Nonwoven fabrics can be used in a wide variety of applications, which may be limited life, single-use fabrics as disposable materials or durable fabrics for automotive and civil engineering applications, explain Rajanna L Gotipamul, SG Kulkarni and Pranshil Gourkar, in the 1st part of a 2-part article.
Over the last 30 years, the nonwovens industry fibre usage has not only grown by a factor of ten. The fibres used have changed from almost exclusively biodegradable to almost exclusively non-biodegradable despite concern for the environment among consumers becoming progressively stronger. In fact in the largest and environmentally-sensitive market, cover stock for disposable diapers, biodegradable products are non existent. An expressed consumer preference for environmentally-friendly products, in the disposables area at least, appears to remain an un met need. The reducing cost of synthetic fibres coupled with their easy conversion into binder-free spunlaid and dry-laid thermally bonded fabrics has caused a steady decline in cellulosic nonwoven market share in all sectors. Viscose rayon now appears relegated to little more than a premium priced niche in a global fibre market largely reliant on cheap fossil fuels for its raw materials. Even cotton, for centuries, the most important of fibres are now taking second place to synthetics.
In disposables even wood-pulp is losing share to synthetic super absorbents.
Reasons for using biodegradable nonwovens
Nonwoven fabrics demonstrate specific characteristics such as strength, stretch, resilience, absorbency, liquid repellency, softness, flame-retardancy, cushioning, washability, filtering, bacterial barrier and sterility. Nonwoven fabrics can be used in a wide variety of applications, which may be limited life, single-use fabrics as disposable materials or durable fabrics for automotive and civil engineering applications. This increasing market share will be driven by the strong growth in many key disposable markets such as adult incontinence products, filters and protective apparel, and key non-disposable markets such as geotextiles and battery separators. Disposable markets were the majority of nonwoven demand, which accounted for a 64 per cent share.
Disposable consumer products, which primarily include baby diapers, adult incontinence and feminine hygiene products, and wipes, were the largest market for nonwovens. Based on the data available, continued growth in nonwovens will be in the disposables area and the share of the short-life nonwovens is going to remain significantly large. Also, looking at the distribution of durables and disposables in terms of yardage or volume, the disposable share is four-fifths of the total nonwovens, making them much more visible in the waste stream. Considering that a large share of these materials is disposable products, it is important that issues related to their disposal be carefully addressed.
Nonwovens are used almost everywhere: in agriculture, construction, military, clothing, home furnishing, travel and leisure, healthcare, personal care and household applications. Of these many applications the number of which continue to grow, more than two-thirds of them are disposables, mostly single use. The environmental impact of disposable products has become a major concern throughout the world in recent years. These disposable products are usually produced from traditional thermoplastic resins, such as polypropylene (PP), polyethylene (PE), polyester (PET), polyamide (PA) and polycarbonate (PC), which are not biodegradable. However, due to increasing environmental consciousness and demands of legislative authorities, the manufacture, use and removal of products made of traditional polymers are considered more critically. The remedy to this problem could be found in the development of substitute products based on biodegradability, and ideally from natural and renewable materials.
Natural fibres, such as cotton, kenaf, coir, jute, flax, sisal, hemp and wood, etc., are the first choice due to their biodegradability.
Some synthetic biodegradable fibres have also been used for nonwoven applications, including cellulosics such as cellulose acetate, rayon, lyocell, etc. manufactured fibres such as polylactic acid (PLA), poly(caprolactone) (PCL), poly(hydroxybutyrate) (PHB), poly(hydroxybutyrate-co-valerate) (PHBV), Biomax, Biopol,polytetramethylene adipate-co-terephthalate (PTAT), etc.; and water solubles such as poly (vinyl acetate) (PVA). Thus the target for biodegradable nonwovens is to replace synthetic fibres with biodegradable fibres in the disposable nonwovens, such as the wetlaid pulp/ polyester spunlaced fabrics used mainly for industrial and professional wipe products and household and hygienic wipes, which are spunbonded or drylaid and then chemically or thermally bonded.
Cost-effective biodegradable nonwovens
The developed process that it says enables recycled paper and cardboard to be used as a raw material for cost effective nonwovens. Hygiene and home care products, such as nappies, sanitary towels and cleaning cloths, are among the many items that the researchers say can be manufactured from the biodegradable nonwovens. The manufacturing costs of cardboard-based nonwovens are around 20 per cent lower than for nonwovens produced from wood raw materials. The forest industry will be among those likely to benefit from new business opportunities opened up by nonwovens based on recycled paper and cardboard.
