In order to investigate the arc resistance of coating modified polyimide fabric, a waterborne polyurethane was used as matrix to prepare a barrier thermal insulating coating with SiO₂ aerogel and a reflective thermal insulating coating with TiO₂ filler, and then two coatings were applied on the polyimide fabric, respectively. The effect of filler addition amount and the matrix on the thermal protection performance and rupture performance of polyimide fabric under the effect of fault arc was studied. The results show that the thermal protection performance of the modified polyimide fabric increases with the increase of filler addition, the thermal protection performance of polyimide modified by thermal insulating coating with 6% of SiO₂ and 6% of TiO₂ increases by 34.79% and 21.78%, respectively. Waterborne polyurethane matrix has no effect on the thermal protection performance of polyimide fabrics, but it can make their rupture performances increase by 20%.

Polyimide films with high porosity were prepared using 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and 4,4′-diamino-2,2′-dimethyl-biphenyl (mTB) as monomers. During the preparation process, pore-forming agent was added into the system, and the high-temperature thermal imidization of polyamide acid was controlled by the principle of thermo-induced phase separation. The micropore morphology, mechanical properties, and dielectric properties of the films were analyzed. The results show that the porosity of porous films reach 50%-60%. Under the frequency of 10 GHz, the dielectric constant and the dielectric loss factor of the sample PI-1-250-4 h is 2.14 and 0.002 8, respectively, while maintaining good mechanical properties and heat resistance. Due to the introduction of rigid biphenyl building blocks, the porous film still maintains a low coefficient of thermal expansion. The adhesive-free double-sided copper clad laminate, which prepared by combining the porous film with thermoplastic polyimide (TPI) and then pressing copper foil at high temperature, has good interface adhesion and solder resistance, and can apply to high-frequency and high-speed flexible copper clad laminates.

In order to improve the weak dispersion of two-dimensional nanosheets in polymer matrix and improve the electrical performance of composite materials, a two-dimensional micron expanded layer molybdenum disulfide (E-MoS₂) was prepared by hydrothermal method, and then polyimide (PI) based super-large lattice molybdenum disulfide nanosheets (PI/E-MoS₂) composite films were prepared by in-situ polymerization method. The surface/cross section structure of the composite films was observed by scanning electron microscopy (SEM), the molecular valence bond composition of the composite film was analyzed by Fourier infrared spectroscopy (FTIR), and the phase structure of the composite film was analyzed by X-ray diffraction (XRD). Furthermore, the dielectric constant, DC electrical conductivity, and dielectric loss factor of the composite films were tested, and the effect mechanism of extended lattice on the breakdown and polarization behavior of composite films was studied. The results show that when a small amount of E-MoS₂ nanosheets is added into PI film, there is little agglomeration phenomenon on the surface of PI/E-MoS₂ films, and there is little obvious holes and a small number of structural defects on the cross section, which indicates a good compatibility between fillers and matrix. The incorporation of E-MoS₂ nanosheets can enhance the interfacial polarization of the composite films, improve both the dielectric constant and electric field strength, and decrease the dielectric loss.

Metal particle pollutants inside gas-insulated metal enclosed switchgear (GIS) equipment can cause severe electric field distortion, leading to surface discharge of insulators. This paper proposed a method of dielectrically functionally gradient insulator for suppressing metal particles. The electric field distribution around the basin insulator and the motion characteristics of metal particles were simulated. The results show that metal particles released from the shell are affected by the axial electric field force and tend to move towards the insulator. The permittivity distribution of the laminated functionally gradient (ε_L-FGM) insulator decreases in the radial direction, which can homogenize the electric field distribution along the insulator surface and drive away the metal particles by reversing the electric force with the axial electric field. However, the ε_L-FGM insulator enhances the electric field on the surface of the shell, and the jump height of metal particle is 2.7 times higher than those around the uniform insulator. Compared with ε_L-FGM insulator, the ε_T-FGM insulator with a spatial permittivity gradient, which designed based on the topology optimization, reduces the jump height of metal particles and performs better effect in regulating the electric field and expelling the particles.

Photosensitive polyimide (PSPI) is a kind of high-performance polyimide with special structures, which is widely used in semiconductor packaging, integrated circuits, optical display, and other fields due to its excellent heat resistance, mechanical properties, insulating properties, and lithographic processability. In this paper, the PSPI patents applied in China were taken as object, the overall situation of these patents, including changes in the number of patent applications, applicants, and their source countries was analyzed systematically. Especially, the patent applicants inside and outside China and the patent subject distribution since 2011 were discussed. The difference of patent technology and protection priorities of enterprise applicants inside and outside China was compared in detail. The patent technology characteristics and development trends of PSPI were explored.

