- Joined
- Nov 24, 2005
- Messages
- 381
Looks like lots of room for everyone's internet searches on the matter. I'm just a simple wood cutter and not a chemist or toxicoligist so have to cut and paste some contributing information. I'll include the source links with mine.
http://www.sciencedirect.com/scienc...serid=10&md5=72ced7674200d539df7f1f111079d432
Abstract
In this article we try to give an overview of the photodegradation of wood and the different ways available to stabilise this complex substrate. The mechanisms of wood photodegradation have been investigated and it appeared that lignin is the key structure because this component is able to absorb in the UV/visible region due to its chromophoric groups. Thus, some solutions can be offered to protect wood against photodegradation. One of the easiest consists in applying finishes such as paints, coatings, varnishes etc., but it is also possible to modify the substrate chemically (e.g. by acetylation) or to stabilise its colour by thermal and photochemical pre-weathering. The use of UV absorbers, HALS, antioxidants and the recent development of new additives help to prevent the degradation of the coated wood system.
Keywords: Wood; Photodegradation; Stabilisation; UV absorbers; HALS
http://www.springerlink.com/content/n2lv612210142114/
Abstract The photodegradation of wood is essentially a surface phenomenon, and although in practical terms it has no effect on strength properties, it does have serious consequences for the surface technologist. A principal concern is photodegradation of the timber surface underlying clear and lightly-pigmented finishesa problem which can lead to early failure of the coating and to expensive remedial measures. Recent thinking is directed towards the development of pretreatments which could stabilise the timber surface against photodegradation. However, in the absence of detailed investigations on the wood-degrading capabilities of different regions of the solar spectrum such developments have so far been restricted. In this paper, thin strips of Scots pine and lime were irradiated behind filters which transmitted selected regions of the ultraviolet and visible spectrum. Tensile tests on irradiated strips show that ultraviolet light is highly active in degrading wood, but indicate that the visible part of the spectrum also contributes significantly to loss of strength. Throughout the exposure period, samples were taken for SEM observation. The loss of strip strength is associated with a light-induced depolymerisation of lignin and cell wall constituents, and to the subsequent breakdown of the wood microstructure.
http://pop.acd.ucar.edu/
What is Photochemical Oxidation?
Oxidation is the process of combining oxygen with some other substance or a chemical change in which an atom loses electrons. Photochemical oxidation is oxidation caused by Ultraviolet (UV) radiation in the earth's atmosphere. This processes creates the free hydroxl radical (-OH). The high energy of UV radiation can also break the chemical bonds of water (H2O) to yeild *OH and hydrogen (*H) radicals.
The rusting of iron is a common form of oxidation
Ultraviolet radiation is part of the electromagnetic spectrum which ranges from gamma rays at the most energetic end to radio waves at the less energetic end. Most people are familiar with UV radiation b/c it is what causes our skin to sunburn.
