Forest Products Laboratory (U.S.)

Keller, Eugene L.

McGovern, John Neilson, 1908-

Undetermined

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AGRICULTURE ROOMSULFITE PULPS FROM SEVERALSOUTHERN HARDWOODSJuly 1942(RPUNITED STATES DEPARTMENT OF AGRICULTURELFOREST SERVICE, FOREST PRODUCTS LABORATORYLL;--	 Madison, WisconsinIn Cooperation with the University of WisconsinSULFITE PULPS FROM SEVERAL SOUTHERN HARDWOODSByJ. N. McGOVERN, Associate. TechnologistandE. L. KELLER, Junior ChemistIntroductionThe sulfite pulping experiments on southern cottonwood (Populus deltoides virginiana), black willow (Salix nigra), and sugarberry (Celtislaevigata) described in this report were made as part of a general inves-tigation of the preparation and properties of a wide variety of pulps fromhardwoods grown in the Arkansas Delta region. The objective of the generalinvestigation was to develop possible uses as pulpwood for the large supplyof hardwoods from this region. A study allied to the present experimentswas reported previously concerning neutral and acid sulfite semichemicalpulps from a number of the Delta hardwoods, including the above species (1).One of the woods, sugarberry, was also pulped in connection with the preparration from hardwoods of sulfite pulps suitable for purification to rayonpulps (2).Of the three species studied, only the cottonwood has receivedany considerable attention. Carpenter and McCall (2) found southern cotton..wood to be readily pulped by the sulfite process to produce a low–bleachingpulp high in alpha cellulose: the purified product prepared from this pulp,however, showed some limitations during conversion to viscose derivatives.This species was considered by Rue and Wells (4) to be similar to aspen inits pulping characteristics. Rue and Wells-(45- found black willow to beeasily reduced to a low.bleaching sulfite pulp in yields of 50 to 55 percent;the pulp, however, was specky. The pulping of sugarberry by the sulfiteprocess has apparently not been reported, although Rue and Wells (4) foundthe closely related hackperry (Celtis occidentalis) to produce a light–colored,easily bleached sulfite pulp.The objectives in the present study were (1) to prepare sulfitepulps by conventional means from southern cottonwood, black willow, end sugar–berry, and to determine their properties; (2) to compere the southern hard-wood pulps with previously prepared birch (Betula papyrifera) and aspen(Populus tremuloides) sulfite pulps; and (3) to Compare the yields end prop-erties of sugarberry sulfite pulps ranging from a high yield semichemical toa low–bleaching pulp.R11409Experimental Part The three hardwoods selected for the sulfite pulping experimentswere included in a shipment of six Arkansas delta species supplied by thePhillips County Chamber of Commerce, Helena, Arkansas, and cut in that county.The physical and chemical properties of the whole shipment have been describedin detail elsewhere (1, ). Average values for the cottonwood, willow, andsugarberry are given in table 1. Representative logs from each of the threespecies were converted into standard 5/8-inch chips for the digestions.The sulfite cooking acid used for digesting the chips was preparedas usual by passing sulfur dioxide from a cylinder into a lead-lined tankcontaining milk of lime. The digestions were made in a stainless-steel clad,steam-jacketed autoclave having a capacity of 1.5 cubic feet. The pulpedchips were defibered with a stirrer and screened through a diaphragm screenwith 0.012 inch slots.The conditions for the digestions of the three southern hardwoodsare given in table 2. Conditions for birch and aspen digestions taken froma Previous report (2) are also included for comparison. All the digestionswere made with indirect steam.'	 The results from the southern hardwood digestions, as well asthose from the northern hardwoods, are found in table 3. These results in-clude yields, pulp bleach requirements, strength, values, and chemical anal-yses of the pulps. In the case of the southern hardwoods the results areaverages from two digestions for each species, whereas only one digestioneach is represented by the northern hardwoods.. The bleach requirement valuesare the average of data from permanganate number and single stage hypochlo-rite determinations, expressed in terms of standard bleach powder. Thestrength values are given for two freeness values, 500 and 550 cc. (Schopper-Riegler), as interpolated from strength-freeness relations obtained by beaterprocessing. Standard Forest Products Laboratory methods were used throughout.Discussion of Results The WoodThe chemical and physical properties of the three southern hard-woods given in table 1 indicate certain differences between the cottonwoodand willow on one hand and the sugarberry on the other. These differences,as will be shown later, reflect on the qualities of these