Cellulose Nanofibrils and Diblock Copolymer Complex: Micelle Formation and Enhanced Dispersibility

A great challenge to the utilization of bioderived cellulose nanofibrils (CNFs) is related to dispersion, where the hydrophilic nature makes them difficult to disperse in both organic solvents and hydrophobic polymers. In this study, an amphiphilic diblock copolymer, poly­(methyl methacrylate-<i>b</i>-acrylic acid) (PMMA-<i>b</i>-PAA), which contains a short interactive block of PAA and a long hydrophobic block of PMMA, was utilized to modify the surface of CNFs covered with carboxylic acid groups (CNF-COOH). The PAA block binds to the surface carboxylic acid groups on the CNFs through the formation of multiple hydrogen bonds, while the hydrophobic PMMA block enables better dispersion of the CNFs as well as interfacial adhesion with the matrix polymer. The attachment of PMMA-<i>b</i>-PAA to the CNFs was confirmed through Fourier transform infrared spectroscopy. Micelles were observed to form from a dispersion of CNF-COOH/PMMA-<i>b</i>-PAA complex in H₂O. Good dispersion with individualized nanofibrils has been achieved in dimethylformamide, dimethyl sulfoxide, ethanol, and methanol even when a low amount of block copolymer was functionalized on the CNF surface. The dispersion level of CNF-COOH/PMMA-<i>b</i>-PAA correlates well with the dielectric constant of the solvents, where solvents with high dielectric constants are better able to disperse the PMMA-<i>b</i>-PAA modified nanofibrils