Enzymatic degradation mechanism of the lamellar stacking structures of poly([R]-3-hydroxybutyrate-co-[R]-3-hydroxyvalerate) fibers

Enzymatic degradation of the lamellar stacking structures of two types of poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyvalerate] melt-spun fibers (undrawn and drawn fibers) was analyzed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM images of undrawn fibers showed that enzymatic degradation proceeded from the amorphous regions of spherulites on the surface and in the interior of the fibers. In addition, the lamellar crystals of undrawn fibers unraveled when the amorphous regions between the lamellar crystals were preferentially degraded. In contrast, on the drawn fibers, periodic stacking structures of lamellar crystals with a thickness of approximately 300 nm were observed at the initial stage of degradation. Some of these lamellar stacking structures were connected in the drawing direction. Furthermore, SEM images showed that the periodic lamellar stacking structures with thickness of approximately 2 mu m appeared as degradation proceeded. TEM images showed that the lamellar crystals of the periodic stacking structures did not unravel at the enzymatic degradation front because the amorphous regions and lamellar crystals were degraded simulta-neously, which was attributed to the strong connection between the lamellar crystals of the periodic lamellar stacking structures through tie molecules.