Nowadays, the practical application for high-performance silicone rubber (SR) was constrained and limited by its intrinsic flammability, which would be usually solved by the incorporation of halogenated or heavily loaded phosphorus-based flame retardants. The extensive reliance on halogen-/phosphorus-based retardants would not only pose the irreversible risk to human health and ecological environment, but also raise the serious sustainability concerns about the progressive depletion of phosphate resources. Moreover, the insertion of these conventional flame retardants would inevitably compromise the mechanical properties of SR materials, which was not feasible for enhancing the application value and scopes in real life. Inspired by hierarchical structure of onion, a halogen-/phosphorus-free and bio-based flame retardant system (CMs@PDA@LDH@MM) was rationally engineered via a hierarchical assembly strategy by integrating renewable glucose-derived carbon microspheres with polydopamine (PDA), Ni-Al layered double hydroxides (LDH), and melamine-malic acid complex (MM). When the content of CMs@PDA@LDH@MM was 16 %, a limiting oxygen index (LOI) of 29.9 % and a UL-94 V-0 rating of SR composites were achieved together with substantial peak heat release rate (PkHRR) reduction of 56 % and smoke production rate (SPR) of 67 %, suggesting the excellent flame retardancy and fire safety performance. This fact was ascribed to the integration of multiple flame-retardant mechanism into a single hierarchical CMs@PDA@LDH@MM hybrid via the synergistic action between catalyzed charring and gaseous dilution/heat absorption ability. Furthermore, SR composites were endowed with the excellent resistance to flame impact and glow-wire ignition (GWFI > 960 °C). Most of all, the mechanical robustness of SR composites was significantly improved with a Young’s modulus increment of 708 % and the elongation at break of 332 %, which would thereby enable the structural self-sustainability under load-bearing condition. In a nutshell, the intrinsic limitation of conventional additive approach was addressed in simultaneously achieving the balanced flame retardancy and mechanical performance, which was expected to provide a new and clean insight for the rational design of sustainable and halogen-/phosphorus-free flame-retardants in the fields of construction and buildings, cables and wire, new energy vehicles and aerospace.
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