Effects of air-blowing on the molecular size and structure of coal-tar pitch components

The results of studies of the effect of air-blowing treatment on the molecular size and structure of coal-tar pitch components are examined. Four air-blown pitches, obtained after treatment at 275 degreesC for 10, 18, 25, and 30 h, and the commercial parent pitch were studied using techniques, such as SEC, MALDI, UV-F, GC, NMR, and thermal analysis, to monitor the chemical changes undergone by pitch components under the air-blowing conditions. The results showed the formation of larger molecules due to polymerization induced by the oxygen, with the subsequent increases in the excluded peaks in the SEC analysis. The polymerization involved mainly aliphatic hydrogens in -CH2- bridges and "bay" zones, promoting the formation of side-bonds between the molecules. Only the pitch treated for 30 h showed stronger signals at long wavelengths of the UV-F spectrum, indicating an increase of the condensed aromatic units. Evidence of these side-bonds was obtained by thermogravimetric analysis, which showed a new band of weight loss around 400 degreesC being developed with the air-blowing treatment, and also by the evolution of the band associated to the glass transition detected by differential scanning calorimetry.