Page 76 - Materials Chemistry, Second Edition

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Cleaner Production
Scouring is carried out to remove impurities that are present in cotton,
both natural (e.g. waxes, fatty acids, proteins, etc.) and processing (e.g. residual
size, dirt, and oil). This is usually done with sodium hydroxide and produces
strongly alkaline effluents (around pH 12.5) with high organic loads.
Bleaching is used to whiten fabrics and yarns, using sodium hypochlo-
rite or hydrogen peroxide. Many cotton processing factories in Egypt use sodium
hypochlorite as it is cheaper than hydrogen peroxide. It is, however, toxic
and is now not preferred or banned in many countries.
Desizing, scouring, and bleaching are frequently undertaken as three sep-
arate steps in the preparatory stages for textile wet processing. Through
chemical substitution and process optimization, it is possible to combine two
or three of the three preparatory processes, thereby reducing water and energy
consumption as well as shortening the processing time (SEAM 1999). As com-
bined scouring and bleaching requires that bleaching by sodium hypochlorite
is replaced with hydrogen peroxide, the overall processing sequence gener-
ates effluents that are less harmful to the environment.
Combined desize and scour was undertaken at Misr Beida Dyers Company
in Alexandria, Egypt, and combined scour and bleach was implemented at
Giza Spinning and Weaving Company, Egypt. These modifications have reduced
operating costs and increased production capacity through a shortened pro-
cessing sequence. Recently, El-Hesn Company, located in the Egyptian indus-
trial estate, 10th of Ramadan, Sharkia, Egypt, combined the three processes
of desizing, scouring, and bleaching in one process.
Misr Beida Dyers Company is a public company in Kafr El Dawar,
Alexandria. It was established in 1938, and occupies a 270 acre site. The fac-
tory pre-treats, dyes, prints, and finishes cotton fabrics and cotton/synthetic
blends, processes yarns, and cotton. During 1997/8, Misr Beida Dyers pre-
treated about 1,182 tons of woven fabric on jiggers, of which about half were
pre-treated using separate processes (desizing, scouring, and half bleaching).
The remaining fabric was pre-treated using a combined process consisting of
desizing/scouring, using a proprietary chemical, followed by half bleaching.
The factory processes and manufactures cotton and polyester/cotton garments
and finished fabrics. In 1996/7, 1,440 tons of fabric were processed, of which
240 tons were full bleached and 1,200 tons half bleached and dyed. Full bleach-
ing is carried out using hypochlorite and half bleaching using hydrogen per-
oxide only. About 90% of the fabric produced by Giza Spinning and Weaving
is knitted, the remainder woven.

CP opportunity assessment
Through an industrial or cleaner production audit at the two factories, a
number of environmental and productivity related concerns were identified
in the desizing, scouring, and bleaching processes, as follows:

• Sodium hypochlorite, a toxic and hazardous chemical, was used in
the bleaching process at Giza Spinning and Weaving.