Meltblown nonwoven webs including nanofibers and apparatus and method for forming such meltblown nonwoven webs

1. A method of making a nonwoven web from a liquid material, comprising:

establishing a first and second flow of the liquid material;

changing the rheology of the liquid material in the first and second flows, the changed rheology of the second flow differing from the changed rheology of the first flow by an amount sufficient to produce a phase separation between the liquid material in the first and second flows when combined, wherein the liquid materials of the first and second flows are chemically identical both before and after changing rheology;

combining the first flow of the liquid material with the changed rheology and the second flow of the liquid material with the changed rheology to form a plurality of meltblown fibers each having a length, a first cross-sectional region formed of the liquid material from the first flow, and a second cross-sectional region formed of the liquid material from the second flow, the first and second cross-sectional regions extending along the length of each fiber;

separating the first cross-sectional region from the second cross-sectional region along the length of at least a majority of the meltblown fibers to form a plurality of nanofibers; and

collecting the nanofibers to form the nonwoven web.

2. The method of claim 1 further comprising:

collecting any un-separated meltblown fibers together with the nanofibers to form the nonwoven web.

3. A method of making a nonwoven web from a liquid material, comprising:

establishing a first and second flow of the liquid material;

changing the rheology of the liquid material in the first and second flows, the changed rheology of the second flow differing from the changed rheology of the first flow by an amount sufficient to produce a phase separation between the liquid material in the first and second flows when combined;

combining the first flow of the liquid material with the changed rheology and the second flow of the liquid material with the changed rheology to form a plurality of meltblown fibers each having a length, a first cross-sectional region formed of the liquid material from the first flow, and a second cross-sectional region formed of the liquid material from the second flow, the first and second cross-sectional regions extending along the length of each fiber;

separating the first cross-sectional region from the second cross-sectional region along the length of at least a majority of the meltblown fibers to form a plurality of nanofibers and impinging the meltblown fibers with air at a velocity effective to split at least the majority of the meltblown fiber into nanofibers; and

collecting the nanofibers to form the nonwoven web.

4. The method of claim 3 wherein impinging the meltblown fibers with air further includes:

attenuating the meltblown fibers before splitting.

5. A method of making a nonwoven web from a liquid material, comprising:

establishing a first and second flow of the liquid material;

changing the rheology of the liquid material in the first and second flows by a process including subjecting the liquid material in the first and second flows to different shear histories, the changed rheology of the second flow differing from the changed rheology of the first flow by an amount sufficient to produce a phase separation between the liquid material in the first and second flows when combined;

combining the first flow of the liquid material with the changed rheology and the second flow of the liquid material with the changed rheology to form a plurality of meltblown fibers each having a length, a first cross-sectional region formed of the liquid material from the first flow, and a second cross-sectional region formed of the liquid material from the second flow, the first and second cross-sectional regions extending along the length of each fiber;

separating the first cross-sectional region from the second cross-sectional region along the length of at least a majority of the meltblown fibers to form a plurality of nanofibers; and

collecting the nanofibers to form the nonwoven web.

6. The method of claim 5 wherein subjecting the liquid material in the first and second flows to different shear histories further comprises:

extruding the first flow of the liquid material from a first extruder having a barrel of a first diameter; and

extruding the second flow of the liquid material from a second extruder having a barrel of a second diameter that differs from the first diameter.

7. The method of claim 1 wherein combining the first and second flows of the liquid material further comprises:

arranging the first and second cross-sectional regions with a side-by-side arrangement extending along the length of each meltblown fiber.

8. The method of claim 1 wherein each of the meltblown fibers includes a third cross-sectional region formed of the liquid from the first flow and extending along the length of each fiber, and combining the first and second flows of the liquid material further comprises:

arranging the third cross-sectional region adjacent to the second cross-sectional region.

9. The method of claim 8 further comprising:

separating the third cross-sectional region from the second cross-sectional region along the length of at least a majority of the meltblown fibers to form nanofibers.

10. A method of making a nonwoven web from a liquid material, comprising:

establishing a first, second, and third flow of the liquid material;

changing the rheology of the liquid material in the first, second, and third flows, the changed rheology of the second flow differing from the changed rheology of the first flow by an amount sufficient to produce a phase separation between the liquid material in the first and second flows when combined and the changed rheology of the third flow differing from the changed rheology of at least one of the first and second flows to produce a phase separation between the liquid material in the third flow and the at least one of the first and second flows when combined, wherein the liquid materials of the first, second, and third flows are chemically identical both before and after changing rheology;

combining the first flow of the liquid material with the changed rheology, the second flow of the liquid material with the changed rheology, and the third flow of the liquid material with the changed rheology to form a plurality of meltblown fibers each having a length, a first cross-sectional region formed of the liquid material from the first flow, a second cross-sectional region formed of the liquid material from the second flow, and a third cross-sectional region formed of the liquid material from the third flow, the first, second, and third cross-sectional regions extending along the length of each fiber;

mutually separating the first, second, and third cross-sectional regions from each other along the length of at least a majority of the meltblown fibers to form a plurality of nanofibers; and

collecting the nanofibers to form the nonwoven web.

11. The method of claim 10 further comprising: collecting any un-separated meltblown fibers together with the nanofibers to form the nonwoven web.

12. The method of claim 11 wherein the third flow has a different changed rheology than the first and second flows.

13. A method of making a nonwoven web from a liquid material, comprising:

establishing a first and second flow of the liquid material;

causing the liquid material in the first flow to experience a different shear history from that of the second flow, the shear histories differing by an amount sufficient to produce a phase separation between the liquid material in the first and second flows when combined;

after experiencing differing shear histories, combining the first flow of the liquid material and the second flow of the liquid material to form a plurality of meltblown fibers each having a length, a first cross-sectional region formed of the liquid material from the first flow, and a second cross-sectional region formed of the liquid material from the second flow, the first and second cross-sectional regions extending along the length of each fiber;

separating the first cross-sectional region from the second cross-sectional region along the length of at least a majority of the meltblown fibers to form a plurality of nanofibers; and

collecting the nanofibers to form the nonwoven web.

14. The method of claim 13 further comprising:

collecting any un-separated meltblown fibers together with the nanofibers to form the nonwoven web.

15. The method of claim 13 wherein separating the first cross-sectional region from the second cross-sectional region further comprises:

impinging the meltblown fibers with air at a velocity effective to split at least the majority of the meltblown fiber into nanofibers; and

collecting the nanofibers to form the nonwoven web.

16. The method of claim 15 wherein impinging the meltblown fibers with air further includes:

attenuating the meltblown fibers before splitting.

17. A method of making a nonwoven web from a liquid material, comprising:

establishing a first, second, and third flow of the liquid material;

causing the liquid material in the first, second, and third flows to experience differing shear histories, the differing shear histories of the first, second, and third flows adequate to produce a phase separation between the liquid material between at least two flows when combined;

after experiencing differing shear histories, combining the first, second, and third flows to form a plurality of meltblown fibers each having a length, a first cross-sectional region formed of the liquid material from the first flow, a second cross-sectional region formed of the liquid material from the second flow, and a third cross-sectional region formed of the liquid material from the third flow, the first, second, and third cross-sectional regions extending along the length of each fiber;

mutually separating the first, second, and third cross-sectional regions from each other along the length of at least a majority of the meltblown fibers to form a plurality of nanofibers; and

collecting the nanofibers to form the nonwoven web.

18. The method of claim 17 further comprising: collecting any un-separated meltblown fibers together with the nanofibers to form the nonwoven web.