50337112 bleaching of textiles using paa

7/29/2019 50337112 Bleaching of Textiles Using Paa

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WHY PERACETIC ACID BLEACHING:- Conventionally used processes are Hydrogen

peroxide, Hypochlorite, Sodium chlorite etc.

These processes gives good whiteness of fabric.

But these processes have some adverse effect onproperties of the fabric and on our environment suchas :-

Peroxide (H2O2) Hypochlorite (NaOCl) Chlorite (NaClO2)

Material Damage Material Damage Environmentally Hazard

Highly Corrosive Corrosive Extremely Corrosive

Environmentally Hazard

Harmful for skin


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INTRODUCTION:- BLEACHING:- It is the process of removal of colour

impurities from the textile substrate.

PAA is an equilibrium solution consisting of hydrogen

peroxide, acetic acid and peracetic acid. It is a very strong oxidizing agent.

It can be used for bleaching of nylon, viscose rayon,cellulose acetate and cotton.

Peracetic acid is commercially available for textilebleaching in 5, 15 and 40% solutions also known as"equilibrium peracid".


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PREPARATION OF PERACETIC

ACID:-

Peracetic acid can be prepared by mixing hydrogenperoxide with acetic anhydride at room temperature in

presence of suitable catalyst like caustic soda.


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An activators can be used such as

tetraacetylethylenediamine (TAED). The chemistry of TAED/H2O2 bleaching is based on

the following mechanism:

TAED DAED Peracetic AcidIon


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pH 8-9

This equilibrium peracetic acid oxidises its own peranion to form active oxygen, which acts as a bleachingagent.

At pH 8-9 the peracetic acid anion is in equilibriumwith the free peracetic acid.


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BLEACHING OF COTTON:- The mechanism of reaction is somewhat similar to

that of hydrogen peroxide.

The degree of brightness increases proportionatelywith the concentration of bleaching agent.

Parameters Of Bleaching:-

pH 7

Temp. 50-80C

Time 20-60 min.


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Advantages of PaA

bleaching :- It gives comparable or higher brightness.

It is environmentally safe and does not produce any

toxic compound.

It is totally bio-degradable.

Less corrosive.

No material damage.

Saving of chemicals and energy.

It also have antimicrobial action.

Neutralization of fabric after bleaching is no required.


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DISADVANTAGES:- Conc. solution of PAA (35-40%) is dangerously

explosive.

The concentrated solution has a pungent odour.

It is an expensive process. The stability of PAA is not quite high as that of

stabilised hydrogen peroxide. Free radicals may beproduced in the presence of Cu and Fe ions.


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Comparison of peroxide and

peracetic acid bleaching:-

Hydrogen Peroxide Bleaching PAA Bleaching

H2O2 50% wt/wt 4% owf PAA 5% solution 3 gpl

Wetting agent(non-ionic)

1.5% Wetting agent(non-ionic)

1.5%

NaOH pellets 2% owf for pH 10.5 pH 7

Temp. 95C Temp. 60C

Time 60 min. Time 40 min.Stabilizer 1.5 % owf Stabilizer 1.5 % owf


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RESULTS:-

Kind OfTreatment

CIEWhiteness

Index(WI)

Tensile Strength(N) Absorbency(sec.)

Fluidity(Rhes.)

Warp Weft

H2O2 81.1 435.1 198.9 1.o 2.3

PAA 83.6 450.7 205.1 1.0 2.1

Results obtained in case of PAA bleaching are betterthan Peroxide bleaching.


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ENVIORONMENTAL ASPACTS:-

PAA is environmentally safe and do not form any toxicproduct.

PAA and TAED are easily Bio-degradable.

They has no carcinogenic or any other toxic properties.

PAA has been used as water treatment compound infood and beverage processing.

Its ultimate fate in the environment are the basicmolecules of carbon dioxide, oxygen, and water.


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CONCLUSION:- PAA bleaching give better results than peroxide

bleaching.

Using PAA bleaching can be carried out at 65C with

neutral pH without producing any harmful chemicals.


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REFRENCES:-

Chemical Technology In Pre-Treatment Processes ByS.R.Karmarkar.

Fibre 2 fashion journal. Scribd.com

The Indian Textile journal.

Textile research journal.

Google search.


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50337112 bleaching of textiles using paa

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