Effect of PVDF characteristics on extruded film morphology and porous membranes feasibility by stretching

Three different polyvinylidene fluoride (PVDF) resins were selected to develop porous membranes through melt extrusion and stretching. The effect of the polymer rheology on chain elongation in the melt state was studied. The possibility of generating a row‐nucleated lamellar crystallization for precursor films was investigated. The arrangement and orientation of the crystalline phase were examined by wide angle X‐ray diffraction (WAXD) and Fourier Transform Infrared Spectroscopy (FTIR). The extrusion conditions and the blend compositions were adjusted to obtain uniform precursor films with appropriate morphology. Annealing, cold and hot stretching were consequently employed to generate and enlarge the pores. It was found that a proper crystalline structure of the precursor films was strongly dependent on molecular weight of PVDF and process conditions. Blending of two PVDF resins having low and high molecular weights improved the water vapor permeability of the obtained membranes. The tensile response was monitored during the stretching process for membrane development and the results revealed a distinct behavior for the membranes having low or high permeability. The membranes with low permeability did not show any significant strain hardening during stretching whereas for highly permeable membranes, a noticeable strain hardening behavior was observed. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1219–1229, 2009     

The salting-out effect and phase separation in aqueous solutions of sodium phosphate salts and poly(propylene glycol)

Phase diagrams and liquid–liquid equilibrium (LLE) data of the aqueous poly(propylene glycol) (PPG) + di-sodium hydrogen phosphate and PPG + tri-sodium phosphate two-phase systems have been determined experimentally at 298.15, 303.15, 308.15, 313.15 and 318.15 K. The effects of temperature and charge on the anion of electrolyte on the binodal curves and tie-lines have been studied and it was found that an increasing in temperature and charge on the anion caused the expansion of two-phase region. The results show that the effect of charge on the anion of electrolyte on the binodal curves becomes smaller by increasing temperatures. It was also found that the concentration of salt, which is in equilibrium with a certain concentration of PPG, decreases by increasing temperature. Based on cloud point values, the energetics of the clouding process has been estimated and it was found that entropy increase is the driving force for biphasic formation.