Microporous sheet product and methods for making and using the same

A microporous sheet product made by a method comprising (a) melt-extruding an extrusion mixture through a die to form a sheet material, the extrusion mixture comprising (i) a thermoplastic polymer, wherein the thermoplastic polymer comprises at least one polyolefin, (ii) a non-cross-linked elastomer, the non-cross-linked elastomer having a molecular weight of at least 50,000 Da, wherein the non-cross-linked elastomer comprises one or more members selected from the group consisting of polyisobutylene, polyisoprene, thermoplastic elastomers of polyolefin, polyurethane, and polyester, and copolymers and terpolymers thereof, and (iii) a compatibilizing agent, the compatibilizing agent promoting mixing of the thermoplastic polymer and the non-cross-linked elastomer, wherein the compatibilizing agent comprises at least one member selected from the group consisting of mineral oil, a glycol, and a surfactant;

• (b) then, cooling the sheet material, wherein micropores are formed in the sheet material;
• and (c) then, stretching the cooled sheet material in exactly one direction, wherein the exactly one direction is one of a machine direction along which the sheet material exits the die and a transverse direction that is both perpendicular to the machine direction and within a plane defined by length and breadth dimensions of the sheet material, wherein a network of interconnected micropores results, with the non-cross-linked elastomer forming fibrils connecting thermoplastic dense regions;
• (d) wherein the microporous sheet product has micropores having an aspect ratio of at least 2:1 in the plane defined by the machine direction and the transverse direction.