Modification of the pyrolysis/carbonization of PPTA polymer by intermediate isothermal treatments

Pyrolysis/carbonization of poly (p-phenylene terephtalamide) (PPTA) was investigated, studying the possibility of modifying the pyrolysis/carbonization behavior and hence the carbon yield by introducing intermediate isothermal treatments. Thermogravimetric analysis (TG) was used to establish the main degradation steps of the material. It showed that the yield of solid residue at 950 °C increases by more than 15 wt.% by introducing an isothermal step at 500 °C for at least 50 min. Intermediate decomposition products at different temperatures/times of PPTA decomposition were characterized by X-ray diffraction (XRD), elemental microanalysis and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). XRD results showed that carbonization progresses during the isothermal step, so that the material is degraded loosing its crystallinity in a continuous way. DRIFTS spectra showed that PPTA undergoes a rupture of polymeric chains during the isothermal stage enhancing aryl nitrile formation. This favors crosslinking reactions that take place with increasing temperature, yielding a solid residue with a higher nitrogen content and higher char yield.