Pulps from the Whole Cotton Plant Comparison of Soda and Nitric Acid Pulps A. R. MACORMAC AND F. K. CAMERON University of North Carolina, Chapel Hill, N. C.
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HE utilization of the whole cotton plant as a possible Processes Used source of material for the production of alpha-cellulose has occupied the attention of workers in this laboraSeveral different processes for making alpha-cellulose are utilized commercially. I n order to test the material and tory for several years. Dockery (8) showed that the mature plant contains approximately 80 per cent cellulose, but obresults by as widely varying methods as possible, two radically contrasting processes were used: (a) the alkali or soda jections were urged that this cellulose was different, at least structurally, from that obtained from wood, and could not process and (b) the nitric acid process. An advantage of be used in the industry. Sanders (11) made alpha-cellulose both of these processes is that pressure cooks are not essential. and derivatives from three commercial woods and compared The soda process is frequently carried out under pressure them with the corresponding when using wood chips, but the productsfrom the whole cotton physical nature of the material plant. Identical x-ray diffracof the present investigation inStudies of the atomic and micelle struction patterns were obtained dicated that pressure would be ture failed to show differences in cellulose for any particular p r o d u c t , unnecessary. of various origins which may affect its use irrespective of the source of C i t a t i o n s from the extenin industry. Investigators have made the cellulose; but x-ray results s i v e l i t e r a t u r e on the soda pulps from the several parts of the cotton are determined by the orientaprocess are not n e c e s s a r y tion of the atom groups, and here; but the nitric acid procplant. The present paper reports results the data at present available ess is of recent development obtained in pulping the whole cotton do not suffice to distinguish and is apparently used on a plant by the soda and the nitric acid procbetween several possible struccommercial scale in only a few esses. Before pulping, the ground plant tures. Dark-field microscopic plants. Pressure c o o k s a r e is extracted and a merchantable oil restudies with the Spierer lens not used in t h i s p r o c e s s . failed to show any significant Essentially, it c o n s i s t s of covered from the extract. Both processes treating the material with a difference in the micelles of give a pulp with an alpha-cellulose conweak solution of nitric acid the cellulose from the several tent suitable for industrial uses. The (0.2 to 5.0 per cent) a t temsources ( 2 ) . pulp from the nitric acid process appears peratures varying from 80' Since n e i t h e r atomic nor to 100" C . for 15 to 120 micellar studies gave evidence to be the better. minutes, washing, and then of differences in cellulose that treating with a solution of would affect its use, it seemed caustic soda (0.5 to 3.0 per cent) a n d sodium sulfite (0.1 per desirable to make cellulose pulps from the whole cotton plant cent) and 100" C. for 30 minutes to 4 hours. Lynch and Goss by methods comparable with industrial practice rather than (7), Payne (Q),and Hachihama, Onishi, and Takemura (4)used the purely laboratory procedures cited. this process with bagasse and report excellent results. Shikata Previous Investigations and Akagi ( l a ) and Korzheniovskii and Raskina (5) used it with cotton stems. It is claimed that the successive acid Aside from articles relating to the present project, there and alkali treatments dissolve the lignins, pentosans, and are no references in the literature to the pulping of the whole other incrusting materials more efficiently than do the usual cotton plant. Investigators have obtained promising repulping methods. The presence of these materials in colloidal sults with various parts of the plant. The use of cotton