Macadamia for robust epoxy coatings

Researchers have described the cationic UV-curing of an isosorbide-based epoxy coating reinforced with macadamia nut shell powder.

The macadamia nut comes from the rainforest of Eastern Australia but it is also present in South Africa which is the third largest worldwide producer. Image source: sunnysun0804 - Pixabay (symbol image).

The development of bio-based plastic is one of the main challenges that needs to be overcome to achieve the goal of sustainability and green economy. Reseachers now have exploited the use of a bio-based monomer, isosorbide, for the production of bio-based resins which can be used in coating applications. The isosorbide was functionalised in a two-step reaction to introduce epoxy groups that subsequently were activated via UV radiation to trigger cross-linking to obtain dry films.

Significant increase in hardness

Furthermore, a bio-based filler from macadamia nutshell was selected as an additive to the formulation with the aim of increasing the surface hardness of the final coating. A significant increase in hardness was observed for coatings containing 30 wt% of macadamia nut shell powder (MAC). In this case, the hardness reached 72 Shore D, whereas the pristine bio-based epoxy resin achieved only 19 Shore D. Interestingly, the addition of MAC also resulted in a noticeable increase of the Tg, from 24 °C for the pristine resin to 39 °C for the coating with 20 wt% of filler.

The study has been published in Progress in Organic Coatings, Volume 185, December 2023.