High Performance Compostable Biocomposites Based on Bacterial Polyesters Suitable For Injection Molding and Blow Extrusion

Nowadays, there is an increasing interest toward the substitution of oil-based polymers with biobased polymers. Poly(hydroxyalkanoates) (PHAs) emerge as a new class of biopolymers, that have gained more and more attention due to their thermoplastic behaviour, acceptable mechanical properties and biodegradability in compost conditions1. Applications based on PHAs, as a matrix, are generally found in the biomedical area due to their biocompatibility characteristic2, but is now extended into short-term areas such as the production of compostable films for the collection of organic wastes, food contact applications, and injected parts. Poly[(R)-3-hydroxybutyrate] (PHB) and Poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyvalerate] (PHBV) are aliphatic and biodegradable polyesters that belong to the PHAs family. The biopolymers are produced from renewable resources by using bacteria that synthetize PHAs as an energy feedstock. PHB, as well as PHBV, are thermoplastic polymers characterized by a high crystallinity content, hydrophobic behaviour, and are completely biodegradable in soil and compost conditions1,3,4. Moreover, both PHB and PHBV have a high melting temperature and a high resistance to organic solvents1. The main drawbacks of the use of PHAs for applications where a good balance between the mechanical properties and processability is required, are: – PHAs have a low melt strength due, in part, to the lack of physical and chemical crosslinking points. – The degradation window for PHB and its copolymers is narrow and in several cases, the melting temperature of PHB is close to its thermal degradation temperature5. – Narrow distribution of its molecular weight due to its particular synthetic route (bacterial)6. – In solid state, PHB is characterized by a large crystalline structure (spherulites) that makes it rigid and brittle due to its low nucleation density1. – Aging behavior has been observed during storage at room temperature7. Moreover, dramatic structural changes have been observed, in terms of reduction of the initial molecular weight of the polymer, by the presence of water molecules that promote chain breakdown reactions8 and by catalytic reactions involving the High Performance Compostable Biocomposites Based on Bacterial Polyesters Suitable For Injection Molding and Blow Extrusion