Thermoplastic natural rubber based on polyamide-12 blended with various types of natural rubber

Abstract

Thermoplastic natural rubber (NR) of dynamically cured 60/40 NR/polyamide (PA) blends has been prepared by using three types of NR: unmodified air dried sheet NR, epoxidized NR (ENR) with 25 and 50 mol% epoxides. Plasticizer (i.e. dioctyl phthalate (DOP)) and processing oils (i.e. treated distillate aromatic extract and paraffinic oils) were incorporated in the blends. Stress relaxation, rheological, mechanical, and thermal properties of the blends were investigated. It was found that mixing torque, shear viscosity, tensile strength, and hardness of the oil-extended blends exhibited lower values compared with the blends without oil. But higher elongation was observed due to the distribution of oil into PA-12 and rubber phases. Furthermore, an increasing trend of stress relaxation behavior and rubber index was observed in the blends with DOP, which revealed an improvement in elastic properties. It was also found that the incorporation of DOP caused an enhancement in thermal behavior in terms of T ₁₀, T ₅₀, T ₉₀, and integral values, but a reduction in the glass transition temperature (T _g) of NR phase and crystallization temperature (T _c) of PA-12 matrix was also observed. This is attributed to the similar solubility parameter of DOP compared with the blend components. It was also found that the dynamically cured blends showed smaller rubber domains dispersed in PA-12 matrix. However, the addition of DOP resulted in an increase in the size of vulcanized rubber particles.