Use of low molecular weight modified polystyrene to prevent photodegradation of clear softwoods for outdoor use

A global stabilization of clear softwoods for outdoor uses is presented. A commercial low molecular weight polystyrene-maleic anhydride copolymer was chemically modified by incorporation of polyethylene glycol (PEG) chains and acyl azide functionality. The PEG units bring antioxidant properties and partial solubility in water, whereas acyl azide groups are reactive with hydroxyl groups of the wood. Wood blocks were impregnated with the polymer and with a hydroxyphenylbenzotriazole UV-absorber, both bearing acyl azide functional groups, and then grafted by microwave activation. The treatment was efficient for dimensional stability against water, for color stability against UV-vis light and for adherence of the finishes after accelerated weathering. Nevertheless after coating, the wood blocks did not present the expected color stability during the accelerated aging in the presence of water, partially due to the sensitivity of the finishes.