Fabric Types Conventional –Basic structures are formed by manipulating yarns Woven knitted Non-Conventional –Made from Fibers (non-woven) Yarns & fabrics (tufted carpets) Fabrics with coatings –Monolithic –Breathable.
Non-Wovens Fabrics made directly from fibers Uses –“disposable” apparel Aprons Hospital gowns Hygiene products “House wraps” Interfacings At the grey area between textiles and paper –“Tyvek” envelopes
Felts Perhaps the oldest of all the textile fabrics are the true felts; formed by mechanical interlocking of hair fibers by agitation in the presence of heat and moisture Felts are a class of nonwoven fabrics— fabrics produced directly from fibers. There is a lot of interest in nonwovens because they’re cheaper to produce than conventional fabrics; you don’t need to make yarn first.
Formation of Non-Woven Fabrics Three steps: – Formation of a fibrous web—sometimes called a batt –Bonding of the web for strength and coherence –Finishing We are only going to look at the first two
Web Formation I Card –Back when we discussed the formation of spun or staple yarns, we described the first step as carding, a process that parallels the fibers, producing a fibrous web in which all of the fibers are (more or less) straight and heading in the same direction.
Web Formation II Random –Fibers are separated from a jumble into individual fibers and then deposited, usually by a stream of air onto a screen—very little fiber orientation
Geometry and Properties Graphically, if we look at the strength of web as a function of the angle of the test, , and graphed the results, the plot would ideally look like: º ºº ºº
Cross Laid (Lapped) Webs Modification of parallel laid webs to decrease anisotropy. Fibers lie at an angle 90° w.r.t. one another. Similar preparation to parallel webs— formed on cards and built up of many layers
Random Webs Batts formed on nontextile machines usually for random webs, because (at least theoretically, the fibers are thrown down with no preferred direction in the x, y, or z directions. Unlike the carded webs that are built by layer, the thickness of random webs is controlled by the speed of the collection apron. Ideally a random web is isotropic, it has the same properties in all directions. In reality, there is still some anisotropy.
Bonding As produced, webs have little or no strength and, with the exception of uses such as medical cotton or filling for quilted blankets, &c., the webs must be bonded in such a way as to make them useful. Bonding techniques fall into three (very) broad categories: 1.Adhesive/chemical 2.Mechanical 3.Stitch
Adhesive Defined as a bonding method where the web is held together by adhesion (other than friction); the adhesion can come from an externally applied adhesive, in either solid or liquid form, or from self-adhesion in thermoplastic fibers.
Spray An adhesive (usually latex-based) is sprayed on the web and then dried & cured. Generally, only the surface fibers are bonded, and, because of the mobility of the center fibers, flexibility is imparted to the web. The strength and stiffness of the web comes, in large part from the properties of the adhesive, and the degree of saturation.
Saturation The web is immersed in an adhesive bath for total saturation. Saturation is usually complete; fabrics are stiffer & stronger than spray bonded webs.
Spunbonded Single-step, continuous process of fiber formation and web formation. Uses range from insulation for houses (Tyvek®), to tennis ball covers (Cerex®), to geotextiles
Polymer Type Trade Mark nylonCerex polyesterReemay, Trevira polyethyleneTyvek polypropylene/nylonMirafi polypropyleneTypar, Fibertex, Celestra, Accord Evolution Spunbonded Fabrics
Mechanical Bonding Fabrics held together by frictional entanglement of fibers; no chemical adhesive is used. 1.Felting (described earlier) 2.Needle-punching/needle felting Fibers are entangled using barbed needles that penetrate the web entangling the fibers.
Needle Punching Fibers are entangled using barbed needles that penetrate the web entangling the fibers.
Needle Punching Properties The strength and cohesion of the web depend, to a large extent on the needle density, which controls the degree of entanglement. If added stability is desired a woven or nonwoven fabric, called a scrim is incorporated between layers before punching.
Spunlaced Formed by fiber entanglements produced by high-pressure jets of air or water. Spunlaced fabrics are usually very soft and supple, but relatively weak.
Stitch Bonding The web is held together by stitching through, usually with a machine similar to a warp knitting machine. A common stitch bonded fabric technique, Arachne®, is commonly used to produce inexpensive blankets and as backing for vinyl upholstery. Named for the women turned into a spider by the Greek goddess, Athena. This is why spiders today are called arachnids.