Supported water vapor transport membrane comprising polyethylene oxide copolymer
An air-impermeable water vapor transport membrane comprises an active layer on a microporous polymeric substrate. The active layer comprises a polyethylene-oxide containing copolymer and a polar protic solvent in an amount of about 3% to about 100% of copolymer weight in the active layer. Molecules of the protic solvent are bonded to the copolymer. The polar protic solvent reduces temperature-dependent variability in the water-vapor permeability of the membrane.
1. A method for making a water vapor transport membrane, the method comprising:
applying a polymer coating to a microporous polymeric substrate, the polymer coating comprising a polyethylene-oxide-containing (PEO-containing) copolymer;
allowing the polymer coating to dry and cure for a curing period to form an active layer on the substrate;
after the curing period contacting the active layer with a polar protic solvent; and
drying the active layer.
2. A method according to claim 1 , wherein the polar protic solvent is water.
3. A method according to claim 1 , wherein contacting the active layer with the polar protic solvent comprises allowing the active layer to take up the polar protic solvent in an amount of 3% to 100% of the weight of the active layer.
4. A method according to claim 1 , wherein the polymer coating comprises a thermoplastic polyurethane (TPU) formed by the reaction of at least one polyol with one or more of one or more poly-isocyanates and one or more di-isocyanates.
5. A method according to claim 1 , wherein, after drying, the active layer of the membrane has a permeability to water vapor of at least 20000 Barrer units over a temperature range of about −5° C. to about 40° C.
6. A method according to claim 1 , wherein, after drying, the active layer has a FTIR peak at about 1349 cm −1 .
7. A method according to claim 1 , wherein, after drying, the selectivity ratio of the membrane for water vapor over carbon dioxide is at least 50.
8. A method according to claim 1 , wherein:
the polymer coating comprises a PEO-containing polyethylene-polyurethane copolymer and a crosslinker;
the substrate comprises a microporous polymeric substrate, the substrate having a porosity of at least 30% by volume, a thickness of less than 75 microns and an inorganic solids content of less than 3% by weight; and
the curing period is at least 24 hours;
the active layer after curing is air-impermeable and water insoluble and has a thickness of 10 microns or less;
the polar protic solvent comprises molecules having one or more hydroxyl groups;
after drying the active layer, in a temperature range spanning at least −5° C. to 40° C., the active layer has a permeability to water vapor of at least 20000 Barrer units, and
the membrane provided by the method has a selectivity ratio for water vapor over carbon dioxide of at least 50.
9. A method according to claim 1 , wherein contacting the active layer with the polar protic solvent and drying the active layer modifies the water vapour transport characteristics of the active layer.
10. A method according to claim 9 wherein, prior to contacting the active layer with the polar protic solvent, the active layer exhibits a step change in water vapour permeability with increasing temperature; and, after contacting the active layer with the polar protic solvent and drying, the step change in water vapour permeability with increasing temperature is substantially eliminated.
11. A water vapor transport membrane comprising a microporous polymeric substrate and an air-impermeable active layer coated on a surface of the substrate, wherein the active layer comprises a polyethylene-oxide-containing (PEO-containing) copolymer and a polar protic solvent in an amount of about 3% to about 100% of weight of the active layer, wherein:
the microporous polymeric substrate has a porosity of at least 30% by volume, a thickness of less than 75 microns and an inorganic solids content of less than 3% by weight; and
the polyethylene-oxide-containing (PEO-containing) copolymer comprises a cross-linked polyethylene-oxide-containing (PEO-containing) polyethylene-polyurethane copolymer, and the polar protic solvent has one or more hydroxyl groups,
the active layer is air-impermeable and water insoluble and has a thickness of 10 microns or less; and
the membrane is characterized by the active layer having a permeability to water vapor of at least 2000 Barrer units over a temperature range spanning at least −5° C. to 40° C. and the membrane having a selectivity ratio for water vapor over carbon dioxide of at least 50.
12. A water vapor transport membrane according to claim 11 , wherein the polar protic solvent is water.
13. A water vapor transport membrane according to claim 11 , wherein the substrate comprises a microporous polyolefin.
14. A water vapor transport membrane according to claim 13 , wherein the polyolefin comprises polyethylene (PE) or polypropylene (PP), and the substrate has a thickness of less than about 50 microns.
15. A water vapor transport membrane according to claim 11 , wherein the material of the active layer has a Fourier transform infrared spectroscopy (FTIR) peak at about 1349 cm −1 .