Gel extruded articles made from high density polyethylene with narrow molecular weight distribution
A polymer composition for producing gel extruded articles is described. The polymer composition contains polyethylene particles combined with a plasticizer. The polyethylene polymer has a narrow molecular weight distribution. Polymer articles made in accordance with the present disclosure have enhanced strength properties. In one embodiment, the polymer composition is used to form a porous membrane for use as a separator in electronic devices.
1. A polymer composition for producing gel extruded articles comprising:
a plasticizer; and
high density polyethylene particles comprising a high density polyethylene polymer, the high density polyethylene particles having a median particle size by volume of greater than about 50 microns, the high density polyethylene polymer having an intercrossing point (ICP) of greater than about 150 kPa.
2. A polymer composition as defined in claim 1 , wherein the high density polyethylene polymer has a polydispersity index (PDI) of less than about 8.
3. A polymer composition as defined in claim 1 , wherein the high density polyethylene polymer has an intercrossing point (ICP) of greater than about 168 kPa and has a polydispersity index (PDI) of less than about 6.5.
4. A polymer composition as defined in claim 1 , wherein the high density polyethylene particles have a median particle size by volume of from about 70 microns to about 210 microns.
5. A polymer composition as defined in claim 1 , wherein the high density polyethylene particles are present in the composition in an amount up to about 50% by weight.
6. A polymer composition as defined in claim 1 , wherein the plasticizer comprises mineral oil, a paraffinic oil, a hydrocarbon, an alcohol, an ether, an ester, or mixtures thereof.
7. A polymer composition as defined in claim 1 , wherein the high density polyethylene polymer has a molecular weight of greater than about 400,000 g/mol and less than about 4,000,000 g/mol.
8. A polymer composition as defined in claim 7 , wherein the composition only contains a single high density polyethylene polymer.
9. A polymer composition as defined in claim 1 , wherein the polymer composition is polypropylene-free.
10. A polymer composition as defined in claim 1 , wherein the high density polyethylene polymer has been Ziegler-Natta catalyzed.
11. A polymer composition as defined in claim 1 , wherein the high density polyethylene polymer has a bulk density of greater than about 0.31 g/cm 3 and the high density polyethylene particles have a median particle size by volume of less than about 150 microns.
12. A polymer composition as defined in claim 11 , wherein the high density polyethylene polymer has a molecular weight of greater than about 1,000,000 g/mol.
13. A polymer composition as defined in claim 11 , wherein the high density polyethylene polymer has a molecular weight of less than about 3,000,000 g/mol.
14. A molded article formed from the polymer composition as defined in claim 1 , wherein the molded article contains the plasticizer in an amount of less than about 2% by weight, such as in an amount less than about 1% by weight.
15. A molded article as defined in claim 14 , wherein the molded article comprises a film or a fiber.
16. A process for producing polymer articles comprising:
forming the polymer composition as defined in claim 1 into a gel-like composition; and
extruding the gel-like composition through a die to form a polymer article, the polymer article comprising a film.
17. A process as defined in claim 16 , further comprising the step of removing at least part of the plasticizer from the polymer article.
18. A porous membrane comprising:
a high density polyethylene polymer having an intercrossing point (ICP) of greater than about 150 kPa, the high density polyethylene polymer having a molecular weight of greater than about 400,000 g/mol, the porous membrane having a tensile strength in at least one direction of greater than about 90 MPa and having a puncture strength of greater than about 500 mN/μm;
wherein the porous membrane is formed from a polymer composition comprising high density polyethylene particles.
19. A porous membrane as defined in claim 18 , wherein the membrane has a thickness of from about 7 microns to about 11 microns.
20. A porous membrane as defined in claim 18 , wherein the membrane has a Gurley permeability of greater than about 105 sec/100 ml.
21. A porous membrane as defined in claim 18 , wherein the porous membrane has a puncture strength of greater than about 700 mN/μm.
22. A porous membrane as defined in claim 18 , wherein the porous membrane has been biaxially stretched.
23. A porous membrane as defined in claim 18 , wherein the high density polyethylene polymer has a bulk density of greater than about 0.31 g/cm 3 and the high density polyethylene particles have a median particle size by volume of less than about 150 microns.
24. A porous membrane as defined in claim 23 , wherein the high density polyethylene polymer has a molecular weight of greater than about 1,000,000 g/mol.
25. A porous membrane as defined in claim 23 , wherein the high density polyethylene polymer has a molecular weight of less than about 3,000,000 g/mol.
26. A porous membrane as defined in claim 23 , wherein the porous membrane has a puncture strength of greater than about 600 mN/μm.
27. A porous membrane as defined in claim 26 , wherein the porous membrane has a puncture strength of less than about 1,200 mN/μm.
28. A polymer composition for producing gel extruded articles comprising:
a plasticizer; and
high density polyethylene particles comprising a high density polyethylene polymer, the high density polyethylene polymer having a molecular weight of greater than about 400,000 g/mol, the high density polyethylene polymer having an intercrossing point (ICP) of greater than about 150 kPa.
29. A polymer composition as defined in claim 28 , wherein:
the high density polyethylene polymer has a bulk density of greater than about 0.31 g/cm 3 ;
the high density polyethylene polymer has a polydispersity index (PDI) of less than about 8;
the high density polyethylene particles have a median particle size by volume of less than about 150 microns; and
the high density polyethylene polymer has an intercrossing point (ICP) of greater than about 168 kPa.
30. A polymer composition as defined in claim 28 , wherein:
the high density polyethylene polymer has a bulk density of greater than about 0.31 g/cm 3 ;
the high density polyethylene polymer has a polydispersity index (PDI) of less than about 6.5; and
the high density polyethylene particles have a median particle size by volume of less than about 150 microns.