This invention relates to processes for treating textiles, and more particularly, it relates to processes for desizing and bleaching woven fabrics or similar goods based on textile fibers, in a single operation.
It is known that the preparation of fabrics made of cellulose fibers, by dyeing, printing and other finishing treatments, generally comprises the operations of desizing, boiling off, bleaching, and optionally mercerizing. The purpose of desizing is to eliminate the sizing products previously applied to the warp threads to improve their characteristics on the loom, as well as any products which may have been applied to the weft threads.
The sizing products applied to the threads before weaving may be based either on starch dispersions alone or in admixture with starches which have been more or less converted chemically, or on derivatives of polyvinyl alcohol, or polyacrylate derivatives or etherified cellulose. The sizing products may be retained to a greater or lesser extent in the fabric, depending on the drying temperature, the twisting of the threads and the texture of the fabric.
The presence of such sizes makes it impossible to obtain a uniform, solid shade during dyeing and printing with many dyes, and such sizes have to be eliminated before the dyeing or printing operations can be effected. For some fabrics intended for white sales, the removal of the size is also desirable to ensure that the treated goods are pleasant and supple to the touch. Desizing is generally effected by impregnation in an enzyme and surfactant bath heated to a temperature of between 60.degree. C. and 75.degree. C. The impregnated fabric may either be left to stand, or it may be steamed at a temperature of 100.degree. C. It is then washed at 95.degree. C., then at 60.degree. C. and optionally in running water.
Boiling off, which is designed to saponify the greases in the cotton and solubilize the ligneous residues, is effected in a caustic soda medium at a temperature of between 100.degree. C. and 140.degree. C.
The purpose of bleaching is to oxidize the impurities which are a part of the unbleached or previously boiled off cotton, linen or other cellulose fiber. In virtually every case, it is carried out with oxidizing agents such as hydrogen peroxide, alkali peroxides and per-salts, peracetic acid, sodium hypochlorite, sodium chlorite, and the like.
The operations of desizing, boiling off and bleaching are generally carried out in an aqueous medium, with heat. Each operation is followed by hot and cold washes, resulting in considerable water and energy consumption.