Preparation and properties of new thermoplastic elastomer based on ethylene vinyl acetate (EVA)/ natural rubber blends

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Date
2007
Authors
Yong, Mun Kong
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Abstract
Preparation and properties of new thermoplastic elastomer (TPE’s) based on ethylene vinyl acetate (EVA)/ natural rubber blends were examined. Mixing torque, morphology, tensile properties, swelling as well as thermal properties such as thermogravimetric study and thermo-oxidative aging were evaluated. In the first part of investigation, two series of unvulcanized blend namely, ethylene vinyl acetate/ natural rubber blends (EVA/SMR L) and ethylene vinyl acetate/ epoxidized natural rubber blends (EVA/ENR-50) were prepared and a comparative study on the effect of blend ratio on the properties of TPE was carried out. In the second part of studies, the effect of compatibilizer, i.e. polyethylene acrylic acid (PEA) or ENR-50 on properties of EVA/SMR L blend (50:50 wt/wt) were investigated. The effect of dynamic vulcanization on the properties of EVA/SMR L blend was also investigated. The experimental results indicated that mixing torque values in TPE with ENR-50 blends are lower than with SMR L blends. The processing efficiency of EVA/ENR-50 blends is better due to less viscous nature of the blend compared to EVA/SMR L blend as indicated in stabilization torque graph. For the compatibilized blend, EVA/SMR L blend with PEA displayed lower mixing torque value than ENR-50 in EVA/SMR L blend. The lubricant effect from PEA resulted in the ease of processing in comparisons to ENR-50 in EVA/SMR L blend. In the case of dynamic vulcanization, the stabilization torque values increased with increasing sulfur content. This could be due to more crosslink were generated during melt mixing. Tensile properties like tensile strength, M100 (stress at 100% elongation) and Eb (elongation at break) also increased with increasing EVA composition in the blend. At the similar blend ratio, EVA/ENR-50 blend exhibited better tensile properties than SMR L blends. For the effect of compatibilization study, both of the PEA or ENR-50 as compatibilizer exhibited substantial improvement in tensile properties. The tensile properties in blends with ENR-50 are better due to better interfacial adhesion generated between EVA and SMR L than PEA. Scanning electron microscopy (SEM) of tensile fractured surface indicated that EVA/ENR-50 blend need higher energy to cause catastrophic failure compared to EVA/SMR L blend. The incorporation of compatibilizer as well as crosslinking agent tend to increase the thermal stability and heat resistance of the blend compared to the unvulcanized blend. For unvulcanized blend, EVA/ENR-50 blends exhibit better thermal stability and heat resistance than EVA/SMR L blends.
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Master
Keywords
Chemical science , Thermoplastic elastomer , Ethylene vinyl acetate (EVA) , Natural rubber
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