Effects of supercritical carbon dioxide sorption on the microstructure of poly(vinylidene fluoride)

Abstract Polyvinylidene Fluoride (PVDF) is a high performance polymer with wide technical applications. Often PVDF is in contact with high-pressure fluids which affect its microstructure and properties. Such effects are particularly remarkable in presence of supercritical carbon dioxide. Several PVDF samples with varying molecular weights ranging from 7850 to 109,000 g mol−1 were synthesized. These were subjected to CO2 sorption at 40 °C and 150 bar. At these conditions, negligible swelling was measured. A two-stage sorption process was observed. The equilibrium concentration and the saturation time increased with increasing molecular weight. Investigating the semi-crystalline microstructure by FT-IR, XRD and DSC showed no phase-transition of the crystallites except for the polymer with the lowest molecular weight. However, the size and arrangements of the crystalline lamellae within the amorphous phase seemed to be altered. These observations are discussed with respect to the effect of supercritical CO2 on the mobility of the amorphous chain segments.