Effects of solid-state structures on the enzymatic degradability of bacterial poly(hydroxyalkanoic acids)

The effects of solid-state structures on the rate of enzymatic erosion for melt-crystallized films of bacterial poly(hydroxyalkanoic acids) (PHAs) have been studied at 37 degrees C and pH 7.4 in the aqueous solution of an extracellular PHB depolymerase from Alcaligenes faecalis. In this study, the following PHA homopolymer and copolymers were used; poly(3-hydroxybutyric acid) (P(3HB)), poly(3-hydroxybutyric acid-co-7 mol % 3-hydroxyvaleric acid), poly(3-hydroxybutyric acid-co-22 mol % 3-hydroxyvaleric acid), poly(3-hydroxybutyric acid-co-10 mol % 4-hydroxybutyric acid), poly(3-hydroxybutyric acid-co-4 mol % 3-hydroxyhexanoic acid), and poly(3-hydroxybutyric acid-co-ll mol % 3-hydroxyhexanoic acid). All PHA films were crystallized isothermally at temperatures of 60-140 degrees C for different periods from the melt. The crystallinity of the films of P(3HB) homopolymer ranged from 53 to 80%, while those of PHA copolymers ranged from 39 to 71%, determined by X-ray crystallography and depending on the crystallization conditions. The rates of enzymatic erosion decreased with an increase in crystallinity. The erosion rates for PHA copolymer films were several times higher than the rates of P(3KB) homopolymer films with the same degree of crystallinity. It has been suggested that the rate of enzymatic erosion on PHA films is influenced not only by the degree of crystallinity but also by the structure of thin PHA lamellar crystals.