Microwave-assisted maleation of tung oil for bio-based products with versatile applications

In this work, a simple, “green” and convenient chemical modification of tung oil for maleinized tung oil (TOMA) was developed via microwave-assisted one-step maleation. This modifying process did not involve any solvent, catalyst, or initiator, but demonstrated the most efficiency of functionalizing plant oils: at a reaction time of 4 min, the yield of purified TOMA target product reached 94.5 wt.%. A mechanism of this microwave-assisted maleation was investigated by nuclear magnetic resonance (NMR) and gel permeation chromatography (GPC). The results clearly showed that without initiator, TO can react with MA not only via Diels-Alder reaction, but also via free radical copolymerization. Moreover, three oil-based epoxides including epoxidized glycidyl ester (EGS), epoxidized soybean oil (ESO), and epoxidized octyl soyate (EOS) as well as hydroxyl-terminated polydimethylsiloxane (PDMS) were employed to react with the optimized TOMA product. Novel fully oil-based epoxy resins and silicon-containing alkyd resins were prepared. Mechanical, thermal, thermo-mechanical, and hydrophobic properties of the as-prepared epoxy and alkyd resins were carefully evaluated. The surface morphologies at the failure of the cured resin materials were studied by scanning electron microscopy (SEM). The results indicate that these oil-based materials have potential applications as hydrophobic coatings.