Abstract
The dynamic crosslinking of polyamide 6,12 and ethylene vinyl acetate (PA6,12/EVA) blends in the mixing chamber of a torque rheometer was investigated. EVA was selectively crosslinked within the PA6,12 phase through free radical reactions using dycumil peroxide. The degree of EVA crosslinking in the PA12,6/EVA materials was estimated based on the gel content (insoluble EVA fraction). The PA6,12/EVA phase morphology was investigated by scanning electron microscopy. The mechanical properties were investigated by determining the tensile strength and hardness. The half-life time (t1/2) for homolytic scission of the dcumil peroxide (DCP) was ~6s, and this time is longer than the dispersion time of the DCP in the blends. The addition of DCP resulted in increased torque values due to specific crosslinking in the EVA phase. For the pure EVA and its blends with PA6,12 the stabilized torque values increased proportionally with the amount of DCP in the system, due to a higher degree of crosslinking of the elastomeric phase. The gel content of the dynamically crosslinked blends increased with the amount of DCP incorporated until 4 phr. At 1 phr the gel content value was 2.6wt.%, while at 4 phr it was 17wt.%. For the polymer blend with 8 phr of DCP a lubricating effect contributed to reducing the gel content. The dynamically crosslinked blends, regardless of the amount of DCP added, showed a reduction in the mechanical properties, which is related to the morphological features of the system due to the low mechanical fragmentation during melt processing. http://dx.doi.org/10.18226/23185279.v3iss1p23
Highlights
Thermoplastic vulcanizates (TPVs) are an emerging class of thermoplastic elastomers (TPEs) that provide the processing characteristics of thermoplastic polymers and the performance of conventional crosslinked elastomers
The addition of larger amounts of dcumil peroxide (DCP) to the Ethylene vinyl acetate (EVA) resulted in increased torque, as shown in Figure 1 (a)
Crosslinked PA6,12/EVA blends were obtained through melt-mixing in a torque rheometer at temperatures and time-scales suitable for industrial polymer processing equipment
Summary
Thermoplastic vulcanizates (TPVs) are an emerging class of thermoplastic elastomers (TPEs) that provide the processing characteristics of thermoplastic polymers and the performance of conventional crosslinked elastomers. The mechanical, thermal and chemical properties of a TPV are dependent on the morphology developed during melt processing [1]. TPVs are produced by a dynamic process of vulcanization/crosslinking achieved through specific chemical reactions in the elastomeric phase using a crosslinking agent, resulting in the formation of new covalent bonds and an increase in the molecular weight and viscosity. The elastomeric phase in TPVs is fragmented by the action of mechanical forces during melt processing and dispersed in the thermoplastic phase (1-5 μm in diameter) [1]–[3]. The combination of behaviors similar to those of rubber and thermoplastic melts results in polymer system with a two-phase morphology: the soft phase, an elastomer, gives the rubber-like properties in the solid state, whereas the hard phase shows the properties of a thermoplastic polymer with a high glass transition temperature, which gives strength to the blend [4], [5].
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