Numerical modeling of the carbonization of polyimide fibers in a cylindrical furnace

Carbon fiber is widely used as a reinforcing material in polymer composite such as carbon fiber reinforced plastic (CFRP) due to its high specific strength, elastic modulus and lightweight. The majority of the industrial carbon fiber is produced from synthetic precursor polymer such as polyacrylonitrile (PAN), pitch and polyimide. While relatively many studies have been published for the carbonization of PAN, little studies have been found on the heat transfer during carbonization of polyimide precursors. In this study, we numerically analyzed the carbonization process of a polyimide (PI) precursor for carbon fibers in a lab-scale cylindrical furnace. Gas flow, temperature distribution and concentration profiles including the off-gases from the precursor fibers were included in the analyses. First, we established mathematical models for the off-gases behavior from the precursor fibers. The models were incorporated into computational fluid dynamics in order to find behavior of the mixture gas of the working nitrogen gas and the off-gases. And then, numerical simulation results using the model were obtained and compared to the experimental results to verify the model. Finally, we evaluated the application scalability of the established numerical model through changes in wall temperature and precursor fiber moving speed. The results showed that the model can be used to study the PI carbonization process in the industrial size carbonization furnace.