Imagine the Future of Viscose Technology 2002

 

Two hundred and twenty delegates attended this tri-annual meeting arranged by Lenzing Technik, the plant and process engineering division of the fiber company. Most of their customers, i.e. the world's viscose makers, were in attendance as were the main suppliers of pulp, additives and finishes. Perhaps surprisingly, there were no users of viscose fibers to be seen.

Keynote Speech

Prof. Wilhelm Albrecht aired the now familiar theme: Unlike oil, cellulose is a basic substance of life which will still be around at the end of this century. The viscose process is the most versatile way of turning cellulose into fiber, but further progress is needed to reduce its environmental impact and increase the efficiency of the derivatisation step. To this end he called for:
• More work on activating the cellulose to improve its reactivity. Electron beam treatment had been shown to be effective, but the mechanism of the effect remained to be understood.
• The development of much faster spinning processes.
• Further moves towards an emission free, closed-box process.
• The development of “just-in time” delivery of spun-dyed viscose (days rather than weeks between order and delivery)
• The development of spun-bonded viscose processes to compete with the spunbonded synthetics in nonwovens.
• Further development of fiber reinforced plastics.
• The development of cellulose-synthetic composite fibers.

Trends in Asia Viscose Markets

Craig Barker, President Director of PT South Pacific Viscose identified regional agreements such as NAFTA and the Caribbean Basin Initiative as outweighing the World Trade Organisation where tariffs were concerned.
• Mexico now supplied the US with twice as much textile as China , up from half the Chinese level in 1994. China was now in third place. Canada exported more textiles to the USA than China since 1999.
• The EU is similarly shifting textile imports away from Asia to Eastern Europe and North African countries.
• Asian producers can no longer assume that their cost advantages guarantee success in exporting to the West.
• Textile production capacity is moving rapidly to countries with even lower labour costs and to countries with grants encouraging industrialisation.
• Asian producers must now look to their domestic markets for growth, and must upgrade their spinning and weaving if they are to compete.

With regard to Indonesian viscose, three modern plants supply high quality fibers to support downstream textile production, most of which has been exported in the form of higher value spun yarn or fabric. 90% of output goes into apparel related markets. Asked about nonwovens, Mr Barker said that a regional nonwoven industry was lacking and that the standard of living needed to rise before this market would be of significance to the Indonesian viscose producers. “You need a kitchen before you need a kitchen wipe”.

Viscose Production In China

Yuan Zhiguang, Divisional Chief of the China Chemical Fibers Association said that in 2001 China made 450,000 tonnes of viscose staple in factories which were 84% state owned, and 126,000 tonnes of filament in factories which were 97% state owned. Imports of viscose staple were 49,000 tonnes in 2001, down from 187,000 tonnes in 1998. By 2005 it targets a staple fiber capacity of 570,000 tonnes and expects to produce 505,000 tonnes. In 2000, the industry imported 176,000 tonnes of cotton pulp to make viscose, but in 2001 the figure had fallen to 88,700 with imported woodpulp making up the difference. One of the key environmental problems of the Chinese viscose industry was identified as the effluent from their cotton bleaching/pulping operations. Another, giving economic problems as well, was the abundance of small (<15,000 tpy) plants. They now plan to build two new viscose plants.

Viscose Production In Japan

Mr Hirata of Daiwabo Rayon reviewed the viscose business in Japan . Only two producers remain, Daiwabo with ~30,000 tpy capacity and Omikenshi with ~20,000 tpy. ~10,000 tonnes were imported in 2001, the vast majority from Indonesia in the form of spun yarn.

Daiwabo's strategy is to try to survive as a viscose producer until the effects of oil-shortages begin to affect the synthetics. To do this they will:
• focus on special high quality products
• seek ways to reduce pulp costs (fast growing hybrid species)
• rationalise production – Lenzing's compact SXS system (see later) mentioned as becoming more necessary.

