Regularities of lamellae ordering in the formation of polypropylene membrane porous structure

The lamellar structure of porous polypropylene membranes prepared by the extrusion of the polymer melt, annealing of extruded films, and their uniaxial extension has been investigated using data of computer analysis of scanning electron microscopy images. It has been shown that the formation of pores at the stage of uniaxial extension is accompanied by an ordering of lamellae or their self-organization controlled by the annealing temperature $T_{\mathrm{ann}}$. It has been found that the self-organization of lamellae can occur through two mechanisms depending on the spin draw ratio at the stage of extrusion of the polymer melt: in the first case, an increase in the temperature $T_{\mathrm{ann}}$ leads to a gradual transition of the disorder-order type; in the second case, a bifurcation transition occurs with a nonmonotonic change in the order parameter. The conditions of the preparation of regular spatial lattices of lamellae have been discussed.