Method of Producing Paper and Cardboard

Abstract

A method of producing paper or cardboard using a bleached cellulosic pulp, which contains hemicelluloses. According to invention a significant portion, at least 5 wt-%, preferably about 8 to 30 wt-%, of the hemicelluloses are removed from the pulp. The hemicelluloses taken from one bleached pulp can then be transferred to another resulting in two pulps with varying properties, one pulp with properties related to low hemicelluloses content in the fiber wall and the other with properties related to high hemicelluloses content on the fiber surface.

1 - 30 . (canceled) 
   
   
       31 . A method of producing paper or cardboard using a bleached cellulosic pulp, which contains hemicelluloses, wherein a significant portion of the hemicelluloses is removed before the pulp is used for making paper or cardboard, and wherein the hemicelluloses recovered are contacted with chemical, chemimechanical or mechanical pulps used for production of paper and paper board products under conditions conducive to adsorption of them onto the cellulosic or lignocellulosic fibers; or the hemicelluloses recovered are used as a raw material for the manufacture of chemicals. 
   
   
       32 . The method according to  claim 31 , wherein at least 5 wt-%, preferably less than 50 wt-%, in particular about 8 to 30 wt-%, of the hemicelluloses are removed from the pulp. 
   
   
       33 . The method according to  claim 31 , wherein the bleached cellulosic pulp comprises a pulp prepared by alkaline pulping of a raw-material predominantly composed of deciduous tree. 
   
   
       34 . The method according to  claim 31 , wherein the bleached cellulosic pulp comprises a pulp prepared by kraft pulping of wood of the  Betula  species. 
   
   
       35 . The method according to  claim 31 , wherein the hemicelluloses are removed by extraction using an aqueous solution or dispersion of an alkaline substance or an enzyme or a mixture thereof. 
   
   
       36 . The method according to  claim 35 , wherein the extraction is carried out at a consistency of about 0.1 to 25%, preferably about 0.5 to 20%, in particular about 1 to 15%. 
   
   
       37 . The method according to  claim 35 , comprising using an aqueous solution containing an alkaline substance selected from the group of alkali metal and earth alkaline metal hydroxides and carbonates or mixtures thereof. 
   
   
       38 . The method according to  claim 35 , wherein the aqueous solution of an alkaline substance comprises white liquor or green liquor. 
   
   
       39 . The method according to  claim 35 , wherein the aqueous solution contains 0.01 to 5 M of the alkaline substance. 
   
   
       40 . The method according to  claim 35 , wherein the extraction with an aqueous solution or dispersion of an alkaline substance or a mixture of alkaline substances is carried out at ambient temperature and pressure for 1 min to 24 hours, preferably about 5 min to 12 hours, in particular about 10 min to 6 hours. 
   
   
       41 . The method according to  claim 35 , wherein the extraction with an aqueous solution or dispersion of an alkaline substance or a mixture of alkaline substances is carried out at an elevated temperature of 20-150° C. for 1 min to 24 hours, preferably about 5 min to 4 hours. 
   
   
       42 . The method according to  claim 35 , wherein the aqueous solution contains at least one hydrolytic enzyme selected from the group of hemicellulases and pectinases. 
   
   
       43 . The method according to  claim 42 , wherein the hydrolytic enzyme comprises a xylanase. 
   
   
       44 . The method according to  claim 31 , wherein the hemicelluloses are selectively removed from the pulp essentially without degrading them. 
   
   
       45 . The method according to  claim 31 , wherein the hemicelloses are recovered in the form of an aqueous dispersion or solution. 
   
   
       46 . The method according to  claim 31 , wherein the hemicelluloses are recovered in the form of an aqueous dispersion which is fed to the headbox of a paper or cardboard machine where they are contacted with the fibres in the furnish. 
   
   
       47 . The method according to  claim 31 , wherein the hemicelluloses are adsorbed onto the fibers at a consistency of about 0.05 to 20%, preferably about 0.1 to 20%, in particular about 0.5 to 10%. 
   
   
       48 . The method according to  claim 47 , wherein the adsorption of the hemicelluloses onto the fibers is carried out at alkaline conditions, preferably at a pH of about 7 to 13, in particular at a pH of 7.5 to 10. 
   
   
       49 . The method according to  claim 31 , wherein the concentration of hemicelluloses in the aqueous dispersion or solution used for adsorption of hemicelluloses onto the fibres is about 0.1 to 50 g/l, preferably about 0.5 to 30 g/l, in particular about 1 to 20 g/l, more particularly about 1.5 to 15 g/l. 
   
   
       50 . The method according to  claim 31 , wherein the recovered hemicelluloses comprise mainly xylan. 
   
   
       51 . The method according to  claim 31 , wherein the hemicelluloses, in particular xylan, are adsorbed onto cellulosic or lignocellulosic fibres used for paper or cardboard in order to improve mechanical strength properties, including tensile strength, bonding and elasticity. 
   
   
       52 . The method according to  claim 51 , wherein the hemicelluloses taken from one bleached pulp are transferred to another similar or identical pulp resulting in two pulps with varying properties, one pulp with properties related to low hemicelluloses content in the fiber wall and the other with properties related to high hemicelluloses content on the fiber surface. 
   
   
       53 . The method according to  claim 31 , wherein the total yield of the bleached cellulosic pulp is lowered by a maximum of 15%, preferably by a maximum of 10%, preferably about 1 to 8% by weight, by the removal of the hemicelluloses. 
   
   
       54 . The method according to  claim 31 , wherein the bleached pulp is, subsequent the hemicellulose removal step, used as a raw-material for the production of various paper and cardboard products. 
   
   
       55 . The method according to  claim 54 , wherein the bleached pulp is used for producing a paper or cardboard product exhibiting one or several improved properties from the group of brightness, resistance against yellowing, drainability and water retention. 
   
   
       56 . The method according to  claim 54 , wherein the bleached pulp is used for producing fine papers. 
   
   
       57 . The method according to  claim 31 , wherein xylan removed from bleached birch pulp is used as a raw-material for producing xylitol or furfural.