PLASTICIZATION OF BARLEY STARCH WITH GLYCEROL AND WATER

Barley starch was plasticized in a melt mixer using glycerol and water as plasticizers. Plasticizer concentration, time, temperature, and sh ear were varied, and their effects on the molecular weight of starch a nd the glass transition temperature and mechanical properties of the m ixtures were studied. Depolymerization of amylopectin was observed in all experiments, and starch degradation proceeded further at low glyce rol concentrations. The glass transition of the plasticized starch-gly cerol mixtures occurred in the temperature range -50 to -100 degrees C and was probably induced by glycerol, not by starch. The tensile stre ngth 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 degrees C.