Controlled preparation of cellulose acetate by deep eutectic solvent homogeneous catalysis

Abstract

This work proposed a homogeneous preparation strategy of cellulose acetate by using a deep eutectic solvent consisting of zinc chloride/phosphoric acid/water (ZnCl₂/PA/H₂O). The results showed that the DES (the molar ratio of ZnCl₂: PA: H₂O = 1:1:3) had good solubility for bamboo pulp with high degree of polymerization. The dynamic dissolution behavior of cellulose in DES was also studied. Cellulose was first moistened and swollen and then dissolved. The crystalline state of cellulose changed from type I to type II after regeneration. Under the synergistic effect of acetic anhydride (Ac₂O), the dissolved cellulose in DES could be uniformly acetylated. The effects of temperature, reaction time and molar ratio of Ac₂O/anhydrous glucose on degree of substitution (DS) were investigated in their respective ranges (30–50 °C, 2–10 h and 4–24). Cellulose acetate with DS of 0.42–1.81 was successfully prepared. The substituent distribution of the sample was analyzed as C-6 > C-2 > C-3. Moreover, the entire process required no additional catalysts or activation steps, reducing the difficulty of solvent recovery. The insight from this study provides a new idea for the development of greener methods for the homogeneous preparation of cellulose acetate.