Preparation of general purpose carbon fibers from coal tar pitches with low softening point

This paper describes the different procedures applied for the preparation of general purpose carbon fibers from four coal tar pitches. The four raw materials have a low softening point (of about 373 K) for this application and, hence, must be subjected to a treatment before spinning to increase this temperature. The treatments applied are the following: (i) heating in N2, (ii) heating in air, (iii) consecutive heating in N2 and air, and (iv) blending of the coal tar pitch with a petroleum one and further treatment in air. The changes in chemical composition, softening point and yield of the treatments used have been followed by different techniques. Only treatments (iii) and (iv) produce materials with an adequate viscosity for spinning and a sufficiently high softening point to be transformed in carbon fibers. The carbon fibers obtained have similar mechanical properties to those prepared in a previous work from a suitable petroleum pitch with the same experimental system. However, the mechanical properties of these fibers are inferior to those of a commercial carbon fiber, the differences being due to the lower diameter of the commercial fibers.