Availableonlineatwww.sciencedirect.com BCIENCE DRECT● CARBON ELSEVIER Carbon4302005)591-597 Biopitch-based general purpose carbon fibers Processing and properties M.J. Prauchner a, *v.M.D. Pasa b.s. otani c.C. otani c Instituto de quimica, Universidade de brasilia, C P. 4478, CEP: 70910 970, Bro Departamento de quimica, Universidade Federal de Minas gerais, At. Antonio Carlos, 6627, CEP: 31270 901, Belo Horizonte, Brazil Departamento de Fisica, Instituto de Tecnologia Aeronautica, Centro Tecnico Aeroespacial, CEP: 12228 901, Sao Jose dos Campos, Brazil Received 17 September 2003: accepted 17 October 2004 vailable online 24 November 2004 Abstract Eucalyptus tar pitches are generated on a large scale in Brazil as by-products of the charcoal manufacturing industry. They pres- ent a macromolecular structure constituted mainly of phenolic, guaiacyl, and siringyl units common to lignin. The low aromaticity (60-70%), high O/C atomic ratios (0.20-0.27%), and large molar mass distribution are peculiar features which make biopitches behave far differently from fossil pitches. In the present work, eucalyptus tar pitches are evaluated as precursors of general purpose carbon fibers(GPCF)through a four-step process: pitch pre-treatment and melt spinning, and fiber stabilization and carbonization Homogeneous isotropic fibers with a diameter of 27 um were obtained. The fibers had an apparent density of 1.84g/cm,, an electrical esistivity of 2 x 10Q2m, a tensile strength of 130 MPa, and a tensile modulus of 14 GPa. Although the tensile properties advise against using the produced fibers as structural reinforcement, other properties give rise to different potential applications, as for example in the manufacture of activated carbon fibers or felts for electrical insulation. C 2004 Elsevier Ltd. All rights reserved Keywords: A Carbon fibers, Pitch; B Heat treatment, Stabilization; D. Mechanical properties 1. Introduction from isotropic pitches, usually called general purpose carbon fibers(GPCF) or isotropic carbon fibers, have Fossil pitches(petroleum pitches and coal tar pitches) poor ordering and low or no preferred orientation have been largely investigated as carbon fiber precursors therefore having moderate or poor mechanical proper mainly because pitches are cheaper raw materials than es[46] the traditionally used polyacrylonitrile(PAN) and pres Due to the comparatively high production cost of ent a simpler and less expensive processing [1-6. Pitch- HPCFs, their applications are mainly restrained to the based carbon fibers can be classified into two types aerospace and sports goods industries, where the perfor- according to their properties: the first type, usually mance/weight quotient is by far the predominant factor called high performance carbon fibers(HPCF), are pro- [7]. In contrast, GPCFs are produced at a much lower duced from mesophase pitches and have high degrees of price, and therefore, they are employed in applications ordering and orientation, and consequently, improved where mechanical properties are not the most relevant mechanical properties [1-3]. Conversely, those obtained factor. For example, as concrete reinforcement [8], elec- trodes for energy storage systems [9, 10), and in the pro Corresponding author. Tel. +55 61 307 2167: fax: +55 61 273 duction of activated carbon fibers(ACF). In turn, ACFs are used as catalysts [ll], catalyst supports [12], mole- cular sieves for the separation and purification of gas 6223/. see front matter 2004 Elsevier Ltd. all rights reserved 0.1016 carbon2004.10.023Biopitch-based general purpose carbon fibers: Processing and properties M.J. Prauchner a,*, V.M.D. Pasa b , S. Otani c , C. Otani c a Instituto de Quı´mica, Universidade de Brası´lia, C.P. 4478, CEP: 70910 970, Brası´lia, Brazil b Departamento de Quı´mica, Universidade Federal de Minas Gerais, Av. Antoˆ nio Carlos, 6627, CEP: 31270 901, Belo Horizonte, Brazil c Departamento de Fı´sica, Instituto de Tecnologia Aerona´utica, Centro Te´cnico Aeroespacial, CEP: 12228 901, Sa˜ o Jose´ dos Campos, Brazil Received 17 September 2003; accepted 17 October 2004 Available online 24 November 2004 Abstract Eucalyptus tar pitches are generated on a large scale in Brazil as by-products of the charcoal manufacturing industry. They pres￾ent a macromolecular structure constituted mainly of phenolic, guaiacyl, and siringyl units common to lignin. The low aromaticity (60–70%), high O/C atomic ratios (0.20–0.27%), and large molar mass distribution are peculiar features which make biopitches behave far differently from fossil pitches. In the present work, eucalyptus tar pitches are evaluated as precursors of general purpose carbon fibers (GPCF) through a four-step process: pitch pre-treatment and melt spinning, and fiber stabilization and carbonization. Homogeneous isotropic fibers with a diameter of 27lm were obtained. The fibers had an apparent density of 1.84 g/cm3 , an electrical resistivity of 2 · 10
4 Xm, a tensile strength of 130MPa, and a tensile modulus of 14GPa. Although the tensile properties advise against using the produced fibers as structural reinforcement, other properties give rise to different potential applications, as for example in the manufacture of activated carbon fibers or felts for electrical insulation. 2004 Elsevier Ltd. All rights reserved. Keywords: A. Carbon fibers, Pitch; B. Heat treatment, Stabilization; D. Mechanical properties 1. Introduction Fossil pitches (petroleum pitches and coal tar pitches) have been largely investigated as carbon fiber precursors mainly because pitches are cheaper raw materials than the traditionally used polyacrylonitrile (PAN) and pres￾ent a simpler and less expensive processing [1–6]. Pitch￾based carbon fibers can be classified into two types according to their properties: the first type, usually called high performance carbon fibers (HPCF), are pro￾duced from mesophase pitches and have high degrees of ordering and orientation, and consequently, improved mechanical properties [1–3]. Conversely, those obtained from isotropic pitches, usually called general purpose carbon fibers (GPCF) or isotropic carbon fibers, have poor ordering and low or no preferred orientation, therefore having moderate or poor mechanical proper￾ties [4–6]. Due to the comparatively high production cost of HPCFs, their applications are mainly restrained to the aerospace and sports goods industries, where the perfor￾mance/weight quotient is by far the predominant factor [7]. In contrast, GPCFs are produced at a much lower price, and therefore, they are employed in applications where mechanical properties are not the most relevant factor. For example, as concrete reinforcement [8], elec￾trodes for energy storage systems [9,10], and in the pro￾duction of activated carbon fibers (ACF). In turn, ACFs are used as catalysts [11], catalyst supports [12], mole￾cular sieves for the separation and purification of gas 0008-6223/$ - see front matter 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2004.10.023 * Corresponding author. Tel.: +55 61 307 2167; fax: +55 61 273 4149. E-mail address: marcosjp@unb.br (M.J. Prauchner). Carbon 43 (2005) 591–597 www.elsevier.com/locate/carbon