Geotextiles processes

Olefin fiber is an important material for nonwovens (77). The geotextile market is stiU small, despite expectations that polypropylene is to be the principal fiber in such appHcations. Disposable nonwoven appHcations include hygienic coverstock, sanitary wipes, and medical roU goods. The two competing processes for the coverstock market are thermal-bonded carded staple and spunbond, both of which have displaced latex-bonded polyester because of improved strength, softness, and inertness. 

There are several different processes and polymers used ia the manufacture of geotextiles which affect their appearance and physical properties. Geotextiles are produced ia various weights and thicknesses, which also determine their physical properties and ultimately the performance of the material when iastaHed on a project (see also high performance fibers). 

In order for it to perform the reinforcement function, the geotextile must be allowed to deform to develop its strength. When stabilization of a site occurs, there is consolidation of the soil, and with tbis comes deformation of the geotextile. Due to the deformation of the geotextile, strength is required to ensure that a site failure does not occur, ie, there can be a reinforcement component in the stabilization process. 

Granular starch and copolymers of ethylene and acrylic esters and alkyl(meth)acr-ylates or vinylacetate are produced as master batches for the production of mulch films, geotextiles and molded articles.146 The polar copolymers act as compatibilizers by lowering the interfacial energy between starch and the polyolefin and eliminate the need to coat granules. Processing via a vented twin-screw extruder also eliminates the need for anhydrous starch. 

Nailing is done to protect slopes as excavation proceeds—that is, it is a process that works from the top down. In contrast, when fill is placed to raise an area, the slope is created from the bottom up. For high fills, it may be necessary to reinforce the soil in order to prevent a slope failure. This may be done with geotextile sheets, which are placed horizontally to cover the entire fill surface at vertical intervals of several feet. The geotextile sheets add shear resistance to possible slip or failure planes. In order to be effective, the sheets must extend a significant distance beyond the failure planes for unreinforced soil. Rigorous design procedures are not yet available, and the parameters for field use are selected on the basis of past field experience. 

Nonwoven geotextiles. Nonwoven fabrics are defined as a sheet, web, or batt of directionally or randomly oriented fibres/filaments, bonded either by friction, and/or cohesion, and/or adhesion. In general, nonwoven fabric formation can be considered as a two-step process web formation (aligning the fibres with certain orientation characteristics) and bonding these fibres by mechanical, thermal, or chemical means. This two-step process has formed the classification of nonwoven structures, i.e. carded, airlaid, spunlaid, meltblown, needlepunched, hydroentangled, adhesive bonded, thermal bonded, stitch bonded, etc. Some of the important processes that are used for the manufacture of nonwoven geotextiles are discussed below. 

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