Fornaro, Mattia (2026) Sustainable PVA-based packaging films with starch and zeolite additives. [Tesi di dottorato]

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Abstract

Conventional polyolefin-based packaging films provide excellent mechanical strength and moisture barrier, but their fossil origin and persistence in the environment are increasingly incompatible with the transition toward a circular packaging economy. In parallel, the European Packaging and Packaging Waste Regulation (PPWR) is pushing the development of structures that are recyclable, material-efficient, and, where appropriate, biodegradable. In this framework, water-soluble poly(vinyl alcohol) (PVA) is an attractive candidate for thin functional layers thanks to its excellent film-forming ability, high dry oxygen barrier, and intrinsic biodegradability, but it remains limited by moisture sensitivity and by the need to tailor its end-of-life in real environments. At the same time, inorganic fillers such as zeolites and bio-based polymers such as starch offer opportunities to tune functional performance and environmental fate. This dissertation investigates the combined effect of starch and synthetic zeolites (types 4A and 13X) on the properties and soil biodegradation of thin PVA-based films prepared from aqueous formulations by rod coating. First, the formulation and processing window required to obtain defect-free, highly transparent films with a homogeneous zeolite distribution was established, using an ATR-FTIR “up–down surface” method to monitor additive sedimentation during drying. Two families of films were then produced at constant overall polymer concentration (20% w/v): (i) plasticized PVA films (20P) and their zeolite-filled counterparts, and (ii) PVA/starch blend films (18P/2S) with and without embedded zeolites at 2 and 4 wt% with respect to total polymer. The pristine films were characterized in terms of surface morphology (optical microscopy and SEM), thermal stability (TGA/DTG), degree of crystallinity (XRD), water uptake, and water vapour transmission rate (WVTR). The environmental behaviour of the films was assessed by soil burial tests in a controlled, highly moist soil at 30 °C for 16 weeks. At each unburial, weight loss, surface morphology, and ATR-FTIR spectra were collected, while XRD was used to compare crystallinity before and after burial. Finally, the metabolic activity of the soil microbiota was quantified by an AlamarBlue® assay on liquid extracts of the test soils and appropriate references. The results show that the optimized 18P/2S formulations allow for industrially relevant rod-coating viscosities and, when dried at 105 °C, yield a nearly uniform zeolite distribution throughout the film thickness. Starch addition and zeolite loading both influence film microstructure: starch introduces additional surface defects but also markedly increases the thermal stability of plasticized PVA, while zeolites—especially type 13X at 4 wt%—further shift the main degradation peak to higher temperatures. All PVA-based films remain highly hydrophilic, with water uptake above 130% and WVTR of the order of 10³ g m⁻² d⁻¹, and zeolite addition at the tested loadings has limited impact on moisture barrier. Under soil burial, neat 20P films undergo primarily an initial loss associated with plasticizer leaching and show limited further mass loss, whereas starch-containing films exhibit significantly higher weight loss and more severe surface erosion, consistent with preferential starch biodegradation and a modest enhancement of PVA degradation. Zeolites do not hinder soil biodegradation; on the contrary, both 4A and 13X slightly increase the overall mass loss, likely by favouring water retention and micro-erosion around filler domains. FTIR and XRD analyses confirm the disappearance of glycerol and starch bands, moderate reduction of PVA crystallinity and the persistence of the inorganic phases. Soil bacterial activity is comparable across all films and higher than in the bare reference soil, essentially reflecting the availability of readily metabolizable carbon. Overall, the study provides a coherent picture of how starch and zeolite microfillers can be combined with fully hydrolysed PVA to obtain rod-coatable, thin films with tailored thermal response and controlled biodegradation in soil. These results support the future design of PVA-based, zeolite-modified coatings as functional layers in recyclable packaging structures in line with emerging PPWR requirements, and they delineate the key trade-offs and open questions that must be addressed for industrial implementation.

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