Morphological structure, thermal and mechanical properties of tough poly(lactic acid) upon stereocomplexes

Abstract

Poly(d-lactide)–Pluronic F68–poly(d-lactide) (PDLA–Pluronic F68–PDLA) multiblock copolymer is synthesized and incorporated into poly(lactic acid) (PLA) as a novel tough agent by melting blend. The 1H NMR spectrum shows the PDLA–Pluronic F68–PDLA multiblock copolymer is synthesized successfully. The presence of the polylactide stereocomplex in the blends is confirmed by Infrared spectroscopy (IR), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). Polarization optical microscopy (POM) shows that the crystal morphology of the stereocomplex crystals is different from that of neat PLA. PLA/multiblock copolymer blends have a continuous amorphous phase with crystalline regions being the discontinuous portion. In addition, the thermal properties of the tough PLA are improved because of the presence of the stereocomplex from the results obtained by DSC and thermogravimetric analysis (TGA). The improvements in mechanical properties potentially can increase the utility of this biomass-based polymer. Both types of morphological features can contribute to the improvement in mechanical properties. Therefore, the successful toughening behaviors in PLA may be due to several mechanisms working synergistically.