It is 15 years since the development of applications for lyocell fibres commenced in earnest at what was then the Courtaulds Research Laboratory in Coventry, UK. Many new uses have been developed for the fibre, both by Courtaulds/Acordis and Lenzing, and several fashion apparel products have become major outlets for the new cellulosic fibre. It is however surprising that the sector that at first sight appeared to provide the best match with the properties of the new fibre, industrial textiles, remains substantially undeveloped.
For the purposes of this paper, industrial textiles are defined in the broad sense as those applications where technical performance outweighs the more aesthetic and subjective characteristics demanded by the fashion apparel sector. Nonwovens both long and short-life are thereby included in this review, which covers the early marketing approaches, the attributes of the fibre that have proved useful in industrials, and current activities in the sector.
Courtaulds’ development of the lyocell process was driven by the need to find a more environmentally acceptable way of converting woodpulp into fibres than the viscose process . While early process screening certainly looked for ways of approaching the properties of viscose fibres , the inability of almost any solvent system to provide the high extensibility of standard viscose fibres was not felt to be a serious issue compared with meeting the environmental and economic objectives. As is now well known, the dissolution of cellulose in NMMO proved the most attractive process, and it was the fibre from this route, known generically as lyocell, that went forward into application and market development.
That this route produces a high modulus fibre, in essence a polynosic rayon, was not felt to be a disadvantage. However, many rayon companies, Courtaulds included, had experience of polynosic viscose rayon production and marketing, and with the exception of the Japanese none had persevered with the approach.
A short historical digression is perhaps needed to allow some appreciation of the status of high modulus cellulosic fibres as the new lyocell fibre emerged from the laboratory into the consciousness of those who would be responsible for developing markets for it. Polynosic rayons had been developed in the 50’s and 60’s to match the wet performance of cotton, and to survive the sort of finishing treatments to which cotton fabrics could be subjected. Unlike cotton with its collapsed tube cross-section, polynosics had a smooth round shape and a freedom from chemical crimp that led to low fibre cohesion and lean yarns. They were more expensive to make, prone to fibrillation, difficult to dye and soon developed a reputation for being troublesome in both dry and wet processing. They were nevertheless good in blend with cotton and gave some of the properties of combed cotton, especially in knitted underwear.
Attempts to overcome the disadvantages of polynosics led to the development of several variations, notably “economical” versions of the fibre, but polyester was emerging as an excellent blend fibre for viscose, and polyester did not need a high modulus companion. So, higher extensibility lower modulus “modal” viscose rayons replaced the polynosics, except in Japan where the two types coexisted and even merged into newer high-strength polynosics. Courtaulds stopped producing their “Vincel 28” and cheaper “Vincel 28E” polynosics and focussed on their higher extensibility, lower modulus, fibrillation-free “Vincel 64” modal fibre in 1973-74.
Modal, being more costly to make than regular viscose, suffering some of the leanness disadvantages of the polynosics, and relatively unsupported by marketing campaigns, could easily be replaced by the cheaper, more crimped and extensible but weaker regular viscose in polyester blends. ITT Rayonier (a pulp supplier) made a bold attempt to establish a bulkier crimped modal fibre in fashion apparel by licensing it’s Prima™ process to Avtex and Saeteri, and by advertising its merits on US television (a first and last for a viscose fibre?), but to no avail. Modal fibres survive, but remain small volume compared with regular viscose. When Courtaulds stopped production of Vincel 64 in the late 70’s, the only customers who appeared to be seriously disadvantaged were those using the fibre in industrial textiles: coating bases, abrasive substrates, protective clothing and sewing threads. It is also worth adding that although no commercial sales resulted due to the high price of the polynosics, they had been successfully fibrillated in refiners to make special papers and latex bonded to make strong dry-laid nonwovens.
As the attributes of lyocell unfolded in the early 80’s it was therefore understandable that comparisons with polynosic rayons were made and concerns were expressed over its likely performance in yarn spinning, dyeing and finishing leading to apparel end-uses. In fact the first lyocell fibres to emerge into market testing (1985) were much easier to fibrillate than the current products made in the production plants, were slightly lower in extensibility and had a far from optimised crimp/finish/moisture/cohesion balance. The first and cautious strategy was therefore to develop those nonwoven and industrial textiles markets where the drawbacks of the early lyocell would be of reduced significance. As lyocell properties improved, selected apparel markets would be opened.
