Synergistic flame-retardant effect of modified hydrotalcite and expandable graphite for silicone rubber foam

Silica gel-coated hydrotalcite (LDHs) flame retardants (SiLDHs-Ce) are prepared by the sol-gel method. The synergistic effect of SiLDHs-Ce and expandable graphite (EG) on the silicone rubber foam (SRF) is studied through limiting oxygen index (LOI), Cone Calorimeter Test (CC), thermogravimetric infrared spectrometer (TG-IR), and scanning electron microscopy. The results show that SiLDHs-Ce and EG can improve the flame retardant properties of the SRF materials. The LOI value of the SRF material can reach 40.1% when the ratio of EG to SiLDHs-Ce is 2:1, and the heat release rate (HRR) and total heat release (THR) are reduced by 66.60% and 52.76%, respectively, compared with the original. The minimum SPR of the SRF material is 0.010 m(2) s(-1) when 1 wt% SiLDHs-Ce has been added. TG-IR results show that the addition of EG and SiLDHs-Ce increased the carbon residue rate of SRF materials. Results show that the residual carbon-containing EG and SiLDHs-Ce is denser. It is inferred that the synergistic flame retardant mechanism of SiLDHs-Ce and EG on the SRF is mainly condensed phase flame retardant, augmented by gas-phase flame retardant. The results of this study can provide guidance for the development of environmentally friendly silicone rubber foam.