凝固浴组成对PVDF/PVDF-g-PAA共混膜结构与性能的影响

The influence of coagulation bath composition on the structure and performance of PVDF/PVDF-g-PAA blend membrane

为了进一步提高PVDF膜的亲水性及渗透性能,本文通过在膜内引入聚偏氟乙烯接枝聚丙烯酸(PVDF-g-PAA),提高共混膜的亲水性,并在凝固浴中加入N,N-二甲基乙酰胺(DMAc),改善聚偏氟乙烯/聚偏氟乙烯接枝聚丙烯酸(PVDF/PVDF-g-PAA)共混膜的结构与性能。利用浊点法对PVDF/PVDF-g-PAA共混膜的成膜热力学进行了研究,相比于水/乙醇凝固浴,水/DMAc凝固浴的使用会抑制PVDF/PVDF-g-PAA的相分离速度,体系变得更加稳定。采用傅里叶红红外光谱仪(FT-IR)和X-射线光电子能谱仪(XPS)表征聚合物及膜的化学结构,并通过原子力显微镜和扫描电镜观察膜的表断面结构。结果表明,随着凝固浴中DMAc含量的增加,膜的致密皮层逐渐变薄,膜断面中的指状孔结构逐渐向海绵状结构转变,膜表面变粗糙,平均孔径增加,共混膜纯水通量变大。当DMAc含量为50%时,膜的纯水通量最高,可达(1084±74)L/(m^(2)·h),同时具备较高的断裂强度(2.6±0.1)MPa。

In order to further improve the hydrophilicity and permeability of PVDF membranes,we introduces polyvinylidene fluoride grafted polyacrylic acid(PVDF-g-PAA)into the membrane to improve the hydrophilicity of the blend membrane,and adds it in the coagulation bath N,N-Dimethylacetamide(DMAc)which can improve the structure and performance of polyvinylidene fluoride/polyvinylidene fluoride grafted polyacrylic acid(PVDF/PVDF-g-PAA)blend membrane.The membrane-forming thermodynamics of PVDF/PVDF-g-PAA membrane was studied by the cloud point method.Compared with the water/ethanol coagulation bath,water/DMAc coagulation bath would inhibit the phase separation rate of PVDF/PVDF-g-PAA,making the system more stable.The delayed phase conversion technology was adopted to add different amounts of DMAc to the coagulation bath to regulate the crystallization nucleation rate of PVDF,reduce the membrane formation rate of PVDF,and optimize the membrane structure.FT-IR and XPS were used to characterize the chemical structure of polymers and membranes,and the surface cross-sectional structure of the membrane was observed by atomic force microscope and scanning electron microscope.The results showed that with the increase of DMAc content in the coagulation bath,the dense skin layer of the membrane gradually thinned,the finger-like macrovoids in the membrane cross-section gradually changed to the spongy structure.The membrane surface became rougher,the average pore diameter increased,and the pure water flux of the blending membrane increased.When the DMAc content reached 50%,the pure water flux of the membrane was the highest,reaching(1084±74)L/(m^(2)·h).Meanwhile,the membrane had a high breaking strength(2.6±0.1)MPa.