Thursday, 12 September 2002
5th International Alternative Cellulose Conference
The event was organised by the Thüringisches Institut für Textil und Kunststoff-Forschung (TITK), and the Materials of Regenerative Resources Research Association. About 100 delegates from 10 countries attended. The conference was distinctly less international than its predecessor: no Japanese and only one Chinese delegate.
Summary of Key Points
• Lenzing expect a 700,000 tonne lyocell market by 2050.
• Silyl cellulose developed by Rhodia can be melt-spun and hydrolysed back to cellulose. The technology is for sale.
• Weyerhauser's cheaper Kraft pulp is being evaluated by Tencel for use in nonwovens
• Stockhausen has developed a lyocell/SAP alloy fibre with apparently excellent properties and economics.
• SAP-filled cellulose beads (3mm) could be an interesting for new absorbent products.
• Zimmer is promoting lyocell alginate alloys in textiles for skin-care and “wellness”, wound-care and heavy metal absorbtion.
• TITK has spun alloys of lyocell with numerous starches, PVOH, casein, polyacrylic acid, gelatine, CMC's and chitosan.
• TITK is now installing a melt-blown/spunbond pilot line (not Reifenhauser) but would not comment on its possible use with lyocell dopes.
Lenzing Lyocell Update(G)
Dr Harms of Lenzing said the recently announced 20,000 tonne expansion of lyocell production would take their capacity to 40,000 tonnes. Was this sensible when Acordis still has at least that amount of unused capacity? Yes, because Lenzing's strategic market analysis showed a strong demand for special fibres from 2004 onwards, and their Lyocell plant at Heiligenkreutz was already flat out. Furthermore, Lenzing could take a more consistent long-range view of lyocell potential because they were dedicated to cellulosic fibres. Their in-house pulp plant was also being expanded by 35,000 tonnes (to 210,000 tpa), and this facility gave them lower costs than other rayon producers. In particular their recovery and sale of acetic acid, furfural, xylose, magnesium lignosulphonate and caustic soda from black liquor coupled with a policy of transferring pulp to the fibre operations at cost gave them an ability to sell fibre at lower prices than others.
Dr Harms claimed they had invested €75M on lyocell, this sum being equally split between dope-making, solvent recovery and fibre production.
They were now spending €13-15 Million on R&D: a department employing 130 people currently. They had introduced three new varieties of lyocell, but these appeared to be more marketing than innovation:
• Lyocell Micro (0.9dtex fibre)
• Lyocell Tech (finished for technical textiles)
• Lyocell NW (matt fibre finished for nonwovens)
Of more significance was a proposed collaborative project to screen alternative uses for the NMMO solution where around €0.3M would be spent to identify the best area for the next €25-30M investment.
A briefly-shown slide giving market projections through to 2050 (not in the printed version) showed viscose staple declining from 2M to 1.7M tonnes, and lyocell increasing linearly from in around 70,000 tonnes in 2004 to 700,000 tonnes in 2050.
Lyocell Fibre from Kraft Pulp
Mr M Luo of Weyerhaeuser provided data on the properties of lyocell fibre made from Kraft pulp by the process he presented at the 4 th TITK conference in 2000. The presence of 12% hemicellulose in the resulting fibre:-
• Reduces strength and modulus by 10-20%
• Increases the absorbency (65 to 80% water imbibition)
• Increases dye uptake.
• Reduces strength loss in dyeing.
• Improves absorbtion of triazines (anti-fibrillation cross-linkers)
• Improves fibrillation resistance after reactive dyeing
• Increases weight loss in enzyme finishing
• Increases the diameter change on drying.
Lenzing had no interest in the pulp because they make their own lyocell pulp – and this is already cheaper than market pulps.
Melt spinning of Silyl Cellulose (G)
Dr Ties Karstens of Rhodia Acetow gave the first paper on a new process he claimed made a fibre similar in properties and cost to viscose without the environmental problems. In outline this involved:
• Reacting hexamethyl disiloxane (HMDS) with isocyanic acid to form N,O-Bis(trimethyl)carbamate (BSC)
• Reacting BSC with ammonia-preactivated cellulose to form the trimethylsilyl cellulose derivative (TMSC).