species as pulp-wood.The cottonwood and willow were very rapid-growing and had rela-tively low densities but high total and alpha-cellulose contents. The sugar-berry, in contrast, had a medium growth rate and density, but rather lowcontents of alpha and total cellulose. The sugarberry, nevertheless, had aslightly lower lignin content than the others, although it was somewhat highin pentosans and material soluble in 1-percent sodium hydroxide. None of thethree woods was high in material soluble in ether.R1409-2-Sulfite Pulps from the Southern Hardwoods Application of the pulping conditions outlined in table 2 to thethree southern hardwoods resulted in the production of sulfite pulps havingbleach requirements of approximately 12 percent, as shown in table 3. Thepulping conditions to obtain the same degree of pulping were the same for thethree species except for a slightly shorter time, 9.5 compared to 10 hours,for the sugarberry. The shorter time may possibly have been a result of thesomewhat lower lignin content of the sugarberry in comparison with the othertwo species.The pulp yields from the cottonwood and willow were approximatelythe same high value of 52 percent, whereas that from the sugarberry-was lowerby nearly 10 percent. The large difference in pulp yield can be traced tothe same relative difference between the woods in their cellulose contents.The chemical analyses of the three pulps, nevertheless, showed them-to be verysimilar in their composition. .The , sugarberry pulp had a slightly higher lignincontent than the Others, rhereas the willow pulp was slightly lower , in alphacellulose and pentosang .' The chemical composition of all the pulps appearedto be typical for hardwoods pulped under, the specified conditions.The strength values of the equal bleaching pulps from cottonwood,and sugarberry, as shown in table 3, were the same for all the strength char-acteristics, while the same bleaching pulp from the willow had strength valueslower throughout than the others. The low values for the willow pulp can notbe explained by any differences in the chemical composition of'the three pulpsor the original chips. The strength values of the pulps on the whole wereperhaps somewhat low for hardwood sulfite pulp in general and certainly con-siderably below the strength of softwood sulfite pulps.The relatively high density of the sugarberry permitted a larger charge of chips than possible with the cottonwood or willow. The volume ofcooking liquor charged for a unit weight of . chips was therefore appreciablylower for the sugarberry than the others, as indicated in table 2. The lowpercentage yield of pulp from the sugarberry, on the other hand, offset to alarge extent the advantage of high density. Thus, the yield of pulp for agiven digester volume would be about the same for all three species.Comparison with. Birch and Aspen Sulfite Pulps Birch and aspen pulps prepared for purifying to rayon pulps (2)showed certain similarities and dissimilarities to the southern hardwoodsulfite pulps, as indicated in table 3. The pulping, conditions for thenorthern and southern hardwoods were the same except for the low combinedsulfur dioxide in the cooking liquor used to digest the birch and , aspen.Apparently, because of the low combined sulfur dioxide, the pulping time forthe birch and aspen was considerably less than for the southern hardwoods.The bleach requirement of the birch pulp was the same as that of thesouthern hardwood pulps, but its yield was 4 percent lower than that of eithercottonwood or willow, although 6 percent higher than that_of the sugarberry.The aspen pulp had a very low bleach requirement but was produced in about thesame yield as were the cottonwood and willow pulps.91409	 —3—Although the birch and aspen pulps were made with an acid low incombined sulfur dioxide, a condition favoring production of a pulp with ahigh alpha-cellulose and a low pentosan content, they contained about thesame general percentage of alpha cellulose and a higher percentage of pento-sans than the southern hardwood pulps made with a conventional acid. Further,the southern hardwood pulps had less than half the material soluble in ethercontained in the birch and aspen. On the basis of the chemical characteris-tics shown in table 3, the cottonwood, willow and sugarberry pulp would appearto be more promising pulps for purifying to rayon-type pulp than the birchor aspen pulps.The strength values of the willow pulp were approximately the same'as the low bleaching aspen pulp, whereas those of the cottonwood and sugar-berry pulps were intermediate to the aspen and birch pulps.As might be expected the botanically related species, southerncottonwood and aspen, gave pulps in similar yields and having fairly similarproperties. A harder bleaching aspen pulp would perhaps have strength prop-erties nearly the same as the cottonwood pulp. An