Study on the Thermal Stabilization Behavior of Poly(Acrylonitrile-co-2-Carboxyethyl Acrylate) Copolymer as Potential Precursor of Carbon Fiber

The thermal oxidation stabilization process of polyacrylonitrile (PAN) is a violent exothermic reaction process, which is not conducive to the improvement of carbon fiber quality. The highly exothermic reaction was often alleviated by adding unsaturated vinyl carboxylic acid monomers. In this investigation, poly(acrylonitrile-co-2-carboxyethyl acrylate) P(AN-co-CEA) copolymers with varying contents of CEA monomers were synthesized. The effects of CEA on the thermal behavior and structural evolution of copolymers were systematically investigated by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), differential scanning calorimetry (DSC), and thermal gravimetric analyzer (TGA). The results indicated that the introduction of CEA facilitated the cyclization reaction at lower temperatures through the ionic mechanism of the carboxyl group, broadened the exothermic peak, and reduced the heat release rate (Δ H /Δ T ). The activation energies (E a ) decreased from 157.7 KJ/mol for PAN homopolymer to 122.3 KJ/mol for P(AN-co-CEA) copolymer. Moreover, the CEA monomer promoted both the cyclization and dehydrogenation reactions, forming more stable cyclic structures and inhibiting the thermal decomposition of random chain segments. Consequently, higher carbon yield and a greater extent of stabilization (Es) were achieved. Additionally, the combined action of CEA and O 2 jointly enhanced the thermal oxidation stability process, resulting in the formation of oxygen-containing structures and promoting the transition to a graphite-like carbon network. Among the copolymers studied, the composition containing 2 wt% CEA exhibited the most favorable balance in the development of a well-stabilized structure. It was found that the CEA comonomer has the ability to promote the thermal oxidation stabilization process, alleviate the highly exothermic reactions, and reduce the heat release rate. Hence, these findings suggest that P(AN-co-CEA) copolymers have the potential to become carbon fiber precursor materials.