2720 E. Mora et al. Carbon 40(2002)2719-2725 ory scale [22, 23] and an isotropic pitch that is as-spun fibres was optimised according to the properties of ed in this study as a precursor of general purpose the E2 residue(softening point and reactivity in air). The fibres. Finding applications for both of the phases stabilisation conditions finally used were treatment in air at obtained by filtration is of great interest for the viability of 180C for I h, followed by treatment at 200C I h, 220C the whole process. This paper studies the properties and for 2 h, 240C for I h and finally 260C for 1 h. After optimisation of the carbon fibre precursor, as well as fibre each of these stages the samples were studied in the preparation and characterisation thermobalance(samples labelled st180, st200, st220, st240 and st260, according to the highest temperature used), sing a similar procedure to the one described above. The 2. Experimental stabilised fibres were carbonised in a horizontal furnace The temperature was raised to 1000C at a rate of 1C 2./. R materials min under a nitrogen atmosphere A commercial impregnating coal-tar pitch (B15) was 2.5. Characterisation of carbon fibres thermally treated at 430C under nitrogen for 4 h. The treatment was carried out in a 2 I stainless steel reactor in a Green and carbonised fibres were studied by optical similar way to that described in [24]. The pitch obtained microscopy, in order to determine the diameter of the was labelled C3. The resultant pitch was submitted to hot fibres. The fibres were individually stuck on a small piece filtration[21] in order to separate the isotropic phase from of paper, which was then embedded vertically in epoxy the mesophase. The resultant isotropic phase was labelled resin, Next the resin pellets were polished for optical microscopy examination so that the cross-sections of the fibres could be observed and measured the texture of the 22. Solvent extraction fibres was studied by scanning electron microscopy(SEM) and any possible defect in their structure was evaluated Pitch 13 was extracted with solvents of different ex- The tensile properties of the carbonised fibres were mea- traction capability in order to optimise its softening point sured and compared to commercial general purpose carbon for fibre spinning and stabilisation. Initially, hexane(H), fibres acetone(A), acetonitrile(AN) and toluene (t)were used Extractions were performed with 25 g of pitch and 100 ml of solvent placed in a 250 ml flask and maintained under 3. Results and discussion reflux for 30 min. The solution was then filtered on a number 4 ceramic plate. The residue obtained was labelled A commercial impregnating coal-tar pitch(B15) 3H, 13A, 113AN and 13T, respectively. Extractions were thermally treated at 430C for 4 h to obtain pitch C3, with also performed with mixtures of acetonitrile and acetone. a 37% mesophase content. After filtrating C3, a 100% The resultant residues were labelled El(75% acetonitrile isotropic pitch (13)was obtained. Some of the main and 25% acetone), E2(60% acetonitrile and 40% acetone) properties of these two pitches and the parent coal-tar pitch and E3(50% acetonitrile and 50% acetone) are summarised in Table 1. The relatively high carbon yield and insoluble content in the toluene and N-methylpir 23. Characterisation of the pitches rolidone of pitch 13 indicates that it has a high degree of polymerisation. As a result of the distillation of the lightest Pitch 13. and the different extraction residues ob compounds during the initial thermal treatment, and the were characterised by measuring its Mettler softening point removal of the mesophase( the most polymerised fractio and ALCan carbon yield, and also through elemental of the pitch) during filtration, pitch 13 has a narrower analysis, infrared spectroscopy, thermogravimetric analysis molecular weight distribution. These characteristics make and differential scanning calorimetry. The procedures followed have been described elsewhere [21, 24, 25 Table I 2. 4. Carbon fibres preparation Properties of parent, thermally treated and isotropic pitch NMP Carbon fibres were prepared using pitch E2 as precurso (wt%) The spinning of the fibres was performed in stainless steel B15 9549.0 6421.3 equipment, fitted with a graphite spinneret 300 Hm in C3 202 76.9 1.95 60.0 40.2 0.71 diameter. The temperature was 300C and the 3 183 69.8 1.85 49.7 18.8 0.71 itrogen pressure applied was 0.5 MPa. The fibres were SP, softening point in inert atmosphere; CY, carbon yield; C/H wound at different winding speeds(300-1000 rev /min)to atomic ratio; Tl, toluene insoluble content; NMPL, N-methylpir- obtain fibres of different diameters. Stabilisation of the rolidone insoluble content; lar, aromaticity index2720 E. Mora et al. / Carbon 40 (2002) 2719–2725 laboratory scale [22,23]; and