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Making The Right Fiber Choice

Fibers - new and old - are finding new and improved uses in nonwovens.

Richard G. Mansfield, Technical Editor

 Making The Right Fiber Choice Fibers - new and old - are finding new and improved uses in nonwovens. When considering the fibers used in nonwoven applications, those that initially come to mind are polypropylene, polyester and rayon.However, there are a large number of specialty fibers and polymers that are also useful as raw materials for producing nonwovens. With the prevalence of such fibers as Kynol novoloid fibers and polyvinyl alcohol fibers, which are produced in Japan; and P-84 polyimide fibers, which are made in Austria, it becomes crucial to have an understanding of the fibers available on the market today.The ability to blend different fibers in producing nonwovens provides an almost infinite number of choices for raw material selection in engineering new nonwoven products. The real challenge is to pick the right combination. PolypropyleneThe use of polypropylene in fibers and related structures, has made a major impact on the nonwovens industry because of its versatile properties and favorable economics.Polypropylene is used in many fibrous forms including staple, bicomponent staple, monofilament, multifilament, slit-film yarns, slit-fibrillated film yarns, spunbonds, melt-blown nonwovens, synthetic pulps and extruded nettings.Olefin feedstocks are readily available throughout the world. There are a large number of merchant suppliers of extrusion grade resins throughout the world.Continuing improvements in catalyst efficiencies have resulted in increases in plant productivity and improvements in resin properties. Polypropylene is a relatively forgiving polymer to extrude and enables many textile companies to back integrate. It does not require nitrogen blanketing or pre-drying for most products.  P-84P-84 is a polyimide fiber that was originally developed by the Upjohn Co. in the United States. Upjohn sold the technology to Lenzing of Austria who commercialized the fiber. Lenzing then sold the P-84 fiber plant and technology to the INSPEC Group in April 1996.P-84 fibers do not melt and are non-flammable. P-84 is used for filtration at temperatures up to 260oC. The polyimide fibers are resistant to most organic solvents except polar solvents such as DMF. The trilobate letter-shaped cross-section provides for high-filtration efficiencies in needlefelts. The P-84 fiber has a relatively low-modulus and high breaking strain, so it can not be considered a reinforcing fiber in a class with some of the aramids. P-84 has become an important fiber for dry gas filtration, where it competes with DuPonts Nomex aramid fiber. P-84 is now used in protective clothing.Albany International worked with Lenzing in developing Pyropel high temperature insulation panels using P-84 needlefelts. The P-84 needlefelts are treated above the glass transition point, 315oC, this produces extreme densification of the needlepunch structure. Shrinkage as high as 44 percent have been obtained at 350oC. The degree of stiffness can not be explained by shrinkage behavior alone. PENPEN polyester fiber and fiber-related products can be made from a new high-performance polyester resin, polyethylene napthalate (PEN). Amoco Chemical Co., Chicago, is making the key intermediate chemical Amoco NDC (dimethyl 2, 6 napthalenedicarboxylate) for PEN in Decatur, Ala.In the United States, Shell Chemical Co., Houston, is making PEN resin for use in fibers, film and molded products. Fibers produced from PEN polyester resins have higher strength, stiffness and dimensional stability and better hydrolytic stability, as well as better resistance to heat and chemicals than conventional PET fibers.Teijin, Japan, has done considerable development work with PEN-based fibers. Multifilament fibers produced by a two-stage draw process can be subjected to either a one- or two-stage heat treatment to provide a high melting point fiber (greater than 287oC) and extremely low shrinkage (0.1 percent after five second exposure at 255oC) at high temperatures.Potential applications for PEN-based fibers include tire cord, radiator hose, V-belts, conveyor belts and dryer felts for the paper industry. PTTAs a polymer, PTT (polytrimethylene terephthalate) has been known for over 50 years. It was never commercialized because of the expense of one of its components, 1,3 propanediol. Shell now has developed a lower cost process for making this intermediate and is now producing PTT.Shell Chemicals Corterra® PTT has a melting point of 2,280oC, and can be extruded into fibers between 155 and 2,700oC.Shell has targeted the carpet fiber market for its Corterra PTT polymer. It is likely, however, that Corterra will also be evaluated in nonwoven products.The ability to produce low denier per filament at moderate air pressures indicates that the polymer may have good potential in spunbonded fabrics. The nylon-like resilience of PTT could be a major advantage in nonwoven fabrics for interlinings and interfacings (See Quality Fabric of the Month in this issue). TencelCourtaulds Tencel is a regenerated cellulose fiber made by the use of an amine oxide solvent spinning system. Tencel, unlike most regenerated cellulose fibers, has a high wet strength as well as a high dry strength. The fiber also has a much lower wet elongation than conventional regenerated