Dynamic Vulcanization and Morphology

TP Vs are prepared from blends of isotactic PP and EPDM with curatives, such as peroxides, phenolic resins, or sulfur, by using a process called dynamic vulcani- 

Before dynamic vulcanization After dynamic vulcanization 

The typical commercialized TPV is composed of PP, EPDM, and a high concentration of extender oil, which are used to reduce the modulus and improve the processability. The performance of TPV is also determined by the morphology of the PP/EPDM blend, /W , and MWD of each components and the degree of vulcanization in the hnal products. 

Dynamic vulcanization is the key process of TPV to create suitable morphology and thus desired physical properties. Before dynamic vulcanization, the blend of PP and EPDM often shows that the major EPDM component is the matrix and the minor PP component is the dispersed domain, as shown in Fig. 8.12 (19). However, after dynamic vulcanization, the PP component becomes continuous phase and the EPDM component forms the dispersed domain. 

This can be explained as follows. It is known that PP and EPDM are immiscible materials and they exhibit a lower critical temperature (LCST) phase diagram (19). During mixing, especially at high shear rates, the LCST curve elevates with temperature and shear-induced mixing takes place. Thus, in the process of dynamic vulcanization, PP and EPDM can be considered as miscible materials under high shear rates. As a result, after the cross-linking reaction, the unmixed EPDM component forms the dispersed domain, while the matrix consists of mixed PP (dominant) and EPDM (minor) components connected by chemical cross-links (20). 

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