Lyocell spinning

Most recent, extensive rheological studies [59] on the stabilized NMMO-water solution proved that the apparent viscosity of the anisotropic solutions is relatively high (see Figure 10.26). Therefore, most commercial Lyocell spinning dopes usually have concentrations less than 17% and are isotropic. 

As an example using NMMO solution, the spinning of fibers consisting of blends of cellulose with cationic starch was investigated for the purpose of improving moisture absorbability, dyeability, and enzymatic degradability compared with standard Lyocell fibers [69]. 

The process of cellulose regeneration in the form of lyocell fibers is significantly simpler than that of the viscose rayon process. It is illustrated in O Fig. 16. A solution containing 14% cellulose, 10% water, and 76% NMMO plus stabilizers is extruded at a temperature slightly above 100 °C into an aqueous NMMO-bath from which cellulose is precipitated [74,75]. The extrusion has been described as a melt-spinning process that has recently made it possible to manufacture cellulosic self-bonded meltblown nonwovens as well [76]. 

For synthetic and regenerated fibres, the fibre production (primary spinning) is mainly made by melt spinning (polyester, nylon etc.), dry spinning (elastane etc.) or wet spinning (viscose, lyocell etc.). Lenzing AG has produced carbon footprints of viscose and lyocell fibres and compared these with other fibres (Shen and Patel, 2008 Shen et al., 2010 Terinte et al., 2014 Van der Velden et al., 2014). The production of natural fibres via agriculture or forestry has been studied elsewhere (e.g. Sandin et al., 2013). 

NMMO process has a short production cycle. The dissolution and spinning process is usually done within 5 h. Currently, full continuous dissolution of cellulose is implemented in the Lyocell process. 

As Rosenau et al. [49] indicated that paper grade pulp, unbleached chemical pulp, cotton and rayon fiber wastes, or even paper wastes can be used as raw materials for Lyocell fiber production, even though problems with spinnability may be encountered in some cases. In preparation for spinning dope, a 50-60% aqueous NMMO is used with the addition of 0.01 0.10% antioxidant to prevent cellulose degradation. A typical antioxidant is PG [50]. In a typical Lyocell industrial process, the slurry is produced from cellulose pulp and an aqueous NMMO solution. Typical compositions are 50-60% NMMO, 20 30% water, and 10-15% pulp [48]. Subsequently excess water is efficiently evaporated at temperatures lower than 150°C and... 

The production of lyocell is a new technology for producing cellulosic fibers by means of a direct solvent process. This means that a genuine solution of the cellulose in N-methylmorpholine-N-oxide (NMMO) monohydrate is produced and spun, and not a cellulose derivate as in the case of viscose. The cellulose can, however, be obtained from used textiles or by crushed wood pulp. After filtration of the honey-like spinning solution, it is spun through an air gap into diluted aqueous NMMO solution. 

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. 

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. 

Tencel Lyocell, to give it its full name, is produced exclusively from the wood pulp of Eucalyptus trees certified by the Forestry Stewardship Council (FSC), and the fibre carries the Pan-European Forest Council (PEFC) quality seal. Eucalyptus is woody and therefore needs energy input to convert it into a soft fibre, suitable for clothing. The Eucalyptus is reduced down then reformed into a spin-able fibre. This is done in a process with similar principles as other semi-synthetic natural fibres, such as Viscous bamboo fabric, but importandy the Lyocell process used to make Eucalyptus is much more benign and eco-friendly. It is simply the most environmentally friendly man made cellulosic fibre available today. 

Cellulose wet spinning rayon polymer is derivatized during dissolution in NaOH lyocell direct dissolution in NMMO... 

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