Anenvironmentally friendly and simple method, named SolReact, has been developed for a solvent-free esterification of cellulosenanocrystals (CNC) surface by using two nontoxic carboxylic acids(CA), phenylacetic acid and hydrocinnamic acid. In this process, thecarboxylic acids do not only act as grafting agent, but also as solventmedia above their melting point. Key is the in situ solvent exchangeby water evaporation driving the esterification reaction without dryingthe CNC. Atomic force microscopy and X-ray diffraction analyses showedno significant change in the CNC dimensions and crystallinity indexafter this green process. The presence of the grafted carboxylic wascharacterized by analysis of the “bulk” CNC with elementalanalysis, infrared spectroscopy, and 13C NMR. The abilityto tune the surface properties of grafted nanocrystals (CNC-g-CA) was evaluated by X-ray photoelectron spectroscopyanalysis. The hydrophobicity behavior of the functionalized CNC wasstudied through the water contact-angle measurements and vapor adsorption.The functionalization of these bionanoparticles may offer applicationsin composite manufacturing, where these nanoparticles have limiteddispersibility in hydrophobic polymer matrices and as nanoadsorbersdue to the presence of phenolic groups attached on the surface. [ABSTRACT FROM AUTHOR]