The principle raw material in nonwovens manufacture is biologically non-degradable polyester and that up to now, market entry for bio-based nonwovens derived from wood has stalled because of prohibitive production costs.
The new process means that bio-based nonwovens are now more competitive on price in comparison with plastic-based products. New business opportunities should open up fairly rapidly, since the technology required for manufacturing nonwovens from recycled materials is already in place.
It could extend future possibilities for re-use, particularly in the case of cardboard, which is more cost-effective as a raw material than fine paper, the researchers say. Cleansing the cardboard of filler material, lignin and hemicellulose is a key part of the nonwovens manufacture.
Biodegradation of fibres occurs when their constituent polymers are depolymerised, usually by the action of enzymes secreted by microorganisms.
These enzymes act by hydrolysing or oxidising the polymer, and can work on the ends of the chains (exo-enzymes) or randomly along their length (endo-enzymes). To do its work, the enzyme has to be able to bond to the fibre and gain access to sites capable of being oxidised or hydrolysed. The most biodegradable fibres therefore tend to be hydrophilic, and made up of short, flexible chains with low levels of crystallisation. They will often have chain backbones with oxygen or nitrogen links and/or pendant groups containing oxygen or nitrogen atoms. This description clearly fits most natural fibres and fibres made of natural polymers.
Biodegradation-resistant polymers have the opposite characteristics and unsurprisingly are used to make the stronger more durable fibres. Oxygen-free polymers such as polypropylene and polyethylene resist biodegradation totally. Polyester (i.e. the aromatic polyethylene terephthalate), despite its oxygen content is degradation resistant probably because it has rigid, rod-like chains. The same is true for polyamides despite their nitrogen content. Unlike the aromatics, aliphatic polyesters are generally biodegradable. More than a hundred species of bacteria are known to synthesise and store aliphatic polyesters for future use as an energy source. While being naturally biodegradable, these polyesters are also thermoplastic and capable of being extracted and formed into films and fibres like any other polyester.
Man-made biodegradable aliphatic polyesters are however still based mainly on the industrial polymerisation of monomers such as glycolic acid (PGA), lactic acid (PLA), butyric acid (PHB), valeric acid (PHV) and caprolactone (PCL). These copolymers have already found application in implants, absorbable sutures, controlled release packaging and degradable films and mouldings.
Natural And Renewable fibres
Demand for nonwovens is increasing globally, particularly in the disposable products area. As the consumption of nonwoven products with short life increases, the burden on waste disposal also rises. In this context, biodegradable nonwovens become more important today and for the future. As a result, there is increasing effort to design and develop biodegradable nonwovens, with research and development efforts from both academia and industry. Several new biodegradable polymers such as polylactic acid (PLA) and Biomax have helped the industry to produce larger amounts of biodegradable nonwovens. In addition, the use of natural fibres in nonwoven products is also increasing. There is continuing effort to develop new ways to produce biodegradable nonwoven materials by combination of natural fibres and other biodegradable resins or fibres.
Cotton is used in nonwoven hygiene products including wipes, feminine hygiene products, diapers and adult incontinence products. It is soft, comfortable, hypoallergenic and naturally absorbent; and has greater wet strength than dry. Most hygiene products are spun laced; but cotton also may be needle punched for wipes such as decontamination wipes, and also in its relatively unprocessed raw state for oil absorption, such as cotton boom used in the recent Gulf of Mexico oil spill cleanup efforts.
Polylactic acid was first made in 1932 by Carothers, who developed a process involving the direct condensation polymerisation of lactic acid in solvents under high vacuum. He abandoned the polymer as too low in melting point for fibres and textiles and went on to develop nylon. More recently PLA was developed as an alternative binder for cellulosic nonwovens because of its easy hydrolytic degradability compared with polyvinyl acetate or ethylene-acrylic acid copolymers. Spunlaid and meltblown nonwovens based on PLA were researched at the University of Tennessee Knoxville in 1993 . Kanebo (Japan) introduced Lactron® (poly L-Lactide) fibre and spun-laid. In order to improve the biodegradability and reduce the costs of the nonwovens, blends with rayon were also developed.
Polylactide (PLA) biopolymers offer a renewable and biodegradable or recyclable alternative to petrochemical-based fibres. Applications include spunlaced wipes and hygiene products, in which PLA may be blended with cotton or viscose; agricultural textiles that may be tilled under at the end of a growing season; needlepunched carpet and automotive products; spunbond filtration and geotextile products as well as teabags and other such products; and meltblown filtration products.
