Study of the hydrophobization of TEMPO-oxidized cellulose gel through two routes: amidation and esterification process

In this paper, we studied the hydrophobization of TEMPO-oxidized cellulose gel (TOCgel) by covalent coupling of long carbon chains via esterification and amidation processes. In this context, amidation process was achieved by covalent coupling of stearylamine (SA) on the carboxyl moieties of TOCgel using carbodiimide and hydroxysuccimide as catalyst and amidation agent. In parallel, esterification process was realized by grafting of alkyl ketene dimer (AKD) on the hydroxyl groups of TOCgel in the presence of 1-methylimidazole as a promoter. The grafting state of the final products obtained under heterogeneous conditions was confirmed by fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), transmission and scanning electron microscopy, and contact angle measurement (CAM). The hydrophobic behavior of the obtained products was discussed based on the results of CAM and absorption rate of water drop in their film surface. FTIR and XPS results indicated the formation of amide bonding for the SA-g-TOCgel (amidation), and β-keto ester linkages for the AKD-g-TOCgel (esterification). As confirmed by CAM, the both chemical treatments enhanced the transition hydrophilic/hydrophobic behavior of the TOCgel fibers. It appeared also that CA values of grafted samples showed a slightly greater hydrophobicity of AKD-g-TOCgel (115° ± 2°) relatively to SA-g-TOCgel (102° ± 2°). However, the absorption rate of water drop seems to be relatively faster for AKD-g-TOCgel than for SA-g-TOCgel. Indeed, the water resistance of amidation product could be due to the high graft efficiency obtained (46.3 %) in comparison with that of the esterification product (30 %). In parallel, this result was confirmed by the dispersion test of modified TOCgels in hexane solvent which indicated clearly the high stable dispersion of SA-g-TOCgel obtained through the amidation process. Moreover, TGA result demonstrated that the thermal stability was found to be slightly higher for SA-g-TOCgel than for AKD-g-TOCgel. Finally, the excellent hydrophobic properties of modified TOCgel material could be suitable to be used as reinforcement for nonpolar polymer matrices in industrial applications.