凝固浴组成对PVDF高度疏水微孔膜结构和性能的影响

Effect of coagulation bath composition on morphology and property of microporous PVDF high hydrophobic membrane

采用浸没凝固法制备聚偏氟乙烯(PVDF)高度疏水微孔膜,以光滑板为制膜基底,以N-甲基吡咯烷酮(NMP)和不同浓度的NMP水溶液分别作为溶剂和凝固浴,研究了凝固浴组成对制膜过程的相分离行为及其膜结构和性能的影响.研究发现:凝固浴中NMP含量增加,使单纯的液-液(L-L)相分离变为固-液(S-L)相分离较液-液相分离占优的混合相分离,相应地膜底面由单纯的海绵结构转变为海绵孔与粒子结构交织的混合形态.这源于凝固浴中NMP增加,凝固浴和溶剂间的化学势渐降低,瞬时分相变为延时分相.结果表明:膜底面疏水性显著提高,水滴接触角最高可达131°,同时透过性能提高,拉伸强度略有降低.

The method of immersion precipitation processes was proposed for preparing high hydrophobic poly （vinylidene fluoride） （PVDF） microporous membranes. The blank plate was used as the substrates, while N-methyl pyrroli-done（NMP） and aqueous solutions of different NMP concentrations were respectively chosen as solvent and non-solvent in the process. Then, in order to study the effects of the coagulation bath compositions on the the way of phase separation and morphology of membrane, the membranous structure, hydrophobic degree of the bottom surface and other properties of the membrane were characterized. Generally the liquid-liquid demixing process contributed to the asymmetric spongy structures while the solid-liquid demixing process caused the uniform par-ticulate morphology. The study found increasing of NMP of coagulation bath changed the way of phase separation：the pure liquid-liquid demixing process changed to the solid-liquid demixing process had advantaged to liquid-liquid demixing process gradually. Accordingly, the asymmetric spongy structures transformed to particulate mor-phology. It was because when adding NMP to the coagulation bath, the chemical grads between the cast solution and coagulation bath is decreased, so the gelation rate decreases and instantaneous type phase separation changes to delayed type phase separation. Consequently, the results were：with increasing of NMP of coagulation bath, it led to the contact angle of the membrane with water was as high as 131°, indicating high hydrophobic property. In addition, the membrane permeability was improved while the mechanical tensile properties reduced slightly.