Sunday 31 May 2009

Lyocell Staple Fibre in Industrial Applications


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.

First thoughts

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.

Latex Bonding

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%.

Thermal Bonding

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:-
  • handle/aesthetics
  • barrier properties
  • opacity/cover
  • moisture absorbency/transport
  • tear and tensile strength
  • air permeability
  • particle capture
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.
Calvin Woodings

Friday 29 May 2009

EDANA – International Nonwovens Symposium - Stockholm 5th and 6th May 2009


The economic climate and the fact that several companies were restricting travel meant that this meeting was less well attended than in previous years.  Nevertheless EDANA reported a total of 200 delegates.

Hydroentangled Spunlaid Nonwovens

Achim Grefenstein, Director of Corporate R&D for RKW (Germany) described their experiences with the world's first spunbond system with on-line hydroentanglement.  The 2-drum HE stage with 2 injectors per drum comes before a thermal bonding calender and can be used as well as or instead of the thermal system.  When HE is used instead of thermal, a belt,  which can also use an injector, transfers the fabric over the calender.  The drums have microperforated metal sheaths rather than wire-mesh to allow greater patterning and aperturing flexibility.  The benefits of HE over thermal bonding of a PP spunlaid web were listed as follows:

Monday 11 May 2009


Paper presented at the Insight Conference 2000


The imminent large-scale production of biodegradable polyesters from corn-starch will give nature's most abundant polymer, cellulose, increasing competition in the nonwovens industry. Is a further decline in the use of cellulose in nonwovens inevitable or could interest in the new "nature-based" fibres and plastics enhance the prospects for all crop-based materials? How will the costs of the two approaches compare? Will the absorbency advantage of cellulose prevail over the thermoplasticity advantage of polylactic acid. This paper compares and contrasts the two main "natural" routes to polymers and the properties of the resulting fibres.

Introduction: The PLA Investment

The US no longer has abundant oil reserves but does have a super-abundance of agricultural resources capable, given appropriate levels of chemical (fertiliser/pesticide) input, of annual regeneration. The US currently imports 50% of its domestic petroleum consumption, yet exports 20% of its grain production. The production of ethanol from grain was an early example of an attempt to better balance this resource budget, and the current PLA project appears to be part of a similar but separate program with the objective of allowing agriculture to provide 10% of the US chemical industry building blocks by 2020 and 50% by 2050. The program, called the Plant/Crop-based Renewable Resources Vision at the US Department of Energy has had the full support and co-funding of the National Corn-Growers of America since 1997. The resulting “Renewable Resources 2020” is a broad-based coalition of agricultural, forestry, and chemical industry experts working to create plant-based replacements for fossil-fuels.
The NCGA commenced funding of PLA research in 1994 while working with Cargill to help them seek funding through US Department of Commerce grants. Cargill first joined forces with Purac Biochem BV to perfect the fermentation step and then with Dow in 1997 to build the first pilot-plant. At that stage they projected large-scale production in 2001 to give a PLA polymer at “around 50 cents/lb”. This first 140,000 tonne/year Blair PLA plant would cost $300M and consume 14 million bushels of corn per year, but to the NCGA, the market potential for PLA would be 500 million bushels per year of corn - almost as much as the current usage in ethanol production - estimated to add 25 cents per bushel to the price of corn.
The technological vision was bold and clear, and maybe as a natural consequence, the marketing vision is now broad and evolving. Early announcements said PLA would be the first renewable resource to stand alone on price and performance in applications such as fabrics for clothing, plastics for cups, food containers, packaging, and home/office furnishing such as carpets.
Cargill-Dow Polymers LLC, (the 50/50 joint venture between Cargill Inc and The Dow Chemical company formed in 1997), has, in a series of announcements this year, made it clear they believe crop-based biodegradable fibres to have a bright future in comparison with the fossil-fuelled synthetics. Blair, now due to commence production of PLA in early 2002, was chosen because of its proximity to the lowest cost source of the dextrose sugar from which the PLA is made - a large Cargill wet-milling plant - thereby allowing it to achieve the best possible supply chain costs. The earlier JV between Cargill and Purac Biochem BV brought a 34,000 tonne per year plant on stream, also at Blair in 1998, to manufacture lactic acid from dextrose. This feeds, amongst other end-uses, the 4000 tpa Dow PLA pilot plant in Savage MN.
A biodegradable polyester with the cost and easy-care properties of real polyester, yet based on renewable resources rather than oil is clearly an unmet need. It should be highly saleable in both woven and nonwoven products as well as in many types of plastic containers. While the publicly available information makes it clear that conventional polyester, polystyrene and polypropylene are major targets for this new crop-based polymer, comparisons with the old biodegradable crop-based polymer, cellulose, are largely absent. PLA fibre is said to “bridge the gap” between natural polymers and the synthetics, offering a unique combination of properties combining the best attributes of natural and synthetic fibres. It’s positioning, in a world where the synthetics continue to displace the natural polymers on cost/performance grounds, is excellent. Most people are vaguely concerned that the plastics are in some way bad for the environment, but, in the mass market at least, have not been concerned enough to pay more for less convenient natural products.

