Asymmetric membranes and related methods

1. A method of making an asymmetric microporous membrane comprising:

providing a polymethylpentene (PMP) polymer skin resin and a substrate resin, the substrate resin including one or more of polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), and a combination thereof;

co-extruding the PMP polymer skin resin and the substrate resin to form a membrane precursor; and

stretching the membrane precursor to form an asymmetric microporous membrane having a PMP polymer skin on a thermoplastic polymer substrate; and

wherein co-extruding the PMP polymer skin resin and the substrate resin to form a membrane precursor includes co-extruding the PMP polymer skin resin and the substrate resin through a co-extrusion die to form the membrane precursor.

2. The method of claim 1 , wherein providing a polymethylpentene (PMP) polymer skin resin and a substrate resin includes providing the PMP polymer skin resin and the substrate resin exclusive of any oils for subsequent removal to form pores or any pore-forming particulate to facilitate pore formation.

3. The method of claim 1 , wherein the substrate resin includes polymethylpentene (PMP).

4. The method of claim 3 , wherein PMP polymer skin has a crystallinity that is less than a crystallinity of the PMP of the substrate resin.

5. The method of claim 4 , wherein the crystallinity of the PMP polymer skin resin is less than about 40%, and wherein the crystallinity of the PMP of the substrate resin is greater than about 40%.

6. The method of claim 4 , wherein the crystallinity of the PMP of the substrate resin is greater than about 60%.

7. The method of claim 1 , wherein the PMP polymer skin has a thickness of less than about 2 microns.

8. The method of claim 1 , wherein the thermoplastic polymer substrate has a thickness of less than about 150 microns.

9. The method of claim 1 , wherein the asymmetric microporous membrane is a non-homogeneous membrane.

10. The method of claim 1 , further including annealing the membrane precursor.

11. The method of claim 10 , wherein annealing the membrane precursor includes annealing the membrane precursor prior to stretching the membrane precursor.

12. A method of making a multi-layered membrane comprising the method of making an asymmetric microporous membrane of claim 1 , wherein the PMP polymer skin comprises an outer layer and/or an inner layer of the multi-layered membrane.

13. A method of making an asymmetric microporous hollow fiber membrane comprising:

providing a polymethylpentene (PMP) polymer skin resin and a substrate resin, the substrate resin including one or more of polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), and a combination thereof, wherein when the substrate resin includes PMP, the PMP polymer skin resin has a crystallinity that differs from a crystallinity of the PMP of the substrate resin;

co-extruding the PMP polymer skin resin and the substrate resin to form a hollow fiber membrane precursor; and

stretching the hollow fiber membrane precursor to form an asymmetric microporous hollow fiber membrane having a PMP polymer skin on a thermoplastic polymer substrate; and

wherein co-extruding the PMP polymer skin resin and the substrate resin to form a hollow fiber membrane precursor includes co-extruding the PMP polymer skin resin and the substrate resin through a co-extrusion die to form the hollow fiber membrane precursor.

14. The method of claim 13 , wherein providing a polymethylpentene (PMP) polymer skin resin and a substrate resin includes providing the PMP polymer skin resin and the substrate resin exclusive of any oils for subsequent removal to form pores or any pore-forming particulate to facilitate pore formation.

15. A method of making a multi-layered hollow fiber membrane comprising the asymmetric microporous hollow fiber membrane of claim 13 , wherein the PMP polymer skin comprises an outer layer and/or an inner layer of the multi-layered hollow fiber membrane.