States of Water in Cellulose Hydrogels and Influence on the Crystallization of Cellulose†

doi:10.7503/cjcu20150528

Abstract

Abstract:

A study inspired by biosynthesis of cellulose in higher plant was made on an attempt to investigate the state of water in cellulose hydrogels and its influence on the crystallization of cellulose. The differential scanning calorimetry(DSC) results indicate that there are 3 types of water in cellulose hydrogels: nonfreezing water, freezing bound water and free water. The ratio of the nonfreezing water to dry cellulose in the hydrogels is about 1.6 g/g, 5 times more than the adsorbed water in dry cellulose. In such a highly hydrated state, the aggregation and crystallization of cellulose are inhibited, the lower the water content, the completer the crystallization of cellulose, which is characterized by X-ray diffraction(XRD), polarizing optical microscope(POM) and scanning electron microscopy(SEM). It is suggested that the little inhibition effect of nonfreezing water on the crystallization is due to the instability of the hydrogen bond between the water and cellulose. The results demonstrate the high content of nonfreezing water in cellulose hydrogels.

Key words: Cellulose, Bound water, Hydrogen bond, Crystallization

CLC Number:

O636.1

TrendMD:

CHEN Feng, LIU Zhengying, HUA Sun, KAN Ze, YANG Mingbo. States of Water in Cellulose Hydrogels and Influence on the Crystallization of Cellulose^†[J]. Chem. J. Chinese Universities, 2015, 36(10): 2034.

Figures/Tables 8

Fig.1 Digital photographs of the preparation(A) and stewing for 24 h(B) of cellulose hydrogel

Fig.2 Freezing(A) and heating(B) DSC curves of the cellulose hydrogels with different water contentsWater content(%): a. 30; b. 46; c. 50; d. 59; e. 70; f. 81; g. 90; h. 91.

Table 1 Information obtained from endotherm(heating trace)*

w_c(%)	(m_w/m_d)/(mg·mg^-1)	ΔH/(J·g^-1)	TFW/(mg·mg^-1)	NFW/(mg·mg^-1)
10	0.111		0	0.111
30	0.429		0	0.429
46	0.579	24.69	0.117	0.462
50	1.000	39.82	0.238	0.761
59	1.445	70.90	0.514	0.931
70	2.333	104.50	1.044	1.289
81	4.263	165.00	2.604	1.659
90	9.000	245.30	7.355	1.645
91	10.111	253.50	8.448	1.665

Fig.3 Variation of the quantity of nonfreezing bound water and that of the total freezable water content in cellulose(A) and comparison of the saturated nonfreezing bound water content in cellulose hydrogels and water-associated cellulose(B)GEL means cellulose hydrogels in our study, CEL means water-associated dry cellulose, the data was derived from a study by Park et al.[7].

Fig.4 XRD patterns of the cellulose hydrogels during the drying processWater content(%):a. 30; b. 46; c. 50; d. 59; e. 70; f. 81; g. 90; h. 91.

Fig.5 Polarizing microscope images of cellulose hydrogelTest time/min: (A) 0; (B) 5; (C) 15; (D) 25; (E) 60.

Fig.6 SEM images of cross-section morphology of cellulose samples prepared by freeze-dryingWater content(%): (A)91; (B) 81; (C) 70; (D) 50; (E) 46; (F) 30.

Fig.7 Pore size of cellulose samples prepared by freeze-drying

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