Thermoplastic roofing membranes

1. A multi-layered membrane comprising:

a first polymeric layer including (i) a plastomer, (ii) a low density polyethylene, (iii) a propylene-based polymer, and (iv) a flame retardant; and

a second polymeric layer, wherein the second polymeric layer optionally includes from 0 to about 50% of the flame retardant present in the first polymeric layer.

2. The membrane of claim 1 , where the plastomer includes an ethylene-α- olefin copolymer characterized by a density of from about 0.865 g/cc to about 0.900 g/cc.

3. The membrane of claim 1 , where the low-density polyethylene includes linear low density polyethylene.

4. The membrane of claim 3 , where the linear low density polyethylene includes an ethylene-α-olefin copolymer including from about 2.5 to about 13 mole percent mer units deriving from α-olefins.

5. The membrane of claim 4 , where the linear low density polyethylene is characterized by a density of from about 0.885 g/cc to about 0.930 g/cc per ASTM D-792.

6. The membrane of claim 1 , where the propylene-based polymer includes propylene homopolymer or copolymers with propylene and a comonomer, and where the copolymer includes, on a mole basis, a majority of mer units deriving from propylene.

7. The membrane of claim 6 , where the propylene-based copolymers include from about 2 to about 6 mole percent mer units deriving from comonomer, with the balance including mer units deriving from propylene.

8. The membrane of claim 1 , where the flame retardant is selected from the group consisting of halogenated flame retardants, non-halogenated flame retardants, and mixtures thereof.

9. The membrane of claim 8 , where the halogenated flame retardants include halogenated hydrocarbons, where the halogenated hydrocarbons include hexabromocyclododecane, N,N′-ethylene-bis-(tetrabromophthalimide), and mixtures thereof, and where the non-halogenated flame retardants include magnesium hydroxide, aluminum trihydrate, zinc borate, ammonium polyphosphate, melamine polyphosphate, and mixtures thereof.

10. The membrane of claim 9 , where the magnesium hydroxide includes a treated magnesium hydroxide or a functionalized magnesium hydroxide.

11. The membrane of claim 10 , where the magnesium hydroxide includes magnesium oxide treated with or reacted with a carboxylic acid, or where the magnesium hydroxide includes that treated or reacted with stearic acid, or where the magnesium hydroxide includes that treated or reacted with silicon-containing compounds selected from the group including silanes, and polysiloxanes, or where the magnesium hydroxide includes magnesium hydroxide treated with titanates.

12. The membrane of claim 1 , where the first polymeric layer includes i) from about 5 to about 50% by weight plastomer, ii) from about 10 to about 90% by weight low density polyethylene, and iii) from about 5 to about 50% by weight propylene-based polymer based upon the total weight of the plastomer, low density polyethylene, and propylene-based polymer, and also includes iv) from about 10 to about 50% by weight magnesium hydroxide, based upon the total weight of the at least one layer.

13. The membrane of claim 12 , where the first polymeric layer includes i) from about 10 to about 45% by weight plastomer, ii) from about 15 to about 85% by weight low density polyethylene, and iii) from about 10 to about 45% by weight propylene-based polymer based upon the total weight of the plastomer, low density polyethylene, and propylene-based polymer, and also includes iv) from about 15 to about 45% by weight magnesium hydroxide, based upon the total weight of the at least one layer.

14. The membrane of claim 1 , where the membrane includes a scrim positioned between said first and second layers.

15. The membrane of claim 1 , where the gel content of the first layer is less than 10 weight percent of the sheet.

16. The membrane of claim 1 , where the propylene-based polymer is characterized by 1% secant modulus in excess of 120,000 psi.

17. The membrane of claim 7 , where the propylene-based polymer is characterized by 1% secant modulus in excess of 137,000 psi.

18. The membrane of claim 1 , where the first layer includes less than 10 weight percent rubber.

19. The membrane of claim 1 , where the first layer is substantially devoid of rubber.

20. The membrane of claim 1 , where the first layer includes at least 31% by weight low density polyethylene based upon the total weight of the plastomer, low density polyethylene, and propylene-based polymer.

21. The membrane of claim 20 , where the at least one layer includes at least 35% by weight low density polyethylene.

22. A membrane comprising:

at least one polymeric layer including (i) a plastomer, (ii) a low density polyethylene, and (iii) a propylene-based polymer, where the polymeric sheet includes at least 31% by weight of the low density polyethylene based upon the total weight of the plastomer, low density polyethylene, and propylene-based polymer.

23. A membrane comprising:

at least one polymeric layer including (i) a plastomer, (ii) a low density polyethylene, and (iii) a propylene-based polymer, where the polymeric sheet is substantially devoid of a rubber.

24. A membrane comprising:

at least one polymeric layer including (i) a plastomer, (ii) a low density polyethylene, and (iii) a propylene-based polymer, where the low density polyethylene includes a linear low density polyethylene including one or more mer units deriving from butane-1, pentene-1, hexane-1, octane-1, or 4-methyl-pentene-1.

25. A membrane comprising:

at least one polymeric layer including i) a plastomer, ii) a low density polyethylene, iii) a propylene-based polymer, and optionally iv) flame retardant.

26. The membrane of claim 1 , further comprising a scrim positioned between the first and second polymeric layers.