CELLULOSIC FIBERS CHESTER H. HAYDEL, JEUEL F. SEAL, HERMANN J. JANSSEN, and HENRY L. E. VIX U. S. Department of Agriculture, Southern Utilization Research and Development Division, New Orleans, La.
DecrystaIIization of Cotton Cellulose
Using evaporative procedures rather than solvent extraction to remove monoethylamine from swollen fibers of decrystallized cotton cellulose controls the type of residual crystal lattice in the product and reduces fractionation requirements. Also, they are cheaper and less toxic
D E C R Y S T A L L I Z E D COTTON is an experimental product having an elongation at rupture nearly twice that of native cotton, Other properties include greater fabric tear strength, improved dye receptivity, and chemical reactivity which in recent years has become particularly important because of new chemical treatments for cotton cellulose. Research is being done to cross-link decrystallized cotton to impart elasticity to the product and thereby yield cotton fabrics having greater consumer interest. I n small-scale experiments, liquid monoethylamine has been used to reduce crystallinity ( 9 ) and crystallite length (70) of cotton cellulose. Generally, the ethylamine was removed from swollen fibers of the ethylamine-cellulose complex by extraction with nonaqueous solvents of low polarity to preserve the increased amorphous component (9, 7 7 ) . Organic solvents such as chloroform and hexane were recommended ( 9 ) for retaining both the high degree of decrystallization achieved and the cellulose I crystal lattice of native cotton. I n this way, crystallinity was reduced without fiber damage or loss of fibrous structure. T h e difficulty in recovering ethylamine from the effluent mixtures of ethylamine and chloroform by fractional distillation has been attributed to a 1 to 1 molecular association between rhe two molecules (7). I n contrast to this, effluent mixtures of ethylamine and a commercial hexane behaved normally during distillation and presented no serious problem in their separation. Further, hexane is cheaper and less toxic than chloroform and was therefore
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selected as an extractive solvent for initial pilot plant preparation of decrystallized cotton materials for product evaluation and cross-linkage studies. Decrystallized cotton having residual crystalline areas of cellulose 111, a relatively expanded and skewed crystal lattice (7), has been prepared also by a laboratory procedure (8) which utilizes evaporative removal of the ethylamine. This procedure was carried out in the pilot plant to provide larger samples for comparative tests with mercerized cottons.
Results and Discussion Hexane Extraction of Ethylamine. The pilot plant equipment comprised a reactor unit, reagent- and solventstorage facilities, fractionation apparatus for reagent and solvent recovery, and a refrigeration system for supplying low temperature brine to the reactor jacket and vapor condensers. The reactor unit and auxiliary recovery apparatus have been previously described (2). The procedure of Segal and others (i'O), adopted for this work, involves repeated evacuation and flushing of the reactor unit and the enclosed cotton bundle with nitrogen prior to admitting the alkaline ethylamine reagent. This removed sufficient air to retard damage to the cellulose through alkaline oxidation and enough reagent was then added to immerse completely the cotton fiber, yarn, or fabric, and decrystallization allowed to continue for 4 hours a t a temperature not above 4" C. Reagent to cotton ratios were about 7 or 8 to 1, by weight.
INDUSTRIAL AND ENGINEERING CHEMISTRY
At the conclusion of the treatment period, excess reagent, drainpd and pumped to storage, was slightly greater than half that originally added, leaving an estimated 4 pounds of reagent with each pound of cotton. Successive batches of fresh hexane solvent were then used to wash the cotton until its ethylamine content was reduced to roughly 1%-this was considered sufficiently low to reduce the danger of alkaline oxidation without materially influencing subsequent product evaluation. Each batch of hexane was circulated through the bundle until equilibrium between the ethylamine content of the cotton and the solvent was established. M'ith direction of solvent flow reversed every 5 minutes, this required about 25 minutes. Hexane was largely removed from the extracted cotton by drying in a forced draft of air without heat; however, about 6%, based on weight of the cotton, was too firmly absorbed for removal by this treatment. Up-scaling the hexane extraction process disclosed two major problems. First and unexpectedly, the product crystal lattices, as determined from radial x-ray spectrometer tracings, were consistently mixtures of cellulose I and cellulose 111. Hexane preheated to temperatures of 60' to 65' C., which approaches its boiling point, increased the percentage of cellulose I but in no case could a product of essentially pure cellulose I be prepared. These mixed lattices precluded using spectrometer tracings to estimate Crystallinity (5) and therefore, a modified acid-hydrolysis method (6) was used. Residual crys-
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Figure 1. Ethylamine content of cotton and hexane after successive solvent washes