The insulation status of the cable intermediate joint plays an important role in the safe and stable operation of cable. In view of the immaturity of terahertz imaging technology and the limitation of finite element analysis method, an ultrasonic signal characterization method for typical internal defects of silicone rubber in cable accessories was proposed in this paper. At first, different types of typical defect in silicone rubber were designed by simulation. Then the time-domain characteristic quantity and correlation analysis were carried out on the reflected echoes received in the ultrasonic detection simulation, and the correlation coefficient between the time-domain waveform characteristic quantity and the size and angle of defects was obtained. Finally, an ultrasonic test platform was built on the basis of pulse echo method to carry out ultrasonic test on the flat silicone rubber samples with defects. The results show that the size and angle of the internal defects of silicone rubber have a good correlation with the amplitude peak of the first echo, and the detection results of crack defects are more affected by the angle than that of bubble defects, and the amplitude peaks of defects at different angles are significantly different. It is concluded that the ultrasonic signal can effectively characterize the typical internal defects of silicone rubber in cable accessories.

This paper introduced the research and application progress on green solvents in the preparation of polyimide from the views of the classification, manufacturing procedures, solvent composition of polyimide films, and the application status of green solvents. Emphatically, the current research status of biobased solvents, including γ-valerolactone (GVL), dimethyl isosorbide (DMI), and dihydrolevoglucosenone (Cyrene^TM) and their applications on the preparation of PI films were presented. The future developing trends of the applications of green solvents in the manufacturing of PI films were prospected.

In order to investigate the improving mechanism of polysiloxane with different substituents on atomic oxygen (AO) erosion resistance of polyimide in space environments, reactive molecular dynamics (MD) simulations was used to analyze the AO erosion resistance of PI composited with polyhedral oligomeric silsesquioxane (POSS) with trifluoromethyl (-CF₃) group and methyl (-CH₃) group. The results show that both the composites exhibit strong AO erosion resistance by forming an SiO₂ layer that blocks AO propagation into the polymer matrix and and heat transfer. The PI/CF₃-POSS shows the best performance, and its normalized mass is 0.83 after 35 ps of AO exposure, while the nomalized mass of the PI/CH₃-POSS composite is 0.78.

Three fluoro-containing polyimide (PI) resins (PI-II_a, PI-II_b, and PI-II_c) were prepared by two-step chemical imidization procedure using a fluoro-containing dianhydride 9,9-bis(trifluoromethyl)xanthene-2,3,6,7-tetracarboxylic dianhydride (6FCDA, II) and three kinds of aromatic diamines, including 2,2ʹ-bis(trifluoromethyl)-4,4ʹ-diaminodiphenylether (6FODA, a), 1,4-bis[(4-amino-2-trifluoromethyl)phenoxy]benzene (6FAPB, b) and 2,2-bis[(4-aminophenoxy) benzene]propane (BAPP, c), respectively. For comparison, the referenced PI resins (PI-I_a, PI-I_b, and PI-I_c) were prepared with the same procedure except that 6FCDA was replaced by 4,4ʹ-(hexafluoroisopropylidene)diphthalic anhydride (6FDA). And then six kinds of PI films were prepared by high temperature curing process, and their properties were studied. The results show that the solubility of PI-II_a, PI-II_b, and PI-II_c resins in organic solvents is lower than that of PI-I_a, PI-I_b, and PI-I_c resins. Compared with PI-I_a, PI-I_b, and PI-I_c films, PI-II_a, PI-II_b, and PI-II_c films show higher glass transition temperature (T_g), lower linear coefficient of thermal expansion (CTE), little lower optical transparency, and relatively higher dielectric constant (D_k). The PI-II_a film has the optimal comprehensive properties, its T_g and CTE is 362.5℃ and 39.6×10^-6 K^-1, respectively, its optical transmittances at the wavelength of 450 nm (T₄₅₀) is 83.9%, and the D_k at the frequency of 10 GHz is 3.00.

Submarine cable is a transmission component of high-voltage power, and the heat generated during the operation of submarine cable will cause the structural temperature rise and expand. Under the constraint of each layer, the submarine cable will produce large thermal stress and deformation, which will cause structural damage. In addition, the increase of temperature will lead to the decrease of elastic modulus of the polymer material inside the submarine cable, resulting in the change of mechanical properties of the submarine cable section. Therefore, it is necessary to study the stress and deformation caused by thermal expansion during the operation of submarine cables, and analyze the influence of temperature on the mechanical properties of submarine cables. In this paper, based on an offshore wind power project, a finite element model of submarine cable-soil was established in finite element software ABAQUS, and the temperature field distribution under steady-state current carrying capacity was obtained. Based on the results of temperature field, the thermal stress and thermal deformation of the submarine cable were calculated by the thermal-mechanical coupling method, and the change of mechanical properties of the submarine cable section under the action of temperature was analyzed. The results show that the highest temperature appears in the copper conductor during the operation of submarine cable, and the outer coating layer has the lowest temperature. With the copper conductor as the center, the temperature drop gradient along the inside radial direction is small, and the temperature drop gradient along the outside radial direction is large. The thermal stress is mainly concentrated in the metal structure, and the maximum deformation occurs in the steel wire armor. When the copper conductor and the optical fiber are located at the top of the cross section, the displacement is the largest, and the displacement is the smallest at the bottom. After considering the influence of temperature, the stress of copper conductor and optical fiber will increase, while the tensile and torsional stiffness of submarine cable will decrease, and the reduction of inverse torsional stiffness is greater than that of clockwise torsional stiffness.