The Evolving Roles Of Nonwovens In Technical Textiles
By Dr. Dong Zhang, Textile Research Associate
The textile industry is one of the largest consumer-supported industries with significant impact on the worldwide economy. Advancements in applications of nonwovens technology to improve textile properties offer a great economic potential for the industry’s growth. It has been demonstrated in recent years that nonwovens technology can be used to enhance technical textile attributes, such as durability, breathability, water repellency, fire retardancy, antimicrobial properties, absorbency and barrier properties, etc. By weight, technical textiles represent about 40% of the total textile industry. In 2007 the worldwide market for technical textiles was estimated around 21 million tons with a value of $115 billion. It will increase to 24 million tons with a value of $127 billion by 2010.
Among technical textiles, about 40% are nonwovens in terms of tonnage. The drivers for future growth of the industry are mainly expected to be emerging markets like Asian countries (China and India), Eastern European countries and South America.
Nonwoven fabric consists of a manufactured sheet, web or batt of directionally or randomly orientated fibers bonded by friction and/or cohesion and/or adhesion, excluding paper and products that are woven, knitted, tufted, stitch-bonded incorporating binding yarns or filaments or felted by wet-milling, whether or not additionally needled. The fibers may be of natural or man-made origin. They may be staple or continuous filaments or be formed in situ.
Nonwovens for technical textiles are predominantly synthetic polymer-based because of inherent advantages of strength and versatility of such fiber and this trend is expected to continue in the future. Raw material consumption indicates that polyolefin and polyester account for 50% of the consumption followed by glass and jute at 15% and 14% respectively. Cotton and viscose account for 7% and 6% respectively. The specialized fibers and webs such as aramids and carbon fibers account for the rest of total nonwovens used in technical textile applications.
There is increasing interest in nonwoven fabrics that combine the advantages of different textile constructions, including knitted fabrics, wovens, composites and membranes. Worldwide, the nonwovens industry continues to expand about 8.5% in term of tonnage annually. This world growth is in part due to several industrializing economies and their increasing demand for nonwoven materials and key markets such as hygiene, consumer wipes, liquid and gas filtration, furnishing and bedding, automotive, building and roofing and geotextiles. Further growth will derive from increased market penetration in many applications, including industrial wipes, garments and clothing and special functional materials, as new technologies improve the characteristics of nonwoven fabrics. However, growth will be limited by price pressure in consumer markets, where converting companies will try to find cost reduction by decreasing the amount of nonwovens in their end user products.
Advantages of Nonwovens for
Nonwovens as technical textiles have many advantages. Nonwovens’ resistance to tears, soil, chemicals, puncture, UV light exposure, mildew, rot, freeze/thaw conditions, excellent strength, breathability and barrier properties, attractive fiber and structural appearance of various surface tension at relatively low cost makes them an ideal choice for technical applications.
• Abrasion resistance: Nonwoven webs can be up to five times more durable than other traditional fabrics.
• Acoustic insulation: Polyester nonwoven webs have reached same or higher absorption value than comparable standard materials. Some nonwoven webs used for acoustic insulation can also weigh 50% less than comparable materials and withstand temperatures up to 180°C or higher.
• Barrier: Nonwoven webs can filter virtually all particles or aerosol or microorganism larger than two microns and can be manufactured to filter smaller particles down to nano scale in air or liquid. Nonwoven webs can be made with a high loading of activated carbon to remove hydrocarbon vapor, gases and other intolerable odors in the air.
• Cost-effective: The quality and flexibility of nonwoven webs make the materials more cost-effective than comparable materials. Plus, since they are generally lighter than woven materials, they help manufacturers improve vehicles’ fuel efficiency to meet federal requirements and consumer demands.
• Durable: Relative to their weight, nonwoven webs can be designed to be stronger than traditional textiles. They can also be designed to be extremely abrasion- and heat-resistant.
