聚丙烯分子量对热致相分离制备微孔膜的影响

EFFECT OF POLYPROPYLENE MOLECULAR WEIGHT ON MICROPOROUS MEMBRANE FORMATION via THERMALLY INDUCED PHASE SEPARATION

通过对等规聚丙烯与邻苯二甲酸二戊酯体系的相分离过程进行研究,绘制了3种分子量等规聚丙烯与邻苯二甲酸二戊酯体系的相图.研究结果表明,聚丙烯分子量的增大导致聚合物单个分子占据的晶格数Np增加,总分子数减少,使混合熵对混合自由能的贡献降低,因此浊点曲线向高温方向移动,而结晶曲线基本不变.聚丙烯分子量的增大延长了聚合物贫相分散液滴的生长时间、增加了聚合物富相黏度和过冷度.聚丙烯分子量变化不仅改变了微孔尺寸,而且改变了微孔结构.在相同淬冷条件下,微孔平均尺寸的变化趋势是贫相分散液滴的生长时间、聚合物富相黏度和过冷度3种因素共同作用的结果.

Thermally induced phase separation （TIPS） is one of the most important methods to prepare microporous polymer membranes. In this paper, isotactie polypropylene （iPP） was dissolved in diamylphthalate （DAP）, and the effects of polymer molecular weight on their phase diagram and micro-structure of membranes prepared are studied. Different i PPs and DAP were mixed in a Haake torque rheometer to obtain homogeneous solution. To determine the phase diagram, the cloud points （liquid-liquid phase separation temperatures） and the crystallization temperatures of the iPP/DAP system were examined by microscope with a heating device and DSC, respectively. The micro-structures of the films prepared by TIPS were observed under SEM. The results showed that the liquid-liquid separation temperatures of the solution shifted to higher temperatures when the molecular weight of polypropylene increased. On the other hand, their crystallization temperature curves changed little. These phenomena are interpreted by using Flory-Huggins theory. The molecular weight of polypropylene has a great effect on the resulting average pore size and pore shape in the film via influencing not only the droplet growth time but also the super-cooling temperature range and the coarsening rate.