Research Of Polyimide Pyrolysis Mechanism

The characteristic structure of polyimide film such as imide ring and aromatic ring makes it high strength and high modulus,and has excellent properties like high temperature resistance,high dielectric,high insulation and corrosion resistance.It is used in national defense,electronic circuits,aerospace,etc.many fields.At the same time,polyimide film has the characteristics of high carbon content,strong structural rigidity and well-preserved morphology after carbonization so it is considered to be an ideal precursor for carbon film.In order to prevent the material from losing performance due to unknown reasons in extreme environmental applications,this project uses experimental testing,characterization analysis,and simulation calculations to work together to conduct pyrolysis,carbonization and thermal oxidation of polyimide films in different systems.They have carried out a mechanism study,and conducted a detailed study on the change trend of its structural properties,the progress of the reaction stage with temperature,and the possible influencing factors.The experiment uses molecular dynamics simulation to calculate the bond-level bond energy of the chemical bonds in the structure and the breaking order in the reaction,assists in the observation of the characteristic peaks of the structure at different temperatures by infrared spectroscopy,and integrates the thermogravimetric infrared mass spectrometry to determine the reaction overflow gas.The general process of polyimide pyrolysis is obtained:the reaction starts from the separation of the hydrogen atom connecting the benzene ring,and the opening of a carbon-nitrogen bond on the imide ring enters the breaking stage of the molecular chain,and the characteristic structure of each monomer And the benzene ring gradually decomposes to form large molecular chain fragments,the pyrolysis time increases,the non-carbon atoms are separated and combined into small molecules and the gas overflows,and the remaining product is restructured into a polyimide-based carbon film.XRD,Raman,SEM,etc.were used to characterize and analyze the condensed structure,graphitization degree,and carbon layer morphology of the product carbon film.It was found that as the carbonization temperature increased the carbon atom structure after pyrolysis of polyimide was reorganized.A graphitized hexagonal net-like carbon layer structure is formed,and the carbon film is gradually perfected and dense.At the same time,the polyimide film with insulating properties is transformed into a polyimide-based carbon film with good conductivity.In this work,it was found that the monomer structure has different effects on the pyrolysis and carbonization process of polyimide.The single bond connecting the benzene ring in the monomer BPDA in the experiment is easy to deform torsionally at high temperature and affects the heat resistance of the system.The commonality of PMDA the yoke structure will increase the stability of the system,the ether bond in ODA will break earlier in the reaction and the degree of polymerization will be greatly reduced.The imidazole structure in BIA has a strong crystallization ability,which is beneficial to the construction of carbon layer structure.The TGA test is used to compare the heat resistance of each system,verify by calculating the thermal decomposition activation energy,and determine the reaction order n=1 in the polyimide pyrolysis process.