Flame Retardancy and Smoke Suppression of Silicone Rubber Foam with Microencapsulated Sepiolite and Zinc Borate

The flame-retardant micro-encapsulated sepiolite (MSEP) was successfully prepared by sol-gel method. Fourier transform infrared, X-ray photoelectron spectroscopy, scanning electron microscopy, and energy dispersive spectroscopy were utilized to prove that sepiolite was encapsulated. Then, the mechanical properties, flame retardance, smoke suppression, and pyrolysis characteristics of silicone rubber foam (SiFs) with MSEP and zinc borate (ZB) were analyzed. The results indicated that the tensile and compressive properties of SiFs could evidently improve with the incorporation of MSEP/ZB. SiFs with 3 wt% MSEP and 6 wt% ZB could achieve an limiting oxygen index value of 30.9 vol% and UL-94 V-0 rating, the time to ignition was 64.7% above that of pure SiFs, the peak heat release rate and total heat release were 42.7% and 25.0% lower than that of pure SiFs, respectively. Furthermore, the peak smoke production rate and total smoke production of SiFs with 3 wt% MSEP and 6 wt% ZB were merely 54.22% and 64.10% of pure SiFs. Especially, the thermal stability of SiFs was significantly enhanced, and the carbon residue of SiFs became denser and more complete after adding 3 wt% MSEP and 6 wt% ZB.

Comparative Study of M(Ⅱ)Al (M=Co, Ni) Layered Double Hydroxides for Silicone Foam: Characterization, Flame Retardancy, and Smoke Suppression

To compare the different actions of the two representative transition metal cations of Co²⁺ and Ni²⁺ in layered double hydroxides (LDHs), CoAl-LDH and NiAl-LDH intercalated with CO₃²⁻ were synthesized, and the chemical structures, microstructures, and surface areas thereof were successfully characterized. Then, the two LDHs were utilized as flame retardants and smoke suppressants for silicone foam (SiF). The densities, flame retardancy, smoke suppression, thermal stabilities, and compressive strengths of the two SiF/LDHs nanocomposites were investigated. The introduction of LDHs slightly decreased the density of SiF due to the catalytic actions of Co and Ni during the foaming process of SiF. With respect to the flame retardancy, the addition of only 1 phr of either CoAl-LDH or NiAl-LDH could effectively improve the limiting oxygen index of SiF from 28.7 to 29.6%. Based on the results of vertical flame testing and a cone calorimeter test, the flame retardancy and fire safety of the SiF were effectively enhanced by the incorporation of LDHs. In addition, owing to the good catalytic action and large specific surface area (NiAl-LDH: 174.57 m² g⁻¹; CoAl-LDH: 51.47 m² g⁻¹), NiAl-LDH revealed higher efficiencies of flame retardancy and smoke suppression than those of CoAl-LDH. According to the results of energy-dispersive X-ray spectroscopy, Co and Ni participated in the formation of protective char layers, which inhibited the release of SiO₂ into the gas phase. Finally, the influences on the thermal decomposition and compressive strength for SiF resulting from the addition of LDHs are discussed.