Enhancing mechanical durability and moisture stability in low-energy citric acid-crosslinked carboxymethyl cellulose films for cherry tomato preservation

Carboxymethyl cellulose (CMC) is a highly promising biopolymer for sustainable packaging; however, its application is restricted by inherent brittleness and moisture sensitivity. Although citric acid (CA) crosslinking strengthens the polymer matrix, conventional high-temperature curing often induces thermal degradation, thereby reducing mechanical strength. To solve these limitations, this study developed a low-energy crosslinking strategy. Instead of conventional high-heat curing, the optimal formulation (2.25 wt% CMC, 20 wt% CA) was established through a two-phase mechanism: a brief kinetic activation at 80°C (3 min) to initiate esterification, followed by a thermodynamically driven drying phase at 40°C that shifts the esterification equilibrium forward. This optimised matrix exhibited exceptional durability, demonstrating a 1.3-fold increase in tensile strength and a 4.7-fold increase in elongation at break compared to pristine CMC films. Structural and thermal evaluations (ATR-FTIR, TGA) verified the formation of a stable covalent ester network. The mechanical durability of this network effectively provides superior moisture stability and a reduced water vapour transmission rate. In practical trials, the crosslinked films maintained the sensory quality of cherry tomatoes over 21 days. These findings present a highly efficient, low-energy strategy for fabricating biodegradable films for fruit preservation.