed to a common minimumviscosity. However, the decreases effected during purification ranged from4 to 53 centipoises.

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Yield and Test Values for the Purified Pulps

Yield and analytical values for the purified pulps are given in table 5.

Although the yields of the purified pulps are not directly comparable becauseof the differences in alpha and beta cellulose contents, it is believed eventhe lowest would compare favorably with the yields obtained in present commer-cial production. It is understood that the potential yield of viscose rayonyarn is sometimes estimated to be the sum of the amount alpha cellulose plusone..half the amount of beta cellulose in the pulp. The following tabulationarranges the pulps in descending order of yield on that basis:

Estimated yield ofKind of pulp viscose rayon yarn

Percent based on wood-

Coigue neutral sulfite semichemical 44Coigue prehydrolysis-neutral sulfite semichemical 42Coigue sulfite . 42

Ulmo pre hydrolysis-sulfate 41

Ulmo prehydrolysis-neutral sulfite semichemical 41Tepa neutral sulfite semichemical 41

Tepa prehydrolysis-neutral sulfite semichemical 40Ulmo sulfite 39Tepa prehydrolysis-sulfate. 39Coigne prehydrolysis-sulfate 9 37Tepa sulfite. .. 36

The foregoing tabulation indicates that the highest yield of yarn from thethree hardwoods can be obtained by means of the semichemical process, the nexthighest by the prehydrolysis-sulfate process, with the sulfite process thirdin order. The yield value given for the coigue pre hydrolysis-sulfate pulp isbelieved to be somewhat low due to the conditions used in pulping and purifica-tion or to experimental error. The results also indicate that slightly higheryields may be expected from coigue and ulmo than from tepa.

In general, the chemical composition of the purified pulps met the require-ments, which had been selected on the basis of analytical values typical ofcommercial sulfite viscose pulps, known to be acceptable for continuous-threadviscose rayon. The tepa sulfite pulp was definitely high in sodium hydroxidesolubility and the ulmo prehydrolysis-semichemical and sulfite pulps were atthe upper limit of acceptability in this respect.

There was indication of a trend toward higher disperse viscosity in thesemichemical pulps than in the other two kinds. There was also a trend toward

6–Values adjusted to nearest whole number. Order was not affected by so doing.

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higher viscosity in the sulfite pulps than in prehydrolysis-sulfate pulps,if the greater degree of pulping used in the preparation of the tepa sulfitepulp is discounted.

With the exception of the tepa sulfite pulp, all of the experimental pulpswere high in pentosans in comparison with values typical of commercial soft-wood sulfite viscose rayon pulps. Data obtained in the present study andearlier but unpublished data, indicate that in a softwood viscose pulp onlya small proportion of the total pentosans are in the alpha cellulose, but thatin a purified hardwood pulp, from 75 to 100 percent of the pentosans are in

the alpha cellulose and, furthermore, they appear in the yarn. An analysisfor pentosans made on yarn from the coigue semichemical pulp gave a value of

6.6 percent.

It would be desirable to have available a comparison of the properties ofyarns and films made from a series of hardwood prehydrolysis-sulfate pulpsvarying as widely as feasible in pentosan content.

Despite the final steeping in acidic solution, the iron content of all of thepurified pulps was very high. This indicates the residual iron was presentas discrete particles. Since the experiments described here were made, acomprehensive survey of sources of contamination by iron in the small-scaleand pilot plant bleaching operations has resulted in the practical eliminationof this difficulty.

The pulps differed in viscosity over a range of about 6 to 23 centi-

poises.

Screen-fractionation data for three of the coigue pulps are given in table 6.These data show that about 60 percent by weight of coigue pulp was retainedon an 80-mesh screen and about 20 percent passed through a 150-mesh screenunder the conditions of fractionation used.

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Strength of Sheets Wet with Sodium Hydroxide

As previously mentioned, the low strength of sheets of hardwood dissolvingpulps when wet with a strong sodium hydroxide solution has been said to be asource of difficulty in the conventional process for the manufacture ofviscose rayon.

It was reported that sheets of purified coigue sulfite pulp split to some ex-tent during the steeping treatment in connection with viscose filtrabilitytests. No failures of any sort, however, were reported for the sheets of thepurified tepa prehydrolysis-sulfate pulp. This suggests the possibility ofadequate strength in the sulfate type of pulp.

