Organisms wood-decay

Lead in building can be corroded by organic acids from new wood, decaying wood and lichens see Sections 9.3 and 18.10). This is a common phenomenon with run-off from lichens which grow on tiles and slates. Where this occurs, a sacrificial strip of lead has been advocated... 

Lignin comprises about 17-33% of the dry weight of wood. It is a complex aromatic polymer which appears to function both as a strengthening agent in the composite wood structure and also as a component which assists in the resistance of the wood towards attack by micro-organisms and decay. 

It is thermally stable up to 170 C and has solubility in water of about 33 ppm. Its primary promotion has been in the wood preservation industry as it is effective against a range of wood decay organisms. Its use in the plastics industry is only so far promotional. It is a white to yellow solid that is both metal and halogen free (Figure 40). 

Table 2 Radio sensitivity of wood decay organisms (After Pointing, 1995)...

Bruce A., Kundzewicz A. and Wheatley R. (1996) Influence of culture age on the volatile organic compounds produced by Trichoderma aureoviride and associated inhibitory effects of selected wood decay fungi. Mat. Org., 30, 79-94. 

Significant Decay. Wood decay organisms produce enzymes that break down the chemical structure of the wood and provide food for the decay s growth. This breakdown results in a progressive loss of the wood substance. The process is reflected in reduced density and strength, increased fluid permeability, and altered color and texture. 

Extractives and Ash. The amount of extractives in wood varies from 5 to 20% by weight and includes a wide variety of organic chemicals (11). Many of these function as intermediates in tree metaboUsm as energy reserves or participate in the tree s defense mechanism against microbiological attack. The extractives contribute to wood properties such as color, odor, and decay resistance. 

Decayed wood is eventually converted to humus, a dark and amorphous form of organic matter in the soil, or, after very long periods of time (running... 

This the reverse of the process occurring in Equation 6.1, the decay of 14C, and results in a nearly constant concentration of 14C in the atmosphere. Any living organic synthesis on Earth, such as photosynthesis, will then capture the 14C and produce a 12C/14C ratio in living things to be fixed. When a tree is used for wood in an object such as a museum artefact then the 12C/14C ratio changes and the age of the sample can be calculated using Equation 6.5 as before. 

As noted previously in Chapter 3, the improved dimensional stability of wood as a result of anhydride modification has been found to be a function of WPG only, irrespective of the anhydride used for modification (Stamm and Tarkow, 1947 Hill and Jones, 1996b Li etal., 2000b). This shows that improved dimensional stability arises due to a bulking phenomenon, caused by the volume occupied by the bonded acyl adducts in the cell wall. The dimensional stabilization of wood modified with crotonic anhydride has also been reported ( etin and Ozmen, 2001). Reductions in the EMC have also been attributed to a bulking phenomenon (Papadopoulos and Hill, 2003), and in at least one example of decay protection (Papadopoulos and Hill, 2002). Further research is needed to determine if this is the case for resistance to other decay organisms. Only with the phenomenon of surface wettability does the relationship between a physical property of chemically modified wood and WPG seem to be broken (Hill and Jones, 1996c) (Table 4.1). 

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