• Melt-spinning the TMSC conventionally into fibre. (250 m/min now, 1000m/min looks possible. While the obvious route to spunbonded nonwovens was not mentioned, a spunlaid web could clearly be made at this stage)
• Regenerating (desilylating) the TMSC fibre to cellulose by hydrolysis with 0.1N H 2 SO 4 , recovering 99% of the HMDS.
The TMSC can have a DP of 290-790, melts between 240 and 280, and degrades above 300 0 C. It contains 20% of silicon, all but 0,2% being removed in the regeneration process. From the micrographs shown, the desilylation step halves the fibre diameter. (giving a useful denier reduction and an easier route to microfibres?)
Asked about fibrillation and absorbency properties, Mr Karstens said they had yet to be evaluated.
Lyocell/Polyacrylate alloy fibre(G)
Stockhausen has collaborated with TITK to produce an alloy fibre by adding finely ground superabsorbent fibre to the spinning dope. The otherwise conventional polyacrylate-based superabsorbent is subjected to fluidised bed milling to get an average particle size of 5 micron with a maximum of 10. This was injected into dope on the small TITK pilot line to give fibres (4 to 10 dtex) with 5, 25, 33 and 50% superabsorbent content.
As the SAP content increased to 50%:
• Fibre tenacity fell from 42 to 10 cN/tex.
• Loop tenacity ( a measure of brittleness) fell from 10 to 4 cN/tex.
• Moisture regain at 65%RH rose from 11.5 to 22%
• Water imbibition rose from 60 to 950% in distilled water and from 60 to 410% in 0.9% NaCl.
• The fibre cross-section became crenellated (like viscose) and full of large pores (like sponge)
Clearly the superabsorbent's collapse on drying leads to cross-section changes, and leaves the air spaces for the SAP to swell into on next wetting.
Needlefelt nonwovens were made at Dilo with 0, 50% and 70% of the CLY/33%SAP fibre in blend with polypropylene. Total free saline absorbency of the webs rose from 850% to 1250% as the SAP content increased, and saline retention value rose from zero to 180%. Blood absorbency data matched the saline data.
The work will now be repeated on the large pilot line.
In response to questions Dr Waldermar Dohrn of BGB Stockhausen had no data on the levels of extract from the new fibres.
Lyocell/Alginate alloys (G)
Alceru Schwarza GmbH, now a 100% Zimmer company since TITK withdrew, has introduced Seacell®, an alloy of alginate and cellulose, as a high value commercial product from the lyocell pilot line. The new fibres are targeting skin-contact textiles which promote “wellness”, wound-care textiles and films, and fibres for heavy-metal absorbtion from effluents. Dr Zikeli dealt primarily with the latter application here.
Silver uptake from a 0.1M AgNO 3 solution is 90-100gms per kg of alginate in 10 minutes of immersion. The silver can be recovered from the fibre by washing with dilute nitric acid, and the fibre reused. Absorbtion efficiency for the second cycle was put at 80% of the first.
In a separate investigation where the silver result was 18g/kg Alg. , the fibre absorbed 118 g/kg mercury or 34g/kg lead or 21 g/kg of tin or 16 g/kg of cadmium.
While the alginate content was not revealed, the alloy was 10-15% weaker than 100% lyocell both wet and dry, and had similar extensibilities. It does fibrillate and can be refined and made into filter papers.
In response to questions, Dr Zikeli could not say whether the alginate used was high in the mannuronic or glutamic form, but did reveal that the alginate did not dissolve in the NMMO. Dissolution would in fact have been undesirable because they need to maintain its ion-exchange capability. In use, some dissolution of alginate occurs at the fibre surface.
Lyocell/Starch alloys etc (G)
Dr Meister of TITK revealed work on adding starches and other polymers to lyocell dope. While not all of the following were described, one slide provided data on the fibre properties of alloys of lyocell and:
• Polyacrylic acid
• CMC, both low and high viscosity types
• Polyvinyl pyrrolidone, and copolymers
The motivation for the work was said to be to improve the dyeability of lyocell (cationic-modified starches carry the necessary N- groups into the fibre). However the addition of 20% of starch could also lower the cost of the final fibre, and, from Mr Meisters data, increase the water retention value from 65 to 115%.
