Scalable production of crosslinked rubber nanofibre networks as highly efficient toughening agent for isotactic polypropylene: Toughening mechanism of Non-traditional anisotropic rubber inclusion

Abstract

Incorporation of homogenous rubber microparticles is a widely adopted toughening method for extending the range of applications of polypropylene (PP). Herein, a new toughening strategy with nano-structured rubber inclusion is devised and its efficiency is evaluated against the classical counterpart. The presented methodology integrates two well-established processes, namely vulcanization and in situ fibrillation, to allow scalable fabrication of PP nanocomposites toughened with crosslinked ethylene-propylene-diene terpolymer (EPDM) nanofibrils, which is otherwise technologically challenging. Morphological observation of the PP nanocomposites, supported by the drastic change in rheological behaviour under shear flow, substantiates the self-assembly of physical EPDM network nanostructure throughout the entire composite system above their rheological percolation threshold. The distinct morphology imparts unique characteristics that are vastly different from classical PP blends produced with the equivalent material composition. Massive improvement in macroscopic fracture behaviour is observed as the tensile fracture toughness is markedly enhanced at a comparatively low EPDM loading while the yield strength and elastic modulus are only marginally decreased. In our attempt to explain the superior toughening efficiency of crosslinked EPDM nanofibrillar network, we propose a collective toughening mechanism which is possibly triggered by several micro-scale mechanisms in play. This industrially relevant process potentially opens up a new avenue in material design for high-volume/lost-cost applications in the transportation sectors where excellent strength/toughness balance is indispensable.