Development and Characterization of Monolayers and Multilayers Based on Biodegradable Materials Derived from Waste and By-Products of Interest in Food Packaging

The production and consumption of petroleum derived plastics that are not biodegradable has grown exponentially in recent decades, with the consequent impact on nature and organisms.The food packaging sector is today considered the main source of plastic contamination.Therefore, the study and development of new materials derived from renewable and biodegradable resources has emerged as a new field of great scientific, social, economic and political interest.The current PhD thesis focused on the development and characterization of polyhydroxyalkanoate (PHA) biopolymers derived from agro-industrial by-products (fruit pulp and cheese whey) and from the organic fraction of municipal wastewater, the municipal biowaste, synthesized by mixed microbial cultures (MMCs) and produced by electrospinning and melt compounding technologies.The resultant materials were particularly developed to obtain high-oxygen-barrier active monolayers and multilayers for use in Circular Bioeconomy-based food packaging.In order to achieve the objectives, this PhD thesis has been divided into three blocks according to the technology used to obtain the materials.The first block consisted of the extraction of PHAs derived from agro-industrial waste for their optimal use in production processes.After this, the PHAs were then processed using the electrospinning technique, whereby polymeric fibers were obtained and thermally post-treated by an annealing process, at temperatures below the melting temperature of the polymer used, to form continuous and homogeneous films, also known as "biopapers".These monolayers showed good thermal and mechanical properties, as well as a high barrier to both vapors and gases.In addition, the fibers were functionalized with eugenol, an organic compound present in essential oils, to provide them with active antimicrobial function against foodborne microorganisms.On the other hand, the electrospinning of poly(ethylene-covinyl alcohol) (EVOH) copolymers, a synthetic polymer that is claimed to biodegrade under specific conditions and with high oxygen barrier, was performed.Cellulose nanocrystals (CNCs) were added to EVOH, to create high barrier more sustainable hybrid monolayers.In the second block, the materials were processed using the melt compounding technique.For this purpose, the biomass derived PHAs extracted in the first block were blended with commercial PHAs as well as with cellulosic fillers, in this case rice husk flour (RHF), in order to form "green composites", where all the materials were based on renewable and biodegradable resources.After film formation by hot pressing, the blends showed excellent miscibility and optical properties, improved flexibility, as well as barrier properties similar to the neat biopolyester material.Finally, in the third block, multilayer systems were produced using ad-hoc developed PHA blends, and PHA electrospun monolayer materials developed in the first block.They were based on the adhesive properties of the electrospun fibers after thermal treatment, which allowed the elimination of synthetic adhesive substances normally used in the industry, and on the use of the CNCs coatings as oxygen barrier interlayers.Thus, the multilayer systems developed were fully compostable, with high oxygen barrier, being potential candidates to replace current food packaging based on non-renewable petroleum-based materials.Therefore, the materials developed herein are very promising bioadhesives showing antimicrobial and high barrier properties, as well as outer layers for structural or thin film purposes.Thus, by lamination, these materials can result in self-standing multilayer films, which can be used in rigid or semirigid packaging as well as in flexible packaging.They are sustainable and environmentally friendly, as they are made from renewable sources or waste, and are biodegradable by composting, and, in some case, even biodegradable in the environment.Furthermore, they are potentially capable of providing comparable quality and food safety to those currently marketed from petrochemical sources. INDEXI. Introduction…………………………………………………...…1 1. Food packaging materials………………………………………………...…...3 1.1.Current packaging status………………………………………………...……….3 1.2.Polymers used in packaging……………………………………………….….….4 1.3.Biopolymers as a new alternative………………………………….….….…...….6 2. Polyhydroxyalkanoates for sustainable food packaging………………………8 2.1.Polyhydroxyalkanoates production through mixed microbial cultures using by-products………………………………………………………………………….….10 2.2.Circular Bioeconomy…………………………………………………...………13 3. High-oxygen-barrier materials…………………………………………...….14 3.1.Poly(ethylene-co-vinyl alcohol) copolymers…………………………...………16 3.2.Cellulose nanocrystals……………………………………………………....….18 4. Processing technologies in