Physical Properties of Thermoplastic Cassava Starches Extruded from Commercial Modified Derivatives in a Pilot Scale

Abstract

Properties of thermoplastic starch (TPS) produced from commercial-grade modified cassava starches were investigated in a pilot scale for future practical production in plastic industry. Five types of commercial cassava starches including native, oxidized, acetylated, octenyl succinate and pregelatinized starches were transformed into TPS by extrusion. The morphology implied that degree of destructuration could be manipulated by adjusting amount of glycerol of the starch melt. All types of TPS exhibited strong water sensitivity especially when exposed to humid atmosphere (>0.75 water activity). Compared among these selected five commercial cassava starches, there were no significant differences in sorption properties. Tensile strength of the thermoplastic starches increased with increasing starch content, and a drastic gain was recorded for 80% starch content for all types of starches. The elongation at break seemed to reach a maximum value for native TPS and pregelatinized TPS when composition of starch was 70%. The concavity of elongation at break of both TPS’s could arise from greater mobility of starch molecules during deformation due to the presence of glycerol and water, so that the properties shifted from glassy to more fluid-like. When compared among the types of modification, pregelatinized starch produced a highly elongated TPS with lowest strength due to its complete destructuration of starch granules, and the octenyl succinate starch yielded the highest strength and most brittle TPS. This study proved that cassava starch had a considerable potential to further developed for biodegradable applications but higher degree of modification than these of common commercial grade was required to improve water resistance of its thermoplastic starch.