Fabrication And Properties Of Graphene/PMMA Microcellular Composite Foams

Microcellular foam is considered as a new kind of cellular plastics with high cell density.The microcellular composite foam with lightweight,high strength and special properties has a wide range of applicitions in the areas of defence and military,auto protection,electromagnetic shielding,it can be obtained by adding a small content of nanoparticles on the basis of preparing microcellular foam.In this study,the graphene was added to PMMA matrix as a heterogeneous nucleation agent and reinforced filler,then the graphene/PMMA composite foams were prepared by supercritical carbon dioxide batch foaming in a special mold.The effect of surfaces chemical structure and morphology of graphene on the foaming condition,cellular structure and properties of graphene/PMMA composite foam had been investigated.Firstly,the graphene oxide（GO）was mixed with PMMA to fabricate GO/PMMA composites by solution blending.Subsequently,supercritical carbon dioxide was applied to fabricate dimensional controllable GO/PMMA composite foams by a batch foaming in a special mold.The cell morphology shows that the addition of a small number of GO caused a fine cellular structure with a high cell density and small cell size（less 1μm）.Due to the inhibitory effect of GO on the cell growth and highly heterogeneous nucleation efficiency,the changes of cell size with the increase content of GO are not very obvious.The thermogravimetric analysis shows that the degradation temperature of GO/PMMA composite foam increased about 10 ^oC compared with the degradation temperature of pure PMMA.Moreover,the stress-strain curve shows that the compressive yield strength of GO/PMMA composite foams are significantly improved compared with pure PMMA foam,and an improvement in specific compressive strength of 50%owing to its unique cell structure and strong interfacial strength.Secondly,GO was reduced by solvent thermal reduction in dimethylformamide（DMF）,and the reduced graphene oxide（RGO）/PMMA composites were prepared by solution blending.Then supercritical carbon dioxide was applied to fabricate RGO/PMMA microcellular foams.The UV-Vis absorption spectra of GO and RGO shows that a red shift in the maximum absorption wavelength was observed.The FT-IR spectra of RGO shows that the adsorptions of oxygen-containing groups evidently drop.And the XPS results further confirms that the GO has been reduced.The absorbing capacity of CO₂ in GO/PMMA and RGO/PMMA composites was measured by gravimetric analysis.It shows that the absorbing capacity of CO₂ in GO/PMMA and RGO/PMMA composites was decreased with the increase of GO an RGO content.And the absorbing capacity of CO₂ in RGO/PMMA is greater than GO/PMMA composites owing to the poor interaction of RGO with PMMA.The addition of a smaller number of RGO also caused a fine cellular structure with a high cell density and smaller cell size compared with pure PMMA foam.The RGO/PMMA microcellular foams exhibits a prominent improvement of conductivity when the RGO was reduced in DMF/N₂H₄ solution.Besides,the RGO also could increase the compressive yield strength of RGO/PMMA composites foam.Finally,GONRs and GNRs were obtained by oxidative unzipping multiwalled carbon nanotubes（MWCNTs）and solvent thermal reduction in DMF.Then they were mixed with PMMA to fabricate composites by solution blending and they were applied to fabricate microcellular conposite foams by a batch foaming in a special mold.The UV-Vis absorption spectra of MWCNTs and GONRs shows that a blue shift in the maximum absorption wavelength was observed.The FT-IR spectra of GONRs shows that the adsorptions of oxygen-containing groups evidently increased.And the TEM images further confirms that the MWCNTs has been unzipped.The morphology of cell structure shows that the addition of a smaller content of GONRs caused a fine cellular structure with a higher cell density and smaller cell sizes.The theoretical calculation indicate that the GNRs have a higher nucleation efficiency compared to MWCNTs.The obtained GNRs also could be used as a reinforcing filler to increase the mechanical properties of PMMA foams.An improvement in the specific compressive strength of 39%,and the thermal stability of GNRs/PMMA composite foams was enhanced too.