Microbial Synthesis and Characterization of Poly (3-Hydroxybutyrate-co- 4-Hydroxybutyrate) Copolymers

Abstract

The research is focused on the prospective representative of the family of biodegradable polymers – polyhydroxyalkanoates (PHAs), the copolymer poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3HB-co-4HB). Difficulties with producing this type of PHA are associated with the fact that the precursor for the 4-hydroxybutyrate (4HB) monomers synthesis, the γ-butyrolactone, is toxic for the bacteria producers and reduces the total biomass production and the polymer yield when it is added to the medium. Having used the natural strains of hydrogen-oxidizing bacteria Ralstonia eutropha B5786 and Cupriavidus eutrophus В10646, the latter possessing the increased sustainability to the γ-butyrolactone influence, the conditions for efficient synthesis of P(3HB-co-4HB) have been determined. A set of highly purified samples of P(3HB-co-4HB) with different content of 4HB (from 8.7 to 24.3 mol %) was produced. It has been determined that the incorporation of 4HB in the copolymer of a higher degree than 3-hydroxyvalerate and 3-hydroxyhexanoate leads to the decrease of the copolymer’s crystallinity; samples with the crystallinity of 12 % and 25 % have been obtained. It has been demonstrated that the average molecular weight of the P(3HB-co-4HB) samples and the polydispersity do not depend on the ratio of monomers and vary within the wide range from 540 to 1100 kDa and from 1.91 to 2.76 correspondingly. It has been determined that the 4HB content in the studied range (8.7-24.3 mol %) does not effect the melting temperature of the copolymers (168.9172.5 oC).