A new synthetic method of cellulose triacylate in the carboxylic acid-LiCl and -CaCl_2 systems

摘要

A new method for synthesizing cellulose triacylates using the carboxylic acid-LiCl and -CaCl_2 systems was developed. Cellulose triacylates such as cellulose triacetate, tripropionate, tributyrate and acetate butyrate were synthesized under a heterogeneous reaction condition, using the carboxylic acid-carboxylic acid anhydride-LiCl and -CaCl_2 systems. Cellulose triacete samples were synthesized at 20 ℃ for the system with LiCl, and also at 65 ℃ for the system with CaCl_2. Cellulose acetate butyrate was also synthesized in the acetic acid- LiCl-butyric anhydride system at 40 ℃ in the system with the molar ratio (1:1) of acetic acid to butyric anhydride. The chemical structures of cellulose acylate samples were analyzed by Fourier transform infrared spectroscopy (FTIR). The FTIR spectra indicated that cellulose triacylates (degree of substitution, D.S = 3.0) could be obtained. The ~1H NMR spectrum of the above cellulose acetate butyrate sample showed that the degrees of substitution of acetyl and butyryl groups in cellulose molecules were 1.56 and 1.44, respectively. The number and mass average molar masses (M_n and M_w) and their distributions (M_w/M_n) were measured by gel permeation chromatography (GPC). The values of M_n and M_w/M_n for cellulose triacylate samples were as follows: triacetate, 2.76 x 10~5 (M_n) and 2.12 (M_w/M_n); tripropionate, 2.84 x 10~5 (M_n) and 1.86 (M_w/M_n); tributyrate, 2.95 x 10~5 (M_n) and 2.01 (M_w/M_n); and acetate butyrate, 2.80 x 10~5 (M_n) and 2.20 (M_w/M_n). The thermal properties of the obtained samples with different reaction times were studied by differential scanning calorimetry (DSC) and thermogravimetry (TG). The glass transition temperatures (T_g's) of cellulose triacetate, tripropionate, tributyrate and acetate butyrate were ca. 181.6, 124.0, 90.9 and 128.6 ℃, respectively. The thermal decomposition temperatures (T_d's) increased from ca. 335 to 350 ℃ after acylation of cellulose. Activation energies of thermal decomposition in the initial step (E's) also increased from ca. 184 to 196 kJ/mol after acylation of cellulose.