Page 170 - Advances in Textile Biotechnology

Engineering of plants for improved fi bre qualities 151

the derived products, and plant fibres are no exception (Batista and Oliveira,
2009). The dramatic increase in the availability of genomic and biological
information is now allowing scientists and plant breeders to utilise different
biotechnological approaches to improve the quality of plant fi bres.

7.2 Defining plant fi bres

Despite such a long history of fibre use, a clear, simple definition of a fi bre

does not exist. In reality, this reflects the fact that fibres can be classifi ed/

described according to their botanical origin, their chemical structure, or
alternatively, in terms of their industrial use. For example, from a botanical

point of view a single fibre (elementary fibre) corresponds to a single elon-

gated cell, usually tapering with a narrow diameter and a lignified or non-
lignified thick cell wall (Esau, 1977). Plant cells, unlike animal cells, are

surrounded by a relatively rigid structure called the cell wall that is com-
posed mainly of polysaccharide polymers such as cellulose. After harvest,
more or less all that remains of the elementary fibre is the cell wall and it is

this structure that enters into the fabrication of yarns for textiles. In contrast,
from an industrial point of view, the ‘technical fibre’ (for textiles and/or

composites) often consists of an agglomeration of individual cells (elemen-
tary fibres) giving rise to an elongated narrow structure (McDougall

et al., 1993). For composite materials, such a technical fibre can then be

granulated to facilitate subsequent production. In addition, it is clear that
when nutritionists tell us to eat more fruit and vegetables because they are

rich in fibres they are not necessarily thinking of the same type of cell. In

this review we will use the term fibre to refer to a single elongated plant cell.
Plant fi bres can be classifi ed into three main groups (for detailed review,

see Ilvessalo-Pfafli, 1995, McDougall et al., 1993) according to their botani-
cal origin:
(1) stem fi bres,
(2) leaf fi bres,
(3) seed and fruit fi bres.
Stem fibres can be further divided into two main groups according to the

chemical composition of their cell walls. Thus, one can distinguish lignifi ed

fibres, typical of the inner woody tissues (xylem) of angiosperm dicotyle-
dons and gymnosperms (conifers), from the cellulose-rich fibres (bast fi bres)

that contain little or no lignin and are found in the outer non-woody stem
tissues of plants such as fl ax (Linum usitatissimum L.), ramie (Boehmeria
nivea), jute (Corchorus capsularis) and hemp (Cannabis sativa). It should
be noted that the relative quantity of the phenolic polymer lignin has an
extremely important impact on both the mechanical and chemical proper-

ties of plant fibres, and therefore represents a major target for engineering.

© Woodhead Publishing Limited, 2010