Effect of pH on Hydrogen Peroxide bleaching:

Hydrogen peroxide is applied under alkaline conditions, and the optimum pH for bleaching is between 10 and 11. At a pH below 10 hydrogen peroxide is quite stable, and oxidation will occur too slowly. When pH of the bleaching bath is above 11, hydrogen peroxide decomposes too fast and may cause damage to the fibres. Beyond pH 11.8, all the hydrogen peroxide converted to HOO and reaction is out of control.

Effect of Time duration and Temperature:

The ideal bleaching temperature for hydrogen peroxide is 95 to 100 degree C. Below 80 degree C, the evaluation of perhydroxyl ions are slow. Due to this rate of bleaching is also slow.  The time duration of bleaching depends on the temperature, type of fibre and machines. 

Concentration of Hydrogen peroxide:

The concentration of hydrogen peroxide also depends on type of machinery being used. In the case of Batch process (Jigger etc), 2 to 4 % Hydrogen peroxide (o.w.f) is taken with MLR of 1:10 to 1:20. While in the continuous process 1-2% (o.w.f) [resultant concentration as in the continuous process it is used in g/l) will be sufficient as higher concentration may damage the fibres. 

Stabilizer: 

Beside hydrogen peroxide and a base (Sodium hydroxide or sodium carbonate), the bleaching bath also contains stabilizing agent. Sodium silicate (Na2SiO3.5H2O) has been found to be the most suitable stabilizer. It is a base that acts as a buffer at the proper pH of 10.5 to 11.5, and in addition, it prevents the catalytic decomposition of hydrogen peroxide caused by heavy metals. As we have already discussed that the catalytic effect of transition metal ions (e.g Fe+++ or Cu++) on hydrogen peroxide is accelerating its decomposition may cause great damage to the fibres. Sodium silicate also act as a sequestering agent and with transition metals forms soluble complexes. Mg++ ions, however, have been found to posses a stabilizing effect on hydrogen peroxide. Accordingly, when using soft water a small amount of a magnesium salt is added to the bleaching bath.

Now a days organic stabilizer also being used also known as silicate free or non silicate stabilizers. 

Beside stabilizer,  sequestering agents and wetting agents also used during bleaching process. Most common sequestering agents are EDTA and Sodium hexa phosphate.

Advantage and uses:

Hydrogen peroxide is also known as universal bleaching agent as it is most widely used for bleaching fibre like cotton, rayon, wool and silk, environment friendly and economical viable also. Unlike hypochlorites bleach, it does not require full scouring. It gives permanent whitening effect and less damage to the fibres.

 Bleaching recipe for guidance:

The process wise recipes of bleaching of cotton for guidance are given below: 

i) Batch process:

a) Formulation:
Hydrogen peroxide (35%)=4 to 8% (o.w.f)
Wetting agent=0.1 to 0.5 % (o.w.f)
NaOH=0.5 to 1.0% (o.w.f)
Sodium Silicate=2 to 4% (o.w.f)
b) Process parameters:
Temperature=95 to 100 degree C
Time= 60 to 90  Minutes 

After the above process, drop the bath and material rinse well with slightly basic solution to avoid the formation of insoluble silicates. Finally it may be neutralized using acetic acid or green acid. 

ii) Continuous process:
 In a typical continuous process in open bath the padding bath contain the following:

Hydrogen peroxide (50%)=1.5 to 2.5% 
Wetting agent=0.1 to 0.2 % 
NaOH=0.2 to 0.6% 
Sodium Silicate=1.0 to 1.5% 

After padding, the fabric is passed through a steamer. Steaming time may be vary from as little as a few minutes to one hours or more, depending on the type of steam and steamer used.

Combined scouring and bleaching process:

For saving time, energy, labour etc, combine scouring and bleaching is very popular.

In oxidative desizing, where scouring takes places as well, the cotton fabric is padded with a solution containing sodium hydroxide, hydrogen peroxide, a stabilizer, and wetting agent. After padding, the fabric is steamed for the proper amount of time depending on the type of steamer and the concentration of chemical used. After steaming the fabric is rinsed with hot water several times to remove the polyvinyl alcohol and other emulsified. During the tratment, sizing chemical is oxidized and become water soluble. 

The combine scouring and bleaching process is very popular in the cotton hosiery processing.