Filtrability of Viscose Solutions from Experimental Pulps

The filtrability of viscose solutions made from the tepa-prehydrolysis-sulfate, the coigue sulfite, and certain commercial pulps was determinedby an industrial viscose laboratory. In comparison With a European soft-wood sulfate pulp of viscose grade, the tepa sulfate pulp had the samedispersed viscosity, the alkali cellulose required less aging, the combinedsulfur in the viscose was the same, the rate of ripening of the viscose wasessentially the same, and the viscose was definitely superior in filtrability.

The coigue sulfite pulp had three times the dispersed viscosity of a sulfite.-viscose pulp, prepared commercially from a North American hardwood, and twicethat of a similar softwood, but its reaction rate during aging was notsignificantly slower. The combined sulfur in the viscose from coigue pulpwas about the same as that in the softwood control pulp, but less than thatin the hardwood pulp. Its rate of ripening was similar to the softwood pulpbut faster than that of the hardwood pulp, and its filtrability was almost

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as good as that of the hardwood and definitely better than that of the softwoodsulfites.

Spinning Trials

Viscose rayon yarn of continuous-thread grade was made by an industrial labo-ratory from 5-pound samples of the tv'o coigue semichemical pulps and thecoigue and ulmo prehydrolysis-sulfate pulps, which ranged from 3.6 to 7.4percent in pentosans. It was reported that the experimental pulps reactednormally toward the viscose-making process and that the experimental yarnswere of commercially acceptable quality.

Conclusion

The results of the filtrability tests, the spinning trials, and the generalsimilarity in chemical composition of all of the experimental pulps warrantthe conclusion that pulps, chemically satisfactory for continuous-threadrayon, can be made from Chilean coigue, tepa, and ulmo by, (1) the neutralsulfite semichemical process, with or without a prehydrolysis step, (2) theprehydrolysis-sulfate process, and (3) the sulfite process in conjunctionwith suitable but simple purification treatments. The study also indicatesthat pentosans closely associated with the alpha cellulose of hardwoods may beless harmful to the quality of viscose products than the pentosans of softwoods.

Appendix

The standards used in evaluating the wood and pulps, listed in table 7,are those of the Technical Association of the Pulp and Paper Industry.

The solubility of the purified pulps in sodium hydroxide solution wasdetermined according to Joint Army-Navy (U.S.) Specification, JAN-C-216,Cellulose, Tood Pulp. May 29, 1945.

Alpha, beta, and gamma celluloses were determined by the gravtmetricprocedure given in Forest Products Laboratory Report No. R19.

Amounts of iron and copper were measured according to Forest ProductsLaboratory spectrophotometric procedures. In either instance a pulp sampleis put into solution by the oxidizing action of nitric, sulfuric, andperchloric acids. Orthophenanthroline is used to form the colored complexwith iron and tetraethylene pentamine, with copper.

Rept. No. 81906 -13-

Page 15: VISCOSE-RAYON PULPS FROM HARDWOODS COIGUE, TIEPA, …

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(2) Davis, W. E.1951. Polymolecularity of Viscose Rayon and Rayon-grade Pulps.

Ind. Eng. Chem. 43(2) 516-21, February.

Dorr, R. E.1942. The Problem of Cellulose and Cellulose Yarn. Kunstseide U.

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16.

(6) Hill, Allan C., and Campbell, BoydZellstoffabrik Waldhof. PB Report 7918. Office of the Publica-

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Husemann, E.1940. Constitution of Wood Polyoses. J. prakt. Chem. 155(1-5),

13-64, February 20.

(8) Kienitz, G. A.1937. Beech Pulp by Alkaline Cooking Process. Holz Roh-u.

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Klauditz, W., and Stegmann, G.1944. Morphologically Conditioned Reactivity Differences on Xanthation

of Fractions of Commercial Beech Sulfite Pulps. Cellulose-chemie 22, 20-27.

(10) Kleinert, T., Hingst, G., and Simmler, I.1944. Influence of Properties on Behavior in the Viscose Process.

Kolloid-Z. 108, 137-44.

(11) Kraemer, Elmer 0.1938. Molecular Weights of Cellulose and Cellulose Derivatives.

Ind. Eng. Chem. 30(10) 1200-03, October.

(12) Lindpainter, E,1942. The Significance of Pentosans in Rayon Pulp and Their Removal

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(3)

(4)

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(13) McGovern, J. N.1946. Manufacture of High Alpha Pulps in Wartime Germany. The Paper

Ind. & Paper !World, 28, 988-90, October.

