Preparation And Properties Of PVDF Micropores By Thermally Induced Phase Separation

Polyvinylidene fluoride(PVDF)is an excellent semicrystalline polymer,with high mechanical strength,thermal stability,chemical resistance and high hydrophobicity and so on.PVDF as a membrane material have been extensively applied to various fields such as water treatment,membrane distillation,gas separation,pollutants removal,bioethanol recovery,separator for lithium ion battery,etc.Compared with the traditional non-solvent induced phase separation(NIPS),the membranes prepared by thermally induced phase separation(TIPS)have the advantages of high strength,high porosity and narrow pore size distribution.In this paper,PVDF membranes were prepared via TIPS,then their structure and properties were studied.PVDF flat membranes were prepared via TIPS,dibutyl phthalate(DBP)and dioctyl adipate(DOA)as mixed diluents.The effects of PVDF concentration and mixed diluent composition on the structure and properties of the membranes were investigated.The results shows that PVDF/DBP/DOA systems in the membrane formation process was mainly S-L phase separation,and has typical spherulite structure.With increase of PVDF concentration and DOA rate in mixed diluent,the sizes of membrane cross-sectional spherelites structure reduced,the membrane surface porosity were reduced and increasing the density.the sizes of membrane cross-sectional spherelites structure reduced,the membrane surface porosity were reduced and increasing the density.In addition,as DOA rate in mixed diluent increased,the mechanical properties changed for the better,but flux decreased.The addition of inorganic additive nano-SiO2 can significantly reduce the membrane porosity,improve the membrane contact angle and membrane strength.PVDF hollow fiber hybrid membrane was prepared via TIPS,DBP and dioctyl phthalate(DOP)as mixed diluents,nano-SiO2 and graphene as modifiers.The results show that the obtained membrane was homogeneous sponge-like pore structure,the outer surface of the membrane was smooth and the pore surface was smaller,the inner surface was rough and porous.With the increase of the amount of nano-SiO2,the pore diameter,breaking strength and elongation of membrane increased and then decreased.The graphene sheets were dispersed in the membrane in the form of an insert.The graphene sheets were intercalated in the membrane.The membrane pure water flux increased and the membrane porosity was higher than 70%after the addition of graphene.While adding 3wt%nano-SiO2 and 0.5wt%graphene prepared hollow fiber hybrid membrane better permeability,pure water flux up to 418L/m2·h,the mechanical properties of the hollow fiber hybrid membrane were improved compared with the single additive.