Improved photoprotection of wood by chemical modification with silanes: NMR and ESR studies

Silylation of wood specimens was performed with the aim of providing weathering protection, in particular photoprotection from the detrimental effect of sunlight. Primer formulations containing various silanes, were prepared and applied to wood specimens. Si-29 NMR, C-13- and Si-29-CP/MAS NMR spectroscopy were employed to investigate silane oligomer formation in primers, the extent of reaction occurring between wood and silanes, and the type of polysiloxane network formed inside the wood structure. Furthermore, the weathering performance of silylated wood was tested by exposing specimens to UV radiation, and subsequently measuring the photo-induced free radicals using electron spin resonance spectroscopy. Remarkable differences of individual silanes have been observed regarding polymerization patterns and reactivity with wood. Aminosilanes oligomerized most readily in primer formulations to produce siloxanes whereas gamma-epoxysilane was least reactive. alpha-Silanes and di-functional silanes showed higher reactivity with wood than gamma-silanes and tri-functional silanes. alpha-Amino- and alpha-methacryloxysilanes provided long chain and highly cross-linked polysiloxane networks, while gamma-epoxysilane formed a modestly cross-linked structure. Best photoprotection was achieved with alpha-aminosilanes; however, wood specimens turned yellow during silylation. Nevertheless, silylation of wood was considered successful in providing superior photostability using alpha- and gamma-methacryloxysilanes and gamma-epoxysilane. Approximately, 35% less free radicals were generated compared with no treatment, and negligible color change was observed. Copyright (C) 2012 John Wiley & Sons, Ltd.