Polylactic Acid Development

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 nonwovens in 1994 claiming a capacity of 2000 tpa being expanded to 3000 tpa. It targeted agricultural applications to start with, and in 1998 was re-launched for apparel end-uses. At that time, Japanese demand for PLA fibres was said to be 500-1000 tpa. In order to improve the biodegradability and reduce the costs of the nonwovens, blends with rayon were also developed.
Fiberweb (now BBA, France) disclosed nonwoven webs and laminates made of 100% 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 by 2008 at prices around $2/kg. Their estimate of 70,000 tonnes for 2002 looks about right with the new Cargill-Dow plant due to start during that year. It remains to be seen if the price will be right also.
And this year, Cargill Dow Polymers LLC, as mentioned in the introduction plan to double their 4000 tpa capacity for the polymer EcoPLA™, now rebranded NatureWorks™ “to meet immediate market development needs". In January they also announced the construction of the Blair plant to make "a family of polymers derived entirely from annually renewable resources with the cost performance necessary to compete with traditional fibres and packaging materials"Fibre Innovation TechnologiesParkdale, Unifi, Interface, Woolmark, Unitika, Kanebo and Kuraray are mentioned as Development Allies.
Several other producers are still active. At Index 99, NKK ( Japan) showed a PLA spunbond nonwoven at 15gsm with apparently excellent formation and properties, although they later admitted that this was to demonstrate the flexibility of their spunbond machinery, and not a commercial product. Kuraray ( Japan) showed PLA fibres and provided some data on their properties and biodegradation rates. PLA polymer is made in Japan by Toyobo, Dai-Nippon Ink Chemicals, Showa PolymersShimadzu Corp and Mitsui Toatsu , the latter under the LACEA™ brandname. Unlike CDP, MT’s process polymerises the lactic acid direct from the monomer)At Anex 2000 in Osaka, Shinwa were showing a PLA version of their Haibon® spunbond: “a natural biodegradable nonwoven”. Kanebo again promoted their Lactron® fibre, but this time based on the CDP polymer.

The PLA Fibre Process

The CDP processinvolves extracting sugars (mainly dextrose, but also saccharose) from cornstarch, sugar beet or wheat starch and then fermenting it to lactic acid. 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% L-isomer and 0.5% D-isomer.
Conversion of this lactic acid to the dimer can be controlled to give three forms, the L, D, and Meso lactides.
Polymerisation of the lactide to give polymers rich in the L-form gives crystalline products, whereas those rich in the D-form (>15%) are more amorphous. The enhanced control of the stereochemistry achieved in the dimer route accounts for the superiority of the current products over those from the 1932 Carothers approach.
In block diagram form the PLA production sequence is:
Seeds, Soil, Water, Carbon dioxide, Sunlight
Biomass, ideally corn
 Harvest/Wet Mill
Acid/Enzyme Hydrolysis
Lactic Acid 
Crude Polylactic Acid Pre-polymer 
Crude Lactide monomer 
↓Fractional Distillation↓
Pure lactide monomers 
Polylactic Acids 
Modification for end-use
Granules for extrusion etc. 
Melt Spinning
“Crop-Based” Polyester Fibres
Producing the lactide with the right purity and stereochemistry to make decent fibres is not trivial. In a recent Cargill patent, the refining process, intended to be able to cope with crude lactic acid feedstock, was illustrated as follows:
Feed Crude Lactic Acid to Evaporator continuously

Remove water or solvent → discard or recycle water, solvent or by-products

Feed concentrated lactic acid to a pre-polymer reactor

Polymerize to form pre-polymer by removing water → discard or recycle water, solvent or by-products contaminated with lactic acid

Feed in catalyst→ Feed pre-polymer to lactide reactor→Remove high-boiling unreacted polymer

