Effect of Water-Impurities on Wet Processing

Effect of Water-Impurities on Wet Processing
Impurities in water can seriously affect quality of wet processing and even damage the fibers depending on their nature and concentration. The major impurities and their effects are briefly discussed below:
Organic Matter, Turbidity and Colour
Turbidity and colour are usually due to presence of organic matter in water and these detract 1 brightness of the bleached and purity of shade of the dyed goods. The organic matter whether dissolved or suspended also breeds micro organisms that may develop mildew, fungi etc. which in turn produce colored spots, foul smell and even holes in the fibrous material. The microorganism also grows inside the water pipes and chokes these and sometimes even dissolves the pipe-metal.
Hardness creates many other undesirable effects in wet processing. The textile dyes for each fibre are designed to have low solubility in water and these become difficult to dissolve in very hard water Due to insufficient solubility the dye-shade becomes weaker and may also produce spots on the dyed fabric. Further on heating or on coming in contact with alkalis during dyeing and soaping, calcium and magnesium ions are precipitated on fabrics as whitish carbonates and hydroxide particles.
Total Dissolved Solids
In addition to hardness causing calcium and magnesium salts, water contains other dissolved salts that are mainly sodium cations and chloride, sulphate and bicarbonate anions. These sodium salts increase TDS of water and also create many difficulties in processing of textiles. Dyes of low solubility are likely to be precipitated even in softened water of high TDS on dissolving and the same can happen in preparing printing pastes. Presence of excessive amount of sodium ions also gives a damp and limp handle to the finished fabric due to their tendency to hold water. High TDS in the boiler feed water causes foaming and carry over Problems that lower efficiency of the boilers and also create difficulties in processing. Excessive concentration of sodium ions in boiler water also accelerates corrosion of the iron plates due to their high electrical conductivity. Such waters also require more frequent blow-downs and result in f loss.

Dissolved Gases
Water normally has small quantities of oxygen and carbon dioxide dissolved in it. The latter reacts with steel pipes carrying water and steam, to form soluble ferrous bicarbonates. The dissolved ferrous ions, besides producing unsightly stains, catalyze reactions of hypochlorite and hydrogen peroxide during bleaching and damage cotton goods by lowering their strength and even making holes. The dissolved oxygen can cause serious damage to the boilerplates by converting the ferrous bicarbonate, formed initially, into ferric oxide and releasing carbon dioxide to react again with more iron. The reaction continues till the entire dissolved oxygen is exhausted by reacting with the boiler-plates. Oxygen in water also wastes the reducing agents like dithionite that is used in application of vat dyes.

About the Editor-in-Chief:

Mazharul Islam Kiron is a textile consultant and researcher on online business promotion. He is working with one European textile machinery company as a country agent. He is also a contributor of Wikipedia.

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