Blends of Bacterial Poly(3-Hydroxybutyrate) with Cellulose Acetate Butyrate in Activated Sludge

Blends of bacterial poly(3-hydroxybutyrate) (PHB) with cellulose acetate butyrate (CAB) were prepared by compression molding followed by different thermal treatments. The morphology of the blends, which are totally miscible in the melt, was investigated by differential scanning calorimetry, x-ray diffraction, and optical and scanning electron microscopy. Depending on composition and thermal treatments, the blends are either single-phase amorphous PHB/CAB mixtures or partially crystalline materials composed of space-filling spherulites, where a constant fraction of the PHB present in the blend (about 65%) constitutes the lamellar crystalline phase, while the interlamellar amorphous phase is formed by the remaining PHB mixed with CAB. PHB/CAB blends over the whole composition range show no weight loss after 12 months of exposure to activated sludge. In the same experimental conditions, pure PHB quickly biodegrades at a rate which is found to be affected–at a constant degree of crystallinity–by small morphological variations. The results suggest that crystalline PHB lamellae can be attacked only after some interlamellar amorphous material has been removed. In the blends, nondegradability of interlamellar PHB/CAB mixtures prevents enzyme action toward the pure PHB lamellar crystals.