Cotton pulp is a base product used to manufacture a range of fiber products such as high-quality paper and filter materials. Cotton-based pulps are preferred for these applications, as they contain none of the acids and lignin present in wood pulp. The pulp is predominantly produced from cotton linters harvested from cotton plants or cotton waste, such as rags and off-cuts. The cotton pulping process involves “cooking” the finely-chopped cotton fibers with various chemicals and water. During this process, the pulp slurry is subjected to several cleaning stages prior to being formed into finished products or half-stock sheets destined for further processing by end users.
Cotton is one of the purest forms of cellulose found in nature. Pulps produced from cotton are free of almost all lignin, acid, and non-cellulose contaminants common to wood pulps, making products manufactured from them more stable, reliable, and robust. These characteristics make paper produced from cotton far more desirable as archival-grade bases for artwork and documents, as they do not degrade under artificial light as quickly. Cotton pulp, due to its lack of lignin, is also inherently brighter than wood pulp, thus requiring very little bleaching.
Most cotton pulp is produced from cotton linters or from rag waste. Linters are short, fine natural fibers that surround the seeds of cotton plants. The linters are collected during the harvesting of the cotton bolls and graded to separate the fibers suitable for the production of cotton pulp. Rag waste is generally any cotton fabric off-cuts from textile or garment manufacturing processes that would otherwise be destined for disposal. These rags may be of a wide variety of weights, sizes, and colors, all being suitable for the cotton pulp process if properly prepared.
The cotton pulping process begins with the sorting of the linters or rags to remove any foreign contaminants. Then, the raw materials are finely chopped and placed in a pressure vat with water and a variety of chemicals. The mixture is then “cooked” at carefully-controlled temperatures and pressures, typically under computer control, to break the cotton fibers down into a cellulose-rich slurry. Once the cotton pulp has reached the required consistency, it is passed through several refining processes that remove all fine dirt and any remaining contaminants.
Once cleaned, the cotton pulp is either pumped out to storage vats, semi-finished, or processed into end products. Stored cotton pulp and semi-finished, or half stock, pulp is generally sold to non-pulp producing end users to make a range of high-grade paper products. Half stock is produced by forming the pulp out into thick sheets where they are drained by suction and dried prior to packaging in bales for distribution.