Fabrication And Flame Retardant Properties Of Graphene/Waterborne Polyurethane Nanocomposites

Waterborne polyurethane (WPU) as a coating polymer material with excellentperformances has been widely used in wood, leather, fiber, textiles, plastics, and otherfields. However, the material is flammable and thus endanger the lives and lead to lossof property. Currently, most flame retardant WPU currently is an additive-type. But,additive type flame retardant waterborne polyurethane also have many disadvantages,such as poor dispersion, bad film reforming properties, precipitation anddemulsification; in addition, a good fire retardancy is often dependent on a largenumber of additives.The studies of graphene provide a effective approach for solving this kind ofproblem. Based on rich hydrophilic groups of graphene oxide (GO) surface, GO has ahigh stability in waterborne polymers. In addition, the WPU provides a suitableenvironment for the in situ reduction of GO to rGO. Thus the rGO sheets weredispersed homogeneously in the matrix and the problem of poor dispersion was solvedand more details is as follows.In this study, the graphite oxide was prepared from expansible graphite by themodified Hummers method, and samples were characterized by using XRD, UV-visand TEM. Graphite oxide/waterborne polyurethane (GO/WPU) nanocomposites werefabricated by in-situ emulsion. The effect of GO content on the stability, fracturemorphologies, thermal degradation and flame retardant properties of GO/WPUcomposites was investigated by Zeta Potential Analyzer, SEM, TGA and ConeCalorimeter. The results of Zeta Potential and SEM analysis indicate that GO has agood stability and dispersibility in GO/WPU nanocomposites. TGA showed that thethermostability of GO/WPU nanocomposites decreased slightly compared to pureWPU, but carbon residue increased from0.99%to2.90%when the mass fraction ofGO in WPU is2%. Cone Calorimeter test indicated that the flame retardant and smokesuppression properties of GO/WPU composites increased with the increasing of GO. When the mass fraction of GO is2%, the peak heat release rate, total heat release, totalsmoke release and smoke factor decreased by34%,19%,27%, and43%respectivelycompared to those of pure WPU.Based on these considerations above, the graphene/WPU nanocomposites(rGO/WPU) were produced by the self-assembly behavior of graphene layers insolution, and GO was restored to rGO by hydrazine in GO/WPU dispersion. Inaddition, we also restored GO to graphene (GNs) in aqueous dispersion, and thenGNs/WPU nanocomposites were prepared by solution blend method. The structure andproperties, such as the emulsion stability, mechanical, thermal stability and flameresistance of GNs/WPU and rGO/WPU composites were characterized using SEM,Zeta Potential, Universal material experiment machine, DMA, TGA and Conecalorimeter. Compared to pure WPU, the mechanical properties and flame retardancyof GNs/WPU and rGO/WPU nanocomposites have greatly improved. But thedispersion of graphene, emulsion stability, mechanical properties and flame retardancyof GNs/WPU were far worse than the properties of rGO/WPU nanocomposites. Whenthe mass fraction of rGO is2%, the tensile strength of rGO/WPU (22.0MPa) increased727.1%compared to those of pure WPU (2.66MPa), and PHRR decreased by22%.When the mass fraction of rGO is only1%, the total smoke release and smoke factordecreased by25%and38%respectively compared to those of pure WPU. And thedigital photos for the residues present that the residues of GNs/WPU composites arepoor and discrete. For rGO/WPU composites, a uniform, dense and more compact charis obtained. The phenomenon also explains the reason why the flame retardant effectof rGO/WPU is better than GNs/WPU to some extent.