Structural evolution and thermal property of carbon films prepared with polyimide and polyacrylonitrile

A series of carbon-graphite films was prepared via gradient heating based on polyimide (PI) and polyacrylonitrile (PAN) films under N-2 atmosphere. It was observed that the segment fracture and thermal cross-linking reaction occur first during the low temperature pyrolysis process of PI and PAN films, meanwhile, the thermal cross-linking reaction changes the structure of PI and PAN. When it reaches a certain temperature, the crystal structure is further improved, and the films can be transformed into polycrystalline graphite structure. With the increase of temperature, the carbon content of films gradually increases and the thermal conductivity gets better. But these two kinds of films have different carbonization processes. The carbon graphite layer prepared by PI as precursor has a relatively smaller interplanar spacing and less flaws. The thermal conductivity of the films prepared by PI is 3.9 times of the films prepared by PAN.