The effect of wood modification with nano aluminum oxide on surface characteristics and adhesion behavior of the coating after weathering

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Abstract

The durability and long-term performance of wood coatings are strongly influenced by surface condition and environmental exposure. This study investigates the effectiveness of nano aluminum oxide (Al 2 O 3 ) pretreatment as a surface modification strategy to enhance the weathering resistance and adhesion performance of coated poplar wood ( Populus tremuloides ). Wood specimens were impregnated with aqueous nano Al 2 O 3 suspensions at concentrations of 200 ppm and 400 ppm using a full-cell process and subsequently coated with three common coating systems: two-component polyurethane, water-based acrylic, and an anti-UV transparent coating. Surface roughness ( R a , R z ), color change ( ΔE ∗), leachability, and pull-off adhesion strength were evaluated before and after 180 days of natural weathering and 2000 h of accelerated UV exposure. The results demonstrated that nano Al 2 O 3 pretreatment significantly reduced color change, surface roughness levels after aging, and adhesion strength loss under both aging conditions, with the most pronounced improvements observed at 400 ppm. Natural weathering caused substantially greater adhesion degradation than UV exposure alone, highlighting the dominant role of moisture-assisted mechanisms in interfacial failure. Statistical analysis confirmed that both coating type and nanoparticle concentration significantly affected surface and adhesion properties (p < 0.05). Principal component analysis further revealed a strong multivariate coupling between surface degradation indicators and adhesion performance, indicating that nano Al 2 O 3 enhances coating durability through simultaneous stabilization of surface and interfacial characteristics rather than by improving a single parameter. Overall, the findings demonstrate that nano Al 2 O 3 impregnation is an effective and complementary pretreatment approach for improving the long-term performance of wood coatings intended for outdoor applications.

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