PLA also has inherent flammability characteristics, Green noted. It is difficult to start burning and generates little smoke, he said; and its self-extinguish time is significantly shorter than polyester or cotton. It also is inherently ultraviolet-transparent, moisture-wicking and hypoallergenic; and has low odor retention. These properties can be further improved using topical treatments or additives.
Bicomponent fibres also may be used in nonwoven applications. fibreVisions’ sister company ES fibreVisions manufactures bicomponent fibres for hygiene, cosmetics, filtration, medical, industrial and agricultural applications. These might be biodegradable, or have a PP or polyester core and a PP or polyethylene sheath; or they may be based on specialised polymers. They often are used in low-level blends to bind other fibres. Processes include thermal bond, carded through air, airlaid, wetlaid, carded needlepunch and carded spunlace. Teabags and wipes are two wetlaid applications using short cut fibres. Airlaid nonwovens using bicomponent fibres are used primarily for baby wet wipes, industrial oil absorbent pads and feminine hygiene product components. Basic principles of PLA fibre production: PLA fibres typically are made using lactic acid as the starting material for polymer manufacture. The lactic acid comes from fermenting various sources of natural sugars. These sugars can come from annually renewable agricultural crops such as corn or sugar beets.
PLA fibre characteristics and uses: The fundamental polymer chemistry of PLA allows control of certain fibre properties and makes the fibre suitable for a wide variety of technical textile fibre applications, especially apparel and performance apparel applications such as:
oLow moisture absorption and high wicking, offering benefits for sports and performance apparel and products oLow flammability and smoke generation oHigh resistance to ultra violet (UV) light, a benefit for performance apparel as well as outdoor furniture and furnishings applications oA low index of refraction, which provides excellent color characteristics oLower specific gravity, making PLA lighter in weight than other fibres oIn addition to coming from an annually renewable resource base PLA fibres are readily melt-spun, offering manufacturing advantages that result in greater consumer choice
As a melt-spinnable fibre with a vegetable source, PLA has many of the advantages of both synthetic and natural fibres. Perhaps most distinctive among these, though, is the fact that, like natural fibres, its raw material is both renewable and non-polluting. This eliminates the often-underestimated problems associated with using a finite supply of oil as a raw material. Beyond having a renewable raw material, though, PLA is also compostable. After hydrolysis at 98 per cent humidity and 60°C or higher, PLA is readily consumed by microbes and its component atoms are converted for possible re-use in growing more corn, beets, rice, or etc. for future conversion to PLA. Thus PLA is less environmentally costly than polymers that are recyclable, because there is a limit to the number of recycling iterations that can occur before the material loses its usefulness.
PLA is even less environmentally costly than other biodegradable thermoplastics, since the entire mass of PLA can eventually be re-converted into new PLA, whereas many other biodegradable thermoplastics incorporate at least some material derived from fossil fuels. This ability of PLA to be completely recycled at the atomic level and by natural processes is summed up in the term sustainability. PLA is not a perfectly sustainable polymer, since some energy must be irretrievably used in its polymerisation and in converting the polymer into fibres and fabrics. But it offers superior sustainability and lower environmental impact than any other non-cellulosic synthetic fibre, and possibly even superior to some natural fibres.
PolyLactic acid (PLA) fibres are used to achieve the following properties:
- improved wicking
- odor control
- reduced shrinkage
- tear resistance
- UV stability
- flexural strength
- increased bulk
- porosity control
- thermal bonding
PLA is the first melt-processable synthetic fibre produced from annually renewable resources, combines ecological advantages with excellent performance in textiles. PLA successfully bridges the gap between synthetic and natural fibres and finds a wide range of uses, from medical and pharmaceutical applications to environmentally benign film and fibres for packaging, houseware, and clothing. Ease of melt processing, unique property spectrum, renewable source origin, and ease of composting and recycling at the end of its useful life has led to PLA fibres finding growing interest and acceptance over a range of commercial textile sectors.
Fiberweb (France) disclosed nonwoven webs and laminates made of 100 per cent PLA in 1997 and introduced a range of melt-blown and spunlaid PLA fabrics under the Deposa™ brandname. The polymer was developed by Neste Oy. Galactic Laboratories (Belgium) provided an excellent overview of polylactic acid polymers, concluding that 390,000 tonnes of the polymer would be produced. Their process involves extracting sugars (mainly dextrose, but also glucose and saccharose) from cornstarch, sugar beet or wheat starch and then fermenting it to lactic acid. Refined sugars are preferred to the cheaper molasses or whey because purification after fermentation is more expensive. The lactic acid is converted into the dimer or lactide which is purified and polymerised (ring opening method) to polylactic acid without the need for solvents. The family of polymers arises in part from the stereochemistry of lactic acid and its dimer. As fermented, lactic acid is 99.5 per cent L-isomer and 0.5 per cent D-isomer.
