Regenerated Cellulose Fibres published by Woodhead Publishing Ltd in 2001 contains a history of the Tencel development, the fourth extract of which appears below. (see the original for references - click here for first extract)
Work on other routes to cellulosic fibres has continued, often driven by a desire to utilize the large capital investment in the xanthate route and hence cost less than a completely new fibre process.
The Finnish viscose producer Kemira Oy Saeteri collaborated with Neste Oy on the development of a carbamate derivative route. This system was based on the original work of Hill and Jacobsen who showed that the reaction between cellulose and urea gave a derivative which was easily dissolved in dilute sodium hydroxide:
Cell-OH + NH2 -CO-NH2 ---> Cell-O-NH2 +NH3
Neste patented an industrial route to a cellulose carbamate pulp which was stable enough to be shipped into rayon plants for dissolution as if it were xanthate. The carbamate solution could be spun into sulphuric acid or sodium carbonate solutions, to give fibres which when completely regenerated had similar properties to viscose rayon. When incompletely regenerated they were sufficiently self-bonding for use in papermaking. The process was said to be cheaper than the viscose route and to have a lower environmental impact. It has not been commercialised, so no confirmation of its potential is yet available.
Chen, working on a small scale at Purdue University, claims that solutions containing 10-15% cellulose in 55-80% aqueous zinc chloride can be spun into alcohol or acetone baths to give fibres with strengths of 1.5 to 2 g/den. However, if these fibres were strain-dried (i.e stretched) and rewetted whilst under strain, strengths of 5.2 g/d were achieved.
Kamide and co-workers at Asahi have been applying the steam explosion treatment to dissolving- pulp to make it dissolve directly in sodium hydroxide. In technical papers,, they claimed a solution of 5% of steam-exploded cellulose in 9.1% NaOH at 4oC being spun into 20% H2SO4 at 5oC. The apparently poor fibre properties (best results being 1.8 g/d tenacity dry, with 7.3% extension) probably arise because the fibres were syringe extruded at 75 denier/fil. Asahi felt at the time that this would be the ultimate process for large scale production of regenerated cellulose fibres but in reality it’s use appears confined to the production of thickeners.