Influence of Additives on Flame-Retardant, Thermal, and Mechanical Properties of a Sulfur–Triglyceride Polymer Composite

Plastics and composites for consumer goods often require flame retardants (FRs) to mitigate flammability risks. Finding FRs that are effective in new sustainable materials is important for bringing them to the market. This study evaluated various FRs in SunBG90 (a composite made from triglycerides and sulfur)—a high sulfur-content material (HSM) promising for use in Li–S batteries, where flame resistance is critical. SunBG90 was blended with FRs from several classes (inorganic, phosphorus-based, brominated, and nitrogen-containing) to assess compliance with UL94 Burning Test standards. Inorganic FRs showed poor flame retardancy and lower mechanical strength, while organic additives significantly improved fire resistance. The addition of 20 wt. % tetrabromobisphenol A enabled SunBG90 to achieve the highest flame retardancy rating (94V-0), while also enhancing wear resistance (52 IW, ASTM C1353) and bonding strength (26 psi, ASTM C482). Selected organic FRs also enhance compressive strength compared to the FR-free SunBG90. This research highlights the potential of HSMs with traditional FRs to meet stringent fire safety standards while preserving or enhancing the mechanical integrity of HSM composites.