| The development of information technology,the wide application of artificial intelligence,Internet of Things and big data information,and the popularization of 5G technology have a profound impact on the development of human society.The development and dissemination of information is inseparable from the use of electromagnetic waves and electronic equipment.They interfere with each other's operation and cause irreversible damage to humans and other creatures.In addition to prohibiting from the source,research and development of electromagnetic shielding materials become the main means to cut off electromagnetic interference,lightweight,efficient,flexible electromagnetic shielding composite materials become the pursuit of the goal.At present,there are two types of composite materials with electromagnetic shielding properties,metal-based and polymer-based.Although metal electromagnetic shielding materials have excellent electromagnetic shielding performance,their electromagnetic shielding mechanism will cause secondary pollution of electromagnetic waves,and metal electromagnetic shielding materials also have disadvantages such as high density,easy corrosion,and poor flexibility.Although polymer-based electromagnetic shielding composite materials have the characteristics of light weight and corrosion resistance,their electromagnetic shielding performance is poor because most polymers themselves do not have electrical conductivity or have low electrical conductivity.In order to improve the electrical conductivity of polymer-based electromagnetic shielding materials,conductive fillers are usually used to improve the performance.The carbon material with light weight,large aspect ratio and good electrical conductivity mainly plays an absorbing role in the electromagnetic shielding mechanism,which can effectively avoid the secondary pollution of electromagnetic wave.The requirements of electromagnetic shielding performance can be partially realized by adjusting the content and types of filler.In order to overcome the shortcoming that single-phase carbon filled nanocomposites cannot provide effective electromagnetic shielding,a two-phase mixture of carbon and metal was applied to the electromagnetic shielding composites.The synergistic effect between them not only improved the conduction loss and dielectric loss,but also provided multiple reflection loss.This paper aims at the problems of low electromagnetic shielding performance,high quality and strong rigidity of polymer-based electromagnetic shielding composite materials at this stage.Based on the light weight of PEEK resin,excellent mechanical properties,corrosion resistance,and strong thermal stability Characteristics,using PEEK as the fiber matrix,by adding MWCNTs to improve the conductivity of PEEK fibers,MWCNTs doped PEEK fibers(MWCNTs/PEEK fibers)were prepared.Soluble PEEK precursor(PEEK-1,3 dioxolane)coated MWCNTs as filler can effectively improve the agglomeration problem of carbon nanotubes,while PEEK-1,3-dioxolane can be converted into PEEK,no other impurities are introduced into the whole system.Using MWCNTs/PEEK fiber as the matrix,by adjusting the content of CNTs in the impregnating liquid and the type and content of conductive fillers(carbon fiber,copper-coated PEEK fiber(Cu@PEEK fiber))in the resin matrix,through suction filtration a series of PEEK fiber composite papers with electromagnetic shielding properties were obtained through the steps of paper,dipping and hot pressing.Due to the existence of conductive fibers and conductive fillers,a 3D conductive network appeared inside the PEEK fiber composite paper,which is beneficial to improve the electromagnetic shielding effectiveness of the material.The results show that the increase of CNTs-COOH content in the impregnation solution has a positive effect on the electrical conductivity and electromagnetic shielding performance of MWCNTs/PEEK fiber composite paper,and the increase of the content of conductive fibers(Cu@PEEK and CF fiber)has a positive effect on the electrical conductivity and electromagnetic shielding performance of Cu@PEEK+MWCNTs/PEEK and CF+MWCNTs/PEEK fiber composite paper.When the content of Cu@PEEK and CF fibers is equal,the electrical conductivity and electromagnetic shielding performance of Cu@PEEK+CF+MWCNTs/PEEK fiber composite paper are the best.MWCNTs/PEEK,Cu@PEEK+MWCNTs/PEEK,CF+MWCNTs/PEEK,Cu@PEEK+CF+MWCNTs/PEEK fiber composite paper are absorption based electromagnetic shielding materials.MWCNTs/PEEK fibers were lapped with Cu@PEEK or CF fibers to form a 2D network structure,and CNTs combined with the 2D network structure constituted a spatial 3D effective conductive network.The conductivity and electromagnetic shielding properties of 0.30CF fiber composite paper are 11.81S·cm-1and 40.6 d B,and those of 0.15CF+0.15Cu@PEEK can reach 14.37 S·cm-1 and 54.4 d B.MWCNTs/PEEK,Cu@PEEK+MWCNTs/PEEK,CF+MWCNTs/PEEK,Cu@PEEK+CF+MWCNTs/PEEK fiber composite paper can maintain a certain conductivity and electromagnetic shielding performance after being treated by harsh temperature.The conductivity of 0.15CF+0.15Cu@PEEK composite paper after being treated by high temperature oven is 11.2 S·cm-1.The electromagnetic shield value is 47.2 d B.After irradiation with 0.3CF and 0.15CF+0.15Cu@PEEK composite paper by circulating n IR high frequency laser,the electrical conductivity and electromagnetic shielding performance of PEEK resin decreased due to the presence of Cu O generated by Cu oxidation and partial softening and melting of PEEK resin during n IR high frequency laser irradiation.However,PEEK fiber composite paper still maintained high electromagnetic shielding performance under harsh near-infrared high-power laser irradiation.The conductivity and electromagnetic shielding value(12GHz)of 0.15CF+0.15Cu@PEEK composite paper were 11.11 S·cm-1 and 43.5d B.In addition,MWCNTs/PEEK,Cu@PEEK+MWCNTs/PEEK,CF+MWCNTs/PEEK,Cu@PEEK+CF+MWCNTs/PEEK fiber composite paper can be used in a high temperature environment for a long time,and has good thermal stability. |
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