Influence of UV curing parameters for bio-based versus fossil-based acrylates in mechanical abrasion

The selection of sustainable solutions for protective coatings should consider the use of bio-based materials and environmentally-friendly processing conditions, while their performance needs to be benchmarked against traditional polymer coatings. Therefore, acrylate coatings were formulated by mixing a viscous oligomer (acrylated soybean oil) with a monomer diluent (triacrylate) and applied as a coating on softwood (beech) substrates by curing under ultraviolet (UV) light. In this study, the processing conditions and performance of coatings is explicitly compared by introducing both fossil-based and bio-based grades of the monomer with similar chemical functionality. The wear of coated wood samples was tested on a rotational Taber abrasion tester recording progressive wear loss over 1000 cycles, investigating effects of photoinitiator concentrations and UV curing parameters (light intensity and number of curing passes) on wear resistance. In parallel, the degree of conversion was investigated in relation to other properties such as hardness, water contact angles and topographical evaluation of the wear tracks. Under conditions providing fully cured coatings, the bio-based acrylate coatings systematically present lower wear. This is in agreement with lower hardness and reduced brittleness of the bio-based versus fossil-based acrylates. Alternatively, additional insight in the wear properties is obtained from transient wear conditions for partially cured coatings. Most interestingly, the presence of a surface layer with more hydrophobic properties and formation of deposits in the wear track with either island-like or more smooth features was confirmed for the bio-based acrylate coatings, in parallel with the better lubrication and progressive wear reduction. The paper illustrates the benefits in mechanical performance of bio-based coatings when applied under specific processing conditions, which can be implemented at industrial scale in the future, e.g., as protective wood coatings.