Combination effects of graphene and layered double hydroxides on intumescent flame-retardant poly(methyl methacrylate) nanocomposites

A novel intumescent flame-retardant poly(methyl methacrylate) (PMMA) nanocomposite has been prepared via in situ polymerization by incorporating intumescent flame retardants (IFRs), graphene and layered double hydroxides (LDHs). Results from X-ray diffraction (XRD) and transmission electron microscopy (TEM) indicate that a fine dispersion of IFR particles, intercalated LDHs and exfoliated graphene is achieved in the PMMA matrix. Thermal and flammability properties of PMMA nanocomposite were investigated using thermogravimetry, cone calorimetry, limiting oxygen index (LOI) and vertical burning (UL-94). The use of IFRs in combination with graphene and LDHs in the PMMA matrix improves greatly the thermal stability and flame retardant properties of the nanocomposites. The PMMA/IFR/RGO/LDH nanocomposites, filled with 10 wt.% IFRs, 1 wt.% graphene and 5 wt.% LDHs, achieve the LOI value of 28.2% and UL-94 V1 grade. Compared with neat PMMA, the PHRR of PMMA/IFRs/RGO/LDHs is reduced by about 45%, while the mechanical properties of PMMA/IFR/RGO/LDH nanocomposites exhibit almost no deterioration. The results from scanning electronic microscopy (SEM) confirm that the compact and dense intumescent char enhanced with LDHs and graphene nanosheets is formed for the PMMA/IFR/RGO/LDH nanocomposites during combustion, which inhibits the transmission of heat and mass when exposed to flame or heat source, and thus improves the flame retardant properties of the nanocomposites.