Remove crude lactide as vapour

Partially condense crude lactide →Remove lactide impurity as a vapour

Purify crude lactide in a distillation column →Remove lactide impurities

Remove purified lactide as high-boiling bottoms from the column

Before examining the claims for PLA fibres in comparison with other crop-based polymers, we should refresh our memories with a review of the routes to other crop-based polymers in the form of cotton and rayon fibres:
Rayon in similar block diagram form would be: 
Seeds, Soil, Water, Carbon dioxide, Sunlight
Wood Pulp 
Cellulose Solution 
Impure fibre 
Pure Wet Fibre 
Bales of Lyocell or Viscose
 Cotton in similar block diagram form would be:
Seeds, Soil, Water, Carbon dioxide, Sunlight 
Grow- months
Cotton bolls 
Raw Cotton Bales
This is clearly the simplest route to crop-based polymers for fibre end-uses. However for many of these end-uses the raw cotton has to be bleached to remove the waxy substances that prevent it from being absorbent. This is done either in fibre form for waddings and nonwovens or in fabric form for apparel:

Raw Cotton Bales/Fabrics
Impure fibre/Fabrics 
Pure Wet Fibre/Fabrics 


Bleached Cotton Bales/Fabrics

PLA Claims , and Comparisons with Cellulose

Fibres from the first mentioned EcoPLA™ polymer were said to be:
  • Reminiscent of PET or PS in some forms and of PP and PE in others.
  • Capable of giving fabrics with the feel of silk and the durability of polyester.
  • Fully biodegradable under composting conditions.
  • Convertible into nonwovens by dry- air- wet- spunmelt- laying systems.
  • Capable of giving improved resilience, moisture transport, breathability and wet strength.
  • The price was, in 1998, said to be $3-6/kg, but capable of reduction to $1.1/kg at full-scale production.
Additional claims for NatureWorks™ recently announced were:
  • Value-added natural-based fibres.
  • Bridges the gap between silk, wool, cotton and the synthetics
  • Superior handle and touch
  • "The comfort of natural fibres with the performance of synthetics"
  • Controlled degradability, enhanced wicking, low linting.
  • Excellent UV resistance and elastic recovery.
  • Reduced flammability with low smoke and heat generation
Nonwoven applications were listed: fibrefill, crop covers, geotextiles, wipes, hygiene, medical, diapers and binder fibres.

Fibre Properties

On the information currently available, PLA looks like an excellent fibre with the right technical credentials to replace polypropylene, and maybe some polyester 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. Furthermore the hydrolytic stability under conditions close to some laundering, dyeing and finishing processes is borderline. Nevertheless, PLA marketing now seems to be concentrating first on higher value textile applications, and it's biodegradability is not featuring so prominently. There are some interesting parallels with lyocell market development here, lyocell’s fibrillation initially being seen as a problem in dyeing, finishing and laundering but an advantage in nonwovens. PLA’s solubility in alkali could yet turn out to be a major selling point in applications not yet thought of.
The fact that PLA has a melting point at all is, in comparison with cellulose, a fundamentally important advantage in fibre manufacture and disposable nonwoven processes. In durable products, its resilience and abrasion resistance will be equally important. On the other hand, while PLA is more wettable than PET, it does not absorb useful amounts of water.
The recent claims to a 210 oC MPt PLA require a 50/50 melt-blend of pure D- and L- lactides which crystallize with their helical structures interlocking. This technique, first described by Dupont, has yet to be made on a commercial scale.


Unlike cellulose, PLA is largely resistant to attack by microorganisms in soil or sewage under ambient conditions. The polymer must first be hydrolysed at elevated temperatures to reduce the molecular weight before biodegradation can commence. Claims of biodegradability can therefore only be made where a composting infrastructure exists. Data from CDP shows that composting at 60 oC causes hydrolytic degradation, which over 10 days depolymerises and embrittles the polymer sufficiently for it to fragment. Complete biodegradation to CO 2 occurs over the next 30-40 days.
Cellulose fibres degrade more rapidly and also degrade under ambient conditions when buried in topsoil or in sewage processing. Cotton and rayon are similar.
CDP pledges to support the development of composting infrastructure in those countries (e.g.USA) that don’t have one. However over the last 12 months, the marketing emphasis seems to have changed in favour of durable products; the biodegradability of the fibre getting fewer mentions.


PLA burns like cellulose to yield 8400 Btu/lb energy.

