Valorization of sunflower protein isolate in biodegradable poly(vinyl alcohol) composite films: Structure,...

Sunflower protein isolate (SP), a byproduct of oil extraction, was blended with polyvinyl alcohol (PVA) to develop degradable composite films for sustainable food packaging. SP/PVA films with varying mass ratios (0:100, 20:80, 50:50, 80:20, and 100:0) and glycerol content (0-50 wt%) were prepared by solvent casting. Intermolecular hydrogen bonding between SP and PVA was confirmed by FTIR and XRD, which disrupted PVA crystallinity and enhanced compatibility. SP imparted excellent UV-blocking properties (transmittance <15% in UVC region) and remarkable antioxidant activity, with SP20GL20 achieving 99.4% ABTS radical scavenging inhibition. Mechanical properties were tunable by composition: increasing SP content reduced tensile strength from 45.2 MPa (SP0GL0) to 5.0 MPa (SP80GL0), while glycerol addition increased flexibility, with elongation at break reaching up to 200% for SP50GL20 and SP50GL50. Soil burial tests revealed composition-dependent degradation: pure PVA showed minimal mass loss (~4% after 40 days), whereas SP80GL0 reached ~65% mass loss, and pure SP films degraded completely within 5-10 days. Physical observations confirmed progressive darkening with increasing SP content, consistent with microbial colonization and phenolic compound oxidation. These results demonstrate that sunflower protein can be successfully valorized into degradable films with tunable mechanical properties, intrinsic antioxidant functionality, and a clear end-of-life pathway for active food packaging applications.