Wollastonite and Xonotlite from Industrial Waste as Functional Fillers in Self-Repairing Photocurable Cinnamon-Derived Vitrimer Composites.

This work aims to reuse calcium-rich waste from the sugar production industry as a precursor for the synthesis of calcium silicates and subsequently to apply the resulting calcium silicates as functional fillers in photocurable, catalyst-free vitrimer composites. To synthesize calcium silicate compounds, a mixture of calcium-rich waste and quartz, with a CaO/SiO2 molar ratio of 1.0, was prepared. Calcium silicates were synthesized using one-step solid-state calcination (400-1300 °C) and a two-step method combining hydrothermal treatment (200 °C, 16-72 h) with subsequent calcination (400-1300 °C). The one-step method led to the formation of multiple-phase mixtures, with wollastonite forming only above 1100 °C and coexisting with other phases. In contrast, the two-step synthesis enabled the formation of calcium silicate hydrates, tobermorite and Xonotlite, which recrystallized into β-wollastonite at 800-1000 °C and α-wollastonite at higher temperatures. Only the products obtained via the two-step route were selected as fillers due to their more suitable phase composition. The obtained Xonotlite and wollastonite were incorporated (10-20 wt %) into photocurable vitrimer matrices based on bisphenol A glycerolate dimethacrylate, 2-hydroxyethyl methacrylate, and cinnamyl methacrylate. Rheological analysis showed rapid photopolymerization for all formulations (gel point ≈1 s). Incorporation of cinnamyl methacrylate increased storage modulus and reduced polymerization shrinkage, while filler addition increased viscosity and stiffness but decreased storage modulus during curing. Self-welding at 180 °C confirmed dynamic bond exchange within the catalyst-free network. This work demonstrates an integrated circular approach in which industrial CaO waste is reused to synthesize functional calcium silicates that can be applied in vitrimer systems to enhance their properties.