Acid hydrolysis of composites based on corn starch and trimethylene glycol as plasticizer

Abstract

Corn starch-based films with trimethyilene glycol (1,3-propanediol) as plasticizer were prepared with the casting technique and subject to acid hydrolysis (HCl 1.0 M) at 20 oC. The film degradation was monitored by changes in surface morphology, crystallinity, thermal properties and surface wettability. In the first two days, the hydrolysis showed low advance to subsequently exhibit a huge increase of the reaction rate. It suggested that surface erosion is the main mechanism involved in the film degradation. XRD showed the presence of poly-1,3-propanediol, attributed to condensation reaction of plasticizer in acidic conditions. Thermal analysis showed two endothermic peaks at 110-120 oC attributed to melting of crystallized amylopectin and to a lesser extent co-crystallized amylose and amylopectin. The temperature of these peaks was not affected by hydrolysis time, supporting the idea that hydrolysis reactions are constrained to the film surface. Contact angle measurements indicated a significant decrease of hydrophobicity caused by fractionation of starch chains.