Kinetic study of the dehydrogenation reaction in polyacrylonitrile-based carbon fiber precursors during thermal stabilization

摘要

The kinetics of dehydrogenation reaction and the structural evolution in polyacrylonitrile precursor fibers during thermal stabilization in air have been studied by Fourier transform infrared spectroscopy. The results indicate that, with the progress of dehydrogenation, the absorbance of methylene groups (-CH _2-) gradually decreases, whereas that of methine groups (=CH-) gradually increases. The dehydrogenation reaction in the fibers is basically completed after 20-min stabilization above 255°C. According to the Beer-Lambert law, the values of the absorbance for both -CH _2- groups and the resulting =CH- groups have been calculated and converted into the concentration fractions of -CH _2- groups via the Lorentzian multipeak fitting. According to the principles of chemical kinetics, the dehydrogenation reaction has been determined as a pseudo-second-order reaction with an activation energy of 107.6 kJ mol ~(-1).