Prepartion Of Crumpled Graphene Micro-Spheres And Its Applications In Composites

Graphene oxide(GO),as a sort of precursor of graphene,can be facilely and massively obtained by oxidation of natural graphite.Different from graphene,there are abundant oxidation groups(e.g.,hydroxyl,carboxyl,epoxy,carbonyl,etc.)on GO sheets.The oxygen-containing groups render GO soluble in water as single-layer sheets,and GO forms liquid crystal(LC)in proper solvents.Generally,the solid content of GO aqueous dispersion is no more than 3 wt%,which brings inconveniences to transportation,storage and application of GO.However,conventional drying procedures including lyophilization and aerosol spray pyrolysis cannot produce soluble GO powder.Accordingly,this thesis produced uniform flower-shaped GO(fGO)microspheres via a low-temperature spray drying procedure.Such GO powder can be dissolved in water and some other solvents,even after being compressed into a compact disk with a density of 1.26 g/cm3.The aqueous dispersion of fGO is identical to pristine GO dispersion.We applied the dissolution strategy of fGO in the fabrication of polymer composite,and prepared graphene/PA6 nanocomposite by in-situ polymerization of fGO and caprolactam.SEM tracking proves that fGO transforms into single-layer GO sheets while stirring in melted caprolactam.Therefore,the following in-situ polymerization produced PA6-grafted reduced GO.The yield stress and tensile modulus of graphene/PA6 nanocomposites increase by 16.7%and 15.9%compared with pure PA6,and there are also remarkable enhancements in flexural strength and flexural modulus.Meanwhile,graphene/PA6 shows outstanding UV ray radiation resistance.The excellent dispersion of graphene in the composite is favorable to high-speed continuous spinning.The strength and modulus of the composite fiber increase by 25.4%and 49.5%,and the fabric displays great UV protection,far-infrared emission,flame retardance,showing extensive potential in high-performance and multifunctional fabrics.Based on the highly crumpled fGO,we fabricated porous crumpled graphene microspheres(Gmfs).Folded graphene sheets assemble into flower-shaped microparticles,forming a skeleton structure with a high surface area of 230 m2 g-1 and a low density of 40～50 mg/cm3.The maximum efficient absorption bandwidth(EAB,reflection loss ≤-10 dB)reaches 5.59 GHz and the minimum RL is up to-42.9 dB,which is higher than pure graphene fillers and most graphene-based materials in literature.Moreover,the low filler content(10 wt%)indicates high cost-efficiency,benefiting practical applications.Furthermore,a thermal annealing of fGO gave rise to graphene micron hollow spheres(GMPs).The fabricated GMPs feature an ultralow tap density(6-8 mg cm-3),a high surface area(947 m2 g-1)and a high solvent absorption capability(62 g g-1).The incorporation of GMPs into paraffin leads to a low percolation threshold of 0.18 vol%(0.51 wt%)and a 358%enhancement in thermal conductivity.The hollow shells of GMPs can enclose paraffin inside with enhanced thermal stability and latent heat storage,showing potential in phase change materials.Besides,the 2.5 wt%GMPs/paraffin composite shows peak absorption up to-45.4 dB with a wide efficient absorption bandwidth(EAB,reflection loss ≤-10 dB)of 6 GHz for the MA application.Such MA performance accompanied with an ultralow filler content surpasses all functionalized graphene and most graphene-based composite fillers ever reported.