PLA/starch bi-layer films reinforced with rice straw cellulose nanofibers and functionalized with organosolv–lignin nanoparticles and grapefruit bioactives for shelf life extension of green grapes

Abstract

The transition toward sustainable food packaging demands biodegradable composites with multifunctional performance. In this study, polylactic acid (PLA)/starch bi-layer composites were developed by reinforcing the PLA layer with succinic anhydride-modified cellulose nanofibers (SACNFs) from rice straw and functionalizing the starch layer with modified lignin nanoparticles (MLNPs) and/or grapefruit flavedo extract (GFE). The addition of 2 wt% MLNPs enhanced tensile strength by 25.3%, while GFE increased flexibility without significant loss in strength. Hybrid MLNPs + GFE films exhibited notable barrier improvements, reducing water vapor permeability and oxygen permeability by 16.5% and 39.3%, respectively. Structural (FE-SEM, XRD) and spectroscopic (FTIR, UV-Vis) analyses confirmed compact morphology, good interfacial compatibility, and strong UV-blocking ability (<9.7% transmittance at 250–300 nm). The active films demonstrated high antioxidant potential and antimicrobial activity against Staphylococcus aureus and Pseudomonas aeruginosa, attributed to synergistic effects of MLNPs and phenolic compounds from GFE. Enhanced thermal stability was also observed in MLNP-containing composites. Importantly, packaging trials with fresh green grapes revealed that the developed film (MLNPs + GFE) effectively reduced weight loss (17.1 ± 1.2%), delayed browning (0.84 ± 0.09), and extended the shelf life up to 18 days under refrigerated storage, significantly outperforming unpackaged and LDPE-packed grapes. Overall, these results highlight that PLA/starch bi-layer films functionalized with biomass-derived nanofillers and natural bioactives are a promising route for sustainable active packaging and shelf life extension of perishable fruits such as green grapes.