Asymmetric membranes and related methods

Abstract

Microporous polymer membranes and related methods of fabrication are provided. An asymmetric microporous membrane embodiment includes, but is not limited to, a thermoplastic polymer substrate defining a plurality of micropores, the thermoplastic polymer including one or more of polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), and a combination thereof; and a polymethylpentene (PMP) polymer skin positioned on the thermoplastic polymer substrate, wherein when the thermoplastic polymer substrate includes PMP, the PMP polymer skin has a crystallinity that differs from a crystallinity of the PMP in the polymer substrate.

What is claimed is: 
     
         1 . A asymmetric microporous membrane comprising:
 a thermoplastic polymer substrate defining a plurality of pores, the thermoplastic polymer substrate comprising polymethylpentene (PMP), and the thermoplastic polymer substrate made from a PMP substrate resin having a first crystallinity; and   a polymethylpentene (PMP) polymer skin positioned on the thermoplastic polymer substrate by co-extrusion, the PMP polymer skin made from a PMP polymer skin resin having a second crystallinity, and wherein the first crystallinity and the second crystallinity differ such that the PMP polymer skin has a crystallinity that differs from a crystallinity of the PMP of the thermoplastic polymer substrate.   
     
     
         2 . The asymmetric microporous membrane of  claim 1 , wherein the thermoplastic polymer substrate defining a plurality of micropores. 
     
     
         3 . The asymmetric microporous membrane of  claim 1 , wherein the PMP polymer skin is less porous than the thermoplastic polymer substrate. 
     
     
         4 . The asymmetric microporous membrane of  claim 1 , wherein the PMP polymer skin is a nonporous PMP polymer skin. 
     
     
         5 . The asymmetric microporous membrane of  claim 1 , wherein the crystallinity of the PMP polymer skin resin is about 40% or less than about 40%. 
     
     
         6 . The asymmetric microporous membrane of  claim 1 , wherein the crystallinity of the PMP polymer skin resin is less than about 40%, and wherein the crystallinity of the PMP substrate resin of the thermoplastic polymer substrate is greater than about 40%. 
     
     
         7 . The asymmetric microporous membrane of  claim 6 , wherein the crystallinity of the PMP substrate resin of the thermoplastic polymer substrate is about 60% or greater than about 60%. 
     
     
         8 . The asymmetric microporous membrane of  claim 1 , wherein the PMP polymer skin has a thickness of less than about 2 microns. 
     
     
         9 . The asymmetric microporous membrane of  claim 1 , wherein the PMP polymer skin has a thickness of less than about 0.5 microns. 
     
     
         10 . The asymmetric microporous membrane of  claim 1 , wherein the thermoplastic polymer substrate has a thickness of between about 10 microns and 150 microns. 
     
     
         11 . The asymmetric microporous membrane of  claim 1 , wherein the thermoplastic polymer substrate has a thickness of between about 30 microns and 75 microns. 
     
     
         12 . The asymmetric microporous membrane of  claim 1 , wherein the thermoplastic polymer substrate has a thickness of between about 40 microns and 60 microns. 
     
     
         13 . The asymmetric microporous membrane of  claim 1 , wherein the thermoplastic polymer substrate has a thickness of between about 5 microns and 10 microns. 
     
     
         14 . The asymmetric microporous membrane of  claim 1 , wherein the asymmetric microporous membrane is a non-homogeneous membrane. 
     
     
         15 . The asymmetric microporous membrane of  claim 1 , wherein the PMP skin completely covers the thermoplastic polymer substrate. 
     
     
         16 . A multi-layered membrane comprising the asymmetric microporous membrane of  claim 1 , wherein the PMP skin comprises an outer layer and/or an inner layer of the multi-layered membrane.