important difference didexist, however, in the amount of material soluble. in ether; this value wasrelatively high in the aspen pulp.Sugarberry Sulfite Pulping Cooking conditions for producing sugarberry pulps ranging from awell-cooked pulp to a partially delignified semichemical pulp and the prop-erties of these pulps are given in table 4. The results for the most de-lignified pulp, number 1, were taken from table 3; the results for the otherpulps were reported previously (1, 2). Although the combined sulfur dioxidein the cooking acid used for number 1 was higher than for the others and themaximum temperature for numbers 3 and 4 was lower than for the others, themain independent cooking variable connecting these data was the cooking time.The effect of cooking time on the yields and properties of thepulps is plainly evident from the figures in table 4. The yields and someof the chemical and physical properties values were also plotted againstcooking time to furnish the curves in figure 1.There were definite relations between cooking time and yield andmany of the, pulp properties, as shown by the curves in figure 1. The totalyield decreased and the cellulose contents increased rather sharply with anincrease in cooking time from 4-to about g 'hours. The changes were moregradual with a cooking time longer than hours. The lignin and pentosanscontents decreased gradually with cooking time, the over-all change beingless than for yield or cellulose contents. The bursting and tensile strengthand• solid fraction values increased sharply as the cooking time increasedfrom that producing an undefibered chip to that producing a material approach-ing the defibering point. The changes in these strength characteristicswith cooking times corresponding to yields of 55 percent or less were rela-tively small. The tearing strength values and the times required to attaincertain freeness levels showed no definite relation to cooking time.It is interesting to note that digestion number 2, table 4, wascarried considerably beyond the point ef , exhaustion of the base in the cook-ing liquor, but the pulp from it had a considerably higher bleach. requirementR1409and was less purified than the pulp from number 1, which was carried justto the point of,exhaustion. It appeared that an insufficient amount ofchemicalwas present in number 2 to , aoMplett the delignifiCation and puri-,fication before the base was exhausted.Summary(1) Sulfite pulps having bleach requirements of approximately 12percent standard bleach powder and an average alpha cellulose content of82.5 percent were prepared by conventional pulping procedures from southerncottonwood, black willow, and sugarberry. The pulp yield from the cotton--wood and willow was 52 percent, whereas that from the sugarberry was lowerby 10 percent. The strength properties of the cottonwood and sugarberrypulps was somewhat superior to those of the willow pulp.(2) Comparisonaf the-southern hardwood pulps with birch and aspensulfite pulps prepared for 'purifying to rayon pulps •showed the former to havethe same alpha cellulose content, lower pentosans content, and lower amountsof material soluble in ether than the latter. The cottonwood and willowpulps were produced in the same yield as the somewhat lower bleaching aspenpulp, but in higher yield than the birch pulp. The birch pulp showed highervalues for strength properties than the others.(3) Sugarberry sulfite,pulps toVering the range from a semichemicalpulp produced in 4.2 hours to 'a low bleaching pulp produced in 9.5 hoursshowed consistent relations between pulping time and yields and propertiesof the pulps. An increase in pulping time caused decreases in pulp yieldand lignin and pentosans contents and increases in the total and alpha cel-lulose content of the pulps and their bursting and tearing strength andsolid fractions. The largest part of the changes occurredwhen the time wasincreased from 4.2 to 6.5 hours.References (1-) McGovern, J. N. and Chidester, G. H. Semichemical pulps from ArkansasDelta hardwoods. Problem B-200; project 1168-5. Mimeographed report.(2) Nihl4n, Hugo. Preparation of rayon pulp from hardwoods. Problem B-202;project 1168-3. Mimeographed report.(3) Carpenter, Charles and McCall, Frank. Progress in hardwood pulping forviscose rayon.. Rayon Textile Monthly 19 (9, 10): 538-9, 618-20(Sept., Oct. 1938)(4) Wells, S. D. and Rue, J. D. The suitability of American woods for paperpulp. U.S.D.A. Bull. 1485 (1927)(5) Pew, J. C. and Schafer, E. R. Physical and chemical properties ofArkansas Delta hardwood pulpwoods: sugarberry, ash, bitter pecan,cottonwood, willow, and elm. 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Sulfite pulps from several southern hardwoods

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Sulfite pulps from several southern hardwoods

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