Morphological changes of PVDF/PMMA blends via CO2 treatments

Supercritical CO2 fluids (scCO2) assisting melting of crystalline/amorphous poly(vinylidene fluoride) (PVDF)/poly(methyl methacrylate)(PMMA) blends were investigated into the morphological changes of the melt-recrystallized blends as a function of scCO2 pressure and PMMA content by means of digital camera, SEM, AFM, WAXD, and SAXS. Three scCO2 conditions at 8.5, 28.7, and 48.2 MPa all at 140 °C for 30 min were studied. Pictures of the scCO2-treated samples found that PMMA in the blends promoted the scCO2-assisted melting of PVDF and the expansion of the PVDF/PMMA blends. Higher CO2 pressures gave bigger expansion for a given blend. SEM images showed that the expanded scCO2-treated blends contained foams and lower PMMA contents in the blends gave bigger sizes of foams. WAXD patterns showed that scCO2 and PMMA did not affect the predominant α crystalline form in PVDF although they lowered the bulk crystallinity of PVDF. SAXS data found that the thickness of the amorphous layer in the lamellar stacks increased whereas that of the crystalline layer insignificantly changed in the scCO2-treated blends. The 28.7 and 48.2 MPa-CO2-treated blends had broader distributions in size of lamellar stacks than the untreated and the 8.5 MPa-CO2-treated blends. For the scCO2-treated blends, the pressure dependence of the increased thickness of the amorphous layer in the lamellar stacks and the increased size distribution of the lamellar stacks decreased with increasing PMMA content in the blends.