Electrospinning of ptfe with high viscosity materials

Abstract

An improved process for forming a PTFE mat is described. The process includes providing a dispersion with PTFE, a fiberizing polymer and a solvent wherein said dispersion has a viscosity of at least 50,000 cP. An apparatus is provided which comprises a charge source and a target a distance from the charge source. A voltage source is provided which creates a first charge at the charge source and an opposing charge at the target. The dispersion is electrostatically charged by contact with the charge source. The electrostatically charged dispersion is collected on the target to form a mat precursor which is heated to remove the solvent and the fiberizing polymer thereby forming the PTFE mat.

1 . A polymeric material comprising: a membrane comprised of serially deposited polymeric fibers, the polymeric fibers having been stretched in a first direction after the fibers are serially deposited. 
     
     
         2 . The polymeric material of  claim 1 , wherein the serially deposited fibers comprise sintered fibers. 
     
     
         3 . The polymeric material of  claim 1 , wherein the serially deposited fibers are exposed to an elevated temperature. 
     
     
         4 . The polymeric material of  claim 1 , wherein the serially deposited fibers are generally aligned in the first direction. 
     
     
         5 . The polymeric material of  claim 1 , wherein the membrane is more resistant to creep in the first direction after the membrane is stretched. 
     
     
         6 . The polymeric material of  claim 1 , wherein the serially deposited polymeric fibers have been stretched in a second direction. 
     
     
         7 . A serially deposited fiber mat comprising a portion of a device, the serially deposited fiber mat comprising serially deposited fibers, wherein all of the fibers have diameters of 400 nm to 3200 nm. 
     
     
         8 . The serially deposited fiber mat of  claim 7 , wherein the serially deposited fiber mat comprises spun polytetrafluoroethylene fibers. 
     
     
         9 . The serially deposited fiber mat of  claim 7 , wherein all of the fibers have diameters from 800 nm to 2.4 μm. 
     
     
         10 . The serially deposited fiber mat of  claim 7 , wherein the serially deposited fibers have an average fiber density from 135 to 326,400 fibers per mm 2 . 
     
     
         11 . The serially deposited fiber mat of  claim 7 , wherein the largest pore diameter is from 2.54 μm to 9.96 μ.m. 
     
     
         12 . The serially deposited fiber mat of  claim 7 , wherein the fibers define between 2 and 2.9×10 12  intersections per mm 2 . 
     
     
         13 . A method of manufacturing a polymeric material comprising: obtaining a membrane comprising a mat of polymeric fibers; sintering the membrane; and expanding the membrane in a first direction to at least partially elongate the membrane in the first direction. 
     
     
         14 . The method of  claim 13 , wherein obtaining the membrane comprises: serially depositing polymeric fibers on a collection surface to form a membrane. 
     
     
         15 . The method of  claim 13 , wherein the membrane is sintered at a temperature of 288° C. to 482° C. 
     
     
         16 . The method of  claim 13 , wherein sintering the membrane comprises heating the membrane to at least the crystalline melt temperature of the polymeric fibers. 
     
     
         17 . The method of  claim 13 , wherein expanding the membrane comprises expanding the membrane such that the polymeric fibers tend to align in the first direction. 
     
     
         18 . The method of  claim 13 , wherein expanding the membrane comprises expanding the membrane on the order of 103 to 200% of its original length in the first direction. 
     
     
         19 . The method of  claim 13 , further comprising stretching the membrane in a second direction. 
     
     
         20 . The method of  claim 13 , further comprising constraining the membrane, wherein the sintering is conducted while the membrane is constrained in place on a surface on which it was collected. 
     
     
         21 . The method of  claim 13 , wherein obtaining the membrane comprises: mixing a PTFE-water dispersion comprising from 50% to 80% PTFE solids by weight with PEO to create a mixture having 0.032 to 0.052 gm PEO/mL of total mixture; spinning the mixture; collecting spun fibers on a cylindrical surface; and wherein the sintering is at a temperature of 288° C. to 482° C.