Dyeing - Total Textile Process at a Glance

Water HardnessGenerally soaps create foam in water, but in present of some materials the foam creation is reduced and need more soap for producing foam, and this condition of water is

Water ,Hardness,Surfectents , Detergent

Total Textile Process at a Glance

The course comprised –

1 Applied chemistry: Water & water treatment,

surfactants

2 Dyeing: Dyeing theory & mechanism,

Mordant dyes, Pigments, Mineral colors

3 Printing: Special types of thickener, Screen

printing technology

4 Finishing: Softener, Special types of finishing

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4 Deep well waters which have usually

percolated through several layer

General characteristics of water

Water shows maximum density at 4ºC,

1 gm/cc its specific gravity is also 1

Freezing temperature 0ºC and boiling

temperature is 100ºC.

Properties of textile supply water

Minimum Standard Acceptable limits

Lead or heavy metals < 0.01 mg/l Alluminium (Al) < 0.25 mg/l Silica < 3.0 mg/l Sulphate < 250 mg/l Sulphide < 1 mg/l Chloride < 250 mg/l Chlorine < 0.1 mg/l Nitrite (NO2 ) < 5 mg/l Nitrate (NO3 ) < 50 mg/l Ammonia < 0.5 mg/l Oil, grease, fat, soap < 1 mg/l Total solids < 500 mg/l

Water Hardness

Generally soaps create foam in water,

but in present of some materials the

foam creation is reduced and need more soap for producing foam, and this

condition of water is called water

hardness.

Reasons of water hardness

Definition of Different Hardness

Other scales for expressing

water hardness -

 Parts per million (ppm): The number of parts of

substances per million parts of water is known ppm It

is also called American hardness It can be expressed

by another way like mg/l or gm/m3.

 Grains per U.S gallon (gpg): The number of grains of

substances per 1 U.S gallon of water (1 U.S gallon of water weighs 8.33 pound) is known gpg.

 Parts per hundred thousand (pp/100,000): The number

of parts of substances per 100,000 parts of water is

known pp/100,000.

 Grains per imperial gallon (gpg imp): The number of

grains of substances per 1 British imperial gallon of

water (1 imperial gallon of water weighs 10.0 pound) is known gpg imp.

Relation of different scales -

1 ppm = 1.0 mg/l = 0.1 pp/100,000 =

0.0583 gpg (U.S.) = 0.07 gpg imp.

Conversion factor of different water hardness scale

Classification of water according to hardness

Problems causes by hard

water in wet processing and

their correction

Consequences of using hard water –

 Precipitation of soaps;

 Redeposition of dirt and insoluble soaps on the fabric

being washed – this can cause yellowing and lead to unlevel dyeing and poor handle;

 Precipitation of some dyes as calcium or magnesium

 Decrease solubility of sizing agents;

 Coagulation of some types of print pastes;

 Incompatibility with chemicals in finishing recipes

(A) Problems in boiler

 Ca(HCO3)2 → CaCO3 + CO2 + H2O

 Mg(HCO3)2 → MgCO3 + CO2 + H2O

 MgCO3 + H2O → Mg(OH)2 +CO2

Heat loss for pipe scaling

Scale thickness (mm) % heat loss (approx.)

Boiler feed water quality:

Parameter Acceptable limit

B) Problems in processing

 Wastage of soap (reaction with soap)

2 C17H35COONa + CaSO4 → (C17H35COO)2Ca + ↓

Na2SO4

 Reaction with dyestuffs

- reaction with dyes and lead dye wastage

- sometimes it produces a duller shade

How does the water hardness

affect the textile processing?

