Melt-spun polypropylene fine-grade nanofibrous web

Abstract

The present invention is directed toward a to fine-grade stand-alone nanoweb and nanofibrous membrane comprising a nanofiber network with a number average nanofiber diameter less than 200 nm and the mean flow pore size less than 1000 nm that yield the selective barrier medium with a superior balance of flow versus barrier properties.

What is claimed is: 
     
         1 . A melt-spun polypropylene fine-grade nanofibrous web comprising a nanofiber network with a number average nanofiber diameter of less than about 200 nm and the mean flow pore size of less than about 1000 nm. 
     
     
         2 . The nanofibrous web of  claim 1 , wherein the nanofiber network has a fiber diameter both mean and median of less than about 200 nm and the individual nanofibers have a fiber diameter in the range of a minimum of about 10 nm to a maximum of about 1000 nm. 
     
     
         3 . The nanofibrous web of  claim 1 , wherein the nanofibrous web has:
 (a) less than about 5% Mw reduction of the nanofibrous web as compared to the polymer used for making the nanofibrous web;   (b) essentially the same thermal weight loss as compared to the polymer used for making the nanofibrous web as measured by TGA; and   (c) higher crystallinity of the nanofibrous web as compared to the polymer used for making the nanofibrous web.