Fully bio-based epoxidized soybean oil thermosets for high performance triboelectric nanogenerators†
For the first time, fully bio-derived thermosets have been synthesized from abundantly available, low cost, renewable feedstocks through a simple, solvent-free and catalytic process for the fabrication of triboelectric nanogenerators (TENGs) for sustainable power generation. Thermoset films synthesized from epoxidized soybean oil (ESO) and bio-derived crosslinkers (succinic anhydride, suberic acid and sebacic acid) were coated onto copper conductive electrodes and PTFE (Teflon) was used as a counter or contact triboelectric material. Importantly, these bio-based thermoset materials demonstrated several properties with significant promise for application as TENGs, including excellent thermal stability, water repellency and surface hydrophobicity. The materials are thermally stable up to 250 °C and their water uptake is less than 1% after 24-hour immersion, with contact angles between 117.5° and 131.3°. The curing of the films was confirmed by FT-IR and the curing process was revealed by DSC, indicating a slightly higher crosslinking in dicarboxylic acid cured resins. As a result, the mechanical properties of diacid cured films were moderately higher than those of succinic anhydride cured resins. However, the anhydride cured films exhibited higher peak to peak output voltage and current of the TENG of 78 V and 8 μA, respectively, with a maximum power density of ≈1.4 W m−2 at a load resistance of 400 kΩ at an optimum molar ratio of crosslinker : ESO of 1.5 : 1. The better output performance of succinic anhydride films compared to that of diacid crosslinkers was attributed to the higher concentration of CO functionalities which was demonstrated by FT-IR results. These promising values are amongst the most significantly reported values for bio-based TENGs, hence thermoset films from ESO present a promising novel alternative for the production of greener TENGs.