The Relationship between Starch Gelatinization and Morphology Control in Melt‐Processed Polymer Blends with Thermoplastic Starch

Critical aspects of starch plasticization in glycerol/excess water mixtures are analyzed in order to determine the time/temperature boundaries ultimately required for the successful plasticization of starch in a polymer melt‐processing environment. These findings are then related to the morphology of melt‐blended TPS in PCL. The onset and conclusion temperatures for wheat starch gelatinization in the presence of various excess water/glycerol mixtures were obtained. Dynamic studies of wheat starch gelatinization show that if the temperature is sufficiently high, gelatinization takes place within 60 s for the excess water/glycerol/wheat starch mixture and within 3 min for the glycerol/wheat starch case. Morphological studies indicate the inability of glycerol alone to plasticize native starch within the time constraints of melt extrusion. The efficacy of plasticization is demonstrated by a dramatic six‐fold reduction in the dispersed TPS phase size and a unimodal TPS phase size distribution in the blend system.