Bridging The Polymer Gap
Engineering polymers take technical fabrics to new levels.
Kari Karandikar, Ramesh Srinivasan and Jeff Sawka
E ngineering polymers have opened the world of technical fabrics to enable them to meet the performance demands of new markets that offer higher profit margins than traditional markets. Thermoplastics such as polybutylene terephthalate (PBT) and linear polyphenylene sulfide (PPS) work effectively in extreme environments, including temperatures near 200°C and in the presence of nearly any chemical.
Manufacturers have traditionally turned to polypropylene (PP) for durable and disposable fibers and nonwovens, although they also have applied such polymers as polyethylene terephthalate (PET) and nylon 6 when the demands of an application warrant their use. While these materials perform well in many situations, there are times when they are pushed beyond their thermal, chemical and mechanical limits. Fluoro-based and aramid polymers often can provide the higher performance needed, but the high price of these materials makes them impractical in many instances. Engineering thermoplastics bridge the cost/performance gap between resins having modest performance characteristics and fluoro-based and aramid polymers. Many families of engineering thermoplastics contain grades configured for the extrusion of fibers used in a variety of woven and nonwoven applications, including monofilaments, multifilaments, staple fibers, needlepunched fabrics, meltblowns, netting, cast/blown films, spunbonds and wetlaid nonwovens.
Celanex® polybutylene terephthalate (PBT) paintbrush filaments from Specialty Filaments Inc., Andover, Mass., provide improved stiffness, softness, flexibility and durability.
Selected Engineering Thermoplastics
The relative inertness and sturdiness of many engineering thermoplastics improve the efficiency and life of liquid and gas filters in the chemical, automotive, health care and pollution control fields. These polymers also find use in furniture seating, apparel, structural supports, brushes, conveying systems, and acoustic and thermal insulation. Many grades offer US Pharmacopoeia (USP) Class VI certification, as well as approval for repeated food contact and US Food and Drug Administration (USFDA) Drug and Device Master Files.
This article looks at five engineering resins to offer those who make and use technical fabrics an understanding of the capabilities of these polymers, which include PBT; PPS; thermoplastic copolyester elastomer (TPE); acetal copolymer, also known as polyoxymethylene (POM); and cyclic olefin copolymer (COC). It also takes a closer look at PBT and the numerous technical fabric solutions that emerge with this engineering polymer.
Greensboro, N.C.-based Matrex produces furniture seating using elastomeric fabric made with Teijin monofilament containing Ticona's Riteflex® thermoplastic copolyester alloy.
PBT resists chemicals and high heat in products made from meltblown fibers, staple fibers, monofilament, multifilament and other materials. It is used in filter media for blood, oil, fuel and other fluids. As a spun yarn, it has good stretch and comfort in apparel textiles and a hand much like that of high-quality cotton. It offers better processing performance than PET. Low-melting-point copolyesters are applicable as melt adhesives used to thermally bond many nonwovens, such as automotive headliners. Linear PPS is stable, tough and chemically resistant at high temperatures. It is inherently flame-retardant and resists hydrolysis, acids, bases, oxidizing bleaches and all known solvents at temperatures below 200ºC. It often is used in tough environments such as bag-house and flue-gas filters, paper machine dryer fabrics, food process screens, and filters for dairy products and hazardous liquids. Linear PPS can be meltblown into lofty or stiff fabrics, spunbonded, and made into staple fibers for needlepunched composites and other felt substrates. TPEs combine elasticity and strength. Fibers made from them have low initial modulus, high elongation at break and good stretch recovery. They withstand abrasion, have good chemical and thermal resistance, and are stable in high-temperature water and steam, such as occurs during dyeing. TPEs are available in a wide range of hardness (durometers from 25 to 77 Shore D), so fabric manufacturers have many strength and stiffness options. They are used in a growing variety of fiber and fabric applications including conventional and suspension seating fabrics; incontinence sheets; non-skid fabrics; and medical applications such as transdermal patches, protective apparel and breathable barriers against infectious diseases.
