Exclusive formation of stereocomplex crystallites in PLLA/PDLA (50/50) blends by the addition of a plasticizer

Abstract

This study examined the effects of loading amounts of a biobased plasticizer, namely, organic acid monoglyceride (OMG), on the formation of homocrystals (HCs) and stereocomplex crystals (SCs) in PLLA/PDLA (50/50) blends by means of differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and polarized optical microscopy (POM) observations. OMG at different concentrations was added to the PLLA/PDLA (50/50) blend from 0.5 to 5% in 0.5% increments. The addition of OMG was found to enhance SC formation while suppressing HC formation in both nonisothermal and isothermal experiments. The total suppression of HC formation and exclusive SC formation was achieved in the specimens with OMG contents higher than 3% after isothermal crystallization at 170 °C for 5 h. This result was confirmed by WAXD measurements of the specimens with 4 and 5% OMG, where only SC diffraction peaks were observed. In addition, the degree of crystallinity was found to be the same for the specimens with 0 and 5% OMG crystallized at 170 °C for 5 h. These findings imply that not only did the SC form exclusively but also that the presence of OMG actively accelerated its crystallization. The effects of an organic monoglyceride (OMG) plasticizer on the crystallization of the PLLA/PDLA (50/50) blend were investigated by examining the isothermal crystallization of the blend with different contents of OMG (1–5 wt%) using POM, DSC, and time-resolved WAXD. It was found that the increase of the OMG content promoted the exclusive formation of stereocomplex crystallites and enhanced its crystallinity while suppressing the formation of homocrystals.