dispersion in the nitric acid solution, it is claimed, prevents a linters is well known. Golova (3), after expressing the oil, degrading action by the acid on the cellulose. The nitric treats the cottonseed meal with caustic soda and obtains a acid process appears to be especially useful for lignocellulose product (hull fiber) which is used like cotton linters to make material and is possibly preferable to the older processes. rayon. Lur'e (6) makes wrapping paper from cotton stems by a treatment with caustic soda. Yakimanskil (IS) claims Raw Material that the addition of 25 per cent of a cotton stem pulp t o the The material used in the present investigation consisted of ordinary wood pulp increases the mechanical strength of the the whole cotton plant, including the lint which had been resulting pulp. Shikata and Akagi ( I d ) treat cotton stems grown and harvested during the 1930 season a t Rockingham, with nitric acid, followed by a treatment with caustic soda N. C. (8). It was baled in the field and had been stored in; and bleaching, to give a pulp of 87 per cent alpha-cellulose, doors a t Chapel Hill since baling. It was run through 9 suitable for rayon manufacture. Korzheniovskil and Raskina hammer mill of the type used on farms t o prepare stock (6) use a similar process on cottonseed hulls, cotton stems, feed. The resulting ground material was a fluffy, uniform and reeds to give a pulp superior to that obtained by the mixtupe. A small proportion of woody stems, approximately usual methods of preparing pulps. 96
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INDUSTRIAL AND ENGINEERING CHEMISTRY
an inch long and 0.25 inch in diameter (25 X 6 mm.) was well dispersed through the mass. This fluffy material was extracted with carbon tetrachloride in a Soxhlet apparatus holding about 3000 grams of the ground plant. The extract was decolorized with norite during extraction. The yield of oil was about 5 per cent of the weight of the whole plant. It was a soft solid a t 20" C. By centrifuging and chilling, it was separated into an oil similar to cottonseed (85 per cent) and a wax (15 per cent). Extraction and refining of the oil will be described in another paper. The extracted plant lost all adhering carbon tetrachloride by a short exposure in air, absorbed the pulping solution easily, and was in an excellent condition for pulping.
For pulping by the soda process, an apparatus was constructed like a double boiler. A large galvanized-iron can with a top was used as a steam bath. Within was a smaller can with a tight cover. The ground extracted plant was placed in the inner can, and dry steam was introduced at the bottom of this container. A current of steam was run into the outer galvanized-iron can near the top and discharged a t the bottom. The grams of material in the alkali treatment were as follows : whole plant, 1568; water, 7840; sodium hydroxide, 784; and sodium carbonate, 196. These proportions were suggested by an expert industrial pulp chemist, although the proportion of chemicals is greater than a survey of the literature would suggest. The mixture was boiled for 8 hours, and then the material was washed with warm water until it remained clear. Agitation was not used and the process required more than 24 hours. At this stage, the material was soft but not fully disintegrated. Matted bunches of cotton fibers, pieces of woody stems, and particles of seed meats were recognizable. The wet pulp weighed 2769 grams. It contained about 80 per cent water so that the dry pulp would weigh 554 grams, a yield of 35 per cent of the dry weight of the whole plant. For the nitric acid process, a similar set-up was used except that the inner can was replaced by a large roundbottom flask. The following mixture was used: 00.
in the case of the nitric acid pulp, 12 per cent was desirable. With both pulps the best results were obtained with a consistency of 1per cent. Accurate yields could not be obtained because of unavoidable mechanical losses in the ball mill.
