Valorization of oil-extraction chia seed flour into injection-moulded biocomposites: Influence of plasticizers

The valorization of agro-industrial by-products into scalable bioplastics is a key strategy for developing sustainable materials. In this work, chia seed flour (CSF), a by-product of cold oil extraction with medium protein (∼41 wt%) and high carbohydrate (∼36 wt%), was directly transformed into injection-moulded biocomposites without protein purification, using an industrially scalable extrusion–injection moulding route. CSF was plasticized with water, glycerol, sorbitol, and their combinations (40–60 wt%). Plasticizer type and content strongly influenced intermolecular interactions, mechanical and thermomechanical performance, thermal stability, water uptake, and compost disintegration. Glycerol/sorbitol systems showed the highest ductility (elongation at break: 18–31.7%), whereas water/sorbitol formulations exhibited the highest stiffness (tensile modulus: 134–315 MPa) due to partial sorbitol crystallization. Water/glycerol systems provided the best balance between mechanical performance and structural stability under water uptake conditions. Overall, the results demonstrate the feasibility of converting oil-extraction-derived CSF into biodegradable, injection-mouldable biocomposites through an industrially relevant process.