Sulfonated pulp fibers, derivative pulp, sulfonated fine cellulose fibers, method for producing sulfonated fine cellulose fibers, and method for producing sulfonated pulp fibers

Abstract

[Object] An object is to provide a sulfonated fine cellulose fiber having excellent transparency a sulfonated pulp fiber suitable for the sulfonated fine cellulose fiber, a method for producing these fibers, and a derivative pulp containing the sulfonated pulp fiber. [Means for achieving the object] The sulfonated pulp fiber of the present invention is a pulp fiber comprising a plurality of cellulose fibers, wherein a part of hydroxyl groups of the cellulose fibers of the pulp fiber is substituted with sulfo groups, an introduction amount of sulfur attributable to the sulfo groups is adjusted to be higher than 0.42 mmol/g while maintaining a fiber shape, and a water retention value of the pulp fiber is adjusted to 150% or more. Since the sulfonated pulp fiber has a predetermined water retaining property or more while maintaining the fiber shape, the degree of flexibility in handling can be improved.

1 . A sulfonated pulp fiber, which is a pulp fiber, comprising:
 a plurality of cellulose fibers,   a part of hydroxyl groups of the cellulose fibers of the pulp fiber being substituted with sulfo groups,   an introduction amount of sulfur attributable to the sulfo groups being adjusted to be higher than 0.42 mmol/g while maintaining a fiber shape, and   a water retention value of the pulp fiber being adjusted to 150% or more.   
     
     
         2 . The sulfonated pulp fiber according to  claim 1 , wherein
 the water retention value of the pulp fiber is adjusted to 200% or more.   
     
     
         3 . The sulfonated pulp fiber according to  claim 1 , wherein
 the water retention value of the pulp fiber is adjusted to 900% or more.   
     
     
         4 . The sulfonated pulp fiber according to  claim 1 , wherein
 an average fiber length of the pulp fiber is adjusted to 50% or more relative to an average fiber length of the pulp fiber before substitution with sulfo groups.   
     
     
         5 . The sulfonated pulp fiber according to  claim 1 , wherein
 the pulp fiber after washing and drying has a whiteness of 30% or more.   
     
     
         6 . The sulfonated pulp fiber according to  claim 1 , wherein
 the hydroxyl group at C6 position of a glucose unit constituting the cellulose fibers is substituted with the sulfo group.   
     
     
         7 . A sulfonated pulp fiber produced, which is produced by a method, comprising:
 bringing a sulfonating agent having sulfo groups and urea and/or a derivative thereof into contact with a pulp fiber constituting pulp, and   introducing sulfo groups into a part of hydroxyl groups of the cellulose fibers constituting the pulp fiber after the contact,   an introduction amount of sulfur attributable to the sulfo groups being adjusted to be higher than 0.42 mmol/g, and a water retention value of the pulp fiber is 150% or more while maintaining a fiber shape.   
     
     
         8 . A derivative pulp, which is a pulp comprising
 a plurality of fibers, the plurality of fibers comprising the pulp fiber according to  claim 1 .   
     
     
         9 - 15 . (canceled) 
     
     
         16 . A method for producing the sulfonated pulp fiber according to  claim 1  from pulp, comprising
 a chemical treatment step of chemically treating the pulp,
 the chemical treatment step comprising 
 a contact step of bringing a reaction solution containing a sulfonating agent having sulfo groups and urea and/or a derivative thereof into contact with a pulp fiber constituting the pulp, and 
 a reaction step of introducing the sulfo groups into a part of hydroxyl groups of cellulose fibers constituting the pulp fiber obtained after the contact step, 
 wherein the reaction step is a step of heating the pulp fiber in contact with the reaction solution after the contact step, thereby allowing a reaction to proceed, and the reaction temperature is adjusted to 100° C. to 200° C., and the reaction time is adjusted to 1 minute or more. 
 
 
     
     
         17 . The method for producing the sulfonated pulp fiber according to  claim 16 , wherein
 the contact step is a step of bringing a reaction solution in which the sulfonating agent and the urea and/or a derivative thereof are mixed into contact with the pulp fiber constituting the pulp, and   the reaction solution contains the sulfonating agent and the urea and/or a derivative thereof at a concentration ratio (g/L) of 4:1 to 1:2.5.   
     
     
         18 . The method for producing the sulfonated pulp fiber according to  claim 16 , wherein
 the method comprises, between the contact step and the reaction step,   the drying step of drying pulp obtained after the contact step, and   the drying step performs drying so that the moisture content of the pulp fiber constituting the pulp after the contact step is in an equilibrium state.   
     
     
         19 . The method for producing the sulfonated pulp fiber according to  claim 16 , wherein
 the method comprises, after the reaction step,   a washing step for washing the pulp obtained after the reaction step.   
     
     
         20 . The method for producing the sulfonated pulp fiber according to  claim 16 , wherein
 the sulfonating agent is sulfamic acid.   
     
     
         21 . A method for producing a sulfonated fine cellulose fiber from pulp,
 the method sequentially performing a chemical treatment step of chemically treating the pulp and a fibrillation step of the pulp obtained after the chemical treatment step,   the pulp obtained after the chemical treatment step containing the sulfonated pulp fiber produced by the production method according to  claim 16 , and   in the fibrillation step, the pulp containing the sulfonated pulp fiber being fibrillated in a state of being dispersed in a water-soluble solvent so that the solid concentration is 0.1% by mass to 20% by mass.   
     
     
         22 . A method for producing a sulfonated fine cellulose fiber, which is a method for subjecting pulp containing a plurality of pulp fibers to a fibrillation step, thereby producing a fine cellulose fiber,
 the plurality of pulp fibers containing the sulfonated pulp fiber produced by the production method according to  claim 16 , and in the fibrillation step, the pulp containing the sulfonated pulp fiber being fibrillated in a state of being dispersed in a water-soluble solvent so that the solid concentration is 0.1% by mass to 20% by mass.