Synthesis and thermal properties of paramylon mixed esters and optical, mechanical, and crystal properties of their hot-pressed films.

Acylation of paramylon, a storage polysaccharide of Euglena gracilis, using multiple acid anhydrides yielded thermoplastic paramylon mixed esters without significant depolymerization. DSC examination showed that the shorter the acyl chain, the higher both the melting and glass transition temperature of the ester. TG analyses revealed their higher thermostability with the 5% weight loss temperature of ∼330°C. Melt volume flow rate examination revealed that the longer the acyl chain, the higher the thermoplasticity of the ester and that the esters exhibited higher thermoplasticity than structurally analogous esters made from cellulose and curdlan. A notable feature of the thermoplastic paramylon mixed esters is the availability of hot-pressing as a means of molding them into a film. Light transmittance and XRD measurements revealed that these films were transparent and in the amorphous state. Tensile tests indicated that the films had adequate mechanical strength comparable to those of the cellulose and curdlan analogues.