Fabricating super-tough polypropylene nanocomposites incorporating silane cross-linked in-situ nano-fibrillated ethylene-1-butene copolymer

In this study, we propose a novel approach to toughening polypropylene (PP) by integrating in-situ fibrillation technology with the silane crosslinking mechanism. Specifically, we graft vinyl trimethoxy silane (VTMS) onto the backbone of ethylene-butene-rubber (EBR) chains using reactive extrusion. Subsequently, we perform the in-situ fibrillation process using a spunbond machine, resulting in PP composites with in-situ nano-fibrillated EBR-g-VTMS. The next step involves crosslinking the fibrillated EBR-g-VTMS using moisture in order to preserve the fibrillar morphology. The unique fibrillar morphology and the substantial interfacial area of the rubber phase significantly enhance the mechanical, rheological, and crystallization behavior of the PP composites. Rheological data reveal that the in-situ nano-fibrillated rubber phase forms an interconnected network at around 3 wt% loading. Scanning Electron Microscopy (SEM) images show that the average EBR-g-VTMS fiber size is approximately 70-80 nm at 10 wt% rubber loading. Notably, the presence of fibrillar EBR-g-VTMS leads to a substantial increase in beta phase content up to similar to 65 %. Moreover, the matrix-spanning network of cross-linked EBR fibers exhibits toughening mechanisms superior to those found in classical sea-island blends, resulting in a dramatic enhancement of PP toughness across various test conditions (such as 50 % in the elongation at break in room temperature, 300 % in sub-zero tensile testing, and 200 % in Izod impact test) while showing only marginal reduction around 10 % in its strength and stiffness. Finally, this innovative and practical approach enables the leveraging of in-situ fibrillation for a wide range of polymer/rubber systems, optimizing rubber performance as a toughening agent.