Synthesis,Characterization And Properties Of Graphene/Polymer Nanocomposites

Graphene has wide applications in the field of polymer nanocomposites due to their excellent mechanical properties and electrical conductivity, large specific surface areas and unprecedented adsorption properties, et al. In this thesis, we obtained the fully exfoliated graphene oxide (GO) solids which were stable at room temperature by colloidal flocculation method. Then GO solids were used as precursors to prepare graphene/polymer nanocomposites by different methods, and the properties of the composites were also studied. The dissertation is mainly focused on:(1) Bulk obtaining the fully exfoliated graphene oxide solids by colloidal flocculation method. Firstly, GO colloidal solutions were prepared from nature graphite by Staudenmaier oxidation method. Then Different flocculants (KC1, NaOH, KI, Na2SO4) were used to coagulate GO colloidal, and it was found that NaOH had the most obvious coagulation effect to GO solution. When the concentration of NaOH is0.3mol·L-1, coagulation began to appear and the higher concentration of NaOH, the more coagulations were observed. Finally, GO solids can be obtained from these flocculates by purifying and drying. The well-dispersed solution is still transparent and bright-yellow when the products were dissolved in deionized water and ultrasonicated dispersion. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD) analysis demonstrated that there were a large number of single-layer GO sheets with thickness of about0.8nm. Liquid state13C NMR and Fourier transformation infrared spectra (FTIR) showed the presence of abundant benzene carboxylic, hydroxyl and epoxide groups in the basal planes of GO. In addition, GO was reduced to graphene by ammonia and hydrazine and the properties of GO and graphene were compared.(2) Preparation and performance of graphene/low density polyethylene (LDPE) nanocomposites. Graphene sheets were functionalized by coupling agent-vinyl triethoxysilane (VTES) and then blend them with LDPE to prepare nanocomposites. After modifing graphene by VTES, the surface energy of graphene was decreased and the affinity with the polymer matrix was enhanced and aggregation among graphene sheets were reduced, so the dispersion of graphene in polymer matrix and the overall performance of the composites would be improved. Structure characterizations proved that graphene sheets were covalently bonded with VTES. SEM proved that the dispersion of modifing graphene was better than the unmodified one in LDPE matrix. Mechanical properties testing proved that after adding a small amount of VTES functionalized graphene, the resulting nanocomposites revealed the increases of up to27.0%,92.8%and17.7%in the tensile strength, Young’s modulus and elongation at break, respectively, compared to neat LDPE. We also studied the solvent permeability property of the composites, which showed that the absorption ratio of the composites decreased from56%to39%. So graphene can be utilized as barrier materials like the clay and montmorillonite.(3) Preparation and performance of graphene/poly vinylalcohol (PVA) nanocomposites films by solution mixing method. Firstly, incorporating GO into PVA aqueous solution and then reduced GO to graphene sheets, finally obtained the graphene-reinforced PVA composite films by vacuum drying method. The resulting nanocomposites revealed the increases of up to212%in the tensile strength and34%in the elongation at break with only0.5wt%graphene contents. We also studied the water resistance property of the composite films by water absorption measurements and contact angle measurements. It was found that the water absorption ratio of the graphene/PVA composites decreased from105.2%to48.8%and the contact angle increased from36°to97°with small graphene content comparing with pure PVA. These measurements showed that the surfaces of PVA films transform from hydrophilic to hydrophobic, greatly improved the water resistance of PVA.