Highly transparent PVA/nanolignin composite films with excellent UV shielding, antibacterial and antioxidant performance

In the present work, polyvinyl alcohol (PVA) nanocomposite films containing various contents of lignin nanoparticles (LNP) (1, 2 and 3 wt%) were formulated by a simple solvent cast method and cross-linked by adding glutaraldehyde (GA) and citric acid (CA). Herein, we investigated the effects of crosslinker types and LNP loading on optical, thermal, mechanical, antioxidant and antibacterial behaviour of PVA nanocomposite films for active food packaging. The results of UV irradiation shielding effect showed that the addition of 3 wt% of LNP reduced significantly the UV-B/UV-C transmittance to 0 for both P-GA-3LNP (PVA film with 3 wt% of LNP cross-linked by GA) and P-CA-3LNP (PVA film with 3 wt% of LNP cross-linked by CA) films. Results of thermogravimetric analysis (TGA) showed that thermal stability for all PVA nanocomposites was improved, ascribing it to the strong interactions between LNP and PVA in presence of GA and CA. In the meanwhile, plasticization was also observed for both GA and CA crosslinked PVA films, with tensile strength increased from 26.0 MPa (PVA) to 38.1 MPa (P-GA-3LNP) and 32.7 MPa (P-CA-3LNP) and constant values of elongation at break (240, 229 and 237%) for these three films. Additionally, P-GA-3LNP film showed more evident antibacterial and antioxidant ability than P-CA-3LNP, with evidence of better maintained freshness of shrimps under UV irradiation fluorescence measurements.