Fuente: Journal of applied polymer Lugar: RESEARCH ARTICLE This study applied irradiation–thermal coupled molecular dynamics simulations to both crystalline and amorphous regions of polyacrylonitrile (PAN). Irradiation lowers cyclization temperature in amorphous PAN regions, with effects propagating to crystalline areas. Irradiation–thermal treatment induces atomic vacancies in amorphous zones and enhances crystalline region stability via a “solidification” effect, thereby improving pre-oxidation efficiency and optimizing fiber structure.


ABSTRACT
Pre-oxidation is crucial in the production of polyacrylonitrile (PAN)-based carbon fiber. Traditional thermal pre-oxidation has high energy consumption and prolonged processing time. Irradiation technology can enhance pre-oxidation efficiency, but its influence on PAN fiber molecular structure is unclear. This work pioneers the application of molecular dynamics simulations integrating irradiation–thermal coupling to the PAN fiber two-phase molecular model, elucidating the nanoscale evolution of its amorphous and crystalline structures. Models for amorphous and crystalline regions were constructed, and atomic deposition and gradient heating simulations were performed to explore their impact on the two-phase structure of polyacrylonitrile. Irradiation lowered the initial cyclization temperature in both regions and initiated reactions in the amorphous region, which then spread to the crystalline region. Irradiation mainly reduced the minimum transition temperature of cyano groups in the amorphous regions of PAN by 40 K. It also caused significant atomic vacancies in the amorphous region and a “solidification” effect enhancing molecular chain stability in the crystalline region. These simulation results elucidate how irradiation–thermal synergy improves PAN fiber pre-oxidation efficiency, reduces energy use, and optimizes fiber structure, offering a strategy to enhance carbon fiber performance.