Miscibility and biodegradation behavior of melt-processed blends of bacterial poly(3-hydroxybutyrate) with poly(epichlorohydrin)

The miscibility of melt processed blends of bacterial poly(3-hydroxybutyrate) (PHB) with poly(epichlorohydrin) (PEC) is investigated over the whole range of compositions by means of differential scanning calorimetry, dynamic-mechanical analysis, and hot-stage optical microscopy. PHB and PEC are miscible in the melt in all proportions. After melt quenching, PHB/PEC blends show a single glass transition that linearly changes with composition between the T(g)s of the pure components (PHB = 2 degrees C, PEC = -21 degrees C). At room temperature all PHB/PEC blends are partially crystalline, owing to crystallization of a constant fraction (58%) of the PHB present in each blend. A space-filling spherulitic morphology develops upon blend crystallization from the melt. Isothermal crystallization measurements show that over the range of crystallization temperatures (40 degrees C < T-c < 130 degrees C) and compositions (20% < PEC < 80%) explored, the spherulite radial growth rate (G) decreases with increasing PEC content. Biodegradation experiments, carried out in activated sludge and in enzymatic solution (PHB-depolymerase from Aureobacterium saperdae on the blend containing 80% PHB, show both weight loss and surface erosion. The biodegradation results are discussed in terms of PHB chain-mobility.