POM combines strength, stiffness and chemical resistance. It withstands exposure to hot water and prolonged contact with fuel and oil, which has made it an excellent choice for auto fuel and oil filters. It processes easily on machines used for polypropylene (PP) at a lower melt temperature of 190°C to 225ºC, versus 230ºC to 260ºC for PP. Its fibers can be extruded in a variety of thicknesses and in textures ranging from soft to stiff. COC has greater charge retention at elevated temperature and humidity than other olefins when used in air filter fabrics. It resists polar solvents, alkalis and hydrolysis and has excellent moisture-barrier properties. When COC is blended into traditional polyolefins, it increases stiffness and reduces elongation in nonwoven fabrics. In PP, it reduces fiber-to-fiber and fiber-to-metal friction.
PBT In Nonwovens
PBT, which is more commonly used for injection-molded products, is seeing increasing application in technical fibers. It is strong and tough and has low creep, even at elevated temperatures. It absorbs little moisture and resists many chemicals, including oils, greases, solvents, dilute acids, bases, salt solutions, organic chemicals and ozone. It also resists fungal growth, can be immersed in water for extended periods, and can resist short-term exposure to steam and water at temperatures as high as 150ºC. Given their wide range of viscosities, PBTs perform well in nearly all fabric and nonwoven processes from spunbond and meltblown to monofilaments, staple fibers and multifilaments. Grades available through Florence, Ky.-based Ticona a business unit of Dallas-based Celanese Corp. have melt indices of about 5 to 350 grams per 10 minutes, and intrinsic viscosities of about 0.57 to 1.40 deciliters per gram. PBT typically melts at 225ºC and undergoes glass transition between 50ºC to 60ºC. As a result, lower-melt-viscosity PBTs can be meltspun at temperatures similar to those of polypropylene. PBT has many advantages over PET in processing as well as end-use. PBT is dried at a lower temperature (121ºC versus 136ºC for PET), has a lower melt temperature (225°C versus 260°C), and generally has a faster throughput than PET. It resists hydrolysis better than PET and tends to shrink and distort less after processing because of its faster crystallinity. PBT also makes softer and more flexible fabrics than PET and yields fine fibers more readily.
This polyester automobile headliner contains Celanex® PBT binder material from Ticona.
PBT has a broad processing window when it is spunbonded. At throughputs of 0.40 to 0.80 grams per hole per minute, extruder temperatures can range from 210ºC to 282ºC and die melt temperatures from 250°C to 280ºC, depending on the viscosity of the grade selected. New PBT grades that are excellent candidates for technical fabrics continue to appear. Celanex® PBT 2000-K, for example, is designed to replace PET in selected homogenous and bicomponent spunbond applications. It yields finer-denier fibers than PET, and fabrics made from this grade shrink less during processing, and are softer and more flexible. When blended with PET, it reduces the stiffness of PET fabrics and increases processing throughput.
Another new grade of Celanex PBT is a low-melt polyester copolymer binder with a melt point of 147°C that is an excellent material for making polyester auto headliners, hood liners and trunk liners that meet European recyclability regulations. These liners weigh significantly less than traditional liners made with cotton shoddy or glass fibers impregnated with phenolic resin.
This PBT grade also can be used in powdered form to fuse mats of PET staple fibers, which typically melt at 250°C to 257°C. Polyester liners involve a simple thermal operation as opposed to phenolic-based liners, which involve curing and the possible release of formaldehyde. The new binder can be used with other fibers in felts or fabrics and can be fabricated as staple fiber, sheet or film, and as a bicomponent fiber.
This cartridge filter made with meltblown Fortron® polyphenylene sulfide fibers on a central support is stable to acids, bases and organic solvents. It also resists high temperatures and has a long service life, according to Ticona.
Paving The Way For New Market Opportunities
Engineering thermoplastics such as PBT, PPS, TPE, POM and COC can open new doors for nonwovens and fiber manufacturers. They provide a broad palette of materials for use in higher-performance niches in markets as diverse as chemical processing, health care, automotive and furniture. The ability to work effectively under demanding thermal and chemical conditions allows technical fabrics made from them to displace other materials, such as stainless steel, ceramics and glass.
Editors Note: Kari Karandikar and Jeff Sawka are marketing specialists, and Ramesh Srinivasan is a business development engineer at Ticona.