Microporous Materials With Fibrillar Mesh Structure and Methods of Making and Using the Same

A method of making a microporous material, comprising:

• (a) melt blending to form a substantially homogeneous melt-blended mixture comprising:
• (i) from about 20 to about 70 parts by weight of a melt-processable, semi-crystalline, thermoplastic (co)polymer component, and
• (ii) from about 30 to about 80 parts by weight of a second component comprising a compound that is miscible with the thermoplastic (co)polymer component at a temperature above a melting temperature of the thermoplastic semi-crystalline (co)polymer but that phase separates from the thermoplastic (co)polymer component when cooled below a crystallization temperature of the thermoplastic semi-crystalline (co)polymer;
• (b) forming a sheet of the melt blended mixture;
• (c) cooling the sheet to a temperature at which phase separation occurs between the second component and the thermoplastic (co)polymer component through crystallization precipitation of the thermoplastic (co)polymer component;
• (d) removing at least a substantial portion of the second component to provide a porous sheet;
• and
• (e) stretching the porous sheet in a direction at a stretch ratio between 1:1 and 3:1, and stretching the sheet in a substantially orthogonal direction at a stretch ratio of more than 4:1, thereby forming a microporous material comprising a network of interconnected pores having a median diameter less than one micrometer, wherein the microporous material is comprised of a plurality of filaments substantially aligned in a first longitudinal direction, and a mesh extending laterally between the filaments,
• optionally wherein the microporous material exhibits a puncture resistance of at least 300 g/25 micrometers.