Synthesis and characterization of dextrin derivatives by heterogeneous esterification

A series of fully-acylated dextrin esters (DS = 3) with varying side-chain lengths (C2-12) were synthesized by heterogeneous esterification using trifluoroacetic anhydride/carboxylic acid. The influence of side-chain lengths on structure and properties of dextrin esters were investigated by structural, thermal, mechanical and hydrophobic analysis. The thermal stability of dextrin was enhanced by esterification, presenting ca. 40-60 degrees C higher decomposition temperatures than that of neat-dextrin. The transition temperatures of melting and crystallization were not observed for all dextrin esters because they were amorphous polymers. The glass transition temperature (T-g) was not observed in dextrin but was observed in dextrin esters. As increasing side-chain length, T(g)s of dextrin esters decreased ranged from 162.2 degrees C (C2) to 49.2 degrees C (C12). Colorless and transparent dextrin ester films were prepared to measure the film properties. Tensile strength of dextrin ester films tended to decrease with increasing side-chain lengths, whereas the elongation at break increased. And, dextrin ester films showed significantly increased hydrophobicity with a contact angle of up to 102 degrees (C12).