Influence of sodium anhydroglucuronate on poly (di(ethylene glycol) methyl ether methacrylate) grafting onto isolated cellulose nanofibrils.

This study investigates the temperature-triggered properties and phase behavior of poly(di(ethylene glycol) methyl ether methacrylate) (PDEGMA) grafted onto cellulose nanofibrils (CNF) before and after the removal of water-soluble cellulose derivatives. Mass conversion and 1H NMR analyses revealed that removing soluble molecules from the pristine nanofibril suspension decreased the quantity of free PDEGMA chains in the solution. Besides, cryogenic transmission electron microscopy (cryo-TEM) imaging above the lower critical solution temperature (LCST) highlighted the formation of unbound PDEGMA globular aggregates through the association of dehydrated chains and increased CNF thickness due to the grafting. Rheology and phase behavior analyses showed significant changes above LCST, with a higher concentration of free chains favoring the collapse of the CNF network at 35 °C. The proposed mechanism suggests that free polymer chains help to bridge neighboring fibrils, producing a robust hydrogel at lower solid content. These findings highlight the role of cellulose residues in grafting reactions and their impact on the structure and flow properties of the materials.