Electret nanofibrous web as air filtration media

1. An air filtration media comprising a single layer polymeric electret nanofibrous web comprising a single source randomly intermingled fiber network having an electrostatic charge, the electrostatic charge being up to −20 kV, the nanofibrous web further having a filtration efficiency range from 70% to 99.99%, and an air resistance less than 2.5 mm wg for 0.3 diameter micron particles;

wherein the nanofibrous web comprises nanofibers, microfibers, and coarse fibers: and

wherein the nanofibrous web comprises:

(a) at least 65% by number of fibers in the nanofibrous web are nanofibers with a number average diameter less than 1000 nm;

(b) at most 30% by number of fibers in the nanofibrous web are microfibers with a number average diameter from 1.0 μm to 3.0 μm; and

(c) at most 5% by number of fibers in the nanofibrous web are coarse fibers with a number average diameter greater than 3.0 μm.

2. The air filtration media of claim 1 , wherein the nanofibrous web has a porosity of at least 70%, a mean flow pore size of at most 15 μm, and a Frazier air permeability from 870 cm 3 /cm 2 /min to 6000 cm 3 /cm 2 /min at 125 Pa.

3. The air filtration media of claim 1 , wherein the nanofibrous web has a basis weight of 5 to 100g/m 2 .

4. The air filtration media of claim 1 , wherein the nanofibrous web has a basis weight of 10 g/m 2 to 60 g/m 2 .

5. The air filtration media of claim 4 , wherein the nanofibrous web has a basis weight of 10 g/m 2 to 20 g/m 2 .

6. The air filtration media of claim 1 , wherein the nanofibrous web comprises a polymer that is a polypropylene or polypropylene blend.

7. The air filtration media of claim 1 , wherein the nanofibrous web is made by a centrifugal melt spinning process.