Structure And Viscoelastic Behavior Of EVA/NBR TPV

Thermoplastic vulcanizate(TPV)based on ethylene-vinyl acetate copolymer(EVA)/nitrile-butadiene rubber(NBR)blends were prepared by dynamic vulcanization.The morphology,mechanical properties and dynamic viscoelastic behavior such as compression set,Mullins effect and stress relaxation of TPV were researched systematically.The influences of the weight ratio of rubber and plastic,together weith the dosage of reinforcing agents on the properties of TPV were investigated.The water-swellable EVA/NBR TPV was prepared by the incorporation of crosslinked sodinm polpacrylate(CPNaAA)wight in TPV.It was found that the content of water-swellable material,together with the water absorption environment,play an important role on the water-swellable behaiver greatly.Water retention ability,repeated water swellable behavior and the morphology before and after water absorption were also studied.The results were as follows:(1)EVA/NBR TPVs with different weight ratios were prepared by dynamic vulcanization;the morphology,mechanical properties and viscoelastic behavior of the prepared EVA/NBR TPVs were investigated systematically.The FE-SEM results showed that the irregular vulcanized NBR particle size was about 10 ?m and the particles were were dispersed evenly on the surface of etched TPV.Research on the mechanical properties showed that when increasing the EVA content,the tensile set at break,tensile strength and tearing strength were improved remarkably.The study of viscoelastic behavior indicated that the compression set and stress relaxation degree of NBR vulcanizate were low,and the Mullins effect was hardly to be found.The test datas of the compression set,the stress relaxation and the Mullins effect of EVA/NBR TPVs were between that of the NBR vulcanizate and that of the EVA resin.Moreover,with the increasing EVA content,the compression set and the stress relaxation degree were increased,the Mullins effect tended to be obvious.Increasing the NBR/EVA ratio and the heat-treatment temperature would improve the recovery of compression set,stress relaxation and Mullins effect.The various rule of stress relaxation could be fitted well by using seven elements genernal Maxwell model.(2)The influences of ZDMA dosage in the NBR rubber on the properties of the EVA/NBR TPV were investigated systematically.Research on the mechanical properties indicated that the mechanical properties of EVA/NBR TPV reinforced by ZDMA were improved significantly.Increasing EVA content,the compression set and the stress relaxation degree were increased,and the Mullins effect tended to be obvious.Compared with the unreinforced TPV,ZDMA reinforced TPV show larger maximum stress and other enhanced mechnical behavior such as residual deformation,internal friction loss,tan? and softening factor.Increasing the heat-treatment temperature would improve the recovery of compression set,stress relaxation and Mullins effect;however,increasing ZDMA dosage was agaist to the reversible recovery of the them.The various rule of stress relaxation could be fitted well by using seven elements genernal Maxwell model.The FE-SEM and EDS results showed that the ZDMA particles covered by NBR particles were dispersed on the surface of etched TPV.(3)The results showed that with the increase of CPNaAA dosages,the mechanical properties of the water swellable rubber(WSR)were decreased slightly;however,water-swelling properties of the WSRs were increased significately.The secondary water-swelling behaviors of WSRs showed significantly rapid equilibrium swelling and remarkable decreasing of weight loss.Morphological study of the etched TPV surface showed that the CPNaAA particles were dispersed evenly in the WSRs and coated with crosslinked NBR rubber.The water-swelling ratio of EVA/NBR/CPNaAA TPV decreased greatly in the salt or acid solutions when the medium concentration increased.However,the water-swelling ratio of EVA/NBR/CPNaAA increased slightly at low concentration of alkaline solution,which was caused by ionizes of the carboxylicion.