Desizing Deactivate enzymes and makes it

insolubilize some size materials like starch and PVA

Scouring Combine with soap, precipitate

metal-organic acids Produce yellowing of white shades, reduce cleaning efficiency, and water absorption

off-Bleaching Decompose bleach baths

Mercerizing Form insoluble metal oxides, reduce

absorbency and luster

Dyeing Combine with dyes changing their

shades, insoubilize dyes, cause tippy dyeing, reduce dye diffusion and hence results in poor washing and rubbing

fastness

Printing Break emulsions, change thickener

efficiency and viscosity, and those problems indicated for dyeing

Finishing Interfere with catalysts, cause resins

and other additives to become nonreactive, break emulsions and deactivate soaps

Estimation of

water hardness

 Using direct reading digital meter or

strip

 In laboratory it is usually determined

by titration with a standardized

solution (e.g Na-EDTA) – for mechanism see my book

Estimation of total (permanent

& temporary) hardness of

supply water (by di-sodium salt of EDTA)

In 1M solution of 1000ml contain 372 gm Na2-EDTA

In 0.01M solution of 1000ml contain 3.72 gm Na2-EDTA

In 0.01M solution of 100ml contain 0.372 gm Na2-EDTA

 Preparation of ammonia buffer

solution:

- 145ml of liquor ammonia (NH4OH) of specific

gravity 0.88+15gm NH4Cl + distilled water to make 250ml solution to give a pH of 10.

 Procedure:

- Add 1ml of buffer solution (NH4OH+NH4Cl) to

100ml of the original water sample Add 3-4

drops of Eriochrome Black T indicator (0.2g dye

in 15ml of triethanol amine + 5ml of ethanol)/

1tablet (making powder) total hardness

indicator.

- Titrate against 0.01M prepared EDTA solutions in

burette until the color charges from wine red (or violet) to pure blue (or turquoise) with no reddish tone; then calculate the total hardness

in terms of ppm of CaCO3.

Table: Experimental data

Total hardness =

Volume of 0.01M EDTA solution in ml

-× 1000 ppm of CaCO3.Volume of sample water in ml

Determination of temporary

hardness of supply water

 Basic principle:

- This can be estimated by titration of

sample water against standard

solution of hydrochloric acid ( 0.05N HCl)

 Procedure:

- Add 1cc or 2 – 3 drop [from the solution of (0.1

gm solid methyl orange + 100cc distilled

water)] methyl orange indicator to 100ml of

fresh distilled water & titrate against 0.05N

HCl Let the titration reading be ‘a’ ml

- Now titrate 100 ml of the sample water against

0.05N HCl using the same indicator

(methyl-orange) Let the titration reading ‘b’ ml

 Observation:

- Reading should be taken when the

color of indicator change orange to red.

 Table I: Experimental data for

reading ‘a’

 Table II: Experimental data for

reading ‘b’

Determination of permanent

di-sodium salt of EDTA)

 Preparation of 0.01M or 0.02N EDTA solution:

Molecular weight of disodium salt of EDTA

In 1M solution of 1000ml contain 372 gm Na2-EDTA

In 0.01M solution of 1000ml contain 3.72 gm Na2-EDTA

In 0.01M solution of 100ml contain 0.372 gm Na2-EDTA

 Preparation of ammonia buffer

solution:

- 145ml of liquor ammonia (NH4OH) of specific

gravity 0.88+15gm NH4Cl + distilled water to make 250ml solution to give a pH of 10

 Procedure:

- Take 100ml of sample water in a conical flask;

boil it (around 30 minutes) to about 50 ml;

cool and filter to remove bicarbonate residual (temporary hardness) and to expel carbon

dioxide Dilute it to by distilled water to make

100 ml Add 2ml of ammonia buffer solution

followed by one tablet of hardness indicator

- Titrate against 0.01M prepared EDTA solutions

from burette until the color charges from wine red (or violet) to pure blue (or turquoise) with

no reddish tone; then calculate the hardness in terms of ppm of CaCO3

 Table: Experimental data

 Calculation:

Total hardness =

Volume of 0.01M EDTA solution in ml

- × 1000 ppm of CaCO3 Volume of sample water in ml

Methods for water softening

 Lime-soda process

 Base exchange process

 Demineralisation process

 Sequestering agent

1 Lime-Soda process

 In this process hydrated lime and sodium

carbonate is used to remove the hardness.

