Pretreatment-2

7/30/2019 Pretreatment-2

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Wet Process Vs. Dry Process

Types of Preparation:

Dry processesbrushing, cropping, singeing,

cutting, setting, stabilization

Wet processeswashing, desizing, scouring,

bleaching, mercerization

Only Few processes are dry process and maximum are the wetprocess in textile processing.

Wet processes : This process is applied on textile in form ofliquid with involves some for chemical action on the textile. So,

some water (actually it should be good quality water ) is

necessary for this wet processing of textile materials.

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Water and Its Quality

Consumption Rate of water In textile industries :

3Source: American Dyestuff Reporters


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Source of water/type of water: Rain water

Surface water

Subsoil water Deep well water

1. Rain water: Rain, collected immediately after precitation, is the purest of all

natural waters. It may contain traces of gases dissolved out of the atmosphere and

possibly an almost infinitely small amount of finely divided solidmatter derived from the air.

It also contain dissolved or suspended impurities such as shoottraces of Sulphar di oxide or Sulphuric Acid ,CO2, NH3, NO2 and

other by products of industrialization. Suspended impurities present in it can be filtered by using sand bed.

Suitable for boiling, washing and dyeing processes.


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2. Surface water: Surface water consists of rain water which has collected from

streams, rivers or lakes.

This type of water contains organic and inorganic matters which

are dissolved in it & also contain suspended impurities.

Then the Nitrifying bacteria will in time convert the organic

substances into nitrates which are not objectionable in dyeingand finishing.

Surface waters may receive considerable additions of dissolved

mineral salts from shallow springs which feed the streams.

Not suitable for dyeing & finishing.


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4. Deep well water:

This type of water is obtained 500m below the surface. It is

free from organic matters.

The soluble impurities in water may be composed of a variety of

substances. Soluble organic compounds, ammonium salts,

nitrates and nitrites of animal or vegetable origin may be found.If they are present in considerable quantities, the sewage

contamination is undesirable for many textile purposes.

The presence of salts of calcium or magnesium in solution can be

most undesirable in many finishing process.


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Hardness of water: The presence of Calcium, Magnesium salt

i.e bi-carbonates, sulphates, chloride in water is called causes ofhardness of water. The water which contains these salt is called

hard water.

Hard water does not easily form foam with soap as the salt of Calcium

and Magnesium react with soap to form insoluble organic salts.

CaSO4+2RCOONa(RCOO)2Ca +Na2SO4

MgSO4+2RCOONa(RCOO)2Mg +Na2SO4


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Water Hardness

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Classification of hardness:

Temporary hardness.

Permanent hardness.1. Temporary hardness: Temporary hardness is due to the presence of

bi-carbonates of calcium and magnesium. This type of hardness is

called temporary hardness. Because it can be removed by easy means

like boiling. When temporary hard water is boiled, the carbonates

decomposes with liberation of Carbon-dioxide and precipitation of theinsoluble Carbonates which are reformed.

2.Permanent hardness: It is due to the presence of Chlorides or

Sulphates of Calcium and Magnesium. This type of hardness is called

permanent hardness. These salts do not decompose on boiling. So

permanent hardness can not be removed.


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Water Hardness

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Methods of expressing hardness of water: The hardness of

water is expressed by the amount of Calcium present in water.

Hardness is expressed by-a. PPM(Parts per million)

b. In degrees(grains/gallon)

PPM: The number of grains of calcium carbonates which is

present in one million grains of water is called PPM. 1 grains of

Calcium Carbonate present in 1 million grains water.

In Degrees: The number of grains of Calcium carbonates which

is present in 70,000 grains of water.

The relation is i.e. PPM=Degrees/0.07

Potential problem caused by hard water in textile wet


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Potential problem caused by hard water in textile wet

processing:

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Process Problem

Desizing Deactives enzymes and insolubize size mtls such as

Starch, PVA etc.

Scouring Combine with Soap, Precipitate metal organic acids.Produce yellowing or off white shades, reduce cleaning

efficiency and reduce water absorption.

Bleaching Decompose bleach bath.

H2O2H2O + [O]

Mercerizing From insoluble metal acids, reduce absorbency and

lusture.

Dyeing Combine with dyes, changing their shades, insolubilize

dyes, cause tippy dyeing and reduce dye diffusion.

Printing Break emulsion, changes thickness, efficiency and

viscosity and those problems associated for dyeing.

Finishing Interfere with catalysts, cause resins and other additives

to become non reactive break emulsion and deactives

soap.

W t H d


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Water Hardness

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Water softening: To remove the impurities of hard water by some

desirable process is called water softening.

Water softening plant/ methods of water softening:

Soda lime process.

Base exchange process (Permutit)

Demineralization Soda alum

Aeration

Chelating on sequestration.

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Water Softening

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Soda lime process:

W t S ft i


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Water Softening

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Base exchange process (Permutit):

W t S ft i


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Water Softening

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Demineralization:

W t S ft i


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Water Softening

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Soda alum:

W t S ft i


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Water Softening

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Aeration:

Water Softening


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Water Softening

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Chelating on sequestration:

Pretreatment-2

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