Nonwoven geotextil
Nonwoven
geotextiles
These structures, as the name implies, are fabrics made by bonding of
fibres through mechanical , chemical or thermal means or by combination of
them. Yarns are not used in non- wovens ,and this is their main differentiation
from weaving and knitting (48) .
Nonwovens are chosen over other conventional materials because of its
economic aspects as nonwovens have fewer processing steps from start ( raw
material) to finish ( roll goods) and line speed are getting faster and faster.
However , nonwovens are selected not only for their cost-effectiveness but
because no other material can offer their specific performance characteristics
. (49)
The nonwovens have the best properties as optimum conformity can be
achieved with the wide choice of production methods , fibre type , fineness and
length. (46)
Filtration is the prime function of
most nonwoven fabrics .They separate the parent soil from the drainage media. They are also
used in other civil applications such as drainage, reinforcement between soil
to soil, soil to stone or aggregate and asphalt to asphalt in road and railway
works, erosion prevention and separation. (47)
For the production of practically all types of nonwovens products, four
stages of production are necessary, namely , fibre preparation , web formation
, web bonding and finishing process .(50)
Of the steps listed above, web formation is one differentiation of the
final fabric end use. There are three ways by which webs are formed :-
1-Random –
In this method the spreading and laying of fibres is carried out by controlled
air currents, sometimes called isotropic structures, that produce a fabric that
has equal strength in all directions.
2-Cross- directional – In this method two layers of fibres are laid at right angles to each
other using cross lappers. The fabric produced is almost equal in strength in
both crosswise and lengthwise direction.
3-Oriented web or unidirectional structures- where the fibres are parallel to the
longitudinal axis. In fabric form, the lengthwise direction is stronger than
the crosswise direction. (38)
