Bleaching hypochlorite

The tetramethylol derivative of DABT, prepared by reaction of DABT with alkaline aqueous formaldehyde, polymerized readily on cotton. It imparted excellent flame retardancy, very durable to laundering with carbonate- or phosphate-based detergents as well as to hypochlorite bleach. This was accomphshed at low add-on without use of phosphoms compounds or antimony(III) oxide (75—77). 

The most common chemical bleaching procedures are hypochlorite bleach for cotton hydrogen peroxide bleach for wool and cotton sodium chlorite bleach for cotton, polyamide, polyester, and polyacrylonitrile and reductive bleaching with dithionite for wool and polyamide. 

There was a tendency to use these resins mixed with urea—formaldehyde or melamine-type resins. Preparation of pure tria2ones or uron resins is difficult and expensive (61,62). Furthermore, the basic nature of the amine nitrogen in tria2one permits the use of mixtures of tria2ones with other agents to yield finishes that retain strength in hypochlorite bleaching. 

Cross-linked finishes are not permanent in the tme sense of the word however, under optimum conditions the finish can last for the usehil life of the material. Wet abrasion during laundering is probably the principal cause of gradual removal of the finish. In order to retain antistatic protection for extended use, an excess of finish is often appHed The extent of chemical interaction between the durable antistatic agents and the fiber substrates to which they are appHed is not perfectiy understood. Certain oxidizing agents such as hypochlorite bleaches tend to depolymerize and remove some durable antistatic finishes. Some of the durable finishes have also produced undesirable side effects on textile materials, ie, harsh hand, discoloration, and loss of tensile properties. 

Calcium Hypochlorite (Bleach Liquor). Bleach hquor is a solution of Ca(OCl)2 and CaCl2 containing some dissolvedhme. The av CI2... 

Hypochlorite Bleaches," Chemical Economics Handbook Stanford Research Institute International, Stanford, Calif., Apr. 1989. 

About 93% of the CaCOs mud is dried and lecalcined in rotary kilns to recover the CaO. Calcium hypochlorite bleaching liquor (p. 860) for paper pulp is obtained by reacting lime and CI2. 

Sodium hypochlorite is commercially available as an alkaline solution, normally containing the equivalent of 12-14% available chlorine. However, this is so unstable that analytical testing of its strength is always necessary before use. Calcium hypochlorite (bleaching powder), stabilised by adding lime, has been used in the past but this product is no longer used in textile bleaching. 

The mechanism of hypochlorite bleaching appears to be considerably less controversial than peroxide bleaching. The pH-related active species in sodium hypochlorite are shown in Figure 10.29 and Scheme 10.33. The pH range 9-11 is the most suitable for hypochlorite bleaching. The active bleaching species is the hypochlorite anion CIO. In fact bleaching... 

Despite its technical usefulness, hypochlorite bleaching faces severe environmental pressures because it yields A OX values well in excess of permitted levels. The A OX value observed increases with the active chlorine content of the bleach liquor (Figure 10.31) and with the time of treatment (Figure 10.32). 

Amines can give rise to chloramines during hypochlorite bleaching (Scheme 10.83). In addition to increasing AOX values, this can result in cellulose oxidative degradation by hypochlorite on subsequent hydrolysis of the chloramines (Scheme 10.84) [448]. 

---