两亲性梳状聚醚硅氧烷对相转化法聚偏氟乙烯多孔膜的共混改性作用研究

以聚醚链段为侧链的两亲性梳状聚醚硅氧烷(ACPS)为改性剂,研究了相转化法制备聚偏氟乙烯(PVDF)多孔膜的改性效果与机理.采用SEM、XPS、接触角、水通量等考察了ACPS对膜结构与性能的影响.研究发现,ACPS在相转化成膜过程中不流失,随着制膜液中ACPS含量的增加,相分离速度降低,膜中微孔由指状结构向蜂窝状结构发展,膜强度提高,亲水性显著提高.提出了ACPS在膜表面的富集现象和在膜中的稳定性机理和模型.结果表明,两亲性梳状聚醚硅氧烷在原理上是一类适合于相转化法制备聚合物微孔膜表面亲水化改性的有效物质.

MODIFICATION EFFECTS OF AMPHIPHILIC COMB-LIKE POLYSILOXANE CONTAINING POLYETHER SIDE CHAINS ON THE PVDF MEMBRANES PREPARED via PHASE INVERSION PROCESS

An amphiphilic comb-like polysiloxane(ACPS) containing polyether side chains is presented as the modification reagent in preparation of hydrophilic porous poly(vinylidene fluoride)(PVDF) membrane via phase inversion process.The effects of blending ACPS on the morphology,crystallinity,mechanical properties,chemistry structure,hydrohilicity and filtration performance of porous PVDF membranes as well as the stability of ACPS in phase inversion process were investigated.Basing on the membrane forming kinetics displayed from measuring the light intensity transmitted through the membrane,it was found that the addition of ACPS would lead the delayed demixing between casting solution and coagulating water during the phase inversion process.The instantaneous demixing resulted in the formation of membranes with "fingerlike" macrovoids in the sublayer,whereas the delayed demixing yieded membrane structure containing a "spongelike" sublayer.And thus,the solidified PVDF membrane with larger pore size was obtained with increasing the content of PVDF in casting solutions.Furthermore,the introduction of ACPS into the membrane system increased the PVDF crystallineity because the delayed demixing permitted a longer crystallization time in membrane formation.Surface and bulk chemical compositions of blend membranes were measured respectively to study the reservation and the enrichment of ACPS molecules in the membrane formation proces.It was revealed that the O/F ratio of membrane bulkwas almost the same as that of the corresponding casting solution,which obviously indicated the higher reservation of ACPS inmembrane formation proces.The fact that the O/F ratio in membrane surface layer was much higher than that in membrane bulk proved the enrichment of ACPS on surface.The reason for such surface enrichments could be explained as follows.In phase inversion process,the ultra-hydrophilic poly(ethylene oxide)side chains in ACPS tended to moving out of the membrane and disslving into the coagulation bath.However,the ACPS molecule as a whole strongly entwisted with PVDF chains is not able to dissolve into the coagulation bath.As a result,the ACPS molecules enrich in the final surface layer,and the hydroiphilic poly(ethylene oxide)side chains stretch toward the outside of the membrane surface.In fact,such enrichment also occurred in wall surface of pores inside the membranes.via Supposing a schematic model,this explanation was clearly illustrated.The enrichment of ACPS with PEO side chain stretching trends endows the membrane with excellent hydrophilicity both for membrane surface and wall of pores inside membrane,which was fully proved by measurements of water contact angle.As the ACPS molecules were greatly entwisted by PVDF chains,the ACPS could be reserved in membranes stably and thus result in the reliable hydrophilic stability for PVDF membranes.Such stability is very important and greatly expected while the filtration performance in practical application of final PVDF membrane is considered.In this work,this stability was also approved clearly through continous shake test(in 60℃ water) simulating the application process.For prepared ACPS/PVDF blend membranes without further hydrophilication treatment(e.g.coated by glycerol,ethanol or other surfactant),the water flux was relative large while the retention property was controlled properly.Form the observed results it is concluded that the ACPS should be contributed to the potenial candidate materials for high performance filtration membranes.