Study On The Degradation Of Cotton Cellulose To Low Polymerization Degree Glucans In Phosphoric Acid Medium

In this work, the raw cellulose material was tailored in phosphoric acid medium,which was designed to keep the same chemical structure as the raw cellulose and decreased its molecular weight by hydrogen ion. The water-insoluble glucans had obtained with the average degree of polymerization(DP) 108 as the following condition: 7g cotton cellulose,60 mL 85wt% phosphoric acid, reaction temperature 55°C, reaction time 8h, and water as the precipitant. The water-soluble glucans with DP≈7 were gotten, and the better reaction conditions were as follows: 7g cotton cellulose, 60 mL 85wt% phosphoric acid, reaction temperature 55°C, reaction time 10 h, and acetone as the precipitant. The degradation methods were investigated on the basis of the cotton cellulose degradation in phosphoric acid medium, and the experimental results indicated that the two-step method, which mean the method of speeding up the reaction rate and the method of slowing down the rate reaction, didn’t make an effect on the preparation of glucans with DP10~100. This indicated that only the glucans with DP100~140 could be obtained from the progress of cotton cellulose degradation in phosphoric acid medium to prepare the water-insoluble glucans. Methanol, ethanol, acetone and tetrahydrofuran were selected as the precipitant to investigate the DP change of the precipitation products. Compared with acetone and tetrahydrofuran, methanol and ethanol as the precipitant could prepare the glucans with the better homogeneous DP. The glucans with the better homogeneous DP60~100 could be prepared by controlling the species of precipitant, the volume ratio(R) of precipitant to degradation solution of phosphoric acid and cellulose and reaction time.The glucans with DP10~60 weren’t obtained in this experiment, it was believed that the DP10~60 glucans degraded to water-soluble glucans(DP≤7) quickly. The generation rate of the water-soluble glucans was investigated, the rate constants(k) at 50°C, 55°C and60°C were 0.075h-1, 0.100h-1 and 0.125h-1 respectively, the average activation energy was45.72kJ·mol-1 at the reaction temperature 50~60°C. This suggested that the average activation energy in the process of cotton cellulose degradation in phosphoric acid medium was comparatively low, which resulted in the reaction rate of degradation of DP10~60glucans to water-soluble glucan quickly.The molecular weight distribution was estimated by gel permeation chromatography(GPC) before and after degradation, the variation of cellulose molecule structure andcrystallinity index was comparatively characterized by FT-IR and X-ray diffractometer(XRD). The experimental results showed that the cellulose didn’t generated new functional groups after the hydrothermal treatment, a part of hydrogen bonding in cellulose molecules were disrupted, DP and crystallinity index of cellulose was reduced according to the designed reaction route and the chemical structure of cellulose was kept steadily.