Phase structure and biodegradation of the bacterial poly(3-hydroxybutyric acid)/chemosynthetic poly(3-hydroxypropionic acid) blend

Two different aliphatic polyesters, bacterially synthesized polyester poly(3-hydroxybutyric acid) [P(3HB)] and chemically synthesized poly(3-hydoxypropionc acid) [P(3HP)], were blended via solvent casting. By differential scanning calorimetry, polarized optical microscopy, wide-angle X-ray diffractometer and dynamic mechanical thermal analytical instrument, thermal and crystallization behavior and dynamic mechanical relaxation of the as-prepared binary blends were systematically studied. Immiscible properties were ambiguously demonstrated for these blends over the whole range of constituent composition. Glass transition temperature and proton spin diffusion times (T-1(H) and T-1 rho(H)) obtained by the high-resolution solid state C-13 NMR measurements indicated that the blend system was immiscible not only on an observation scale of DSC (about 10 nm), but on a T-1(H) scale (several tens of nm). Enzymatic biodegradation of the blend samples by extracellular P(3HB)-depolymerase from the bacterium strain A. faecalis T1 showed an approximately linear relation between the degradation rate and the component composition. In addition, on the basis of biochemical oxygen demand (BOD), pure P(3HP) could not be biodegraded in the river water, while environmental biodegradability was confirmed when it presents as one constitutive component of the binary P(3HB)/P(3HP) blend.