BIODEGRADATION OF BLENDS OF BACTERIAL POLY(3-HYDROXYBUTYRATE) WITH ETHYL CELLULOSE IN ACTIVATED-SLUDGE AND IN ENZYMATIC SOLUTION

Blends of poly(3-hydroxybutyrate) (PHB) and ethyl cellulose (EtC) were prepared by compression molding of solution cast films. The two compo nents were not miscible but the blends showed 'mechanical compatibilit y'. Two PHB/EtC blends (80/20 and 50/50 (w/w in all cases)) were selec ted for biodegradation experiments in activated sludge and in enzymati c solution of PHB-depolymerase from Pseudomonas lemoignei and from Aur eobacterium saperdae. Blend morphology was quite different: blend 80/2 0 was composed of a matrix of impinging PHB spherulites with dispersed EtC inclusions, whereas blend 50/50 was constituted of two continuous phases with interpenetrated domains. Both blends biodegraded in activ ated sludge, but only blend 80/20 was attacked by PHB-depolymerases fr om P. lemoignei and A. saperdae. From weight loss, thickness and compo sition measurements after different exposure times and from scanning e lectron microscopy of the biodegraded blend surface it was concluded t hat in blend 80/20 biodegradation of the PHB matrix caused concomitant release in the medium of the embedded EtC particles. The results on P HB/EtC (50/50) after sludge exposure demonstrated that in this blend t he PHB phase - thanks to its interconnected domains - was continuously accessible to microbial attack, leaving a highly cavitated ethyl cell ulose structure after PHB consumption. The lack of biodegradation of b lend 50/50 in enzymatic solution was tentatively attributed to changes of surface hydrophobicity induced by large amounts of EtC, which disf avored enzyme binding.