TENCEL - THE KEY TO HIGH PERFORMANCE NONWOVEN PRODUCTS

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1 TENCEL - THE KEY TO HIGH PERFORMANCE NONWOVEN PRODUCTS Andy Slater Product Development Manager, Lenzing Fibers Ltd Abstract Lyocell fibres are commercially supplied by Lenzing Fibers under the trade names Tencel and Lenzing Lyocell. These constitute a family of fibre grades that are successfully used in a wide range of nonwovens products that require absorbency, purity, softness, strength and biodegradability. Perhaps best known for their use in carded and spunlaced nonwoven fabrics, additional lyocell fibre grades have been specifically developed for use in dry laid and wet laid applications where short fibre lengths, typically below 20mm, are required. This paper reviews the fibre characteristics of these short staple grades and the properties of the resulting fabrics with specific emphasis on how these fibres can be used to engineer the key fabric attributes for high performance nonwoven products. Introduction Lyocell fibres are 100% cellulosic fibres, solvent spun from purified woodpulp. The lyocell fibres commercially manufactured and supplied by Lenzing Fibres are marketed under the Brand name Tencel and incorporate the fibre grades from the established Tencel and Lenzing Lyocell product ranges. Developed in the 1980 s, these high purity, versatile and fully biodegradable fibres are manufactured using a highly eco-friendly process, designed from the outset to minimise its environmental impact. Full scale commercial manufacture of lyocell fibres commenced in 1992 with the opening of the first Tencel plant in Mobile, Alabama, USA. Although initially targeted at the fashion apparel sector, a niche business in nonwovens was developed through the late 1990 s utilising the unique attributes of lyocell. During the first five years of the 21 st Century, the growth of the nonwovens business for lyocell was targeted as a key strategic area for both the Tencel and Lenzing Lyocell product ranges. This strategy was reconfirmed during the merging of the Tencel and Lenzing businesses in 2004 and today, a significant proportion of Tencel fibre sales are into nonwovens applications. 36 Full scale commercial manufacture of lyocell fibres commenced in 1992 with the opening of the first Tencel plant in Mobile, Alabama, USA. Although initially targeted at the fashion apparel sector, a niche business in nonwovens was developed through the late 1990 s utilising the unique attributes of lyocell. During the first five years of the 21 st Century, the growth of the nonwovens business for lyocell was targeted as a key strategic area for both the Tencel and Lenzing Lyocell product ranges. This strategy was reconfirmed during the merging of the Tencel and Lenzing businesses in 2004 and today, a significant proportion of Tencel fibre sales are into nonwovens applications. Lenzing is the only commercial scale manufacturer of lyocell fibres, with production plants located in the USA, UK and Austria. Key areas of success for Tencel are in wipes, medical & hygiene and filtration applications. Within these sectors, the strong growth of the spunlaced wipes market has been well documented over recent years but the development of short staple length fibre grades (typically below 20mm) specifically tailored for airlaid and wetlaid applications has also been an important area for business growth. Fibre grades are produced for a range of converting technologies including papermaking, wetlaying

2 and airlaying as well as for use as reinforcing fibres in polymeric or inorganic matrices. % Nonwovens Total Tencel sales Figure. 1 The development of Tencel sales into nonwovens applications Tencel Fibre Production and Filament Properties The manufacture of Tencel is based upon the dissolution of purified, dissolving grade woodpulp in an amine oxide solvent (N-methylmorpholine N-oxide) to form a viscous spinning solution. The woodpulp is a renewable raw material sourced from carefully managed forests and purified under tightly controlled conditions to ensure optimum performance in the Tencel process. Once the spinning solution has been formed, it is filtered and extruded through spinnerettes into a dilute solution of the spinning solvent to form continuous filaments. The filaments are washed to remove the solvent, which is recovered, purified and concentrated for re-use in the Tencel process. For short staple Tencel production, the fibre is kept in continuous tow form throughout the washing, finishing and drying stages of the process. Only at the end of the production is the fibre cut into staple. Either reel cutting or off-line guillotine cutting is used, depending upon the cut length required. However, in some cases, the fibre is collected in tow form for special downstream processes. The clear distinction between the tow manufacture and the staple cutting processes maximises production flexibility and enables the optimisation of fibre grades to create an 37 extensive portfolio of carefully tailored products. For short staple Tencel production, the fibre iskept in continuous tow form throughout the washing, finishing and drying stages of the process. Only at the end of the production is the fibre cut into staple. Either reel cutting or off-line guillotine cutting is used, depending upon the cut length required. However, in some cases, the fibre is collected in tow form for special downstream processes. The clear distinction between the tow manufacture and the staple cutting processes maximises production flexibility and enables the optimisation of fibre grades to create an extensive portfolio of carefully tailored products. Tencel fibre is characterised by its smooth, round cross-section, excellent filament tenacity and high modulus, which are retained to a very high degree in the wet state. Water imbibition approaches that of viscose fibre and far exceeds that of polyester (PET) and polypropylene fibres. TENCEL - Production Route Purify Solvent Managed Forests Pulp Dissolve Spin Wash Dry Crimp/Cut Staple Fibre Figure. 2 - Tencel Production Process Nonwovens

