Now a days many commercial products based on innovative clay or mineral chemistry are available for discontinuous bleaching of cotton and its blends with hydrogen peroxide. The clay or mineral technology have several advantages over conventional peroxide bleaching process.
What are these clay or mineral based products
The clay or mineral based products are a composition of naturally occurring mineral or clays such as montmorillonite and/or bentonite in combination with suitable wetting , sequestering agents and viscosity control agents . The clay is finely dispersed in the form of a non settling, non separating emulsion which can be diluted with water and can be used easily. The clay structure is based on sheets. By separating these sheets e.g. by stirring, a very big surface is created This surface (till 800 M 2 per gram) makes it possible to absorb all kind of components like dirt, oil, greases etc. This gives an unique detergency effect .Two properties of montmorillonite crystals enable its use as a highly effective bleaching agent:
•On the one hand, impurities are adsorbed from the fabric and the liquor, due to the high specific surface area.
•On the other hand, montmorillonite has the property to replace disturbing heavy metal ions in the bleaching bath by Na-ions
The result is a dual effect as bleaching stabiliser and extractant.
How these products acts
In water the clay particles are anionic charged and show a large adsorption effect for:
- Hydrophobic waxes and oils
- Metal ions (cation exchange capacity)
- Hydrophilic materials and polymers
It is believed that the clay component provides both a scouring and softening effect, in essence by adsorbing organic contaminants and acting as an ion exchanger, in effect having a contaminant-suspending capacity. The powder or agglomerate particles of the clay divide into primary crystal plates caused by the swelling of the clay. The average size of the primary crystal plates is approximately 1.mu.. After being dispersed in the treatment liquor, the contaminants detached from the treated textile material are adsorbed by the clay particles, resulting in a greatly reduced redeposition of the contaminants. Textile incrustation is reduced due to the hardness elements released during washing having either become attached to the dispersed clay crystals or having been deactivated by the sequestrant. Clay, a natural product, washes off the treated textile material and forms an effluent having low BOD and COD values. The clay does not contribute to the BOD or COD values at all.(Ref: Clay-containing textile material treating composition and method by Brown; Harold M. (Lyman, SC))
The higher whiteness index of the treated textile materials is attributed to the fact that in this bleaching system the hydrogen peroxide is consumed to the maximum extent ,resulting into very low or zero residual peroxide.
Advantages of these single-component multifunctional auxiliaries are
1.No need of Organic peroxide stabilizers,
2.No need of Dye bath Lubricants,
3.No need of Wetting and scouring agents
4.No need of Emulsifiers in most applications,
5.No need of Antifoaming agent.
6.No need of Machine cleaning aids.
7.Very low or no need of peroxide killer treatment.
8.Shortened bleaching cycle , less water and steam consumption.
9. Low loss of degree of polymerisation, due to controlled peroxide degradation
10.Better tensile strength compared with conventionally bleached fabric
11.Lower weight loss.
12, Better removal of oil or silicone
And since these products are derived from clay or natural resources these are eco friendly in nature , having low COD and BOD values
A typical bleaching recipe for cellulosic material is
Best suitable for package dyeing machines , jets and winches .
1-2 ml/l Clay product
2-3 g/l Caustic flakes
2-5 ml/l Hydrogen peroxide 35%
At 95 -98 oC for 45-60 min
Test the peroxide content at equal intervals and ensure maximum utilization of peroxide , to optimize the process timing.
Followed by hot and cold wash, do peroxide killing if necessary.