The rise of soft-touch
The first lyocell to be sent for evaluation in Japan was destined for evaluation in nonwovens. The Japanese trialists, who subjected the early samples of lyocell to a thorough evaluation, probably as a polynosic rayon substitute to start with, had other ideas and demonstrated that even the early lyocell had the makings of a high-value fashion fibre. Like their high-strength polynosics, lyocell was strong enough to survive the new enzyme finishing techniques which were being used to produce soft-touch fabrics with a microfibrillar surface. This technique made virtue out of what had been regarded as the fibrillation disadvantage, and opened the way to some really high returns in designer-apparel markets. The development of industrial applications for lyocell understandably became a low-key second priority activity.
Early Industrial Applications for Lyocell
The development efforts of the early 90’s nevertheless resulted in some small-scale commercial successes.
In the high performance workwear sector a joint development between Courtaulds, Albright and Wilson, and Carrington Career & Workwear led to the launch of the “Fury” protective suit for North Sea oil workers. This capitalised on lyocell’s softness and a favourable interaction between the new fibre and both the Proban® and Pyrovatex® flame-resist finishing techniques. The lyocell was blended with small amounts of polyester (or nylon to boost abrasion resistance and tear strength) and resin finished as necessary to control fibrillation.
In the ladies workwear sector, a joint development between Courtaulds and Klopman International led to a new range of garments for nurses exhibiting some of the characteristics of the Tencel® fashion fabrics while demonstrating the sort of appearance retention and durability required to maximise longevity in industrial laundering.
In sewing threads, the high strength and high-speed sewability of lyocell yarns coupled with enzyme resistance and a dye uptake comparable to the base fabrics led several producers to introduce lyocell threads to their range for use in cellulosic garments to be dyed and/or finished in garment form.
In coating bases, lyocell’s high strength and modulus linked to the ability to make smooth surfaced fabrics which bond well to the coatings led several producers to introduce lyocell fabrics to their range. 3M for example, utilised a woven 100% lyocell substrate to back their new range of abrasive cloths because it provided exceptional surface regularity.
Nonwovens and Special Papers
Lyocell was converted into a range of nonwoven products and papers exhibiting the following general benefits. (Comparisons with viscose fibre nonwovens)
Twice the dry strength.
Nearly three times the wet strength.
Higher wet-cohesion especially when fibrillated
Higher wet resilience and resistance to wet-collapse.
Stronger bonding with latexes.
Stronger thermal bonding with synthetics.
Lighter fabrics/papers possible.
Reduced shrinkage in drying/curing.
Better dimensional stability.
Higher absorbency (rate and capacity) especially when fibrillated.
Hydroentanglement (HE) Bonding
Early trialists were inclined to treat lyocell with the highest possible water pressure to try to fibrillate it. They believed one of the few ways to justify the high price was to try to generate microfibres similar to those obtainable from the more expensive sea-island bicomponents. However cellulose microfibres are more self-bonding than their synthetic counterparts and give harsher rather than softer fabrics. Furthermore the high pressures needed to fibrillate current lyocell are only effective over a narrow range of basis weights. Lightweights get bonded to the conveyor belt before a useful level of fibrillation occurs, and in heavyweights only the surface layers are affected and even then the cushioning effect of the fabric depth prevents efficient fibrillation.
More often than not softness was required, and water pressures had to be reduced below those used for viscose to get best results. A better strength/softness balance than viscose was achievable at these lower pressures. If a really silky-touch product was required, and CD extensibility was not critical, a more parallel laid web gave best results. If a silky appearance was required as well, the lustrous bright form of the fibre would give it.
Raw material cost-savings could be obtained by reducing the basis weight. It was possible to halve the basis weight c.f. viscose when seeking to make the lightest possible covering material with adequate strength. Similarly if additional latex or thermal bonding was needed to boost strength, this could be reduced or eliminated.
The strength benefits obtainable from lyocell in low pressure HE were enhanced at higher pressures up to the point where fibrillation occurs. At higher pressures still the strength plateaued and ultimately declined, while the fabric opacity and firmness increased dramatically. The silky aesthetics were lost, but the toughness of the fabrics made semi‑durable and durable end‑uses possible.
