Bio compatibilizers from brewer’s spent grain for biocomposite production

This study demonstrates that the lipid fraction of brewer's spent grain (BSG), traditionally overlooked in polymer composite applications, can be chemically converted into bio-based compatibilizers while the lignocellulosic fraction simultaneously serves as reinforcement. Two model bio-additives, 6-O-linoleyl-α-D-glucopyranosyl-β-Dfructofuranoside (SE) and 9,10:12,13-diepoxyoctadecanoic acid (EA), were synthesized starting from linoleic acid, main component of BSG lipid fraction, and their performance as additives was evaluated. Poly(butylene succinate) (PBS) was selected as the biopolymer matrix, and PBS/BSG blends (70/30 wt/wt) containing SE or EA at concentrations between 2 and 8 wt% were prepared. Thermal, mechanical, chemical, and morphological analyses (DSC, TGA, ATR-FTIR, and SEM) showed that PBS/BSG biocomposites containing 6 wt% SE exhibited the best overall performance, highlighting an effective compatibilizing effect. Conversely, the addition of 6 wt% EA mainly increased surface hydrophobicity, raising the contact angle to approximately 80◦, compared to PBS and PBS/BSG blends (<70 ◦). The lipid fraction of BSG was extracted using ethyl acetate or supercritical CO₂, achieving yields up to 97%, and subsequently chemically modified to obtain the corresponding sucrose ester (SES) and epoxide (SEO). PBS/BSG blends containing 6 wt% of SES or SEO were then prepared. SES-based biocomposites showed improved thermal stability, mechanical properties, and interfacial adhesion compared to PBS/BSG blends, confirming a strong compatibilizing action. In contrast, SEO imparted pronounced hydrophobicity, with contact angles exceeding 100◦, while only modest variations in mechanical properties were observed. Bio-fragmentation tests confirmed enhanced biodegradability for all modified composites. Overall, this work demonstrates that brewer’s spent grain can simultaneously serve as a reinforcing filler and as a renewable source of functional compatibilizers, providing an integrated strategy for the production of high-performance fully bio-based composites.