A polyhydroxyalkanoates (PHAs) multifaced study: extraction, characterization and applications

In recent years, the problems associated with solid waste management and the dependence on petroleum-based plastics have created great interest, mainly focused on the development of bio-derived and biodegradable polymers. One of the most promising group of biopolymers that can be used as a fossil plastic substitute is the polyhydroxyalkanoates family (PHAs). PHAs are polyesters that can be naturally accumulated as intracellular granules by many prokaryotic microorganisms. The stored copolymer is a biodegradable thermoplastic material. Poly(3-hydroxybutyrate) [P(3HB)] and its copolymers, mainly with 3-hydroxyvalerate monomeric repeating unit [P(3HB-co-3HV)], are among the most investigated biopolymers of this class. The combination of thermoplasticity and biodegradability makes PHAs suitable for several applications, including packaging and biomedical devices. However, problems related to the environmental and economic sustainability of the extraction and purification as well as PHA chemical modification limit the large-scale diffusion. In this thesis, the transition toward eco-friendly methodologies has been addressed both for P(3HB-co-3HV) recovery from biomasses and for chemical functionalization. More in detail, the extraction of P(3HB-co-3HV) from biomass by dissolution in ethyl esters and through innovative coupled treatment based on cell lysis is proposed as an effective alternative to the commonly used chloroform solubilization. As far as the application of PHA in the biomedical field, chemical modification is often necessary to increase the polymer hydrophilicity to humper particles aggregation in body fluids as well as to favour the adhesion of cells and possible internalization processes. Then, a safer alternative to the main approaches described in literature has been proposed. It involves the use of the non-cytotoxic ionic liquid choline taurinate [Ch][Tau] for the surface modification of PHA films and for the preparation of self-surfactant systems, used in nanoparticles fabrication. In addition to the mentioned economic and sustainability-related drawbacks, P(3HB-co-3HV) copolymers with low 3HV content are difficult to process, because of high melting temperature, and the obtained items are brittle, because of the high crystallinity. The possibility of producing 3HV-rich copolymers leads to a reduction of crystallinity and, therefore, to better processability and mechanical properties. On the other hand, a gap of knowledge is still present about the effect of high 3HV concentration on copolymer properties. Then, part of this thesis is dedicated to a basic study of the structure-property relationships of P(3HB-co-3HV) copolymers with various 3HV content and to the evaluation of the effect of copolymer composition processing and compounding.