Novel thermoplastic vulcanizates (TPVs) based on silicone rubber and polyamide exploring peroxide cross-linking

Abstract

Abstract. Novel thermoplastic vulcanizates (TPVs) based on silicone rubber (PDMS) and polyamide (PA12) have been prepared by dynamic vulcanization process. The effect of dynamic vulcanization and influence of various types of peroxides as cross-linking agents were studied in detail. All the TPVs were prepared at a ratio of 50/50 wt% of silicone rubber and polyamide. Three structurally different peroxides, namely dicumyl peroxide (DCP), 3,3,5,7,7-pentamethyl 1,2,4-trioxepane (PMTO) and cumyl hydroperoxide (CHP) were taken for investigation. Though DCP was the best option for curing the silicone rubber, at high temperature it suffers from scorch safety. An inhibitor 2,2,6,6-tetramethylpiperidinyloxyl (TEMPO) was added with DCP to stabilize the radicals in order to increase the scorch time. Though CHP (hydroperoxide) had higher half life time than DCP at higher temperature, it has no significant effect on cross-linking of silicone rubber. PMTO showed prolonged scorch safety and better cross-linking efficiency rather than the other two. TPVs of DCP and PMTO were made up to 11 minutes of mixing. Increased values of tensile strength and elongation at break of PMTO cross-linked TPV indicate the superiority of PMTO. Scanning electron micrographs correlate with mechanical properties of the TPVs. High storage modulus (E!) and lower loss tangent value of the PMTO cross-linked TPV indicate the higher degree of cross-linking which is also well supported by the overall cross-link density value. Thus PMTO was found to be the superior peroxide for cross-linking of silicone rubber at high temperature.

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

“…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]. At the temperature of utilization, the latter is the stiffer phase that acts as a physical crosslinker for the elastomer phase.…”

Influence of network structure on the viscoelastic properties of dynamically vulcanized rubber/plastic blends: An alternative approach to understand the microstructure evolution

“…The constants C 1 and C 2 at reference temperature are determined by using equation 6 and 7 [31] , and the values are reported in Table 5.…”

“…From the degree of swelling the overall cross-link density was calculated by using Flory-Rehner equation [29,30] (Equation 1) relative to the (S-SBR+S-EB-S) phases as expressed by (ν + S-EB-S). The latter was done in order to correct for a part of the S-EB-S, being extracted as amorphous phase [31]. (1) where, M a n u s c r i p t 10 | P a g e χ = polymer-solvent interaction parameter, taken as 0.38 for both S-SBR and toluene at 25°C [32,33].…”

Devulcanization of Elastomers and Applications

“…Several papers also feature improvements in mechanical properties as a result of the dynamic vulcanization, but through the use of compatibilizing agents [36,48,[58][59][60] as a result of greater refinement of morphology [34,61], in general. Among the improvements, it is also found reduced permanent elongation, increased fatigue resistance, greater stability of morphology and better chemical resistance.…”

“…The process produces a cross-linked polymer dispersion in a continuous polymer matrix phase not cross-linked [38,40,[49][50][51][52]. The continuity of the thermoplastic phase provides the thermo-plasticity and mechanical resistance necessary to blends [53], while the dynamically vulcanized rubber particles give elasticity, flexibility and stability [36,46,54].The process can be described as follows: after enough fusion-blend of thermoplastic and rubber, vulcanization agents are added. The vulcanization of rubber phase occurs with a continuation of the mixture.…”