High-pressure hydroentanglement of lyocell fibre enabled the production of nonwovens that were stronger than the equivalent weight of woven cotton in pilot trials but on production machines some losses of fibrils had deleterious effects on the water filters.
In aperturing processes, lyocell gives very precise patterning and a more textile like appearance than other fibres.
In needlefelt technology lyocell fibre strength could be efficiently translated into fabric properties with a threefold increase in wet strength c.f. viscose. Lower basis weights were possible if required. Lyocell formed more open and bulkier needled structures than viscose and this coupled with the higher wet-resilience of lyocell gave increased absorbent capacities. 1.7dtex fibres could be needled commercially and fabrics made from them showed only half the wet collapse of 3.3 dtex rayon structures.
Here too, lyocell gave much stronger fabrics than viscose especially in the wet state. This feature could be used directly to meet tougher customer specifications, or indirectly to reduce raw material usage. (Lower fabric weights through less fibre and/or less binder.) Lyocell bonded with half the latex level needed for viscose gave improved fabric aesthetics and absorbency, allowing this venerable but still important nonwoven route to enter new territory. Lyocell also gave low‑shrink, high stability fabrics during drying/curing which made it possible for the latex bonder to increase the area productivity of his lines by 10‑15%.
Lyocell bonded better to some types of polypropylene and gave stronger thermal blends than viscose especially in the wet state. This could allow the thermal bonder to incorporate a cellulosic at higher concentrations, or to make 50/50 blends at lower basis weights.
Short Fibre Processes - Papermaking
Fibrillation of lyocell can be achieved in many ways (dyeing, finishing, suedeing, hydroentanglement, brushing, ultrasonic treatment), but it is in the papermaking processes that fibrillation can be carried out most efficiently and controllably.
The ability to fibrillate lyocell in beating, refining or hydrapulping allows the manipulation of sheet properties. For example the following can be altered dramatically by fibrillation:-
tear and tensile strength
The last two properties are particularly important in applications such as filtration.
Paper strength depends upon hydrogen bonding, which increases as more fibrillation is generated. Paper tensile strength improves in proportion, but tear strength goes through an optimum at moderate levels of fibrillation. Air resistance of the sheet goes up proportionately, but the permeability of lyocell sheets is still higher than that of equivalent woodpulp papers, due to the fine circular nature of the lyocell fibrils.
Pore size is also affected - increased fibrillation giving smaller average pores. It is therefore possible to manipulate the mean pore and distribution of pore sizes by controlling the level of fibrillation produced. Lyocell papers exhibit a similar pore size/permeability relationship to the more costly microglass fibre which is commonly used in filtration papers. Pulp sheets show lower permeability.
Short Fibre Processes – Air Laying
The low cohesion of lyocell made by the tow-washing route is an advantage in air-laying processes where easy separation of fibres is required. It’s stiffness relative to viscose allows the use of longer fibre lengths, and thereby the more cost-effective reinforcement of air-laid pulp for use in wipes and absorbent core components.
Lyocell’s Current Position in Industrial Applications
Industrial market developments to date have been made against a background of:
The runaway success (1990-96) of Tencel® branded lyocell in the fashion apparel sector resulting from the Japanese development of enzyme processing to develop ultra-soft touch “peach-skin” textures. Restricted fibre availability and high fibre prices could not be tolerated by the more cost-sensitive industrial sector.
Reducing competitive fibre prices: cotton polyester and viscose all became available at significantly lower prices than when the development started.
Courtaulds decision not to use of the Tencel® brand for industrial applications.
Progressive reductions in the fibrillation tendency of Courtaulds fibre that closed down some options in special papers and hydroentanglement.
“Focus-on-fashion” prevented development of new varieties engineered specifically for industrial applications.
Sales of industrial yarn into workwear, careerwear, sewing threads, abrasive substrates, and coating bases were nevertheless developed and continue at a low level. Not unexpectedly the more fashion-conscious career-wear sector with its more structured garments is proving more successful than the industrial workwear sector where lyocell has found it difficult to compete on cost/performance with poly-cotton.
Klopman International reports that the Alexandra nurses uniforms, at the “soft” end of the work-wear sector, continue to use lyocell-containing fabrics. Sales growth has been disappointing due to their relatively high price. Klopman nevertheless spins, weaves, dyes and finishes the fabrics without difficulty and continues to believe 50/50 poly-lyocell constructions will prove competitive with poly-cotton in career-wear. They are therefore repositioning fabrics and colour-lines to target the skirts, blazers and waistcoats worn in this sector and have already had some early successes. Bank staff, hotel receptionists, car-hire staff and retail staff now require more stylish garments which cannot easily be made from the cheaper poly-cottons, and it is here that the Tencel®-branded fibre is likely to have more success.
