Effect of low molecular weight additives on enzymatic degradation of poly(3-hydroxybutyrate)

The effects of low molecular weight additives on various properties of bact erial poly(3-hydroxybutyrate) (PHB) have been examined by utilizing dodecan ol, lauric acid, tributyrin and trilaurin as additives. The analyses of gla ss transition temperature and cold crystallization temperature of PHB in th e PHB/additive mixtures showed that these additives are miscible with PHB a nd act as plasticizers, though the miscibility is found in the limited mixt ures with low additive content. The enzymatic degradation of the melt-cryst allized films of the PHB/ additive mixtures was investigated in aqueous sol ution of PHB depolymerase purified from Alcaligenes faecalis T1. The mixtur es showed degradability different from pure PHB. A fairly small amount (1 w t%) of additive acts as an accelerator for the enzymatic degradation of PHB while a larger amount (9 wt%) of additive acts as a retardant. All the add itives examined in this study showed similar trend. The retardation effect of additives observed for the PHB mixtures containing 9 wt% additive is asc ribed to the segregation of the additive on the film surface. The additives on the surface prevent an attack of the enzymes on the PHB molecules. The higher molecular mobility in the amorphous phase and the thinner lamella ar e possible factors that accelerate the degradation of PHB containing 1 wt% additives. This result shows that the enzymatic degradability of PHB is con trollable by adding low molecular-weight additives. (C) 2000 Elsevier Scien ce Ltd. All rights reserved.