Effect of vulcanization systems on properties and recyclability of dynamically cured epoxidized natural rubber/polypropylene blends

Abstract

Thermoplastic vulcanizates (TPVs) based on dynamically cured ENR/PP with various vulcanization systems were prepared. Rheological, mechanical, dynamic and morphological properties of the TPVs were investigated. Amongst the TPVs with peroxide, sulfur and mixed sulfur peroxide cure systems, the TPVs with peroxide cured system showed the lowest apparent stress, shear viscosity, elastic modulus and mechanical strength, whilst the mixed sulfur peroxide curing system showed the highest values with the sulfur cured system being intermediate. However, it was found that the phenolic containing cure systems (i.e., phenolic cured system with HRJ-10518 and mixed phenolic cure system with 1:1 mixture of HRJ-10518 and SP-1045) exhibited higher shear stress, viscosity, elastic modulus and tensile strength than those of the first three types of TPV. Lower tension set and damping factor were also observed in these mixes, indicating greater elasticity. Moreover, the TPVs with phenolic containing cure systems are a two-phase system with smaller vulcanized rubber domains dispersed in the PP matrix. This causes higher interfacial adhesion and interaction between the vulcanized ENR domains and PP matrix. Hence, higher shear stress, shear viscosity, complex viscosity, elastic modulus and tensile strength of the TPVs with phenolic containing cure system were observed. Lower damping factor and tension set values were also a result of the smaller vulcanized rubber domains. It was also found that the ENR/PP TPVs were recyclable. That is, after the 4th reprocess cycle, the TPVs with phenolic containing cure systems showed tensile strength, elongation at break and tension set of approximately 10 MPa, 300% and 20%, respectively.