Carbonizing
Also searched as: carbonising, carbonization, acid carbonizing, wool carbonizing, burr removal
A wool-cleaning process that uses sulfuric acid and heat to make cellulose-based vegetable matter brittle so it can be crushed and removed from the fiber.
In detail
Scoured wool can still contain burrs, seeds and grass, and in recycled material there may be cotton or other cellulose fibers. Carbonizing exploits a chemical difference: cellulose is hydrolyzed and weakened by strong acid at elevated temperature, while wool keratin tolerates acid far better. The wool is soaked in dilute sulfuric acid, dried and baked so the vegetable matter chars and becomes friable, then passed between crushing rollers and shaken so the fragments fall out. The wool is finally rinsed and neutralized. It belongs mainly to the woollen route, whereas worsted processing relies more on carding and combing.
The science and numbers
Acid-catalyzed hydrolysis cleaves the beta-1,4-glycosidic bonds of cellulose, and baking concentrates the acid as water evaporates, leaving vegetable matter brittle enough to crush. Keratin's amide backbone is far less susceptible under these conditions, and the fiber buffers acid through its amino and carboxyl groups, but protection is incomplete: carbonizing damages wool to some degree, and removing residual sulfuric acid takes large volumes of rinse water. Process control centers on acid concentration, liquor pickup, baking temperature and time. As a possible substitute, laboratory work has used fungal xylanase and cellulase to digest vegetable matter in fleece, and the authors reported removal without measurable fiber deterioration; this remains a research approach rather than standard mill practice.
A practical example
A mill receives a heavily burred lot of fine wool destined for woollen spinning. Carding alone would leave vegetable fragments in the yarn, visible later as specks in the fabric. The mill carbonizes the scoured wool first, then cards it. A student comparing samples before and after would see cleaner fiber but should also test whether strength and handle have changed.
What to distinguish
Carbonizing is not charring the wool, and it has nothing to do with making carbon fiber. It can weaken and yellow wool if acid concentration, temperature or time are excessive, and the acid must be removed carefully. In blends it destroys any cellulosic component, so it changes the fiber composition that ends up on the label.
Origins and history
The name refers to the charred, carbon-like appearance of the vegetable matter after acid baking. The process belongs to the woollen side of the industry, where burrs and seeds must be removed before carding and spinning, and wool industry bodies describe it alongside scouring as part of early-stage processing. Its costs in water use and fiber damage are the main reasons researchers now test enzymatic alternatives.
Related terms
Sources & further reading
- International Journal of Biological Macromolecules: Removal of vegetable matter from wool fleece using xylanase and cellulase (Ismail et al., 2023)
- Woolmark: Scouring and carbonising
- International Wool Textile Organisation: First-stage processing
Technical references reviewed 2026-09-22. Examples are illustrative. Industry organizations and manufacturers describe their own fields; their references are not independent product endorsements. Figures are approximate and depend on the stated test conditions.