Influence of high pressure on higher-order structures of poly(oxyethylene) in its blend with poly(d,l-lactide)

The effect of high pressure on the higher-order structures of poly (oxyethylene) (PEG) crystallites in poly(d,l-lactide)/poly(oxyethylene) (PDLLA/PEG) blends during melting and recrystallization was investigated by in situ small-angle X-ray scattering (SAXS) measurements. It was found that melting temperature (T-m) increases at 50 MPa in accordance with the prediction by the Clausius-Clapeyron equation. However, T-m at slightly pressurized state (5 MPa) surprisingly decreased, suggesting that the effect of pressure is not so straightforward. It may be due to an increase of the miscibility under higher pressure, causing the melting point depression. Meanwhile, an advantage of analyses of SAXS data enabled us to determine directly discrete distribution of lamellar thickness as a function of temperature under pressure. As a result, lamellar thickening was observed at 5 and 50 MPa as temperature approaches closer to the melting point, but the tendency of thickening was lesser as compared to that observed at ambient pressure.