With regard to markets, nonwoven use of rayon in Japan moved ahead of textile uses in 2000, and reached 24,000 tonnes in 2001 compared with ~20,000 tonnes for all other uses. 80% of the nonwoven rayon is in hydroentangled products, mainly wet-wipes. Prices to nonwoven customers were now higher than to yarn spinners, but the quality demands were higher also. Daiwabo expects to develop new fiber types to allow new higher value nonwovens. Needless to say further growth in this sector is expected.

N.B. one of the graphs presented referred to “normal rayon staple”- ~43,000 tpy as well as “total rayon staple” ~65,000 tpy. This implies there is an additional 22,000 tonnes/year of special rayon staple, not included in the above statistics. This is most likely the polynosic rayon from Toyobo (Tufcel®) and Fujibo, both of which shut down in autumn 2001

A low-cost lyocell substitute?

Mr Xu Bin of China's Dandong Chemical Fiber Plant covered their acquisition of the Toyobo Tufcel® polynosic technology and equipment, and how, with the help of Lenzing Technik they planned to produce 15,000 tons/year of polynosic staple. The approach appears to be to replace the old spinning machines with the Toyobo Tufcel® spinning machines, buy in some new filters, shredders, blenders and wash machinery, and be in a position to produce a lyocell-like fiber with much lower capital costs.

Asked through an interpreter if this meant the Chinese lyocell strategy was less likely to go through as previously thought, no clear answer was given. Being told (by Prof Albrecht) that the polynosic process was much more polluting than lyocell, Mr Xu was unconcerned. The main motivation of the approach was economic.

Spun-Laid Viscose Nonwovens

Osamura Kida of Futamura Chemical Industries ( Japan ) gave a rare public presentation of the spun-laid viscose nonwoven process they use to make TCF fabrics. They spin the “thermoplastic” hydroxymethyl cellulose xanthate fibers from a polynosic viscose – the etherification resulting from adding the “necessary chemical” to the spin bath. The fibers are stretched, cut and fed to a wet-lay machine. The sheet is then thermally bonded, bulked and regenerated back to cellulose prior to washing drying and wind-up. One slide (no prints of the slides were available) showed a fiber section with a thick HMCX outer layer concentric on the usual CX core, this being distorted in stretching on a drum to pull the core to one side. This asymmetry was said to give the high crimp in the bulking stage. End uses in medical (gauze replacement), hygienic (wet-wipes), cosmetic (make up removers) and industrial markets (filters) were quoted. A comparison of a 40 gsm airlaid viscose (unspecified bonding method) with 40gsm TCF showed the spun-laid version had triple the dry strength and quintuple the wet strength in both directions.

Trilobal Viscose from Lenzing

Josef Schmitbauer of Lenzing R&D ( Austria ) pointed out that the normally used measures of absorbency for cellulosic fibers do not correlate with the absorbency of tampons. Lenzing therefore recently introduced what they called the novel methods of making tampon-shaped compressed plugs and testing them on a Syngina to optimise fiber properties. Their work showed that a trilobal viscose performed best, and further work optimised the shape into something looking remarkably like Acordis' Galaxy.

Two interesting observations were made along the way:
• When designing the spinnerets, Lenzing's computer modelling found that it was best to have one of the limbs of each hole aligned along a radius to get more consistent acid distribution.
• Syngina absorbency correlated with pulp type: the expensive pre-hydrolysed kraft pulp made from hardwood by an elemental chlorine free process being best (18.8 and 19.8 g/plug), and that made from hardwood by an elemental chlorine-free sulphite process being worst (18.2g/plug).

Comparisons of a 3dtex Viscostar® trilobal fiber by Lenzing with their 2.8 dtex viscose showed a Syngina benefit of 17%, rather less than expected on the basis of Acordis work.

