Polyimide (PI) is a class of insulating materials with great potential in the field of high-voltage and high-power device encapsulation, which has excellent insulating properties. However, its intrinsic thermal conductivity is low, which is easy to cause localized overheating and damage to the device. In this paper, the thermal conductivity of polyimide materials was improved by doping with thermal conductive fillers. PI/c-BN and PI/h-BN composite films were prepared by in situ polymerization with cubic boron nitride (c-BN) and hexagonal boron nitride (h-BN) as filler, and the effects of different content of c-BN and h-BN on the thermal conductivity, thermal stability, and mechanical properties of the composite films were investigated. The results show that the thermal conductivity of the composite films increases with the increase of BN content. The thermal conductivity of PI/c-BN composite films is higher than that of PI/h-BN composite films within the studied content, and the thermal conductivity of PI/40c-BN composite films increases by 1 068% compared to pure PI. The thermal conductivity of PI matrix is improved by c-BN at lower content, and the tensile strength of PI/c-BN composite films still reaches 40 MPa when the filler mass fraction is 30%. In addition, the thermal stability of the composite films is improved.

To develop polyimide (PI)-based composite films with low dielectric constant (D_k), low dielectric loss (D_f), and high temperature resistance at high frequency, a water-soluble polyamic salt (PAAS) was prepared by adding organic base into the polyamic acid, which is the precursor of fluoropolyimide (FPI), and composite films were prepared by compounding low dielectric polytetrafluoroethylene (PTFE) concentrated dispersion with the dried PAAS to form a water dispersion system. The effects of PTFE content on the dielectric, thermal, and mechanical properties of the composite films were studied. The experimental results show that with the increase of PTFE content, the dielectric constant of the composite films decreases continuously, but there will be some effects on the thermal stability and mechanical properties. The dielectric constant of 50%PTFE/FPI reaches the minimum value (D_k=1.5@8.5 GHz), and the dielectric loss of 10%PTFE/FPI in the frequency band of 9.25-10.25 GHz is less than 0.005. The glass transition temperature of the composite films is in the range of 289-297℃, and the thermal decomposition temperature at 5% is higher than 508℃. The thermal expansion coefficient of 40%PTFE/FPI is as low as 59.67×10^-6 K^-1. The tensile strength of 20%PTFE/FPI is 70 MPa, the tensile modulus is 1.59 GPa, and the elongation at break is 7.7%.

With the development of economy and technology, the demand of safer and more stable packaging materials for electronic devices has increased. Traditional polyimide (PI) base materials are extensively used due to their excellent mechanical and heat-resistant properties. In this study, a novel fluorinated polyimide (FPI) porous composite film was developed by introducing fluorine groups and a porous structure into polyimide, along with adding the flame retardant 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO). Experimental results demonstrate that under 80%RH of ambient humidity and 5% of DOPO mass fraction, the new FPI porous composite film exhibits uniform and regularly distributed pore size, excellent mechanical properties, and lower water absorption. The incorporation of flame retardant DOPO forms a protective phosphorus-containing layer on the film surface, which significantly improves the flame retardancy and hydrophobic properties of film. This research provides a new material with enhanced safety for the packaging of electronic devices, which is expected to play a crucial role in improving the stability and safety of electronic equipment.

Epoxy resin/micron-alumina composites are widely employed as supporting and insulating components in electrical power equipment, and their glass transition temperature and thermal expansion coefficient critically influence the long-term performance of electrical power equipment. Epoxy resin composite dielectrics containing 0%, 20%, 40%, and 60% mass fractions of micron-alumina fillers were prepared in this paper. Their thermal expansion coefficients and glass transition temperatures were calculated through numerical fitting of dielectric constant measurements at high-temperature and high-frequency. The results demonstrate that with the increase of the mass fraction of micron-alumina fillers, the thermal expansion coefficient of composite dielectrics reduces significantly, and the glass transition temperature also showing a decreasing trend. Comparative analysis between calculated values and existing experimental data reveals that the calculated value is consistent with the experimental value, confirming the scientific validity and effectiveness of dielectric spectroscopy as a methodology for evaluating the thermal properties of epoxy composite dielectrics. This approach can serves as an effective supplementary technique to conventional experimental methods for investigating the thermal characteristic of polymer.

Bisphenol A epoxy resin is widely used in the field of copper clad laminates. However, its flame retardancy and dielectric properties cannot meet the high-speed development of copper clad laminates. To simultaneously improve the flame retardancy and dielectric properties of epoxy resin, a reactive oligomeric flame retardant (PDDV) based on 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO-HQ), 1,4-dichlorobenzene (DCX), and 4-vinylbenzyl chloride (VBC) was synthesized, and its chemical structure was determined by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR) characterization. EP/PDDV composites were prepared by physical blending, and their thermal, flame retardancy, and dielectric properties were tested. The results show that when the mass fraction of PDDV is 30%, the char yield of EP/PDDV composites increases to 38.74%, the glass transition temperature (T_g) rises to 138.9℃, the limiting oxygen index (LOI) increases to 55%, UL-94 reaches V-0 grade, the dielectric constant (D_k) is 2.69, and the dielectric loss factor (D_f) is 0.007 91. The comprehensive performance of the composites is the best.

