Silicate is used as a stabilizer and to obviate the catalytic
activation of heavy metals as well as acts as a buffer. Colouring materials are
decomposed into soluble products and acidic impurities in cotton fibers.
Buffered systems showed improved whiteness index compared to the un-buffered
system since pH is maintained throughout the bleaching operation. Un-buffered
system the loss in tensile strength was observed after 55-60% of peroxide
decomposition, even though there is no improvement in whiteness4.
Table-1 Recommended Recipes for Single Stage Preparatory
Process2
|
No.
|
Process
|
Recipe
|
|
1.
|
Peroxide-alkali
|
H2o2-1.0 g/L, NaOH 10g/I
Na2 Sio3-5g/L, Wetting Agent 1g/L
Temperature 95oC Time 120 min
PH 10.5 11.5 using soda ash
|
|
2.
|
Peroxide Solvent assisted Scourant Starch sized fabrics
|
Scoring agent 4% Peroxide 2%
Sodium silicate 1% Wetting agent 0.1%
Temperature 95OC,m Time 180 min
pH 10
|
|
3.
|
Peroxide Solvent assisted scourant Acrylic-base size
|
Scouring agent 4% Peroxide 1%
Sodium silicate 1% Wetting Agent 0.1%
Temperature 90oC, Time 180min
pH -10
|
|
4.
|
Peroxide-Solvent assisted scourant
|
Scouring agent 4% owf. H2O2 1%
Na2 Sio3 2% Na3 PO4
2%
Or tetra sodium pyrophosphate
PH 11 Temperature 60 min
Time 12-16/24 hours at 40oC
|
|
5.
|
Peroxide-Alkali Process
|
Sodium Hydroxide 20 g/I
Hydrogen Peroxide 30-40 m/I, Peroxidesulphate-5 g/I
Sodium Silicate 20 m/I, Surfactant 10 g/I
Stabilizer 5 m/I
|
|
6.
|
Flash Steam Process
|
Ciba Tinoclarite FS 15-30 ml/kg
NaOH (100%) 30-50 g/kg, H2O2
(35%)-49-90 ml/kg
|
In another novel approach steam procedure has been use to
combine all the preparation processes into a single step helps to complete the preparation within 2-4 minutes, applying the solution, consisting alkali, hydrogen peroxide and
auxiliary to the fabric, it is steam with saturated steam followed by wash.
EFFECTIVENESS OF THE PROCESSES
Peroxide-Alkali Process
Absence of either sodium hydroxide or hydrogen peroxide in
the peroxide based process, results in very low weight loss, indicating very
low efficiency, Increase in weight loss due to scouring action and desizing
occurs with increase in concentrations of peroxide and sodium hydroxide and
higher weight loss is achieved at a temperature of 95oC. The
whiteness index is found to be directly proportional to the concentration of
sodium hydroxide, which is mainly due to the increased formation of per
hydroxyl ion at higher pH, which acts as the bleaching agent and also with the processing time5.
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