| Electromagnetic radiation that interrupts the function of equipments and affects the human health is ubiquitous in human production and life.Electromagnetic shielding is an effective measure to solve this problem.With the iterative upgrade of electronic technology,electronic device components have become more complex and developed in the direction of miniaturization,weight reduction,densification and high efficiency,which also puts more stringent indicators on new electromagnetic shielding materials.Polyurethane composites have become the ideal new electromagnetic shielding composite matrix due to their advantages of easy processing,chemical corrosion resistance,controllability and ease of construction.In order to impart lightweight and efficient electromagnetic shielding performance to the polyurethane nanocomposite,the microporous structure and the conductive network of polyurethane nanocomposites was constructed by adding fillers with high conductivity.Traditional fillers such as metal particles,graphene,carbon black,carbon fibers and carbon nanotubes need high filling content,and difficult to disperse uniformly in polyurethane matrix,which affects the processing and comprehensive properties of composites.Therefore,controlling the microporous structure of polyurethane and the dispersion and distribution of fillers,and efficiently constructing a perfect three-dimensional conductive network become the key to develop new high-performance polyurethane-based electromagnetic shielding composites.In this paper,a series of polyurethane composites with special microstructures were prepared,which have the advantages of high strength,light weight and high electromagnetic shielding effectiveness.The non-covalent bond modification on the surface of carbon nano-fillers realized the uniform dispersion and controllable distribution of fillers in polyurethane matrix.The effects of filler morphology and dispersion state on the microstructures,electrical conductivity,electromagnetic interference shielding effectiveness(EMI SE)and mechanical properties of composites were studied,and the interaction mechanism between the structure and properties of composites was explored.The main research contents are as follows:1)Water-borne polyurethane(WPU)based nanocomposites with graphene nanoplates(GNs)/Fe3O4 and multi-walled carbon nanotube(MWCNTs)/Fe3O4 as hybrid nanofiller were fabricated using hybrid emulsions polymerization method,and their dielectric properties and electromagnetic interference shielding effectiveness(EMI SE)performance were carefully investigated.The carbon nanofillers showed good dispersion in PU matrix because cation-? interactions between carbon fillers and WPU end-capped by ionic liquid(IL)with amino groups enhance interfacial interaction between carbon fillers and PU matrix.The results show that PU/MWCNTs-IL composites were more efficient in EMI SE and dielectric properties in comparison with PU/GNs-IL composites because of the one-dimensional geometry of MWCNTs and better tendency to form a conductive network of MWCNTs.Magnetic Fe3O4 nanoparticles can enhance the EMI SE of PU/GNs-IL/ Fe3O4,but inhibit the EMI SE of PU/MWCNTs-IL/ Fe3O4 because the two-dimensional geometry of GNs can restrain the strong magnetism attraction interaction between the Fe3O4 and weaken aggregation of GNs.2)Polyurethane/multi-walled carbon nanotubes(PU/MWCNT)nanocomposite foam introducing two different aspect ratio MWCNT(MWCNT-L and MWCNT-S)with closed spherical structures and excellent electric properties have been successfully prepared by an environmentally benign water-blown method.The morphological,electrical conductivity,mechanical and EMI SE were characterized to establish a correlation between the morphologies and EMI shielding performances.It was found that the PU with MWCNT-L and MWCNT-S hybrids(PU/MWCNT-L-S)display better EMI shielding performance and more uniform cell morphological compared with PU/MWCNT-L foams at the same filler loading.The PU/MWCNT-4L-4S foams exhibited low density of 0.30 g/cm3,compressive strength of 3.3 Mpa and excellent specific EMI SE of 60.6 d B/(g/cm3)over the X-band.The regularity and uniformity of cellular microstructure in PU/MWCNT-4L-4S contributed to the remarkably improvement of compressive stress.The lightweight and high-performance EMI shielding composite foams can be applied to electronics and aerospace fields.3)Polyurethane composites with microporous structure were prepared by non-solvent induced phase separation(NIPS),and the microstructure of the composites was controlled by the synthesis of specific structured polyionic liquid(PIL)modified carbon nanotubes.The effects of filler content and surface drying time on the microstructure and electromagnetic shielding performance of the composites were investigated.The results show that the cation-? bond interaction between PIL and MWCNT improves the dispersion of MWCNT in the casting solution,and provides a uniform heterogeneous nucleation site for physical gelation phase separation into pores.The filler content has a positive correlation with the electrical conductivity and EMI SE of the composite.The conductivity and EMI SE of PU/25MWCNT/PIL was 15.39 S/cm and 34 d B,respectively.The conductivity and EMI SE of the composite microporous structure are gradually increased by the surface drying time.The electrical conductivity and EMI SE of PU/20MWCNT/PIL-120 can reach 8.72 S/cm and 58 d B,respectively.The specific shielding effectiveness reached up to 216.1 d B/(g/cm3).4)The combination of Ni-CNT with high magnetic permeability and MWCNT with high conductivity was used as a conductive filler to electromagnetically enhance the electromagnetic shielding performance of the composite.The dispersion and distribution of fillers and the microstructures of composites were regulation by the fillers modification of PIL.The effects of surface dry time and thickness on the microstructure and EMI SE of composites were investigated.The results show that there is a cation-? bond interaction between PIL and the filler,which improves the dispersion of filler,and the microporous structure become compact,uniform and smaller in size.The EMI SE of composite PU/Ni-CNT/PIL and PU/Ni-CNT/MWCNT/PIL was 32 d B and 64 d B,respectively,and the absorption efficiency plays a major role,the specific shielding effectiveness was 88.9 d B/(g/cm3)and 148.8 d B/(g/cm3). |
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