FEATURE / PAN-BASED CARBON FIBRES furnace is divided into the low-temperaturefurnace and the high-temperature-furnace. The same process parameters are used to produce a reference fibre by thermal conversion of an untreated PAN precursor. Samples are taken and analyzed prior to stabilization and after each oven during stabilization. RESULTS Figure 4 and Figure 5 show the comparison of the stabilization degree between treated PAN fibres and the untreated reference fibres throughout the stabilization process. With both the KMnO4 - and the N2 -pretreatment the stabilization degree prior to the stabilization of the pretreated fibres is even higher than the degree of stabilization of the reference fibres after stabilization oven 1. This means that the conventional stabilization process could be adjusted and the oven 1 can be skipped. Throughout the stabilization until after oven 3 the pretreated fibres show a higher degree of stabilization than the untreated reference fibres which indicate higher reaction speeds caused by the pretreatment process. For further investigations, the FTIR spectrum of the fibre samples have to be analyzed (Figure 6). While the FTIR spectrum of the KMnO4 - pretreated fibres haven't shown any clear signs of improved numbers of functional groups which indicate a high reactions speed during stabilization process, a proof for the effectiveness of the N2 - pretreatment can be seen in Figure 6. The C=C, C=N, N-H-group is the main indicator for the cyclization process which forms with proceeding cyclization a more and more distinct minimum of transmission19 . It can be clearly seen that the minimum of the pretreated fibres is always significantly lower than that of the reference fibres until after oven 2. This observation proves that the pretreatment with N2 Figure 4. Comparison of stabilization degree between KMnO4-treated fibres with reference fibre. Figure 5. Comparison of stabilization degree between N2-treated fibres with reference fibre. in fact effect the reaction speed and thus the speed for the formation of cyclized areas within the PAN fibre. The results of the analysis of the mechanical properties are presented in Figure 7. The pretreatment methods have a positive effect on the tensile modulus of the resulting carbon fibres. With the KMnO4 - and the N2 -pretreatment methods the E-modulus of the carbon fibres were increased by 6 and 8,5% in comparison to the reference. CONCLUSIONS With both the KMnO4 - and the N2 -pretreatment methods at least one of the four stabilization Figure 6. FTIR spectrum of N2-treated fibres in comparison to reference fibre (prior stabilization, after oven 1 and 2). ovens can be skipped since the thermal or thermochemical treatment of PAN fibres promote the desired reactions during the pretreatment as well as the stabilization process. With a pretreatment time of only a few minutes the stabilization time could be reduced by at least 11 - 20% (Figure 8). This means that not only the production time could be lowered but also the investment costs for future productions lines. Further, the tensile modulus of the carbon 12 | SAMPE JOURNAL | JANUARY/FEBRUARY 2022 www. sampe.orghttp://www.sampe.org