On the information currently available, PLA looks like an excellent fibre with the right technical credentials to replace polypropylene in nonwovens. As noted by Carothers, the melting point still appears too low for it to challenge the supremacy of aromatic polyester in mainstream textiles.
Biodegradable thermoplastic fibres made from PLA have the potential to bring the production and marketing of biodegradable disposables one step nearer reality. Fibres of this sort appear spinnable on conventional melt spinning equipment into coverstocks that will work in conventional disposable diaper manufacturing plants. The ability to vary the properties of the PLA by careful selection of the blend of isomers and the polymerisation route appears to make it possible to vary the fibre properties from amorphous to crystalline thereby creating a range of melting points, biodegradation rates, fibre strengths, and even bicomponency.
Clearly the fibres can be used in a wide variety of applications and it will be interesting to see how the producers prioritise these applications. When sums of the order of $300m are spent on a polymer at the start of it’s “learning curve” the economic pressure to develop the higher value applications first is enormous. In the case of PLA however the melting points appear to be similar to polypropylene rather than polyester, and its ability to replace polyester in conventional textiles could be similarly restricted.
In nonwovens, compared with the cellulosics, it has the key advantages of simple conversion into fibre and spunlaid nonwovens coupled with the resilience and bulk necessary for good surface dryness in coverstock.
Cotton, hemp and other natural fibres
Natural fibres have come a long way; during the last few years, these fibres have established a positive and highly regarded name for themselves in numerous nonwovens end-use markets because of their reputation for being soft, durable, breathable and coming from renewable resources. These days, traditional natural fibres, including cotton, hemp, flax and jute have been seeing more demand internationally, while other fibres, such as milkweed, are starting to emerge in more developed nonwovens areas. Many manufacturers predict that the use of these fibres will grow as consumers become more aware of their advantages. In the meantime, manufacturers and university researchers are working on new innovations for all natural fibres. Cotton is the most used fibre due to its popularity in apparel and other fabrics. Jute, kenaf and flax come next, with the rest of the fibres having only a small share.
The costs of these fibres vary and cotton is the most expensive of this group of fibres. Although cotton is the most attractive fibre for many applications, cost is the factor that has limited its growth. Cotton is recognised as a durable, breathable and soft fibre. Perhaps no one recognises the benefits of cotton as well as Cotton Cotton’s current global share of the nonwovens market is about 8 per cent. In the major consumer markets of North America, Western Europe and Japan, growth of cotton usage in nonwovens is projected to be 3–6 per cent per year for the next few years. Although cotton in its pure, as-supplied form is widely used and accepted, cotton can also have special properties applied to it, thereby paving a path for new uses and markets. One of these properties relates to bleaching. Barnhardt Manufacturing Company, Charlotte, produces bleached cotton fibres for carded web products, chemically bonded fabrics, and spunlaced and needled fabrics, with approximately 95 per cent of the company’s bleached fibres targeting nonwovens, due to increasing interest in bleached fibres among nonwoven manufacturers.
Cotton, when bleached, is also more aesthetically pleasing to consumers who appreciate the snow-white quality of bleached cotton, and when a natural fibre such as cotton is dyed, the colours tend to be softer and pastel, unlike synthetic fibres that produce much shinier and usually glare-like effects. Cotton fibres give nonwoven fabrics unique characteristics that manufactured fibres cannot duplicate easily. Synthetic fibres are currently being used more in nonwoven fabrics than cotton because of misconceptions regarding cotton’s processability. With improved bleaching techniques and the development of new finish applications, cotton can be processed at speeds comparable to those used with synthetics while providing the superior attributes of cotton to the nonwoven. Most consumer data suggests that consumers prefer cotton fibres. Additional advantages of cotton and other natural fibres include superior wet strength as well as a quick-dry surface, notably in wipes. Bleached cotton fibres have high levels of absorbency and are soft to the touch, breathable and biodegradable.
One fast-growing area, especially throughout Europe and Japan, is spunlaced cotton used for cosmetic wipes and other disposable products; these trends are likely to spread to other markets as well. Consumer demand for cotton is well documented, but because nonwovens are not required to list fibre content in products, consumers often do not know what they are purchasing. There is definitely an opportunity to increase market share by adding cotton as the fibre content, since consumers prefer to purchase cotton-containing products. Although cotton, with all its attributes, can tend to dominate the natural fibres market, hemp, jute, flax and milkweed are some other examples of fibres that are used not only in nonwovens, but are also growing in popularity in many other applications. As companies become more familiar with the benefits and uses of these fibres, new innovations will be developed in the future. Hemp fibres are not as well known as cotton, but they certainly have proven themselves for Hempline in Delaware, Canada. Hempline is a large supplier of hemp fibre to the nonwovens industry, primarily supplying hemp as a reinforcing fibre for substrates.
