  The layer-by-layer (LbL) technique is adopted for the construction of
multilayers encompassing chitosan and graphene oxide (GO) platelets capable of
improving the flame retardant properties open cell PU foams. The LbL assembly
follows a linear growth regime as evaluated by infrared spectroscopy and yields
a multilayer structure where GO platelets are embedded within a chitosan
continuous matrix. 3 and 6 bi-layers (BL) can efficiently coat the complex 3D
structure of the foam and substantially improve its flame retardant properties.
3BL only add 10% to the original mass and can suppress the melt dripping during
flammability and reduce both the peak of heat release rate by 54% and the total
smoke released by 59% in forced combustion tests. Unprecedented among other LbL
assemblies employed for FR purposes, the deposition 6BL is capable of slowing
down the release of combustible volatile to the limits of non-ignitability thus
preventing ignition in half of the specimens during cone calorimetry tests.
This has been ascribed to the formation of a protective coating where the
thermally stable char produced by chitosan serves as a continuous matrix
embedding GO platelets, which control volatile release while mechanically
sustaining the PU foam structure.
