This report presents a continuing study of the morphological changes of polycaprolactone (PCL) with isothermal supercritical CO2 treatments at 304 atm and 35 degrees C in the presence of poly(vinyl chloride) (PVC). DSC and small-angle X-ray scattering (SAXS) data find that the CO2-assisted melting of PCL at 304 atm and 35 degrees C recrystallized in the presence of PVC during depressurization Of CO2 can result in a decreased thickness of crystal lamellar layers. Heterogeneity, with a size (21.7 nm for pure PCL) larger than the crystal layer thickness (8.2 nm for pure PCL) and the amorphous layer thickness (4.4 nm for pure PCL), is formed after the supercritical CO2 treatment. The size of this heterogeneity is found to enhance from 21.7 nm for pure PCL to 29.8 and 34.9 nm for the PCL samples containing 10 and 25 wt % PVC, respectively. These big heterogeneities in the PCL/PVC blends formed during CO2 depressurization might arise from the segregated PVC-rich amorphous domains that are located between bundles of the lamellar stacks, possibly as a result of the molecular dragging on PCL during depressurization of the PCL-interacted CO2. (c) 2005 Wiley Periodicals, Inc.