Chlorite bleaching

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. 

The rate of chlorite bleaching increases as pH decreases, but only between pH 2 and 9 is the rate proportional to the concentration of chlorous acid present in solution. At low pH values, evolution of the noxious and corrosive gas chlorine dioxide increases. In practice it is necessary to keep the pH above 3 in order to minimise the formation of chlorine dioxide. It is necessary to monitor the pH during chlorite bleaching because acid is liberated by the... 

Table 10.20 Effect of surfactant addition on AOX values after chlorite bleaching of synthetic fibres [224]...

The possible benefits of prescouring to remove such contaminants should also be considered. Alkaline pretreatments, including boiling off of cotton, have a profound effect on AOX values after chlorite bleaching (Tables 10.21 and 10.22). It can be beneficial, from the viewpoint of both AOX and whiteness, to follow a chlorite bleach with a peroxide treatment. Linen yarns after an alkaline scour and chlorite bleach gave a whiteness value of 63.9 with an unacceptably high AOX value of 8.0 ppm. These results were improved to 78.5 and 1.2 ppm respectively after peroxide treatment [224]-... 

Table 10.21 Effect of washing on AOX and whiteness values before and after chlorite bleaching [224]...

Most cotton is bleached with peroxide, by far the greater proportion by continuous methods. Synthetic fibres seldom require bleaching, but where it is necessary either peroxide or chlorite bleaches are recommended. Most regenerated cellulosic fabrics are only bleached... 

The light fastness of the vic-triazole 11.17 on nylon is 4-5 as on cotton this is significantly superior to that of the DAST derivatives. Unlike the DAST types, the vic-triazole is also stable towards a sodium chlorite bleach. Applied to nylon in combination with sodium chlorite, compound 11.17 can give exceptionally high whiteness and excellent fastness properties. 

Polyacrylonitriles. An increasing proportion of the polyacrylonitrile fibers produced have a good basis white and do not require further bleaching [130,131], The use of FWAs that can be applied in the chlorite bleaching bath is therefore steadily declining. Suitable types include benzimidazoles such as 46-48. 

Chlorite bleached jute prepared under minimum cellulosic degradation (Lignin content = 10%). 

Activator and Stabilizer for Sodium Chlorite Bleaching POLYRON CB is an additive used in sodium chlorite bleaching in order to activate the process without the addition of acid, to prevent odor nuisance, corrosion, and to increase the whiteness. ... 

Optical brightener for polyacrylonitrile fibers. HOSTALUX NC is stable in sodium chlorite bleaching liquors and can, therefore, be used in combination with such a bleach. 

Optical brightener for polyacrylonitrile fibers. Because of the high brilliance of the brightening effect, most acrylic fibers do not require a sodium chlorite bleach. 

Sodium Chlorite bleaching assistant. Activates and stabilizes bleach bath to increase whiteness and reduce odor problems. Contains corrosion inhibitors. 

Cationic OBA for acrylic fibers. Stable in sodium chlorite bleach baths. Reddish cast. 

Certain acrylic fibres should not be chlorite bleached because of their tendency to yellow/or loose stability to light. Many fluorescent brighteners added to the chlorite bath are also not stable and such materials may exhibit an accelerated fade when... 

The chlorite bleaching process suffers from certain drawbacks as follows ... 

The most effective method of bleaching polyester/cotton is sodium chlorite, which may be followed by peroxide bleaching. Chlorite bleaches the husk, but does not destroy them completely. Polyester/cotton blends may be bleached with sodium chlorite in long liquors and also by pad-steam process [Table 6.10]. The... 

A single stage combined scouring and bleaching of polyester/cotton blended fabric can also be done for economy. There are various approaches which include alkali treatment with detergent and peroxide hot bleach alkali treatment with detergent and sodium chlorite bleach sodium chlorite and peroxide bleach and peroxide cold and peroxide hot bleach. 

Optical brightening agents are applied to textiles at the time of scouring, bleaching or finishing. When chlorite bleaches are used anti-chlorinating measures must... 

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