Effect of dynamic crosslinking on phase morphology and mechanical properties of polyamide 6,12/ethylene vinyl acetate copolymer blends

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 (t 1/2 ) 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.

Influence of dynamic crosslinking on the morphology, crystallization, and dynamic mechanical properties of PA6,12/EVA blends

“…The addition of dicumyl peroxide to PA6,12/EVA blends increased the stabilized torques. Bondan and Soares confirmed this trend in the dynamic crosslinking of the PA12/EVA and PA6,12/EVA blends prepared in a mixing chamber …”

“…However, the stabilized torque of PA6,12 was insensitive to DCP addition, regardless of content. This indicates the DCP is more selectively to EVA . Similar results, in which DCP more easily forms crosslinks in the EVA phase than in the PA phase have been reported in the literature .…”

“…Similar results, in which DCP more easily forms crosslinks in the EVA phase than in the PA phase have been reported in the literature . This trend was due to the greater amount of tertiary carbons in the EVA structure when compared to the polyamide chains …”

“…The mechanical, thermal properties, and chemical behavior of these materials are a result of the phase morphology developed during processing . TPVs are produced by dynamic vulcanization/crosslinking, wherein the elastomeric and thermoplastic phases crosslink during melt processing . These materials can be prepared using conventional thermoplastic processing equipment and are also reprocessed and recyclable .…”

“…Bondan and Soares studied PA12/EVA blends dynamically crosslinked with DCP and showed that the DCP exerts almost no effect on the polyamide properties. In contrast, they later showed that the morphologies and tensile strain behaviors in 50/50 PA6,12/EVA blends depend on the DCP content …”