Preparation and Characterization of PVDF‐HFP Membrane

Poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐HFP) microporous membrane was prepared by supercritical CO₂ extraction of dibutyl phthalate (DBP) template from PVDF‐HFP/DBP film. The effects of extraction conditions such as pressure, temperature, and extraction time on extraction efficiency and the porosity of membrane were studied. The extraction efficiency of DBP and size stability of polymer membrane during extraction was compared with those of solvent extraction process. The structure of the resulting membrane was characterized by scanning electron microphotograph (SEM), X‐ray diffraction (XRD) and differential scanning calorimeter (DSC). With increasing the extraction temperature, pressure and time, the extraction efficiency and the porosity increased. Maximum extraction efficiency is obtained at extraction pressure and temperature higher than 18 MPa and 75°C, respectively. The porosity of membranes depended on the extraction efficiency and shrinkage ratio of membranes. Compared with solvent extraction, supercritical CO₂ extraction of the film generated the membrane with more uniform structure and higher porosity.

Keywords:

• poly(vinylidene fluoride‐co‐hexafluoropropylene)
• dibutyl phthalate
• supercritical CO₂
• extraction
• porous membrane

5 Acknowledgments

This work was supported by the National 973 Foundation of China (No. 2003CB615705) and the National Nature Foundation of China (No. 50433010).