An organic-inorganic hybrid halogen-free barrier layer for thermal insulating, mechanical-reinforced, and flame-retardant expanded polystyrene foam

Endowing expanded polystyrene (EPS) foams with balanced thermal insulation, mechanical strength, and fire safety via a green and efficient way is highly desirable for the development of building energy-saving materials. Herein, a novel organic-inorganic hybrid halogen-free flame-retardant system was established on the basis of the P-containing polysiloxane (PDV), geopolymer cementitious materials (GP), and expandable graphite (EG), in which the obtained organic-inorganic PDV-GP component was designed as a flame-retardant binding agent to firmly anchor EG (synergist filler) on the outer layer of pre-expanded EPS beads. Then, the flame-retardant EPS composite foams featuring thermal-insulating capability can be obtained through a hot-pressing process. Benefiting from the existence of the organic-inorganic hybrid barrier layer, the compressive strength and heat resistance of the resultant EPS composite foams can be effectively enhanced. Importantly, the PDV-GP component exhibited good synergistic flame-retardant effect with EG under low loading, which will accelerate the creation of P- and Si-enriched hybrid carbonaceous layer that is beneficial for blocking air, heat, and smoke species. As expected, the target EPS composite foam exhibited remarkable thermal insulation (0.041 W/(m·K)), outstanding compressive strength of 128.5 kPa (10 % strain), and ideal flame retardancy (LOI value of 32.4 %, V-0 rating), whilst the peak heat release rate and smoke production values were declined by 84.3 % and 60.7 %, respectively. This study proposes a promising strategy for the design of eco-friendly EPS foams with high fire safety and desired overall performance, possessing great potential in building energy-saving field.