T. Iwata
Polymer Chemistry Laboratory, RIKEN Institute, Wako, Saitama 351-0198, Japan
Biodegradable poly[(R)-3-hydroxybutyrate] (P(3HB)) fibers and films with high tensile strength were processed by a method of combining cold-drawing and two-step-drawing procedures, and the molecular structures were analyzed by time-resolved or micro-beam X-ray diffraction with synchrotron radiation. Strong P(3HB) fibers processed from ultra-high-molecular-weight P(3HB), with tensile strength of 1.34 GPa, elongation to break of 35%, and Young's modulus of 18.1 GPa, were processed by the cold-drawing from amorphous preform at the near to glass transition temperature and the two-step-drawing at room temperature [1]. The molecular and higher-ordered structures in the P(3HB) monofilament were analyzed by a micro-beam X-ray diffraction (beam size is 0.5 mm) with Flesnel Zone Plate technique in synchrotron radiation (SPring-8) and linearly scanned perpendicular to the fiber axis with a step width of 2 mm. It was revealed that P(3HB) fiber has a new core-sheath structure with consistent of two types of molecular conformations; one is 21 helix conformation in sheath region and the other is planar zigzag conformation in core region.
On the other hand, melt-quenched films with rubber state were stretched easily and reproducibly to a draw ratio more than 1000%, and, when annealed under tension, acceptable mechanical properties were generated. When the two-step drawing procedure was applied, the tensile strength, elongation to break, and Young's modulus were improved to 287 MPa, 53%, and 1.8 GPa, respectively [2, 3].
The strong P(3HB) films and fibers are completely degraded in a natural river freshwater and by an extracellular PHB depolymerase. Based on these results, P(3HB) produced from renewable resources by recombinant bacteria is considered as a very attractive material with both high tensile strength and biodegradability.
论文来源：International Symposium on Biological Polyesters ,Auguest 22-27, 2004
