Page 159 - Advances in Textile Biotechnology

140 Advances in textile biotechnology

These then necessitate effective treatment of effluent before it can be dis-
charged to the lake or river from which the water was sourced or before

the effluent is sprayed on to land for remediation. Each of these types of

effluent discharges requires permits and is governed by either state or
national regulations, or both.
Alkaline scouring of cotton requires large amounts of rinse water to
lower the pH of the fabric before further chemicals can be introduced.
Given the increasing concern about water usage, both in terms of cost and
in environmental impact, reducing water consumption is a continuing indus-
try goal. Energy consumption is also an environmental and fi scal concern
in conventional alkaline scouring. Scouring is done near the boiling point
of water (100 °C) and multiple rinses are also at elevated temperatures so
that the energy consumption is substantial.

6.5 Enzymatic treatments of cotton

6.5.1 Desizing using enzymes

Most cotton and cotton-polyester blend yarns are sized before weaving in
order to strengthen the yarns and increase their abrasion resistance. The

sizing materials are usually starches, modified starches or starch and cel-
lulose derivatives (Vigo, 1994, p. 4). Synthetic polymers such as polyvinyl
alcohol can also be used alone or in combination with starches. The funda-
mentals of these sizing materials have been extensively reviewed (Drexler
and Tesoro, 1984). Once weaving is accomplished and the greige fabric

comes off the loom, the first step in preparation for chemical dyeing and

finishing is the removal of the size. If the size is not completely removed
after weaving, the results may be uneven dyeing or printing, and poor
reproducibility from batch to batch. For starch and starch derivatives, which
constitute the vast majority of sizing for cotton and cotton/polyester fabrics,
desizing may be done by enzymatic, oxidative or acid desizing. The latter
two approaches are little used because of their potential to damage the
cotton fiber during the process.

Probably more than 75% of the sizing agents used worldwide are starches

or modified starches and, therefore, the use of amylases for desizing is
widespread. These enzymes break the starch polymer molecules down into
small fragments that can either be washed away easily or that dissolve in
hot water.
Amylases are enzymes that hydrolyze starches. The major types of these
enzymes are α- and β-amylase. The α-amylase type is capable of acting at
random locations along the starch chain to break down long-chain carbo-
hydrates, ultimately yielding maltose from amylose, or maltose and glucose
from amylopectin. Because it can act anywhere on the substrate, α-amylase
tends to be faster-acting than β-amylase and is therefore used for textile

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