Weathering and photostability of benzoylated wood

Abstract

Chemical modification shows promise as a means of protecting wood from deterioration by fungi, but the systems tested to date have shown limited ability to photostabilise wood. In this study wood was esterified with benzoyl choride and the photostability of the modified wood was assessed. Benzoyl chloride was chosen because it was thought that the introduction of benzoyl groups into wood might act as a UV screen protecting wood from photodegradation. Benzoylation of wood to high weight gains (∼70%) was effective at protecting wood from photodegradation and there was an inverse relationship between weight gains due to benzoylation and mass losses of modified Scots pine wood veneers during weathering. FTIR spectroscopy and SEM of benzoylated wood exposed to natural weathering provided strong evidence for the stabilisation of lignin as a result of benzoylation. Benzoylation to high weight gain, however, caused extensive swelling of the wood cell wall and large losses in the tensile strength of veneers. The UV absorption characteristics of wood were modified by benzoylation and ESR spectroscopy of UV irradiated veneers clearly showed that benzoylation reduced the concentration of free radicals that are involved in the photodegradation of wood.