High brightness non-wood pulp

Abstract

Disclosed are non-wood pulps having a fiber length greater than about 1.70 mm and a brightness of about 80% or greater. The relatively high degree of brightness is achieved without a loss fiber length or pulp yield. The high degree of brightness and relatively long fiber length makes the pulps well suited for the manufacture of wet-laid fibrous products, particularly wet-laid tissue products. The pulps may be prepared from plants of the family Asparagaceae by mechanical pulping and more preferably by a chemi-mechanical pulping using a sodium hydroxide alkaline peroxide solution where the primary pulp is cleaned to reduce debris prior to bleaching. Preferably the cleaned primary pulp has less than about 5% debris prior to bleaching.

We claim: 
     
         1 . A method of manufacturing a non-wood pulp comprising the steps of:
 a. providing a non-wood biomass derived from a plant of the family Asparagaceae;   b. cutting the non-wood biomass to a nominal length;   c. extracting water soluble solids from the cut biomass to produce bagasse;   d. impregnating the bagasse with a first sodium hydroxide alkaline peroxide and maintaining the impregnation for a first reaction time to produce impregnated bagasse;   e. feeding the impregnated bagasse to a refiner comprising a refining disc encased in a housing having an inlet and an outlet;   f. refining the impregnated bagasse under first refining conditions to produce a primary pulp;   g. discharging the primary pulp out of the refining housing through the outlet and adding a second sodium hydroxide alkaline peroxide solution to the discharged primary pulp;   h. cleaning the primary pulp to yield a cleaned primary pulp having less than about 5% debris;   i. delivering the cleaned primary pulp to a bleaching vessel; and   j. adding a third sodium hydroxide alkaline peroxide solution to the cleaned primary pulp in the bleaching vessel to yield a bleached primary pulp having a fiber length greater than about 1.70 mm and a brightness of about 80% or greater.   
     
     
         2 . The method of  claim 1  wherein the first sodium hydroxide alkaline peroxide solution comprises at least about 2% peroxide, at least about 1.5% sodium hydroxide, and at least about 1% stabilizer, based upon the dry weight of the bagasse, the second sodium hydroxide alkaline peroxide solution comprises at least about 3% peroxide, at least about 2% sodium hydroxide, and at least about 2% stabilizer, based upon the dry weight of the primary pulp, and the third sodium hydroxide alkaline peroxide solution comprises at least about 5% peroxide and 4% sodium hydroxide, based upon the dry weight of the cleaned primary pulp. 
     
     
         3 . The method of  claim 1  wherein the biomass is derived from one or more plants of the genus  Hesperaloe.    
     
     
         4 . The method of  claim 3  wherein the one or more plants are selected from  H. funifera, H. parviflora, H. nocturna, H. chiangii, H. tenuifolia, H. engelmannii and H. malacophylla.    
     
     
         5 . The method of  claim 1  further comprising the step of compressing and macerating the bagasse using a plug screw having a compression ratio of at least 2:1. 
     
     
         6 . The method of  claim 1  wherein the refiner housing comprises a superatmospheric casing and the step of refining comprises feeding the impregnated bagasse having a consistency from about 20 to about 60% to the refiner and refining at a pressure of at least about 240 kP. 
     
     
         7 . The method of  claim 1  wherein the primary pulp temperature is at least about 80° C. when the second sodium hydroxide alkaline peroxide solution is added. 
     
     
         8 . The method of  claim 1  further comprising the step of mixing the sodium hydroxide alkaline peroxide solution and the primary pulp after the second sodium hydroxide alkaline peroxide solution is added. 
     
     
         9 . The method of  claim 8  wherein the sodium hydroxide alkaline peroxide solution and the primary pulp are mixed for at least one hour. 
     
     
         10 . The method of  claim 1  further comprising the steps of washing the bleached primary pulp, thickening the bleached primary pulp and adding a fourth sodium hydroxide alkaline peroxide solution to the washed and thickened bleached primary pulp.