热致相分离技术制备聚氨酯多孔膜的条件控制

采用自制的模具 ,利用热致相分离 (TIPS)的原理制备了聚氨酯 (PU)多孔膜 ,并重点研究了聚合物浓度对多孔膜的表面形貌、孔度大小、孔隙率和透湿率的影响 .在不同的聚合物浓度条件下制备的PU多孔膜的共同特征是底面 (与成膜平台接触面 )光滑平整 ,孔洞尺寸较小 ,为纳米级 ;而表面 (与空气接触的自由面 )的形貌结构较为复杂 ,但都有明显的孔洞出现 ,且孔洞的尺度大于底面 ,在微米级以上 .聚氨酯 1,4 二氧六环 (DO)形成的是上临界共溶温度 (UCST)体系 ,在发生相分离后底面与表面粗化时间的不同是导致形貌结构差异的主要原因 .改变冷台温度或调整DO H2 O的比例也会对PU多孔膜的孔度大小和形貌结构产生明显的影响

FACTORS CONTROLLING THE PREPARATION OF POROUS POLYURETHANE MEMBRANES VIA THERMALLY INDUCED PHASE SEPARATION

Porous polyurethane (PU) membranes were prepared via thermally induced phase separation (TIPS) technique by employing a home-made mould consisting of a solution container, a membrane-forming platform, a coldplate, a temperature-decreasing system and a temperature-supervising system.The influences of polymer concentration on the surface morphology, pore size, porosity and water vapor transmitting ratio of the porous PU membranes were studied. The bottom surfaces, the surfaces contacting with the membrane-forming platform, of the porous PU membranes are planar and smooth for all the selected polymer concentrations, e.g. φ2 from 0.025 to 0.078. The pore sizes are smaller and are estimated in the range of nanometer. While the top surfaces, the free surfaces toward air, possess variable surface morphology and have micrometer-sized pores that are larger than those of the bottom surfaces. This phenomenon is mainly caused by the different coarsening time after spinodal phase separation (polyurethane/1,4-dioxane (DO) solution is an upper critical temperature phase separation system). Preliminary studies showed that the pore sizes and surface morphology of porous PU membranes were also influenced by the temperature of the coldplate and by the composition of solvents, DO/H2O, a good solvent and a poor solvent for the PU, respectively.