Method for preparation of absorbing substances

Abstract

The invention relates to a method for preparing absorptive substances from lignocellulosic materials, such as straw of cereal plants, peels or hulls of cereal grains, plant leaves, bagasse, jute or wood chips. The method according to the invention comprises as its essential stages an alkaline pretreatment for partial removal of lignin and hemicellulose, an initiation treatment for forming reactive radicals, addition of at least one monomer and cross-linking agent, and finally a polymerization. As a preceding treatment, washing with water for removal of extraneous matter and/or disturbing components can be included, and potentially a wet milling or another defibration for increasing the reactive surface. For initiation, an oxidative chemical such as hydrogen peroxide is suitable, for the monomer especially compounds containing a vinyl group, such as acrylic acid. For obtaining or improving ion exchange properties, an ionizable atomic group can be included either as a part of a monomer, or forming it after the polymerization.

1 . A method for the preparation of an absorbing substance from lignocellulosic material, characterized by steps in which: 
 (a) lignocellulosic material is treated with alkali to remove a part of its lignin and/or hemicellulose content,    (b) after step (a), the material is treated to provide its cellulose content with reactive radicals capable of functioning as polymerization initiators,    (c) after step (b), at least one polymerizable monomer and at least one cross-linking agent are added to the maerial,    (d) the composition obtained at step (c) is polymerized.    
     
     
         2 . A method according to  claim 1 , wherein the lignocellulosic starting material is fibrous or foil-formed.  
     
     
         3 . A method according to  claim 2 , wherein the lignocellolosic material is straw, peels or hulls of a cereal crop.  
     
     
         4 . A method according to  claim 1 , wherein before the alkali treatment of step (a), the lignocellulosic material is washed with water for removal of impurities.  
     
     
         5 . A method according to  claim 1 , wherein by the alkali treatment of step (a) and a possible preceding water washing, 30 to 95%, preferably 50 to 80% of the sum of lignin and hermicellulose present in the starting material is removed.  
     
     
         6 . A method according to  claim 1 , wherein at step (a) or before it, lignocellulosic material is defibrated by subjecting it to wet milling.  
     
     
         7 . A method according to  claim 1 , wherein the lignocellulosic material is defibrated by using an extrusion operation.  
     
     
         8 . A method according to  claim 1 , wherein the initiation treatment of step (b) for forming reactive radicals is performed by treating with an oxidative chemical.  
     
     
         9 . A method according to  claim 8 , wherein the initiation treatment is performed by treating with hydrogen peroxide.  
     
     
         10 . A method according to  claim 8 , wherein the initiation treatment is performed by treating with sodium persulfate.  
     
     
         11 . A method according to  claim 8 , wherein after the alkali and oxidation treatments at steps (a) and (b), the moist solid material is subjected to polymerization without any intermediate washing treatment.  
     
     
         12 . A method according to  claim 8 , wherein one or several monomers and cross-linking agents are added at step (c) simultaneously.  
     
     
         13 . A method according to  claim 12 , wherein one or several monomers and cross-linking agents are added as a mixture.  
     
     
         14 . A method according to  claim 12 , wherein the monomer or monomers are compounds, which contain a vinyl group.  
     
     
         15 . A method according to  claim 14 , wherein the monomer is acrylic acid, methacrylic acid or their derivative.  
     
     
         16 . A method according to  claim 1 , wherein the monomer contains an ionizable atomic group, which does not participate in the polymerization reaction.  
     
     
         17 . A method according to  claim 1 , wherein the polymer obtained from step (d) is subjected to a reaction for forming an ionizable atomic group in it.  
     
     
         18 . A method according to  claim 16  wherein the ionizable atomic group is sulfonic acid.  
     
     
         19 . A method according to  claim 16  wherein the ionizable atomic group is a basic group.  
     
     
         20 . A method for the preparation of an absorbing substance from lignocellulosic material, comprising the steps of: 
 (a) treating said lignocellulosic material with alkali to remove at least a part of its lignin, hemicellulose, or a combination thereof;    (b) after step (a), treating said lignocellulosic material with an oxidative chemical to provide its cellulose content with reactive radicals capable of functioning as polymerization initiators;    (c) after step (b), adding to said lignocellulosic material at least one polymerizable monomer and at least one cross-linking agent to form a composition; and    (d) polymerizing said composition    
     
     
         21 . A method for the preparation of an absorbing substance from lignocellulosic material, comprising the steps of: 
 (a) treating said lignocellulosic material with alkali to remove at least a part of its lignin, hemicellulose, or a combination thereof;    (b) after step (a), treating said lignocellulosic material to provide its cellulose content with reactive radicals capable of functioning as polymerization initiators;    (c) after step (b), adding to said lignocellulosic material at least one polymerizable monomer and at least one cross-linking agent to form a composition, wherein said polymerizable monomer comprising an ionizable atomic group; and    (d) polymerizing said composition.