Chlorine-Hercosett process

Chlorine heptoxide, 18 275 Chlorine-Hercosett process/treatment,... 

Table 4 Concentrations for AOX Determined in the Chlorination Bath of the Chlorine-Hercosett Process...

The features and chemistry of chlorination shrink-resist treatments are best illustrated by consideration of the chlorine-Hercosett process for wool top (99). This process uses a dedicated plant, of which there are about 40 around the world. A web of parallel slivers is treated with water and chemicals in a series of bowls (tanks), separated by squeeze rollers. The wool is then dried. Usually, 30-40 slivers (20-30 g/m) are treated simultaneously at a speed of 5-10 m/min. Overall production rates range from 200 to 500 kg/h. 

Therefore, shrinkproofing processes aim at the modification of the fibre surface either by oxidative or reductive methods, and/or by the application of a polymer resin onto the surface. The most frequently used commercial process (the chlorine/Hercosett process) consists of a chlorination step followed by a dechlorination step and polymer apphcation. The chlorination results in the oxidation of cystine residues to cysteic acid residues in the surface of the fibre, and allows the cationic polymer to spread and adhere to the wool surface. Chlorination produces byproducts (AOX) which appear in the effluent and ultimately may generate toxicity in the whole food chain by being taken up by aquatic organisms. There is therefore an increasing demand for environmentally friendly alternatives. 

Chlorine/Hercosett Also called Hercosett. A process for making wool shrink-resistant by chlorination followed by resin treatment. The resin is made by Hercules, hence the name. Developed by the International Wool Secretariat. 

Kroy A variation on the Hercosett process for making wool fire-resistant. The chlorination step is effected by hypochlorous acid. Invented in Toronto in 1975 by F. Mains of Kroy Unshrinkable Wools. 

The surface of a wool hair is covered by keratin sheds, which cause a distinct tendency to shrinkage and formation of felts. This behavior is usually undesirable and thus an antifelt finishing is the most important treatment during the processing of woolen textiles. One of the most important standard procedures, the Hercosett finish, is based on the oxidative treatment of wool by application of compounds that release chlorine. Examples for applied chemicals are NaOCl, CI2 gas, and dichloroisocyanuric acid (DCCA) [14]. 

HERCOSETT 125 provides a means of utilizing a highly effective, completely aqueous system for preventing felting shrinkage of wool. The process involves pretreatment of the wool with aqueous chlorine at low pH, followed by neutralization and application of HERCOSETT 125. This process can be used to treat wool sliver continuously, or fabrics and piece goods by a batch process. 

The polymers are apphed to the wool fibers or fabrics as solutions or emulsions. The polymers contain reactive side-chains, which form cross-links between the polymer chains during a curing process after apphcation and may form covalent links with the wool protein. For example, Hercosett 57 is a polyaminoamide with reactive azetidinium side-chains, which form cross-links between the polymer chains. They also form covalent links with amino and thiol groups in the wool protein. In the case of some polymers (e.g., Hercosett 57), it is necessary to give the wool a mild chlorination treatment to modify the surface of the fibers before applying the polymer. Such a treatment allows the polymer to spread evenly on the surface. 

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