Plasticization of Barley Starch with Glycerol and Water

Abstract

Barley starch was plasticized in a melt mixer using glycerol and water as plasticizers. Plasticizer concentration, time, temperature, and shear were varied, and their effects on the molecular weight of starch and the glass transition temperature and mechanical properties of the mixtures were studied. Depolymerization of amylopectin was observed in all experiments, and starch degradation proceeded further at low glycerol concentrations. The glass transition of the plasticized starch-glycerol mixtures occurred in the temperature range −50 to −100°C and was probably induced by glycerol, not by starch. The tensile strength of a starch plate containing 29 wt% glycerol was about 0.5 MPa 1 week after molding, but increased to 2–3 MPa during 5 weeks of storage at 50% relative humidity and 24°C.