Analysis of the Thermal Behavior of Poly(lactic acid)/ Montmorillonoid (I.34TCN) Composites

Abstract

To investigate the occurrence of recrystallization of poly(lactic acid) (PLA), the complex thermal behavior of pure PLA and PLA composites (1 wt % montmorillonoid (I.34TCN)/PLA, 2 wt % I.34TCN/PLA, 3 wt % I.34TCN/PLA, 4 wt % I.34TCN/PLA), either isothermally or non-isothermally, was studied by differential scanning calorimetry (DSC). The changes of the thermal behavior with crystallization temperature and cooling rate was recorded and analyzed. Due to the introduction of I.34TCN, up to two melting and different cold-crystallization peaks during DSC second heating scans are observed. It is concluded that these effects could be largely based on the mechanism of melt-recrystallization. The effect of I.34TCN content is small and the cooling rate has the great influence on the melting temperature of PLA composites. Especially, the melting temperature can be significantly increased by 20 oC when I.34TCN content is 4 wt %. After non-isothermal crystallization at low cooling rates that develop high crystallinity, an obvious double crystallization peak appears at modest cooling rate. During DSC second heating scans, the appearance of different cold-crystallization peak of pure PLA and PLA composites is effect of cold crystallization and melt-recrystallization of metastable or partially crystalline crystals formed during the cooling process. With increasing of cooling rate, these samples exhibit only single melting, and the main melting peaks move to higher temperature. The introduction of I.34TCN improves the PLA thermal stability, and the thorough understanding of thermal deformation and cold-crystallization mechanism can enhance the application of PLA in the packaging material field.