Phase structure of poly(3-hydroxy butyrate)/poly(vinyl acetate) blends probed by small-angle X-ray scattering

The semicrystalline morphology of poly(3-hydroxy butyrate) (PHB)/poly(vinyl acetate) (PVAc) blends at four crystallization temperatures (T-c = 70, 90, 110, and 125 degrees C) was probed by small-angle X-ray scattering (SAXS). Morphological parameters including the crystal thickness (l(c)) and the am orphous layer thickness (l(a)) were deduced from the interphase distributio n function. Blending with PVAc thickened the PHB crystals. The amorphous la yers were also swollen upon blending, but l(a) displayed a maximum in its v ariation with PVAc composition. A zero-angle scattering was observed in the Lorentz-corrected SAXS profiles of PHB/PVAc 60/40 blend crystallized at 11 0 and 125 degrees C and 50/50 composition crystallized at 90-125 degrees C. Such a zero-angle scattering was attributed to the presences of amorphous domains between the lamellar stacks so as to generate gaps in the sequentia l stacking of lamellae. These amorphous domains were generated by the inter fibrillar segregation of PVAc, where PVAc was expelled beyond several layer s of lamellae and subsequently resided in the regions between the lamellar stacks. On the basis of the composition variation of l(a), the observation of zero-angle scattering, and the magnitude of the volume fraction of lamel lar stacks, it was concluded that when PVAc composition was less than or eq ual to 20 wt %, the morphology was predominantly characterized by the inter lamellar segregation; above this composition, interlamellar and interfibril lar segregation coexisted, and the extent of interfibrillar segregation inc reased with the increases of PVAc composition and crystallization temperatu re.