Effect of dynamic crosslinking on impact strength and other mechanical properties of polypropylene/ethylene-propylene-diene rubber blends

Abstract

The deformation and fracture behavior of several dynamic vulcanizate blends of isotactic polypropylene with ethylene‐propylene‐diene rubber (EPDM) was examined and compared with those of uncrosslinked blends of PP/EPDM. These blends were prepared by melt mixing in an internal mixer at 190°C in a composition range of 10–40 wt % EPDM rubber. The variation in yield stress, the strength of fibrils of the craze, and the number density of the EPDM rubber domains (morphology fixation) that are dominant factors for enhancing interfacial adhesion and toughness in dynamic vulcanizate blends were evaluated. The ductility and toughness of these materials were explained in light of the composition between crack formation and the degree of plastic deformation through crazing and shear yielding. The physicomechanical properties including the hardness, yield stress, Young's modulus, percentage elongation, impact strength, flexural strength, and flexural modulus of dynamic vulcanized blends were found to be consistent and displayed higher values compared with uncrosslinked blends. The nucleation effect of the crosslinked particles and the decrease of crystallinity of the EPDM rubber were also considered to contribute to the improvement in the impact strength. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2089–2103, 2000

Crystallization kinetics and crystalline morphology of poly(ε‐caprolactone) in blends with grafted rubber particles

“…Several authors have reported an increase in the crystallization temperature after (reactive) compatibilization and/or dynamic vulcanization of polymer blends consisting of a semi‐crystalline thermoplastic matrix and a dispersed amorphous phase 3–10. The results presented here indicate that the formation of graft copolymers on the interface of the dispersed amorphous phase and the matrix is the major reason for the increased crystallization temperature.…”

“…Additionally, an increase in the crystallization temperature ( T c ) from 115 °C before vulcanization up to 120 °C after vulcanization was reported 5. The formation of graft copolymers during dynamic vulcanization and an increase in the nucleating efficiency of the crosslinked rubber particles was also reported by Jain et al6 and López‐Manchado et al7 for PP/EPDM blends and by Huang et al8 for nylon/EPDM blends compatibilized with an anhydride‐grafted EPDM copolymer. Several studies on blends of poly(ε‐caprolactone) (PCL) with epoxy resins prepared via reaction‐induced phase separation (RIPS) showed a significant nucleating effect of the dispersed, amorphous epoxy phase on the PCL matrix 9–11.…”

“…The properties of polymer blends can be further optimized by controlled chemical reactions that proceed during melt blending, such as reactive compatibilization or crosslinking. For polymer blends consisting of a semi‐crystalline thermoplastic matrix and an amorphous dispersed phase, several examples show that crosslinking of the amorphous phase and/or interfacial reactions to improve the blend compatibility often lead to an increase in the onset temperature of crystallization upon cooling from the melt 3–13. These changes in the crystallization process are known to affect the properties of the blend.…”

Partial replacement of EPR by GTR in highly flowable PP/EPR blends: Effects on morphology and mechanical properties

“…This behavior can be explained by the resulting morphology and elastomeric nature of EPR. On the P 70 V 30 and P 50 V 50 blends, the existence of very small EPR domains, below 0.1 µm, highly dispersed in a continuous thermoplastic phase and with smaller interparticle distances, can induce a predominantly shear yielding mechanism of failure, rather than crazing, enhancing the matrix toughness . This mechanism can be verified by the existence of a homogeneous fracture surface on a P 70 V 30 blend specimen after the tensile test (Figure ).…”

Morphology and properties of PP/EPDM binary blends and PP/EPDM/nano‐CaCO3 ternary blends

“…In past several decades, many methods have been taken to modify the toughness of PP 5–7. Blending with elastomer is one of the effective methods to toughen PP, but at sacrifice of the strength of PP 6, 8–11. To reach a perfect balance of toughness and strength, the ternary polymer blends of PP/elastomer/nano‐particles were developed.…”