Correlative study of critical reactions in polyacrylonitrile based carbon fiber precursors during thermal-oxidative stabilization

The correlations and differences among the processes of critical reactions in polyacrylonitrile (PAN) copolymer [containing itaconic acid (IA)] [P(AN-IA)] and terpolymer [containing itaconic acid (IA) and methyl acrylate (MA)] [P(AN-IA-MA)] fibers during thermal-oxidative stabilization have been studied by the comparative method. Fourier transform infrared spectroscopy (FTIR) analyzed the chemical kinetics and structural evolution in two types of PAN precursor fibers; the results indicates that P(AN-IA) possesses lower reaction rates and higher activation energies for critical reactions compared with P(AN-IA-MA). Differential scanning calorimetry (DSC) analyses show that the thermal stability of P(AN-IA) is superior to that of P(AN-IA-MA). FTIR and DSC results demonstrate that the stabilization process of P(AN-IA) is easier to control. By solid state 13C nuclear magnetic resonance, the mechanism of critical reactions verifies that the isomerization among quasi-pyridone, hydroxyl pyridine and pyridone structures in oxidized PAN leads to the amount of resultant groups first increasing and then decreasing.