Impact of TEMPO-oxidization strength on the properties of cellulose nanofibril reinforced polyvinyl acetate nanocomposites

摘要

Nanocomposites of polyvinyl acetate (PVAc) reinforced with two different TEMPO-oxidized cellulose nanofibrils (CNF) were prepared by casting/evaporation method. These two sets of CNF, designed as CNF-O-5 min (5 min of oxidation) and CNF-O-120 min (120 min of oxidation), are different by their surface charge, geometrical characteristics and crystallinity index. The weight fraction of CNF was changed from 1 to 10 wt%. The mechanical and thermal properties of the nanocomposite films were studied by dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and tensile tests, and their morphology was investigated by scanning electron microscopy (SEM). For all nanocomposites, increasing amounts of CNF led to a significant increase in the mechanical properties (increase in Young's modulus and tensile strength) and in the water uptake. On the other hand, the lost of transparency became very significant when the weight fraction of CNF exceeded 3 wt%. The comparison between the two sets of CNF showed that PVAc/CNF-O-5 min nanocomposite films had a tendency to display higher tensile strength and elastic modulus than those of PVAc/CNF-O-120 min films. In addition, the water uptake is higher for PVAc/CNF-O-120 min. Finally, the thermal stability analyses for PVAc/CNF films show that shorter and more charged fibrils (CNF-O-120 min) appear to slightly increase the thermal stability compared to other larger and less charged fibrils (CNF-O-5 min). All these results are discussed in connection with the CNFs characteristics.