• Easily customized: Nonwoven webs are able to be molded and contoured to fit most interior and some complex surface. Manufacturers are also able to manipulate webs’ thickness, rigidity and fiber compositions for the most demanding requirements.
• Flame resistance: Specialized nonwoven webs are comparable to woven or knit materials in this respect.
• Strength and weight: Nonwoven webs can be designed to be considerably stronger than woven or knit materials of the same weight.
• Appealing integrity: Nonwoven webs can be used throughout the vehicle. They offer superior color and texture matches. When colorant is incorporated during the fiber formation process such as spunbond, they are highly resistant to color fading and rub-off. In addition, these materials provide a more uniform draw across the length and width of carpet than do woven materials, resulting in a more homogeneous appearance.
• Thermal protection: Mechanically bonded glass fibers can be used at continuous operating temperatures up to 1000°F, basalt mats can be used at continuous operating temperatures of up to 1500°F; silica materials can be used up to 2000°F.
Applications of Nonwovens in Technical Textiles
Typically, nonwovens in technical applications include:
1. Agrotech: crop covers, seed blankets, weed control fabrics, greenhouse shading, root bags, biodegradable plant pots, capillary matting cover, protection and collection, fishing and tying.
2. Buildtech: roofing and tile underlay, underslating, thermal and noise insulation, house wrap, facings for plaster board, pipe wrap, concrete moulding layers, foundations and ground stabilization, vertical drainage, protection and display, textile construction, building components, reinforcements and high quality wall ‘paper.’
3. Clothtech: shoe components, insulation and structure, sewing products, interlining, cleanroom garments, and shoe and leather goods applications.
4. Geotech: asphalt overlay, soil stabilization, drainage, sedimentation and erosion control, pond liners, impregnation base, drainage channel liners, separation, reinforcement, filtration, offshore land reclamation, roadside, railside, river and canal banks, and reservoirs.
5. Hometech: Carpet components, furniture components, consumer wipes (baby, personal and household wipes), and industrial wipes (foodservice, general industrial general, industrial specialty and medical wipes), air and water filtration, interior design, drapes, covers, tickings, and composites.
6. Indutech: Electrical components (cable insulation, floppy disc liners, insulation tapes and microfilters), filtration and separation (air, liquid and gases), satellite dishes, clothing surfacing tissues/veils, conveyor belts, reinforced plastics, PVC substrates, flame barriers, noise absorbents, battery separators (alkaline, acid and fuel cells), anti slip matting, lifting and pulling.
7. Medtech: drapes and gowns, sterile wrap, swabs (operating room ward use) and dressings, cleaning, coverstock, woundcare, protective apparel, bedding and sheets and masks.
8. Mobiltech: boot liners, parcel shelves, heat shields, shelf trim, molded bonnet liners, boot floor covering, fuel/oil filters, headliners, rear parcel shelves, airbags, cabin air filters, engine intake and exhaust air filters, silencer pads, insulation materials, car covers, underpadding, car mats, tapes, backing for tufted carpets, seat covers, door trim, and insulation, floorcoverings, protection, and composites.
9. Packtech: bulk packaging with predefined 3D structure, scrap and disposables, spacer and tying and absorbent food pads.
10. Protech: chemical and biological protection, particulate protection, flame retardant, cut resistant, shields and gowns worn in emergency response, chemical handling, hazardous waste control, cleaning and filtration.
11. Sporttech: Luggage components, sports equipment, sports wear, wipes, covers, disposables and camping equipment.
12. Oekotech: environmental protection, exhaust air and waste water filtration, dust collection, leak oil absorbent, gas and odor removals.
In this report, nonwovens in technical applications are classified as disposable nonwovens and durable nonwovens. Disposable nonwovens include the nonwovens used for hygiene, medical, consumer wipes and industrial wipes. Durable nonwovens include the nonwovens used for garments, Interlinings, shoes and leather goods, furnishings and bedding, floor coverings, liquid filtration, air and gas filtration, building and roofing, geotextiles, automotive, agriculture and electronics.
