Needle-punched

Within the plane of a nonwoven material, the fibers may be either completely isotropic or there may be a preferred fiber orientation or alignment usually with respect to a machine or processing direction. In the case of thicker dry-laid nonwovens, fiber orientation may be randomized in the third dimension, ie, that dimension which is perpendicular to the plane of the fabric, by a process known as needle-punching (7). This process serves to bind the fibers in the nonwoven by mechanical interlocking. 

V. Mrstina and E. Eejgl, Needle Punching Technology, Elsevier Pubhshers, Amsterdam, the Nethedands, 1990. 

Fig. 2. Photomicrographs of geotextiles made by various methods (a) woven geotextile, (b) needle-punched, (c) heat-bonded, and (d) resin-bonded.

Typical textile fibers used, for example, in a needle-punched filter fabric, are a blend of 3.3- and 6.6-dtex (3- and 6-denier) polyester staple. These fibers are - 5 cm long, have diameters ranging from 18 to 25 pm, mass-per-unit-length or linear density values ranging from - 350 to 650 mg per 1000 m, and length-to-width ratios in the order of 1000 to 1. 

The basic elements of a needle-punch machine, or needle loom, are illustrated ia Figure 7 and consist of a web-feeding mechanism, a needle beam with a needle board and needles (ranging ia number from 500 to 7500 per meter of machine width), a stripper plate, a bed plate, and a fabric take-up mechanism. 

Principle appHcations of needle-punched nonwovens for the 1990s include automotive, apparel components, blankets, carpeting, carpet pa dding, coating substrates, filtration, furniture, geotextiles, insulation, roofing substrates, and wall coverings. In 1990, the production of needle-punched fabric was estimated to approach 91,000 t and 606 million square meters (15). 

Fig. 2. Typical stress—strain curves of nonwoven fabrics, where (—) is woven (-), thermally bonded nonwoven and (-), needle-punched...

Of the three standard bonding methods used in spunbonded manufacturing, mechanical needling, also called needle-punching or needle-bonding, is... 

Geotextiles. Nonwoven fabrics have played an important part in the development of geotextile appHcations. Both needle-punch fabrics... 

Spunbonded fabrics have a relatively small percentage of the coated fabric market which is dominated by other nonwovens. Needle-punched nonwovens offer more of the bulk and resiHency required for functionaHty in automotive and furniture seating. 

Nonwoven fabrics are generally described by the method of production, eg, needle-punched or spun-bonded (120). ASTM D1117 discusses various physical properties to be deterrnined for nonwoven fabrics and the standard procedures used. 

Pollutant Loading Typical inlet concentrations to cartridge collectors are 1 to 23 grams per cubic meter (g/m ) (0.5 to 10 grains per cubic foot (gr/ft )). Cartridge filters, which utilize synthetic, nonwoven media such as needle punched felts fabricated of polyester or Nomex, are able to handle inlet concentrations up to 57 g/m (25 gr/ft ). 

In nonwoven geotextiles, the fibers are much thinner but far more numerous. The various types are needle-punched, resin-bond, and melt-bond. All contain a labyrinth of randomly oriented fibers that cross one another so that there is no direct line of flow. The fabric must have enough open space to allow liquid to pass through, while simultaneously retaining any upstream movement of particles. The needle-punched nonwoven type is very commonly used as a filter material. 

In gas-collector systems, either a granular soil layer or a needle-punched nonwoven geotextile is placed directly beneath the LML or clay of a composite cap system. Gas compatibility and air transmissivity are the design factors that must be considered. Methane, the most predominant gas, should be compatible with most types of geotextiles including PET, PP, and PE. 

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