The starch-modified lyocell's were said to be stable to bleaching, but attacked more readily by enzymes. Hydrolysis removes the starch content.
Ceramic-loaded Lyocell fibres and beads (G)
Dr Vorbach of TITK described their process for spinning hollow lyocell fibres, simultaneously filling the tube with a ceramic paste to give a 50/50 ceramic/cellulose bicomponent. The fibres could then be formed into end-products prior to burning off the cellulose coat and sintering the ceramic into fibres. The ceramics could also be uniformly dispersed through solid lyocell fibres.
3mm diameter beads of cellulose could also be made on their “kugelformigen” pilot line and these too could be filled with ceramics.
Other materials said to be compatible with lyocell dope were:
• Oxides, carbides and nitrides
• Lead-zirconia-titanate-based ceramics
• Graphite and Metal powders for conductivity
The latter fibres could be used to make “smart” high performance materials, examples of which were:
• Helicopter blades and wings which changed shape on demand.
• Tennis racquet handles which damped vibration on ball-impact.
High-Loft Lenzing Lyocell (G)
Lenzing has introduced a 6 dtex, 60mm silicone treated lyocell fibre for use in quilts and pillow fillings. The very slick coarse fibre shows excellent dry-resilience while providing high levels of thermal insulation and moisture transport. With regard to the latter feature, Mr Feilmair claimed a performance better than wool or down and very much better than the cheaper polyester fillings. Surprisingly, after washing, the lyocell-filled quilts dried faster than the polyester-filled quilts.
Mr Feilmair also claimed that some customers were reporting that lyocell, even without the silicone finish, was killing micro-organisms, a favourable feature which had to be investigated in more detail.
One slide provided new soil-biodegradation data on fibres. Cotton disappeared totally in 20 weeks, and at this point viscose was 70% degraded, lyocell 20% degraded and siliconised lyocell was 30% degraded. Polyester was intact.
The siliconised lyocell fibre is apparently selling well, and several independent members of the audience who had bought products containing it spoke highly of its comfort.
One questioner working on alternatives to NMMO as a cellulose solvent suggested that the anti-microbial tendency could only be due to NMMO residues at the fibre surface – a point which Lenzing strongly denied.
The Synthesis and Properties of Aminoethyl cellulose (G)
The methods available to convert cellulose to aminoethyl cellulose were:
• Esterification with amino acids
• Etherification with amino-organohalides
• Oxidative C-C splitting and reductive amination
• S N 2 reactions of primary leaving groups (O-Tos, O-Mes)
Dr Klemm has focussed on the last method, preparing the tosylate by reacting the cellulose with p-toluene sulphonyl chloride in a DMA/LiCl, triethylamine solution. The tosylate on C6 could then be substituted with a variety of diamines. The resulting compound (DS=2.1) could be cast into transparent, elastic and exceptionally smooth film (roughness <12nm by AFM method). It bonded well to glass and was stable to oxygen. The film would immobilise enzymes for medical applications
Hiroshi Kamitakahara of the Friedrich Schiller University in Jena ( Germany ) reported the first synthesis of cellulose in 1996. He then used ring-opening polymerisation of a glucose orthopivalate derivate. This proved difficult, so here he focussed on the influence of substituent groups and ring structures on the synthesis of regioselectively functionalised cellulose derivatives. These derivatives could be converted into cellulose if required. A 3-O-benzyl group was shown to be indispensable to obtaining polymers with high stereoselectivity. D.P's of 20 to 70 were mentioned.
Structure in blown and cast lyocell films
Yaopeng Zhang of Dong Hua University has cast lyocell dope onto a nonwoven prior to coagulation, and has also produced tubular films using a conventional blown-film technique. In this paper he compared their structures. Unsurprisingly, the cellulose film cast onto the nonwoven, being unoriented, had little structure, while the drawn blown film showed more orientation in the MD than TD. Undrawn blown film has more TD orientation than MD.
