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 = methylmorpholine- N-oxide), instead of CS2/NaOH, which has the effect of eliminating the odorous and noxious emission of sulphurous gases. The properties of the products 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.
The core part of the Lyocell process is the direct dissolution of cellulose through NMMO (Nmethyl-morpholine-n-oxide). The solvent, which is 100 % biodegradable, is able to dissolve cellulose physically without any chemical pretreatment. Therefore, the chopped pulp is mixed with NMMO. Water is removed from the socalled ‘premix’ to form a solution, which is then filtrated and spun through spinnerets into an aqueous NMMO solution to make the filaments.
The wet filaments are cut and the staples run through several after-treatment sections. After washing out residual NMMO, spin finish is applied and the fibre is dried and packed.
Through a multistage cleaning process, more than 99.6 % of the solvent can be recovered. Also the water that is regained during the evaporation step is recycled back into the washing section of the fibre line. This leads to a low specific water demand and overall low environmental emission figures.
Generally, the process includes the following steps:
Figure shows a simplified diagram of the Lyocell process.