Cellulosic impurities such as burrs and vegetable fibers that were not removed during carding must be removed from wool cloth by chemical treatment before it can be further processed. In the carbonizing process, the wool cloth is treated with dilute sulfuric acid, dried, and then heated until the impurities are converted to carbon. Next, the cloth is fed through corrugated rollers, which crush the charred particles and shake them free. Finally, the cloth is washed and neutralized to remove residual acid. Sometimes it is necessary to carbonize wool fibers or yarn before they are made into cloth. The strength of the wool is not appreciably affected by carbonizing if the process conditions are carefully controlled.
When cotton cloth comes from the loom, the fiber ends or fuzz must be removed, because a smooth surface is necessary, particularly if the cloth is to be printed. This is especially important for fabrics known for their smooth surface. Singeing is the name given to the finishing process used to remove these fiber ends or short hairs by burning without causing damage to the cloth. Since burning entails oxidation, this process may be thought of as a chemical process.
Before singeing, the cloth is thoroughly dried and brushed so the short fiber ends will be brought to the surface. There are two singeing techniques. In the plate technique, the cloth is passed rapidly over a curved copper plate heated to a bright red. In the gas technique, two gas burners are placed so that both the front and back of the cloth is singed in a single pass through the equipment. The hot cloth is then passed through water or steam to extinguish any sparks that may be present.
Singeing is traditionally the first finishing process for woven cotton cloth. But sometimes starches and waxes may be more firmly fixed during singeing, making desizing more difficult. So, even though it is more economical to singe first, in some cases it is advantageous to modify or reverse the sequence of these finishing operations.
The use of polyester staple in blends with cotton, with the resultant pilling problem during wear, has increased the importance of singeing for these cloths. It is also important to singe knitted cloth to obtain a smooth surface. Improved machines have been introduced which insure clean singeing across the entire width of the cloth with less tension in the lengthwise direction.