Orientation Efforts as Regulatory Factor of Structure Formation in Permeable Porous Poly(vinylidene fluoride) Films

The manufacturing process of poly(vinylidene fluoride) microporous films containing through flow channels and permeable to liquids has been elaborated. The process is based on polymer melt extrusion with subsequent stages of annealing, uniaxial extensions (“cold” and “hot” drawing), and thermal stabilization. The effect of orientation parameters (melt draw ratio and extension degrees) on overall porosity, permeability, morphology, and content of polar piezoactive β-phase in crystalline structure of the films was investigated by filtration porosimetry, sorptometry, scanning electron microscopy, X-ray scattering, and mechanical properties measurements. It is shown that the through pores were formed by a percolation mechanism. It is observed that permeability and the β-phase content increased with the growth of extension degree at the pore formation stages but the portion of β-crystallites decreased with increasing melt draw ratio at extrusion, which permitted to regulate the combination of through permeability and piezoactivity values by variation of the preparation process parameters.