Nonwovens in Disposable Applications
Disposable nonwovens are those nonwovens for short life applications in single use including hygiene, medical, consumer wipes, industrial wipes, and others. Hygiene nonwovens include baby diapers, training pants, adult diapers, and feminine care products (external and internal). Medical nonwovens include drapes and gowns, sterile wrap, swabs (OR use and ward use), and dressings. Consumer wipes include baby wipes, personal care wipes and household cleaning wipes. Industrial wipes include food service wipes, industrial general wipes, industrial specialty wipes, and medical wipes. Other disposable nonwovens include fabric softener substrate, sorbents, sterile and non-sterile packaging materials, tabletop items (airlaid napkins and table cloths) and soaker pads for food packaging.
Disposable hygiene nonwovens include baby diapers, training pants, adult diapers (adult incontinence) and feminine care products (external and internal). The external feminine care products include sanitary napkins and pads. The internal feminine care products refer to tampons. Nonwoven hygiene products include coverstock and airlaid core. Coverstock is a generic used to describe the several nonwoven materials used in hygiene products’ construction, which includes topsheet, barrier leg cuff, back sheet, stretchy panels, fastening and landing strips, acquisition/distribution layer and airlaid pulp absorbent core materials.
Medical nonwovens include drapes and gowns, sterile wrap, swabs (OR use and ward use) and dressings. Among them, surgical gowns, drapes and drape pack parts account for almost two thirds. Surgical drapes made of nonwoven materials have captured about 95% of the total drapes market. Surgical gowns have captured an estimated 90% of the gown market.
Consumer wipes includes baby wipes, personal care wipes, and household cleaning wipes. The increasing popularity of specialty wipes for specific applications has brought about a decline in baby wipes, which were once also used for everything from adult hygiene to cleaning leather car seats. Personal care wipes encompasses anything that touches human skin including antibacterial wipes, acne medication pads, alcohol prep pads, deodorant and refreshment wipes, eye pads, feminine hygiene wipes, general clean-up wipes, hemorrhoid wipes, incontinence wipes, make-up remover wipes, wet and dry wipes, moist flushable wipes, wound wipes and more. Household cleaning wipes are wet or dry wipes used for surface cleaning including automotive care wipes, computer wipes, disinfectants wipes, dry cleaning wipes, furniture polish wipes, glass cleaner, household cleaners, jewelry wipes, paint removal wipes, pet wipes (dog bath wipe and a dander-zapping cat wipe), silver and brass cleaners, dishwashing wipes, stain remover wipes and tough task soil remover wipes.
Industrial wipes are disposable nonwoven products used for a variety of applications in industry and institutions, including food service wipes, industrial general wipes, industrial specialty wipes and medical wipes. Wipes for foodservice are mainly used in restaurants including fast food restaurants in the food preparation area to the dining area and service counters and tables. Industrial general wipes include general and surface cleaning, skin cleansing, tough task, scrubbing, dusting and electrostatic, critical task controlled environment, polishing and glass cleaning. They are also used in industrial factory shop cleaning, maintenance repair operation, janitorial commercial cleaning, automotive military aerospace, geotextiles landscaping and spill control absorbent mats. The main end markets for industrial specialty wipers are: cleanroom, photography and printing industry, and auto and aerospace industry, also referred to as transportation or surface preparation, for applying paint. The common feature of these specialty markets is that the wipes must be non-linting to prevent microscopic particles from contaminating the product. Medical wipes, which include hard surface antibacterial, bathing and incontinence wipes, are designed for use in hospital and healthcare facilities.
Nonwovens in Durable Applications
Durable nonwovens are those nonwovens for long-life applications or in multiple uses including garments, interlinings, shoes and leather goods, coating and laminating, furnishings and bedding, floor coverings, liquid filtration, air and gas filtration, building and roofing, geotextiles, automotive, agriculture and electronics. The other durables include apparel insulation, mold release materials, electrical insulation, paper making felts, thermal barriers, scrims, wall coverings, polishing and grinding materials, scrub pads (needlepunched), auto and boat tarpaulins, bale wrap and can separators.
