Use of modified lignin as a wet end strength additive

Abstract

A method of increasing paper strength is provided. The method includes adding a lignin-based compound to a pulp slurry: and adding a cationic polymer to the pulp slurry. When added to a pulp slurry. the combination of a lignin-based compound and a cationic polymer produce a comprehensive paper strength increase.

1 . A method of increasing paper strength, comprising:
 adding a lignin-based compound to a pulp slurry; and   adding a cationic polymer to the pulp slurry.   
     
     
         2 . The method of  claim 1 , wherein the lignin-based compound is soluble in water at a pH of about 4 to about 14 at a concentration of about 1 wt % to about 20 wt % of the lignin-based compound at about 25° C. 
     
     
         3 . The method of  claim 1 , wherein the lignin-based compound has a weight average molecular weight of less than about 100,000 g/mol. 
     
     
         4 . The method of  claim 1 , wherein the lignin-based compound has a negative zeta potential. 
     
     
         5 . The method of  claim 1 , wherein the lignin-based compound is free of pulp. 
     
     
         6 . The method of  claim 1 , wherein the cationic polymer comprises monomers selected from the group consisting of: acrylamide, methacrylamide, diallyldimethylammonium chloride (DADMAC), N-vinylamine, 2-dimethylaminoethyl acrylate (DMAEA), N,N,N-trimethylethanaminium chloride, diallylamine, poly (amidoamine), polyethylenimine, and any combination thereof. 
     
     
         7 . The method of  claim 1 , wherein the cationic polymer is crosslinked epichlorohydrin-dimethylamine, poly (amidoamine), or polyethylenimine. 
     
     
         8 . The method of  claim 1 , wherein the cationic polymer has a weight average molecular weight of about 50,000 Da to about 2,000,000 Da. 
     
     
         9 . The method of  claim 1 , wherein the cationic polymer has a charge density of about 0.1 meq/g to about 15 meq/g. 
     
     
         10 . The method of  claim 1 , wherein the lignin-based compound and the cationic polymer are added to the pulp slurry in a wet end of a papermaking process. 
     
     
         11 . The method of  claim 1 , wherein the lignin-based compound and the cationic polymer are added to the pulp slurry in a whitewater system, pulp stock storage chest, blend chest, machine chest, headbox, saveall chest, or any combination thereof in the papermaking process. 
     
     
         12 . The method of  claim 1 , wherein the lignin-based compound is added to the pulp slurry in an amount ranging from about 10 1b/ton to about 100 lb/ton. 
     
     
         13 . The method of  claim 1 , wherein the cationic polymer is added to the pulp slurry in an amount ranging from about 1 lb/ton to about 30 lb/ton. 
     
     
         14 . The method of  claim 1 , wherein the lignin-based compound is added to the pulp slurry before the cationic polymer is added. 
     
     
         15 . The method of  claim 1 , wherein the lignin-based compound is added to the pulp slurry after the cationic polymer is added. 
     
     
         16 . The method of  claim 1 , wherein the lignin-based compound and the cationic polymer are added to the pulp slurry at different locations in the wet end. 
     
     
         17 . A composition, comprising:
 a lignin-based compound; and   a cationic polymer.   
     
     
         18 . The composition of  claim 17 , wherein the lignin-based compound has a weight average molecular weight of less than about 100,000 g/mol and a negative zeta potential. 
     
     
         19 . (canceled) 
     
     
         20 . The composition of  claim 17 , wherein the cationic polymer is crosslinked epichlorohydrin-dimethylamine, poly (amidoamine), or polyethylenimine. 
     
     
         21 . The composition of  claim 17 , wherein the composition is free of pulp. 
     
     
         22 . (canceled)