New wet-opener system

Breaking up the highly cohesive wet fiber bed after washing and mangling in order to lay an even bed in the dryer has long been one of the problem areas of viscose staple manufacture. If the opening is too vigorous, the fragile wet fibers are broken and/or entangled. Hans Weber of Lenzing Technik described their solution: a gentle full-width wet-opener roll, fed with 10,000 m 3 /hr of air at 160 0 C. On a 50 tpd production line (in the USA ) this reduces the moisture content by 20% making the fibers stronger and significantly more easy to open. It also improves the evenness of dryer bed formation and increases the drying capacity of the production line. It also eliminates the wet-hopper and spiked lattice dryer feeders which have been a significant source of contamination since they were first thought of.

Therapeutic fiber

Liu Zhong, VP of the Yibin Grace Group (Chinese viscose filament producer – 24,000 tpy) described a new silkier viscose yarn, essentially an alloy fiber made by mixing “pod-protein” into viscose. Pod-protein contains 18 amino acids (MWt 10,000 to 200,000) and can be dissolved in dilute alkali to give a stable dope which blends easily with viscose. When spun in the usual way, the proteinaceous component migrates to the skin region giving a bicomponent fiber where the protein is efficiently hydrogen bonded to the cellulose. An analysis showed a total of 12.8% of the amino-acids in the finished fiber, and the claims made for it in skin contact were:
• Promotes cell metabolism due to serine, threonine and leucine.
• Heals wounds faster.
• Prevents skin ageing.
• Protects the skin from the adverse effects of sunlight (alanine content).
• Prevents skin diseases “e.g. skin tickle”
• Therapeutic effect on scapulohumeral periarthritis, rheumatoid arthritis, and gastropathy.
• Keeps dry skin moist.

However, while having tensiles between silk and viscose, its properties are destroyed quickly by bleaching and slowly by sunlight. It was impossible to elucidate the nature of the pods during the Q&A, but in private conversation they were said to be the pupa or cocoons of the silkworm which had been sorted to eliminate the “dead and rotten pods”.

Viscose Casings

Dr Heinrich Henze of Casetech GmbH (a division of Bayer) presented the history of casings, or, as he quipped, tubular viscose fibers with diameters of between one and ten inches. The one-inch diameter casings had been developed in the ‘40's to form hot dogs and were stripped off before they were packed.

The larger sizes were mainly for salamis, and these were typically fiber reinforced, being produced by coating and regenerating viscose on either side of a wet-laid nonwoven as it was formed into a tube. Nowadays, barrier coats were added as well, either inside or outside the tube.

Western markets for casings are declining, but South American and Asian markets are growing. Different attitudes to meat-eating and BSE are behind the trends. Plastic casings are gaining share, but these are hard to remove, impermeable to smoke and moisture and fail to give the traditional appearance needed for the high quality market. Viscose-based hot-dog casings still account for over 50% of the total market.

Asked about the lyocell casings project undertaken by his competitor (Viskase) he commented that the resulting tubes were good, but that the project failed for NMMO-recovery reasons.

Cationic Cellulose

Alexander Brandner of Cellcat ( Austria ) described their cationic cellulose fibrids made by injecting cationinc polymers into viscose prior to mixing with sulphuric acid in a disc refiner. The resulting fibrous precipitate is collected and washed on a band-filter and sold as a moist off-white crumb for use in papermaking where it improves runnability and retains additives such as OBA's in the sheet. Savings of up to 50% more OBA than achievable with polyamines were claimed. Cationic charges of up to 2000 micro-equivalents/gm and Schopper-Riegler values of up to 90 0 were achievable.

Carboxymethyl Cellulose Markets

Dieter Lehner of Mare Austria GmbH provided an overview of the global market for carboxymethyl cellulose. Of the 300,000 tonnes used in 2000:
• Europe used 37%, North America 31%, Asia 26% and Latin America 3%
• The food industry used 22% as a thickener, stabiliser, moisture content regulator, suspending agent (prevents crystals in ice-cream), and fat-content substitute.
• The oil industry used 20% to control the properties of water-based drilling mud.
• The pharmaceutical/personal care industry used 12% as a thickener, foam stabiliser and binder.
• The paper industry used 12% as a binder and as a formation and surface improver.
• Detergents used 6% to improve washing power, to protect fiber from acids and to stop dirt sedimentation. It is also used in detergent tablets as a disintegrant.
• Textiles used 6% mainly in sizing synthetic yarns.
• The remaining 24% was split between wallpaper adhesives, water-based paint thickeners, ceramics, and ore floatation.

