Polybutadiene Modification of Brown Grease‐Sulfur Materials

High sulfur‐content materials (HSMs) prepared via inverse vulcanization are attractive for a range of sustainable material applications, particularly when synthesized from waste‐derived feedstocks such as brown grease (BG). Two BG‐based composites, SunBG 90 and aBG 90 , were prepared using elemental sulfur and either native or allylated brown grease, respectively. This study explores the effect of reinforcing these sulfur‐rich networks with low loadings (0.5–2 wt. %) of high cis ‐1,4‐content liquid polybutadiene (PBD). Incorporation of PBD resulted in significant increases in storage modulus, with a near‐linear relationship between PBD content and stiffness enhancement for both material types. At −60°C, storage modulus increased more than fivefold for aBG 90 and more than tripled for SunBG 90 . In contrast, flexural strength and flexural modulus exhibited non‐linear responses, with diminishing or reversed gains at higher PBD loadings, suggesting limits to rubber domain compatibility and dispersion. Thermal analysis confirmed high decomposition temperatures (212°C–226°C) and stable glass transitions, indicating thermal robustness of the reinforced networks. Compared with previous studies requiring higher PBD loadings, these results demonstrate that BG‐based HSMs can be effectively reinforced at low additive levels, offering mechanically robust, low‐cost, and renewable alternatives for structural applications.