BLENDS OF BACTERIAL POLY(3-HYDROXYBUTYRATE) WITH CELLULOSE-ACETATE BUTYRATE IN ACTIVATED-SLUDGE

Blends of bacterial poly(3-hydroxybutyrate) (PHB) with cellulose aceta te butyrate (CAB) were prepared by compression molding followed by dif ferent thermal treatments. The morphology of the blends, which are tot ally miscible in the melt, was investigated by differential scanning c alorimetry, x-ray diffraction, and optical and scanning electron micro scopy. Depending on composition and thermal treatments, the blends are either single-phase amorphous PHB/CAB mixtures or partially crystalli ne materials composed of space-filling spherulites, where a constant f raction of the PHB present in the blend (about 65%) constitutes the la mellar crystalline phase, while the interlamellar amorphous phase is f ormed by the remaining PHB mixed with CAB. PHB/CAB blends over the who le composition range show no weight loss after 12 months of exposure t o activated sludge. In the same experimental conditions, pure PHB quic kly biodegrades at a rate which is found to be affected-at a constant degree of crystallinity - by small morphological variations. The resul ts suggest that crystalline PHB lamellae can be attacked only after so me interlamellar amorphous material has been removed. In the blends, n ondegradability of interlamellar PHB/CAB mixtures prevents enzyme acti on toward the pure PHB lamellar crystals.