Fibrillated acrylic fibre

Abstract

Fibrillated acrylic fibers which are suitable for oxidation in the form of staple fibers are formed as copolymers of acrylonitrile and an unsaturated carboxylic acid such as itaconic acid or methacrylic acid. A further monomer may also be included, such as methacrylate, methylmethacrylate or vinyl acetate. Fibers having a Canadian Freeness value of 350-500, and a decitex value of 1.2 to 1.7 may be produced.

1 . A fibrillated oxidisable acrylic staple fibre which is formed from a copolymerisation of acrylonitrile and an unsaturated carboxylic acid.  
     
     
         2 . A fibre as claimed in    claim 1    wherein the unsaturated carboxylic acid is one of itaconic acid or methacrylic acid.  
     
     
         3 . A fibre as claimed in    claim 2    wherein the fibre contains 0.5-2% of itaconic acid units within the polymer chain.  
     
     
         4 . A fibre as claimed in any one of    claims 1    to    3    wherein the fibres have a decitex value in the range 0.6-6.0 decitex.  
     
     
         5 . A fibre as claimed in any one of    claims 1    to    4    wherein the fibre has a decitex value in the range 1.2 to 1.7 decitex.  
     
     
         6 . A fibre as claimed in any one of    claims 1    to    5    wherein the staple fibres have a cut length of 4-12 mm, preferably 6-8 mm.  
     
     
         7 . A fibre as claimed in any one of    claims 1    to    6    wherein the fibrillated fibres have a Canadian Freeness value of less than 700 and preferably in the range 350 to 450.  
     
     
         8 . A fibre as claimed in any one of    claims 1    to    7    when used as a precursor for oxidation into oxidised acrylic fibre.  
     
     
         9 . A fibre as claimed in any one of    claims 1    to    8    the copolymer further comprising at least one further monomer selected from methyl acrylate, methyl methacrylate and vinyl acetate.  
     
     
         10 . A method of manufacture of oxidised acrylic fibres, in which a staple acrylic fibre is made from a copolymerisation of acrylonitrile and an unsaturated carboxylic acid, and then fibrillated in the gel state prior to drying and oxidation.  
     
     
         11 . A method according to    claim 10    wherein the staple acrylic fibre is copolymerised from acrylonitrile and itaconic acid.  
     
     
         12 . A method according to    claim 10    or    claim 11    wherein at least one further monomer selected from methyl acrylate, methyl methacrylate and vinyl acetate, is incorporated into the fibre during the copolymerisation step.  
     
     
         13 . A method according to any one of    claims 10    to    12    wherein the fibre is fibrillated to produce a Canadian Freeness value of less than 700, preferably a value in the range 350-700.  
     
     
         14 . A method according to any one of    claims 10    to    13    wherein the staple fibre is cut to a length of 4 to 8 mm, preferably 6 mm.  
     
     
         15 . A method according to any one of    claims 10    to    14    wherein the fibre is spun to a decitex value in the range 0.6 to 6.0 decitex.  
     
     
         16 . An oxidised fibrillated acrylic fibre made from a fibre as claimed in any one of    claims 1    to    9   , or by a method as claimed in any one of    claims 10    to    15   .