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.
Description
Master
Keywords
Chemical science , Thermoplastic elastomer , Ethylene vinyl acetate (EVA) , Natural rubber