| Fluorosilicone rubber is a kind of elastomer with excellent properties.However,it is costly to synthesizing fluorosilicone rubber at present.What's more,low strength and surface energy of fluorosilicone rubber makes it difficult to processing.And it is not easy to develop a new material to instead fluorosilicone rubber,since it will be subject to many factors.Comparing with chemical synthesis,blending and grafting is more simple and effective to fabricate fluorosilicone elastmers.In this paper,a new method called core-shell dynamic vulcanization was used to prepare polyvinylidene fluoride/fluororubber/silicone rubber elastomer.This new method greatly improved the properties of the material.In addition,the blends were thermoplastic which was good for environment and recycling.Profound researches on its structure and performance were conducted that would be of important significance.In this paper,polyvinylidene fluoride(PVDF)was used as the plastic matrix,and fluororubber(FKM)and silicone rubber(SR)were used as the rubber phase.A specific curing agent was used for FKM and SR,respectively.The effects of cross-linking degree on the morphology,rheology,crystallization and melting,mechanical,stress relaxation and softening,solvent resistance and other properties of PVDF/FKM/SR blends were investigated.Morphology study showed that simple blends had bicontinuous phase structure,while all the thermoplastic vulcanizate(TPV)had typical “sea-island” morphology,but the cross-linking degree of core-SR and shell-FKM still had great influence on morphology.TPV prepared by dynamic vulcanization has higher storage modulus,lower loss factor and better mechanical properties than simple blends and the core-shell cross-linked samples had the highest storage modulus,the lowest loss factor,the best mechanical properties.Researches of tensile test showed that core-shell crosslinked TPV had the best performance both at 25 oC and 150oC.Solvent resistance test showed that PVDF greatly improved the resistance of TPV to polar solvent,especially for the core-shell crosslinked TPV which had the best resistance to butyl acetate,and the tensile strength of it were 11 MPa after immersed in butyl acetate for 72 h.The effect of FKM/SR ratio on interfacial crystallization,crystallization kinetics and crystallization morphology of the PVDF phase in the blend were studied by differential scanning calorimetry(DSC),polarizing microscope(POM)and X-ray diffraction(XRD),respectively.The results showed that the effect of interface-induced nucleation of FKM-PVDF interface was more obvious than that of SR-PVDF interface.When the TPV formed perfect core-shell structure,the interface crystallization effect was almost the same.Isothermal crystallization kinetics of PVDF/FKM/SR TPV showed that the isothermal crystallization behavior of PVDF was closely related to the ratio of FKM/SR.When the content of fluorine rubber in the blends was 50% or more than that,the isothermal crystallization behavior of PVDF/FKM/SR TPVs with core-shell structure were similar to PVDF/FKM TPV.When the content of fluorine rubber was 25%,the isothermal crystallization behavior of PVDF in PVDF/FKM/SR TPV biased to PVDF/SR TPV.The non-isothermal crystallization kinetics showed that the crystallization rate of PVDF decreased with the increase of FKM content in the blends,but when the content of FKM was greater than or equal to the content of SR,the ratio had little effect on crystallization rate.WXRD and POM photographs showed that PVDF only had ? crystal form in the blends which means dynamic vulcanization and addition of rubber phase did not change the crystal form of PVDF in the TPVs.The effect of crosslinking degree of SR on the morphology,crystallinity and mechanical properties of TPVs were investigated by controlling the dosage of DCP.Formation mechanism of core-shell structure was also presented.The effect of crosslinking degree of FKM on mechanical properties and oil resistance of TPVs were also investigated by controlling the amount of bisphenol AF/BPP. |
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