What is cotton pulp?

Cotton bolls on a branch.

Cotton pulp is a staple product used to manufacture a variety of fiber products such as high quality paper and filter materials. Cotton based pulps are preferred for these applications as they do not contain any of the acids and lignin present in wood pulp. Pulp is predominantly produced from cotton linters harvested from cotton plants or cotton waste such as rags and leftovers. The cotton pulping process involves “cooking” the finely chopped cotton fibers with various chemicals and water. During this process, the cellulose pulp undergoes several stages of cleaning before being transformed into finished products or half-stock sheets destined for further processing by end users.

A cotton field.

Cotton is one of the purest forms of cellulose found in nature. Pulps made from cotton are free from nearly all of the lignin, acid and non-cellulosic contaminants common to wood pulps, making products made from them more stable, reliable and robust. These characteristics make cotton paper much more desirable as a basis for archiving 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, therefore requiring very little bleaching.

Most cotton pulp is produced from cotton linters or rag waste. Liners are short, thin natural fibers that surround the seeds of cotton plants. The linters are collected during the cotton boll harvest and classified to separate the fibers suitable for the production of cotton pulp. Rag waste is generally cotton fabric waste from textile or apparel manufacturing processes that would otherwise be destined for disposal. These rags can come in a wide variety of weights, sizes and colors, all of which are suitable for the cotton pulp process as long as they are properly prepared.

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The cotton pulping process begins with sorting the linters or rags to remove any extraneous contaminants. Then the raw materials are finely chopped and placed in a pressure vessel with water and a variety of chemicals. The blend is then “cooked” at carefully controlled temperatures and pressures, usually under computer control, to break down the cotton fibers into a cellulose-rich paste. Once the cotton pulp reaches the required consistency, it goes through several refining processes that remove all fine dirt and any remaining contaminants.

After cleaning, the cotton pulp is pumped into storage vats, semi-finished or processed into final products. Stored and semi-finished cotton pulp, or half stock, pulp is generally sold to non-pulp producing end users to make a variety of high quality paper products. Half of the stock is produced by pulping into thick sheets, where they are suction drained and dried before being packed into bales for distribution.

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