Modified fiber, methods, and systems

Abstract

Methods of forming crosslinked cellulose include mixing a crosslinking agent with an aqueous mixture of cellulose fibers containing little to no excess water (e.g., solids content of 25-55%), drying the resulting mixture to 85-100% solids, then curing the dried mixture to crosslink the cellulose fibers. Systems include a mixing unit to form, from an aqueous mixture of unbonded cellulose fibers having a solids content of about 25-55% and a crosslinking agent, a substantially homogenous mixture of non-crosslinked, unbonded cellulose fibers and crosslinking agent; a drying unit to dry the substantially homogenous mixture to a consistency of 85-100%; and a curing unit and to cure the crosslinking agent to form dried and cured crosslinked cellulose fibers. Intrafiber crosslinked cellulose pulp fibers produced by such methods and/or systems have a chemical on pulp level of about 2-14% and an AFAQ capacity of at least 12.0 g/g.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 
     
         1 . A system, comprising:
 a mixing unit being configured to form, from an aqueous mixture of unbonded cellulose fibers having a solids content of about 25-55% and a crosslinking agent, a substantially homogenous mixture of non-crosslinked, unbonded cellulose fibers and crosslinking agent, at ambient conditions;   a drying unit downstream of the mixing unit and configured to dry the substantially homogenous mixture to a consistency of 85-100% without curing the crosslinking agent; and   a curing unit downstream of the drying unit and configured to cure the crosslinking agent, thereby forming dried and cured crosslinked cellulose fibers.   
     
     
         2 . The system of  claim 1 , wherein the mixing unit includes a first zone configured to form the aqueous mixture of unbonded cellulose fibers, and a second zone configured to receive both the aqueous mixture and the crosslinking agent and form the substantially homogenous mixture. 
     
     
         3 . The system of  claim 2 , wherein the first and second zones are two subsequent regions of an extruder. 
     
     
         4 . The system of  claim 1 , wherein the mixing unit includes a high consistency mixer. 
     
     
         5 . A method of forming a crosslinked cellulose product, comprising:
 mixing a crosslinking agent with an aqueous mixture of unbonded cellulose fibers having a solids content and containing little to no excess water, the crosslinking agent being added in an amount suitable to achieve a desired level of crosslinking of the unbonded cellulose fibers based on the solids content;   drying the resulting mixture to 85-100% solids; and   curing the dried mixture under conditions effective to crosslink the unbonded cellulose fibers,   wherein the amount of crosslinking agent added corresponds to a chemical on pulp range of about 2-14%, and wherein the crosslinking agent comprises one or more of a polyacrylic acid and a polycarboxylic acid.   
     
     
         6 . The method of  claim 5 , wherein the aqueous mixture has a solids content of about 25-55%. 
     
     
         7 . The method of  claim 6 , wherein the aqueous mixture has a solids content of about 35-55%. 
     
     
         8 . The method of  claim 6 , wherein the aqueous mixture has a solids content of about 40-50%. 
     
     
         9 . The method of  claim 5 , wherein the crosslinking agent is mixed with the aqueous mixture of unbonded cellulose fibers at ambient conditions. 
     
     
         10 . The method of  claim 5 , wherein the crosslinking agent is added in an amount no more than that required to achieve a desired level of crosslinking of the unbonded cellulose fibers. 
     
     
         11 . The method of  claim 5 , further comprising, prior to mixing, processing the aqueous mixture to reduce fiber clumps. 
     
     
         12 . The method of  claim 5 , wherein mixing is performed in one or more of an extruder, a refiner, and a high-consistency mixer. 
     
     
         13 . The method of  claim 5 , wherein mixing includes adding the cros slinking agent at a solids content of 10-50% to the aqueous mixture. 
     
     
         14 . The method of  claim 5 , further comprising, prior to mixing, forming the aqueous mixture. 
     
     
         15 . The method of  claim 14 , wherein forming the aqueous mixture includes mixing one or more of wet lap, previously-dried cellulosic fibers, and never-dried cellulosic fibers, with water. 
     
     
         16 . The method of  claim 15 , wherein forming the aqueous mixture is performed in one or more of an extruder, a hydrapulper, and a high-consistency mixer. 
     
     
         17 . The method of  claim 15 , wherein forming the aqueous mixture includes adding the cellulose fibers in bale or roll form to a hydrapulper in the presence of water. 
     
     
         18 . The method of  claim 14 , wherein forming the aqueous mixture includes mixing cellulose fibers with water at a solids content of about 25-55%. 
     
     
         19 . The method of  claim 14 , wherein forming the aqueous mixture includes mixing cellulose fibers with water at a solids content of lower than about 25%, followed by at least partially dewatering the mixture in order to achieve a solids content of about 25-55%. 
     
     
         20 . A method of forming a crosslinked cellulose product, comprising:
 forming an aqueous mixture of unbonded cellulose fibers having a solids content of about 40-50%;   mixing a polyacrylic acid crosslinking agent with the aqueous mixture in an amount to achieve a chemical on pulp level of about 2-14%, wherein said crosslinking agent is mixed at ambient conditions;   drying the resulting mixture to 85-100% solids; and   curing the dried mixture under conditions effective to crosslink the unbonded cellulose fibers.