Cotton Linters

It is worth being precise, because the physical route and the commercial logic point in slightly different directions. Linters are not taken off a bale of lint. They are cut from the seed — the other stream leaving the gin — in a separate operation at a separate site, usually the oil mill that is about to crush that seed for oil, and they are recovered in successive passes known as cuts.

AgricultureID nonetheless models linters as a by-product of cotton lint, and the reasoning is that linters are defined entirely by the lint stream: they exist as a category only because ginning did not take them. A saw gin is built to remove the long fibre and cannot reach the fuzz, and what it leaves is what a linter is. Cut the definition any other way and linters are simply "cotton fibre" — it is the gin’s boundary that makes them a distinct commodity at all.

Delinting machines take the fuzzy seed as it arrives from the gin and cut the fibre from it with closely set saws. The work is done in stages, and the stages produce genuinely different products. The first cut takes the longest of the remaining fibres and yields the most fibrous, least pure material; later cuts take progressively shorter fibre and produce the shortest, purest cellulose. Mills sell the cuts separately, because their buyers want different things.

The operation serves the seed as much as the fibre. A crusher wants a clean, hulled seed, and residual fuzz interferes with hulling and with oil extraction, so delinting would be done even if the linters themselves had no market. That is part of what makes them a by-product in the true sense: the process would run regardless, and the fibre is value recovered from a step taken for another reason.

Almost every use of linters turns on cellulose purity. Cotton fibre is nearly pure cellulose to begin with — far purer than wood, which must be pulped hard to remove lignin — so linters give chemical manufacturers a feedstock that starts where wood pulp finishes. Purified linters are the base for cellulose derivatives: acetate, nitrocellulose, carboxymethylcellulose, and viscose among them.

• Chemical cellulose — the feedstock for cellulose acetate, nitrocellulose, and other derivatives
• Absorbent products — cotton wool, swabs, and medical and hygiene absorbents
• Speciality papers — including banknote and security papers, where cotton fibre gives durability
• Food and pharmaceutical cellulose ingredients
• Padding, batting, and filling for furniture and mattresses
• Mulch, filler, and lower-grade uses for the coarsest cuts

The banknote use is the one people find surprising and it follows directly from the material: paper made with cotton fibre survives folding, crumpling, and washing in a way wood-pulp paper does not. The security paper trade has drawn on cotton fibre, including linters, for a very long time for exactly that reason.

Linters are bought on the cut they came from, cellulose purity, colour, fibre length, and freedom from trash, hull fragments, and motes. Chemical buyers are the most demanding on purity and the least interested in length; absorbent and padding users care about colour and bulk; paper makers care about fibre length. The specifications belong to the buyer, and no general grade table is reproduced here.

Handling resembles that of lint. Linters are baled for transport and storage, kept dry — damp fibre yellows and moulds — and treated with respect for fire, since a warehouse of compressed short cellulose fibre is exactly the material a fire wants. Dust is a bigger issue than with lint, because the fibre is shorter and carries more fine material.