cellulose fibers.Tencel can also be fibrillated and this property should be of interest in making wet-laid and possibly hydroentangled nonwovens.An end use for Tencel is in wiping cloths where its ability to absorb moisture and its high wet strength are an advantage. DuPont is marketing a consumer drying towel called The Gulper.This product absorbs nearly twice as much water as chamois products and stays soft even when dry. The Gulper is made from a hydroentangled web using Tencel that is thermally bonded to a reinforcing polyester nonwoven. RytonAmocos Ryton has found use in filters for dry gas filtration where its higher temperature resistance provides performance levels higher than many of the polyester fabrics now used. Ryton also has excellent molding characteristics and is useful in making filters and other parts that are thermoformed. MiraflexOwens-Cornings Miraflex bicomponent glass fiber has properties that give the fiber an irregular twist along the length of the fiber.This makes the fiber soft, resilient and form-fitting, characteristics not usually associated with glass fibers. Miraflex can be processed similarly to other man-made fibers. BasofilBasofil is based on BASFs patented melamine technology. Basofil fiber combines good chemical, hydrolysis and ultraviolet resistance and can be processed on standard textile manufacturing equipment. The fiber has an ivory white color, but is dyable.Because of its excellent heat insulating and flame resistance, Basofil can be used in applications of high-temperature filtration, fire-blocking fabrics, protective apparel, molten metal splash apparel and heat-insulating fabrics Natural FibersPolyester and polypropylene are two of the materials having the widest use in nonwovens. However, there are a large number of natural fibers that are also useful when considering the development of nonwoven products.Cotton One of the earliest nonwovens produced in the United States was carded or garnetted batting for furniture and automotive seat stuffing. Several of the cotton fabric manufacturers originally entered the nonwoven business as a means of using their waste cotton products.Cotton Incorporated, New York, has stimulated the use of cotton as a primary raw material for nonwovens with their development of technology for producing purified 100-percent cotton fiber.Commercial production of 100-percent cotton fiber for nonwovens is being done by Veratech and the Barnhardt Corporation. Greenville Machinery has patented a new machine for continuous scouring and bleaching of cotton fibers which could produce cotton fibers suitable for nonwoven processing.Abaca Abaca, or Manila hemp, from the Philippines, has lost a significant portion of its share of the cordage market to polypropylene and other man-made fibers.Abaca is still a major material for the making tea-bag paper. It is produced on the wet-laid nonwoven system for the Dexter Company.Coir Coir, or coconut hair, is used in filters, furniture pads and for doormats.The fiber is processed on Rando-Web units and then spray bonded with a latex to give it resilience.Asbestos Asbestos is the only example of a major commercial natural inorganic fiber.Because of the hazards of ingesting asbestos fibers, there has been considerable work done to find suitable replacements for it.The unique properties of asbestos such as high-temperature resistance and frictional characteristics, plus modest cost have not been duplicated in any one single fiber.The replacement of asbestos by other fibers such as fiberglass, Nomex, Kevlar, Nextel and Kynol has presented a challenge to both woven and nonwoven fabric producers.Asbestos has already been replaced in hard surface floorcoverings by the use of synthetic pulps and in some types of insulation and gasketing. Cooperative work by DuPont and the 3M Company has resulted in the development of materials suitable for brake linings that replace asbestos.Wool Wool has the unique capability of felting or fulling under the influence of pressure, heat and moisture through a migration in the direction of its root end because of its scales.Wool felts can be produced by several methods including weaving and then fulling, or needle-punching and fulling, or a combination of weaving, needlepunching and fulling.One of the major producers of nonwoven wool felts is National Felt Company. National Felt makes banners and craft items by needlepunching and fulling. Other manufacturers of true wool felts include American Felt and Filter Co., Bacon Felt Co. and The Felters Co.There has not been a manmade fiber that has a wool-like structure that is capable of felting. Ole Bendt Rasmussen, the father of the fibrillated film yarn process, has made some experimental polyolefin fibers with a scale-like structure, but these products were not commercialized.Animal Hair Animal hair is another natural product that was used in nonwoven-like structures before the term nonwoven was ever used.Curled horse hair for furniture stuffing was widely used in the late 1890s and early 1900s. As horse hair became less plentiful and more expensive, cattle hair treated with a natural latex rubber was used as a replacement.Needle-punched cattle and goat hair blended with jute was a major component of carpet padding approximately 20 years ago. The needle-punched blend of animal hair and jute was rubberized to provide fabric integrity and to improve the resilience of the carpet underpadding.

August 1999