Preparation And Properties Of Cnts/Nano-Fe₃O₄ Composite Polyimide

The existence of a series of characteristic structures for instance imide ring and aromatic ring in the molecular chain of PI makes the PI film and fiber material have excellent comprehensive properties such as high strength,high modulus,high temperature resistance,good high temperature resistance,good corrosion resistance,and good dimensional stability,which make PI have broad application in many high-tech fields.With the advancement of science and technology,the integrated design of structure and function has become the main research direction in the field of materials science,especially in the field of wave absorption materials.In this work,CNTs with dielectric loss effect and nano-Fe₃O₄with magnetic loss effect were used as the wave absorber,and PI with low dielectric and excellent mechanical properties was used as a matrix to prepare PI composite films and composite fibers.The comprehensive performance has been systematically analyzed and studied.PI composite films with different CNTs contents were studied.FT-IR and XRD analysis showed that the introduction of CNTs did not alter the imidization course of the films.When the content of the CNTs was 0.5 wt%,the mechanical properties of the PI composite films were the best in the experimental range,and the tensile strength and tensile modulus were 281.34MPa and 4.90 GPa,respectively.The TG,DMA and TMA data analysis make clear that the CNTs can obviously improve the thermal stability and Tg of the film,and also reduce the CTE of the film.The wave absorption properties of the film were tested using a vector network analyzer.When the CNTs content was 6.0 wt%,the RL_minof the film was-18.62 d B with the matching thickness was only 2.0 mm and the effective absorption bandwidth can reach to 2.72GHz.On this basis,nano-Fe₃O₄with magnetic loss effect was introduced into the system to explore the effect of different ratios of CNTs/nano-Fe₃O₄on the properties of composite film.As a positive effect,when the ratio of CNTs/nano-Fe₃O₄is 3:1,the RL_minof the composite film with a matching thickness of 2.0 mm can reach to-28.18 d B.Furthermore,fiber spinning was carried out on the basis of the composite film formulation.By changing the thermal imidization temperature in the wet spinning process,the effect of the imidization temperature on the comprehensive properties of the composite fibers was explored.It was found that the higher the imidization temperature can lead to the higher the imidization degree,higher orientation,higher mechanical properties,higher the 5 wt%thermal decomposition temperature,and the better wave absorption performance of the fiber.When the imidization temperature was 380℃,the tensile strength of the fiber was about 321.14 MPa,the tensile modulus was21.91 GPa,the degree of orientation is 84.68%,the thermal decomposition temperature of 5 wt%is 567.10℃,and the RL_mincan reach to-18.04d B.In addition,by changing the coagulation bath condition of the spinning process to explore its effect on the properties of fiber.It was found that under the premise of the same volume fraction of the coagulation bath,the higher the temperature of the coagulation bath,the more irregular the shape of the fiber section under SEM observation,and the larger the average radius of the micropores inside the composite fiber under X-ray small Angle scatterometer test analysis,leading to the worse mechanical properties,but the better the wave absorption properties of the fiber.When the temperature of coagulation bath is 50℃,the average radius of the micropores in the fiber is 4.97 nm,and the RL_minof the composite fiber is-54.61 d B.