Cellulose ethers and method of preparing the same

Abstract

The present inventors have discovered that the solution rheology of cellulose ethers prepared from cellulose pulp is altered by mercerizing and recovering cellulose pulp before preparing the cellulose ethers. For example, the solution viscosity of carboxymethyl cellulose (CMC) produced from mercerized and recovered cellulose pulp is significanitly greater than that produced from non-mercerized cellulose pulp. The present invention provides a method of preparing, cellulose ethers comprising the steps of (a) obtaining mercerized and recovered cellulose pulp, and (b) converting the mercerized and recovered cellulose pulp into the cellulose ethers. According to one embodiment, the cellulose pulp is southern softwood kraft and the mercerized cellulose pulp has a TAPPI 230 om-89 viscosity of at most 12 cP. This method, however, may be applied to all cellulose pulps, regardless of their viscosities, including those which, when mercerized, have a viscosity greater than 12 cP. The mercerized cellulose pulp is typically substantially free of cellulose III. Mercerized cellulose pulp prepared by this method has a greater percentage of crystalline cellulose II and a smaller crystalline area than that of non-mercerized cellulose pulp. The present invention also provides a method of preparing a cellulose floc comprising the steps of (a) obtaining mercerized and recovered cellulose pulp, and (b) treating the mercerized pulp to form the cellulose floc. Alternatively, the method comprises mercerizing and recovering a cellulose floc. Cellulose floc prepared by this method have a greater bulk density than cellulose floc prepared from similar non-mercerized cellulose pulp. Furthermore, the bulk density gain is greater than that expected from the coarseness (weight per unit of fiber length) gain from preparing a cellulose floc.

1 . A method of preparing cellulose ethers comprising the steps of: 
 (a) obtaining mercerized and recovered cellulose pulp; and    (b) converting the mercerized and recovered cellulose pulp into the cellulose ethers,    wherein the mercerized cellulose pulp in step (a) was mercerized with a cellulose II mercerizing agent, the cellulose pulp is southern softwood kraft, the mercerized and recovered cellulose pulp has a TAPPI 230 om-89 viscosity of at most 12 cP, and when the cellulose ether prepared is hydroxyethyl cellulose, the mercerized and recovered cellulose pulp has at least one of the following properties: 
 (i) a TAPPI 230 om-89 viscosity less than 10.4 cP or greater than 11.2 cP,  
 (ii) a solubility in 10% sodium hydroxide as determined by ASTM D 1696-95 of greater than 2.3%,  
 (iii) a solubility in 18% sodium hydroxide as determined by ASTM D 1696-95 of greater than 1.3%,  
 (iv) not been prehydrolyzed, or  
 (v) not been bleached with elemental chlorine.  
   
     
     
         2 . The method of  claim 1 , wherein the cellulose ether prepared is hydroxyethyl cellulose and the mercerized and recovered cellulose pulp has a TAPPI 230 om-89 viscosity less than 9.25 cP.  
     
     
         3 . The method of  claim 2 , wherein the cellulose ether prepared is hydroxyethyl cellulose and the mercerized and recovered cellulose pulp has a TAPPI 230 om-89 viscosity less than 8 cP.  
     
     
         4 . The method of  claim 1 , wherein the mercerized and recovered cellulose pulp has a TAPPI 230 om-89 viscosity less than 9.25 cP.  
     
     
         5 . The method of  claim 4 , wherein the mercerized and recovered cellulose pulp has a TAPPI 230 om-89 viscosity less than 8 cP.  
     
     
         6 . The method of  claim 1 , wherein the mercerized and recovered cellulose pulp has a solubility in 10% sodium hydroxide as determined by ASTM D 1696-95 of greater than 3.0%.  
     
     
         7 . The method of  claim 6 , wherein the mercerized and recovered cellulose pulp has a solubility in 10% sodium hydroxide as determined by ASTM D 1696-95 of greater than 5.0%.  
     
     
         8 . The method of  claim 1 , wherein the mercerized and recovered cellulose pulp has a solubility in 18% sodium hydroxide as determined by ASTM D 1696-95 of greater than 2.0%.  
     
     
         9 . The method of  claim 8 , wherein the mercerized and recovered cellulose pulp has a solubility in 18% sodium hydroxide as determined by ASTM D 1696-95 of greater than 4.0%.  
     
     
         10 . The method of  claim 1 , wherein the cellulose pulp is not regenerated cellulose pulp.  
     
     
         11 . The method of  claim 1 , wherein the mercerized and recovered cellulose pulp is a cellulose floc.  
     
     
         12 . The method of  claim 1 , wherein step (a) comprises: 
 (i) mercerizing cellulose pulp; and    (ii) washing, neutralizing, or neutralizing and washing the mercerized cellulose pulp.    
     
     
         13 . The method of  claim 12 , wherein the cellulose pulp in step (a)(i) is mercerized with an aqueous solution containing from about 9 to about 24% by weight of sodium hydroxide, based upon 100% weight of total aqueous solution.  
     
     
         14 . The method of  claim 13 , wherein the cellulose pulp in step (a)(i) is mercerized with an aqueous solution containing from about 13 to about 24% by weight of sodium hydroxide, based upon 100% weight of total aqueous solution.  
     
     
         15 . The method of  claim 1 , wherein step (a) comprises: 
 (i) mercerizing cellulose pulp; and    (ii) washing the mercerized cellulose pulp.    
     
     
         16 . The method of  claim 12 , wherein the mercerized cellulose pulp in step (a)(ii) is washed with an aqueous solution.  
     
     
         17 - 45 . (canceled)  
     
     
         46 . A method of preparing cellulose floc comprising the steps of: 
 (a) obtaining mercerized and recovered cellulose pulp, and    (b) treating the mercerized pulp to form the cellulose floc,    wherein the cellulose pulp is southern softwood kraft and the mercerized and recovered cellulose pulp is substantially free of cellulose III and has a TAPPI 230om-89 viscosity of at most 12 cP.    
     
     
         47 - 61 . (canceled)  
     
     
         62 . A method of preparing mercerized cellulose floc comprising the steps of: 
 (a) mercerizing the cellulose floc; and    (b) recovering the mercerized cellulose floc,    wherein the mercerized and recovered cellulose floc is substantially free of cellulose III, the cellulose floc is derived from southern softwood kraft, and the mercerized and recovered cellulose floc has a TAPPI 230 om-89 viscosity of at most 12 cP.    
     
     
         63 - 73 . (canceled)  
     
     
         74 . A cellulose floc prepared by the method of  claim 62 .  
     
     
         75 . A method of preparing cellulose ethers comprising the steps of: 
 (a) selecting a desired viscosity for the cellulose ethers;    (b) obtaining mercerized and recovered cellulose pulp having the appropriate viscosity for yielding cellulose ethers having the selected viscosity; and    (c) converting the mercerized and recovered cellulose pulp to the cellulose ethers,    wherein the mercerized and recovered cellulose pulp is substantially free of cellulose III, the cellulose pulp is southern softwood kraft, and the mercerized and recovered cellulose pulp has a TAPPI 230 om-89 viscosity of at most 12 cP.    
     
     
         76 - 84 . (canceled)