Dr Sacchina of St. Petersburg State University ( Russia ) reported that a cellulose solvent comprising two-thirds NMMO monohydrate and one third dimethyl sulphoxide could dissolve cellulose with a lower risk of exothermic reactions occurring to give a better solution than NMMO alone. Other co-solvents studied were formamide, dimethyl formamide and dimethyl acetamide.
Sensitive NMMO analytical method (G)
Mr A Kolbe of TITK has developed a liquid chromatography/mass spectrometry method for detecting NMMO which is 10,000 times more sensitive than the current HPLC/UV method. To create the ions needed for the mass spectrometry, electrospray ionisation has proved better than atomospheric pressure chemical ionisation because it has less tendency to break up the NMMO molecule.
The method, said to be accurate to +/- 3% can detect down to 0.01 mg/kg of NMMO or 0.03 mg/kg morpholine on fibres. (2gm fibre extracted with 250ml water, 25 microlitres of this being used in the HPLC/MS)
Structure of Carbamate-route Fibres (G)
Dr Fink of the Frauenhofer Institute compared the structure of carbamate, viscose and lyocell fibres. The best carbamate fibres had similar crystalline and amorphous orientation factors to recent lyocell fibre, where early lyocell had been much more oriented. However despite their similar orientation factors, the carbamate route gave about a quarter of the wet-strength of lyocell.
In response to questions, the carbamate cellulose fibre had 0.1% of residual nitrogen and was available in 5kg batches from the Institute. Dr Fink said there had been a recent large scale trial in a filament viscose plant.
Structure formation in Lyocell Fibres
Dr Christian Schuster of Lenzing described work arising out of a friendship with personnel at the Institut Laue-Langevin in Grenoble . A small lyocell spinning machine had been set up to allow spinning into a deuterium oxide bath where a neutron beam from the research reactor in Grenoble could be scattered by the forming cellulosic fibres. The Atomic Institute in Vienna had provided the ultra small angle neutron scattering and detection kit, and measurements had been taken in the air-gap and at three depths in the spinbath. 0.9, 1.3 and 6 dtex fibres had been spun from one-hole and 37 hole jets. The conclusions were:
• Thinner fibres contain more (and smaller) internal structure – i.e. macro- and micro-fibrils
• Lyocell seems to fit a “structured cylinder bundle” model where macrofibrils of about 1 micron in diameter are held within a thin skin, these macrofibrils being made up of nano-sized microfibrils.
• When the fibre first fibrillates, the hairs are macrofibrils or bundles of macrofibrils.
• High primary gel-swelling equates to high levels of fibrillation in the final fibre
• Fibre structure develops on drying, but is not complete until the 5 th wetting and drying cycle is over.
Alkali Dissolution of Cellulose revisited
Prof. Henryk Struszczyk of the Institute of Chemical Fibres Lodz ( Poland ) reviewed the methods of “activating” pulp so that it would dissolve in caustic soda alone. Steam explosion as practiced by Asahi and Weyerhaeuser fell short of the requirements for fibre spinning but was usable as food additives. Ammonia pre-treatment (Carbacell®), and the enzyme biotransformation of pulp (Celsol®)were still awaiting commercial backers.
A new method of cellulose structure transformation appeared to involve an extension of the Celsol process called “AW” or aggressive water pre-treatment. However Prof. Struszczyk would not define aggressive water, confining himself to saying that the resulting solution had good filterability and could be spun to give a fibre with viscose-like properties. Cellulose concentrations of 7% had been achieved, with 8% being the next target.
Sausage Casing Update (G)
Dr K Berghof of Kalle Nalo reviewed the market for casings and progress with the NMMO blown-film casings pilot line. They were successfully coating manila hemp and lyocell wet-laid nonwoven tubes with lyocell dope containing 10% of 520DP cellulose on. The dope was cast onto the inflated nonwoven tube prior to immersion in the aqueous spinbath and washing in a three-stage countercurrent wash machine. Glycerine finish was applied to plasticise the structure.
