Abstract
The terpolymer of 3-hydroxybutyrate (3HB), 3-hydroxyvalerate (3HV), and 4-hydroxybutyrate (4HB) was produced employing Cupriavidus sp. DSM 19379. Growth in the presence of γ-butyrolactone, ε-caprolactone, 1,4-butanediol, and 1,6-hexanediol resulted in the synthesis of a polymer consisting of 3HB and 4HB monomers. Single and two-stage terpolymer production strategies were utilized to incorporate the 3HV subunit into the polymer structure. At the single-stage cultivation mode, γ-butyrolactone or 1,4-butanediol served as the primary substrate and propionic and valeric acid as the precursor of 3HV. In the two-stage production, glycerol was used in the growth phase, and precursors for the formation of the terpolymer in combination with the nitrogen limitation in the medium were used in the second phase. The aim of this work was to maximize the Polyhydroxyalkanoates (PHA) yields with a high proportion of 3HV and 4HB using different culture strategies. The obtained polymers contained 0–29 mol% of 3HV and 16–32 mol% of 4HB. Selected polymers were subjected to a material properties analysis such as differential scanning calorimetry (DSC), thermogravimetry, and size exclusion chromatography coupled with multi angle light scattering (SEC-MALS) for determination of the molecular weight. The number of polymers in the biomass, as well as the monomer composition of the polymer were determined by gas chromatography.
Highlights
Polyhydroxyalkanoates (PHA) represent a very attractive family of materials which are considered as an alternative to petrochemical polymers in applications which may benefit from their fully biodegradable and biocompatible nature
PHA are produced via fermentation since they are biosynthesized by numerous prokaryotes in the form of intracellular granules primarily as storage of carbon and energy [1]
Since a substantial amount of the final cost is attributed to the cost of the carbon substrate, there are many attempts to produce PHA from inexpensive or even waste products in the food industry [4] such as waste lipids [5,6], crude glycerol formed as a side product of biodiesel production [7,8], various lignocellulose materials [9], or even carbon dioxide [10,11]
Summary
Polyhydroxyalkanoates (PHA) represent a very attractive family of materials which are considered as an alternative to petrochemical polymers in applications which may benefit from their fully biodegradable and biocompatible nature. The resulting copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P[3HB-co-3HV]) reveals substantially improved material properties and decreased crystallinity [13]. PHA possessing 4HB subunits demonstrate increased biodegradability because lipases, which with PHA depolymerases, have the ability to degrade P(3HB-co-4HB) [15], show higher activity at a higher fraction of 4HB [16]. They find numerous high-value applications in the medical field [17]. Terpolymer P(3HB-co-3HV-co-4HB) containing all of the above-mentioned monomer subunits demonstrate even superior properties and could be used in numerous fields and applications [18]
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