Microporous polyvinylidene fluoride membrane

Hydrophobic hollow-fiber membrane made from a vinylidene fluoride polymer with a wall and a wall thickness, an outer surface on its outer side, an inner surface on its inner side and facing its lumen and adjacent to the inner surface a supporting layer having a structure that is substantially isotropic across the wall thickness, the supporting layer extending over at least 80% of the wall thickness and comprising pores having an average diameter of less than 1 μm, and wherein the hollow-fiber membrane has pores on its outer surface and on its inner surface, characterized in that the vinylidene fluoride polymer has a weight-average molecular weight MW in the range from 550 000 to 700 000 daltons and a polydispersivity greater than 3.0; the pores in the outer and in the inner surface are formed like islands and have a maximum ratio of their longitudinal extension to the transverse extension of 10; the porosity lies in the range from 50 to 90 vol. %, the wall thickness in the range from 50 to 300 μm, and the diameter of the lumen in the range from 100 to 500 μm; and the hollow-fiber membrane has a maximum separating pore diameter dmax in the range from 0.3 to 0.7 μm, determined according to the bubble point method.