It was all looking very practicable and successful, but when asked when they intended to replace their viscose-based casing technology, Dr Berghof said that they would only implement the lyocell technology on a larger scale when forced to by the environmental regulations.
Lace production by NMMO dissolution of ground fabrics (G)
Some lace fabrics were made by embroidering patterns using polyester yarns on a viscose ground fabric, followed by dissolution of the viscose either in alkalis or with enzymes. Dr Christoph Michels of TITK described their pilot process for dissolving these ground fabrics in NMMO and claimed this route had environmental advantages over the others because it could be run as an effluent free closed system. The lace precursor was dipped in NMMO, heated to 85-115 0 C and then taken through a multi-stage counter-current wash system to remove the solublised viscose. The liquid output of the wash machine at the fabric entry point was said to contain 12-14% cellulose and have a viscosity of 3000-30,000 Pas. The cellulose was precipitated and discarded: the NMMO concentrated and recycled.
Hydroentanglement of Lyocell (G)
Klaus Volker of Rieter-Perfojet presented data on the spunlace market and the performance of lyocell in hydroentanglement.
Spunlacing was said to account for 8% of worldwide nonwoven production or 280,000 tonnes. Of this 33% went to wipes, 20% to surgical, 16% to medical, 13% to industrial, 13% to coating bases, 4% to cosmetics and the remainder to clothing and textile applications.
In addition to the now well-established strength and stability benefits of using lyocell (double dry strength and triple wet strength c.f. viscose), Mr Volker confirmed the better clarity of aperturing and watermarking found with lyocell webs.
Benefits of Fibrillation
Calvin Woodings (consultant) described how to make a highly fibrillating version of lyocell and pointed out that it would be cheaper than the current textile versions. Furthermore the fibrillation would not be a problem in most products:
• Soft-touch textiles rely on fibrillation for the effect.
• Classic finished textiles need to be cross-linked to give them wash stability. The same cross linking could also stabilise a highly fibrillating fibre.
• No disposable products would suffer from fibrillation problems.
• Suede-like and micro-fibre wipes would be possible at normal water pressures through hydroentanglement bonding.
• High performance filters – including cigarette filter-tows - could be made at lower cost.
• The nanometer-scale microfibrils in lyocell could be liberated much more easily than at present.
Mr Woodings described highly fibrillating lyocell as the ultimate islands-in-sea bicomponent fibre, with millions of crystalline nanofibres floating in a sea of potentially-dissolvable amorphous cellulose. He suggested that current lyocell was proving to be a niche fibre, unlikely ever to reach the scales predicted by the pioneers. Perhaps the highly fibrillating form should be introduced now in an attempt to try to broaden the market.
Mr Schwippl of Rieter presented a 52 page manual on how to spin lyocell yarns on Rieter ring-spinning equipment.
Finishing Lyocell Fabrics (G)
Mr Rolf Brier of Textilechemie Dr Petry GmbH reviewed 10 years of developing finishing technology and finishes for lyocell fabrics.
Information from a TITK Tour:
A tour of the non-secret parts of TITK was provided for the author on the day after the conference. Key points were:
• Excellent small scale needlepunching facilities (50mm Dilo loom)
• Wet-lay nonwoven pilot line working mainly on natural fibres for composites.
• All the usual chemical and physical testing equipment used by fibre companies
• Evidence of shape-modified lyocell fibre work, with trilobal jets being used – but the visible fibre cross-sections were triangular at best.
• 10 dtex oval lyocell fibres from 500x50 micron rectangular jets
• 500dtex hollow lyocell fibres (dialysis tubes?)
• Lyocell fibres filled with ion-exchange resins.
• Space was being cleared in the dyeing and finishing hall for a new melt-blowing and spunbonding pilot line. This would not be Reifenhauser technology. Further information, for instance would it convert lyocell dope, was not obtainable.
Dr Bauer, the new head of TITK said that following the breakup of their collaboration with Zimmer they have completed a contract with a Chinese group to provide the know-how for the construction of a lyocell plant. They also report that Zimmer are very close to concluding a deal to supply another lyocell plant to a different Chinese group.