Due to their different molecular structures, epoxy resins (EP) can exhibit different properties. And because it is easy to be mixed with different curing agents, diluents, auxiliaries, etc., to prepare epoxy resin materials with excellent mechanical, mechanical, thermal, adhesion, insulation and anti-corrosion properties, and is widely used in anti-corrosion coatings. . However, with the complication of the application environment, the simple EP coatings show some deficiencies: First, due to poor thermal conductivity, resulting in poor heat resistance, most EP is only suitable for the environment below 100 °C; Second, due to the high cross-link density after curing, As a result, the friction coefficient is high, and the wear resistance and impact resistance are poor. Third, the resistivity is high and the electrostatic effect is easily generated. The fourth is that after curing, defects are easily generated and the corrosion resistance is affected. To better utilize the advantages of EP, fillers are often added to improve performance.
Graphene has great potential in improving the properties of resin-based materials due to its unique crystal structure and excellent physical properties and its derivatives can initiate the polymerization reaction. Since graphene has a large specific surface area and a high surface energy, it is easily agglomerated when added as a filler to an epoxy resin, thereby affecting the performance of the coating. In order to evenly disperse graphene into epoxy matrix, scholars have conducted a lot of research. From the initial simple mixing, ultrasonic dispersion technology was developed, and a silane coupling agent was used to improve the adhesion and compatibility between graphene and epoxy resin. It was found that the addition of graphene improves the performance of the coating, but when added to a certain amount, the accumulation of graphene will affect the further improvement of the coating performance. In recent years, some scholars have prepared functionalized graphene by functional group modification on the surface of graphene. It was found that while retaining the graphene-based properties, it can improve the adhesion to the epoxy matrix, making graphene/epoxy. Research on resin composite coatings has made new progress.
1. Research Progress of Graphene/Epoxy Resin Coatings
From the thermal performance point of view, graphene is the material with the highest thermal conductivity currently known (a single layer is about 5000W/mK), as a filler can increase the heat resistance of epoxy; from the mechanical and mechanical properties, Graphene is composed of sp2 hybrid planar carbon atoms. It has high modulus, high strength, and low shear force and low friction coefficient between graphene layers. It is easy to transfer to the epoxy coating surface to form a transfer film. After being combined with epoxy, the wear resistance and impact resistance of the coating can be improved; from the viewpoint of electrical properties, the theoretical resistivity of the graphene monolayer is about 10-6 Ω·m, and due to its low bulk density, the epoxy is When a small amount of graphene is added to the resin, it can have good conductivity; from the viewpoint of anti-corrosion performance, due to the small size effect of graphene and the two-dimensional sheet structure, the defects in the epoxy coating can be improved so that it can be coated. A dense barrier layer is formed in the layer to reduce corrosion.
1.1 Thermal properties
Huang Kun et al. used graphene as a filler to add epoxy, epoxy-modified silicone and vinyl resin in three systems. The graphene coating temperature resistance and electrical aging resistance were tested by baking and electrical aging tests. The impact of sex. The results show that compared with no graphene, the temperature resistance of the three are improved, and after the 500h of electricity, epoxy similar post-curing process, making the cross-linking after curing more dense, graphene also shrink more Compact, better heat resistance. Yang et al. studied the graphene sheet (G)/multi-walled carbon nanotubes (MWCNTs)/epoxy resin (EP) composites and found that there is a synergistic effect between G and MWCNTs. Due to this bridging effect, they are associated with EP's. The contact area becomes larger to avoid filler agglomeration. The thermal conductivity of the composite was measured to be 0.321 W/mK, which is 146.9% higher than that of the pure EP (0.13 W/mK).
1.2 Wear resistance and toughness
Wu Fang used graphene (G) and graphene oxide (GO) to improve the interfacial structure between silicon carbide and epoxy resin. Experimentally, the friction coefficient of G/EP composite coating in dry friction and seawater friction was measured. Pure EP coating reduced by 14.5% and 33.7%, wear rate decreased by 69.1% and 32.1%; GO/EP composite coating reduced friction coefficient by 15.6% and 35.5% compared with pure EP coating, and wear rate decreased by 79%. And 67.9%. Ren Xiaomeng and others prepared G, GO/EP composites, and investigated their toughening and reinforcing effects on EP. The results show that when the mass fraction of G and GO is 2%, the fracture toughness of the composite increases 102% and 48.5%, respectively; when the mass fraction of G and GO is 1%, the strength of the composite increases by 18% and 2%, respectively.
1.3 Electrical properties
Wang Guojian et al. used self-made graphene and commercial grade carbon nanotubes, fullerenes, and graphite as nano-conductive materials to add EP to prepare composites and study their electrical properties. Studies have shown that G is a conductive filler that is superior to carbon nanotubes, fullerenes, and graphite. When the volume fraction of G is 0.25%, the conductivity of the composite material undergoes a percolation sudden change, indicating that G has been formed in EP at this time. Conductive network channels; when the volume fraction exceeds 0.5%, the electrical conductivity tends to stabilize to 2.02 x 10-7 S/m. Serena et al. compared the electrical properties of the two by using self-made diamond and graphene/epoxy composites. The results show that the threshold of graphene is much lower than that of synthetic diamond. When the addition amount of graphene is 0.5% (volume fraction), the resistivity of the composite decreases from 7.14×10 7 Ω·m to 1.02×10 3 Ω·m, which is due to graphite. Alkene is an excellent electrical conductor.
Zhou Nan and others used gallic acid (GA) and epichlorohydrin (ECP) as raw materials to synthesize gallic acid-based epoxy resin (GEP) as a graphene dispersant to prepare GEP-G/EP. Composite coating. The corrosion resistance was characterized by using the coating water absorption, Tafel polarization curve and neutral salt spray test. The research shows that compared with the pure EP coating, the polarization resistance and self-corrosion current density of the coating increase by one order of magnitude, and the water absorption rate decreases by 0.22%, and the salt spray resistance is also effectively improved. Wang Yuqiong and others used sodium polyacrylate as a dispersant, dispersed in a high-speed centrifuge for 2 hours, and then ultrasonically dispersed for 30 minutes to obtain an aqueous graphene dispersion, and a G/waterborne epoxy resin with a G content of 0.5% (mass fraction) was prepared. E44 composite coating. Studies have shown that the addition of graphene improves the water-repellent effect of waterborne epoxy, and the Fick diffusion coefficient of pure E44 coating is reduced by 2 orders of magnitude; the self-corrosion current density of pure E44 coating is 0.13μA/cm2, and G/ The self-corrosion current density of the E44 composite coating is only 0.038 μA/cm2.