PVC MEMBRANES PREPARED VIA NON-SOLVENT INDUCED PHASE SEPARATION PROCESS

ABSTRACT Polyvinylchloride (PVC) based membranes are prepared via a phase inversion method using N,N-dimethylacetamide (DMAc) as solvent and water as precipitation bath. Polyvinylpyrrolidone (PVP) and lithium nitrate (LiNO3) are used as additives. Experimental cloud point data and solution viscosity measurements are evaluated. Precipitation rates, transport properties and membrane morphology are quantified. Membranes with different morphologies and transport properties are prepared by changing the additive and its concentration, changing the PVC concentration and by varying the exposure time to the environment before immersion. An augment in PVC concentration increases solution viscosity, reduces precipitation rate and water permeability (Jw), but it does not affect the instantaneous precipitation mechanism. PVC solutions with additives present higher viscosity values, slower light transmittance decay and membranes with higher Jw (highest: ~1,350 L.h-1.m-2.bar-1). LiNO3 in the polymeric solution results in delayed demixing. A combination of high PVP concentration and environment exposure time changes the membrane morphology, suggesting spinodal demixing.

摘要 以N,N-二甲基乙酰胺（N,N-dimethylacetamide, DMAc）为溶剂、水为凝固浴，通过相转化法制备聚氯乙烯（polyvinylchloride, PVC）基膜。以聚乙烯吡咯烷酮（polyvinylpyrrolidone, PVP）和硝酸锂（lithium nitrate, LiNO3）作为添加剂。对实验测得的浊点数据与溶液黏度进行了表征与评估，定量考察了沉淀速率、传输性能及膜形貌。通过改变添加剂种类与浓度、聚氯乙烯浓度以及浸入凝固浴前的环境暴露时长，制备得到具有不同形貌与传输性能的聚氯乙烯基膜。聚氯乙烯浓度的提升会增大溶液黏度、降低沉淀速率与透水通量（Jw），但不会改变瞬时沉淀机制。添加添加剂的聚氯乙烯溶液具有更高的黏度，透光率衰减更缓慢，所制得的膜透水通量更高（最高可达~1350 L·h⁻¹·m⁻²·bar⁻¹）。聚合物溶液中添加硝酸锂会延缓分相过程。高浓度聚乙烯吡咯烷酮与较长的环境暴露时长的组合会改变膜形貌，表明此时膜形成过程遵循旋节线分相（spinodal demixing）机制。