Lyocell fibre processing

Main chemistry in viscose (A), cupro (B) and Lyocell (C) fibre processes. 

Lenzing of Austria commenced production of their lyocell fibre in 1997. This rapid expansion led to a temporary overcapacity and no further production occurred until Lenzing expanded their capacity by 20,000 tonnes per year in 2004. Development of a continuous filament spinning process by AKZO/ Tencel continued throughout the 1990s but has not yet been commercialised because of the decline in the market for filament rayon and the high investment cost required. 

Staple fibre grades are produced to suit carded dry laid, air laid and wet laid processes. The attributes of lyocell fibre are discussed with reference to each of these conversion technologies below. 

During processing and often for the sake of processing cellulose into fibres or films, the DP is reduced considerably depending on the type of processing (see below). Typical values are in the order of 300 (Viscose) to 600 (Lyocell) for this type of material, which is called regenerated cellulose [9]. 

However, since 1998 the Lyocell process has been used in Austria and the special feature of this process is the solution of the pulp which is in an organic solvent (NMMO = N-methyl-morpholine-N-oxide), instead of CS2/NaOH, which has the effect of eliminating the odorous and noxious emission of sulphurous gases. The properties of the produets from this Lyocell process are different to the standard viscose fibre, and therefore this process should not be regarded as an environmentally compatible alternative to the viscose process. 

Most fibres made from regenerated cellulose such as viscose, lyocell, and Celsol are characterised by stiffness as well as a fuzzy and uneven surface that makes fabrics susceptible to pilling, even over a short period of use. In order to modify the surface properties of cellulosic fibres and fabrics and to improve their quality biotechnological approaches based on specialised enzymes are widely used. Finishing processes, employing cellulases and xylanases, can replace a number of mechanical and chemical operations, which have been applied until now to improve comfort and quality of fibres and textiles. The principle of enzyme action in the finishing process is controlled hydrolysis of cellulose, in which impurities and fuzz are removed from the surface of fibres, without decreasing their mechanical tenacity or the elasticity of the fabric. 

Lyocell is the first in a new generation of cellulosic fibres made by a solvent spinning process. A major driving force to its development was the demand for a process that was environmentally responsible and utilised renewable resources as their raw materials. The first samples were produced in 1984 and commercial production started in 1988. A wide range of attractive textile fabrics can be made from lyocell that are comfortable to wear and have good physical performance. This physical performance combined with its absorbency also make lyocell ideal for nonwoven fabrics and papers. 

Lyocell is a cellulosic fibre derived from wood pulp produced from sustainable managed forests. The wood pulp is dissolved in a solution of an amine oxide (usually A-methylmorpholine-A-oxide (5.1)). The solution is spun into fibres and the solvent extracted as the fibres pass through a washing process. The manufacturing process recovers >99.5% of the solvent. The solvent itself is non-toxic and all the effluent produced is non-hazardous. 

Wood pulp is the principal raw material of the lyocell process in terms of cost and volume. The grade used is similar to the dissolving pulp used for viscose rayon but has a slightly lower degree of polymerisation (DP) Tencel fibres have a DP of 500 to 550. The pulp is pulled from the reels into a shredder, which cuts the pulp into small pieces for mixing with the amine oxide solvent. The amount of pulp fed to the mixer has to be accurately measured so that the cellulose content in solution is closely controlled. 

Lyocell can be processed via established yam manufacturing routes, using, for example, 1.7 dtex 38 mm, 1.4 dtex 38 mm and 1.25 dtex 38 mm fibre for short staple routes. The fibre can be processed on conventional machinery, usually requiring a few setting changes in order to optimise processing performance. 

Biodegradable and sustainable fibres Basic process for standard lyocell... 

TAHT (Triacroyl hexahydrotriazine (5.4)) will cross-link lyocell under alkaline conditions. Pre-treatment of the fibre using this chemical during the manufacturing process has proved successful. In the AlOO process developed... 

Natural origin eeo fibre - Organic cotton, organic silk, Ahimsa silk, organic wool. Hemp, bamboo, Kenaf, jute, Sasawashi, Nettle, Sisal, Coconut fibre or Coir, [Banana] fibre. Ramie and Mesta/Roselle. Highly processed natural origin fibre - Rayon type Modal, Lyocell/ Tencel, Ingeo, Seacell. 

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