The largest segment within the nonwoven garment market is protective apparel used for work in health and safety environments. This includes gowns worn in emergency response, chemical handling, hazardous waste control and agriculture. Cleanroom garments, used to protect the wearer from chemical or biological hazards, is another important segment.
Nonwovens interlining materials have largely replaced traditional interlining textiles in garment applications due to their superior performance combined with their lower cost. Over 70% of interlining materials are nonwovens now. The primary applications include men’s tailored suits (lapels, jacket fronts, cuffs, collars, pocket stays, chest pieces and stabilizing tabs) and women’s garments (blazers, skirts, dresses, purses and outerwear).
Shoe and leather goods
The majority of the nonwovens utilized in shoe and leather goods are for “brown shoe” applications. Several nonwoven technologies have been utilized by this segment. Carded thermal bonded nonwovens dominate, accounting for almost two-thirds of materials consumed. Coated and laminated substrates are usually made of needlepunched nonwovens that are used to produce artificial leather. Other important nonwovens supplying this market are spunbonded and wetlaid. Significant influence has been placed on the development of nonwoven composite structures for added strength and durability. Antimicrobial treatment is becoming routine for these materials as well as other applications.
Furnishings and bedding
Nonwovens used in furnishings and bedding include upholstered furniture, bedding and other furnishing applications. The largest segment is bedding nonwovens and accounts for half of the total nonwovens consumed. Upholstered furniture nonwovens follow this and use an estimated 37% of all nonwovens consumed by this segment. The remaining nonwovens volume for furnishings and bedding is used in other furnishing applications such as mattress pads, bedspread quilt backings, dust ruffle platforms, various window treatments and room dividers. The areas of nonwoven in the upholstered furnishings segment include spring insulator pads, foundation dust covers, pull strips, pillow or cushion wrap and skirt linings. In bedding, the largest areas of use are mattress quilt backing, flanging, spring insulators, spring wrap, box spring dust covers and mattress ticking on some lower priced bedding.
The floor covering nonwovens include six major segments and they are broadloom and pattern carpet backings, automotive carpet backings, modular carpet backings, carpet underlay, walk-off mats and others such as needlepunched carpet backing and film and nonwoven floor protector laminates. These floor coverings are not all growing at the same pace. Primary and secondary automotive carpet backing is the largest nonwoven floor covering market. Primary carpet backings comprise the majority of this segment. The tufted carpet is used as a backing to lock in the tufts and provide extra body for secondary backing.
The liquid filtration is a fast-growing market for nonwovens, including water filtration (tap water and wastewater), food and beverage filtration, pharmaceutical and electronic processes, blood filtration, tea bags and coffee and juice filters, edible cooking oil filters and oil/fuel filters for automotives. Nonwovens have been successfully applied in the industry as membrane support for microfiltration (MF), ultrafiltration and reverse osmosis (RO) filtration.
Air and Gas Filtration
The air and gas filtration market includes domestic filters, industrial filters and automotive filters. Domestic filters are those for HVAC, cooking filters, vacuum cleaners and various portable filters on the market. Industrial filters are in general, HVAC/HEPA/ULPA filters, dust removals such as filters for power stations, incinerators, paint spray house and many industrial processes, where air is contaminated and needs to clean, or super clean environment is required for production. Automotive filters include engine air filters (intake and exhaust), cabin air filters and fuel/oil filters. Nonwoven media are economical and perform well in many filtering applications. They will continue to increase their share in many end applications.
Building and Roofing
Building and roofing nonwovens are primarily used for house wrap and roofing. Various materials are used to supply this house wrap market, but nonwovens have captured a reasonably high share of the total business. The materials are barriers to make a building more airtight, thus reduce heating and air conditioning costs. The house wrap is designed to be a breathable membrane that reduces air leakage and protects the structure against the elements. But, at the same time the barrier material is breathable and enables interior moisture to gradually move through the barrier preventing the build-up of moisture within the structure’s walls.
