Wide liquid-liquid phase separation region enhancing tensile strength of  poly(vinylidene fluoride)

Wide liquid-liquid phase separation region enhancing tensile strength of   poly(vinylidene fluoride)   membranes   via TIPS method with a new diluent

Zhaoliang Cui   *, Yangming Cheng , Ke Xu , Juan Yue , Yue Zhou ,Xiaogang Li ，   Qian Wang， Shi-Peng Sun, Yong Wang , Xiaozu Wang ,Zhaohui Wang

A b s t r a c t

Poly(vinylidene fluoride) (PVDF) membrane is widely used in water purification and wastewater treatment.In present paper, thermally induced phase separation (TIPS) was employed, and maleic acid dibutyl   ester   (DBM),   a   new   diluent,   was   introduced   for   PVDF   membrane preparation. Phase diagram and the   effects   of   polymer   concentration and quenching temperature on the structure, morphologies,

properties, and performances of PVDF membranes were investigated. During the quenching process of PVDF/DBM   system, liquid -liquid   phase   separation   happened,   and   PVDF   membranes with a bi-continuous structure    were   fabricated .   What   is   interesting   is   that the liquid-liquid phase separation region was much wider   than   other PVDF/diluent   systems.   Thus,   it is   possible to fabricate PVDF   membrane   with a   bicontinuous structureat   high polymer concentrations, without   stretching or additives. With the increase in polymer concentration and quenching temperature,   mean pore size and pure water flux of the PVDF membrane decreased. Tensile   stress   of   the prepared   PVDF membranes reached to 6.18MPa,because the wide liquid-liquid phase separation region induced a bi-continuous structure when the

concentration   of the PVDF membrane was at around 30%.