Preparation, structure analysis and enzymatic degradation of poly [(R)-3-hydroxybutyrate-co-(R)-3-hydroxyhexanoate] gel-films

Gel-films of poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyhexanoate] (P(3HB-co-3HH)) with 12 mol% 3HH comonomer were prepared from a dilute solution of 1,2-dichloroethane by rapid quenching and slow drying. Uniaxial drawings were applied to the gel-films at room temperature. The gel-films were possible to stretch up to 8 times, leading to enhancements of the mechanical properties. The tensile strength, Young's modulus, and elongation to break of 8 times drawn gel-film were 151 MPa, 0.21 GPa, and 58 %, respectively. The orientation of lamella crystals in gel-films and drawn gel-films were analyzed by wide-angle and small-angle X-ray diffraction. In the drawn gel-films, a planer zigzag conformation consisting of extended molecular chains was observed. Furthermore, the lamella crystals in drawn gel-film were revealed to orient two directions, which are parallel and perpendicular to the film surface. It was indicated that a part of the oriented lamella crystal parallel to film surface rotated in the direction of perpendicular to the film surface during drawing of the gel-film. The drawings of gel-films accelerated the rate of enzymatic degradation by PHB depolymerase. The result was explained that the planer zigzag conformation in the drawn gel-films was easier to be broken down by the enzyme than the lamella crystals.