Preparation and characterization of cellulose derivatives by regioseleclive esterification of biodegradable cyclic esters

New cellulose derivatives were prepared by the regioselective derivatization of cellulose with L-lactide (LA) and ε-caprolactone (CL) in a lithium chloride/N, N-dimethylacetamide solvent system, and investigated for their characteristics by spectroscopic analyses, calorimetry, solvent solubility/enzymatic degradability tests. Fourier transform Raman spectra of cellulose derivatives confirmed that the LA and CL molecules were covalently introduced into cellulose at the hydroxyl groups through the ring-opening esterification catalyzed by LiCl. The ¹³C nuclear magnetic resonance analysis indicated that the ring-opened LA and CL were regioselectively combined with cellulose C6-OH. Moreover, LA and CL portions were partially grafted on the cellulose backbone, like a comb-shaped architecture. Both cellulose derivatives were highly soluble in dimethyl-sulfoxide available for material forming. A part of cellulose-LA was swollen or soluble in water, while cellulose-CL had poor affinity for water. The solvent solubility depended on the introduced amounts of cyclic esters. Enzymatic degradation of cellulose derivatives immediately occurred by the cellulase treatment even under the mild conditions that commercial cellulose diacetate could not be hydrolyzed. The cellulose derivatives also showed thermodynamic characteristics. Thus, the cellulose derivatives prepared in this study are expected as a biomass-based eco-material in practical applications.