Water and Water Hardness for Textile

 

Water:  Water is a chemical substance with the chemical formula H2O. Its molecule contains one oxygen and two hydrogen atoms connected by hydrogen bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice and gaseous state, water vapor or steam.  In wet processing, water consumption is greater than the number of fibres processed. Water is a universal cleaning agent as rinsing and washing operations alone consume enormous amount of water.  In industries, the daily requirement of water is about 200000-300000 gallons.

 Water is considered as the lifeline of the wet processing:  Water is used extensively throughout Textile industries.  A plentiful supply of suitable water is essential for a Textile manufacturing industry. Moreover, among various manufacturing industries, wet processing is the third important industry where huge volume of water is necessary.  Water is considered as the life line of the wet processing industry because it is the single most used chemical and is also universal cleansing agent.  The amount of water used varies widely in the Textile industry, depending on specific processes operated in the mill, equipment used, and existing management philosophy concerning water used.

Water is used in the plant in –

^·          In Boiler for supplying steam for heating and drying

In different types of wet processes-

^·          In Sizing

^·          In Desizing

^·          In Scouring

^·          In Bleaching

^·          In Mercerizing

^·          In Dyeing

^·          In Printing

^·          In Finishing

^·          In Rinsing and Washing

Water consumption in the different stage of wet processing

Process	Water consumption
	(Litre/kg)
Scouring & Bleaching (Batch method)	50
Scouring & Bleaching (Continuous method)	40
Mercerizing	25
Fabric dyeing (Batch method)	45
Fabric dyeing (Continuous method)	35
Yarn dyeing	60
Printing	40
Finishing	15

Water consumption for different shades of knit dyeing

	Shade	Water consumption
		(Litre/kg)
Light shade		70
Medium shade		90
Dark shade		120
R/Black		130
White		35-45
Y/D wash		20-30
Ready for dyeing		30

Water Hardness

• Hardness in water is defined as the presence of multivalent cations.

• In other words, hardness is defined as the presence of soluble calcium and magnesium salts in the water.

• The presence of sulpahates, chlorides, carbonates and bi-carbonates of calcium, magnesium and ferrous salts make water hard.

• Due to water hardness, soaps and detergents cannot create foam easily. Rather they react with hardness creating metals and form insoluble organic salts.

For example, sodium stearate reacts with calcium as follows-

CaSO4+2RCOONa→ (RCOO)₂ Ca ↓ + Na₂SO4

MgSO4+2RCOONa→ (RCOO)₂ Mg ↓ + Na₂SO4

Types of Water Hardness:

There are two types of water hardness-

a) Temporary Hardness:

• The presence of bi-carbonate salts of calcium, magnesium and iron makes the water temporary hard.

• Temporary hardness of water can be removed easily by simply boiling the water.

• When the water is boiled, the bi-carbonates decompose with the liberation of CO2 and insoluble carbonates deposits as precipitation under water.

             Ca (HCO3)2 → CaCO3 ↓ + CO2 + H2O

b) Permanent Hardness:

•        Permanent hardness arises when water contains soluble salts of calcium and magnesium such as their sulphates and chlorides.

•        Permanent hardness is hardness (mineral content) that cannot be removed by boiling.

•        Permanent hardness can be removed by converting the sulphate salts into carbonates with the help of soda ash (Na2 CO3).    

•        CaSO4 + Na2CO3 → Na2SO4 + CaCO3

•        Permanent hardness can also be removed with using a water softener or ion exchange column, where the calcium and magnesium ions are exchanged with the sodium ions in the column.

Expression of Water Hardness:

Irrespective of the salt present, hardness is expressed in terms of calcium carbonate (CaCO3).

Hardness may be expressed in degrees or in parts per million (ppm).

·         Parts per million (ppm): It is usually defined as one milligram of calcium carbonate (CaCO₃) per litre of water.

·         In degree: Degree of Hardness is the number of grains of calcium carbonate (CaCO₃) per gallon of water.

1 gallon	=	70,000 grains
1 pound (lb)	=	7000 grains
1 gallon	=	10 lb
Ppm	= English degree/0.07

Various Degree of Hardness:

Degree	Expression	Definition
German Hardness	1deg. dH	10 milligrams of calcium oxide per litre of water, equivalent to
		17.848 ppm.
French Hardness	1deg. fH	10 milligrams of calcium carbonate per litre of water, equivalent
		to 10 ppm.
English Hardness	1deg. eH	One grain (64.8 mg) of calcium carbonate per imperial gallon
		(4.55 litres) of water, equivalent to 14.254 ppm.
American	1deg. H	One milligram of calcium carbonate per litre of water, equivalent
Hardness		to 1 ppm.

Classification of water hardness based on English hardness

Water quality	PPM	GdH
Very soft	0-50	0-4
Soft	50-100	4-8
Slightly hard	100-150	8-12
Moderately hard	150-200	12-18
Hard	200-300	18-30
Very hard	>300	>30

Standard or Quality of Dye-house water:

SL No.	Parameters	Acceptable limit
1	Colour	Colour less
2	Odour	Odour less
3	PH	7-8
4	Hardness	<5 degree (German)
5	Dissolved solid	< 1mg/litre
6	Solid deposit	< 50mg/litre
7	Organic substances	< 20 mg/litre
8	Inorganic salt	< 500 mg/litre
9	Iron content	< 0.1 mg/litre
10	Copper content	< 0.005 mg/litre
11	Nitrate content	< 50 mg/litre
12	Nitrite content	< 5 mg/litre

Quality of water used in Boiler:

SL No.	Properties	Acceptable limits
1	Appearance	Clear, without residue.
2	Residual hardness	<0.050 dh
3	Oxygen	<0.02 mg/L
4	Temporary CO2	0 mg/L
5	Permanent CO2	<25 mg/L
6	Iron (Fe)	<0.05 mg/L
7	Copper(Cu)	<0.01 mg/L
8	Phosphate(PO4)	4-5 mg/L
9	PH(at 25OC)	»9 (generally 8-9)
10	Conductivity	2500 us/cm
11	Temp. of boiler feed water	»900C

Potential problem caused by the hard water in textile wet processing:

1.	Process		Problem
2.	Desizing	De-actives enzymes and insolubilize size materials such as starch, PVA etc.
3.	Scouring	React with soap and precipitate metal organic acid.
		Produce yellowing or off white shade.
		Reduce cleaning efficiency.
		Reduce water absorption.
4.	Bleaching	Decompose bleach bath. Eg. H2O2	H2O + [ O]
5.	Mercerizing	Form insoluble metal acid.
		Reduce absorbency and lusture.
6.	Dyeing	React with dyes
		Change the shade.
		Insolubilize dyes.
		Cause tippy dyeing.
		Reduce dye diffusion.
7.	Printing	Break emulsion.
		Change thickness.
		Reduce efficiency and viscosity.
8.	Finishing	Interfere with catalysts.
		Cause resin and others additives to become non-reactive.
		Break emulsion.
		De-activate soap.