an isotropic pitch that is as-spun fibres was optimised according to the properties of evaluated in this study as a precursor of general purpose the E2 residue (softening point and reactivity in air). The carbon fibres. Finding applications for both of the phases stabilisation conditions finally used were treatment in air at obtained by filtration is of great interest for the viability of 180 8C for 1 h, followed by treatment at 200 8C 1 h, 220 8C the whole process. This paper studies the properties and for 2 h, 240 8C for 1 h and finally 260 8C for 1 h. After optimisation of the carbon fibre precursor, as well as fibre each of these stages the samples were studied in the preparation and characterisation. thermobalance (samples labelled st180, st200, st220, st240 and st260, according to the highest temperature used), using a similar procedure to the one described above. The 2. Experimental stabilised fibres were carbonised in a horizontal furnace. The temperature was raised to 1000 8C at a rate of 1 8C 21 2 .1. Raw materials min under a nitrogen atmosphere. A commercial impregnating coal-tar pitch (BI5) was 2 .5. Characterisation of carbon fibres thermally treated at 430 8C under nitrogen for 4 h. The treatment was carried out in a 2 l stainless steel reactor in a Green and carbonised fibres were studied by optical similar way to that described in [24]. The pitch obtained microscopy, in order to determine the diameter of the was labelled C3. The resultant pitch was submitted to hot fibres. The fibres were individually stuck on a small piece filtration [21] in order to separate the isotropic phase from of paper, which was then embedded vertically in epoxy the mesophase. The resultant isotropic phase was labelled resin. Next the resin pellets were polished for optical I3. microscopy examination so that the cross-sections of the fibres could be observed and measured. The texture of the 2 .2. Solvent extraction fibres was studied by scanning electron microscopy (SEM) and any possible defect in their structure was evaluated. Pitch I3 was extracted with solvents of different ex- The tensile properties of the carbonised fibres were mea￾traction capability in order to optimise its softening point sured and compared to commercial general purpose carbon for fibre spinning and stabilisation. Initially, hexane (H), fibres. acetone (A), acetonitrile (AN) and toluene (T) were used. Extractions were performed with 25 g of pitch and 100 ml of solvent placed in a 250 ml flask and maintained under 3. Results and discussion reflux for 30 min. The solution was then filtered on a number 4 ceramic plate. The residue obtained was labelled A commercial impregnating coal-tar pitch (BI5) was I3H, I3A, I13AN and I3T, respectively. Extractions were thermally treated at 430 8C for 4 h to obtain pitch C3, with also performed with mixtures of acetonitrile and acetone. a 37% mesophase content. After filtrating C3, a 100% The resultant residues were labelled E1 (75% acetonitrile isotropic pitch (I3) was obtained. Some of the main and 25% acetone), E2 (60% acetonitrile and 40% acetone) properties of these two pitches and the parent coal-tar pitch and E3 (50% acetonitrile and 50% acetone). are summarised in Table 1. The relatively high carbon yield and insoluble content in the toluene and N-methylpir- 2 .3. Characterisation of the pitches rolidone of pitch I3 indicates that it has a high degree of polymerisation. As a result of the distillation of the lightest Pitch I3, and the different extraction residues obtained compounds during the initial thermal treatment, and the were characterised by measuring its Mettler softening point removal of the mesophase (the most polymerised fraction and ALCAN carbon yield, and also through elemental of the pitch) during filtration, pitch I3 has a narrower analysis, infrared spectroscopy, thermogravimetric analysis molecular weight distribution. These characteristics make and differential scanning calorimetry. The procedures followed have been described elsewhere [21,24,25]. Table 1 Properties of parent, thermally treated and isotropic pitch 2 .4. Carbon fibres preparation Pitch SP CY C/H IT NMP Iar (wt.%) (wt.%) (wt.%) Carbon fibres were prepared using pitch E2 as precursor. The spinning of the fibres was performed in stainless steel BI5 95 49.0 1.64 21.3 4.9 0.63 equipment, fitted with a graphite spinneret 300 mm in C3 202 76.9 1.95 60.0 40.2 0.71 diameter. The spinning temperature was 300 8C and the I3 183 69.8 1.85 49.7 18.8 0.71 nitrogen pressure applied was 0.5 MPa. The fibres were SP, softening point in inert atmosphere; CY, carbon yield; C/H, wound at different winding speeds (300–1000 rev./min) to atomic ratio; TI, toluene insoluble content; NMPI, N-methylpir￾obtain fibres of different diameters. Stabilisation of the rolidone insoluble content; Iar, aromaticity index