Polyxydroxyalkanoates (PHA) are a family of linear optically active polyesters produced by bacterial fermentation and known for their overall sustainability, including biodegradability and biocompatibility. Because of their thermoplasticity and good mechanical properties, somehow similar to those of commercially relevant standard polymers, a study aimed at correlating their molecular structure to their behavior in terms of transport properties was initiated.
The case study is a random copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-4-hydroxyvalerate) (PHBVV), gently supplied by Bio-on S.p.A. (Italy). This PHA copolymer contains 24%mol of 3-hydroxyvalerate (3-HV) units and <1%mol of 4-hydroxyvalerate (4-HV) units. Compared to pure homopolymer poly(3-hydroxybutyrate) (PHB), the simplest and most diffused polymer of the PHA family, PHBVV is more flexible, transparent and less crystalline.
The thermal properties of PHBVV were investigated by differential scanning calorimetry (DSC), it’s structure and physical properties were investigated by Fourier Transform Infrared Spectroscopy (FT-IR) and by Gel Permeation Chromatografy (GPC). Ultimately it’s transport properties were analysed through permeability and absorption tests. At last, the capability of PHBVV to form very thin films through spin coating was examined.
The main conclusion, which can be made analysing experimental data, regards the fact that the presence of HV monomeric units affects drastically both structural and thermal properties of the material. In particular, it destabilises the crystalline structure which is typical of PHB, causing the on-set of melting at low temperatures and the presence of multiple peaks in the DSC curve.
From the point of view of transport properties, PHBVV presents a mixed behaviour. It is characterized by the solubility-driven selectivity and reduced size-sieving ability although a direct dependence of permeability from the kinetic diameter of penetrants is observable.
The ultimate purpose of this project is to promote industrial sustainability through the analysis of potential applicability of bio-based polymers in typical industrial applications