In order to realize the synergistic enhancement of electrical-mechanical properties of epoxy resin for power electronics encapsulation, CaCO₃ oligomer inorganic nanoparticle filler was prepared by solution method, epoxy resin was carried out organic matrix-inorganic filler modification together with organic silicone, and single inorganic modified, single organic modified, and organo-inorganic jointly modified epoxy resin composites were prepared. Taking the pure epoxy resin as a reference, the AC electric strength, DC volume conductivity, surface potential attenuation characteristics of the four epoxy resin composites were investigated, and the internal trap energy levels were calculated from them, while their bending strength and impact strength characteristics were also investigated. The results show that the electrical properties of single inorganic modified, single organic modified, and organic-inorganic co-modified epoxy resin composites are significantly improved, and their electric strength increases by 6.55%, 12.66% and 9.61%, respectively. Their DC volume resistivity is 5 times bigger than that of pure epoxy resin, the surface potential decay rate decreases, the trap density and trap energy increase, but the improvement of electrical properties by the organic-inorganic co-modification do not superimpose compared with single modification. The flexural and impact strengths of the modified epoxy resin composites significantly increase, with exponential growth compared to the pure epoxy resin. The research results provide a reference for the performance improvement of modified epoxy resin composites in the field of power electronics insulation and encapsulation.

To address the challenges of epoxy resins in electrical insulation and flame-retardant applications, a phosphorus-containing bio-based flame-retardant resin—bis(methacryloyloxy-4-hydroxy-3-methoxyphenyl) phenyl phosphate (DGEBDB) was synthesized from 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and renewable vanillin, and cured materials were prepared through blending it (0%, 25%, 50%, and 75%) with bisphenol A epoxy resin (DGEBA). Their flame retardancy, thermal properties, mechnical properties, and electrical properties were analyzed. The results show that when the mass fraction of DGEBDB is 75%, the limiting oxygen index (LOI) of epoxy bending system increases from 22.6% to 34.2%, and the flame retardant grade achieves V-0 in UL 94 tests. Cone calorimetry reveals that the DGEBDB can reduce the heat release rate (HRR) and total heat release (THR), showing excellent fire suppression. Electrical properties tests show that the electrical properties of the cured epoxy maintain good when the mass fraction of DGEBDB is as high as 75%, which ensures the reliability of DGEBDB in electrical application. Mechanical properties indicate that with the increase of DGEBDB content, the flexural strength and tensile strength increase, indicating an increase in structural integrity and load bearing capacity of the cured epoxy. Therefore, the addition of DGEBDB significantly enhances the flame retardantcy of composite, while maintaining the excellent thermal, mechanical, and electrical properties of epoxy resin, and when the mass fraction of DGEBDB is 25%, the overall performance is the best, which has a better prospect for practical applications.

A kind of silicone encapsulant with excellent thermal conductivity, self-leveling properties, mechanical properties, and flame retardancy was prepared by employing end vinyl silicone oil with different viscosity as matrix, containing hydrogen silicone oil as cross-linking agent, and spherical alumina as thermal conductive and reinforcement filler. The effects of ratio of end vinyl silicone oils with different viscosity, molar ratio of active hydrogen and vinyl, filler ratio and filling amount on the performance of silicone encapsulant were investigated. The results show that the silicone encapsulant has the best performance when the PDMS-1 and PDMS-2 vinyl end silicone oil are mixed at a mass ratio of 1∶1 as the matrix, the molar ratio of active hydrogen and vinyl is 1.2, and the ratio of spherical alumina with different particle sizes m(5 μm)∶m(15 μm)∶m(50 μm)=2∶5∶3. When the total filling amount of different sizes of spherical alumina reaches 500 parts, the silicone encapsulant has up to 1.50 W/(m·K) of thermal conductivity, up to 1.70 MPa of tensile strength, FV-0 of vertical combustion grade, and excellent operation and processing performance as well as dispersing stability, and its comprehensive performance is excellent.

Meta-aramid insulation paper is widely used in transformers and high-voltage bushings due to its excellent dielectric and mechanical properties, but its low thermal conductivity limits its application in high thermal load environments. To enhance the thermal conductivity of nano-filler/aramid insulation paper, this study employed simulation-guided experimental design to calculate the thermal conductivity of aramid simulation models. Three nano-fillers with excellent thermal conductivity properties, namely nano SiO₂ (KH570), nano TiO₂, and nano C₃N₄, were screened out. The mechanical and insulation performance of laboratory composite aramid paper hand sheets were compared, and the optimal filling amount was determined. Further, the influence of nano-fillers on the thermal conductivity of composite aramid paper was explored, and their inherent thermal conduction mechanism was analyzed. The results show that the optimal addition amounts of three nano-fillers are: nano SiO₂ (KH570) at 10%, nano TiO₂ at 4%, nano C₃N₄ at 4%. Through thermal conductivity testing, nano C₃N₄ is determined to be the optimal nano-filler, and the composite aramid paper with 4% of nano C₃N₄ showing an increase in elastic modulus by 135%, Young's modulus by 198%, electric strength by 60.24%, volume resistivity by 3 713%, and thermal conductivity by 304.31% compared with pure aramid paper.

Under the high temperature conditions (90, 105, 120, and 135°C), accelerated ageing tests of nitrile rubber (NBR) were conducted in hot air, hot oil, hot air compression, and hot oil compression. The ageing mechanisms were investigated through Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA/DTG), and scanning electron microscopy (SEM), and the effects of ageing temperature, time, and deformation conditions on the ageing behavior of NBR were revealed. The results indicate that crosslinking, oxidation, and chain-breaking reactions occur during the ageing process of NBR, and the crosslinking reaction is the predominant reaction. After ageing at 120°C, grooves appear on the surface of NBR, and after ageing at 135°C, defects such as holes and damages appear on the surface. In the early stage of ageing, transformer oil has a suppressive effect on the increase of permanent deformation under compression. In the later stage of ageing, transformer oil plays a promote role for the decrease of tensile strength, and the higher the temperature, the more obvious the effect.