Page 156 - Advances in Textile Biotechnology

Enzymatic versus chemical processing of cotton 137

–
OOC
O
H 3 CO
HO H C O
3
OH
O O
HO O O HO O
O O O
O O
OH n
O
O OH
H CO
3
O OH
HO
6.5 Structure of xylan with ferulic acid linked.

these to break into fragments. In turn, portions of these seed fragments

remain attached to the fibers and are eventually embedded in the yarn
during the spinning process. In the greige fabric they appear as black or

dark brown colored material with fibers or linters attached to its surface.
Because fibers are attached to the surface of a seed coat fragment, they can

be difficult to eliminate during the normal cleaning and fiber spinning pro-
cesses.
Chemically, seed coat fragments are composed of 22–26% lignin, 5–10%
pentosan (xylan, Fig. 6.5), 43–48% cellulose, and small amounts of wax,
protein and inorganics (Reicher and Csiszar, 1992). Lignin forms a complex
matrix around the other components, providing a protective shield, but also
making the seed coat fragments difficult to break down for removal. Phys-

ically, the cotton seed coats consist of six layers, which are segregated into

two main groups identified as internal and external integuments, depending
on their positioning in the seed coat. The internal integument consists of an
inner epidermis towards the center of seed followed by inner pigment layer
and palisade cells. The external integument consists of an outer epidermis
layer followed by an outer pigment layer and a colorless layer (Himmels-
bach et al., 2003; Kim et al., 2001). Figure 6.6 shows this diagrammatically.
Dhandapani has examined the weight loss in seed coat fragments artifi -
cially created, and subjected to 0.5% and 4.0% NaOH for 1, 5 and 10 h
(Dhandapani et al., 2008). The results showed weight losses from the seed
coat fragments ranging from 31–42% for the 0.5% treatments to 59–64%
for the 4.0% treatments. These weight losses may be on the high side since
some linters attached to the fragments are clearly removed after treatment.
However, the results do seem to indicate that even with vigorous alkaline
treatment the fragments are diminished and broken up, but are not elimi-
nated from the fabric.

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