Free-solvent Synthesis and Properties of Higher Fatty Esters of Starch — Part 2

Abstract

A solvent-free synthesis and the properties of esters of starch from different sources (maize, waxy maize, Eurylon 7, potato, wheat, rice, amylose, and amylopectin) and higher fatty acids are described. Higher fatty acid esters (C8-C18) of potato starch were synthesized by chemical gelatinization using formic acid, followed by treatment with fatty acid chlorides. Esterification was readily carried out at 105°C and a reaction time of 40 min. Formic acid permits esterification of starch by longchain acid chlorides with minimum degradation. The results indicated that the degree of substitution of the starch esters diminishes with increase in fatty acid chain length. All starch esters have a hydrophobic character which rises with length of the fatty side chain. X-ray and Differential Scanning Calorimetry (DSC) showed that the fatty acid side chains (Cn > 16) grafted onto starch form cristallites between them. This phenomenon provokes the decrease of elongation at break for these starch esters. On the other hand, the tensile strength at break and thermal stability of fatty esters of starch increase both with a higher fatty chain grafted onto starch.