CMC will lose some of the food market to natural thickeners like guar-gum, pectins, and alginates, and to some synthetic thickeners. On the other hand its use will grow to replace fat in low-fat foods, in new applications in the pharmaceutical and personal care sectors, in papermaking as more recycling occurs, and in increased oil-exploration. Overall 2-3% annual growth is forecast. Asked about CMC's use in alloys with viscose, Mr Lehner admitted to a project with Lenzing where cross-linkers were being used to improve its retention in spinning and washing.

Dynamic Surface Tension

Anders Cassel of Akzo Nobel ( Singapore ) described their work comparing Dynamic Surface Tension (maximum bubble pressure method) with Equilibrium Surface Tension (De Nouy method) of viscose spin-baths containing their additives. Beyond “the DST of the spinbath is related to the concentration and type of surfactant added”, hard conclusions were in short supply, but their additives were said to look even better by the new technique. Perhaps most interesting was the fact that a viscose modifier (Berol Visco 32/315) was a good DST reducer, leading to speculation that it assists more rapid dispersion of gas bubbles from the viscose in spinning, and thereby contributes to the modifier effect.

The DST equipment (a Sita t60® bubble pressure tensiometer) is cheap and reliable and can be used on-line.

Sulphuric Acid from Waste Gases

Peter Björklund of Kvaerner Chemetics, Sweden described how the pulp industry now burnt sulphur containing gases and made sulphuric acid from the resulting sulphur dioxide stream. Used in the viscose process this could reduce sulphur emissions and reduce the need for new acid. According to a viscose producer present, better processes were already in use, and the maximum saving of acid would amount to about €0.05/kg fiber.

Maybe the better process was the Sulphox system covered later by Walter Kanzler of Kanzler Verfahrenstechnik . Using similar principles this process was said to be in use in several European viscose plants and had worked well for up to six years.

Both of these incinerator systems required fuel injection to burn the gases. One chemical engineer said the best approach was simply to feed the gases into the sulphur furnace of the standard Contact acid manufacturing process in use on most viscose sites.

Bacteria cleans up waste

Karel De Waal of Bioway ( Netherlands ) showed how bacteria could deal with CS 2 in waste gases. The recently developed strains were happy at zero pH and fed on gas with 150-3000ppm of CS 2 (and other unspecified nutrients) they excreted 2-3% sulphuric acid for a cost of about $1600 (sic) per tonne of CS 2 processed. The method was in use to clean up pesticide production effluent and they were now demonstrating its applicability to rayon and sponge production, hoping to reduce the costs/tonne CS 2 to about $250. The sulphuric acid is unfortunately too dilute to reuse in fiber production, so they recommend conversion to gypsum.

Wolfgang Ott of Acordis Kelheim felt that their Biohoch® reactor was the best available technology for cleaning viscose process wastewater. Since installing the first one in 1981, their COD (t/day) in effluent fell from 12 to 8, and the second unit installed in 1991 reduced it further to 2 t/day. They too add nutrients to the bacteria which were said to be unaffected by the 2 mg/l Zn in the stream.

Miscellaneous papers

• Autefa advertised their automatic baling presses
• Sniaco Engineering promoted their yarn spinning system
• Lenzing showed how easy it was to reduce steam and cooling water use in spin-bath recovery by buying their multiple effect evaporators and crystallisers.
• Enka described how they reached 500m/min spinning speed in yarn production using a machine which proved too expensive to be economic.
• Lenzing described their new video microscope linked to image analysis for quantifying particles in viscose.

Calvin Woodings

12 th June 2002