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1. Raw materials
To achieve their protective purpose, preservation enclosures are made of durable, archival quality materials. Paper and paper-based board are versatile, cheap, and well tested for use in protective storage. In the last two decades the variety of paper products available has increased and individual products often relate specifically to particular needs. There are new materials being developed constantly and while some commercial specifications are detailed and relevant, others are unclear and make it difficult to determine whether the material should be used and if so in what circumstances. The following descriptions introduce the main raw materials from which any product will be made.
1.1. Paper
Machine-made papers are generally used for packaging and storage so this article does not cover the process of handmade paper in detail. The following descriptions will focus on the quality of the paper, the different types of pulp and the manufacturing process of machine-made papers.
1.1.1. Paper quality.
Paper is made from vegetable fibres, which, for modern machine made papers, are derived almost exclusively from wood. Specialist papers, eg traditional Japanese papers, can be made from fibres obtained from stems, leaves or the inner bark of certain trees; the classic example is the oriental `paper mulberry', the inner bark yielding long fibres known as `bast fibres'. The fibres need to be easily separated from other unwanted plant tissues and resins that would spoil the paper, and be of a type that will mesh easily together. The earliest European papers were made from linen and hemp rags, and cotton rags began to be used in large quantities in the eighteenth century. New technology and a shortage of rags led to experiments with different fibres and by the 1840s wood pulps were beginning to be used commercially.
The highest quality papers are characterised by the percentage of pure cellulose from which they are composed. Cotton is 100% cellulose and pure cotton paper is potentially one of the most stable papers available. High levels of alpha cellulose (that proportion of cellulose most resistant to chemical breakdown) reduce the likelihood of damage by oxidation. For a given fibre furnish, the folding and tensile strengths of a sheet of paper are affected primarily by the degree of beating to which the fibres...