Yoshihiro Aoyagi

Thermal degradation of poly((R)-3-hydroxybutyrate), poly(e-caprolactone), and poly((S)-lactide)

Thermal degradations of poly[(R)-3-hydroxybutyrate] (PHB), poly[e-caprolactone] (PCL), and poly[(S)-lactide] (PLA) were investigated under both isothermal and non-isothermal conditions. In isothermal degradation experiments, the three polyesters showed quite different time-dependent profiles of weight loss and the number–average degree of polymerization, reflecting their different degradation mechanisms. Thermogravimetric analysis and pyrolysis coupled with GC/MS suggest that PHB is degraded by a random chain scission (cis-elimination), while PCL is degraded by an unzipping depolymerization from the hydroxyl end of the polymer chains. In contrast, the thermal degradation behavior of PLA was very complex because various reactions occurred concurrently. # 2002 Elsevier Science Ltd. All rights reserved.

Mechanical properties of uniaxially cold-drawn films of poly([R]-3-hydroxybutyrate)

Abstract Independently of molecular weight, uniaxially oriented films of poly([ R ]-3-hydroxybutyrate) (P(3HB)), with sufficient strength and flexibility were prepared by cold-drawing from an amorphous preform at a temperature below, but near to, the glass transition temperature. Melt-crystallized and solvent-cast films of P(3HB) are usually quite brittle, and the orientation is critical and difficult to reproduce consistently. 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. The tensile strength, elongation to break, and Youngs modulus were 237 MPa, 112%, and 1.5 GPa, respectively. When the two-step drawing procedure was applied, the mechanical properties were further improved (287 MPa, 53%, and 1.8 GPa). In X-ray fibre diagrams of highly oriented films, shape reflections assigned to the β -form (zigzag conformation) together with those derived from the normal orthorhombic crystal system ( α -form, 2 1 helix conformation) could be observed. The improvement of mechanical properties is due to not only the orientation of molecular chains but also the generation of zigzag conformation and network structure formed by fibril and lamellar crystals (shishkebab structure). The mechanical properties of uniaxially oriented films remained almost unchanged for 4 months at room temperature, suggesting that the high orientation and crystallinity avoid secondary crystallization.

Biodegradation of poly(3-hydroxyalkanoic acids) fibers and isolation of poly(3-hydroxybutyric acid)-degrading microorganisms under aquatic environments

Biodegradabilities of poly[(R)-3-hydroxybutyric acid-co-14mol%(R)-3-hydroxyvaleric acid] (P(3HB-co-14%3HV)) monofilament fibers were evaluated at 25C for 28 days by monitoring the time-dependent changes in the biochemical oxygen demand (BOD) and weight-loss (erosion) of fibers under aerobic conditions in a temperature-controlled reactor containing natural waters from various aquatic environments (seawater, lake freshwater and river freshwater in Japan). Two types of fibers with diAerent diameters (213 and 493m) were used in this test. The biodegradabilities of fibers decreased in the following order: river freshwater > lake freshwater > seawater. By analyses of scanning electron microscopy and X-ray diAraction of eroded fibers, it has been concluded that the biodegradation proceeded from amorphous regions on the surface of fibers by the function of microorganisms in freshwater or seawater. In addition, 13 strains of P(3HB)-degrading bacteria were isolated from diAerent sources of seawater and identified. Majority of isolates grew well on P(3HB) or P(3HB-co-14%3HV) as sole carbon source and excreted extracellular polyhydroxybutyrate (PHB) depolymerases. # 1998 Elsevier Science Ltd. All rights reserved.