| Plastic film capacitors,with their ultra-fast charging and discharging speed and high operating voltage,are essential core components in equipment such as ultra-high voltage transmission and electromagnetic catapults.In the civilian sector,they are widely used due to their low production costs,high reliability,and stability.However,the current Plastic film capacitors mostly use linear dielectric materials,which have a generally low dielectric constant,resulting in a low energy storage density that cannot meet actual application needs.Poly(methyl methacrylate)(PMMA)is a near-linear dielectric material.The dielectric constant of PMMA is higher than traditional linear polymers,and the energy efficiency is higher than that of fluoropolymers.It has been widely researched as a high-energy polymer matrix and excellent modified composite material with high-energy fluorinated polymers.However,most of the currently commercially available PMMAs have the problem of high dielectric loss.This paper aims to solve this problem through structural design and provide a reference for the research of low-loss PMMA.Based on the design idea of the all-organic polymer dielectric,two methods to reduce the dielectric loss of PMMA were proposed,a variety of composite modification systems were designed,and the following work was carried out:(1)To reduce PMMA dielectric loss,two research approaches were attempted.Firstly,low-impurity PMMA matrix was synthesized using the homopolymerization method.The influence of different initiator contents on the electrical properties of PMMA was systematically studied,and PMMA synthesized with higher initiator content had higher breakdown voltage.Secondly,low-loss monomer styrene(St)was introduced and copolymerized with methyl methacrylate(MMA)monomer to synthesize copolymers(referred to as MS),which effectively reduced dielectric loss.The MS copolymer synthesized with MMA-to-St monomer volume ratio of 2:8 had a dielectric loss of 0.7%at an electric field frequency of 1 k Hz.(2)Design and prepare a variety of all-organic multi-component composite systems The low-loss PMMA and MS synthesized in this article were compounded as modified composite materials into a high-energy and high-loss poly(vinylidene difluoride-hexafluoropropylene)(P(VDF-HFP))matrix.It was found that PMMA had good compatibility with P(VDF-HFP),and it improved the energy efficiency,Withstand voltage resistance,and insulation performance of the composite system.The insulating performance and charge-discharge efficiency of the MS/P(VDF-HFP)binary composite system are enhanced.However,the insulation performance and energy efficiency of the polymer matrix have been enhanced Compounding low amounts of MS into low-loss PMMA,the dielectric energy storage performance of linear polymer systems was studied.The results showed that the composite system had good compatibility,reduced dielectric loss,increased energy efficiency,and obtained a discharge energy density of 5 J/cm~3 at an electric field of 5500 k V/cm.The energy efficiency remained at a high level of 83%,and the energy storage performance was relatively high in linear dielectrics.(3)In this paper,two kinds of multi-layer composite systems were designed and prepared,among which the five-layer composite film has better dielectric energy storage properties.The study found that the multilayer composites can effectively improve the dielectric energy storage characteristics of the polymer matrix.The prepared five-layer composite film maintains a charge-discharge efficiency of 90%under a 4500 k V/cm electric field and achieves a discharged-energy density of 4.7 J/cm~3. |
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