No abstract

Thermoplastic vulcanizates (TPVs) have attracted considerable attention as typical "green" polymers in recent years and have been widely used in industry because they combine the excellent resilience of conventional elastomers and the easy recyclability of thermoplastics. With a new understanding of the formation and agglomeration of the rubber nanoparticles in ethylene propylene diene monomer/polypropylene (EPDM/PP) TPV, we revealed a new mechanism for the morphology evolution of TPV during dynamic vulcanization (DV). The phase inversion in TPV is dominated by the formation and agglomeration of the rubber nanoparticles rather than the elongation and breakup of the crosslinked rubber phase as previously reported. The size of the rubber agglomerates increases with increasing DV time and then remains constant after DV. In addition, we studied the relationship between the cross-linking of the rubber phase, formation and agglomeration of the rubber nanoparticles, and phase inversion and variation of the rubber network during DV. This study provides guidance to control the microstructure of TPV in preparation of high performance TPV products for automobile and electronic applications.

The breakup of the rubber phase in an ethylene-propylene-diene monomer (EPDM)/polypropylene (PP) blend at the early stage of dynamic vulcanization is similar to that in an unvulcanized EPDM/PP blend because of the low crosslink density of the EPDM phase. In this work, the minimum size of the rubber phase in the unvulcanized EPDM/PP blend was first calculated by using the critical breakup law of viscoelastic droplets in a matrix. The calculated results showed that the minimum size of the rubber phase in the unvulcanized blend was in the nanometer scale (25-46 nm), not the micrometer scale as reported in many works. Meanwhile, the actual size of the rubber phase in the thermoplastic vulcanizate (TPV) at both the early stage and the final stage of dynamic vulcanization was observed by using peak force tapping atomic force microscopy (PF-AFM). The results indicated that the EPDM phase indeed broke up into nanoparticles at the early stage of dynamic vulcanization, in good agreement with the calculated results. More interestingly, we first revealed that the micrometer-sized rubber particles commonly observed in TPV were actually the agglomerates of rubber nanoparticles with diameters between 40 and 60 nm. The mechanism for the formation of rubber nanoparticles and their agglomerates during dynamic vulcanization was then discussed. Our work provides guidance to control the microstructure of the rubber phase in TPV to prepare high performance TPV products for a wide range of applications in the automobile and electronic industries.

No abstract

Bromo-isobutylene–isoprene rubber (BIIR)/polyamide 12 (PA 12) thermoplastic vulcanizate (TPV) were prepared by dynamic vulcanization (DV) and the microstructure and properties of BIIR/PA 12 TPV toward recyclable green inner liners were studied.