Textiles 63
of 1,4--(D-galacturonic acid) units, along with some galactose and arabinose;
the acid groups are generally present as either methyl esters or metal salts (pri-
marily magnesium, calcium and iron). Lignin is a small heterogeneous acidic
phenylpropanoid polymer, with a complex amorphous structure; it is found
within the hemicellulose matrix, to which it may be covalently bound, and is
also a major component of the intercellular matrix (middle lamella). Lignin is
rather hydrophobic and is highly light sensitive, particularly to ultraviolet radi-
ation, and discolours to a deep yellow-brown hue after prolonged exposure; an
increase in acidity also results.
The remainder of the fibre is composed of: waxes, which are generally found
on the fibre surface; pigments, primarily chlorophyll, xanthophyll and carotene,
along with other coloured material; and residual protein.
(a) Cellulose Chains(b)Micelles
MicrofibrilsMacrofibrilsFibre BundleFibre CellMagn
500x 0.9 Torr^50 μmOHOH OH OHOHOH OH OH OHOH OH OH OH OH OH
OO OO OO OO OOOHOH OH OHOH
OH OH OH OHOH OH OH OH OH OH
OO OO OO OO OOOHOH OH OHOHOH OH OH OHOH OH OH OH OH OHOO OO OO OO OOFigure 5Hierarchical microstructure of a linen fibre: (a) from cellulose chains to the fibre
and (b) a scanning electron micrograph showing the ultimate cells bundled in fibres