Thermal and mechanical properties of tailor-made unbranched α-1,3-glucan esters with various carboxylic acid chain length

The convenient and environmentally friendly method for in vitro polymerization catalyzed by glucosyltransferase, designated as GtfJ, extracted from recombinant E. Coli was used to synthesize tailor-made α-1,3-glucan (α-1,3-D-glucan) having moderate molecular weight (M_w = 2.0 × 10⁵) and no branches. With the aim to improve thermoplasticity of this polysaccharide, after in vitro synthesis, chemical modification by acylation was selected and then fully substituted α-1,3-glucan esters were successfully obtained via both homogeneous and heterogeneous methods. Thermal degradation temperature of α-1,3-glucan esters was improved after esterification and dependent on neither side chain length nor synthesis methods. DSC curves suggested a presence of crystal structure in α-1,3-glucan acetate, propionate, butyrate, valerate and hexanoate due to detectable melting endotherm, whereas octanoate exhibited amorphous behavior. T_m’s of α-1,3-glucan esters were relatively high, more than 200 °C, in comparison with commercial plastics. The shorter chain length of acid component, the higher T_m and T_g ester products exhibited. In addition, tensile strength of α-1,3-glucan esters decreased in contrast with elongation at break with an increase in alkyl chain length of an acid component. Thus, crystalline and amorphous α-1,3-glucan esters with adjustable thermal and mechanical properties obtained from this research are promising materials for continuing applied researches and contemplating the future application in bio-based thermoplastic materials.