Comparison of Hydrogen peroxide bleaching and conventional sodium chlorite bleaching

 

Hydrogen peroxide Bleaching.

Hydrogen peroxide is most widely used bleaching agent. Beside the good removal of the seeds, there peroxide bleach delivers a high degree of whiteness, the white effects are stable and do not tend to yellow during storage.

Results expected from hydrogen peroxide bleaching

Degree of whiteness: High degree of whiteness for white goods and pastel shades.

Seed removal :  Complete removal of seeds coats.

Criteria	Hydrogen peroxide	Sodium Chlorite
Accelerated Continuous process	Yes	No
Applicability by all possible methods, e.g. cold bleach	Yes	No
Suitability for natural fiber	Yes	Yes
Efficient removal of husks	Yes	Limited
High water absorbing power	Yes	NO
Odor Irritation	No	YES
Corrosion problems(Vessel of resistant material required)	No	Yes
Suitability for combination processes (Boiling off/Bleaching)	Yes	No
One bath application with brighteners for cellulosic fiber	Yes	Limited
Deposits on fabrics and machines	Limited	No

On the whole, there are so many points in favor of hydrogen peroxide bleaching that it is easy to understand why it so widely used.

Utilizing Bifunctional reactive dyes for reactive printing.

SUBJ:

Utilizing Bi functional reactive dyes for reactive printing.

Chemistry of dyes which are used in reactive printing is different from other classes. Among them one is MCT (Mono chlor Triazine), A dye having single chlorine attached to functional Triazine.

This Chemistry of dyes (MCT) provided better fastnesses, Specially washing fastness ISO 105 CO3, Dipping fastness. 

A common practice is to use other family of reactive dyes in printing although this fulfills the task and advantages associated with this phenomena are 
1) cheap/Economical dyes. 
2) Bulk amount available 
3)Nearly same shade depth and tone 

But, disadvantages are poor fastnesses. Commonly in use dyes for reactive dyeing includes bi functional dyes including new generation high built dyes. These dyes have high fixation values and percentage of hydrolyze dye in dye bath is quite low but these dyes can not stand on with alkaline medium for longer period of time. 

Stock paste used for printing include alginate, mild oxidizing agent, urea and above all quite huge quantity of soda ash (25g/Kg), which is recommended for fixation of reactive dyes in printing. As, already mentioned these dyes are not quite good with alkaline medium when left for longer period of time. So, when these dyes are mixed with stock paste and not printed soon or after immediate addition. These start to hydrolyze and lose up its strength and tone. Temperature work as catalyst here. Temperature effect inversely to the hydrolyzation. More the temperature more quickly dye is going to hydrolyze. As, major areas of Pakistan are hot and quite hardly hit in summer. So, for this experiment 50°C is chosen to check the hydrolyzation rate of bi functional and Purely MCT dyes.

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