Use of ozone for increasing the wet strength of paper and nonwoven

Abstract

A treatment sequence includes ozonation under acidic conditions followed by an acidic wash for enhancing the wet strength of a cellulosic fibrous material. Preferably the ozone treatment and the acidic wash are followed by a second ozonation step under acidic conditions. The fibrous cellulosic material obtained by this treatment sequence has a breaking length of at least 100 m. The wet strength of the cellulosic fibrous material is increased without the use of additives, such as wet strength agents. This use of ozone is very simple and efficient, and leads to highly pure products. The use of ozone as the only treatment chemical in particular avoids the introduction of so-called “non-process elements” (NPE) into the treatment system, for instance metal oxides such as MgO, which are frequently used in the oxidative treatment of pulps.

1 . Method of enhancing the wet strength of a fibrous cellulosic material, which comprises the following treatment sequence: 
 subjecting the fibrous cellulosic material to an ozone treatment under acidic conditions to obtain an ozonated material; and    subjecting the ozonated material to an acidic wash of the ozonated material to obtain a fibrous cellulosic product having enhanced wet strength.    
     
     
         2 . The method according to  claim 1 , wherein the ozone treatment is preceded by a further acidic wash.  
     
     
         3 . The method according to  claim 1 , wherein the acidic wash is followed by a second ozonation step under acidic conditions.  
     
     
         4 . The method according to  claim 3 , wherein the second ozonation is followed by a further acidic wash.  
     
     
         5 . The method according to  claim 3 , wherein the first ozone treatment is preceded by a further acidic wash.  
     
     
         6 . The method according to  claim 3 , further comprising maintaining acidic conditions after the last ozonation step of the treatment sequence.  
     
     
         7 . The method according to  claim 1 , wherein the treatment sequence comprises at no point in time an alkaline wash.  
     
     
         8 . The method according to  claim 1 , wherein the entire treatment sequence is performed under acidic conditions.  
     
     
         9 . The method according to  claim 1 , wherein the cellulosic material is selected from sulfite pulps, bisulfite pulps, Kraft pulps, cotton linters, or fibers from Esparto Grass, bagasse, hemp, flax and agricultural crops.  
     
     
         10 . The method according to  claim 1 , wherein the cellulosic fibrous material to be treated has an initial kappa number of less than 50.  
     
     
         11 . The method according to  claim 10 , wherein the initial kappa number is more than 13.  
     
     
         12 . The method according to  claim 1 , wherein the ozone-treated cellulosic product has a final kappa number of less than 15.  
     
     
         13 . The method according to  claim 1 , wherein the ozone treatment leads to a Kappa reduction of at least 10.  
     
     
         14 . The method according to  claim 1 , wherein ozone is used as the only oxidant in the treatment of a cellulosic pulp material obtained by a pulping process.  
     
     
         15 . The method according to  claim 1 , wherein prior to the ozone treatment no bleaching or other oxidizing step is employed.  
     
     
         16 . The method according to  claim 1 , wherein the initial pH of the ozone treatment is 5 or lower.  
     
     
         17 . The method according to  claim 1 , wherein an inorganic acid, carboxylic acid having 1 to 4 carbon atoms or dicarboxylic acid having 2 to 4 carbon atoms is used for acidifying.  
     
     
         18 . The method according to  claim 17 , wherein the inorganic acid is sulfuric acid.  
     
     
         19 . The method according to  claim 1 , wherein the consistency of the cellulosic fibrous material to be ozonated is at least 30% per weight.  
     
     
         20 . The method according to  claim 1 , wherein the ozone is wetted before contact with the cellulosic fibrous material.  
     
     
         21 . The method according to  claim 1 , wherein the cellulosic fibrous material is fluffed immediately before subjecting to the ozone treatment.  
     
     
         22 . The method according to  claim 1 , wherein the ozone-treated cellulosic product has a final kappa number of less than 10.  
     
     
         23 . The method according to  claim 1 , wherein the ozone treatment leads to a Kappa reduction of at least 15.  
     
     
         24 . A fibrous cellulosic material obtained by the method according to  claim 1 .  
     
     
         25 . A fibrous cellulosic material obtained by the method according to  claim 2 .  
     
     
         26 . A fibrous cellulosic material obtained by the method according to  claim 3 .  
     
     
         27 . The fibrous cellulosic material according to  claim 24 , containing no effective amount of wet strength-enhancing additives.  
     
     
         28 . The fibrous cellulosic material according to  claim 24  having a wet breaking length of at least 100 m.  
     
     
         29 . Paper or nonwoven comprising the fibrous cellulosic material of  claim 24 .  
     
     
         30 . Paper according to  claim 29 , wherein the paper is a tissue paper.