The ”hard” workwear sector has however proved less attractive. The flame retardant overalls for oil-workers did offer a demonstrably better balance of FR protection and handle than possible with cotton. There were however difficulties with appearance retention in laundering the darkest shades, the problems with Navy being particularly acute. The Pyrovatex® finish that provided the FR character and protection against fibrillation in laundering was insufficient to stop fibrillation damage in repeated severe laundering of navy overalls. The majority-lyocell Fury® range has now been discontinued as a stock item by Carrington Career and Workwear, but is still occasionally made to order in the less difficult colours. Summarising the development experience, Carrington comment that the Pyrovatex® lyocell/polyester fabrics were just too expensive for the level of improved performance offered, and the predicted economies from lyocell production scale-up did not materialise. The fact that one of their main potential customers switched to Nomex/Kevlar overalls while others opted for the stiffer but cheaper Proban treated 100% cotton suggests that lyocell offered a middle of the road product in a market polarised towards low price or high performance.
In Europe, the USA and to a lesser extent in the Far East, lyocell continues to be converted into excellent sewing threads for small and relatively specialised applications. It gives high strength, high-speed sewing and better enzyme resistance, but does dye darker than cotton in a competitive situation. Majority-lyocell garments processed on the garment-dye/garment-wash system have to use lyocell threads if the sewing is to be invisible. On the other hand lyocell thread is less likely to be used for the larger garment-processed cotton sector.
Price c.f. cotton prevents the fibre growing into the more mainstream sewing applications and the same appears to be true in the woven coating base sector. Excellent speciality abrasives backed with lyocell cloths continue to be produced by 3M and others, but the growth predicted 5 years ago has not materialised.
In special papers, the fibre continues to provide low pressure drop and high particle retention characteristics to a few cigarette filters, but the continuing very high price c.f. acetate tow or crepe paper still prevents its more general adoption. The even nichier but higher valueelectrical papers sector now show signs of growing faster.
Acordis currently expect most growth to come in short-life nonwovens, and in the wiping sector in particular. Despite its good performance and amazing strength and durability, the early synthetic-chamois fibrillated lyocell hydroentangled car-cleaning cloth failed to make inroads against the real thing and was withdrawn, but other wet-wipes have proved much more successful. Microwavable cleansing wipes benefit from the softness achievable with lyocell in a needled fabric, and are now a major user of the fibre in the US nursing-care sector.
The fibre’s wet strength, resilience and absorbency make it an ideal absorbent component when bulkier, more absorbent products are required. Here the key conversion technologies remain hydroentanglement and needling, but air-laid materials using lyocell are now commercial and look set for good growth.
Progress has inevitably been slow, but maybe the biggest surprise in view of the sustained high pricing is that it has not been negligible. The fibre has established itself in several profitable industrial niches and is in the process of breaking out of those niches, especially in short-life nonwovens. By and large, it has gained a reputation for good technical performance and an ability to add value - up to a point.
The high price and renewed high demand in apparel still militate against its more widespread use in industrials, but the benefit side of the cost-benefit equation has been quantified and the fibre has proved itself to be worth a premium over other cellulosics. Clearly the size of the ultimate industrial market for lyocell will depend on the size of that premium over cotton and viscose.
Acordis remains optimistic about industrials and has now set up new Technical Products teams in Europe, the USA and in Asia. It is, for the first time, using the Tencel® brand for industrial as well as fashion applications. Sales into technical applications are said to be growing strongly and now amount to about 10% of current output: significantly ahead of 1998-99 levels, and expected to show a further strong increase in the next 12 months as new projects go commercial.
Both Lenzing and Acordis have announced capacity increases, Lenzing to 20,000 tonnes/year and Acordis, already close to full capacity at Grimsby, is progressively re-opening the 43,000 tonne/year Mobile plant which was mothballed in 1999 following the fashion-apparel demand collapse in 1998. These increases are of course fuelled by the resurgence in apparel demand for lyocell, but both companies expect the industrial market to take an increasing slice of the cake in the years to come.