Light-stable lignocellulosic materials and their production

Abstract

A novel method for the production of light-stable lignocellulosic materials, in particular, the production of mechanical wood pulps with much improved light stability is described, as well as the resulting pulps of improved light stability and papers containing such pulps. The novel method involves the reaction of lignocellulosic materials such as bleached thermomechanical pulp (BTMP) with a water-soluble, fiber-reactive yellowing inhibitor possessing a primary or secondary amino (—NH 2 or —NHR) functional group in an aqueous medium, or with a water-soluble, fiber-reactive hindered amine light stabilizer possessing a primary or secondary amino (—NH 2 or —NHR) functional group in an alkaline peroxide bleaching medium or in an aqueous medium with a subsequent bleaching of the materials in an alkaline peroxide bleaching medium. Examples of such water-soluble, fiber-reactive yellowing inhibitors and hindered amine light stabilizers are the commercially available 4-amino-2,2,6,6-tetramethylpiperidine-N-oxyl (4-amino-TEMPO) and 4-amino-2,2,6,6-tetramethylpiperidine, respectively.

I claim  
     
         1 . A method for the production of a light-stable, lignocellulosic material comprising reacting the material with a water-soluble, yellowing inhibitor possessing a primary or secondary amino group of the formula A, B, C or D wherein Y is oxyl (O) or hydroxyl (OH) in an aqueous medium, or with a water-soluble hindered amine light stabilizer of the formula A or B wherein Y is hydrogen (H) in an alkaline peroxide bleaching medium or in an aqueous medium with a subsequent bleaching of the reacted material in an alkaline peroxide bleaching medium  
       
         
           
           
               
               
           
         
       
       wherein R 1  is hydrogen or an alkyl group (CH 2 ) n H that is unsubstituted or substituted by 1 to 2n+1 number of a hydroxyl, ether, thio, thioether, benzyl, amino, ester, amide, carboxyl, and/or carboxylate [(COO − ) r M r+ ] group, and/or radicals derived from an organic ultraviolet absorber; R 2 , R 3 , R4 and R 5  are independently alkyl groups (CH 2 ) n H that are unsubstituted or substituted by 1 to 2n+1 number of a hydroxyl, ether, thio, thioether, benzyl, amino, ester, amide, carboxyl, and/or carboxylate [(COO − ) r M r + ] group, and/or radicals derived from an organic ultraviolet absorber; X is an inorganic or organic anion, n is 1 to 14, preferably 1 to 6, and more preferably 1 to 4, k is 1 to 3, p is 1 or 2, M is an ammonium or metal ion and r is 1, 2 or 3, and the total charge of 2m is equal to kp.  
     
     
         2 . A method according to  claim 1  wherein said material is reacted with said yellowing inhibitor in said aqueous medium.  
     
     
         3 . A method according to  claim 1  wherein said material is reacted with said stabilizer in said alkaline peroxide bleaching medium.  
     
     
         4 . A method according to  claim 1  wherein said material is reacted with said stabilizer in an aqueous medium with a subsequent bleaching of the reacted material in said alkaline peroxide bleaching medium.  
     
     
         5 . A method according to  claim 1  wherein said lignocellulosic material is a wood pulp and including steps of 
 forming a paper from the resulting pulp and coating the paper with an ultraviolet absorber.  
 
     
     
         6 . A method according to  claim 1 , wherein at least one of R 1 , R 2 , R 3 , R 4  and R 5  is a said alkyl group substituted with an organic ultraviolet absorber derived from 2,4-dihydroxybenzophenone or 2-hydroxybenzophenone.  
     
     
         7 . A method according to  claim 1  wherein X is selected from carbonate, chloride bisulfate, sulfate, formate, acetate, citrate, phosphate and ascorbate.  
     
     
         8 . A method according to  claim 1  wherein the yellowing inhibitor is 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl.  
     
     
         9 . A method according to  claim 1 , wherein the hindered amine light stabilizer is 4-amino-2,2,6,6-tetramethylpiperidine.  
     
     
         10 . A method according to  claim 1 , wherein the reaction of the lignocellulosic material is conducted with a charge of the yellowing inhibitor or hindered amine light stabilizer of 0.01 to 2.0%, by weight, based on the oven dry weight of the lignocellulosic material.  
     
     
         11 . A method according to  claim 10  wherein said amount is 0.2 to 1.0%, by weight.  
     
     
         12 . A method according to  claim 1  wherein the reaction is conducted at a temperature of 20-120° C., a consistency of 1.5-50%, and a time of 5 minutes to several days.  
     
     
         13 . A method according to  claim 1 , wherein the reaction in an aqueous medium is conducted at a pH of 3.5-12.5.  
     
     
         14 . A method according to  claim 1 , wherein a reducing agent or an acid is added to the reaction medium.  
     
     
         15 . A method according to  claim 1 , wherein the material is a pulp and the resulting pulp is treated with a reducing agent or an acid.  
     
     
         16 . A method according to  claim 1  wherein the reaction and/or bleaching is conducted in the presence or absence of air or oxygen.  
     
     
         17 . A method according to  claim 1 , wherein the lignocellulosic material is a mechanical wood pulp and the reaction is carried out in a single-stage or multi-stage in one or more than one refiner, bleach tower, pulp mixer, a storage vessel, or any other reaction vessel suitable for performing the alkaline hydrogen peroxide bleaching of the pulp.  
     
     
         18 . A method according to  claim 1  wherein the lignocellulosic material is wood chips and at least one of said reacting and bleaching is carried out in a single-stage or multi-stage in one or more than one impregnator.  
     
     
         19 . A method according to  claim 18  wherein the impregnation of the wood chips is conducted at a temperature of 40-90° C., a solid content of 30-60%, by weight, and an impregnation time of 5 minutes to 2 hours.  
     
     
         20 . A light stable lignocellulosic material comprising a lignocellulosic material having a yellowing inhibitor of formula A, B, C or D wherein Y is oxyl (O − ) or hydroxyl (OH) covalently linked thereto via a primary or secondary amino group of the inhibitor or stabilizer:  
       
         
           
           
               
               
           
         
       
       wherein R 1  is hydrogen or an alkyl group (CH 2 ) n H that is unsubstituted or substituted by 1 to 2n+1 number of a hydroxyl, ether, thio, thioether, benzyl, amino, ester, amide, carboxyl, and/or carboxylate [(COO − ) r M r+ ] group, and/or radicals derived from an organic ultraviolet absorber; R 2 , R 3 , R 4  and R 5  are independently alkyl groups (CH 2 ) n H that are unsubstituted or substituted by 1 to 2n+1 number of a hydroxyl, ether, thio, thioether, benzyl, amino, ester, amide, carboxyl, and/or carboxylate [(COO − ) r M r+ ] group, and/or radicals derived from an organic ultraviolet absorber; X is an inorganic or organic anion, n is 1 to 14, preferably 1 to 6, and more preferably 1 to 4, k is 1 to 3, p is 1 or 2, M is an ammonium or metal ion and r is 1, 2 or 3, and the total charge of 2m is equal to kp.  
     
     
         21 . A material according to  claim 20  wherein the lignocellulosic material is a mechanical wood pulp.  
     
     
         22 . A paper sheet containing a material according to  claim 20 .  
     
     
         23 . A paper sheet according to  claim 22  containing said pulp in conjunction with a chemical pulp.