Biosynthesis And Properties Of A Novel Polyhydroxyalkanoate Block Copolymer

Polyhydroxyalkanoates(PHAs)is kinds of biopolyester produced by many bacterial. Due to its biodegradability and biocompatibility, it has attracted much interst and advance researches in plastic industry and biomedical area etc. Even by commercial production, PHAs can replace the plastic derived from petroleum.In our study, polyhydroxyalkanoates (PHA) synthesis genes phaPCJ cloned from Aeromonas caviae were transformed into Pseudomonas putida KTOY06, a mutant of Pseudomonas putida KT2442, resulting in the ability of the recombinant to produce a short-chain-length and medium-chain-length PHA block copolymer consisting of poly-3-hydroxybutyrate (PHB) as one block and random copolymer of 3-hydroxyvalerate (3HV) and 3-hydroxyheptanoate (3HHp) as another block. The novel polymer was studied by differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR) and rheology measurements. DSC studies showed the polymer to possess two glass transition temperatures (Tg), one melting temperature (Tm) and one cool crystallization temperature (Tc), and rheology studies clearly indicated a polymer chain re-arrangement in the copolymer, these studies confirmed the polymer to be a block copolymer of over 70mol% homopolymer (PHB) of 3-hydroxybutyrate (3HB) as one block and around 30mol% random copolymers of 3HV and 3HHp as the second block. The block copolymer showed the highest tensile strength and Young's modulus compared with their same ratio random copolymer, same ratio blend of homopolymers of PHB, PHV and PHHp. Compared with other commercially available PHA, the short-chain and medium chain length block copolymer PHB-b-PHVHHp enjoyed application advantages and should draw more attention from the PHA researchers.