Carbon fibers have become materials that are of great techno-logical and industrial importance because of their unique chemical, electrical, magnetic, and mechanical properties [1,2]. Fossil pitches and polyacrylonitrile (PAN) are widely used as precursors for the carbon fiber production and their choice is dictated by the end application of the carbon fiber. PAN-based carbon fibers exhibit the highest tensile strengths whereas pitch-based carbon fibers exhibit high modulus and high thermal conductivity. Renewable sources of carbon have also been studied as carbon-fiber precursors [3]. Lignin is the second most abundant polymer in nature after cellulose. This
natural, aromatic (phenolic), heterogeneous bio-macromolecule exists in the cell wall of plants. It is obtained, also, as a co-product of the papermaking industry [4]. The low cost
and high availability of lignin have brought interest on its use as precursor of carbonaceous materials like activated car-bons [5–8], carbon catalysts [9] or composite materials [10,11]. The use of lignin as a precursor for carbon fibers has been previously reported [12,13]. The lignin glass transition tem-perature is much lower than the decomposition temperature, as it happens with most of carbon-fiber precursors, thus a pretreatment must be performed to avoid fiber softening and fusion. Braun et al. [14] suggested air oxidation at low heating rates as a simple and low cost method of thermosta-bilization. After the thermal stabilization, the fibers are usu-
ally carbonized to yield carbon fibers. The use of blends that