High flux high efficiency nanofiber membranes and methods of production thereof

Abstract

A membrane is provided including a coating layer having cellulose nanofibers produced from oxidized cellulose microfibers and an electrospun substrate upon which the coating layer is applied. The nanofibers of the electrospun substrate have a diameter greater than that of the cellulose nanofibers. The membrane also has non-woven support upon which the electrospun substrate is disposed. Microfibers of the non-woven support have a diameter greater than that of the nanofibers of the electrospun substrate. Application of electrospun membrane is in microfiltration area, while the cellulose nanofiber membrane serves in ultra-filtration, nanofiltration, and reverse osmosis after chemical modification.

1 . A membrane comprising:
 a coating layer having a non-woven structure of polysaccharide nanofibers, wherein the polysaccharide nanofibers have a diameter between 5 to 50 nanometers (nm);   an electrospun substrate having a non-woven structure upon which the coating layer is applied, wherein nanofibers of the electrospun substrate have a diameter greater than that of the polysaccharide nanofibers; and   a non-woven support upon which the electrospun substrate is disposed, wherein microfibers of the non-woven support have a diameter greater than that of the nanofibers of the electrospun substrate.   
     
     
         2 . The membrane of  claim 1 , wherein the nanofibers of the electrospun substrate have a diameter between 50 and 300 nm. 
     
     
         3 . The membrane of  claim 1 , wherein the microfibers of the non-woven support have a diameter between 5 and 20 micrometers (μm). 
     
     
         4 . The membrane of  claim 1 , wherein the polysaccharide nanofibers comprise at least one of cellulose nanofibers, oxide cellulose nanofibers, chitin nanofibers and chitosan nanofibers. 
     
     
         5 . The membrane of  claim 1 , wherein the electrospun substrate comprises polymers from a group consisting of polyolefins, polysulfones, fluoropolymers, polyesters, polycarbonates, polystyrenes, polynitriles, polyacrylates, polyacetates and copolymers thereof. 
     
     
         6 . The membrane of  claim 1 , wherein a thickness of the coating layer is smaller than a thickness of the electrospun substrate and the thickness of the electrospun substrate is smaller than that of the non-woven support. 
     
     
         7 . The membrane of  claim 6 , wherein the thickness of the coating layer is between 10 and 500 nm. 
     
     
         8 . The membrane of  claim 6 , wherein the thickness of the electrospun substrate is between 10 and 50 μm. 
     
     
         9 . The membrane of  claim 6 , wherein the thickness of the non-woven support is between 100 and 250 μm. 
     
     
         10 . The membrane of  claim 1 , wherein a maximum pore size of the electrospun substrate is approximately three times a mean pore size of the electrospun substrate when a porosity of the electrospun substrate is approximately 80%. 
     
     
         11 . The membrane of  claim 1 , wherein a mean pore size of the electrospun substrate is approximately three times larger than the diameter of the nanofibers of the electrospun substrate, when a porosity of the electrospun substrate is approximately 80%. 
     
     
         12 . The membrane of  claim 1 , wherein the polysaccharide nanofibers of the coating layer are cross-linked via at least one of a heating process, immersion in glutaraldehyde (GA), and incorporation of polyacrylic acid (PAA) in the coating layer. 
     
     
         13 . A membrane comprising:
 a coating layer comprising a mixture of nanofibers comprising PolyVinyl Alcohol (PVA) and cellulose;   an electrospun substrate upon which the coating layer is applied, wherein nanofibers of the electrospun substrate have a diameter greater than that of the nanofibers of the coating layer; and   a non-woven support upon which the electrospun substrate is disposed, wherein microfibers of the non-woven support have a diameter greater than that of the nanofibers of the electrospun substrate.   
     
     
         14 . The method of  claim 13 , wherein a defined amount of the electrospun substrate is embedded into the coating layer to reinforce mechanical strength of the coating layer. 
     
     
         15 . The membrane of  claim 13 , wherein a maximum pore size of the electrospun substrate is approximately three times a mean pore size of the electrospun substrate when a porosity of the electrospun substrate is approximately 80%. 
     
     
         16 . The membrane of  claim 13 , wherein a mean pore size of the electrospun substrate is approximately three times the fiber diameter of the nanofibers of the electrospun substrate, when a porosity of the electrospun substrate is approximately 80%. 
     
     
         17 . A membrane comprising:
 a coating layer having a non-woven structure format of at least one of cellulose nanocrystals and microcrystals;   an electrospun substrate having a non-woven structure format upon which the coating layer is applied, wherein nanofibers of the electrospun substrate have a diameter greater than that of the cellulose nanocrystals and microcrystals; and   a non-woven support upon which the electrospun substrate is disposed, wherein microfibers of the non-woven support have a diameter greater than that of the nanofibers of the electrospun substrate.   
     
     
         18 . A method for producing a membrane, the method comprising steps of:
 producing a coating layer having a non-woven structure format from polysaccharide nanofibers, wherein the polysaccharide nanofibers have a diameter between 5 to 50 nanometers (nm);   immersing an electrospun substrate having a non-woven structure format into a water-based solution; and   applying the coating layer to the electrospun substrate, wherein a gel barrier is formed at an interface between the electrospun substrate and the coating layer to slow diffusion of the coating layer into the electrospun substrate, and wherein nanofibers of the electrospun substrate have a diameter greater than that of the polysaccharide nanofibers;   wherein the electrospun substrate is disposed on a non-woven support having microfibers with a diameter greater than that of the nanofibers of the electrospun substrate.   
     
     
         19 . The method of  claim 18 , further comprising heating the coating layer after application to the electrospun substrate to cross-link the polysaccharide nanofibers. 
     
     
         20 . A membrane comprising:
 an electrospun substrate having a non-woven structure format; and   a non-woven support upon which the electrospun substrate is disposed, wherein microfibers of the non-woven support have a diameter greater than that of nanofibers of the electrospun substrate;   wherein a maximum pore size of the electrospun substrate is approximately three times a mean pore size of the electrospun substrate when a porosity of the electrospun substrate is approximately 80%; and   wherein a mean pore size of the electrospun substrate is approximately three times the fiber diameter of the nanofibers of the electrospun substrate, when a porosity of the electrospun substrate is approximately 80%.   
     
     
         21 . The membrane of  claim 20 , wherein the nanofibers of the electrospun substrate have a diameter between 50 and 300 nanometers (nm). 
     
     
         22 . The membrane of  claim 20 , wherein the microfibers of the non-woven support have a diameter between 5 and 20 micrometers (μm). 
     
     
         23 . The membrane of  claim 20 , wherein a thickness of the electrospun substrate is smaller than that of the non-woven support. 
     
     
         24 . The membrane of  claim 23 , wherein the thickness of the electrospun substrate is between 10 and 50 μm. 
     
     
         25 . The membrane of  claim 23 , wherein the thickness of the non-woven support is between 100 and 250 μm.