A geotextiles fabric functions include separation, reinforcement, filtration, drainage and/or as a moisture barrier (when impregnated) for roads and railways, offshore land reclamation, roadside, railside, river and canal banks, and Reservoirs. Nonwovens’ resistance to tears, soil chemicals, puncture, UV light exposure, mildew, rot, freeze/thaw conditions, etc., makes them an ideal choice for the applications. Major uses of nonwovens in the geotextiles market include asphalt overlays, separation of dissimilar materials, lining systems, reinforcement of weak soils and other materials and drainage/ filtration systems.
More than 40 automotive parts are made from nonwovens, from hood trunk liners to heat insulation to sound proofing, from carpeting to roof lining, and from engine air intake to exhaust, including boot liners, parcel shelves, heat shields, shelf trims, molded bonnet liners, boot floor covering, oil filters, headliners, rear parcel shelves, airbags, cabin air filters, silencer pads, insulation materials, car covers, underpadding, car mats, tapes, backing for tufted carpets, seat covers, door trim and insulation, floorcoverings, protection and composites. Nonwovens compete with woven fabrics, paper, and foam or glass fiber materials for automotive construction. However continuing trends to minimize costs and reduce weight indicate that nonwovens will likely take share away from these materials.
The market for agriculture nonwovens includes crop protection, weed control, greenhouse shading. In agriculture, the nonwoven material is used as a ground cover to inhibit weed growth, protection against the elements (frost, wind, hail, and excessive rain), protection against harmful insects, moisture retention, erosion control, seed germination, row crop covers and shade cloth. The advantage of nonwoven materials is that they are porous while offering protection. Also, nonwovens resist mildew, rotting and destructive microorganisms.
The nonwovens electronics market is primarily comprised of battery separators and floppy disk liners. Other smaller applications include cable wrap, insulation and circuit board materials. The battery separator market is the largest segment and is directly impacted by shifts in battery technology. Most of this is various wetlaid glass used in lead acid batteries. In the smaller rechargeable battery market, nickel metal hydride batteries are growing faster that nickel cadmium batteries. Both types of batteries only use nonwovens for the separator material therefore there is a positive link between the two growth rates. A potential use for fuel cell battery in cars and other places provides another promising market for nonwovens as battery separators.
Development of Nonwovens Processes
Nonwoven Web-forming Process
Nonwoven processes include drylaid, airlaid, wetlaid and spunlaid. Drylaid nonwovens, which include thermal bonded, needlepunched, spunlaced (hydroentangled) and chemical bonded (latex bonding) materials, is the lead web forming process for now. Drylaid mainly refers to carding as web forming process and so produced webs are bonded by thermal bonding, mechanical bonding, chemical bonding and spunlacing. Drylaid also includes parallel lay, random, card and crosslay and aerodynamic (long fiber airlay from cardwebs). Carding is a web forming process and is to separate small tufts into individual fibers to begin the process of parallelization and to deliver the fibers in the form of a web. Carded nonwoven fabrics are made from a variety of fibers, including rayon and polyester with fiber length ranging from 1.2 to 20 cm.
Airlaying (airforming) is a method of forming web by mixing fibers with air to form uniform air-fiber mixture, which is then deposited on a moving air-permeable belt or wire. So webs can be bonded using latex bonding airlaid (LBAL), thermal bonded airlaid (TBAL), a combination of the two (MBAL) or high pressure bonded airlaid (HBAL) such as hydroentanglement. The so-called airlace is the process of hydroentangling airlaid webs.
