Nanocrystalline cellulose, its preparation and uses of such nanocrystalline cellulose

Abstract

The present invention relates to nanocrystalline cellulose, an efficient way of its preparation and to uses of such nanocrystalline cellulose. The present invention also relates to porous metal oxides having a chiral nematic structure which are prepared using nanocrystalline cellulose.

1 . A method of preparing nanocrystalline cellulose, comprising the steps:
 a) providing cellulose fibers,   b) subjecting said cellulose fibers to an acidic hydrolysis,   c) stopping the hydrolysis by addition of a base.   
     
     
         2 . The method according to  claim 1 , comprising the further step:
 d) isolating the nanocrystalline cellulose resulting from the performance of steps b)-c).   
     
     
         3 . The method according to  claim 2 , wherein isolating the nanocrystalline cellulose in step d) is achieved by centrifugation and washing. 
     
     
         4 . The method according to  claim 3 , wherein step d) is achieved by performing a first centrifugation on the product of step c), followed by a washing step and a further centrifugation step. 
     
     
         5 . The method according to  claim 4 , wherein the washing step and the further centrifugation step are performed n-times, wherein n=1-10. 
     
     
         6 . The method according to  claim 1 , wherein said hydrolysis in step b) is performed by the presence of a mineral acid. 
     
     
         7 . The method according to  claim 1 , wherein said base that is added in step c) is selected from the group comprising metal hydroxides, metal oxides and NH 3 . 
     
     
         8 . The method according to  claim 1 , wherein said hydrolysis in step b) is performed by the presence of a mineral acid, and wherein said base is
 i) a metal hydroxide or NH 3 , and wherein said metal hydroxide or NH 3  is added in step c) in a molar ratio of base:mineral acid in a range of from 1:5 to 5:1, or   ii) a metal oxide, wherein said metal oxide in step c) is added in a molar ratio of metal oxide:mineral acid in a range of from approximately 1:10 to 1:1.   
     
     
         9 . The method according to  claim 7 , wherein said metal hydroxide is an alkali metal hydroxide or an earth alkali metal hydroxide or a metal hydroxide selected from Al(OH) 3 , Zn(OH) 2 , Mn(OH) 2  and Cu(OH) 2 , and wherein said metal oxide has a general formula selected from MeO, MeO 2  and Me 2 O 3 , wherein Me=metal and O=oxygen. 
     
     
         10 . Nanocrystalline cellulose prepared by the method according to  claim 1 . 
     
     
         11 . Nanocrystalline cellulose prepared by the method according to  claim 7  wherein said base is a metal oxide or metal hydroxide, and/or is characterized by:
 a content of metal ions, wherein said content of metal ions is in the range of from 10 mg/g of sample nanocrystalline cellulose to 800 mg/g of sample nanocrystalline cellulose. 
 
     
     
         12 . Nanocrystalline cellulose according to  claim 10 , further characterized by
 a chiral nematic structure, and   a left handed pitch in the range of from 0.1 μm to 1 μm.   
     
     
         13 . Use of the nanocrystalline cellulose according to  claim 10 ,
 as a substrate, matrix or coating in an electronic or pharmaceutical application,   as an additive in paper or food,   as a coating in a medical or pharmaceutical application, or   as a reinforcing agent/filler for enhancement of mechanical strength.   
     
     
         14 . A method for preparing a porous metal oxide with chiral nematic structure, comprising the steps:
 a′) performing the method according to  claim 1 , wherein the base that is used is a metal oxide or a metal hydroxide,   b′) casting the resultant nanocrystalline cellulose in a three-dimensional shape or as a thin film, wherein said thin film has a thickness in the range of from 50 nm to 500 μm, and   c′) subjecting said casted shape or thin film to a heat treatment for annealing and for removal of the nanocrystalline cellulose, said heat treatment thus resulting in a porous metal oxide with chiral nematic structure.   
     
     
         15 . A porous metal oxide prepared by a method comprising the steps:
 a′) performing the method according to  claim 1 , wherein the base that is used is a metal oxide or a metal hydroxide,   b′) casting the resultant nanocrystalline cellulose in a three-dimensional shape or as a thin film, wherein said thin film has a thickness in the range of from 50 nm to 500 μm,   c′) subjecting said casted shape or thin film to a heat treatment for annealing and for removal of the nanocrystalline cellulose, said heat treatment thus resulting in a porous metal oxide with chiral nematic structure characterized by an average pore size in the range of from 2-50 nm, and/or having a chiral nematic structure characterized by:
 a content of metal ions, wherein said content of metal ions is in the range of from 10 mg/g of sample nanocrystalline cellulose to 800 mg/g of sample nanocrystalline cellulose. 
   
     
     
         16 . The method, according to  claim 8 , wherein
 (i) said metal hydroxide or NH 3  is added in step c) in a molar ratio of base:mineral acid in a range of from 1:2 to 2:1, or   ii) a metal oxide, wherein said metal oxide in step c) is added in a molar ratio of metal oxide:mineral acid in a range of from approximately 1:3 to 1:1.   
     
     
         17 . The method, according to  claim 14 , wherein said thin film has a thickness in the range of from 100 nm to 30 μm. 
     
     
         18 . A method for packaging a product, wherein said method comprises the use of a material according to  claim 10  as a packaging material, or as a coating on a packaging material. 
     
     
         19 . The method, according to  claim 18 , used to package a food product. 
     
     
         20 . The method, according to  claim 18 , wherein the material is used as a coating on a packaging material.