Biodegradable, High-Strength, Antiswelling Fluorescent Cellulosic Hydrogels via Salting-Out for Underwater Information Encryption and Anticounterfeiting

Fluorescent cellulosic hydrogels are suitable for information encryption and anticounterfeiting. However, their underwater application remains a major challenge due to insufficient antiswelling and mechanical properties affecting anticounterfeiting accuracy and durability. This study reports a strategy to prepare high-strength, biodegradable, and antiswelling fluorescent cellulosic hydrogels through salting-out and hydrophobic interactions. Salting-out and hydrophobic polycyclic structures (acrylpimaric acid) enhance the H-bonds, hydrophobic interactions, and coordination bonds of hydrogels, increasing the network cross-linking density. The subsequent improvement in the energy dissipation mechanisms results in a hydrogel with high compressive strength (18.52 MPa) and tensile toughness (12.16 MJ/m3). Furthermore, the enhanced network density and hydrophobic interactions provided the hydrogel with a high diffusion energy barrier, restricting the ingress and mobility of H2O and resulting in a swelling ratio (SR) of 0.04%. This hydrogel was capable of complete biodegradation in soil within 20 days. The perylene-3,4,9,10-tetracarboxylic acid (PTCA)-Eu/Tb ligands imparted fluorescence to the hydrogel; when they are combined with Python, they enable efficient information encryption and decryption underwater. Furthermore, the biodegradable fluorescent cellulosic hydrogel, prepared from inexpensive and ecofriendly raw materials (cellulose and rosin), offers a strategy for the sustainable development of underwater anticounterfeiting materials.