Fossil Fuel Usage

The CDP-PLA process is said to use 20-40% less fossil fuel than fossil-fuel-based polymers. This appears to be less than the saving to be expected from obtaining the monomer from something other than fossil-fuel and CDP admit that the process currently uses more conversion energy than conventional polyester manufacture. In the CIRFS ecoprofiles study, polyester was estimated to use 80 MJ/kg of fossil-fuel energy per tonne of fibre compared with 54 MJ/kg for for viscose fibre. CDP recently 13 quoted 57 MJ/kg for PLA fibre and pledged to reduce this to 34 MJ/kg and then 5 MJ/kg by adopting alternative energy sources in future plants. (Of course any fibre or polymer plant could choose to switch from fossil-fuel and achieve similar reductions, at a price.)

Reduced Global warming

This is due to the corn absorbing CO2 during growth. The CO 2 is released back to the atmosphere on degradation, so over the full life-cycle, “CO 2 neutral” may be a more accurate claim. Trees do the same, and any process based on fresh biomass will show an advantage over those based on pre-historic biomass.

Land/Chemical Usage

  • PLA requires 3100 m 2 land per tonne of fibre 7. US corn production used about 260kgs of fertilizer/Ha in 1996 equivalent to 840 kgs fertilizer per tonne of PLA fibre.
  • Rayon (South African forests) requires 3000 m 2 land per tonne of fibre.
  • Rayon (European forests) requires 8000 m 2 land per tonne of fibre.
  • Cotton ( Texas) requires about 20,000 m 2 land per tonne of fibre
  • Cotton (California 17) requires 8,000 m 2 land per tonne of fibre
  • Cotton (World Average 17) requires 15,384m 2 per tonne of fibre
  • Cotton requires 700-1100 kg fertilizers/tonne fibre 16, along with herbicides, insecticides, fungicides, plant growth regulators, and harvest aid chemicals (defoliants). The land has to be of good quality, well irrigated and could be used for food.
  • Trees can be grown with no irrigation or chemical inputs on land unsuitable for food crops.

Post consumer recycling

PLA can be hydrolysed back to lactic acid and repolymerised, the economics of such a process being dependent on the price of fresh lactide. There is no equivalent economic route for cellulose, except via the atmosphere.

Other issues

CDP pledges to address other environmental issues related to the PLA process:
  • They will encourage the use of variable rate fertiliser technology to reduce farming emissions.
  • They will try to develop processes to use non-food agricultural sources of dextrose.
  • They will address the Genetically Modified corn issue. (Cotton has similar problems with GM varieties being mixed with non-GM. Some consumer organisations are concerned by the resulting inability to choose GM-free products. The trees used for rayon production have not been genetically modified.)

Pollution from manufacturing processes

In life-cycle inventory terms, a comparison of the effluents from the PLA route with those from the viscose and lyocell routes is clearly important, and is an area where PLA should show an advantage. CDP has already made the Life Cycle Inventory for the Blair plant available to customers and pledged to make it available to the public. At the time of writing it had not been received. A few general observations may however be helpful.
Wood pulping and corn processing have similar problems of separating biomass into a variety of useful materials. Corn processing appears to have a clear advantage because milder treatments can effect the necessary separations, and the majority of its constituents have economic value. Starch processing and fermentation are well-understood processes whereas wood chemistry is much more complex. Separating cellulose from lignin is difficult and today’s processes use aggressive chemicals and produce effluent that is hard to deal with. Furthermore the second most important constituent of wood, the lignin currently has little or no economic value due to the low value placed on fossil reserves.
Technology already exists to allow most of the constituents of wood to be harvested with much reduced environmental impact, and the US Department of Energy are funding several schemes. The fossil-fuel price increases needed to accelerate the development of PLA will also accelerate the investments in these new wood-processing plants.
PLA, like polyester, is likely to remain ahead of cellulose when the effluents from fibre manufacture are considered. While lyocell is a great improvement on viscose, it has to be regenerated in water and will always need washing and drying.

