The division of biodeterioration into topics is convenient but artificial. Many ‘natural’ or non-synthetic materials have specific major uses: for example,wood and stone are common building materials and are therefore considered in Chapter 4 as ‘materials in use’. Where materials, such as wood, are dealt with elsewhere, only the basic mechanisms involved in their biodeterioration are considered in this chapter.
Cellulose is the main structural component of plant cell walls and is probably the most abundant biological compound on Earth, the total world estimate being approximately 26.5 × 1010 tonnes. Cellulose is produced in vast quantities, and the fact that it is recycled relatively quickly emphasizes both its susceptibility to attack by organisms and the range of organisms able to do so and utilize the breakdownproducts. In green plants, cellulose is the main material found in the primary cell walls, which are thickened in structural and conductive tissues. These special tissues provide many of the plant fibres used by humans. Cellulose is also found in the higher fungi and algae. It occurs alone in the fungi and algae, but in higher plant groups it is frequently associated with lignin, which is much less readily biodegraded.
Cellulose is a linear polysaccharide made up of β-(1–4) linked D-glucopyranose residues (Figure 2.1), occasionally cross-linked to other similar chains by means of hydrogen bonding to produce microfibrils.
Lignin, however, although made of the same basic chemical elements as cellulose, namely carbon, hydrogen, and oxygen, is not built of sugar, but of phenylpropane subunits, and is not a carbohydrate.