Preparation And Properties Of High-performance Polyimide Fiber Paper-based Electromagnetic Shielding Materials

With the rapid development of the 5G industry and the arrival of the era of artificial intelligence,the problem of electromagnetic interference between high-frequency components and electronic and electrical equipment has become increasingly severe,and the requirements for electromagnetic shielding materials in related products have become higher.However,traditional electromagnetic shielding materials cannot meet future demands due to their narrow shielding frequency range,poor mechanical properties,temperature resistance,corrosion resistance,and moisture resistance.Therefore,it’s urgent to develop a high-performance electromagnetic shielding material that is efficient,lightweight,easy to process,has a wide shielding frequency range,and has excellent corrosion resistance and mechanical properties.As a lightweight,shape-controllable structure-functional integrated composite material,paper-based electromagnetic shielding materials have a simple preparation process and meet the development needs of lightweight electromagnetic shielding materials,becoming an ideal alternative to traditional electromagnetic shielding materials.Based on wet papermaking technology and in-situ synthesis methods,this dissertation uses polyimide（PI）fibers with excellent properties such as high and low-temperature resistance,flame retardance,corrosion resistance,and radiation resistance as raw materials to prepare high-performance PI fiber paper-based electromagnetic shielding materials,achieving the functional utilization of PI fibers and expanding their application in the fields of conductivity and electromagnetic shielding.This research has important significance for the application of PI fibers in the field of high-precision materials and high-value utilization.The main research content and conclusions are as follows:（1）PI fibers were modified by alkali etching and dopamine impregnation,and then polypyrrole（PPy）/PI fiber conductive paper was prepared by wet papermaking and vapor-phase polymerization.Acid-base etching and dopamine impregnation can effectively improve the surface inertness of PI fibers,and then effectively improve the mechanical properties of PI fiber paper.In addition,by exploring the vapor-phase polymerization process of PPy,the optimal preparation process of PPy/PI fiber conductive paper was determined:the concentration of oxidant ferric chloride（Fe Cl₃）solution was 1.2 mol/L,the oxidant treatment time was 1 min,the polymerization reaction time was 60 min,the vacuum degree of the reaction environment was 0.08 MPa,and the drying temperature was 35℃.The preparation of PPy/PI fiber conductive paper achieved the functional application of PI fibers and expanded the application of PI fibers in the field of conductive materials,which also established a working foundation for the research of PI fiber paper-based electromagnetic shielding materials in the future.（2）A flexible,lightweight,and high-temperature resistant nickel-iron-phosphorus（Ni-Fe-P）/PPy/PI electromagnetic shielding paper was prepared by using the palladium-free chemical nickel plating process to metallize the surface of PPy/PI fiber conductive paper.The introduction of the metal coating gave the PPy/PI fiber conductive paper electromagnetic shielding properties and achieved secondary functionalization of PI fibers.The Ni-Fe-P/PPy/PI electromagnetic shielding paper attenuates electromagnetic waves through three mechanisms:dielectric loss and magnetic loss of the Ni-Fe-P alloy layer,dielectric loss of the internal PPy layer,and multiple interface losses.Its electromagnetic shielding effectiveness in the X-band can reach 85.07 d B.In addition,the electromagnetic shielding paper exhibited excellent high-temperature resistance,acid-alkali corrosion resistance,and fire safety performance,as well as good flexibility.Even after being bent repeatedly for 200times,its resistance only increased by 7.96%.Therefore,the prepared Ni-Fe-P/PPy/PI electromagnetic shielding paper has the potential to be used as a flexible conductive material or electromagnetic shielding material,and has broad application prospects in the fields of lightweight and portable electronic equipment or communication equipment.（3）The palladium-free chemical plating method can obtain good shielding performance,but it causes environmental pollution,so a simpler and environmentally friendly in-situ synthesis method was designed to replace the palladium-free chemical plating method.Firstly,a conductive metal framework materials（MOFs）Ni₃（HHTP）₂（also known as Ni-CAT）,was synthesized in situ,and a flexible and lightweight PPy/Ni-CAT/CF/PI electromagnetic shielding paper was prepared by combining vapor phase polymerization using carbon fiber（CF）as a high temperature resistant conductive reinforcement.The study found that the in-situ growth assembly of Ni-CAT and PPy was successfully achieved through in-situ synthesis and gas-phase polymerization strategies.The PPy/Ni-CAT/CF/PI electromagnetic shielding paper exhibited excellent conductivity and electromagnetic shielding effectiveness（～41.85 d B,X-band）,as well as resistance to acid corrosion and fire safety,making it possible for use in harsh environments.Therefore,the electromagnetic shielding paper has potential applications in the fields of flexible,lightweight conductive materials and electromagnetic shielding materials.In addition,the preparation method of PPy/Ni-CAT/CF/PI electromagnetic shielding paper provides a flexible and feasible,as well as simple and environmentally friendly strategy for preparing PI fiber-based electromagnetic shielding materials.（4）In order to further improve the electromagnetic shielding performance and alkali corrosion resistance of PI fiber paper-based electromagnetic shielding materials,a multifunctional MWCNTs/PPy/Ni-CAT/CF/PI electromagnetic shielding paper was prepared by introducing PI/multi-walled carbon nanotubes（MWCNTs）functional coating on its surface through a coating process using a self-made PPy/Ni-CAT/CF/PI electromagnetic shielding paper as the base material.The results show that the introduction of the PI/MWCNTs functional coating enhances the electromagnetic shielding effectiveness of the MWCNTs/PPy/Ni-CAT/CF/PI electromagnetic shielding paper in the X-band（～57.83 d B）,and also significantly improves its mechanical strength,increasing the tensile strength index from 22.31 N·m/g to 29.84 N·m/g,which is an improvement of almost 33.56%.The MWCNTs/PPy/Ni-CAT/CF/PI electromagnetic shielding paper also exhibits excellent acid and alkali corrosion resistance,flame retardancy,and fire safety.In addition,the electromagnetic shielding paper can also be used as an electric heating material,giving the paper-based electromagnetic shielding material multi-functionality.（5）In order to further improve the electromagnetic shielding performance and mechanical properties of PI fiber paper-based electromagnetic shielding materials,a MWCNTs/PPy/Ni-CAT/CF/PI composite board with a multilayer structure was prepared by hot pressing using self-made MWCNTs/PPy/Ni-CAT/CF/PI electromagnetic shielding paper as the base material.The study shows that the multi-layered structure design can effectively enhance the electromagnetic shielding efficiency of the electromagnetic shielding paper without affecting its electromagnetic shielding mechanism.However,the electromagnetic shielding efficiency of the MWCNTs/PPy/Ni-CAT/CF/PI composite board does not continuously increase with the stacking of shielding layers,but shows a tendency to saturate.When the shielding layer reaches 5 layers,its electromagnetic shielding efficiency in X-band can reach 81.70 d B.In addition,the multi-layered structure design not only does not affect the fire safety performance of the electromagnetic shielding paper,but also enhances its mechanical properties.Compared with the single-layer electromagnetic shielding paper,the tensile strength of the 5-MWCNTs/PPy/Ni-CAT/CF/PI composite board is increased by nearly379.61%.Therefore,the multilayer structure of MWCNTs/PPy/Ni-CAT/CF/PI composite board can serve as an efficient electromagnetic shielding material with potential applications in electronic devices,aerospace,automotive industry,and other fields.The above results show that multiple technical means such as in situ synthesis and gas-phase polymerization have realized the functional expansion of PI fiber paper in the field of electromagnetic shielding,which provides theoretical basis and technical support for the preparation of PI fiber paper-based electromagnetic shielding materials.