雾化微珠诱导相变下聚乳酸结晶行为及其调控

Two problems, the fast exchange rate between solvent and non-solvent during phase inversion and the limitation regulation ability, prevent from the application of the method of phase inversion induced by non-solvent on the preparation of advanced porous membrane. In order to overcome above technical disadvantage, Polylactide (PLA) membrane with controlled morphology and excellent mechanical properties were prepared via a method involving a phase inversion induced by water micro-droplets, which were generated by an ultrasonic atomizer. In present study, systematic investigation would be performed on the crystallization behavior during phase inversion induced by water micro-droplets through the method of in situ observation and spectrometry. The phase inversion process of polymer/solvent/micro-droplets three-phase system would be study in detail. The exchange rate between solvent and non-solvent would be confirmed in the phase inversion process induced by one or many water micro-droplets. The formation and growth behavior of PLA nucleation would be observed by the method of spectrometry. The microstructure of porous PLA membrane prepared via phase inversion induced by water micro-droplets would be investigated by scanning electronic microscopy and atomic force microscopy. The synergistic effect between the binary phase behavior and crystallization regulation would be explored as well. Based on above studies, it was possible to control the crystallization behavior of PLA molecules during phase inversion process by selecting polymer with appropriated molecular weight and applying corresponding preparation parameter.

针对溶液诱导相变过程中溶剂与凝固浴交换速度快，且调控范围小的共性技术难题，本项目拟以聚乳酸（PLA）作为研究对象，1,4-二氧六环作为溶剂，借助超声雾化技术，降低凝固浴蒸馏水界面张力，将其转变成为自由漂浮状态的微珠，定量连续诱导PLA溶液发生相变。通过原位在线观察和光谱法深入探讨PLA溶液在微珠诱导下的相变结晶机理，特别是聚合物/溶剂/微珠三相体系相变流程、单复微珠诱导下溶剂与非溶剂之间的交换速度、聚合物成核过程、核增长行为，微珠诱导下PLA高分子结晶行为及其微观结构，相变速度对时间的依赖关系以及结构与性能之间的构效关系。详细描述相变过程中成核机理以及核增长过程，通过选择合适的PLA分子，并合理控制制备工艺参数，实现对PLA多孔膜微观结构和结晶行为的有效调控。

为了更清晰的控制非溶剂诱导相变过程中溶剂与非溶剂之间的交换速度，达到控制聚乳酸多孔膜微观结构、热力学性能和结晶行为的目的，本项目首次通过雾化原理将液态水转变成为漂浮的微珠缓慢诱导聚乳酸溶液相变成型，减缓溶剂与非溶剂之间的交换的速度。项目开展过程中利用先进的表征手段深入研究了聚乳酸分子量、聚合物溶液浓度和周围温度对聚乳酸多孔膜微观形貌、热力学性能和结晶行为的影响。大量实验数据表明通过改变聚乳酸分子质量和聚乳酸溶液质量分数可有效调控聚乳酸多孔膜结构。分子质量越低多孔膜内部多孔体积越大，形成的多孔膜厚度越小；铸膜液质量分数越高，聚乳酸多孔膜结构越紧密，当铸膜液质量分数达到25%时，多孔膜内部有球状多孔结构形成。聚乳酸多孔膜结晶度和晶粒尺寸随着分子质量的增加先增大后减小；多孔膜结晶度和晶粒尺寸随着质量分数的增加则是先增大，质量分数增加到20%和25%时则多孔膜结晶度和晶粒尺寸基本不变。当改变聚乳酸多孔膜固化温度时，由于有三种不同因素的互相影响，实验温度升高，多孔膜截面结构越致密，由多孔网状结构向多孔球状结构进行转变。固化温度为20℃时，聚乳酸多孔膜内部就出现微球状多孔结构，且温度越高微球分布越密。聚乳酸多孔膜结晶度和晶粒尺寸随着固化温度的升高先增大后减小。20℃时，聚乳酸多孔膜结晶度和结晶尺寸最大，晶粒形状呈扁圆状；温度升高聚乳酸多孔膜结晶度和结晶尺寸略有下降，晶粒形态有向圆球状变化的趋势。本项目不仅为聚乳酸多孔膜的制备提供了一种新型的成型方法，同时对于理想结构聚乳酸多孔膜的制备提供理论支持。