Syntheses of cellulose branched ester derivatives and their properties and structure analyses

Traditionally, cellulose linear acyl esters such as cellulose acetate or cellulose propionate have been used as thermo-plasticized materials from renewable resources for decades. The properties of these kinds of cellulose esters can be varied by changing carbon number (C) of acyl substituents. In this study, a series of cellulose ester derivatives with branched acyl substituents were synthesized by the heterogeneous reaction, and their thermal, mechanical, and structural properties were investigated in comparison with cellulose linear acyl esters. All cellulose branched esters have crystallinity, and tended to show higher melting temperature and glass transition temperature than those of cellulose linear esters with the same C number. Cellulose isobutyrate (branched ester, C = 4) had especially high melting temperature (248 degrees C) compared with those of cellulose linear esters such as cellulose butyrate (C = 4, 182 degrees C) and cellulose propionate (C = 3, 235 degrees C). Colorless and transparent films of cellulose branched esters were fabricated by solvent-casting method. These films showed harder and less flexible properties than those of cellulose linear esters. Structural analyses were conducted by 1D- and 2D-WAXD measurements. Crystal lattice parameters and molecular conformation with 3-fold screw symmetry of cellulose isobutyrate indicated that it has similar crystal structure with cellulose propionate, which could cause high melting temperature and high tensile strength of cellulose isobutyrate. Thus, material properties of cellulose acyl esters can be controlled not only by carbon number of acyl substituents but also by branching structure of acyl groups. (C) 2018 Elsevier Ltd. All rights reserved.