Wood surfaces protected with transparent multilayer UV-cured coatings reinforced with nanosilica and nanoclay. Part II: Application of a standardized test method to study the effect of relative humidity on scratch resistance

Coated wood surfaces of components constituting flooring and furniture for interior end uses that exhibit good tribological properties are highly desirable. Surfaces of yellow birch wood (Betula alleghaniensis Britton) were protected with six different types of multilayer coatings (MCs) developed in this study. Each MC consisted of three layers: primer, sealer, and topcoat. UV-curable primer and topcoat formulations were, respectively, reinforced with a hydrophobic fumed silica (NS: 0 and 0.5 wt% in the formulation) and nanoclay (NC: 0, 1, and 3 wt% in the formulation). The scratch resistance of MCs on wood surfaces conditioned at 40% and 80% relative humidity (RH) was quantitatively and qualitatively studied. Quantitative evaluation was performed according to a standardized scratch test, while scanning electron microscopy (SEM) analysis was used for qualitative evaluation. Statistical results have shown that NS, NC, and NS × NC do not have a significant effect on scratch resistance of coated wood surfaces, whereas the effect of RH is significant. Regardless of RH, SEM images reveal that: (i) there is no sign of lack of adhesion between coating layers and the MCs/wood surfaces interface and (ii) all the MCs seem to have a ductile/brittle response to scratching. Qualitative information was in accordance with quantitative results.