Preparation And Properties Of Dynamically Cured Thermoplastic Blends Based On Poly(Vinylidene Fluoride) And Special Kind Rubbers

Lots of studies have been reported on the rubber blends based on common plastic matrices so far, but they cannot satisfy the thermal stability and oil resistance required in new productions. Hence, high performance plastic/rubber blends have gradually attracted more attention. In this paper, PVDF/NBR and PVDF/FKM/MVQ blends were prepared via dynamic vulcanization based on poly(vinylidene fluoride)(PVDF), acrylonitrile butadiene rubber(NBR), flurorubber(FKM) and silicone rubber(MVQ). The morphology, structure and properties of PVDF/NBR and PVDF/FKM/MVQ blends were investigated.For PVDF/NBR blends, the NBR phase was in the form of sp herical particles dispersed in the PVDF phase, namely ―sea-island‖ structure, good compatibility between PVDF and NBR can be achieved in both plastic-rich and rubber-rich blends. With increasing FKM content, the increased probability of touching of the effective DCP radicals and NBR phase during mixing increased the crosslink density of the NBR phase, which resulted in the Tg of NBR phase in the blends moving to higher temperature, whereas that of the PVDF phase remained almost constant. The addition of the NBR phase reduced the crystallinity and the melting temperatures of PVDF.For the PVDF-rich blends, the PVDF can be highly toughened by NBR, the izod impact strength of PVDF/NBR(70/30) blend was 77.5 k J/m2, which was about six times higher than that of pure PVDF, while the tensile strength remained 30 MP. For NBR-rich blends, the PVDF component was beneficial to the mechanical properties of the blends, the tensile strength and tear strength of PVDF/NBR(30/70) blend were about three times higher than that of pure NBR, while the elongation at break remained 230%.For PVDF/FKM/MVQ blends, the spherical rubber particles were dispersed in the PVDF phase, namely ―sea-island‖ structure. With increasing FKM content, the Tg of MVQ phase in the blends moved to higher temperature, whereas that of the PVDF and FKM phase moved to lower temperature, which indicated that the compatibility between PVDF and rubber phase was enhanced with the addition of FKM. Hence, the tensile strength, tear strength and elongation at break were improved significantly with increasing FKM concentration. The crystallization temperature of PVDF was improved at higher FKM loadings, but the crystal inity of PVDF phase is decreased gradually at the same time.The effects of FKM/MVQ ratio, strain level and strain rate on the stress relaxation behavior of PVDF/FKM/MVQ blends were investigated. It was found that the rate of relaxation gradually increased with increasing FKM content, strain level and strain rate. The PVDF/FKM/MVQ blends had good reprocessing property. The mechanical properties of the 1st-reprocessed samples(F10 and F20) decreased slightly, but obviously decreased for the samples with higher FKM content, compared with that of virgin ones. Further increasing the number of reprocessing cycles did not cause significant changes of mechanical properties. The effect of reprocessing cycles on the rheology properties was also studied, the result showed that both storage modulus and complex viscosity were obviously declined for the 1st-reprocessing cycle, but almost unaffected with increasing the number of reprocessing cycles.