Preparation And Properties Of Graphene/Waterborne Polyurethane-Acrylate Hybrid Emulsion

With the development of society and the enhancement of people’s environmental protection consciousness, the requirement for environmental-friendly coatings progressively increased, and more researchers focused on the research of water-based coatings instead of the traditional solvent-based coatings. Graphene, as nano-filled material, has gotten extensive application in the field of composite materials. The purpose of this paper was to develop a kind of solvent-free graphene/waterborne polyurethane-acrylate anti-corrosion coating, which was environmental-friendly and endowed with excellent comprehensive performance.In this thesis, a series of solvent-free polyurethane-acrylate hybrid emulsions were prepared through in-situ polymerization based on molecular design. Isophorone diisocyanate (IPDI), polycaprolactone diols (PCL1000), 2,2-dimethylolbutanoic acid (DMBA), trimethylolpropane (TMP), 2-hydroxyethyl methacrylate (HEMA), triethylamine (TEA), methyl methacrylate (MMA), butyl acrylate (BA), homemade graphene and graphene oxide were utilized as the main raw materials. The hybrid emulsions were applied as anti-corrosion coating. The structure of self-made graphene oxide and graphene were characterized. Effects of graphene oxide and graphene content on the properties of emulsion, film and coating were discussed, and the optimum experimental conditions were determined. In addition, the micromorphology of colloidal particles and coating was observed by transmission electron microscopy (TEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The water absorption, contact angle, thermal behavior and mechanical property were measured, as well as the anti-corrosion properties. The main results are summarized as the following:(1) Graphene oxide (GO) was successfully obtained through improved Hummers method. The results showed that the self-made GO had higher degree of oxidation, low-rise and better dispersibility in water system.(2) The stability of hybrid emulsion was improved, since chemical bonds were formed due to the reaction between reactive groups in GO and - NCO groups in polyurethane. The particle size increased with increasing GO content. The interactions among colloidal particles and density of films were improved with the incorporation of GO. When the GO content was 0.5%, the water absorption decreased from 38.28% to 27.94%, thermal degradation temperature increased from 160 ℃ to 300 ℃, the thermal stability was greatly enhanced. Moreover, the crosslinking density of composite films was increased, and the glass transition temperature increased by 56 ℃. The anti-corrosion properties increased as increasing GO content, and the anti-corrosion properties reached optimum when the GO content was 0.5%. In comparison with pure waterborne polyurethane-acrylate, the salt fog resistance prolonged by 10 days, the self-corrosion current density decreased by one order. However, the comprehensive properties were weakened when the GO content was greater than 0.5%.(3) Graphene was successfully prepared through reduction reaction, with hexadecyl trimethyl ammonium bromide (CTAB) as a cationic surface active agent, and hydrazine hydrate as the reductant of graphene oxide. The results showed that graphene has higher degree of reduction and better dispersibility in water system.(4)The thermal degradation temperature of polyurethane-polyacrylate was increased with the addition of appropriate amount of graphene, as well as the water resistance. Compared with waterborne polyurethane-polyacrylate, the water adsorption of composite film reduced to 12.08% when the graphene content was 0.5%. The thermal degradation temperature increased by 87 ℃, and the tensile strength increased from 30.5 MPa to 61.2 MPa. The graphene modified polyurethane-polyacrylate film displayed improved anti-corrosion properties. The anti-corrosion properties increased with increasing graphene content, and the salt fog resistance prolonged by 10 days. The polarization curve and impendence spectrum showed that the impendence and the radius of capacitive loop increased with an increase in graphene content, whereas the self-corrosion current density reduced. The anti-corrosion properties reached optimum when the graphene content was 0.5%. Self-aggregation tended to take place when excessive graphene was adopted, and the uniformity and density of composite films were thereby decreased, resulting in weakened performance. In comparison with GO modified polyurethane-polyacrylate, the graphene modified polyurethane-polyacrylate coating was endowed with improved performance.