Property Uniit Tencel Viscose Polyester Polypropylene Dry Tenacity (CN/tex) 30-40 20-25 40-50 25-35 Dry Extensability % 10-16 20-25 15-55 200-300 Wet Tenacity (CN/tex) 25-35 10-15 40-50 25-35 Wet

3 Property Uniit Tencel Viscose Polyester Polypropylene Dry Tenacity (CN/tex) Dry Extensability % Wet Tenacity (CN/tex) Wet Extensability % Initial Wet Modulus (CN/tex) Water Imbibition % <5 0 Cellulose DP N/A N/A Figure. 3 Filament Properties of Tencel fibre Tencel in Short Cut Fiber Applications All of the applications for short cut grades of Tencel are characterised by their requirement for fibre staple lengths below 20mm, for filaments that are easily opened and separated and that the fibre is dispersed easily in either air, aqueous or organic media. To fully optimise the fibre grades for each application, fibre variables such as cut length, fibre end cut quality, titre, finish type, finish level, lustre and crimp are tailored to match the processing and performance characteristics of the fibre to the product requirements. specifications have been developed to optimise web formation and hence maximise fabric quality and performance. Airlaying Tencel fibre grades for airlaying usually lie within the range of cut lengths from 4 to 10mm. Tencel imparts a luxurious, soft hand feel to the fabric and this may be maximised by using the fibre in layered fabric structures in the outermost layers. Compared to pulp fibres, Tencel gives a major increase in fabric thickness as well as an associated improvement in fabric absorbency. The high filament strength and long fibre length, in comparison to pulp fibres, enables fabric strength to be maximised as the proportion of Tencel is increased. The webs are consolidated and integrity is imparted by either chemical (resin) bonding, thermal bonding using meltable binder fibres, or by hydroentanglement (airlace). Studies (1) carried out in conjunction with the University of Leeds in the UK, identified how fibre variables such as cut length, finish type and fibre crimp affect filament dispersion in the air chamber. Fibre 38 Figure. 4 - Tencel Fibres in an Airlay Chamber Applications for airlaid Tencel fabrics include high performance wipes, food packaging and medical products. Wetlaying The parallel and untwisted filaments produced from the tow-based Tencel process, combined with the high wet fibre modulus, promote good dispersion of the fibres in the mixing chest of wetlay systems, even at relatively long cut lengths. Typical cut lengths for such applications range from 5 to 12mm, although dispersion is possible at up to 16mm staple length using low stock concentrations. The smooth fibre surface enables good interfibre contact in the web, thereby imparting high wet web cohesion and giving high efficiency

transfer of the web prior to bonding. During drying, the fibre s high wet stability reduces fabric shrinkage and maintains fabric evenness.

