Abstract
The exploitation of self-assembled coatings comprising graphite oxide (GO) nanoplates has been recently demonstrated as a promising route to improve the fire safety of flexible polyurethane (PU) foams. However, limited knowledge has been gathered on the correlations between the physical and chemical properties of different GO grades and the performance obtained in this application. This work addresses the effects of the nanoparticle dimensions on the layer-by-layer (LbL) assembly and flame-retardant properties of GO-based coatings deposited on PU foams. To this aim, three GO bearing different lateral sizes and thicknesses were selected and LbL-assembled with chitosan (CHIT). Coating growth and morphology were evaluated by FTIR and FESEM, respectively. The resulting CHIT/GO assemblies were demonstrated to be capable of slowing down the combustion of the PU both in flammability and forced combustion tests. In addition, compressive stress/strain tests pointed out that the LbL-coated foams (22–24 kg/m3) could easily replace denser commercial PU foam (40–50 kg/m3) with weight reduction potentials in the transport field. These results are correlated with the properties of the employed GO. The production of assemblies characterized by a high density of CHIT/GO interfaces is identified as the main parameter controlling the FR efficiency and the mechanical properties of the coatings.
Highlights
This work evaluated the effects of different graphite oxide (GO) dimensions on the layer-by-layer assembly and properties of CHIT/GO coatings deposited on PU foams
The coating growth monitored by FTIR spectroscopy evidenced a linear assembly regime for all GO grades under study, highlighting that the thinnest nanoplates achieved the highest density of CHIT/GO interactions
Cross-sectional morphological observations confirm the dependence of the coating thickness from the GO thickness and the concentration of functional groups involved in the LbL assembly, highlighting a thickness coating trend as GOA >
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. By combining polyelectrolytes and nanoplates, such as clay- or graphene-related materials, it is possible to deposit nanostructured coatings that exhibit a “brick and mortar” fashion where nanoparticles are embedded in a polymer matrix [21,22,23,24,25] This particular structure has been proved to significantly increase the flame retardancy of PU foams due to a combined effect of heat shielding/reradiating and delayed release of combustible volatiles [25,26]. It has been demonstrated that an LbL coating comprising of six bi-layers (BLs) alternating chitosan (CHIT) and graphite oxide (GO) nanoplates can improve the flame retardancy of PU foams by limiting the flaming ignition in forced combustion tests and suppressing the melt-dripping phenomenon during flammability tests [22]. On PU foams and their flame-retardant properties were evaluated to establish a correlation between GO size and FR performance
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