The evolution of carbon fiber elements and their effects on fiber mechanical properties from molecular dynamics

• Published in: Computational materials science Vol. 220; p. 112029
• Main Authors: Ma, Yuanyuan, Wang, Jiangtao, Lu, Kuan, Xiang, Yang, Liu, Yaqing
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 05.03.2023
• Subjects: Carbon fiber; Carbonization; Mechanical properties; Molecular simulation; Non-carbon element; Molecular simulation; Carbonization; Mechanical properties; Non-carbon element; Carbon fiber
• ISSN: 0927-0256; 1879-0801
• DOI: 10.1016/j.commatsci.2023.112029

[Display omitted] •The evolution of Si element during fiber carbonization is first illustrated.•The various structures containing N, S and O elements are first supplemented and comprehensively explored.•The mechanism of elemental structure-fiber mechanical properties was explored.•Embedding 1.0-3.0 wt% N element into the carbon ring imparts high tensile strength and high elongation to the carbon fiber. Carbon fibers are ideal light-weight materials for aerospace applications due to their properties such as high strength, high modulus. As a result, there are significant efforts aimed at studying the theory of fiber structure and fabrication methods. The mechanical performance of carbon fibers can be controlled by the interaction of many complex factors, one of them being the element characteristic. Here, we use the molecular dynamics simulations to predict the evolution of non-carbon elements during heating and their responses to mechanical behavior. Particularly, the possible structures of N, O and Si are comprehensively studied. It is observed that Si results in the formation of CNSi chains and OH residues, which hinders the improvement of the strength of the carbon fibers. The oxygen-containing groups of the terminal ester can increase the content of adjacent chain structures that preferentially participate in carbonization. The O groups of hydroxypyridine lead to significantly lower carbonization onset temperature of polyacrylonitrile (PAN) via the pathway for H2O elimination, while the reaction rate of the H2O molecules is relevant to the PAN chain length distribution and local density. Interestingly, in the case of oxygen-modified carbon fibers, the Young’s modulus is predominantly affected. The release temperature of N, ranked from lowest to highest, is given by the chain-end CN group > hydrogenated-CN > unhydrogenated-CN, and the “transfer hopping” effect of the N element on the activated carbon chains contributes to carbon rearrangement during carbonization. The modified carbon ring structure comprising of 1.0–3.0 wt% N element is beneficial factor for conferring high tensile strength and large elongation to the carbon fibers. Our results provide valuable insights for the preparation and screening of high-performance carbon fibers from an elemental perspective, which can pave the way for a systematic framework for optimizing their performance.