Ammonium polyphosphate (APP) is not an efficient flame retardant for polypropylene (PP) when it is used alone. In order to improve its flame-retardant efficiency, ethanolamine (ETA) was used to chemically modify APP via ion exchange reaction. The resulting ethanolamine-modified ammonium polyphosphate (ETA-APP) was alone applied to flame retard PP, the limiting oxygen index (LOI) value could reach 35.0% and the vertical burning test (UL-94) could pass the V-0 rating at a loading of 35 wt% ETA-APP. Moreover, cone calorimeter (CC) test results showed that the heat release rate (HRR), the total heat release (THR), the mass loss rate (MLR), the smoke production rate (SPR) and the total smoke production (TSP) of PP/35 wt% ETA-APP composite largely decreased, for example, by 77.2%, 88.5% and 77.9% for THR, TSP and the fire growth rate (FGR), respectively, compared with PP containing an equal amount of APP. In addition, the residual char of PP/35 wt% ETA-APP increased by 195.6% compared with that of PP/35 wt% APP. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to analyze the flame retardant mechanism of ETA-APP. It was confirmed that the formation of P–O–C and P–N–C structures, resulting from the incorporation of ETA could greatly improve the stability of intumescent char layer and consequently lead to the much better flame retardancy of ETA-APP than that of unmodified APP. Experimental results demonstrated that the prepared ETA-APP acted not only as the acid source and blowing source as efficient as unmodified APP, but also as an excellent charring agent beyond the unmodified APP.

Excellent electroconductivity, fire resistance, and mechanical properties are several important indexes for electromagnetic shielding sealing materials. In this work, a novel functionalized graphene decorated with a nickel-Schiff base (rGO-Salen-Ni) was first synthesized via a chemical modification process, and applied in enhancing the mechanical properties, electroconductivity, and fire resistance of a thermoplastic polyurethane elastomer (TPU). The experimental result illustrated that the rGO-Salen-Ni significantly improved the above vital properties of TPU. First, the tensile strength, elongation at break, and storage modulus of the TPU containing only 1.5 wt% rGO-Salen-Ni (TPU/rGO-Salen-Ni1.5) were respectively increased by 1.50 times, 1.58 times, and 2.17 times; second, the electrical conductivity of the TPU/rGO-Salen-Ni1.5 was increased by 5 orders of magnitude in comparison with that of a pure TPU, up to 7.3 × 10⁻⁵ S m⁻¹; finally, the TPU/rGO-Salen-Ni1.5 displayed excellent flame retardancy; for instance, the peak of heat release rate, total heat release, and total smoke production were respectively decreased by 43%, 22%, and 28% compared with the corresponding values of pure TPU. The analysis of the enhancement in mechanical properties and electroconductivity of TPU/rGO-Salen-Ni revealed that the uniform dispersion of rGO-Salen-Ni, resulting from the incorporation of the nickel-Schiff base into the GO, was the leading reason for their improvements. The study on the flame-retardant mechanism demonstrated that a more continuous and compact protective layer related to the nickel-Schiff base played the key role in the excellent fire resistance of TPU/rGO-Salen-Ni. The rGO-Salen-Ni shows great potential for application in electromagnetic shielding sealing materials.