Radiation-Induced Modification of Antioxidant-Active Biodegradable Starch–PVA Films: Effect of Phenolic Additive Structure and Nanofiller Reinforcement

Starch-based films containing natural antioxidants are of interest for active food packaging, but the combined effects of reinforcement, phenolic structure and radiation processing remain underexplored. Starch–poly(vinyl alcohol) (PVA) films prepared from gamma-pre-irradiated starch, containing cellulose nanocrystals (CNCs, 1%), sodium alginate (5%) or both, and loaded with gallic acid (GA) or propyl gallate (PG), were irradiated with γ-rays or electron beams at 5 and 10 kGy. Tensile properties, swelling, solubility, insoluble fraction, contact angle, thermal behaviour, antioxidant capacity of ethanol extracts and gas evolution were measured. Formulation and additive effects were interdependent. PG increased tensile strength in the unfilled, alginate and CNC films (up to 16.88 ± 0.66 MPa for starch–PVA–alginate–PG), whereas the CNC/alginate/GA film combined 14.36 ± 0.61 MPa with an elongation at break of 506 ± 20%. CNC/alginate films had the highest insoluble fraction before irradiation (about 54%). Irradiation left tensile properties unchanged in most formulations but reduced the insoluble fraction by up to 24% in six of the eight films and lowered swelling mainly in CNC-containing films, indicating a net loss of retained material; crosslinking and chain scission were not measured directly. All films remained hydrophilic (contact angles 55–70°). The antioxidant capacity of the ethanol extracts changed little with irradiation, and H2 and O2 yields were higher in PG than in GA films. The mechanisms behind these observations were not tested. Barrier, migration, microstructural, biodegradation and food-preservation properties were not evaluated.