New understanding of microstructure formation of the rubber phase in thermoplastic vulcanizates (TPV)

Abstract

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.

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

“…Figure 10(A), (B) and (C) represent the magnified view of the domain morphology of P33, P34 and P35 TPV systems respectively and the distribution of particle size M a n u s c r i p t 22 | P a g e for the respective TPVs is given in Figure 11. From these images it is evident that the dispersed rubber particles are actually the disintegrated rubber agglomerates containing nano-sized rubber particles ranging from 60-100 nm which is quite similar to the observation recently made by Wu et al [40] and Abolhasani et al [41]. For P33 TPV (Figure 10(A)), the rubber nano-particles are heavily shadowed by the S-EB-S phase due to the higher proportion of S-EB-S (60 weight percentage), which makes the rubber network less responsive during the scan resulting in poor quality photo-micrographs.…”

Morphology Development via Static Crosslinking of (Polylactic Acid/Acrylic Rubber) as an Immiscible Polymer Blend

“…However, coalescence will not proceed in the rubber phase since the broken rubber particles are in situ vulcanized. At the later stage of dynamic vulcanization, the broken rubber particles agglomerate and form the final morphology . Unlike to dynamic vulcanization in which shear forces are applied to the sample, in the static vulcanization only a self‐generated elastic force exists.…”

Preparation and properties of novel fluorosilicone thermoplastic vulcanizate with cross‐linking–controlled core‐shell structure

“…6,7 The effective way to prepare TPVs is through dynamical vulcanization, [8][9][10] which is the process of cross-linking an elastomer during its melt mixing with a molten plastic under dynamic condition. 11,12 A significant number of TPVs are produced through this method, such as polylactide (PLA)/natural rubber (NR), 13,14 PLA/epoxidized natural rubber (ENR), [15][16][17] PLA/nitrile butadiene rubber (NBR), 18 poly(vinylidene fluoride) (PVDF)/acrylic rubber (ACM), 19 ethylene-propylene-diene monomer (EPDM)/polypropylene (PP), [20][21][22][23] PVDF/ENR, 24 polyamide 12 (PA12)/hydrogenated acrylonitrile butadiene rubber (HNBR), 25 and ethylene octene copolymer (EOC)/poly dimethyl siloxane (PDMS) rubber. 26 The properties of TPVs strongly depended on the final morphology, which were affected by many factors, such as the cross-linking degree of the rubber phase, composition, viscosity and elasticity of individual components, preparation method, and processing condition.…”

“…However, a new mechanism about the morphology evolution of TPV based on PP/EPDM was revealed by Tian et al It was found that the EPDM phase was broke up into nanoparticles at the early stage of dynamical vulcanization, and the rubber microparticles in TPVs obtained at the end of dynamical vulcanization were actually the agglomerates of rubber nanoparticles. 20 Meanwhile, the phase inversion was dominated by the formation and agglomeration of the rubber nanoparticles rather than the elongation and breakup of the cross-linked rubber phase. 7 This work provided new insights into the morphology evolution of TPVs during the dynamical vulcanization.…”