Brown Grease Esterification: A Design Strategy to Modulate Homogeneity, Cross-Linking, and Upcycled Mass Economy in High Sulfur-Content Materials

Abstract

Brown grease (BG) is a high-free fatty acid (FFA) waste coproduct from the food industry that remains largely unexploited. Herein, we describe a design strategy to upcycle BG into high sulfur-content materials (HSMs) via inverse vulcanization, circumventing the need for costly transition metals or food-grade compatibilizers. First, BG was esterified with methyl or allyl groups, yielding MeBG and aBG, respectively. This modification masked the polar carboxylic acids and enhanced miscibility with molten sulfur. Subsequent inverse vulcanization produced remeltable HSMs at 80 or 90 wt% sulfur with uniform elemental distributions by SEM–EDX. FT-IR spectroscopy revealed the consumption of C=C moieties and the formation of C–S bonds, signifying robust cross-linking. Thermal analysis (TGA, DSC) indicated good thermal stability (Td,5% up to 223°C) and glass transitions characteristic of polysulfide networks. Mechanical evaluations demonstrated compressive strengths up to 19.2 MPa, exceeding the minimum requirement for residential foundation-grade cement (17 MPa) and rivaling previously reported HSMs containing similarly high sulfur content. Notably, MeBG and aBG incorporate organics comprising up to 97 wt% BG, significantly improving the upcycled mass efficiency relative to earlier BG-based composites. This esterification-driven approach thus offers a practical, scalable pathway to convert low-value BG into advanced materials with tunable thermomechanical properties.