Octadecylamine as chemical modifier for tuned hydrophobicity of surface modified cellulose: toward organophilic cellulose nanocrystals

A novel, environmentally friendly and simple method for chemical functionalization of microcrystalline cellulose (MCC) to produce organophilic cellulose nanocrystals (CNC-ODA) is herein proposed. Surface modification of MCC was successfully achieved by simple chemical oxidation followed by citric acid esterification and amidation reactions. The resultant nanocrystals were fully characterized for their chemical structure, morphology, crystalline structure, thermal stability, and surface hydrophobicity. FTIR analysis revealed that the long chain hydrocarbon structure was successfully grafted onto CNC surfaces. The crystallinity index of the cellulosic materials calculated by the Segal equation from the corresponding X-ray diffraction (XRD) patterns was relatively reduced from 83.27% for microcrystalline cellulose to 71.12% for organophilic cellulose nanocrystals (CNC-ODA). Moreover, CNC-ODA showed improved thermal stability than unmodified MCC as elucidated by TGA. Scanning electron microscopy, atomic force microscopy and transmission electron microscopy showed significant change in the size and shape of the produced nanocrystals. The effectiveness of ODA grafting was evidenced by the enhanced hydrophobicity and the long-term stability of the colloidal suspension of organophilic cellulose nanocrystals in various organic solvents which enables this material to be used as highly hydrophobic coating and reinforcing agent for solvent-borne nanocomposites systems. The adopted approach is qualified as environmentally friendly for mass-production of organophilic cellulose nanocrystals without any use of organic solvents or toxic reagents.