Sustainable Fabrication of Mono-Component, Halogen-/Phosphorus-Free, and Tartaric Acid-Derived Flame Retardants for Silicone Rubber Based on Waste Chinese Fir

Nowadays, conventional multi-component flame-retardant systems suffer from numerous challenges, such as multi-component incompatibility, toxic smoke emission, limited recyclability/sustainability, and efficiency problems. Aiming to break through these bottlenecks, the development of single-component, biobased, and high-efficiency flame retardants for silicone rubber (SR) emerged as a promising and pivotal research hotspot. In this paper, a single-component hybrid flame retardant (CCF@PDA@TAM) was prepared via a multi-stage construction strategy using recycled waste Chinese fir (CCF), which was obtained as biochar to serve as an inert synergist, subsequently coated with polydopamine (PDA), and co-deposited by comprising tartaric acid (TTA) and melamine (MEL). When 18 phr of CCF@PDA@TAM was introduced into SR, a limiting oxygen index of 29.5% and a UL-94 V-0 rating were achieved. Additionally, the reduction in PHRR and total heat release rate (THR) reached 30.7% and 29.6%, and the glow-wire flammability index exceeded 960 °C. During the burning tests, non-flame-exposed surface temperature of the SR composites with its structural integrity was reduced by 279 °C. These findings confirmed the exceptional flame retardancy of the SR composites, indicating that the underlying mechanism was ascribed to the synergistic interplay among the thermal insulation barrier of CCF/PDA and the gas-phase effect of MEL/TTA. Moreover, the limitations in mechanical strength of the SR composites were effectively addressed and maintained. Consequently, this study offered an environmentally sustainable and highly effective strategy in simultaneously tackling the critical flame-retardant challenge of SR and efficiently recycling waste biomass materials.