| Polypropylene(PP) hollow fiber membrane has been widely used in membrane distillation, industrial and municipal wastewater treatment, drinking water purification and other fields due to its good chemical stability, thermal stability and low cost. PP is difficult to be dissolved in solvent at room temperature due to the nature of nonpolar crystallization polymer. Melt-spinning cold-stretching(MSCS) and thermal induced phase separation(TIPS) are two main techniques for preparing PP hollow fiber membranes. The membrane pore structure is easily controlled by TIPS and the interaction between diluent and PP is one of the key factors for structure control. Because the interaction between the single diluent and PP is strong, the membrane with spherulitic structure is often obtained. This structure has low strength, thick skin-layer, and small flux, so it isn’t applicable to water treatment. PP hollow fiber membrane was prepared by TIPS with mixture diluents in the present work, and the PP membrane pore structure regulation has been successfully implemented. In addition, hydrophilic modifications on PP were carried out, and the hydrophilic PP hollow fiber membranes were developed.PP hollow fiber membrane was prepared by TIPS with mixture diluents(DS/GA) in the present work, and the effect of PP content, weight ratio between diluents and preparation process on the structure and performance of PP hollow fiber membrane were studied. The results show that the strength of the membrane is relatively appropriate when the PP content is 20% in the DS/GA system. Because of fast cooling, the system would enter into crystallization temperature zone, resulting in solid-liquid phase separation. As a result, spherulites formed occurred for the system. The network structure through liquid-liquid phase separation can be obtained by increasing the distance of air gap to decrease the cooling rate. This suggests that the kinetics has a great effect on the phase separation process during the non-isothermal cooling process. The form of phase separation changed for the system as DS/GA was between 10wt/5wt and 10wt/6wt under the same degree of supercooling. The phase separation shifted from S-L to L-L. The membrane pore structure also shift from spherical particles to mesh holes and then to the cellular structure. At the same time, it is found that the opening of endodermis was affected by core liquid and mass transfer of spinning solution. The mass transfer of coagulation bath would be improved by water-soluble solvent joining in the spinning solution. Therefore, the outside surface of open holes was improved.The hydrophilic modification of PP hollow fiber membrane was prepared by TIPS. Results showed that pure water contact angle of PP containing five hydrophilic modifier decreased to below 20°, but the angle will raise to more than 60°after soaking in water. The EAA sodium salt was selected to compound with hydrophilic modifier for modifying PP to solve the loss of hydrophilic additive in the process of hydrophilic modification. Hydrophilicity of PP can be obviously improved and keep for a long time by measuring pure water contact angle test. The pure water flux of membrane increased from 122ml/m2 h to 200ml/m2 h. In addition, the crystallization of PP would be slightly influenced by EAA sodium. The modified membrane structure changed slightly.The PP/PA6 alloy membrane was prepared by TIPS. The non-isothermal crystallization kinetics of PP/PA6 alloy system was studied by DSC、XRD and so on. The effect of PA6 on crystallization of PP was investigated, which provided theoretical basis for the membrane preparation by TIPS. The results showed that the crystallization of PP almost not changed by the addition of 25wt% amorphous PA6 with 10wt% PP-g-MAH as compatilizer, but promoted β crystal formation of PP. When PA6 content is below 25wt%, the PP/PA6 alloy hollow fiber membrane almost has the same structure as PP, but the hydrophilicity and strength of membrane obviously increased. |
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