FABRICS, SPUNBONDED

Fig. 10. Flow sheet for typical spunbond fabric manufacture.

Polyesters are also used in continuous filament spunbonded nonwovens (see Nonwoven fabrics). Reemay spunbonded fabric is composed of continuous filament PET with a polyester copolymer binder. These spunbonded fabrics are available in a wide range of thicknesses and basis weights and can be used for electrical insulation, coated fabric substrates, disposable apparel for clean rooms, hospitals, and geotextiles (qv). 

Early marketing efforts for spunbonded fabrics centered on their substitution for existing, ie, woven, textile fabrics. Generally, success was achieved ia areas where only fiinctionahty was important. Extremely slow progress has occurred ia areas where textile-like aesthetics are required. Nevertheless, spunbonded fabrics are recognized as a unique class of materials within the general category of nonwoven fabrics (see Nonwoven fabrics, staple fibers). 

Fabric Composition. The method of fabric manufacture dictates many of the characteristics of the sheet, but intrinsic properties are firmly estabhshed by the base polymer selected. Properties such as fiber density, temperature resistance, chemical and light stabiUty, ease of coloration, surface energies, and others are a function of the base polymer. Thus, because nylon absorbs more moisture than polypropylene, spunbonded fabrics made from nylon are more water absorbent than fabrics of polypropylene. 

The majority of spunbonded fabrics are based on isotactic polypropylene and polyester (Table 1). Small quantities are made from nylon-6,6 and a growing percentage from high density polyethylene. Table 3 illustrates the basic characteristics of fibers made from different base polymers. Although some interest has been seen in the use of linear low density polyethylene (LLDPE) as a base polymer, largely because of potential increases in the softness of the final fabric (9), economic factors continue to favor polypropylene (see OlefinPOLYMERS, POLYPROPYLENE). 

Most off-quahty or scrap polypropylene fibers may be repeUetized and blended in small percentages with virgin polymer to produce first-grade spunbonded fabrics. The economics are of great importance in a process where high yields are required in order to be competitive. Some manufacturing equipment direcdy recycles edge-trim back into the extmder where it is blended back into the polymer melt (see Fibers, olefin). 

Flashspun high density polyethylene fabrics have been commercial since the 1960s however, this is a proprietary and radically different process of manufacturing a spunbonded fabric, more technically challenging to produce, and highly capital intensive. 

With the possible exception of geotextiles and housewrap, however, there have been virtually no new markets estabUshed as a result of the special characteristics of spunbonded fabrics. Growth has come about in an evolutionary fashion where spunbonded fabrics were substituted for woven fabrics. 

Spunbonded fabrics are effective filters in that they are layered stmctures of relatively fine fibers, the three-dimensional stmcture of which creates a torturous path. Even relatively thin spunbonded fabrics (eg, 0.2—0.25 mm) present a significant challenge to the passage of soil fines and are suitable for use in some filtration appHcations. The porosity of geotextile fabrics is classified by means of several procedures such as flux (volume flow/area per time) and equivalent opening size (EOS), which is a measure of the apparent pore size of the openings in the fabric. The flux measures the porosity to Hquid water, and the EOS measures the porosity to soHd particles of a known diameter. Literature is available on limitations of particular styles of fabrics within an apphcation (63). 

Other Durable Applications. Other durable appHcations such as interlinings and coating/laminating substrates do not appear to offer much near-term opportunity for growth for spunbonded fabrics. In interlinings, however, spunlaced nonwovens have received wide acceptance because of the outstanding drape and softness previously unavailable from any other fabric. 

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. 

The uses of spunbonded fabrics as coverstock in diapers and other personal absorbent devices will most likely remain unchallenged for the near term. Virtually any other nonwoven production method appears to be at a cost disadvantage opposite spunbonded polypropylene. There have been composite products developed from meltblown and spunbonded combinations, where areas of either improved hydrophobicity or hydrophilicity are desired. These products can be produced on-line at relatively low additional cost and offer high value to diaper manufacturers. Any competitive threat is likely to come from advances in film technology such as large improvements in perforated film used in segments of absorbent product appHcations, particularly sanitary napkins. 

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