Amidation of TEMPO-oxidized cellulose nanocrystals using aromatic aminated molecules

Abstract

In this study, the grafting of 1-methyl-3-phenylpropylamine (1-M-3-PP) on cellulose nanocrystals (CNCs) via a two-step reaction route was investigated and compared with physico-chemical surface adsorption. The first step involved subjecting CNCs to a 2,2,6,6-Tetramethyl-1-piperidinyloxy (TEMPO)-mediated oxidation. The carboxylic groups present on recovered oxidized TEMPO-CNC were quantified by several characterization methods (conductometric titration, elemental analysis, and X-ray photoelectron spectroscopy), and a degree of oxidation close to 0.2 was found. The second step was an amidation reaction carried out in an aqueous medium under mild conditions and in the presence of N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide (EDC)/N-hydroxysuccinimide (NHS) as catalyst. The recovered modified CNCs after amidation reaction with 1-M-3-PP (CNC-1-M-3-PP) were extensively washed and then characterized. The amount of grafted molecules was determined by several techniques like X-ray photoelectron spectroscopy (XPS), and the calculated degree of substitution was found to be close to 0.05 with respect to the bulk CNC. This low amount is sufficient to enhance the modified CNC dispersion and their colloidal stabilization in organic solvents, allowing the preparation of nanocomposites. Furthermore, such CNC-1-M-3-PP units with aromatic molecules attached to it can find applications in barrier materials in which the sorption of aromatic molecules can be very useful.