Miscibility, thermal characterization and crystallization of poly(l-lactide) and poly(tetramethylene adipate-co-terephthalate) blend membranes

Binary blend membranes of biodegradable poly(l-lactide) (PLLA) with poly(tetramethylene adipate-co-terephthalate) (PTAT) copolymer were prepared by solution casting via air evaporation. The miscibility of PLLA/PTAT blends was studied by dynamic mechanical analysis (DMA) and thermal mechanical analysis (TMA) in a tensile mode. Differential scanning calorimetry (DSC) measurement was carried out. The surface microstructure and tensile properties of the blend membranes were examined using atomic force microscopy (AFM) and tensile tester. It was concluded that PLLA/PTAT blends should be partially miscible for all ranges of compositions. Higher roughness and porosity were observed for the blend containing 50% PTAT, suggesting more phase separation occurred. The DSC analysis showed that the fusion enthalpy and crystallinity (X_c) of the PLLA-rich phase decreased with increasing PTAT content. Solidification process strongly suggested that the crystallization rate was accelerated by blending with 25% PTAT content, which served as the nucleation agent. Furthermore, the crystallization rate coefficient (CRC) depended on the blending miscibility and cooling rate in the non-isothermal crystallization process. Besides, PTAT addition could be proved to enhance the thermal stability and elongation of resulting blend membranes, even superior to those properties of poly(lactic acid-co-glycolic acid) (PLGA).