- For temporary hardness –

Ca(HCO3)2 + Ca(OH)2 → 2 CaCO3 + 2 H2O

Mg(HCO3)2 + Ca(OH)2 → MgCO3 + CaCO3 + 2 H2OMgCO3 + Ca(OH)2 → Mg(OH)2 + CaCO3

- For permanent hardness –

CaSO4 + Na2CO3 → CaCO3 + Na2SO4

MgCl2 + Ca(OH)2 → CaCl2 + Mg(OH)2

CaCl2 form is removed by –

CaCl2 + Na2CO3 → 2 NaCl + CaCO3

Permutit process (Base/ Ion

exchange method)

Permutit’ means exchange; in this

process, hard water is treated with base

exchange complex or Zeolites to remove

the hardness of water Zeolites are naturally occurring insoluble mineral of the sodium

aluminosilicate type complex (e.g NaAlSiO4 3H2O ≈ Na-Permutit) This type of ion

exchanger may produce artificially

Basic Principle

 For temporary hardness –

2Na-Permutit + Ca(HCO3)2 → Ca-Permutit + ↓2NaHCO3

 For permanent hardness –

2Na-Permutit + CaSO4 → Ca-Permutit + ↓

Demineralization method

The newer synthetic polymer ion exchangers are much more versatile than the zeolites and are widely used for water softening and

demineralization They are often called ion

exchange resins This reagent can remove all mineral salts to complete demineralisation of hard water It has two types of ion exchanger – Cation exchanger and Anion exchanger

 For temporary hardness –

H2R + Ca(HCO3)2 → CaR + 2H2CO3

H2CO3 → CO2 + H2O

 For temporary hardness –

 Water can be totally demineralised by firstly exchanging all

cations using s strongly acid form of a cation exchanger Thus a solution of salts M+X¯ becomes a solution of acid H+X¯, the M+ ions being retained by the resin Subsequently a strongly basic form of an anion exchanger absorbs the X¯ ions and liberates

OH¯ ions into water These then neutralize the H+ ions from the first step The reslt is retention of all anions and cations and the neutralization of H+ and OH¯ to form pure demineralization

water

 2H+ (aq) + 2OH¯ (aq) 2H2O ↔

Regeneration of reagents:

1 Cation exchanger –

(Polymer – SO3¯)2Ca²+ (s) + 2HCl ↔2(Polymer – SO3¯H+) (s) + Ca2Cl

2 Anionic exchanger –

2(Polymer – NR3+Cl¯) (s) + 2NaOH ↔2(Polymer – NR3+OH¯) (s) + 2NaCl

Sequestering agents

 Addition of a sequestering agent to the water

avoids many problems from relatively low

concentrations of undesirable metal ions

EDTA (ethylenediamine tetra-acitic acid), related aminocarboxylic acids, polyphosphates such as sodium tetrametaphosphate Na4P4O12, Calgon -Sodium hexametaphosphate Na6P6O18

Surface Active Agents

 The term surfactant is a blend of surface

active agent Surfactants are usually

organic compounds that are amphiphilic,

meaning they contain both hydrophobic

groups (their "tails") and hydrophilic groups (their "heads")

 when added to a liquid, reduces its surface

tension, thereby increasing its spreading

and wetting properties

 In the dyeing of textiles, surface-active

agents help the dye penetrate the fabric

evenly

 A detergent (as a noun; "detersive" means

"cleaning" or "having cleaning properties";

adjective "detergency" indicates presence or degree

of cleaning property) is a material intended to

assist cleaning

 Today, detergent surfactants are made from a

variety of petrochemicals (derived from petroleum) and/or oleochemicals (derived from fats and oils).

 Although the cleansing action of soaps and

detergents is similar, the detergents do not react as readily with hard water ions of calcium and

magnesium Detergent molecular structures consist

of a long hydrocarbon chain and a water soluble

ionic group

Anionic detergents:

The detergents which

consist negative ionic

group are called anionic

detergents The majority

are alky sulfates and

others are generally

known as alkyl benzene

sulfonates.

Cationic detergents

 The cationic classes of

detergents have a

positive ionic charge and

are called "cationic"

detergents In addition

to being good cleansing

agents, they also

possess germicidal

properties which makes

them useful in hospitals

Most of these detergents

alcohol and then

reacting the fatty

alcohol with ethylene

oxide They are not

ionize in water They

are very popular in

textile uses

Advantages and disadvantages

of synthetic detergents

 Effective cleaning in hard water

 They are not precipitate as insoluble

Ca/Mg salts (gummy substance) on material

 They are not very good detergent as

soap

 Incompatibility, in case of opposite

ionic nature

 Environmental hazard