Acid-Cured Norbornylized Seed Oil Epoxides for Sustainable, Recyclable, and Reprocessable Thermosets and Composite Application

Abstract

Reprocessable and recyclable thermosets were produced from the epoxidized norbornene seed oils (soybean oil and linseed oil). The epoxides were copolymerized using disulfide-based aromatic carboxylic acid to mold thermosets and composites. Both the neat and reprocessed thermosets were characterized for cross-linking efficiency by dynamic mechanical analysis (DMA), Soxhlet extraction, and swelling tests; for thermal stability by thermogravimetric analysis (TGA); and for Tg by differential scanning calorimetry (DSC). Mechanical properties of the thermosets were also investigated. Further, carbonized biomass sorghum fillers were added into the system to assess their effect on the final properties. Increased bio-based content, cost, and weight savings were introduced into the system by virtue of biomass filler addition. Lastly, glass-fiber-reinforced composites were molded, and their mechanical and thermal properties were evaluated using an impact tester and a universal testing machine (UTM) and by DMA and TGA, respectively. It was noticed that higher seed oil functionalization resulted in higher the reactivity and final performance properties like cross-linking density, thermal stability, and tensile modulus. Nonfilled epoxy systems in comparison to the sorghum-filled thermosets and composites showed enhanced thermomechanical properties. Chemical recycling and reprocessing abilities of these highly bio-based materials were also investigated. The research thus demonstrates the systems’ possible use in environmentally friendly, sustainable, and lightweight composites.