Synthesis of biodegradable polyhydroxyalcanoate copolymer from a renewable source by alternate feeding

Polyhydroxyalcanoates copolymers with 3‐hydroxybutirate (3HB) and 3‐hydroxyvalerate (3HV) co‐monomers, P3(HB‐co‐x%HV), were produced in fed‐batch culture by Ralstonia eutropha DSM428 using fructose as a single carbon source in the first step and adding propionic acid in the second step by alternating feeding. Polymer yield was 0.18 g/L with a content of 24 mol% of the 3HV fraction determined by 1 H NMR. NMR measurements indicated that the polymer obtained is isotactic. The copolymer attained 35% of crystallinity according to X‐ray diffraction measurements, and two (020) planes were observed. Thermal behavior presented melting temperature at 154°C and the crystallization temperature was 65°C. A glass transition temperature was observed at −10°C. Average molecular weight measured by GPC was 4.9 × 10 5 Dalton. Isothermal radial growth rates of spherulites of P3(HB‐co‐24%HV) were studied. All experimental facts and the analysis of the sequence distribution of diads and triads of 3HB and 3HV units led to the conclusion that it is not a completely statistical random copolymer once it contains different types of segments. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers.