Experimental and Statistical Optimization of the Tensile Strength of Carbon Fibers from Pitches with Different Composition

A factorial analysis was used to maximize the tensile strength of the carbon fibers obtained from pitch by means of a rational selection of variables and precursor properties. The combined influence of the fiber diameter, the soaking time at the optimum stabilization temperature, and the effect of the polycondensation degree of the pitch on the tensile strength of the carbonized fibers was assessed using a factorial design. For the first time, the strong influence of the degree of polycondensation of the parent pitch was evidenced, even though less polycondensed pitches were spun at a higher yield and favored the homogeneous fixation of oxygen during stabilization. Fibers prepared from the most polycondensed pitches exhibited the best values of tensile strength. However, very highly polycondensed pitch compositions may hinder oxygen diffusion and the formation of cross-linked structures during stabilization, leading to a poorer mechanical performance that can be overcome by increasing the stabilization time.