Advances in citric acid–crosslinked starch biopolymer chemistry, processing, and applications in sustainable packaging – A critical review

Biobased materials are increasingly being developed to replace petroleum-derived counterparts as renewable, recyclable, biodegradable, and environmentally friendly packaging products. This review focuses on starch-based biopolymers, given their abundance in the global supply chain and their potential to produce high-barrier, mechanically robust composites, films, and coatings. The barrier and mechanical performance of starch-based materials is critically examined, with emphasis on structure-property relationships. Key physical and chemical modification strategies used to overcome the inherent limitations of native starch are discussed, with a particular focus on citric acid crosslinking as a scalable and environmentally friendly approach for enhancing barrier performance in commercial packaging applications. Crosslinking starch with citric acid, a naturally derived multifunctional carboxylic acid, significantly improves the physical, chemical, morphological, thermal, crystalline, and hydrophobic properties of starch films and coatings. Optimal performance is achieved through precise control of processing parameters, including pH, temperature, citric acid concentration, plasticizer levels, and curing conditions. Importantly, citric acid crosslinking imparts enhanced structural stability while preserving the recyclability, compostability, and biodegradability of starch-based materials, consistent with green chemistry principles. Overall, this review highlights citric acid-crosslinked starch as a promising platform for circular packaging solutions aligned with Extended Producer Responsibility (EPR) frameworks and European Union (EU) regulatory requirements.