The Morphology Development Of POE/PP TPV During Dynamic Vulcanization And Its Interfacial Crystallization

Thermalplastic vulcanizates (TPVs) are a group of thermalplastic elastomers prepared by dynamic vulcanization which consist of a high content rubber phase (about 50%-80%). TPVs (high content rubber phase as dispersed phase, low content plastic phase as continuous phase) are widely used in automotive, electronics, medical equipment field for the high excellent resilience of the conventional vulcanized elastomers and good processability. Structure decision performance, the structure directly determines the properties of TPV, and phase structure of TPV is controlled by various factors in the process of dynamic vulcanization, thus it’s of great significance to study the microstructure and morphological evolution during dynamic vulcanization.POE (ethylene-octene copolymer)/PP (polypropylene) TPV is considered most likely to replace the current commercial EPDM/PP TPV for its excellent anti-aging mechanical properties, low cost. At present there is few studies about the microstructure and morphological evolution of POE/PP TPV and no unified understanding The purpose of this project is to explore the mechanism of microstructure formation and morphological evolution in the dynamically vulcanized POE/PP blends, and the effect of crosslinking degree, crosslinking rate, shearing rate on them are also been studied. In addition to this, we studied the mechanism of interfacial crystallization in the POE/PP TPVs and used peak force taping atomic force microscopy(PF-AFM) observed the dynamically process of interfacial crystallization for the first time. This found supports the mechanism of acceleration crystallization induced by interface nucleation extensively and directly. Both the microstructure and the crystallization of PP in the dynamically vulcanized POE/PP TPVs are very important to the properties, and our research result will be helpful to the production of TPVs.Many previous studies generally thought that the dispersed rubber phase in the plastic matrix after dynamic vulcanization is about 0.5-3um, but recently some TPVs researchers found that the micron level rubber phase was actually the agglomerate of many rubber nanoparticles and suggested a new mechanism of morphology development based on the rubber nanoparticles. In this study, through AFM would found that the POE dispersed phase are the agglomerate of many 30-60nm POE nanoparticles. Then we took samples at different dynamic vulcanization stages (cooled in liquid nitrogen), through the observe of AFM we found that the POE phase broke up into nanoparticles at the earth stage of dynamic vulcanization and form the agglomerate and aggregate of POE nanoparticles for the crosslinking inhomogeneity. The crosslinking degree of POE phae increase with the process of dynamic vulcanization, then all the nanodropletstransform into nanoparticles and spontaneously agglomerate with one another but cannot coalesce anymore. The formation of POE nanoparticles and agglomerate is push the continuous rubber phase become the dispersed phase. The mechanism purposed above is different from tradition view.We continued to stuy different factors-crosslinking rate, crosslinking degree and shear rate on the microstructure and morphological evolution based on the mechanism of POEnanoparticles. Different copies crosslinking agent are are used to studied the effect of crosslinking agree and found that the crosslinking degree has no influence on the phase inversion, the diameter of nanoparticles decrease with the increasing crosslinking degree. Different kinds of crosslinking agents are used to studied the effect of crosslinking rate and found that faster crosslinking rate push the phase inversion happen earlier, the diameter of POEnanoparticles decrease with the increasing crosslinking rate. Different speed of the rotor is used to studied theeffect of shear rate and found that increasing shear rate can let the phase inversion happen earlier, the diameter of POE nanoparticles decrease with the increasing shear rate.Besides the microstructure and morphological evolution of POE/PP TPV, we also studied the interfacial crystallization. We design a new method to prepare POE/PP TPVthin film through dissolution and observe the dynamic crystallization on the AFM sample stage under heating condition. The PPcrystalliation nucleation is found first appear at the interface of rubber phase and plastic phase, and then the crystallization extends to the PP matrix. This phenomenon prove the correctness of mechanism of acceleration crystallization induced by interface nucleation extensively and directly.