Structure-property And Applications Of PVDF In Its Blends

Poly(vinylidene fluoride)(PVDF) is not only a fluoropolymer with the various crystal forms, but also presents good stability to rigorous temperatures and chemical stability. It makes PVDF widely used as actuator, energy harvesting materials, filtration membranes, and so on. The main crystal forms of PVDF are α, β,γ, respectively. However under normal circumstances, crystallization of PVDF can yield α-form which is electrically inactive. So preparing β-form was very attractive. On the other hand, due to The C-F bond, PVDF exhibits strong hydrophobicity. It is easily to cause the membranes fouling during separation, therefore the membranes should have surface hydrophilicity.whatever study on polymorphic transition or hydrophilic modification of PVDF,compositing with other polymers is the common means for material modification. In this paper, The effect of presented second component to the morphology and properties of the PVDF in the blend have been investigated. On the other hand, through coating to surface hydrophilicity and modification of PVDF electrospun membranes are achieved to filtrate the oil in water emulsion. The main results are as follows:(1) Crystalline behavior, mechanical properties, and α→β phase transformation of PVDF upon stretching in its miscible blends have been investigated. Result show that The presence of miscible poly(3-hydroxybutyrate-co-4-hydroxybutyrate)(P34HB) component significantly inhibits crystallization of the PVDF component in its blends above a critical P34 HB content. Meanwhile, the P34 HB component remains amorphous in the amorphous phase of the PVDF component. The amorphous P34 HB in its blends as diluents is responsible for the sharp decrease in the yield strength as well as in the α→βtransformation induced by stretching. What is more, α→β transformation of PVDF induced by stretching exhibits a remarkable dependence on the P34 HB content in the blends, irrespective of the adopted stretching temperatures. Otherwise, crystallization of the P34 HB component exhibits a remarkable dependence on this critical P34 HB content.Only above the critical content could the P34 HB component crystallize.(2) Thermal behavior, rheological behavior and the effect of the profuse β form of PVDF have been investigated. Result reveals that the presence of a miscible PBS component lowers the crystallization temperature and the melting point of the PVDF component in the blends. It becomes more significant above a critical PBS content about45wt%. Through rheological behavior of the blends can further evidence that critical PBS content is about 45wt%. Above a critical PBS content about 45wt% where PVDF chains are dispersed in the matrix composed by PBS chains, so this is why the melting point and crystallization temperature of PVDF decreased obviously. On the other hand, the β form of the PVDF component can be induced at low temperatures. There exists a critical PBS content, below which the relative fraction of the β form is increased with PBS content.Rather, above this critical PBS content, generation of the β form is remarkably suppressed with the reappearance of the α form.(3) By doping with a certain polyamide 6(PA6) solutions to PVDF Membrane through Electrostatic Spinning Method, surface hydrophilicity and interconnected pores with submicron size are successfully achieved. As a result, highly efficient separation(99%)of the emulsion is exhibited by the doped PVDF membranes, accompanied by superior antifouling performance towards oil droplets. In addition, mechanical strength of doped membranes is enhanced. So the doped PVDF membranes could have great potentials in practical stable oil/water emulsion separation prospectively.