| Isotactic polypropylene (iPP) membrane is an outstanding membrane in terms of low cost and good risistance to chemicals, etc. The iPP membrane via thermally induced phase separation (TIPS) has a series of advantages than that one via melt spinning-cold stretching, such as higher permeability, narrower pore size distribution, and better mechanical properties. The domestic manufactories haven't produced the membrane via TIPS. The membrane via TIPS from international market is expensive. There are few investigations to prepare membrane by TIPS in literature as well. So the preparation of iPP membrane via TIPS has significant value. However, membrane via TIPS is apt to forming close pores, which greatly decreases membrane permeability. Nucleating agents may improve the situation. So the aim of this paper was to indicate membrane formation with iPP/DBP/DOP/nucleating agents systems via TIPS, as well as effect of nucleating agents on morphology and permeability of iPP membrane.The membrane via TIPS was in urgent need of solving the problem of low permeability. The paper adopted the pure water flux as evaluation criterion to screen nucleating agents. It was indicated that the pure water flux increases with subsequently decreases and has a maximal value when amount of nucleating agent increases. On the basis of pure water flux value, we screened out three typical nucleating agens, which were A,B and G respectively. Among the nucleating agents the pure water flux of A and B are the smallest and biggest respectively, and G isβ-nucleating agent.The effect of nucleating agents on crystallization behaviors for iPP/DBP/DOP system was investigated by using wide angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC). It was indicated thatβ-nucleating agent didn't formβcrystal, as well as the changing of nucleating agents can affect crystallization parameters, such as nuclear density(N),crystallization temperature(tf),half width (Wh),cryatallization scope(△t) and crystallinity etc. When adding nucleating agent A, N and tf increased about 10 times and 3.1℃respectively,Wh and△t decreased 0.7℃and 1.8℃as well. When adding nucleating agent B, N,tf,Wh and△t increased about 100 times,6.5℃,1.5℃and 4.8℃respectively.The effect of nucleating agents A or B on morphology and permeability of membrane was investigated. It was found that the morphology of all membrane was a mixture of typical particulate structure originating from polymer crystallization and typical cellular one relating to liquid-liquid separation. With increasing the content of nucleating agent, the porosity,the pure water flux and the retention rate of membrane increased with subsequently decreased, which was in accord with the changing of membrane morphology. In general, the membrane morphology first becomed loose and then compact with increasing nucleating agent. When A or B was added to the casting solution, the maximal pure water flux increased 156.7% and 80.5% respectively compared with iPP/DBP/DOP systems. Obviously the effect of B is better than A'. The increasing of cooling rate reduced the sensitivity of effect of nucleating agents on morphology and permeability of membrane. When the cooling rate was 90K/min, the maximal pure water flux enhanced 7.14% compared with iPP/DBP/DOP systems. It was indicated that the morphology of the resulting iPP porous membrane can be adjusted and the permeability of the membrane can be improved by choosing proper nucleating agent addition(γopt), andγopt had relation with cooling rate,the kind of nucleating agent,etc. It was concluded that the morphology and permeability of membrane was the synergistic action of nucleating agents and cooling rate in this investigation.It was suggested that the rise of crystallization temperature,the increase of nuclear density,the decrease of spherulite growth rate and the extend of crystallization scope are favorable to improving membrane structure and membrane permeability. |
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