Study On Modification Of Different Characteristics Polyhydroxyalkanoates Produced By Two Strain

Polyhydroxyalkanoates(PHA) is an environmental friendly material, It can be biodegradabled, But the defect properties of PHA, such as low melting point, poor toughness and so on, limiting its processing and application scope, It has important significance to improve the performance of the expansion application fields of PHA.In this paper. We used the S8 strains who produced polyhydroxybutyrate(PHB) and U-yuan strains who produced Poly-?-hydroxypelargonate as the original strains, S8 strain whoes cell dry weight and PHA content were 22.60 g/L and 52.48%, Morphological, physiological and biochemical characteristics and 16S rDNA sequence identified as Achromobacter, The molecular weight of PHB was 4.37 � 10~5, melting point was 174.6 ?, elongation at break was 4.5%, melting point was high, but toughness was poor. U-yuan strain whoes cell dry weight and PHA content were 24.87 g/L and 55.21%, It was identified as Pseudomonas alcaligenes, Molecular weight of Poly-?-hydroxypelargonate was 1.31� 106, melting point was 51.6 ?, the elongation at break was 282.1%, toughness was good, but melting point was poor. To obtain a higher melting point and better toughness of PHA by protoplast fusion, adding precursors and mixed bacteria fermentation. Analyzed the chemical structure of polymers by fourier transform infrared spectroscopy (FTIR), Measured polymer molecular weight by the ubbelohde method, Determinated thermal properties by integrated thermal analyzer, Testing mechanical properties by universal material testing machine, the main contents results as follows:S8 and U-yuan strain protoplast fusion, PHA production of screened F-68 fusant was 13.14 g /L, Molecular weight was 8.46�10~5 Da, melting point was 95.5 ?, elongation at break was 205.3%, Melting point of PHA was higher, compared to PHA produced by S8 strain of mechanical properties, the elongation at break improved 200.8%, toughness improved significantly, performance had changed.Improved toughness of PHA produced by S8 strain by screening a suitable precursor substance. Adding 0.1% n-pentanol after the fermentation time was 24 h, PHA yield was high, the molecular weight of this substance was 6.57�10~5 Da, melting point was 147.3 ?, elongation at break was 130.4%, tensile stress was 8.5 Mpa, elongation at break increased by about 29 times than PHA produced by S8 strain, toughness improved drastically, toughness of PHA was better.Mixed fermentation of S8 and U-yuan strain produced better performance of PHA, Accessing S8 strains based on proportions of S8:U-yuan=1:3 after U-yuan strain fermentation 24 h. The molecular weight of PHA was 5.36�10~5 Da, melting point was 68.5 ?, elongation at break was 16.6%, tensile stress was 12.5 Mpa, strength was moderate, but toughness was low, Mixed fermentation of S8 and U-yuan produced PHA whose performance had no centralized their respective advantages.Protoplast fusion changing performance of PHA is obvious, but the process was complex and cumbersome, mixed strains fermentation changing performance of PHA is not obvious, Method of joining precursors to improve the toughness of PHA was simple and the effect was obvious. These studies could provide a reference for modified of PHA.