The effects of crystallinity and spherulite size on the enzymatic degradation of microbial poly(3-hydroxybutyrate) (PHB) films have been studied at 37 "C and pH 7,4 in aqueous solutions of an extracellular PHB depolymerase from Alcaligenes faecalis TI. The rate of enzymatic degradation of PHB films decreases with an increase in crystallinity, but it is little influenced by the size of PHB spherulites. It was suggested that the PHB depolymerase firstly hydrolyzes the PHB chains in the amorphous state on the surface of the films and subsequently erodes the PHB chains in the crystalline state.
IntroductionThe hydrolysis of synthetic polymers containing labile ester linkages, such as poly(glyco1ic acid), poly(glyco1ic-co-lactic acid), and polydioxanone, has been extensively studied as degradable materials in medical and pharmaceutical applications Recently, microbial polyesters have attracted much attention as biodegradable and biocompatible materials ').A variety of microorganisms produce poly(hydroxya1kanoate)s as intracellular storage polymers, and these microbial polyesters can be isolated in high purity from cells by solvent extraction 3). A copolymer of 3-hydroxybutyrate(3 HB) and 3-hydroxyvalerate(3 HV) has been produced by Alcaligenes eutrophus from propionic acid4ss) or pentanoic acid'). The copolyester has been shown to have a statistically random distribution of 3 HB and 3 HV units'~*). The static and dynamic mechanical properties of P(3 HB-co-3 HV) films and fibers are strongly dependent on their compositions. The films and fibers become more flexible and tougher as the 3HV content increases from 0 to 25 mol-Vo4). The hydrolysis of solution-cast films of
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