Functionalized recycled nanosilica with sustainable biomass extracts for aging-resistant rubber nanocomposites

Improving the durability of rubber materials while reducing dependence on synthetic additives is essential for cleaner and more sustainable material systems. In this work, polyphenols extracted from red grape seeds and green tea leaves were evaluated as biomass-derived antioxidants and used to functionalize nanosilica recycled from waste battery separators. Radical-scavenging activity assessed by the DPPH assay showed that red grape seed extract (RGSE, EC50 = 15.42 μg /mL) exhibited significantly stronger antioxidant performance than green tea extract (GTE, EC50 = 70.79 μg /mL). The extracts were immobilized on recycled nanosilica through chemical anchoring and strong hydrogen-bond interactions, enabling uniform dispersion and improved interfacial adhesion in natural rubber-styrene butadiene rubber (NR-SBR) composites. Rubber nanocomposites containing bio-functionalized recycled nanosilica showed enhanced mechanical strength, thermo-oxidative stability, and ozone resistance compared with those incorporating unmodified recycled nanosilica. Among the formulations, RGSE-modified recycled nanosilica provided superior protection against accelerated aging, effectively mitigating surface cracking and mechanical degradation. These results demonstrate that combining low carbon black content (5 phr), recycled nanosilica reinforcement (15 phr), and small amounts of biomass-derived additives (1.5 phr) represents a promising sustainable strategy to extend the service life of green rubber nanocomposites through waste valorization and bio-based functionalization.