Study On Preparetion, Structure And Properties Of Graphene/Polymer Composites

Graphene is a novel filler to improve properties of polymer. The dispersion of grapheneis the key point to prepare graphene/polymer composites. Graphene oxide (GO), modifiedGO and reduced graphene oxide (rGO) could be well dispersed in polymers to solve thedispersion problem. GO is an important derivative of graphene. There are plenty of oxygen-containing groups on the edge of GO sheets, so that GO could be well dispersed in waterand other polarity organic solvents. In this thesis, we prepared GO by Hummers methods.GO/ethylene–vinyl acetate copolymer (EVM) composites and rGO/Fluoroelastomer (FKM)composites were made by solution blending. Polyamide6(PA6)/GO/polystyrene (PS) wereprepared by melting blending. GO/Poly(styrene-co-butyl methacrylate)(P(St-co-BMA))composites were synthesized by in situ emulsion polymerization. The dispersion ofgraphene in each system were studied. The mechanical, thermal and dielectric properties,thermal conductivities and microwave absorption of the composites were also studied. Themajor contents are follows:GO was prepared by modified Hummer’s method. GO/EVM composites were made bysolution blending. The homogeneous dispersing state of GO in EVM matrix is identified bythe scanning electron microscopy (SEM) and X-ray diffraction (XRD) results. The Halpin-Tsai model was used to predict the modulus (at300%extension) of different distributedfiller-reinforced composites and the dispersing state of GO in EVM, which confirms thatthe GO sheets were dispersed in EVM randomly throughout the composites. The tensilestrength of EVM increased from19.4to22.8MPa, and the modulus at300%elongation ofEVM increased from2.7to4.8MPa as the GO content increased to1phr. The enhancementin strength and modulus of GO/EVM composites was attributed to good dispersion of GOand strong interfacial interactions between GO and EVM matrix. The thermogravimetricanalysis tests showed the GO/EVM composites had higher thermal stability than EVM.rGO/FKM composites were in situ prepared by solvent thermal reduction method in N,N-dimethylformamide (DMF) solution. The reduction of GO was certified by X-Rayphotoelectron (XPS), Ultraviolet-Visible (UV-Vis) and Fourier transform infrared (FTIR)spectra. The dispersibility of rGO was improved after solvent thermal reduction, which wasconfirmed by SEM and XRD. GO and rGO were both efficient fillers to improve themechanical properties of FKM. The dielectric permittivity of rGO/FKM (5phr) was26.4atthe frequency of10-1Hz, higher than that of FKM (8.1). The thermal conductivity ofrGO/FKM composites was also higher than that of FKM.The unique amphiphilic structure of GO creates the possibility of using it as a newcompatibilizer in certain immiscible blends. GO was incorporated into immiscible PA6/PS(80/20wt%) blend as a compatibilizer. SEM images clearly showed that the dimension ofPS dispersed particles decreased markedly and became more uniform by the incorporationof GO, indicating a significantly improved compatibility in the GO-filled PA6/PS blends,which was further proved by dynamic mechanical analysis (DMA). The improvedcompatibility was possibly attributed to the matched surface energy as well as lowinterfacial energy between PA6and PS/GO. The application of GO led to enhanced tensileand impact properties. The elongation at break increased as much as270%and the ruptureenergy increased nearly340%after the addition of0.1wt%of GO. The compatibilizing andreinforcing effects of GO were contributed to the remarkably enhanced mechanicalproperties.GO/P(St-co-BMA) composites were synthesized by in situ emulsion polymerization.Then GO was reduced by hydrazine. The structure and properties of the composites werecharacterized. The results showed that the addition of GO could increase the glass-transitiontemperature of P(St-co-BMA). The initial thermal decomposition temperature of rGO/P(St-co-BMA) is much higher than P(St-co-BMA) or GO/P(St-co-BMA). The mechanicalproperties were highly improved after the addition of GO. The tensile stress of rGO/P(St-co-BMA) was further increased.