Construction of Halogen-/Phosphorus-Free and Carbon/Metal-Based Flame-Retardant System for Silicone Rubber

Abstract

Aiming at extending its functional application, the critical environmental and efficiency issue of flame-retardant silicone rubber (SR) must be urgently addressed. Except for replacing the toxic/contaminated halogen-/phosphorus-containing compounds, the reduction of the loading filler became an effective strategy in improving the flame-retardant efficiency of SR. Inspired by the native charring ability of transition-metal elements, a carbon/metal-based flame-retardant system was fabricated by combining hydrophobic zeolitic imidazolate framework-8 (H-ZIF-8) and expandable graphite (EG). This combination was conducive to avoiding the adverse effects of halogen- and phosphorus-containing flame retardants on environmental pollution and personal safety. Compared with the single component, when a mixture of H-ZIF-8/EG (mass ratio: 3:8) was introduced at a total loading of 11 phr, a limiting oxygen index (LOI) of 43.1% and a UL-94 V-0 rating were achieved for SR composites. Additionally, both the peak heat release rate (PHRR) and total heat rate (THR) of SR composites were reduced by 25.8% and 35.9%, highlighting the enhanced fire safety via good charring ability and a heat barrier effect. Despite the improved flame retardancy, the flame-retardant durability of SR composites was maintained when exposed to harsh environments (acid solution, alkali solution, hot water, and seawater). The achieved flame-retardant efficiency was derived from the catalyzed-charring action and the inherent expansion capacity. Thanks to the ideal flame-retardant efficiency, the comprehensive properties of SR composites were well-balanced including the mechanical properties and thermal conductivity, which were feasible for raising the application value of SR materials in more fields.