Influence of aliphatic amine grafting on the barrier properties of TEMPO-CNF films

In response to increasing environmental concerns and the growing demand for sustainable materials, this study presents a new approach for enhancing the functional properties of TEMPO-oxidized cellulose nanofiber (TEMPO-CNF) films through aliphatic amine grafting. Surface amidation was carried out using C4–C16 alkyl amines and 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methyl-morpholinium chloride (DMTMM) as a coupling agent in water–ethanol mixtures under mild conditions (room temperature and neutral pH), thereby avoiding the use of toxic reagents and complex purification steps. Successful covalent grafting was confirmed by ATR-FTIR, elemental analysis, and X-ray photoelectron spectroscopy (XPS). The functionalised films exhibited substantially improved surface and barrier properties, including higher water contact angles (+61%), reduced moisture and water uptake (up to −98%), enhanced water stability (mass loss reduced from 27% to ∼3–5%), and lower water vapor permeability (−63%). These improvements were achieved while maintaining high optical transparency and largely preserving the oxygen barrier properties of the films. Soil burial tests revealed a clear relationship between surface hydrophobicity and biodegradation behaviour. Films modified with short-chain amines underwent complete degradation within a few weeks, whereas those functionalised with longer alkyl chains showed only partial degradation after 24 weeks. Overall, the DMTMM-mediated aqueous amidation strategy provides a simple, environmentally friendly, and effective route for tailoring the surface characteristics of TEMPO-CNF films, expanding their potential for advanced packaging and barrier applications.