| With the development of information technology,intelligent electronic equipment has been widely used,followed by increasingly serious electromagnetic radiation pollution,for electronic equipment and human safety and health to provide safe and reliable electromagnetic protection is becoming more and more important.Polymer-based electromagnetic shielding composites have developed rapidly in the field of electromagnetic protection due to their advantages of light weight,easy processing and strong designability.However,the current electromagnetic shielding composite materials usually only have a single shielding performance,which can not meet the multiple functional requirements in the application environment.How to develop a variety of properties of polymer-based electromagnetic shielding composites and realize the multifunctional materials is the focus of current research direction.In this paper,three new multifunctional electromagnetic shielding composites are prepared with the aim of interface structure design,conductive network construction and performance research of conductive polymer composites.The specific research contents are as follows:(1)Based on the S-Ag coordination between polyphenylene sulfide(PPS)and metallic silver(Ag)at high temperature,high-performance PPS resin particles were selected as the deposition substrate.Ag/PPS conductive particles were prepared by chemical deposition.Then,the hot pressing process was used to extrude the metal Ag at the boundary of the adjacent PPS particles by using the volume repulsion effect caused by the weak flow of PPS particles at slightly lower melting temperature,and the isolated conductive network was prepared.Based on the structural advantages of the isolated conductive network,the prepared Ag/PPS composite has a conductivity of 88,000 S/m when the silver content is only 1.48 vol%,a shielding efficiency of 87.8 d B in X-band,and a thermal conductivity of 1.15 W M-1 K-1.At the same time,thanks to the interface strengthening effect of S-Ag coordination,the tensile properties of Ag/PPS composites are not weakened by the introduction of Ag,but improved to a certain extent.When the silver content is 0.89 vol%,the tensile strength reaches 59.62 MPa.In addition,the Ag/PPS composite also has good tribological properties,with a friction coefficient as low as 0.15 and a wear rate of 6.94×10-5 mm~3/Nm.With the excellent corrosion resistance and flame retardant of PPS,Ag/PPS composite has good solvent resistance and flame retardant,and also shows excellent electromagnetic shielding stability in solvent resistance and flame retardant test.In addition,due to the strong antibacterial capacity of Ag+,the Ag/PPS composite has good antibacterial activity.(2)In view of the strong adhesion of polydopamine(PDA),the pretreatment process was simplified by introducing PDA instead of chemical deposition.Poly-p-phenylene terephthamide(PPTA)was selected as the substrate and metallized by dopamine-assisted chemical deposition.Then,the Ag/PDA/PPTA composite films were encapsulated by PPS resin with excellent comprehensive performance.By virtue of dense continuous conductive network and laminated structure,the electromagnetic shielding efficiency of the film is up to 64.3 d B.Due to the excellent mechanical properties of PPTA and the interface strengthening effect of S-Ag coordination,the tensile strength of the film is higher than 200 MPa at low temperature,normal temperature and high temperature,showing excellent tensile properties.Furthermore,the Ag/PDA/PPTA/PPS composite films have excellent tribological properties,with the friction coefficient as low as 0.22 and the wear rate as low as 0.7×10-5 mm~3N-1m-1.The high efficiency three-dimensional conductive silver network gives the Ag/PDA/PPTA/PPS composite film excellent electric heating performance.When the driving voltage is 2 V,the film can reach the saturation temperature of 91.2?in only 50 s.In the face of gradient voltage changes,the film can respond instantly;Moreover,the film has reliable long-term heating stability and can maintain the saturation temperature of 3600 s when the driving voltage is 1.5 V.PPTA fiber brings good flexibility to Ag/PDA/PPTA/PPS composite film.The structure of sulfur atom and benzene ring alternately connected in PPS molecular chain gives the film excellent flame retardant and solvent resistance.In addition,the film shows excellent shielding stability after several times of bending,high temperature combustion and solvent immersion.(3)The melamine foam(MF)with three-dimensional network structure was selected as the matrix skeleton,and Ag layer was deposited on the MF surface by dopamine-assisted chemical deposition technology,so as to construct a dense and uniform conductive network.Based on the high density and high conductivity of the conductive network,when the silver content is only 3.04 wt%,the shielding efficiency is up to 60.5 d B.Moreover,the highly efficient conductive network also brings excellent electric heating performance to the material,and the precise control of the material temperature can be realized by adjusting the driving voltage.Thanks to the enhanced protection of elastomer PDMS,the Ag/PDA/MF/PDMS composite also has excellent compression performance,with compression strength up to 258k Pa and compression modulus up to 1.64 MPa.At the same time,the material also has good hydrophobicity,can effectively prevent the corrosion of different p H solutions. |
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