Dan-Web and Oerlikon Neumag (former M&J Fibertech) are two major air former manufacturers. Major airlaid nonwoven producers include Buckeye Technologies, Concert Industries, Georgia-Pacific Nonwovens, Rexcell (Duni), McAirlaid, Oji, FiberWeb (formerly BBA, adding its second line in Tianjin, China in 2007), and recently Danish Airlaid. This technology's growth continues to be propelled by the expanding use of airlaid pulp materials in disposable hygiene nonwovens. Airlaid technology generally differs from other drylaid webs in its use of very short fibers, mainly wood pulp. As a result, most products obtained through this method offer high absorbency. They are inexpensive and biodegradable.
Wood pulps and pulp/synthetic blends are the main raw fibers for airlaid nonwovens. Airlaid pulp has been and will continue to expand, due to their use in wipes and absorbent applications. The baby wipes market largely drove airlaid pulp’s growth. Airlaid pulp was adopted as an absorbent core material by the absorbent hygiene industry and this again boosted airlaid pulp’s volume considerably. While capacity and demand are relatively in balance in Europe, North America still suffers from an overcapacity position. The major end markets for airlaid pulp materials include wipes (baby, personal, household and industrial), absorbent core materials, tabletop items (napkins, tablecloths) and medical dressings. Emerging product applications include protective-cushioning materials for packaging, filtration media, new composite wiping materials and food soaker pads.
In the wetlaid process, the formation of the precursor web for entanglement is best achieved by using wet-formed nonwoven systems. Fibers are dispersed in water at very high dilution and then deposited on a screen to separate the water from fibers. Hence, uniform, almost perfectly isotropic sheet structures for hydroentangling can be formed by wet-forming systems. Wet-forming systems are fast and efficient compared with other web forming technologies. Several bonding technologies can be applied to wetlaid webs. Wetlaid nonwovens are used for a wide variety of different application fields, especially in the hygiene market, in the filtration applications, and in disposable nonwovens for medical/surgical purposes, including tea bag media, filter materials, medical barrier fabrics, specialty wipes, battery separators, coated/laminated substrates as well as several other smaller markets. The largest producer of wetlaid nonwovens worldwide is Ahlstrom, followed by Hollingsworth & Vose. They both have plants in Europe and North America.
Spunlaid nonwovens, which include spunbonded, meltblown, flashspun, and electrospinning, showed potential growth and will be the leading position in next few years, especially when electrospinning is becoming commercialized with large-scale production. Spunlaid is web forming process, in which the polymers are molten, extruded and laid down to form webs. Normally, meltblown webs are self-bonded due to the hot quenching air and short distance between die and collecting device. Spunbonded webs are thermally bonded, although they can be chemically or mechanically bonded. In spunlaid nonwovens, meltblown and spunbonded take the major parts.
Flashspinning is a complex and difficult method of manufacturing spunbonded fabrics because of the need to spin a heated pressurized solution under precise conditions. The largest market for flashspun PE is protective apparel. Tyvek from DuPont is, by far, the most important nonwoven produced in this segment. The use of protective apparel in the many diverse end use segments served is growing at an attractive rate. Tyvek remains the most important fabric used in this market. Other end uses for Tyvek include envelopes, house wrap, sterile packaging, graphics, and packaging.
Electrospinning provides a process to produce superfine fiber webs with fiber diameters in nanometer scale. Although the feasibility of electrospinning has been known for several decades, it has recently gained considerably increasing interest due to the unique properties of fibers, which can be tailor-made by controlling spinning conditions and spinning solutions. The applications of electrospun nonwovens are expanding recently from medical to filtration, from military to consumer. Nanofiber-lined chem-bio suits result in lightweight, breathable, multifunctional clothing with the addition of chemical functionalities to offer protection against harmful liquids, vapors and aerosolized toxins. There are a few commercial nonwovens in the market today. Nanofiber filters by Donaldson, DuPont, Finetex and Nano-Tex's spill repellant fabric are some of the few but rapidly growing commercial nanofiber nonwovens that have penetrated the market.