tallinities in card sliver approximated 50% after treatment with ethylamine and hexane extraction. The other problem encountered was the excessively slow extraction rate. Two factors were considered generally responsible-low solubility of ethylamine in hexane, and the time required for ethylamine content of each hexane wash to reach equilibrium with the residual ethylamine in the cotton. The equilibrium factor was exaggerated in pilot plant operation-channeling the solvent through the cotton bundle tended to expose only the extracted portions to fresh hexane. Twenty to twenty-five hot hexane washes were usually necessary to reduce the ethylamine content of the cotton from the initially estimated 400% before washing to the desired value of 1% or less. Corresponding ethylamine contents of hexane and of cotton card sliver after each such wash, as determined by titration for alkalinity with methyl red indicator, is shown in Figure 1. Impracticality of slow extractiofi rates, excessive solvent and fractionation requirements, and undesirable lattice changes encountered discouraged further experimentation with the large-scale hexane extraction process. Evaporative Removal of Ethylamine. A heat exchanger to provide hot nitrogen a t approximately 8 0 ” C., was installed to vary evaporation rate of the residual ethylamine. Employing a constant immersion period of 1 hour in the reagent, three pilot plant experiments were performed, altering only evaporation rates. The effect of slow evaporation was first tested by leaving the decrystallized product, after drainage of excess ethylamine, under vacuum overnight. Intermediate rates were obtained by using unheated nitrogen as the drying medium and rapid evaporation was achieved by passing the preheated nitro-
gen for 2 hours through the treated cotton. Any tendency of the hot nitrogen to effect recrystallization was generally counterbalanced by the cooling effect from heat of vaporization of the ethylamine. From preliminary tests, evaporation times employed in these three experiments were chosen to yield products containing about 1% ethylamine, based on the weight of the cotton. Slowest evaporation rates resulted in decrystallized products having essentially pure cellulose I11 in the remaining crystalline regions while rapid evaporation gave the cellulose I pattern. The intermediate rate produced mixed lat-
tices. Radial x-ray spectrometer tracings of samples of these products are shown in Figure 2. No significant variation of the cellulose pattern beyond the range of accuracy for the x-ray method was observed in cotton exposed to treatment in different portions of the apparatus. Through judicious control of the evaporation rate, either crystal lattice could be produced in the remaining crystalline regions of the products. These results confirm those recently reported by Marrinan and Mann ( 4 ) . Despite the short immersion time of only 1 hour in ethylamine, product crystallinities of 26% and 30% were determined from the spectrometer tracing of decrystallized 20s/l and 60s/2 cotton yarns, respectively, after rapid evaporation of the reagent. Another principal advantage of evaporative removal of ethylamine was reduction of fractionation requirements. The ethylamine reagent was diluted only by water present in the cotton. Stripping the reagent from this minimal quantity of water was easily accomplished because of wide differences in the relative volatilities. Ethylamine of 90% purity or better is considered satisfactory for re-use ( 3 ) . This pilot plant evaporative procedure for removing the monoethylamine reagent, which also controls the type of residual crystal lattice in the product, should be useful to those interested in preparing large quantities of experimental decrystallized cotton for product evaluation. Acknowledgment
The authors wish to thank Joseph J. Creely of the cotton fiber section for determining crystallinity values and crystal lattice patterns from radial x-ray spectrometer tracings. literature Cited (1) Barry, A. J., Peterson, F. C., King, A. J., J . A m . Chem. Sod. 58, 333-7
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SPECTROMETER
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Figure 2. Radial traces after ethylamine evaporation for decrystallized cotton yarn (29.5 Tex) and an untreated control
(1936). (2) Greathouse, L. H., Haydel, C. H., Janssen, H. J., IND.ENG. CHEM. 47, 187-91 (1955). ( 3 ) Loeb, L., Segal, L., Textile Research J. 25. 516-19 11955). (4) MarrinAn, H. J.,’Mann, J., J . Polymer Sci. 21, 304-11 (1956). (5) Martin, A. E., to be published. (6) Nelson, M. L., Conrad, C. M., Textile Research J . 18, 149-54 (1948). Sepal, L., Jonassen, H. B., J. Am. chem. SOC.74, 3697-9 (1952). Segal, L., Loeb, L., Creely, J. J., J . Polymer Sci. 13. 193-206 (1954). Segal, L., Nelson, ‘M. L., Conrad, C . M.. J . Phvs. @ Colloid Chem. 5 5 , 325-36 (1551). (10) Segal, L., Nelson, M. L., Conrad, C. M., Textale Research J . 23, 428-35 (1953). (11) Sisson, W. A., “Cellulose and Cellulose Derivatives” (Emil Ott, ed.), Chap. IIIA, Intkrscience, . New York, 1946, RECEIVED for review April 24, 1957 ACCEPTED August 8, 1957 VOL. 50, NO. 1
JANUARY 1958
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