Polyvinyl alcohol (PVOH) exhibits outstanding gas-barrier properties, which favor its use as a biodegradable, high-barrier coating on food-packaging films, possibly in combination with modified atmospheres. Nonetheless, its high sensitivity to water can result in a severe loss of barrier properties, significantly limiting its applications with fresh foods and in high-humidity conditions. In this work, the water vapor (P_WV) and oxygen permeability (PO₂) of high-barrier biodegradable films with PVOH/PLA + wax double coatings were extensively characterized in a wide range of relative humidity (from 30 to 90%), aimed at understanding the extent of the interaction of water with the wax and the polymer matrices and the impact of this on the permeation process. What is more, a mathematical model was applied to the P_WV data set in order to assess its potential to predict the permeability of the multilayer films by varying storage/working relative humidity (RH) conditions. The carbon dioxide permeability (PCO₂) of the films was further evaluated, and the corresponding permselectivity values were calculated. The study was finally augmented through modified atmosphere packaging (MAP) tests, which were carried out on double-coated films loaded with 0 and 5% wax, and UV-Vis analyses. The results pointed out the efficacy of the PLA + wax coating layer in hampering the permeation of water molecules, thus reducing PVOH swelling, as well as the UV-shielding ability of the multilayer structures. Moreover, the MAP tests underlined the suitability of the double-coated films for being used as a sustainable alternative for the preservation of foods under modified atmospheres.

Biodegradable polymers suffer from inherent performance limitations that severely limit their practical application. Their functionalization by coating technology is a promising strategy to significantly improve their physical properties for food packaging. In this study, we investigated the double coating technique to produce multifunctional, high barrier and heat-sealable biodegradable films. The systems consisted of a web layer, made of poly(lactide) (PLA) and poly(butylene-adipate-co-terephthalate) (PBAT), which was first coated with a poly(vinyl) alcohol based layer, providing high barrier, and then with a second layer of PLA + ethylene-bis-stereamide (EBS) wax (from 0 to 20%), to provide sealability and improve moisture resistance. The films were fully characterized in terms of chemical, thermal, morphological, surface and functional properties. The deposition of the PVOH coating alone, with a thickness of 5 μm, led to a decrease in the oxygen transmission rate from 2200 cm³/m² d bar, for the neat substrate (thickness of 22 μm), to 8.14 cm³/m² d bar (thickness of 27 μm). The deposition of the second PLA layer did not affect the barrier properties but provided heat sealability, with a maximum bonding strength equal to 6.53 N/25 mm. The EBS wax incorporation into the PLA slightly increased the surface hydrophobicity, since the water contact angle passed from 65.4°, for the neat polylactide layer, to 71° for the 20% wax concentration. With respect to the substrate, the double-coated films exhibited increased stiffness, with an elastic modulus ca. three times higher, and a reduced elongation at break, which, however still remained above 75%. Overall, the developed double-coated films exhibited performances comparable to those of the most common synthetic polymer films used in the packaging industry, underlining their suitability for the packaging of sensitive foods with high O₂-barrier requirements.

The application of biodegradable polymeric coatings is an effective strategy to enhance the functional performance of paper-based materials while preserving their recyclability.This study investigates the relationship between polymer concentration, processability and performance of an ethylene-modified poly(vinyl alcohol) (m-PVOH) coating applied to a Kraft paper (KP) substrate.The rheology of aqueous m-PVOH solutions (5–30 wt%) were measured to assess their suitability for high-speed coating processes such as gravure and flexography, and the effect of ageing on their stability. Viscosity increased with polymer concentration, with a critical transition between 20 and 30 wt% where polymer–polymer interactions and irreversible structural rearrangements became dominant.Formulations containing 10–20 wt% m-PVOH were selected for paper coating based on the rheology and processability criteria. Higher polymer concentrations reduced impregnation into the paper matrix, leading to the formation of compact and continuous coating layers. The coated papers exhibited significantly enhanced air and water resistance, while maintaining stable oxygen and water vapour barrier properties (OTR ≈ 580 cm³/(m²·day·bar), WVTR ≈ 4 g/(m²·day)). The coatings also increased surface polarity and preserved the mechanical integrity of the substrate. m-PVOH formulations can enable scalable, recyclable, and environmentally friendly paper-based packaging solutions.

Biodegradable polymer blends are promising materials for flexible packaging films with tunable properties. In this work, poly(butylene succinate)/poly(vinyl alcohol) (PBS/PVOH) blown films were produced by twin-screw melt compounding followed by film blowing, and the effect of PVOH content on phase organization, processability, morphology, and functional performance was investigated. The blends showed phase-separated morphologies and composition-dependent structural evolution. DSC indicated that both polymers largely retained their crystallization ability, although the crystallinity decrease was more evident for PVOH. Rheological analysis revealed limited compatibility and increasing elastic response at higher PVOH contents, consistent with the formation of structured PVOH insoluble gel-like domains. SEM confirmed droplet–matrix morphologies, becoming coarser and more heterogeneous at high PVOH content, with film-blowing instability for PBS/PVOH 20/80. PVOH incorporation improved oxygen and water-vapor barrier properties and increased stiffness, but progressively reduced ductility. Model fitting supported the structure–property correlations, relating film performance to blend composition, morphology, and PVOH phase organization. Among the processable formulations, PBS/PVOH 80/20 showed the best balance between improved barrier properties and acceptable extensibility for food packaging application. Overall, PBS/PVOH blown films are promising biodegradable systems for flexible food packaging, provided that PVOH phase structuring is properly controlled.