Self-reinforcement in filled rubber via strain-induced crystallisation

Strain-induced crystallisation in elastomers markedly increases their elastic moduli and rupture resistance. However, the mechanisms underlying this self-reinforcement in filled elastomers remain unclear owing to the nanoscale nature of the involved processes. Herein, isoprene rubber with/without silica nanoparticles is stretched to strains of >5 and concomitantly imaged via in situ transmission electron microscopy. Nanoscale electron diffraction mapping and in situ transmission electron microscopy results reveal that the self-reinforcement mechanism depends on the filler presence/absence. The unfilled isoprene rubber exhibits a spatially homogeneous strain-induced crystallisation behaviour resulting in drastic elastic modulus enhancement above the crystallisation onset strain. In contrast, the silica-filled isoprene rubber displays preferential crystallite formation in highly stressed regions along the silica aggregates aligned in the stretching direction. This reinforces the stress propagation pathways within the material and results in a lower crystallisation onset strain and higher rupture strength than those of the unfilled system. The insights on the role of fillers in determining strain-induced crystallisation phenomena and mechanical properties facilitate the rational design and development of elastomers.