One-step construction of halogen-free, phosphorus-free, mono-component and Mn-doped diatomite for effectively improving the fire safety of silicone rubber

Aiming at settling the critical problems of ecological and environmental safety caused by traditional halogen-containing and phosphorus-containing flame-retardant system, this paper has fabricated a transition metal manganese ion (Mn²⁺) loaded diatomite (Mn@DE) via a simple chemical modification process, which can be employed as raising the flame retardancy of silicone rubber (SR). Compared with traditional flame retardants, the unique lamellar shielding ability and Mn-enhanced catalytic charring ability from designed mineral-based flame retardants are conductive to upgrading the flame-retardant level of silicone rubber/Mn-modified diatomite (SR/Mn@DE) composites. The results demonstrate that when the amount of Mn@DE reaches 30 phr in the composites, the limiting oxygen index (LOI) and vertical combustion tests of SR/30 phr Mn@DE can reach 27.3% and UL-94 V-0 ratings, respectively. Simultaneously, the reduction for peak heat release rate (PHRR) and total heat rate (THR) of SR/Mn@DE can achieve 55.3% and 66.1%, revealing that the fire hazard of SR has been effectively decreased. Thermogravimetric analysis (TGA) has enlightened that the introduction of Mn onto diatomite can effectively reinforce the thermal stability and char-forming ability of SR composites. Through the systematic analysis for combustion residues, the condensed flame-retardant mechanism of SR/Mn@DE via restraining the heat transfer and fuel feedback can be primarily inferred. Therefore, this paper have provided a fast and practical flame-retardant strategy in order to discarding the halogen-/phosphorus-containing flame retardants, which will open up the key problem of limited application for SR composites in more fields.