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.