(14) McKinney, J. V.1946. The Effect of Alkaline Pulping on the Acetylating Properties of

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(15) Meller, Alexander1946. The Hot Alkaline Purification of Cellulose I. Paper Trade Jour.

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1950. Eucalypt Pulps from Water Prehydrolysis and Sulfate Pulping.Tappi 33(5) 248-53, May.

(18) Mitchell, R. L.1946. Chain Length Measurements on Nitrated Cellulosic Constituents

of Wood. Ind. Eng. Chem. 38(8) 843-50, August.

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(20) Nickel, S.1938. The Chemical Conversion of Pulps Made by Alkaline Pulping.

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(16)

(17)

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(25) Ritman, E. L.1933. The Real Meaning of Beta and Gamma Cellulose. World's Paper

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(28) Smith, Leroy H.1946. Synthetic Fiber Developments in Germany. P. 14 Textile

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(29) Spurlin, H. M.1943. Influence of Polymolecularity on Physical Properties. Cellu-

lose and Cellulose Derivatives, Emil Ott, Editor, New York.

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(31) Tasker, C. V,, and Libby, C. E.1946. The Manufacture of Viscose from Sugar Maple. Paper Trade Jour.

123(24) 139-48, December 5.

(32) Tippets, E. A.1950. The Position of Cellulose as a Chemical Raw Material. Tappi

33(2), 32A, 34A, February.

(33) Trivedi, S. A.1950. Indian Patent 42,068, December 6.

(34) Wicker, Don B.1945. Sulfate Dissolving Pulp for Rayon Manufacture. P. B. Report

1130, Office of the Publication Board, Department of Commerce,Washington D. C., USA, September 19.

(35) Winkler, Werner1950. Determining the Suitability of Dissolving Pulps for Viscose

Manufacture. Kunstseide U. Zellwolle 28(5), 153-55.

(36) Yundt, Albert P.1951. Crystalline Hemicelluloses. Tappi 34(2) 89-95, February.

Rept. No. R1906 -16-

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Page 22: VISCOSE-RAYON PULPS FROM HARDWOODS COIGUE, TIEPA, …

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Page 23: VISCOSE-RAYON PULPS FROM HARDWOODS COIGUE, TIEPA, …

Table 6.--Screen-fractionation data for unbleached and _purified pulps fromcoigue

Fractions and amounts:Purifi-:---------------:cation tRetained:RetainedtRetainediRetainedtPassing:number ; on : betweim' oil'uvecn- be ;wean: a 200-

: 80-mesh: 80- anch115- and; '_5Q'- and: megh: screen :115-mesh:150 .mes,:u200,-3,es h sc.reen,

: screens: screens: screens:by dif-:ference

:Percent :Percent :Percent :Percent :Percent

: •

• : : -.

• 67.2 : 9.8 : 3.5 : 1.5 : 18.0Purified • 1,268 : 66.7 : 14.5 : 4.9 : 2.0 : 11.9

: : :Prehydrolysis-neutral sulfite: : : :

semichemical, Digestion : : : : . :5266N: : : : : -.

Unbleached .- 56.6 : 16.9 : 4.2 : .6 : 21.7• 1,331 : 64.4 : 16.1 : 3.1 : 1.6 : 14.8Purified

: : : :Sulfite, Digestion 52361: : . : : :

Unbleached.. .• • 60.6 ; 17.6 : 3.5 : 2.7 : 15.6Purified 1,368 : 50.8 : 21.0 . 3.1 . 3.3 . 21.8

Pulp

Neutral sulfite semichemicalDigestion 5238N:Unbleached •

Rept. No. R1906

Page 24: VISCOSE-RAYON PULPS FROM HARDWOODS COIGUE, TIEPA, …

Table 7.—TAPPI Standards]; used in the evaluation ofChilean woods and the pulps made from them

Determination Method

number

Wood •

...Specific gravity, density T 18 m-47Lignin T 13 m-45

Holocellulose • T 9 m-45•Total pentosans T 223 m-43

Ash T 15 m-45Solubilities:

Hot water • T 1 m-45

One percent sodium hydroxide • T 4 m-44T 5 m-45Ether

Alcohol-benzene • T 6 m-45

Pulp

Permanganate number • T 214 m-42T 222 m-!&3

Lignin 43-m223TTotal pentosans •

Ash • T 211 m-44

•Ether solubility T 5 m-45Dispersed (solution) viscosity T 230 sm-46

T 217 m-47Brightness

1-Technical Association of the Pulp and Paper Industry,

122 E. 42nd St., New York 17, N. Y.

Rept. No. R1906