Biochar and Natural Antioxidants as Components of Eco-Friendly Elastomer Composites

Modern trends in advanced material design increasingly emphasize sustainability and the use of naturally derived resources. One promising approach involves replacing synthetic additives with natural compounds that exhibit stabilizing properties. The aim of this study was to evaluate the effects of selected natural auxiliary substances—thymol (2-isopropyl-5-methylphenol), quercetin (3,3,4,5,7-pentahydroxyflavone) and caffeic acid (3-(3,4-dihydroxyphenyl)prop-2-enoic acid)—on the properties of elastomeric composites based on natural rubber. Biochar was used as the filler in the composites, serving as an eco-friendly alternative to conventional carbon black. The evaluation included measurements of crosslink density, hardness, mechanical properties and microstructural analysis of the resulting materials. The samples were also subjected to accelerated aging under thermo-oxidative conditions and UV radiation to assess their resistance to degradation. For comparison, the commonly used synthetic antioxidant BHT (2,6-di-tert-butyl-4-methylphenol) was also analyzed. The results enabled the assessment of the potential of natural additives as environmentally friendly stabilizers in elastomeric systems, with respect to their effectiveness and impact on material durability.