Thermal and Mechanical Properties of Blends of Polylactide and Poly(ethylene glycol-co-propylene glycol): Influence of Annealing

Two kinds of polylactide (PLA) which was named PLA1 with L-lactide content of 98% and PLA2 with L-lactide content of 88% were blended with poly(ethylene glycol-co-propylene glycol) (PI-PG) in a batchwise mixer and pressed into films. The effect of annealing on the thermal properties, crystallization behavior, and mechanical properties of the quenched blends were Studied by means of differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), polar optical microscopy (POM), and tensile tests. PEPC was miscible with the two kinds of PLA in the blend composition range of 5-20 wt % and can effectively decrease the,lass transition temperature of PLA. Neat PLA2 lost the ability to crystallize in the DSC and DMA measurements; however, it could crystallize after annealing for long time and crystallize more easily due to the improved crystallizability with the addition of PFPG. Both of the PLAs underwent cold crystallization when annealing at 90 degrees C, and there were signs of phase separation occurring in the blends at the same time. The crystallization morphology and tensile properties of the annealed blends were different and dependent of the Optical purity of PLA. The blends with PLA2 after annealing regained the brittleness with maximum of elongation at break about 20% and showed larger spherulites in the POM images, whereas the blends with PLA1 after annealing still kept some flexibility with maximum of elongation at break about 65% and showed fine spherulites. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 116: 2050-2057, 2010