Thermal Properties and Miscibility of Semi-Crystalline and Amorphous PLA Blends

The focus of this research is the study of the microstructures and miscibility at the interface between semi-crystalline and amorphous PLAs [poly (L-lactic acid)(PLLA) with poly (L,D-lactic acid)(PDLLA), respectively]. The blends are prepared through thermal processing (extrusion and hot-pressing). To increase the area of interface between PDLLA and PLLA, the fibers from PLLA and PDLLA are used. Thermal and microstructures of the blends were studied by differential scanning calorimetry (DSC), polarized optical microscopy (POM), dynamic thermogravimetric analysis(DMA), small-angle X-ray diffraction(SAXS) and wide-angle X-ray diffraction (WAXD). The two PLAs are miscible in molten state. However, phase separation is detected after various thermal treatments, with PDLLA being excluded from the regions of interlamellar PLLA regions when PDLLA content is low, as determined from X-ray diffraction studies. The compatibility between the two PLAs is not perfect in the molten state, since enthalpies of the various blends at T-g are lower than any pure PLA material. The semi-crystalline PLLA fiber can recrystallize alone in the molten amorphous PDLLA, and a higher nuclei density is observed at the interface. (C) 2014 Wiley Periodicals, Inc.