One of the challenges in commercial nano fiber production is low throughput in the electrospinning process. Finetex, eSpin, Donaldson and NanoStatics are active players in the front of this scale up development. They showed commercial scale throughput capacity for high volume production of nanofibers and nanofiber nonwovens. Their commercial technology can produce nanofibers with diameters ranging from 50 to 500 nm. The thickness of the nanowebs can range from 100 nm to more than 200 microns. With the availability of a commercial electrospinning technology, it is possible now for the industry to undertake capital investments in the electrospinning technology, but it is still in the very early stage of commercialization process for large-scale nanofiber production.
Nonwoven Web-bonding Process
Nonwovens (mainly drylaid, airlaid and wetlaid) can be bonded by four basic bonding technologies: needlepunching, thermal and resin bonding, spunlacing (hydroentangling) and chemical (latex) bonding. Needlepunching is web bonding process and needlepunched nonwovens are created by mechanically orienting and interlocking the fibers of a spunbonded or carded web. This mechanical interlocking is achieved with thousands of barbed felting needles repeatedly passing into and out of the web. The fibers can be natural or synthetic.
Spunlace is a nonwoven web bonding process. The web can be formed by drylaid (carded), wetlaid, airlaid (called airlace when spunlacing), and recently spunbonded nonwovens. Spunlacing (hydroentanglement or hydraulic needling) is a process of entangling a nonwoven web of loose fibers on a porous belt or forming wire to form a sheet structure by subjecting the fibers to multiple rows of fine high-pressure jets of water. The spunlaced technologies’ advantages are its pleasing aesthetics of softness, modest strength and good absorbency. In North America and Europe, a principal end market for spunlaced materials is medical applications such as surgical gowns and related apparel, operating room pack parts, sponges, bandages and medical wipes. Dry wipes has always been a significant market for spunlaced materials, but the expanding pre-moistened wipes market worldwide is now the most important end-use, especially in Europe. A recent development is Freudenberg’s “Evolon” material, a spunlaid web/spunlaced technology. The web is made from spunbond PET/PA bicomponent fibers and then hydroentangled by high-intensity water jets, which splits the segmented-pie bicomponent fibers into its microfibers and binds them into a strong, soft and durable fabric. Considerable capacity has been added in emerging markets including China, South America and Eastern Europe. Major producers of spunlaced nonwovens are DuPont, Orlandi, Jacob Holm and Spuntech.
Thermal bonding includes calendering (plain or patterned), through air, infra red heating and ultrasonic bonding. The largest single market for carded thermal bonded polypropylene was cover stock, but it has switched from carded thermal bonded coverstock to spunbonded polypropylene materials.
Chemical bonding includes overall saturation, foamed binders, solvents and patterned (print bond). Bonding a web by means of a chemical is one of the most common methods of bonding. The chemical binder is applied to the web and is cured. The most commonly used binder is latex, because it is economical, easy to apply, and very effective. Several methods are used to apply the binder and include saturation bonding, spray bonding, print bonding and foam bonding. For industrial wipes, chemical bonded nonwovens have a larger percentage than for consumer wipes, but remain behind spunlaced nonwovens that have increased in the last five years in these end uses. Short-fiber airlaid fabrics come third. For household wipes, chemical bonded nonwovens are almost on par with spunlaced ones. Other applications for chemically bonded nonwovens include building and roofing materials, medical and packaging.
Raw Materials for Nonwovens in
Raw materials for technical nonwovens have two general categories: polymer resins and staple fibers. Polymer resins are used for spunlaid processes, including spunbond, meltblown, flashspun and electrospun. Staple fibers are used for drylaid, airlaid and wetlaid processes using different bonding methods as discussed earlier, such as thermal bonding, needle bonding, chemical bonding and hydroentanglement. Polypropylene and polyester remain two primary polymers used in nonwovens for technical application. Bicomponent fibers have been increasingly used in staple fibers for enhanced uniformity and superior performance in technical nonwovens, such as PP/PE, PET/PE, PET/Nylon6 bicomponent fibers.