柠檬酸酯类溶剂对超临界CO_2诱导相转化法制备PVDF膜的影响

Effect of Citrate-based Mixed Solvents on PVDF Membrane by Supercritical CO_2-induced Phase Separation

通过超临界CO_2诱导相转化法,以不同比例的环境友好型溶剂乙酰柠檬酸三丁酯(ATBC)或柠檬酸三乙酯(TEC)部分取代传统溶剂二甲基甲酰胺(DMF),制备聚偏氟乙烯(PVDF)微孔膜。利用扫描电子显微镜、差示扫描量热仪、傅里叶红外光谱仪和接触角仪对所制备的PVDF膜的形貌、热力学性能、晶型转化和亲水性能等进行了研究。结果表明,ATBC和TEC的加入,显著影响PVDF膜的形貌结构,当ATBC或TEC的添加量达到50%(质量分数,下同)时,PVDF膜表层结构和断面结构的粗糙度提高,明显不同于以DMF为纯溶剂时制备的PVDF膜;膜表面的亲水性和表面粗糙度呈正相关;在误差允许范围内,制备的PVDF膜的热力学性能并不受ATBC和TEC含量的影响;当ATBC或TEC的含量达到50%时,PVDF膜的晶型发生了转变,趋向于形成β结构的晶型。

Acetylene tributyl citrate(ATBC)and triethyl citrate(TEC)were taken as ecologically friendly hydrophobic diluents to partially replace dimethyl formamide(DMF)and then used as a mixed solvent to fabricate poly(vinylidene fluoride)(PVDF)membrane through supercritical CO2-induced phase separation.The morphologies and structures of the prepared PVDF membranes were influenced significantly with the addition of ATBC or TEC.The membrane surface and cross section were found to become much rougher especially when the amount of ATBC or TEC was increased to50wt%.Such a phenomenon is quite different from the membrane prepared with pure DMF.Contact angel measurement proved that the hydrophobicity of the membrane was associated with the surface roughness.The thermodynamic properties of the membrane were not affected by the amounts of ATBC or TEC used for preparation.However,there was a crystal transformoccurred when the amount of ATBC or TEC reached50wt%,which resulted in the formation of moreβ-form crystals.