Preparation, Structure And Properties Of EVA/BR Thermoplastic Vulcnizates

Thermoplastic vulcanizates (TPVs) based on ethylene-vinyl acetate copolymer (EVA)/ cis-1,3-Butadiene rubber (BR) blends were prepared by dynamic vulcanization, the influence of composition, preparing technique on the morphology and mechanical properties of EVA/BR TPVs were researched. The dynamic viscoelastic behavior, the morphology of TPV, the influence of remilling and ultraviolet light aging on mechanical properties of the prepared EVA/BR TPVs were also investigated systematically. The results were as follows:(1) The dynamic vulcanization was processed by different feeding methods, considering the mechanical properties of the prepared TPVs, masterbatch method was the most appropriate process method. A series of TPVs were prepared by changing the composition and species of raw materials, the mechanical properties and microstructure were researched. Considering the proper hardness and the mechanical properties, the weight ratio of EVA/BR blend should range from 50/50 to 35/65.(2) Changing the amount of sulfur in the crosslinking system, it was shown that the mechanical properties of TPVs were well when the the amount of sulfur was 1.0~1.5phr. The microstructure research showed that the island-like structure of the system TPVs were prepared,the size of the vulcanzied BR particles was in the range of 5～10μm; scanning electron microscopy (SEM) photos of fracture surface of the tensile specimens of EVA/BR TPV showed that the interaction between the rubber phase and thermoplastic phase were strong.(3) The influence of DOP and POE content on mechanical properties of the TPVs were researched. The results showed that when the content of DOP was 5phr, the mechanical properties of TPVs were better; however, the tensile strength, tension set at break, elongation at break and tearing strength decreased with the increasing DOP content. The hardness of the TPVs was lower with the addition of POE, furthermore, when the content of POE was 5phr～10phr, the mechanical properties were improved obviously.(4) The mechanical properties of TPVs were markedly enhanced by the addition of HDPE, the hardness, tensile strength, tension set at break and tearing strength were gradually increased, the elongation at break arrived the maxmium when the HDPE content was 20phr or so. The fracture sufrace of tensile specimens of EVA/HDPE/BR TPVs shows that it could be clearly observed with plastic deformation and tearing strips. The mechanical properties of TPVs were markedly enhanced by filling carbon black(CB), and clear tearing strips could be found in the SEM images of fracture surface.(5) SEM shows that there were visible BR particles on the surface of EVA/BR TPVs etched with p-xylene, and the interface of the dispersed BR particles was clear.The size of the dispersed phase particles was uniformity, the average size was 5～10μm.(6) A systematic viscoelastic behavior of EVA/POE/BR TPVs was investigated with RPA. RPA result showed that TPVs showed the increasing storage modulus, loss modulus, composite modulus with increasing scanning frequency while lower tanδwas decreaed with the increasing scanning frequency. In the temperature scan, because EVA was semi-crystalline polymer and the continuous phase in the TPVs, the mechanical loss peak was near the melting point of EVA, and in high temperature, the twining among macromolecular chains and the internal friction were enhanced, leading to the increasing tanδ. TPVs showed the higher storage modulus, loss modulus, composite modulus with the increasing strain, however it became decreased significantly when the strain was 20% above; tanδhad almost no change when the strain was 60% below, while the tanδwas increaed rapidly when the strain was 60% above, due to the the interface interaction was damaged under large strain.(7) The influence of remilling times and ultraviolet light aging time on the mechanical properties and microstructures of the EVA/HDPE/BR TPVs were researeched. The results showed the maintenance of the tensile strength and the tearing strength was over 77% and 65% after 240 hours'UV aging, indicating the TPVs had well UV aging performance; after 5 remilling times, it had less influences on TPV's properties, the maintenance of the tensile strength and the tearing strength were over 78% and 92%, it shows that, the system had excellent remilling properties of TPVs.