$In this instance, the smooth fibre surface and consistent refractive index promote reduced light scattering and hence maximises transmission of light through the fabric.$

4 transfer of the web prior to bonding. During drying, the fibre s high wet stability reduces fabric shrinkage and maintains fabric evenness. In use, the high fibre strength and excellent bonding efficiency of wetlaid Tencel gives fabrics with excellent low linting characteristics utilised in critical task wipers for clean room environments. In an interesting contrast to fabrics used in medical applications, in which fabric opacity and cover are required, bright luster grades of Tencel fibre have been used in wetlaid fabrics to give excellent fabric transparency, where the quality of the product held within the nonwoven is a key marketing objective. In this instance, the smooth fibre surface and consistent refractive index promote reduced light scattering and hence maximises transmission of light through the fabric. Lenzinger Berichte, 84 (2005) Ease of disposal is an increasingly important factor in the design of wetlaid, or indeed drylaid fabrics. For instance, fabric strength increases with the cut length of the Tencel fibres but if the product is required to be dispersible upon disposal into domestic plumbing and sewerage systems, then shorter fibre lengths may be favored. A number of companies have developed dispersible fabrics using short cut Tencel fibre in conjunction with water sensitive binder systems. Some of these are published in the patent literature (e.g Kimberly-Clark {USP 5,986,004} and Oji Seishi {JO }), whereas others are even more commercially sensitive. The concept of using Tencel in such structures is to give sufficient strength to allow the fabrics to be used but to make fabrics lighter weight and bulkier by reducing consolidation to allow them to fold in flushing and then break up. Once immersed in water, Tencel plasticizes and the fibre modulus decreases, potentially initiating the disentanglement process. Tencel is fully biodegradable, so when the fibre has entered the sewage or waste treatment system, it will break down into carbon dioxide and water under enzyme action. This is illustrated in the following micrographs for fibres degrading under the action of soil burial: 39 Figure. 5 - Biodegradation of Tencel Speciality Papers The unique fibrillar, crystalline structure of Tencel can be broken down through mechanical wet abrasion, for example at the beating stage of a traditional papermaking process. This wet abrasion generates submicron diameter round cross-section fibrils, which are retained within the fibre network, creating a micro-porous structure, ideal for fine filtration. In addition to controlling filtration characteristics and fabric permeability, manipulation of the fibrillation of Tencel can be used to vary fabric opacity, tensile strength and tear strength. By virtue of the nature of the papermaking process, the shortest staple lengths of Tencel are used, with cut lengths typically of 4mm or less. Applications for papers comprising Tencel include electronic component insulating papers, hot oil filtration for food contact and automotive end-uses, as well as cigarette filter papers. In all of these applications, the high purity of Tencel and the controllability and reproducibility of its fibrillation are of key importances.

5 Figure. 6 Increasing fibrillation of Tencel Composite Reinforcement Tencel fibre can be used as a reinforcement in polymeric or inorganic matrices in either short cut staple or continuous tow form. Dispersion of short cut, uncrimped fibre in polymeric matrices, such as polypropylene, gives composite properties comparable to glass reinforced materials. Relative Performance Fibre Reinforced Polypropylene Tensile Strength Tensile Modulus Bending Strength Bending Modulus HDT Glass Tencel Figure. 7 Tencel for reinforcement of polypropylene (2) In comparison to the glass-reinforced material, Tencel reinforcement imparts better acoustic and thermal insulation and offers the possibility of improved recycleability. Inorganic matrix materials such as ceramics or cements also benefit from Tencel reinforcement. Compression and bending strength are improved at addition levels as low as 1kg/m3 but the greatest benefits are obtained in improved crack resistance against failure mechanisms such as dynamic fatigue, freezethaw action and extreme heat cracking. The non-melting nature of Tencel means that it can be reliably used in autoclave cured or high exothermic cements in the production of high performance cement mouldings. Summary A plethora of exciting opportunities for product differentiation and market growth have been described where the incorporation of Tencel short cut fibre grades gives improvements in: Fabric bulk, softness and strength Filtration performance Composite toughness and strength These benefits are attained across a wide range of applications and Tencel fibre grades have been tailored to give optimal performance in papermaking, wetlaid, airlaid and composite conversion technologies. The rapid growth of Tencel in nonwovens has been built on continuing market demand for absorbent fibres in wipes. This paper has illustrated that the fibre offers much wider opportunities to develop new products for diverse applications based on a unique combination of inherent fibre properties and progressive product development. It is a story in its early stages and one that is set to continue. 40

6 Acknowledgements 1. Dr S J Russell and M Osman, Nonwovens Research Group, School of Textile Industries, University of Leeds, UK study of Tencel in an airlaid process. 2. Dr H. P. Fink, Fraunhofer Institut Angewandte Polymerforschung, Potsdam- Golm, Germany 41

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