Economic Factors

The production of dextrose and lactic acid from biomass is well established and already a major industry. Lactic acid for polyester manufacture has to compete with the other uses of dextrose, such as sweeteners, and as a precursor for ethanol, citric acid and vitamin C. Similarly, the lactide route to polyester has to compete with the other established uses of lactic acid, in food additives, solvents, pharmaceuticals, emulsifiers, chelating agents, cosmetics, propylene glycol, methyl ethyl acrylate, and several fine chemicals.
Worldwide consumption of lactic acid was between 130,000 and 150,000 tonnes in 1999, about half being used in foodstuffs. Plastics, emulsifiers, pharmaceuticals and cosmetics accounted for about 10%-15% each. Food grade material, unsuitable for plastics or fibres cost about 90c/lb in the USA or 65 c/lb in Europe where Chinese material had depressed prices. The cost of the purer lactic acid needed for PLA production was estimated to be $2-3/lb. Annual lactic acid market growth was put at 15% per year.
PLA polymer currently costs around $5/kg and as mentioned earlier, is expected to fall to around $2/kg when production reaches 390,000 tonnes/year, estimated to be in 2008. If it converts to fibre with the efficiency of a regular polyester resin, the staple fibre price could be as low as $2.4/kg. At today’s prices, this would put it on a par with those other crop-based polymers, bleached cotton, viscose rayon and lyocell: i.e. about twice the price of the fossil-fuelled synthetics.
CDP has suggested $1.1-$2.2/kg for the resin from the Blair plant in 2002, although more recently has indicated $1.1/kg will only be possible when cheaper waste biomass can be processed into dextrose. This could not easily be done in the Blair location.


This is an interim report of an ongoing study and any conclusions must be provisional and rather subjective. The promised life cycle inventory on CDP’s PLA process remains to be published and may well contain information that invalidates some of the thinking here. The following observations are nevertheless offered to summarise the work so far:
  1. Pre-historic biomass, on which the 20 th century industrial economy was founded, will, in this century, lose its pre-eminent position as a source of chemical building blocks to freshly grown biomass.
  2. Three major components of fresh biomass, cellulose, lignin and carbohydrates are between them capable of providing precursors for plastics, fibres, fuels and chemicals and will do so increasingly as the price of fossil-fuel increases.
  3. Cellulose is not only the most abundant polymer in biomass. It grows as fibres e.g cotton, linen, hemp, kenaf, ramie etc., or as wood that can be converted into fibres by purification, dissolution and reprecipitation.
  4. Carbohydrates in agricultural crops can be degraded to sugars, fermented to lactic acid and repolymerised to make, amongst other things, a synthetic aliphatic polyester, eg CDP PLA. (Some plants and bacteria synthesise polyesters directly and other biomass utilisation projects are based on their optimisation and extraction).
  5. Wood processing technology currently concentrates on extracting the cellulose, and generally burns (to reduce fossil fuel usage) or rejects as effluents other potentially valuable materials.
  6. Corn processing technology already separates corn into many edible materials, some of which are converted into monomers from which polymers can be made.
  7. PLA resin and dissolving pulp are both nature-based polymers ready for use in fibre forming processes; pulp having the more direct connection with natural processes.
  8. PLA is easily and cleanly convertible into fibres using melt-spinning technology, whereas converting woodpulp to fibre is more complex, uses more energy and for the viscose route at least, produces more effluent.
  9. PLA claims environmental advantages over PET due to its reduced use of fossil reserves, it’s compostability, and its production, albeit indirectly, from an agricultural product.
  10. Cellulose has environmental advantages over PLA due to being present in nature as a fibre-forming polymer, being easily biodegradable in all processes and (in the case of rayon) using less fossil reserves, fertilisers, pesticides, and agricultural land than PLA.
  11. Cellulose in the form of cotton uses least fossil-fuel, but its low cost is due to high yields per hectare achieved by the intensive use of water, pesticides, fertilisers and defoliants.
  12. While not a current problem for US agriculture, farmland will become increasingly needed for food production.
  13. In many textile applications, polyester/cellulose blends provide an ideal combination of durability, easy care, texture and comfort. The current low-melting point aside, PLA would be equally good.
  14. In nonwoven applications, PLA being more wettable than polyester or polypropylene could make an excellent coverstock or acquisition layer fibre. Cellulose is not only wettable, but highly absorbent in comparison.
  15. PLA binders could latex-bond cellulosics: PLA fibres could thermally bond cellulosics.

And Finally…

    • The US Department of Agriculture is backing research into both corn and wood based routes to renewable energy and materials.
    • Corn and PLA are currently centre-stage thanks to the publicity surrounding the CDP Blair investment, but forestry and cellulose, despite a poor image related to past pulp and paper production methods, can also yield fibres, and chemicals -including PLA.
    • PLA has all the strength and processing advantages of a thermoplastic synthetic fibre: the higher melting point versions being technically capable of replacing polyester.
    • Polyester/cotton has been the most successful textile blend of the 20 th Century: High Melting PLA/lyocell blends could replace it with significant environmental advantages.
    • The rate of development of nonwoven products based on PLA, will, like the development of nonwovens based on lyocell, depend on the relative attractiveness of textile and nonwoven applications to the fibre producers.
Copyright: Calvin Woodings Consulting Ltd. 2000


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