Study On The Crystalline And Fundamental Of The Porous PLA Membrane Fabricated Via Phase Inversion By Micro Water Droplets

For having great biocompatibility and biodegrability and being able to prepared directly by the crops fermentation, the biodegradable Polylactic acid(PLA) materials can be completely degrade into water and carbon dioxide, which do no hurt to the environment, and can be widely used in variety of fields such as agriculture,packaging and biological medicine industry. The PLA materials were machining-shaped by the method of phase inversion in the industry, especially the infiltration precipitation method. But during the infiltration precipitation process, the exchange between the solvent and nonsolvent is too fast to control, easily leading to the low crystallinity and much structure defect, thus, limiting the application of PLA materials. In this study, the porous PLA membranes were fabricated by phase separation using water microdroplets produced by an ultrasonic atomizer as coagulation bath. For the tiny volume of the nonsolvent, the exchange rate between the solvent and nonsolvent has been reduced greatly, causing the porous membrane materials with similar size of the pore. With the help of the scanning electron microscope(SEM), the differential scanning calorimetry(DSC) and the X-ray diffraction(XRD), the PLA membranes' micro structure and morphology along with the crystalline behavior had being characterized and being analyzed. When the molecular weight of the porous membranes ranged from 80 KDa to 200 KDa, the size of the pore had been decreased, on the contrary the thickness of the membrane had been increased. At the same time the crystallinity and thermal stability increased with the molecular weight. The structure of the cross section became compact with the increasing of the PLA concentration in the solution, meanwhile the crystallinity of the porous membrane raised and the thermal stability remained. When the temperature of the fabrication of the PLA porous membrane was increased, the structure of the cross section of the PLA membranes changed from the reticulated porous to the spherical porous, and the upper surface as well as the bottom surface tended to be compact. The thermal stability kept constant and the crystallinity raised with the temperature increased. Adding some amorphous biomedical polyurethane(BPU) in thecrystallization PLA solution, the structure of the cross section of the composite membranes prepared with the micro water droplets can be observed with regular spherical porous, while the membranes prepared with liquid water were observed with macro hole along with the spherical porous. The composite membrane prepared with the micro water droplets was uniformly distributed with naked eye visible pores,while the surface of the membrane prepared from infiltration precipitation method was compact and smooth. Increasing the weight concentration of the composite membrane prepared with micro water droplets, the crystallinity of the porous membrane raised and the thermal stability remained. While adding the ratio of the BPU in the composite membrane, the thermal stability trended to raise as well as the crystallinity.