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Flame-retardant and smoke-suppressant expanded polystyrene (EPS) foams were prepared by coating a mixture of thermoplastic phenolic resin (PF) and aluminum hypophosphite (AP) or expandable graphene (EG) onto EPS spheres. The PF reacting with AP by hydrogen-bond interaction formed a facile flame-retardant coating PF/AP, which not only greatly reduced flammability and smoke release, but also remained the thermal conductivities of EPS foams at low level. Compared with those of EPS/PF/EG, EPS/PF/AP could pass the UL-94 test and showed better flame-retardant performances with lower heat release rates and fire growth rates. Especially, the time to ignition (TTI) of EPS/PF/AP achieved 52 s, much higher than those of EPS/PF/EG (9 s) and neat EPS (2 s). Also, the peak of smoke production rate (PSPR) and the total smoke production (TSP) of both composites were significantly reduced, showing an excellent smoke-suppressant performance. The mechanism analysis suggested that the PF/AP coating could form a compact P–O–C cross-linked char layer and effectively protect the matrix from further combusting. Particularly, the EPS/PF/AP had a higher compressive strength and lower thermal conductivity in comparison with EPS/PF/EG. These above results show that the EPS/PF/AP composite has enormous potential in building thermal insulation field.

A phosphorus-containing inorganic compound, aluminum hypophosphite (AP), was used to prepare flame-retardant polystyrene (PS). The flammability of the PS/AP composites was investigated by the limiting oxygen index (LOI), vertical burning test (UL-94) and cone calorimeter test. When the content of AP reaches 25 wt%, the LOI of PS/AP is 25.6% and it passes UL-94 V-0 rating. The results of cone calorimeter test show that the heat release rate (HRR), the total heat release (THR) and the mass loss rate (MLR) of PS/AP composites are significantly reduced. The thermal degradation mechanism of PS/AP was investigated by thermogravimetric analysis (TGA), Fourier transform infrared spectrometry (FTIR), thermal gravimetric-Fourier transform infrared spectrometry (TG-FTIR), pyrolysis gas chromatography-mass spectrometry (Py-GC/MS), and X-ray photoelectron analysis (XPS) tests. The results indicate that PS/AP has a combined gas-phase and condensed-phase activity in the combustion and degradation of the composites. Consequently, a possible flame-retardant mechanism of PS/AP composites is proposed.

An intumescent flame-retardant (IFR) system, which was comprised of a novel carbonization agent (CA) and ammonium polyphosphate (APP), was prepared for general purpose polystyrene. Thermal degradation and flame retardance of the PS/IFR composites were studied. The results of LOI and UL-94 test showed that when the content of APP and CA was 22.5 and 7.5 wt%, respectively, the LOI value of PS/IFR composite was 32.5%, and a V-0 classification could be achieved. The TGA data indicated that there was a synergistic effect between CA and APP. The cone calorimeter data showed that the heat release rate (HRR), the total heat release (THR) and the mass loss rate (MLR) were reduced largely with the addition of IFR. Some cone calorimeter data, such as smoke production rate (SPR), total smoke production (TSP) and carbon monoxide production (COP), revealed that the IFR could greatly suppress the generation of the smoke during the material flaming. The study on the flame-retardant mechanism of IFR indicated that a steady structure containing P–O–C was formed due to the reaction between APP and CA. The mechanical properties of PS and PS/APP/CA 3:1 were also investigated, and the results showed that, compared to those of the neat PS, the tensile strength and the flexural strength of the PS/IFR composite decreased to a certain extent.