Exploring Amine-Epoxy Hybrid Curing Route Toward Development of Stretchable, Transparent, and Hydrophobic Epoxidized...

A new strategy was explored to crosslink the epoxidized natural rubber (ENR) using aminopropyl-terminated polydimethylsiloxane (AP-PDMS), enabling soft, transparent, and stretchable hybrid elastomers. The curing, catalyzed by hydroquinone (HQ) as a co-curing agent, proceeds via an amine-epoxy ring-opening reaction. The effects of HQ loading and curing time are systematically studied. The resulting nanocomposites showed exceptional flexibility (elongation at break ≈ 800%) and lower hardness than sulfur-cured ENR. The incorporation of flexible PDMS chains formed compliant hybrid networks with a glass transition temperature of ∼ -17.5°C, broadening their operational range. AP-PDMS further enhanced the homogeneous dispersion of silica nanoparticles, likely through interfacial interactions between its aminopropyl groups and silica surfaces, creating a well-integrated nanocomposite. High optical transparency arose from refractive index compatibility and uniform phase dispersion, while PDMS segments imparted enhanced hydrophobicity. Nanoindentation confirmed reduced modulus and hardness, underscoring microscale softness. 3D response surface plots mapped the mechanical behavior as a function of HQ content and curing time. This new class of hybrid ENR elastomers combines stretchability, softness, transparency, and hydrophobicity, making them promising candidates for applications where elasticity, transparency, and surface properties are of critical importance, offering a low-toxicity, scalable alternative to conventional crosslinking technologies.