Chemical Modification of Cellulose Fibers for Sustainable Food Packaging: Structure-Property-Sustainability Relationships.

Cellulose fibers offer renewable sourcing and an established recycling infrastructure for food packaging applications. Their hydroxyl groups bind water strongly, which causes dimensional instability and compromises barrier performance at elevated humidity. Chemical modification targets this limitation through controlled changes to hydroxyl reactivity, surface charge, and interfiber hydrogen bonding. This review covers four principal covalent modification routes: esterification, etherification, phosphorylation, and oxidative functionalization. The spatial localization of functional groups-surface-enriched versus bulk modification-is treated as a cross-cutting analytical parameter governing the translation of molecular chemistry into barrier performance, mechanical behavior, and recyclability. We emphasize how molecular parameters (degree of substitution (DS), charge density, and the spatial distribution of functional groups) translate into barrier properties, mechanical performance, and grease resistance under realistic service conditions. Two practical constraints define the design space. Bulk modifications that penetrate the fiber wall can release reagents or by-products into food (non-intentionally added substances, NIASs), whereas surface-confined chemistry reduces this risk substantially. Modifications that resist repulping or introduce persistent contaminants damage recyclability. Life cycle impacts often derive more from processing steps (mechanical fibrillation, solvent use, and multi-stage washing) than from feedstock selection. We focus on three deployment-relevant outcomes: performance retention above 75% relative humidity, migration risk under food contact regulations, and compatibility with industrial fiber recycling. The aim is to identify strategies that can move from laboratory demonstration to production-scale implementation.