Thermoplastic natural rubber based on polyamide‐12: Influence of blending technique and type of rubber on temperature scanning stress relaxation and other related properties

Abstract

Thermoplastic natural rubber based on polyamide-12 (PA-12) blend was prepared by melt blending technique. Influence of blending techniques (i.e., simple blend and dynamic vulcanization) and types of natural rubber (i.e., unmodified natural rubber (NR) and epoxidized natural rubber (ENR)) on properties of the blends were investigated. It was found that the simple blends with the proportion of rubber $ 60 wt % exhibited cocontinuous phase structure while the dynamically cured blends showed dispersed morphology. Furthermore, the blend of ENR exhibited superior mechanical properties, stress relaxation behavior, and fine grain morphology than those of the blend of the unmodified NR. This is attributed to chemical interaction between oxirane groups in ENR molecules and polar functional groups in PA-12 molecules which caused higher interfacial adhesion. It was also found that the dynamic vulcanization caused enhancement of strength and hardness properties. Temperature scanning stress relaxation measurement revealed improvement of stress relaxation properties and thermal resistance of the dynamically cured ENR/PA-12 blend. This is attributed to synergistic effects of dynamic vulcanization of ENR and chemical reaction of the ENR and PA-12 molecules. Furthermore, the dynamically cured ENR/PA-12 blend exhibited smaller rubber particles dispersed in the PA-12 matrix.

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

“…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.…”

“…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].…”

“…Because of their unique characteristics, TPEs have very useful and attractive applications in a variety of markets, including the automotive, building and construction, and wires & cables industries [16]. Polyamide 6,12 (PA6,12) has excellent solvent and oil resistance, acid and alkali resistance, and excellent environmental stress cracking resistance at elevated temperatures [1], [17], [18]. This polymer exhibits good resistance abrasion and fatigue, and melt processability.…”

Novel thermoplastic natural rubber based on polyamide 12 blends

“…This confirms combination effects of dynamic vulcanization and chemical interaction between ENR and PA-12 molecules that enhance the stress relaxation properties. 19,24 Therefore, it is concluded that the dynamically cured ENR/PA-12 blends gave higher area underneath the normalized force-temperature curves than those of the ADS/PA-12 blends. Table 6 summarizes the TSSR results based on Figures 6 and 7.…”

Development and preparation of high‐performance thermoplastic vulcanizates based on blends of natural rubber and thermoplastic polyurethanes

“…The slope of the increasing stress corresponded to the crosslinking density6 and/or the interaction between both phases8 in those materials. For TPV, the entropic effect, therefore, is an important phenomenon related to the interactions of the blend components.…”