[01] Le Quang Dien, Department of Cellulose and Paper Technology, School of Chemical Engineering, Hanoi University of Science and Technology, Hanoi, Vietnam. [02] Thai Dinh Cuong, Department of Cellulose and Paper Technology, School of Chemical Engineering, Hanoi University of Science and Technology, Hanoi, Vietnam. [03] Phan Huy Hoang, Department of Cellulose and Paper Technology, School of Chemical Engineering, Hanoi University of Science and Technology, Hanoi, Vietnam. [04] Doan Thai Hoa, Department of Cellulose and Paper Technology, School of Chemical Engineering, Hanoi University of Science and Technology, Hanoi, Vietnam. [05] Luu Trung Thanh, Faculty of Paper Technology, Vocational College of Paper Technology and Electro-Mechanics, Phu Ninh District, Phu Tho Province, Vietnam.

Two-stage treatment of rice straw was used for preparation of cellulosic pulp containing high content of alpha cellulose, which can be used for production of dissolving cellulose. First, rice straw was pre-hydrolyzed by sulphuric acid solution under the conditions of liquor-to rice straw ratio of 8:1 (ml/g), temperature of about 100°C in 40-45 min. reaction time. Then, pre-hydrolyzed rice straw was treated by Kraft pulping process using sodium hydroxide solution combined with sodium sulphide, with active alkaline dosage of 6.5% (w/w), at temperature of 95-100°C for 95-100 min. After hydrolysis stage, the yield of reducing sugar of 15.2-15.4% (w/w) over dry starting material was obtained. Reducing sugar hydrolysate was analyzed by HPLC showing that the reducing sugars consist of 96% of arabinose and 4% of glucose, which could be converted to bio-ethanol or furfural. The yield of cellulosic pulp of 36.3% (w/w) was achieved in Kraft pulping process which contains 78.7% alpha cellulose. Cellulosic pulp that was obtained after Kraft pulping was then treated by ECF bleaching and sodium hydroxide purification. This stage resulted in yield of 26.4% over dry rice straw with whiteness of 88% ISO and alpha-cellulose content of 86.8%. Moreover, the changes of fibre morphology after treatment of rice straw were revealed by the microscopic observations performed by Scanning Electron Microscope (SEM).

Rice Straw, Acid Hydrolysis, Kraft Pulping, Dissolving Cellulose, Fibre

[01] David N.S. H., Nobuo S., 2000. Wood and Cellulosic Chemistry, CRC Press; 2 edition, 928ps. [02] David I., Viviana K., Monica E., 2010. Behavior of different monocomponent endoglucanases on the accessibility and reactivity of dissolving-grade pulps for viscose process, Enzyme and Microbial Technology 47, 355–362. [03] Herbert S., 2006. Handbook of Pulp, Vol. 1-2, Wiley-VCH Verlag GmbH & Co. KGaA. [04] David I., Viviana K., Per Tomas L., Anna-Stiina J., Monica E., 2010. Combination of alkaline and enzymatic treatments as a process for upgrading sisal paper-grade pulp to dissolving-grade pulp, Bioresour. Technol., 101, 7416–7423. [05] Christov, L.P., Prior, B.A., 1993. Xylan removal from dissolving pulp using enzymes of Aureobasidium pullulans. Biotechnol. Lett. 15, 1269–1274. [06] Behin, J., Zeyghami, M., 2009. Dissolving pulp from corn stalk residue and waste water of Merox unit, Chem. Eng. J., 152, 26–35. [07] Treiber E, Nevell T.P., Zeronian S., 1985. Formation of fibers from cellulose solutions. In: Cellulose chemistry and its applications. Chichester: H. Ellis Horwood Ltd.; p. 456–57. [08] Future Biorefineres products from dissolved cellulose, Programme Report, Copyright Finnish Bioeconomy Cluster FIBIC, 2013. [09] Christov, L.P., Akhtar, M., Prior, B.A., 1998. The potential of bisulfite pulping in dissolving pulp production, Enzyme Microb. Technol. 23, 70–74. [10] Hinck, J.F., Casebier, R.L., Hamilton, J.K., 1985. Dissolving Pulp Manufacture. Pulp and Paper Manufacture, Technical Section Canadian Pulp and Paper Association, pp. 213–243. [11] Ning W., Chen H. Z., 2013. Manufacture of dissolving pulps from cornstalk by novel method coupling steam explosion and mechanical carding fractionation, Bioresour. Technol., 139, 59–65. [12] Reddy, N., Yang, Y., 2005. Biofibers from agricultural byproducts for industrial applications. Trends Biotechnol. 23, 22–27. [13] Rodríguez, A., Serrano, L., Moral, A., Pérez, A., Jiménez, L., 2008. Use of high-boiling point organic solvents for pulping oil palm empty fruit bunches, Bioresour. Technol. 99, 1743–1749. [14] Hurter, R.W., Riccio, F.A., 1998. Why CEOS don’t want to hear about nonwoods-or should they? in: TAPPI Proceedings, NA Nonwood Fiber Symposium, Atlanta, GA, USA, pp. 1–11. [15] Ververis, C., Georghiou, K., Christodoulakis, N., Santas, P., Santas, R., 2004. Fiber dimensions, lignin and cellulose content of various plant materials and their suitability for paper production, Ind. Crops Prod. 19, 245–254. [16] Ek M., Gellerstedt G., Henriksson G. (2009). Pulp and Paper Chemistry and Technology. [17] Miller G.L. (1959). Analytical Chem., 31, 426. [18] Garrote, G., Eugenio, M.E., Díaz, M.J., Ariza, J., López, F., 2003. Hydrothermal and pulp processing of Eucalyptus, Bioresour. Technol. 88, 61–68. [19] Dien, L.Q., Phuong, N.T.M., Hoa, D.T., Hoang, P.H., 2015. Efficient Pretreatment of Vietnamese Rice Straw by Soda and Sulfate Cooking Methods for Enzymatic Saccharification, Appl. Biochem. Biotechnol. 175, 1536–1547. [20] Rahmawati, N., Ohashi, Y., Honda, Y., Kuwahara, M., Fackler, K., Messner, K., Watanabe, T., 2005. Pulp bleaching by hydrogen peroxide activated with copper 2,2-dipyridylamine and 4-aminopyridine complexes, Chem. Eng. J. 112, 167–171.