Cotton cellulose: Ecological and resource-saving raw material for production of viscose fibres. A review

Abstract

The evolution of chemical fibre production in the last ten years has been marked by important changes in the production volumes of the individual kinds and primarily by a marked reduction--to approximately 7% of the total production volume-of the share of viscose fibres, whose production volume in 1998 was around 2 million tons [ 1 ]. An analysis of the causes of this phenomenon is beyond the scope of the present article. Nevertheless, viscose, and on a broader plane, hydrated cellulose fibres will inarguably occupy a relatively important position among other chemical fibres in the future as well due to their well-known properties.For any kind of large-tonnage product, procuring stock for the industrial process is a key problem, and production prospects are highly dependent on its correct solution. Wood cellulose primarily obtained from conifers and to a lesser degree from deciduous species, is the basic kind of polymeric raw material in viscose production. If we consider that the yield of cellulose in wood processing does not exceed 30-35%, the amount of high-quality wood required for ensuring the present production volumes for viscose fibres is 8.3-9.7 million tons a year. At the same time, according to expert estimations [2], the shortfall of wood raw material which will be observed in accessible regions in the next 15-20 years can change from a local problem to a global problem whose solution will require utilization of forests in difficultly accessible places, wide distribution of plantations of rapidly growing species in tropical and subtropical countries, and conversion to use of nonwood cellulosecontaining raw material. The increased attention in the last direction is confirmed by the important number of publications on developing methods of obtaining cellulose, including soluble cellulose (suitable for chemical processing), from nontraditional raw material --jute [3], kenaf [4], rice and wheat straw, reeds [5, 6], cotton stalks [7], perennial grasses and agricultural wastes [8].The use of cotton linters --wastes from the cotton processing industry --can be considered a realistic way of solving the problem of providing the viscose fibre industry with high-quality cellulose. Actually, cotton linters are a natural, annually renewable raw material whose possible volumes can be estimated with the data on cotton fibre production (currently approximately 16 million tons a year). Since textile cotton fibre comprises approximately 40% of the total mass of fibre raw material taken from cotton seed, the share of linters is 24 million tons a year, and the amount of the shortest fibre, type III linters used for fabrication of soluble cellulose is approximately 8 million tons a year. The low concentration of impurities in the linters ensures a high (80-85%) yield of cellulose and thus a sharp decrease in the amount of organic substances transferred into the solution, which makes the cotton cellulose fabrication process much safer environmentally than production of wood cellulose and cellulose from other kinds of nonwo...