Effects of calcium carbonate as the expanding inhibitor on the structural and mechanical properties of expanded starch/polyvinyl alcohol blends

In this study, expanded starch/PVA/CaCO3 blends (ESPCs) were prepared using the pilot system composed of a supermixer and a twin-screw extruder to investigate the effects of CaCO3 as the expanding inhibitor on the structural and mechanical properties of ESPCs. The pore ratio of ESPCs with the interconnecting open-cell structure decreased with increasing CaCO3 content and the structure of ESPCs became more compact. The inhibiting process of CaCo3 during the expansion of starch/PVA blends was proposed and certified by FTIR spectroscopy and X-ray diffraction. At least two parts of CaCO3 were required to obtain a sufficient inhibiting effect on the expansion. The mechanical properties of ESPCs such as tensile strength, elongation at break, modulus, and specific work of rupture were improved by the addition of CaCO3 as the expanding inhibitor. As CaCO3 content increased from one to four parts, the tensile strength increased 2.6-fold, from 70 to 180 kPa, whereas elongation at break increased about 1.5-fold. The moduli of ESPCs also increased with increasing CaCO3 content. (C) 2004 Wiley Periodicals, Inc.