One-Pot Water-Based Hydrophobic Surface Modification\nof Cellulose Nanocrystals Using Plant Polyphenols

Abstract

An environmentally\nfriendly procedure for the surface modification\nof cellulose nanocrystals (CNCs) in water is presented. Tannic acid\n(TA), a plant polyphenol, acts as the primer when mixed with CNCs\nin suspension, which are then reacted with decylamine (DA), the hydrophobe.\nSchiff base formation/Michael-type addition covalently attaches primary\namines with long alkyl tails to CNC-TA, increasing the particle hydrophobicity\n(contact angle shift from 21 to 74°). After modification, the\nCNC-TA-DA particles in the water phase separate, allowing for easy\ncollection of modified material. The dried product is readily redispersible\nin toluene and other organic solvents, as demonstrated by turbidity\nmeasurements, dynamic light scattering, optical microscopy, and liquid\ncrystal self-assembly behavior. Electron microscopy, Fourier transform\ninfrared spectroscopy, X-ray photoelectron spectroscopy, solid-state ¹³C NMR, and X-ray diffraction support the successful surface\nmodification and indicate that CNC particle morphology is retained.\nThe modified CNCs have a slightly decreased onset of thermal degradation\n(ca. 10 °C lower) compared with that of unmodified CNCs. We believe\nthat this surface modification strategy presents a scalable, simple,\nand green approach to the production of hydrophobic biobased nanoparticles\nwhich may lend themselves as reinforcing agents in nonpolar polymer\ncomposites or stabilizers and rheological modifiers in nonaqueous\nliquid formulated products.