Status and prospects for production of carbon fibres based on polyacrylonitrile

Abstract

Production of PAN-based carbon fibres (CF) is a rapidly developing sector. Production in 2006 was 28,000 tons. The production capacities in 2007 increased to 55,500 tons and will attain 66,000 tons in 2008. The Japanese companies Toray, Toho, and Mitsubishi are the leaders and are responsible for 77% of total production. Toray is the leader with respect to fibre quality. The CF manufactured by the company basically have a strength of 500–560 kgf/mm². The properties of the PAN precursor are of decisive importance for the quality of the CF. Each company has its own PAN precursor plant for successfully competing. The fibre manufactured in the RF has a strength of 300–350 kgf/mm². Uglekhimvolokno NlTs has developed technology for production of CF with a strength of 450 kgf/mm². Economy in production of CF is attained by creating units (flow production lines) with individual capacity of 150–200 and even 400 tons/year (the capacity of existing domestic units is 10–20 tons/year). This increase in capacity is attained by using primarily new technical solutions, including conductive tempering of oxidized tows, separate air-oxidant and air-heat carrier circulation, making the PAN tow compact by selecting an appropriate oiling agent, and vertically positioning the carbonization furnace stack. The maximum modulus of elasticity of PAN CF is 60,000 kgf/mm². To attain high orientation and a high degree of crystallinity, boron, which decreases the temperature of transition of the fibre into the highly elastic state and thus facilitates the occurrence of orientation drawing and crystallite growth, should be used as a plasticizer. In semi-industrial conditions, when boron is added in the stage of oxidation in the form of boric acid, CF with a modulus of elasticity of 47,700 kgf/mm² are obtained. To prolong the lifetime of the graphite heaters, it is recommended that they be given a shape that allows focusing radiation on the processed fibre. Thin carbon fillers in the form of prepregs 0.04–0.17 mm thick and fabrics 0.11–0.15 mm thick are manufactured to increase the uniformity of the properties of multilayer composites. Prepregs made of “thick” PAN tow with a linear density of 3.2 ktex which are processed into CF with a strength of 500 kgf/mm², elongation of 2%, and modulus of elasticity of 23,000 kgf/mm², are the most economical. In the RF, unidirectional slivers of the Elur type 0.08 mm thick are manufactured for these purposes, but they have lower strength and due to the low processing speeds, high cost. These drawbacks have been eliminated in the semicontinuous method for manufacturing thin PAN fibres.