Recently, the effectiveness of graphene nanoplatelets (GNPs), dispersed in low quantity in a waterborne epoxy resin, in enhancing the coating anticorrosive properties and strongly contrasting its photooxidative degradation has been demonstrated [1-2]. It is well known that epoxy-based coatings are vulnerable to ultraviolet (UV) damage and their durability can be greatly decreased in outdoor environments. In this work, we aim to focus on the exceptional ability of GNPs incorporated in the epoxy films, at different weight percentages, in increasing the photooxidative resistance of polymeric films, thus consequently determining a strong decrease of the mechanical damages caused by UV irradiation. The effects of UV light on the morphology and mechanical properties of the solidified nanofilled epoxy films are investigated by Atomic Force Microscopy (AFM), in the acquisition mode “HarmoniX”. This work highlights the possibility of extending traditional AFM imaging with a technique, which is sensitive to the punctual changes in the mechanical properties of the surface film, providing information on the heterogeneity of multiphase polymeric systems. The polyharmonic response varies with modifying local mechanical properties. It is worth noting that, by coupling the AFM phase maps with the AFM modulus maps, morphologies and distribution of crystalline aggregates (for both unfilled and GNP filled samples) can be simply identified. In this work, in order to supply pertinent information on the local changes caused by the photooxidative degradation, a comparison of the material properties on located regions, before and after UV irradiation, is shown. In particular, AFM microscopy, in the acquisition mode “HarmoniX”, has allowed studying both qualitative and quantitative nanometric-resolved maps of the mechanical properties, highlighting that the incorporation of low percentages, between 0.1 and 1.0 wt%, of graphene nanoplatelets (GNPs) in the polymeric film causes a significant increase in the mechanical stability of the irradiated films. The advantageous effect increases progressively as the GNP percentage increases. In particular, films (30 ± 1.5 μm thick) unloaded and loaded with GNPs have been subjected to accelerated photo-oxidative degradation by exposing them to 550 hours of UV irradiance, reproducing the ultraviolet (295–380 nm) component of solar radiation at the earth surface. Films without GNPs have proven to be very sensitive to UV treatment. Figure 1 shows for the sample 1GNPs (550): (a) the AFM phase map image; (b) the AFM image of the DMT modulus map and (c) the profile of the value of the elastic modulus. For this sample, as expected, the profile of the value of the elastic modulus is more uniform with respect to that detected for the sample 0GNP. In this case, the effect of the UV irradiation does not cause a decrease in the elastic modulus. It seems that, a slight increase is detected on the region characterized by higher values in modulus. This is most likely due to the effect of UV irradiation on the thin layer of polymer matrix covering the nanoparticles. The UV irradiation consumes part of the polymer on the GNP nanoparticles; it cannot penetrate beneath them, preventing the polymer matrix from further damages.
Role of Graphene-based Nanoparticles on the Resistance of Aeronautical Epoxy Coatings to Sunlight and Corrosion
Marialuigia Raimondo
;Vito Speranza;Roberto Pantani;Carlo Naddeo;Liberata Guadagno
2021-01-01
Abstract
Recently, the effectiveness of graphene nanoplatelets (GNPs), dispersed in low quantity in a waterborne epoxy resin, in enhancing the coating anticorrosive properties and strongly contrasting its photooxidative degradation has been demonstrated [1-2]. It is well known that epoxy-based coatings are vulnerable to ultraviolet (UV) damage and their durability can be greatly decreased in outdoor environments. In this work, we aim to focus on the exceptional ability of GNPs incorporated in the epoxy films, at different weight percentages, in increasing the photooxidative resistance of polymeric films, thus consequently determining a strong decrease of the mechanical damages caused by UV irradiation. The effects of UV light on the morphology and mechanical properties of the solidified nanofilled epoxy films are investigated by Atomic Force Microscopy (AFM), in the acquisition mode “HarmoniX”. This work highlights the possibility of extending traditional AFM imaging with a technique, which is sensitive to the punctual changes in the mechanical properties of the surface film, providing information on the heterogeneity of multiphase polymeric systems. The polyharmonic response varies with modifying local mechanical properties. It is worth noting that, by coupling the AFM phase maps with the AFM modulus maps, morphologies and distribution of crystalline aggregates (for both unfilled and GNP filled samples) can be simply identified. In this work, in order to supply pertinent information on the local changes caused by the photooxidative degradation, a comparison of the material properties on located regions, before and after UV irradiation, is shown. In particular, AFM microscopy, in the acquisition mode “HarmoniX”, has allowed studying both qualitative and quantitative nanometric-resolved maps of the mechanical properties, highlighting that the incorporation of low percentages, between 0.1 and 1.0 wt%, of graphene nanoplatelets (GNPs) in the polymeric film causes a significant increase in the mechanical stability of the irradiated films. The advantageous effect increases progressively as the GNP percentage increases. In particular, films (30 ± 1.5 μm thick) unloaded and loaded with GNPs have been subjected to accelerated photo-oxidative degradation by exposing them to 550 hours of UV irradiance, reproducing the ultraviolet (295–380 nm) component of solar radiation at the earth surface. Films without GNPs have proven to be very sensitive to UV treatment. Figure 1 shows for the sample 1GNPs (550): (a) the AFM phase map image; (b) the AFM image of the DMT modulus map and (c) the profile of the value of the elastic modulus. For this sample, as expected, the profile of the value of the elastic modulus is more uniform with respect to that detected for the sample 0GNP. In this case, the effect of the UV irradiation does not cause a decrease in the elastic modulus. It seems that, a slight increase is detected on the region characterized by higher values in modulus. This is most likely due to the effect of UV irradiation on the thin layer of polymer matrix covering the nanoparticles. The UV irradiation consumes part of the polymer on the GNP nanoparticles; it cannot penetrate beneath them, preventing the polymer matrix from further damages.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
