Microstructure Design Of PVDF/PLA/MWCNTs And Their Electromagnetic Shielding Performances

With the rapid improvement of the utilization rate of electronic equipment,electromagnetic radiation has become one of the main problems concerned by today’s society.It will not only affect the normal operation of electronic equipment and medical instruments,but also bring environmental pollution to our daily life.Therefore,it is necessary to develop shielding materials which can attenuate these harmful radiation.In general,multi-walled carbon nanotubes(MWCNTs),carbon black(CB),graphene nanosheets(GNPs),silver nanowires(Ag NWs)and 2D transition metal carbon(nitrogen)compounds(MXene)are widely used as conductive fillers for the preparation of highly efficient electromagnetic interference shielding conductive polymer composites(CPCs).However,the preparation of CPCs with excellent electromagnetic shielding efficiency(EMI SE)requires a high content of conductive fillers,which results in high cost,reduced machinability and poor mechanical properties of the materials.At present,there are three effective methods to prepare CPCs with high EMI SE,such as packing combination,construction of isolation structure and double percolation structure.These three schemes can achieve high electromagnetic shielding efficiency and electrical performance at a lower content of conductive filler.The selective distribution of fillers in blends,is generally governed by thermodynamic and kinetic factors such as compounding sequence,mixing time,blend viscosity ratio,and the interaction between filler and polymer.In order to reducing the percolation threshold of composites,recent studies have shown that CPCs achieve artificially controlled MWCNTs distribution has become a hot research topic.Firstly,using PVDF as polymer matrix,PLA as template phase and MWCNTs as conductive filler,we prepared PVDF/PLA/MWCNTs ternary mixture by solution flocculation and hot pressing.Then the PLA template phase was selectively etched by DMC,and finally the co-continuous PVDF/MWCNTs composites were prepared.The selective distribution of MWCNTs on the surface of PVDF was achieved by using the full crystallization of PVDF in DMF and the rotation radius of PVDF similar to that of MWCNTs.Therefore,the conductivity of the porous composite is enhanced by the selective distribution of MWCNTs on the PVDF surface.At the same time,this work attempts to systematically clarify the relationship between blend morphology,MWCNTs selective distribution,and electromagnetic interference shielding properties of polymer blends.Based on the first experiment,we selected PMMA surface modified MWCNTs with good compatibility with PVDF to regulate the selectivity distribution of fillers in PVDF/PLA.We realized the selective migration of PMMA@MWCNTs from the PVDF surface to the PVDF matrix.In addition,it is found that the introduction of high content of PMMA@MWCNTs does not change the nature of the polymer as an insulator,making the overall conductivity of the composite material basically unchanged.Therefore,this study opens up new ways for the design of advanced composite materials(such as high dielectric and low loss materials and electromagnetic shielding materials in high frequency range,etc.),which can meet the needs of more fields.To prepare CPCs with low percolation threshold and high electromagnetic shielding performance,MWCNTs were used as conductive filler and PE-UHMW matrix,and PVDF,PMMA and PLA were used as structural regulatory matrix.Multilevel porous PEUHMW/PVDF/MWCNTs composites were prepared by hot pressing,phase separation,crystallization template and selective etching of PLA/PMMA template phases.Based on thermodynamic prediction and morphological observation,it was found that MWCNTs broke through the high viscosity of PE-UHMW and migrated to PVDF phase.Thus,the electrical conductivity of CPCs is enhanced by the migration of MWCNTs in the blend,and the percolation threshold is comparable to that of double percolation structures.In this paper,the electromagnetic shielding properties and mechanism of multilevel pore isolation structural composites are compared and discussed.This work systematically illustrates the relationships among blend morphology,selective distribution and migration of MWCNTs,electrical properties of polymer blends,and electromagnetic interference shielding properties.