Sodium Hexametaphosphate-Modified Thermoplastic Starch Materials Prepared with the Assistance of Supercritical CO2

This paper describes sodium hexametaphosphate (SHMP)-modified thermoplastic starch (TPS) resins (scCO 2 TPS 100 SHMP x ) gelatinized and/or modified with the aid of supercritical carbon dioxide (scCO 2 ). TPS and scCO 2 TPS 100 SHMP x exhibit considerably higher melt flow rates, moisture resistance, and initial and retention tensile strength values than TPS and TPS 100 SHMP x prepared using conventional atmospheric pressure. Only V h -type crystals are found in conditioned scCO 2 TPS 100 SHMP x , which show significantly lower melting temperatures (≈19 °C) than the corresponding conditioned TPS 100 SHMP x . Relative to TPS 100 SHMP x , conditioned scCO 2 TPS 100 SHMP x show a weaker hydrogen bonding network among the hydroxyl groups in the amylopectin chains and considerably less retrogradation. The loosely hydrogen-bonded hydroxyl groups found in conditioned scCO 2 TPS 100 SHMP x can be replaced with stronger hydrogen bonds involving the phosphate groups of SHMP through the proper modification of scCO 2 TPS 100 SHMP x .