“Oaked” silicones: natural tannins as crosslinkers for more sustainable silicone composites

Improved circularity in elastomers and composites requires better opportunities for reusing/repurposing before ultimate disposal, and better degradability once placed in the environment. We report that tannins—commonly used for enhancing fermentation and flavors in wines—are excellent crosslinkers for aminosilicones. Simply mixing a solution of the tannin in alcohol/water with aminosilicones provided an elastomeric composite after evaporation. The physical properties could be tuned simply by varying the quantity of food grade tannin and the molar mass of the telechelic aminosilicones. The products were thermoplastic and could be (re)processed at 140 °C or completely depolymerized by the addition of butylamine to regenerate both the aminosilicone and, after evaporation of butylamine, the tannin, consistent with an enhanced life cycle for these materials. An alternative phenolic filler, lignin, did not lead to composites with useful physical properties.