Formulation Design And Performance Optimization Of EVA Foamed Elastic Materials

Ethylene vinyl acetate(EVA)foamed material is mainly composed of EVA,rubber elastomer and other components including inorganic fillers,cross-linking agents,foam agents and auxiliaries.Compared to non-foamed materials,foamed materials present low density,relatively high strength,good mechanical properties,and accordingly are widely used in sports protection products,shoe sole materials,automobile steering wheels,and yoga column/mats.However,it has been found that EVA foamed materials often display high hardness and poor elasticity when they are used under extreme circumstances,such as at lower temperature.On the other hand,EVA foamed materials exhibit a lower wear-resistance even at room temperature.These drawbacks often hinder the application of EVA foamed materials.This thesis aims to develop an EVA foamed product with excellent softness,high elasticity,and high wear-resistance.The influences of composition,elastomers and compatibilizer on low temperature hardness and low temperature rebound rate of EVA foamed material was studied,and the effect of silane coupling agent-modified nano-silica on the wear property of foamed elastic materials were also investigated.The emphases of this thesis is on the softness,elasticity and wear resistance of EVA foamed elastic materials.(1)The influence of the component in EVA foamed material formula on its harderness and rebound rate at room temperature was studied,and the optimized formula was obtained.The rubber elastomers were introduced this optimized formula,and the effect of the type and content of the rubber elastomers was discussed.The addition of the rubber elastomers resulted in a better elasticity at low temperature.The optimum mass ratio of the soft foamed material was(unit:phr):EVA 70,ethylene propylene diene rubber 30,talc 10,ZnO 2,crosslinker(DCP)0.7,foamed agent(AC)3.0.The final foamed materials produced using this formula display a hardness of 36(shoreA)and a rebound rate of 25%.(2)Through the hydrolysis reaction,the EVA partial hydrolyzate(EVOH)was obtained,and the EPDM-g-MAH was prepard by introducing maleic anhydride(MAH)to ethylene propylene diene rubber(EPDM).The EVOH and EPDM-g-MAH are ultilized as a compatibilizer to promote matrix compatibility between EVA and EPDM in order to improve the processability of the foamed material.The results indicated that when the total addition amount of EVOH and EPDM-g-MAH was 6 phr(the ratio is 1:1),the processing performance of the resulted EVA/EPDM foamed materials was greatly improved.The injection time was reduced from 30-35 seconds to 10-12seconds when EVOH and EPDM-g-MAH were added the EVA-based fomula.In this case,the hardness of the material was decreased by 8%,and the elasticity was increased by 33.3%.(3)The influences of filler type,amount,and particle size of inorganic additive on the wear-resistance of the foamed material were studied.The surface-modified nano-silica with silane coupling agent was selected as an anti-wear additive.It was found an optimal addition amount for the surface-modified nano-silica to improve the wear-resistance of the resultant fomaed product.When the amount of surface-modified nano-silica was 1.5 phr,the abrasion decreased to 240mm~3,implying a desirable wear-resistance.