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

The effects of low molecular weight additives on various properties of bacterial poly(3-hydroxybutyrate) (PHB) have been examined by utilizing dodecanol, lauric acid, tributyrin and trilaurin as additives. The analyses of glass transition temperature and cold crystallization temperature of PHB in the PHB/additive mixtures showed that these additives are miscible with PHB and act as plasticizers, though the miscibility is found in the limited mixtures with low additive content. The enzymatic degradation of the melt-crystallized films of the PHB/ additive mixtures was investigated in aqueous solution of PHB depolymerase purified from Alcaligenes faecalis T1. The mixtures showed degradability different from pure PHB. A fairly small amount (1 wt%) 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 additives examined in this study showed similar trend. The retardation effect of additives observed for the PHB mixtures containing 9 wt% additive is ascribed 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 are possible factors that accelerate the degradation of PHB containing 1 wt% additives. This result shows that the enzymatic degradability of PHB is controllable by adding low molecular-weight additives. (C) 2000 Elsevier Science Ltd. All rights reserved.