Analysis of Pulps The pulps were analyzed for alpha-, beta-, and gammacellulose by the volumetric method of Bray and Andrews (1). Ash determinations were made on separate samples. In the case of the nitric acid pulp, analysis of five samples gave from 86.7 to 94.0 per cent alpha-cellulose. Two typical cases are given. Results are calculated on the basis of the oven-dry weight of the bleached pulp: Soda Pulp
Processing
Whole plant, grams Water, grams Nitric acid (sp. gr., 1.43),
97
1000 7840 160
This is a 2.1 per cent solution of nitric acid. The plant material was wet thoroughly with hot water, and the whole was heated to about 70" C.; the nitric acid was added and then the rest of the water, hot. The temperature was raised as quickly as possible to 85-90' C. and maintained for an hour. The mixture was then washed with cold water in the flask until neutral to methyl orange. It was heated a t 85-90' C. for 3 hours with 1 per cent sodium hydroxide solution and 0.1 per cent sodium sulfite solution, and washed at first in the flask and then by decantation and suction until the wash waters were neutral to phenolphthalein and were a light straw color. The pulp a t this stage was similar to the soda pulp after the boiling treatment-i. e., soft but not fully disintegrated. The wet pulp weighed 2750 grams and contained 85 per cent water. Hence, the yield of dry pulp was 412.5 grams or 41 per cent. Several methods of beating and bleaching were tried. Beating was imitated fairly successfully by grinding in a ball mill until the woody portions were disintegrated and the resulting pulp was a uniform paste. Both pulps were bleached by the Rue and Sconce method (IO), using varying amounts of chlorine in the acid bleach and 1 per cent in the alkaline bleach. After bleaching, the first wash water was made just acid. In the case of the soda pulp, the best result was obtained with 10 per cent of chlorine in the acid bleach;
Alpha-cellulose Beta-cellulose Gamma-cellulose Ash Total
81.4 0.3 8.2 8.8 98.7
Nitric Acid Pulp 89.8 87.0 1.2 2.5 2.6 4.1 6.3
9s.e
6
3
99.9
The high ash content of the pulps is due to the methods of harvesting and unprotected storage. If the ash is neglected, the alpha-cellulose for the soda pulp is 90.5 per cent and for the nitric acid pulp, 95.5 and 94.0 per cent.
Conclusions These results indicate that it is feasible to make a pulp with an alpha-cellulose content suitable for rayon and other industrial uses from the whole cotton plant. It is possible to recover a merchantable oil in good yields from the ground plant; the resulting extracted plant, because of the absence of water-repellent oils and waxes, is in an excellent condition to absorb the pulping solution. For this reason, boiling under pressure is not essential as with wood chips. I n any commercial development it n7ill be important to harvest and store the material under conditions which will keep contaminating sand and dust a t a minimum. There is no problem of deterioration on storage. The results obtained with the nitric acid process harmonize with those obtained by Payne (9) and by Hachihama, Onishi, and Takemura (4) on bagasse, and suggest that a better yield and a purer alpha-cellulose are obtained by this process than by the usual pulping methods. These results suggest further that the nitric acid process is especially effective for lignocellulose material.
Acknowledgment Acknowledgment is made to Nicholas W. Dockery of Rockingham, N. C., for supplying the plant material used in this work.
Literature Cited Bray, M. W., and Andrews, T. M., IND. ENQ. CHEW, 15, 377 (1923). Clifford, A. T., and Cameron, F. K., Ibid., 26, 1209 (1934). Golova, 0. P., Iskusstuennoe Volokno, 5, No. 6, 10 (1934). Hachihama, Y . , Onishi, M., and Takemura, W., J. SOC.Chem. I n d . J a p a n , 38, Suppl. binding, 690 (1935). Korzheniovskii, G. A., and Raskina, R. L., Treat Kblopkw chistiteloni Prom. (Cotton Inrl. Trust), Collection of papers No. 1, 124 (1933). Lur'e, A. I., Bumarhnaya Prom., 13, No. 3, 61 (1934). Lynch, D. F. J., and Goss, M. J., IND. ENQ.CHEM.,24, 1249 (1932). Macormac, A. R., Thesis, Univ. N. C., 1936. Payne, J. H., IND.EIYG.CHEM.,26, 1339 (1934). Rue, J. D., and Sconce, J. S., Paper Trade J . , 95, No. 17, 54 (1932). Sanders, J. P., and Cameron, F. K., IND. ENG. CHEIM.,25, 1371 (1933). Shikata, M., and Akagi, K., J . Agr. Chem. SOC.J a p a n , 11, 635 (1935). Yakimanskii, V. V . , Materiali Vsasoyuz. Nauch.- Issledmatel Inst. Bumazh. Tsellguloz. Prom., 1932, No. 4, 21.
RECEIVED July 28, 1936. Presented before the Division of Cellulose Chemistry a t the 92nd Meeting of the American Chemical Society, Pittsburgh, Pa.,September 7 to 11, 1936.
