Cationic UV-curing of isosorbide-based epoxy coating reinforced with macadamia nut shell powder

Abstract

The scientific community is deeply investigating bio-based derivatives to reduce the consumption of fossil-based material and lessen the environmental impact. 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. In this view, we exploit 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 functionalized in a two-step reaction to introduce epoxy groups that subsequently were activated via UV radiation to trigger cross-linking to obtain dry films. The curing process was followed by means of real time analyses such as FT-IR, photo-DSC and photorheology. The bio-based resin showed the feasibility to be used in UV-cationic curing reaching conversion above 85 %. 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. Thermo-mechanical analysis of the final properties was carried out by means of DMTA, DSC and tensile test. Interestingly, the addition of MAC 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. Lastly, a morphology assessment was performed to investigate the size and shape of the filler and the interaction between the polymer matrix and the filler.