Polymers and Their Degradation

The materials used in producing books are almost exclusively natural or synthetic polymers, formed by linking large numbers of small molecules to form long chains, which may be linear, branched, or form networks. This chapter outlines the chemistry of the important polymers, particularly polysaccharides, proteins, lignin, and synthetic materials, emphasising how the chain structure affects chain packing in the solid state and thus mechanical properties. Because these materials are organic molecules, they are susceptible to degradative influences, notably heat, oxygen, light, moisture, and microorganisms, all of which can cause chain scission, or crosslinking, and loss of mechanical properties, as well as development of colour. The chemistry of the various degradation reactions and their effects on both physical properties and appearance are reviewed for the important polymer types. As well as specific materials, degradation can be influenced by catalytic contact with other materials, like metals, by small molecules in the materials, such as pigments and plasticisers (notably water) in natural polymers, and by external pollutants in the local environment (important in storage). These effects are also reviewed.