E. Mora et al. Carbon 40(2002)2719-2725 2723 ith Fig. 2. This maximum becomes smaller as the acetone content in the solvent mixture increases The reaction with air starts at about the same temperature for all the extracts and continues after the maximum observed, which indi- cates that these samples do not soft completely Of the residues obtained with the mixtures of acetone and acetonitrile, residue E2 seems to be the most suitable F precursor of carbon fibres. It has a softening point要m|=m 248C, a high carbon yield and shows maximum reactivity with air at around 250C. Consequently stabilisation could 一9240 start at relatively high temperatures, i.e. 180C. Residue El would require a lower temperature of stabilisation and therefore much longer stabilisation times. Residue E2 was selected for the preparation of the carbon fibres 01002003004005006007009009001000 Temperature(C) 3.2. Carbon fibre preparation Residue e2 was easily spun into green carbon fibres at a temperature of 300C. The diameter of the as-spun fibres varied from 35 to 16 um as the winding speed increased The stabilisation process was then studied and optimised and the carbonised fibres were characterised The samples obtained at each stabilisation stage were studied by thermogravimetric analysis. The corresponding TG and DTG curves are shown in Fig. 5. The TG curves (Fig. 5a)show an increase in carbon yield as the degree of E&节 stabilisation increases, except for the fully stabilised fibre (st260)which has a slightly lower carbon yield than st220 and st240. This could be due to the greater amount of oxygen functional groups introduced, which decompose during carbonisation. The DtG curves(Fig. 5b)show the distillation band decreasing as the stabilisation degree 01002003004005006007008009001000 increases, this band disappearing completely for sample st260. In the case of samples st220, st240 and st260, there is a band situated at around 400C, not present in the parent sample(E2), which is probably due to two factors () reactions characteristic of pitch pyrolysis, around different des Fig. 5.(a) TG curves and (b) DTG curves of fibres stabilised to 450C; and (ii) decomposition of the functional grou introduced during stabilisation, around 350 and 400C Decomposition intensifies as the stabilisation degree in- the band situated at 2940 cm(aromatic C-H stretching creases, which is in agreement with the more intense band band)and the subsequent increase in the aromaticity index (Table 4). The oxygen was incorporated into the fibres The oxygen taken up during the stabilisation of the fibres was evaluated by elemental analysis, in order corroborate the idea of more functional groups being Table 4 ntroduced into the sample as stabilisation takes place. The Elemental analysis and infrared data of samples at different stabilisation stage were studied and the results are summarised in Table 4. The oxygen C/H content increased progressively as the stabilisation degree E2 185 increased, from 1.04% for the green fibres to 3. 19% for the 1.30 ully stabilised fibres. The samples were also studied by means of infrared spectroscopy in order to determine the increase in oxygen-containing functional groups. The 2.19 results showed that the reaction with air mainly affected t260 the aliphatic hydrogens, which were almost entirely re- C/H, atomic ratio, lar, aromaticity index, O, oxygen content, moved during stabilisation, as indicated by the reduction in wt % and Ico, carbonyl index.E. Mora et al. / Carbon 40 (2002) 2719–2725 2723 with Fig. 2. This maximum becomes smaller as the acetone content in the solvent mixture increases. The reaction with air starts at about the same temperature for all the extracts and continues after the maximum observed, which indi￾cates that these samples do not soft completely. Of the residues obtained with the mixtures of acetone and acetonitrile, residue E2 seems to be the most suitable precursor of carbon fibres. It has a softening point of 248 8C, a high carbon yield and shows maximum reactivity with air at around 250 8C. Consequently stabilisation could start at relatively high temperatures, i.e. 180 8C. Residue E1 would require a lower temperature of stabilisation and therefore much longer stabilisation times. Residue E2 was selected for the preparation of the carbon fibres. 3 .2. Carbon fibre preparation Residue E2 was easily spun into green carbon fibres at a temperature of 300 8C. The diameter of the as-spun fibres varied from 35 to 16 mm as the winding speed increased. The stabilisation process was then studied and optimised and the carbonised fibres were characterised. The samples obtained at each stabilisation stage were studied by thermogravimetric analysis. The corresponding TG and DTG curves are shown in Fig. 5. The TG curves (Fig. 5a) show an increase in carbon yield as the degree of stabilisation increases, except for the fully stabilised fibre (st260) which has a slightly lower carbon yield than st220 and st240. This could be due to the greater amount of oxygen functional groups introduced, which decompose during carbonisation. The DTG curves (Fig. 5b) show the distillation band decreasing as the stabilisation degree increases, this band disappearing completely for sample st260. In the case of samples st220, st240 and st260, there is a band situated at around 400 8C, not present in the parent sample (E2), which is probably due to two factors: Fig. 5. (a) TG curves and (b) DTG curves of fibres stabilised to (i) reactions characteristic of pitch pyrolysis, around different degrees. 450 8C; and (ii) decomposition of the functional groups introduced during stabilisation, around 350 and 400 8C. 21 Decomposition intensifies as the stabilisation degree in- the band situated at 2940 cm (aromatic C–H stretching band) and the subsequent increase in the aromaticity index creases, which is in agreement with the more intense band (Table 4). The oxygen was incorporated into the fibres obtained for st260. The oxygen taken up during the stabilisation of the fibres was evaluated by elemental analysis, in order to Table 4 corroborate the idea of more functional groups being Elemental analysis and infrared data of samples at different introduced into the sample as stabilisation takes place. The stabilisation degrees samples obtained at each stabilisation stage were studied and the results are summarised in Table 4. The oxygen Sample C/H O Iar Ico content increased progressively as the stabilisation degree E2 1.85 1.04 0.68 0.12 increased, from 1.04% for the green fibres to 3.19% for the st180 2.05 1.30 0.69 0.25 fully stabilised fibres. The samples were also studied by st200 2.13 1.64 0.70 0.40 means of infrared spectroscopy in order to determine the st220 2.13 2.08 0.72 0.48 increase in oxygen-containing functional groups. The st240 2.19 2.68 0.74 0.54 st260 2.23 3.19 0.74 0.62 results showed that the reaction with air mainly affected the aliphatic hydrogens, which were almost entirely re- C/H, atomic ratio; Iar, aromaticity index; O, oxygen content, moved during stabilisation, as indicated by the reduction in wt.%; and Ico, carbonyl index