两步法聚酰亚胺纳滤膜的制备——凝胶化过程对膜结构与性能的影响

Polymide Naofiltration Membrane Prepared by Two-Step Method:Influence of Gelation Processing on Membrane Structure and Performance

采取两步法制备了聚酰亚胺(PI)纳滤膜。由于固液相转化法是制备纳滤膜最为广泛应用的方法,为改善加工工艺,文中在固液相转化前首先进行了凝胶化处理,然后再经过相转化制备了一系列聚酰胺酸(PAA)纳滤膜,最后通过化学亚胺化形成PI纳滤膜。XRD结果显示,PAA膜在19°左右显示出较尖锐的反射峰,不同溶剂对PAA诱导结晶产生凝胶结构的能力不同,其诱导PAA结晶的能力强弱关系为N-甲基吡咯烷酮(NMP)>N,N-二甲基乙酰胺(DMAc)>N,N-二甲基甲酰胺(DMF),此步中凝胶强弱会导致其膜结构与性能的很大变化。使用NMP为溶剂并经过凝胶化处理的PAA膜具有最高通量和截留率,分别为98 L/(m2·h)和98%。化学亚胺化会使膜结构前后发生改变,PI膜的皮层变致密,并导致通量变小。

A series of polyimide( PI) nanofiltration membranes were prepared by two-step method. Based on our previous work,a gelation process was taken to prepare polyamic acid( PAA) nanofiltration membranes before phase transformation. Lastly,PI membranes were formed via chemical imidization method. The results show that different solvents and PAA polymer have different crystallization abilities,which lead to different structure and performance of resultant PAA membranes. The different crystallization abilities of different solvents are N-methyl-2-pyrrolidone( NMP) > dimethylacetamide( DMAc) > dimethyformamide( DMF). The PAA membranes after gelation process using NMP as solvent shows the largest flux of 98 L /( m2·h) and the highest rejection of 98% to Bengal Rose aqueous solution( 10 mg/L).However,the advantage can't be kept from the gelation process after chemical imidization,and the top layer of PI membranes becomes denser,resulting the performance reduction of PI membranes.