Surface hydrophobization of TEMPO-oxidized cellulose nanofibrils (CNFs) using a facile, aqueous modification process and its effect on properties of epoxy nanocomposites

This work investigates the effects of surface modified cellulose nanofibrils (CNFs) on the mechanical, thermal, and morphological properties of epoxy nanocomposites. CNFs (extracted from wood pulp) were modified by using a two-step water-based method, where tannic acid (TA) acts as a primer with CNF suspension and reacts with hexadecylamine (HDA), forming the modified product as CNF-TA-HDA. The modified (-m) and unmodified (-um) CNFs were filled into hydrophobic epoxy resin with a co-solvent (acetone), which was subsequently removed to form a solvent-free two component epoxy system, followed by addition of hardener to cure the resin. Better dispersion and stronger adhesion between fillers and epoxy were obtained for m-CNFs than the um-CNFs, resulting in better mechanical properties of nanocomposites at the same loading. Elastic modulus, tensile strength, and work-of-fracture improved with increasing m-CNFs, with the most remarkable improvement observed for 0.5 wt% content, indicating good reinforcement of epoxy. um-CNFs showed incompatibility and lack of dispersion with epoxy leading to insignificant changes in the mechanical properties. Thermal stability and the degradation temperature of m-CNF/epoxy improved when compared to neat epoxy. The glass transition temperature (T-g) also increased substantially up to 5 degrees C for m-CNFs, while um-CNFs showed decrease in T-g.