Microbial synthesis and physical properties of ultra-high-molecular-weight poly[(R)-3-hydroxybutyrate]

Ultra-high-molecular-weight poly[(R)-3-hydroxybutyrate](P(3HB)) was biosynthesized from glucose by a recombinant Escherichia coli XL-1 Blue (pSYL105) harboring Alcaligenes eutrophus PHB biosynthesis phbCAB genes. Six kinds of P(3HB) samples with differ-ent weight-average molecular weight (M-w) from 1.1 x 10(6) to 11 x 10(6) measured by multi-angle laser light scattering were respectively produced at pH values of 7.0 to 6.5 in culture media. Solvent-cast P(3HB) films of High-molecular-weights over M-w of 3.3 x 10(6) were stretched easily and reproducibly at 160 degrees C to a draw ratio of 400-650%. Mechanical properties of the stretched P(3HB) films were markedly improved relative to those of solvent-cast film. The elongation to break, Young's modulus, and tensile strength of stretched film (M-w = 11 x 10(6)) were 58%, 1.1 GPa, and 62 MPa, respectively. X-ray diffraction patterns indicated that the stretched film was highly oriented and had a high crystallinity over 80%. When the stretched film was annealed at 160 degrees C for 2 hours, the mechanical properties were further improved (elongation to break = 67%, Young's modulus = 1.8 GPa and tensile strength = 77 MPa). The mechanical properties of the stretched-annealed film remained almost unchanged for 6 months at room temperature, suggesting that a high crystallinity of the stretched-annealed film avoids a progress of secondary crystallization.