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Viscose fibers represents about 7% of world fiber use. Viscose mass is made of pure cellulose with caustic soda and carbon disulfide that are dissolved to xanthates. In acidic solutions the xanthates regresses and the cellulose falls out. This is done by pressing the viscose mass through fine nozzles in a bath of acid. Viscose fiber is a relatively weak fiber, but it has previously been used as reinforcing fibers in industrial products such as car tires. Its industrial use has now been taken over by synthetic fibers. In order to improve water durability the viscos fibers are subjected to zinc salts during the manufacture, leading to emission of zinc. There have been tries with partly closed processes to reduce emissions.
More recently, it has been experimented with specific solvents for the cellulose to become completely recyclable. One of these fibers is called Lyocell.
Environmental
Aside from reduced water flow in cultivation and reduced need for pesticides up to 10 times more cellulose from trees can be extracted in comparison to cotton per hectare. Manufacture of man-made fibers require chemical additives which may be harmful to the environment when released into the air and water from subsequent processing operations. Most of this pollution comes from chemicals that are added after the production itself. The mineral oils used as spinning oil have significant environmental implications for the next preparation step in the textile chain. These chemicals need to be removed completely before dyeing, which means they will be found in air emissions from high temperature processes and contribute to air pollution, or water pollution from wet-processing. Thus contributing to the mass of organic pollutions. [1].
Air emissions: In the production of the viscose mass and the spinning there are emission of carbon disulfide, which is toxic.
Water emissions: In the past copper oxide ammonia was used as a solvent for cellulose and in that case it is the copper that is a problem. At the spinning of the viscose mass into fibers one sometimes use zink salts which results in zink emission.
Sources
- Textile Environmental Handbook
- [1] IPPC BAT, Integrated Pollution Prevention and Control, Reference Document on Best Available Techniques for the Textile Industry