Water

An abundant supply of clean water is necessary in order to run a dyeing and finishing plant. Dye houses are usually located in areas where the natural water supply is sufficiently pure and plentiful. Knowledge of the impurities and how to remove them is important.

Water Consumption in Textiles

Water is used extensively throughout textile processing operations. Almost all dyes, specialty chemicals, and finishing chemicals are applied to textile substrates from water baths. The amount of water used varies widely in the industry, depending on the specific processes operated at the mill, the equipment used, and the prevailing management philosophy concerning water use.

Textile operations vary greatly in water consumption. Following figure summarizes the water consumption of various types of operations. Wool and felted fabrics processes are more water intensive than other processing subcategories such as wovens, knits, stock, and carpet. Water use can vary widely between similar operations as well. For example, knit mills average 10 gallons of water per pound of production, yet water use ranges from a low of 2.5 gallons to a high of 45.2 gallons.

Water consumption varies greatly among unit processes, as indicated in Figure below. Certain dyeing processes and print afterwashing are among the more intensive unit processes. Within the dye category, certain unit processes are particularly low in water consumption (e.g., pad-batch). Different types of processing machinery use different amounts of water, particularly in relation to the bath ratio in dyeing processes (the ratio of the mass of water in an exhaust dyebath to the mass

of fabric). Washing fabric consumes greater quantities of water than dyeing.

Hardness of water

The presence of Calcium, Magnesium salt of bicarbonates, sulfates, Chlorides in water causes hardness of water. The water containing these salts called hard water.

Hardness is of two types:

• Temporary hardness
• Permanent hardness

The bicarbonate salts of calcium and magnesium are called Temporary hardness because boiling will liberate carbon dioxide and precipitate calcium carbonate. Chloride salts of calcium and magnesium are called Permanent hardness because boiling will not cause a precipitate.

Methods of expressing hardness of water

1. PPM (parts per million)
2. English degree
3. German degree
4. French degree

Potential problem caused by hard water in textile wet processing

The impurities which can seriously impair the quality and reproducibility of the dyeing process are :

• Ca ⁺⁺ and Mg ⁺⁺ can cause “pink cotton” which can be extremely difficult to remove by bleaching
• Fe ⁺⁺⁺ and Cu ⁺⁺ which can catalyse excessive local concentrations of the active peroxy bleach radical during peroxide bleaching of cotton, physical damage and even “pinhole damage” of the fibre.
• Fe ⁺⁺⁺ and Cu ⁺⁺ can cause excessive shade change (eg. red shades move dull and blue)

Fig: Influence of Metal Impurities on Reactive Dyeing

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Water Quality

The raw material used in greatest quantity in virtually every stage of textile wet processing is water. The quality of textiles produced by any manufacturing operation which employs wet processes, such as preparation, dyeing, and/or finishing, is profoundly affected by water quality.

Table 1 Dye house water Standard

Characteristic	Permissible Limit
Color	Colorless
Smell	Odorless
pH value	Neutral pH 7–8
Water hardness	< 5dH (6.25eH; 8.95fH; 5.2USA)
Dissolved solids	< 1 mg/l
Solid deposits	< 50 mg/l
Organic substances	< 20 mg/l (KMnO4 consumption)
Inorganic salts	< 500 mg/l
Iron (Fe)	< 0.1 mg/l
Manganese (Mn)	< 0.02 mg/l
Copper (Cu)	< 0.005 mg/l
Nitrate ( NO3-)	< 50 mg/l
Nitrite ( NO2- )	< 5 mg/l