Substrate

Abstract

A substrate, suitable for the preparation of a composite membrane, which substrate comprises a porous matrix of fibres, characterised in that the fibres comprise mixed amorphous silica fibres that are bound with a binder, a composite membrane comprising the substrate and a process for the preparation of the substrate and composite membrane is disclosed.

1 . A substrate, suitable for the preparation of a composite membrane, which substrate comprises a porous non-woven sheet of fibres, wherein the fibres comprise a mixture of micro-fine amorphous silica fibres and one or more chopped strand(s) of amorphous silica and the fibres are bound with a binder.  
     
     
         2 . (Canceled)  
     
     
         3 . (Canceled)  
     
     
         4 . A substrate according to  claim 1 , wherein the mixture comprises microfibres and chopped fibres in the range of from 95:5% to 5:95% by weight of the mixture respectively.  
     
     
         5 . A substrate according to  claim 4 , wherein the mixture comprises microfibres and chopped fibres in the range of from 70:30% to 30:70% by weight of the mixture respectively.  
     
     
         6 . A substrate according to  claim 1 , wherein the fibres have a diameter in the range of from 0.1 μm to 50 μm.  
     
     
         7 . A substrate according to  claim 6 , wherein the fibres have a diameter in the range of 0.4 μm to 9 μm.  
     
     
         8 . A substrate according to  claim 1 , wherein the binder comprises a solution or dispersion of ion-exchange polymeric materials, non-ion-conducting polymers, or inorganic materials or mixtures thereof.  
     
     
         9 . A substrate according to  claim 1  for use in the preparation of a composite membrane.  
     
     
         10 . A composite membrane comprising a porous substrate of fibres and at least one ion-conducting polymer, wherein the substrate comprises a porous non-woven sheet of a mixture of micro-fine amorphous silica fibres and one or more chopped strand(s) of amorphous silica and the fibres are bound with a binder.  
     
     
         11 . A composite membrane according to  claim 10 , which when dried then boiled in water undergoes less than or equal to about ±9% change in the area.  
     
     
         12 . A composite membrane according to  claim 10 , wherein the total thickness of the membrane is less that 200 μm.  
     
     
         13 . A composite membrane according to  claim 10  for use in a fuel cell.  
     
     
         14 . A process for the manufacture of a substrate, comprising the steps of 
 (a) dispersing a mixture of micro-fine amorphous silica fibres and one or more chopped strand(s) of amorphous silica in water to form a slurry;    (b) depositing the slurry onto a mesh bed to form a fibre network;    (c) drying and compacting the fibre network; and    (d) applying, before or after step (c), a dispersion of binder.    
     
     
         15 . A process for the manufacture of a membrane, comprising the steps of 
 (i) forming a porous substrate according to  claim 14;  and thereafter,    (ii) impregnating the porous substrate with a polymeric material to produce a membrane.    
     
     
         16 . A process according to  claim 15 , wherein step (ii) is carried out by nip roller coating of the substrate to fill it with a solution of ion-conducting polymeric material, and further compaction and drying of the membrane.  
     
     
         17 . A membrane electrode assembly comprising a composite membrane according to  claim 10 .  
     
     
         18 . A fuel cell comprising a composite membrane according to  claim 10 .  
     
     
         19 . A process according to  claim 15 , wherein the fibres are randomly oriented in said porous substrate.  
     
     
         20 . A substrate according to  claim 1 , wherein the fibres are randomly oriented.