this process are relatively thick, typically 1 to 5 mm (40 to 200 mils)
or more.
Nonwoven geotextiles made in a continuous line process, in which
filaments are extruded, drawn, formed into a loose web and bonded, are
called spunbonded. The term spunbonded implies that spinning (extruding and drawing) and bonding of the filaments occurs without interruption (i.e. without any intermediate step, such as cutting filaments to make
staple fibers) regardless of the bonding process. Some people tend to
restrict the use of the term spunbonded to the heatbonded nonwovens;
this is not justified.
2.2.2. Special geotextiles
A two-step manufacturing process is also used to produce some special
geotextiles such as webbings, mats and nets.
Webbings. These are a kind of very coarse woven fabric made of strips
a few centimeters (a few inches) wide. A webbing looks like a very coarse
slit film woven fabric.
Mats. These are made of coarse and rather rigid filaments with a
tortuous shape, bonded at their intersections. These very open structures
have typically a thickness of 1 or 2 cm (½ to 1 in). Some mats look like a
very coarse and open nonwoven fabric.
Nets. These consist of two sets of coarse parallel extruded strands
intersecting with a constant angle (generally between 60 ° and 90°).
Strands of one set are connected to strands of the other set by partial
melting at the intersection. Typically, the size of strands is 1 to 5 mm (~
to ~6 in) and the size of openings is from a few millimeters (¼ in) to several
centimeters (several inches).
The manufacturing process of grids and formed plastic plates does not
include a first step consisting of producing independent linear elements
such as filaments, fibers, slit films or yarns. Grids and formed plastic
plates are made from extruded plastic plates.
Grids ('geogrids'). These are made by drawing, in one or two
perpendicular directions, a perforated plastic plate. In the process, the
small perforations become large quasi-rectangular openings, usually 1 to
10 cm (½ to 4 in). The strands have a large degree of molecular orientation
as a result of the draw, and consequently a high modulus.
Formed plastic sheets. These include corrugated, waffled, alveolate, etc.