Thermomechanical, antioxidant and moisture behaviour of PVA films in presence of citric acid esterified cellulose nanocrystals.

In the present work, poly(vinyl alcohol) (PVA) active packaging films containing different amounts (1, 3, 5, 10 and 15% wt.) of unmodified cellulose nanocrystals (CNC) and citric acid modified cellulose nanocrystals (mCNC) were prepared by solvent casting and their effect on thermal, mechanical and wettability behaviour of the resulted films was investigated. Results showed that both CNC and mCNC improved the thermal stability of the neat PVA matrix, but different mechanical properties and water wettability were found. Thermal stability of the materials was enhanced, by measuring shift of onset and peak temperatures that moved, respectively, from 251.5 to 298.1 °C and from 283.4 to 374.2 °C, in the case of PVA/15CNC and PVA/15mCNC films. The presence of mCNC contribute to increase the crystallinity up to 52% for PVA/10mCNC film, while it was limited to 39% for PVA/10CNC. Interestingly, PVA/mCNC composite films showed a clear UV shielding effect, while no UV resistance behaviour was detected for PVA/CNC films. Overall migration tests revealed that the migration value was well below the legislative limits (60 mg kg-1) for food contact materials, PVA/mCNC composite films have higher radical scavenging activity than PVA/CNC films and moisture content of PVA films containing mCNC was reduced at high RH. In conclusion, PVA/mCNC films could be considered as high-performance active food packaging materials.