Microporous polyolefin membranes from bespoke solvents

Abstract

Halogen-free, microporous polyolefin membranes are disclosed herein. The halogen-free, microporous polyolefin membranes can be manufactured using an environmentally friendly manufacturing process that includes extrusion of polymer-plasticizer mixtures followed by sheet formation and extraction of the plasticizer with a halogen-free solvent. The halogen-free solvent has a flashpoint greater than about 23° C. and an initial boiling point at least about 50° C. lower than the flashpoint of the plasticizer. The process can further be a closed loop process in which the halogen-free solvent can be reused.

1 . A free-standing microporous polyolefin membrane comprising:
 a semi-crystalline polymer matrix resulting from a phase separation of a polymer and a plasticizer having a flashpoint greater than about 215° C. and an aniline point between about 70-140° C.;   the polymer matrix including polyethylene to provide mechanical integrity;   interconnected pores resulting from extraction of the plasticizer with a halogen-free solvent and its subsequent evaporation;   the halogen-free solvent having a flashpoint greater than about 23° C. and an initial boiling point at least about 50° C. lower than the flashpoint of the plasticizer.   
     
     
         2 . The free-standing microporous polyolefin membrane of  claim 1 , wherein the halogen-free solvent comprises a flashpoint greater than about 38° C. 
     
     
         3 . The free-standing microporous polyolefin membrane of  claim 1 , wherein the polymer matrix is stretched or biaxially oriented. 
     
     
         4 . The free-standing microporous polyolefin membrane of  claim 1 , wherein the polymer matrix is stretched or biaxially oriented prior to solvent extraction of the plasticizer. 
     
     
         5 . The free-standing microporous polyolefin membrane of  claim 4 , wherein the polymer matrix is further stretched or biaxially oriented after extraction of the plasticizer and evaporation of the solvent. 
     
     
         6 . The free-standing microporous polyolefin membrane of  claim 1 , wherein the free-standing microporous polyolefin membrane is annealed or heat stabilized prior to being wound. 
     
     
         7 . The free-standing microporous polyolefin membrane of  claim 1 , wherein the polymer matrix further comprises a filler distributed throughout the polymer matrix. 
     
     
         8 . The free-standing microporous polyolefin membrane of  claim 7 , wherein the filler comprises an inorganic oxide, carbonate, hydroxide, or mixtures thereof, or wherein the filler comprises alumina, silica, zirconia, titania, mica, boehmite, magnesium hydroxide, calcium carbonate, hydrotalcites, or mixtures thereof. 
     
     
         9 . The free-standing microporous polyolefin membrane of  claim 1 , wherein the polyolefin comprises a polyethylene having a molecular weight of at least about 0.5 million g/mol. 
     
     
         10 - 11 . (canceled) 
     
     
         12 . The free-standing microporous polyolefin membrane of  claim 1 , wherein the free-standing microporous polyolefin membrane contains about 10-25 wt % residual plasticizer, or about 12-22 wt % residual plasticizer. 
     
     
         13 . (canceled) 
     
     
         14 . The free-standing microporous polyolefin membrane of  claim 1 , wherein the halogen-free solvent comprises an initial boiling point at least about 85° C. lower than the flashpoint of the plasticizer. 
     
     
         15 . The free-standing microporous polyolefin membrane of  claim 1 , wherein the free-standing microporous polyolefin membrane is free of halogen-containing compounds. 
     
     
         16 . The free-standing microporous polyolefin membrane of  claim 1 , wherein the halogen-free solvent is a food grade solvent. 
     
     
         17 . A method for the manufacture of a microporous polyolefin membrane, comprising:
 melt blending a polyolefin and a plasticizer to form a mixture;   casting or extruding the mixture into a non-porous sheet;   cooling the non-porous sheet to induce phase separation of the polyolefin and plasticizer;   extracting the plasticizer from the non-porous sheet with a halogen-free solvent and evaporating the solvent to form a microporous polyolefin membrane, wherein the halogen-free solvent comprises a flashpoint above about 23° C. with an initial boiling point at least about 50° C. lower than a flashpoint of the plasticizer.   
     
     
         18 . (canceled) 
     
     
         19 . The method of  claim 17 , wherein the plasticizer comprises a flashpoint greater than about 215° C. and an aniline point between about 70-140° C. 
     
     
         20 . The method of  claim 17 , wherein the halogen-free solvent comprises an initial boiling point at least about 85° C. lower than the flashpoint of the plasticizer. 
     
     
         21 . The method of  claim 17 , comprising a closed-loop, solvent extraction, drying, and carbon bed recovery system. 
     
     
         22 - 30 . (canceled) 
     
     
         31 . A solvent laden sheet, comprising:
 a cast or extruded polyolefin sheet, the cast or extruded polyolefin sheet resulting from a cast or extruded mixture of the polyolefin and a plasticizer having a flashpoint greater than about 215° C. and an aniline point between about 70-140° C.; and   a halogen-free solvent loaded within the polyolefin sheet.   
     
     
         32 . (canceled) 
     
     
         33 . The solvent laden sheet of  claim 31 , wherein the halogen-free solvent comprises a flashpoint greater than about 23° C. and an initial boiling point at least about 50° C. lower than the flashpoint of the plasticizer. 
     
     
         34 . The solvent laden sheet of  claim 33 , wherein the halogen-free solvent comprises an initial boiling point at least about 85° C. lower than the flashpoint of the plasticizer. 
     
     
         35 - 37 . (canceled)