Study of biodegradable polyesters as materials for applications in the fishing industry

The massive production of short-lived plastics has generated severe pollution, with materials from the fishing industry — nets, ropes, and expanded polystyrene (EPS) packaging — accounting for about 10% of marine litter. These fossil-based, non-biodegradable polymers cause long-term environmental damage through ghost fishing and microplastic formation. This thesis investigates the use of biodegradable polyesters, particularly polylactic acid (PLA) and polyhydroxyalkanoates (PHA), as sustainable alternatives for fishing gear and packaging, with additional applications in biomedical and sensing fields. In the packaging sector, with the goal of replacing EPS fish boxes, sustainable, water-repellent, biodegradable coatings for cardboard were developed. This was achieved by producing aqueous PLA dispersions stabilized with a PEG-PLA-PEG triblock copolymer. Formulations containing about 40 wt% solids remained stable for six months. Thickened with xanthan gum and applied to paper at 60 °C, they formed — as confirmed by SEM analysis — a continuous layer with excellent adhesion due to partial interpenetration with the paper fibers. The coated samples exhibited excellent barrier properties: Cobb60 <5 g/m2 and WVTR <100 g/(m2·day) at coating weights ≤15 g/m2, matching the performance of solvent-based PLA coatings. The coated paper remained repulpable at low coating weights. (1) For fishing equipment, the work focused on producing mussel aquaculture nets using recycled PLA as a replacement for polypropylene (PP), employing the same extrusion processes used for PP nets. Biodegradation tests showed that PLA nets fully degrade within three months under industrial composting conditions, while showing no significant changes after four months in simulated marine conditions and only minimal degradation in soil after one year. This indicates that the nets are suitable for aquaculture use but do not degrade rapidly if accidentally released into the marine environment. To directly replace EPS foam, insulating bio-foams were developed from blends of amorphous PHA with either amorphous or semicrystalline PLA. The blends, characterized by TEM, DSC, TMA, and rotational rheology, showed immiscible morphologies. Foaming was carried out using supercritical CO2: after optimization, low-density foams were produced for all amorphous compositions and for semicrystalline blends containing up to 20% PHA. The accelerated recrystallization of PLA in semicrystalline blends posed challenges to the foaming process. Biodegradation tests in home compost and marine environments showed that blended foams degrade more effectively than neat PLA foams, although PHA degradation in semicrystalline blends was slower. The aqueous dispersions were also exploited in complementary studies. First, PLA/graphene oxide composites were produced via film casting; laser scribing enabled the formation of conductive pathways within the insulating material, creating biodegradable electrochemical platforms suitable for biomarker detection and potential smart-packaging applications. The material proved industrially compostable. Second, the dispersions were used to encapsulate osteogenic peptides: the resulting films promoted the differentiation of stem cells into osteoblasts, showing promise as biodegradable coatings for titanium bone implants. (1) Calosi, M. et al., Progress in Organic Coatings 2024, 193, 108541.