Plant protein-based biocomposites: Structure–processing–property relationships governing mechanical and thermal performance

Petroleum-derived plastics dominate global polymer production, whereas bio-based alternatives account for only a small share. Comparisons among plant-protein materials are limited by differences in formulation and testing conditions. This review examines structure–processing–property relationships across seven major plant-protein feedstocks using a common framework.. It covers soy, wheat gluten, zein, pea, canola, sunflower and cottonseed proteins, from extraction and precipitation to processing, crosslinking, blending and reinforcement. Reported examples include an increase of up to ca. 69% in hydrogel rigidity with cellulose nanofibre reinforcement. Natural-fibre hybridisation increased the Young’s modulus and tensile strength of soy-protein composites by up to ca. 200% and ca. 47%, respectively. Bio-based crosslinkers such as genipin and tannic acid improved selected mechanical and barrier properties, while dynamic network designs offered routes to reprocessing in the systems reviewed. The effects depend on formulation and test conditions and should not be interpreted as general performance gains. Moisture sensitivity, feedstock variability, narrow processing windows and limited industrial validation remain substantial barriers. The review identifies design requirements for packaging, agricultural, biomedical, construction and selected lightweight structural applications.