Characterization of PBS and PBAT biocomposites reinforced with rapeseed press cake: Influence of filler content and particle size

This study investigates the incorporation of rapeseed press cake (RPC), a protein- and fiber-rich industrial by-product, into polybutylene succinate (PBS) and polybutylene adipate terephthalate (PBAT) biocomposites. Composites containing 30–70 wt% RPC and two particle size fractions (50–250 µm, RPC-S; >250 µm, RPC-L) were analyzed for thermal, mechanical, and physical performance. Thermal analysis showed that RPC reduced the onset degradation temperature from 364 °C to 223 °C in PBS, and from 378 °C to 229 °C in PBAT, while the main matrix degradation peak (∼410 °C for PBS, ∼416 °C for PBAT) remained stable. RPC increased the glass transition temperature of PBS (−29.6 °C to −24.3 °C) and slightly increased crystallinity up to 31.8 % upto 50 % RPC). Mechanically, RPC increased stiffness in both matrices: Young’s modulus rose from 675 MPa to 1111 MPa in PBS and from 51 MPa to 138 MPa in PBAT. However, tensile strength dropped from 35 MPa to 5 MPa (PBS) and 18 MPa to 3.6 MPa (PBAT), while elongation at break fell from 183 % to < 10 % in PBS and from 421 % to 46 % in PBAT. RPC also increased water absorption up to 7.8 % in PBS and 10.8 % in PBAT at 60 wt%, with finer particles enhancing hydrophilicity more in PBS. Particle size had minimal impact on PBAT properties, but influenced crystallinity, stiffness, and water uptake in PBS. Overall, RPC is a viable biofiller to enhance stiffness while valorizing side streams, with filler content and matrix type playing key roles in performance. • Rapeseed press cake used as a biofiller in PBS and PBAT biocomposites. • Stiffness increased with RPC content; tensile strength and ductility decreased. • Smaller RPC particles enhanced stiffness but not strength or flexibility. • RPC addition increased hydrophilicity and water uptake, especially in PBS. • Thermal stability retained despite up to 70 % RPC filler loading.