Introduction of UV absorbers to wood surfaces via atom transfer radical polymerization

Wood is a promising material suited for both residential and commercial construction. However, the structure of the wood materials varies depending on the environmental factors such as microorganisms, water, and light. In particular, wood surfaces exposed to outdoor conditions are rapidly degraded because cell wall chemical components such as lignin structure strongly absorb ultraviolet (UV) light, which leads to radical-induced depolymerisation of wood constituents. Thus, wood materials have lower photoresistance under outdoor conditions. In this study, to improve the resistance of the wood surface to ultraviolet (UV) light, we carried out grafting of UV-absorbing vinyl polymers against the cell wall chemical components onto the wood surface via atom regenerated by atom transfer radical polymerisation (ATRP). We compared between of softwood: Japanese red pine (Pinus densiflora) and Japanese cypress (Chamaecyparis obtusa), and hardwood: Japanese beech (Fagus crenata) and walnut (Juglans spp.). First, the hydroxy group derived from cell wall chemical components on the wood surface was modified with an ATRP initiator. Then, a UV-absorbing vinyl monomer, 2-[2-hydroxy-5-[2-(methacryloyloxy)ethyl]phenyl]-2H-benzotriazole (HBT), was polymerised from the ATRP initiator at different rates of mass percent gain. Infrared spectra confirmed the achievement of initiator via esterification and grafting UV-absorbing vinyl polymers onto the wood surface. Moreover, the colour difference (ΔE*) of the samples also changed only slightly. These results showed that the grafted UV-absorbing vinyl polymers protect the cell wall structure of the wood surface against UV light.