Role of urea in alkaline dissolution of cellulose
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ORIGINAL PAPER
Role of urea in alkaline dissolution of cellulose Noriyuki Isobe • Keiichi Noguchi • Yoshiharu Nishiyama • Satoshi Kimura Masahisa Wada • Shigenori Kuga
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Received: 3 August 2012 / Accepted: 4 October 2012 / Published online: 19 October 2012 Ó Springer Science+Business Media Dordrecht 2012
Abstract To elucidate the role of urea in dissolution of cellulose in aqueous alkali-urea solvent, the dissolution process was monitored by differential scanning calorimetry and X-ray diffractometry. Urea had no direct interaction with cellulose in dissolution process, but promoted the decrease of crystallinity. Moreover, the addition of urea increased the dissolved fraction of cellulose in the solvent by 1.5–2.5 times and improved the thermal stability of the solution. Urea might help alkali hydrate to penetrate into crystalline region of cellulose by stabilizing the alkali-swollen cellulose molecules, leading to an increase in dissolved fraction
N. Isobe (&) S. Kimura M. Wada S. Kuga Department of Biomaterials Science, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113-8657, Japan e-mail: [email protected] S. Kimura M. Wada Department of Plant and Environmental New Resources, College of Life Sciences, Kyung Hee University, 1 Seocheon-dong, Giheung-gu, Yongin-si, Gyeonggi-do 446-701, Republic of Korea K. Noguchi Institute of Symbiotic Science and Technology, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588, Japan Y. Nishiyama Centre de Recherches sur les Macromolecules Vegetales (Affiliated with Joseph Fourier University of Grenoble), CNRS, B.P. 53, 38401, Grenoble Cedex 9, France
of cellulose. This stabilization may be due to the local accumulation of urea on the hydrophobic surface, preventing the hydrophobic association of dissolved cellulose molecules. Keywords Alkali/urea solvent Dissolution DSC X-ray diffractometry Solubility
Introduction The strong action of caustic alkalis to cellulose has been exploited in textile processing (Warwicker et al. 1966). Depending on alkali concentration and temperature during the swelling process, cellulose forms several types of crystalline alkali complexes known as Na-cellulose I, II, III, and Q (Sobue et al. 1939; Okano and Sarko 1984; Nishimura et al. 1991; Porro et al. 2007). Of these, the condition of Na-cellulose Q (named after Qwellung = swelling in German) actually was known to be accompanied by high degree of swelling and partial dissolution of cellulose (Sobue et al. 1939), and has attracted special attention. Dissolution of cellulose in this Q region of the pseudo phase diagram (Sobue et al. 1939), i.e. 8–10 % NaOH or 5–10 % LiOH at -5 °C*5 °C (Yamashiki et al. 1988) was studied intensively as possible alternative to viscose or copper-ammonia solvent (Hongo et al. 1996; Yamane et al. 1996; Isogai 1997a, b). The Q
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range dissolution, however, required certain pretreatments for complete dissolution of native cellulose such as steam explosion, wet ball mi
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