Epoxidized linseed lipids as a durable and fast-curing alternative to drying oils

Abstract

Linseed and other unsaturated plant oils continue to be important natural finishes for wood protection. However, they suffer from long drying times and reduced durability due to their susceptibility to microbial colonization. Response surface modelling was used to study the effect of linseed fatty acid methyl ester (ELOME) addition on the curing of epoxidized linseed oil triacylglycerols (ELO) under ultraviolet (UV) light, as an alternative to air-drying of unmodified linseed oil. We found that the hydrolytic (abiotic and enzymatic) degradation was reduced by 20% compared to air-dried linseed oil due to ether cross-link formation at high degrees of epoxy group conversion (≥80%) in the presence of ELOME. Curing under solar irradiation was also tested using curcumin, a natural photosensitizer. In this case, it was found that that oxygen inhibition limited cross-linking on wood surfaces and in thin films unless a tertiary amine is present to scavenge oxygen. A desirability function approach concluded that epoxidized linseed lipids containing a high content of ELOME (75 wt% to 85 wt%) and moderate concentrations of the photoinitiator (35 wt% to 5 wt%), are good alternatives to linseed oil, resulting in films with a similar glass transition temperature but with the benefits of faster curing (seconds to minutes, compared to days or weeks) and improved hydrolytic stability. Such films still maintain a biorenewable content of >93%.