Effects of PVDF Crystallization on Polymer Gelation Behavior and Membrane Structure from PVDF/TEP System via Modified TIPS Process

Abstract

Poly (vinylidene fluoride) (PVDF) hollow fiber membranes are prepared by modified TIPS from PVDF/triethyl phosphate (TEP) system. It is revealed by differential scanning calorimetry (DSC) that PVDF crystallization capacity increase with polymer content increasing. Additionally, crystallization behavior and crystal structure of PVDF in PVDF/TEP systems are investigated by scanning electron microscopy (SEM) and wide angle X-ray diffraction (WAXD). PVDF concentration has a remarkable effect on PVDF crystallization behavior. Dendritic pore structures are obvious when PVDF weight ratio is 30% in polymer/diluent solution. However, discernable spherulitic structures are obtained when PVDF weight ratio reaches to 35%.

Keywords:

• Hollow fiber membranes
• Pore structure
• Thermally induced phase separation

ACKNOWLEDGMENTS

This research is financially supported by the Central Research and Public Service Institutes of Basic Research Program of China (NO. K-JBYWF-2011-T03 and 2012-T7). The authors would also like to thank Professor Wei Yan and Doctor Yu Zhu for valuable input on this research.

Notes

*, onset melting temperature of PVDF; , peak melting temperature of PVDF; , final melting temperature of PVDF; ΔT_m =  − ; ΔH_m, melting enthalpy; X_c, crystallinity of PVDF.

*, onset crystallization temperature of PVDF; , peak crystallization temperature of PVDF; , final crystallization temperature of PVDF; ; ΔH_c, crystallization enthalpy of PVDF;  = ΔH_c/φ (φ is the weight fraction of PVDF in the PVDF/TEP mixture).