Review of the weathering and photostability of modified wood

Abstract

Chemical modification of the molecular structure of polymers is a fundamental approach to improving the resistance of materials to photodegradation, but it is seldom employed because other techniques, such as the use of additives (ultraviolet absorbers and antioxidants) can provide adequate levels of protection. Wood is an exception to this rule because the additives that can protect polymers from photodegradation are less effective at photostabilizing wood. Conversely, chemical modification of wood surfaces with chromic acid is remarkably effective at photostabilizing wood, and this led to significant interest in chemical modification as a way of protecting wood from photodegradation. Early research focused on understanding why chemical modification with chromic acid was so effective at photostabilizing wood, and significant effort was directed towards finding effective alternatives to chromic acid. This search was largely unsuccessful and hence attention then shifted to the development of alternative methods of chemically modifying wood to improve its photostability. Research was also performed to examine the extent to which chemical and other modification systems designed to improve dimensional stability and decay resistance could protect wood from weathering. This paper reviews this research and describes the progress made to date to develop modification systems that can block the photodegradation of wood.