Catalytic Damage

8/12/2019 Catalytic Damage

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Catalytic damage in

peroxide bleaching

Tendering in bleaching due to presence of iron

(Reference: Fabric Defects, J.B.Goldberg 1950.)

The fabric sample shown below was composed of

Warp: 150/40 viscose

Weft: 30/2 combed cotton.

The warp yarns have been broken in several spots, the break being exactly parallel

to and along sections of the cotton weft. On the cotton back of the fabric the weft yarn

running parallel to the broken areas was dyed lighter than normal. Tests showed that

the light-dyed weft and the viscose warp in contact with the faulty weft were

deteriorated chemically and the cotton yarns were very tender. This defect was

attributed to the presence of oily weft yarn containing small amounts of iron from

contact with machine bearings. In bleaching the iron acted as a catalyst, accelerating

the oxidation and producing oxycellulose in the cotton weft and in the viscose warp

yarn through direct contact. The viscose rayon yarns being much weaker when wet,

and excessively tender in those sections, broke when the goods were finally finished.



Natural cellulosic fibres contain varying concentrations of metals depending

on their geographic origin. Two different samples of cotton from Turkey were

analysed and found to contain very different concentrations of metals.

Metal impurities such as chromium, manganese, iron, cobalt, nickel, copper

and zinc, can catalyse the decomposition of hydrogen peroxide in bleaching.

Even a small amount of

1 mg/l of iron in

dissolved form

increases the rate of

decomposition of

hydrogen peroxidetenfold.

This exothermic

reaction results in the

formation of

oxycellulose, and

tendering of the cotton.



If relatively large particles of rust are present, which are liable to contain

metallic iron, even large additions of stabiliser during peroxide bleaching

cannot eliminate the danger of fibre tendering. The metal catalysts must be

removed by some other method before bleaching.

Oxalic acid has

limited ability to

form a soluble

metal complex withiron, but may create

problems with

almost insoluble

calcium and

magnesium salts.

Why not use a cheap, simple acid like oxalic acid?



NEARCHEL SA complexes and disperses alkaline earth and heavy metal ions in

strongly acid and highly alkaline solutions.

The powerful demineralising action of NEARCHEL SA

Suggested recipes

Discont inuou s alkaline demineralisat ion o f wo ven cot ton

1.5 - 30 g/l caustic soda100 %

0.5 - 4 ml/l NEARPON EMS

0.5 - 3 ml/l NEARCHEL SATreat at 90 - 98 °C for 40 – 60 min. at L.R. 1:4 – 1:20. Rinse hott

Discont inuou s acid demineralisation

0.5 - 5 ml/l NEARPON EMS

0.5 - 2 ml/l NEARCHEL SA

Treat 20 – 30min at 30 – 50° C, L.R.: 4 : 1 - 20 : 1

Pad Batch Cold Ac id Demineral isat ion

Grey-state goods: all-cotton, linen, polyester/cotton

5 - 15 ml/l NEARCHEL SA

3 - 6 ml/l NEARPON MK-91 S

0 - 2 ml/l NEARFIL FAC

Impregnate cold with pick-up of 100%. Batch: 2 - 12 hours. Hot rinse.

No agent added 2 g/l NEARCHEL

SA added



Pad Batch Combined Oxidat ive Desiz ing and Demineral isat ion

3 - 5 g/l NEARSTABIL V

3 - 5 ml/l NEARCHEL SA

25 - 40 g/l caustic soda 100 %

20 - 30 ml/l hydrogen peroxide 35 %

4 - 5 g/l NEARPON MK-91S

0 - 4 g/l sodium persulphate

0.5 - 1 g/l NEARFIL FAC if necessary

Pad impregnate cold, pick-up 100%. Batch: 6 - 24 hours. Hot rinse

If fabric is to be subsequently bleached, less hydrogen peroxide will be necessary in

bleaching.

Especially for fabrics containing

difficult-to-remove starch sizes,

(e.g. tapioca), PVA, CMC polyacrylate and starch derivative

sizes

212.5225

212

100

130

160

190

220

250

280

pH 9 pH 10 pH 11 pH12

pH of solutions

m g C a C O 3 s e q u e s t e r e d / 1 g o f

p r o d u c t

200

Sequestering Power of NEARCHEL SA for Fe3+ ions

m g F e s e q u e s t e r e d / 1 g o f

p r o d u c t

280320

515562 577

257

0

100

200

300

400

500

600

700

pH 6 8 9 10 11 12

Sequestering Power of NEARCHEL SA for Ca2+ ions

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Catalytic Damage