Thermoplastic Vulcanizate(TPV) Based On EVM/EVA Blend By Dynamic Vulcanization And It’s Halogen-free Flame Retardancy

A thermoplastic elastomer(TPE) is defined as a polymeric material with properties and functional performance similar to those of a conventional vulcanized rubber; still, it can be processed in a molten state as a thermoplastic polymer. TPE is one of the most environmental friendly materials that have been attracted great interest in recent years. In this work, a novel nanostructured thermoplastic vulcanizate based on two EVAs with different VA contents, ethylene vinyl acetate rubber(VA content=50wt%)(EVM) and ethylene vinyl acetate copolymer(VA content =28wt%)(EVA28), has been successfully prepared by dynamic vulcanization for the first time. The structure and properties of the TPV have been investigated. On the other hand, halogen-free flame retardant thermoplastic vulcanizate composites have been prepared based on the TPVs. The paper can be divided into five parts:(1)Nanostructured Thermoplastic Vulcanizates by Selectively Cross Linking a Thermoplastic Blend with Similar Chemical StructuresEthylene vinyl acetate rubber(vinyl acetate(VA) content=50wt%)(EVM) and ethylene vinyl acetate copolymer(VA content<50wt%)(EVA) are polymers with a very similar chemical structure. SEM and DMA investigation means that EVM and EVA28 are phase separated but highly compatible. In this study, a novel thermoplastic vulcanizate(TPV) based on EVM/EVA28(VA content=28wt%) blend has been successfully fabricated by dynamic vulcanization due to the selective cross-linking of EVM. The morphologies and properties of the TPVs have been investigated. It was found that the cross-linked EVM phase and the thermoplastic EVA28 phase form a perfect cocontinuous structure with the rubber phase size of 100-500 nm. The fabricated TPV exhibits not only excellent stretchability(>900% elongation at break), nice elasticity(only about 19% remnant strain at 100% stretching), and good flexibility but also superior oil resistance.(2)Selectively Located Aluminum Hydroxide in Rubber Phase in a TPV: Towards to a Halogen-Free Flame Retardant Thermoplastic Elastomer with Ultrahigh FlexibilityWe have incorporated aluminum hydroxide(ATH) into the TPV based on EVM/EVA28 for the purpose to fabricate halogen-free flame retardant TPVs with high flexibility. It was found that the ATH particles were finely dispersed into the crosslinked EVM phase, while few ATH particles were observed in the EVA28 matrix. The fabricated TPVs with 45% ATH exhibit LOI of 30.2%, significantly prolonged ignition time, and drastically reduced heat release rate. At the same time, the TPVs show excellent stretchability(>300% elongation at break), nice elasticity(only about 30% remnant strain at 100% stretching), high strength, and good flexibility as well. We have attributed the multifunctional performance of the ATH filled TPVs to both the fine phase structure of the base TPVs and the selective dispersion of ATH fillers in the rubber phase.(3)The reinforcement of TPV Based on EVM/EVA28 by organoclayThe composites based on the TPV and organoclay have been fabricated by two different strategies:1) One-step fabrication by directly dynamically vulcanizing the EVA/EVM blends with organoclay using a peroxide; 2)Two-step fabrication by first preparing the TPV by dynamic vulcanization followed by melt mixing with organoclay. The structure and properties of the composites have been investigated. It was found that the composites fabricated by the two-step strategy have much smaller phase size and the organocaly shows much higher exfoliation efficiency than those fabricated by one-step strategy. Moreover, the composites fabricated by the two-step strategy exhibits much better physical properties(including elongation at break, modules, strength and flame retardant performance) than those by one-step strategy.(4)Synergistic Effects in Flame Retardance Performance of TPV by MH and A small Amount of MMTA small amount of organically modified montmorillonite(MMT) has been incorporated into a thermoplastic vulcanizate(TPV)/magnesium hydroxide(MH) composites for the purpose to fabricate high performance halogen-free flame retardant elastomeric materials. Significant synergistic effects of MH and MMT have been observed for the TPV in terms of both flame retardant properties and mechanical performance. The presence of MMT enhances the formation of char and hinders diffusion of volatile decomposition products within the ternary composites. Therefore, such char structure prohibits the heat and mass transfer during burning and improves the flame retardant performance of TPV.(5)Synergistic Effects in Flame Retardance Performance of TPV by MH and A small Amount of NP-IFRMagnesium hydroxide(MH) and an intumescent flame retardant(IFR) have been incorporated into a thermoplastic vulcanizate(TPV) for the purpose to fabricate halogen-free flame retardant elastomeric materials. Significant synergistic effects of MH and IFR have been observed for the TPV in terms of both flame retardant properties and mechanical performance. The addition of NP induces the improved MH particle dispersion in the TPV matrix; thus the final flame retardant TPV exhibited enhanced mechanical properties. A small amount of IFR accelerates the degradation of the matrix and induces a shrinkage matrix, leading to a compact and unbroken Mg O protective layer. Such compact Mg O layer on the surface of the material prevents the bulk material from further degradation, and a high flame retardant performance was achieved.