Modification of xylan

Abstract

The invention provides a method of modifying soluble xylan which contains glucuronic acid and/or arabinose side chains so that it can be adsorbed onto other substrates. The method includes the steps of enzymatically modifying the xylan by selectively removing glucuronic acid and/or arabinose side chains from the xylan with α-D-glucuronidase and/or α-L-arabinofuranosidase, and allowing the modified xylan to adsorb onto the substrate. The substrate may be a cellulosic substrate like pulp or paper or a non-cellulosic substrate. The enzymes are able to remove a sufficient number of the xylan side chains so as to decrease water solubility of the xylan, induce xylan precipitation and allow adsorption of the xylan onto other substrates. A pulping process which incorporates modification of xylan and adsorption onto cellulosic material is also provided, as are products which contain the modified xylan.

1 . A method of adsorbing xylan onto a substrate, the method comprising the steps of:
 enzymatically modifying xylan which contains glucuronic acid and/or arabinose side chains so that it has reduced solubility in water compared to naturally occurring xylan, by selectively removing glucuronic acid and/or arabinose side chains with one or both of α-D-glucuronidase and α-L-arabinofuranosidase; and   allowing the modified xylan to adsorb onto the substrate.   
     
     
         2 . The method according to  claim 1 , wherein the xylan is modified in the presence of the substrate. 
     
     
         3 . The method according to  claim 1 , wherein the xylan is modified in the absence of the substrate and is brought into contact with the substrate after it has been modified. 
     
     
         4 . The method according to  claim 1 , wherein the xylan is modified by selectively removing glucuronic acid side chains with α-D-glucuronidase. 
     
     
         5 . The method according to  claim 1 , wherein the xylan is modified by selectively removing arabinose side chains with α-L-arabinofuranosidase. 
     
     
         6 . The method according to  claim 1 , wherein the xylan is modified by selectively removing both glucuronic acid and arabinose side chains with α-D-glucuronidase and α-L-arabinofuranosidase. 
     
     
         7 . The method according to  claim 1 , wherein the xylan is modified by also selectively removing acetyl groups with acetyl xylan esterase. 
     
     
         8 . The method according to  claim 1 , wherein the xylan is modified without the main chain being degraded. 
     
     
         9 . The method according to  claim 1 , which is carried out in the substantial absence of other hydrolytic enzymes. 
     
     
         10 . The method according to  claim 1 , which is carried out in the absence of xylanase. 
     
     
         11 . (canceled) 
     
     
         12 . (canceled) 
     
     
         13 . (canceled) 
     
     
         14 . The method according to  claim 1 , wherein the substrate is a cellulosic substrate. 
     
     
         15 . The method according to  claim 14 , wherein the cellulosic substrate is pulp. 
     
     
         16 . The method according to  claim 1 , wherein the substrate is a non-cellulosic substrate. 
     
     
         17 . The method according to  claim 14 , wherein the modified xylan forms a coating on the substrate. 
     
     
         18 - 35 . (canceled) 
     
     
         36 . A pulping process which includes a xylan adsorption step, the xylan adsorption step comprising the steps of:
 adding xylan which contains glucuronic acid and/or arabinose side chains to a pulp composition;   enzymatically modifying the xylan so that it has reduced solubility in water compared to naturally occurring xylan by selectively removing the glucuronic acid and/or arabinose side chains with one or both of α-D-glucuronidase and α-L-arabinofuranosidase; and   allowing the modified xylan to adsorb onto the pulp in the pulp composition.   
     
     
         37 . The process according to  claim 36 , wherein the xylan adsorption step is performed at a stage in the pulping process selected from between the filtering and bleaching steps, during washing post bleaching, during the drying stage and during the paper fining stage. 
     
     
         38 . The process according to  claim 36 , wherein the xylan is modified by removing glucuronic acid side chains with α-D-glucuronidase. 
     
     
         39 . The process according to  claim 36 , wherein the xylan is modified by removing arabinose side chains with α-L-arabinofuranosidase. 
     
     
         40 . The process according to  claim 36 , wherein the xylan is modified by removing both glucuronic acid and arabinose side chains with α-D-glucuronidase and α-L-arabinofuranosidase. 
     
     
         41 . The process according to  claim 36 , wherein the pulp fibres in the pulp composition have increased binding properties compared to pulp fibres to which xylan has not been adsorbed.