Analysis of bio-based epoxy resins: Impact of amine hardeners on thermal, thermomechanical, optical and electrical properties of epoxidized resveratrol with high Tg

Epoxidized resveratrol (RES) has been cured with different amines in order to compare their possibilities to obtain high-temperature resistance of bio-based epoxy resins. Materials obtained from the bio-based monomer present glass transition temperatures (T_g) among the highest ever reported for an epoxy-amine curing system, with extremely high char residue, making them excellent candidates for extremely high-temperature applications. Particularly, epoxidized RES stoichiometrically cured with 4,4′-sulfonyldianiline (DDS) reached 297 °C, measured as the tan δ peak by DMTA, and two other materials, using 4,4′-methylenedianiline (DDM) and 4,4′-diaminodicyclohexylmethane (CAA) as curing agents, exceeded 300 °C. In fact, the material begins to degrade before the chains are fully relaxed, so they are thermosetting that never go completely into the rubbery state. Additionally, this resin improves the direct current (DC) insulating character (∼10¹⁵ Ωcm) while decreasing the optical band gap (∼2 eV) when compared to other epoxy resins available, which is of great interest for photovoltaic applications. Moreover, some of the materials presented a very high char residue proportion when heated (>40 wt% at 800 °C under nitrogen atmosphere), presenting good fire-retardant properties.