Recrystallization behavior of cellulose III from hydrothermal treatment: the dynamic variations of polymorphs and crysta
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Recrystallization behavior of cellulose III from hydrothermal treatment: the dynamic variations of polymorphs and crystallinities Long Feng1 · Zhe Ling2 · Jianfeng Ma1 · Xinge Liu1 · Zehui Jiang1 Received: 8 May 2020 / Published online: 18 September 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The application of cellulose fibers with varieties of allomorphs is of much interest. However, the crystal structural changes of certain allomorphs during the wet chem‑ istry process are often ignored. In this work, the recrystallization behavior of soft‑ wood pulp cellulose IIII back to cellulose Iβ with tg conformation by hydrothermal treatment at different temperatures is carefully evaluated and calculated. The treat‑ ment contributed to the distortion of crystallites and lower crystallinity including the formation of intermediate amorphous phase at 60 °C. Higher hydrothermal tem‑ perature (100 °C) resulted in the reversion to cellulose I (59.7%) as well as retention of 12.5% of cellulose III, suggesting the uncompleted recrystallization during the process. With the loosened fibril structure and more amorphous regions, the thermal stability of recrystallized cellulose I is significantly dropped, far below that of origi‑ nal cellulose I/III materials. This study may provide new thoughts on the industrial processing and application of the polymorphic cellulose materials.
Introduction Crystalline cellulose has been proved to exhibit specific allomorphs (cellulose Iα, Iβ, II, III and IV) due to their different crystal structures. Cellulose III is the allomorph obtained from liquid ammonia swelling or amine treatment of cellulose I and cellu‑ lose II, which results in cellulose IIII and cellulose IIIII, respectively (Salminen et al. 2017; Wada et al. 2006). Depending on the original allomorph before conversion, * Zehui Jiang [email protected] Long Feng [email protected] 1
Key Lab of Bamboo and Rattan Science and Technology, International Center of Bamboo and Rattan, Beijing 100102, China
2
Jiangsu Co‑Innovation Center of Efficient Processing and Utilization of Forest Resources, College of Chemical Engineering, Nanjing Forestry University, Nanjing 210037, China
13
Vol.:(0123456789)
1606
Wood Science and Technology (2020) 54:1605–1616
cellulose IIII has parallel chains similar to cellulose I, while cellulose IIIII shows the antiparallel chains as in cellulose II. Cellulose III is reported to have monoclinic structure with P21 space group (a = 10.25 Å, b = 7.78 Å, c = 10.34 Å, γ = 122.4°) (Sarko et al. 1976; Wada et al. 2004; Liang et al. 1993). The conformation of exo‑ cyclic hydroxymethyl groups is featured in cellulose III, which is gauche to O5 and trans to C4 (gt) rather than trans to O5 and gauche to C4 (tg) as in common cellu‑ lose I allomorph (Funahashi et al. 2017). Recently, the application of cellulose III material was studied as well as other allomorphs. The crystal allomorphic transformation after liquid ammonia pretreat‑ ment was believed to improve the enzymat
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