With 50 per cent of the company’s sales conducted in the nonwovens industry, Hempline is noticing a rapid increase in demand for its products, especially its reinforcement fibres. Aside from its high strength, hemp has been recognised for its elasticity, ease of processing and recyclability. However, there are a few setbacks, the main one being consumers’ unfamiliarity with hemp fibre. Applications of nonwovens in technical textiles Key advantages of using it are its high strength and low cost, and there are many markets still awaiting the use of this fibre as it slowly makes its way into becoming another option for manufacturers.
In addition hemp fibre’s staple length and strength can be modified according to the needs of the consumer. Although the market is price-conscious, using better quality of natural fibres results in a lower reject percentage, reduces downtime on equipment, minimises loss of fibre during processing and, overall, makes better economic sense. Another natural fibre increasing its role in the nonwovens industry is milkweed. Milkweed floss is a silky white seed with a resilient hollow tube that looks like a straw. It is similar to high quality down and is a hydrophobic, cellulose fibre with a high chemical resistance and the ability to be readily dyed.
Some properties milkweed floss can provide nonwovens include super absorbency, softening, hydrophobicity, paper-strength, bulking, self-bonding and tactile change. Milkweed floss fibre from advanced agricultural production has the ability to compete in nonwoven applications, especially in filtration, absorbent products and thermal and sound insulation products. Natural Fibres has introduced a 75 per cent recycled cotton and 25 per cent milkweed fibre mattress pad through its subsidiary, Ogallala Comfort Company, Ogallala, US.12 Although technology is available to use many of the natural fibres in nonwovens, the industry will have to wait for a number of things to happen, including a better economic climate, which may change people’s willingness to pay for improvements.
As the industry is growing internationally, it may force manufacturers and consumers alike to keep up with the competition.
Cotton and flax-based nonwovens
New nonwoven products containing cotton and lyocell, low-temperature thermalbondable bicomponent polyester/polypropylene Bico 256 binder fibre, or cotton comber noils were developed using needle punching and hydroentangling by the cooperative efforts of SRRC, UT, Fleissner and JD Hollingsworth. These low cost hydroentangling developments were for the end use of cotton bedsheet and bleached/grey cotton bed sheets. Blends produced quality products, which cotton alone could not, and the blending improved the processability and uniformity of the webs.
With the recent installment of 1 m wide needle punch and hydroentanglement pilot plant lines, scientists at the SRRC-USDA are embarking on new initiatives to study the cotton’s sustainability features in the context of nonwoven applications. Research on cotton-based nonwovens has been carried out at the University of Tennessee since 1987 by applying different kinds of binder fibres through carding and thermal calendering processes. Cellulose acetate (CA) fibre was first applied successfully as the binder fibre since it is thermoplastic, hydrophilic and biodegradable. Eastar Bio® GP copolyester unicomponent and bicomponent (Eastar/PP) fibres were further selected as the binder fibres in recent studies. Five different kinds of fibre were used for the study: cotton fibre as the base fibre, and four types of binder fibre, ordinary cellulose acetate (OCA), plasticised cellulose acetate (PCA), Eastar Bio® copolyester unicomponent (Eastar), and Eastar Bio® copolyester bicomponent (Eastar/PP) fibres. The chemical name of Eastar Bio® copolyester is poly(tetramethylene adipate-co-terephthalate) (PTAT). The cotton fibre used in this research as the carrier fibre was supplied by Cotton Incorporated, Cary, NC, US. The scoured and bleached commodity cotton fibre had a moisture content of 5.2 per cent, a micronaire value of 5.4 and an upper-half-mean fibre length of 24.4 mm.
The bicomponent Eastar/PP has a sheath core structure with Eastar as the sheath and PP as the core. The nonwoven fabrics in this research were produced by first carding the cotton and the binder fibre and then thermally bonding the carded webs.
Rajanna L Gotipamul and SG Kulkarni are from the DKTE
Society’s Textile Engineering Institute, Rajwada, Ichalkaranji-416115, Kolhapur, Maharashtra
Pranshil Gourkar is from Global Nonwovens
THIS IS THE PART 1 OF A 2 PART ARTICLE ON BIO-DEGRADABLE NONWOVENS. THE CONCLUDING PART WILL BE PUBLISHED IN THE APRIL ISSUE.