Utilization of liquid epoxidized natural rubber as prepolymer and crosslinker in development of UV-curable palm oil-based alkyd coating

Innovation of new products from renewable resources are important for sustainable development. In this work, novel rubber-integrated palm oil-based alkyd resins were prepared using palm oil, glycerol, diacids, and liquid epoxidized natural rubber (LENR50). The synthesis started with alcoholysis of glycerol by palm oil to produce predominant mixture of monoglycerides, followed by polycondensation with diacids to form alkyd chain. In addition to glycerol, LENR50 was introduced as bio-based polyol for the alkyd synthesis. The rubber prepolymer was chemically integrated into the alkyd chain via the reaction between its epoxide or hydroxyl groups with COOH of diacids during polycondensation. Resultant alkyds were mixed with reactive diluent (styrene), crosslinker (trimethylolpropane triacrylate) and photoinitiators (benzophenone and 1-hydroxycyclohexyl phenyl ketone), and the mixtures were cured under UV irradiation. Introduction of LENR50 into the coating formulation has reduced the curing time, as well as improved some of the film properties of the coatings. Some of the LENR50-based coatings required as short as 3 mins of UV irradiation to form dry-hard films, while the control samples required much longer time. There was also notable increase in the gel content of the LENR-based alkyd coating, suggesting that the polyfunctionality of LENR50 could have increased the extent of crosslinking in the cured film. Other improvement recorded includes pencil hardness, film adhesion, solvent resistance, water resistance, and corrosion resistance. Thermal stability of the alkyd coatings is also reasonably good for general purpose coating applications. The findings from this study suggest that LENR50 could serve as an alternative polyol in synthesis of bio-based polyester binder for surface coating.

Automated summary

In this study, novel rubber-integrated palm oil-based alkyd resins were synthesized by reacting liquid epoxidized natural rubber (LENR50) with palm oil, glycerol, diacids, and alcoholyzed glycerol. The integration of LENR50 into the alkyd chain was achieved through the reaction between its epoxide or hydroxyl groups with COOH of diacids during polycondensation. The introduction of LENR50 shortened the curing time and improved some film properties of the coatings.