Abstract: The disclosure provides a process of modifying a seed based fiber (SBF) to form an enhanced fiber additive (EFA). The process includes an acid treatment step and optionally at least one fiber modification step. Preferred EFA products and uses are described.

Abstract: A process for producing high bulk cellulosic fiber exhibiting a durable elevated curl index includes: (a) concurrently heat treating and convolving cellulosic fiber pulp at elevated temperature and pressure at high consistency under conditions selected so as to preclude substantial fibrillation and attendant paper strength and fiber bonding development; and (b) recovering the pulp wherein the length weighted curl index of the treated fiber is at least about 20% higher than the length weighted curl index of the fiber prior to the heat treatment and convolving thereof. The curl imparted to the fiber persists upon treatment for 30 minutes in a laboratory disintegrator at 3000 rpm at 1% consistency at a temperature of 125° F. Moreover, the curl may be imparted to the fiber in a disk refiner at very short residence times, on the order of several seconds or less. In general, the process is carried out in the presence of saturated steam at a pressure of from about 5 to about 150 psig.

Abstract: Methods of bleaching mechanical pulp under alkaline conditions with hydrogen peroxide. The methods include introducing a source of magnesium ions and hydroxyl ions to a refiner. The wood particulates are refined into a pulp in the presence of the magnesium ions and hydroxyl ions, and optionally perhydroxyl ions to simultaneously refine and bleach the pulp in a refiner.

Abstract: There is a need for a cheaper method of producing bleached TMP and CTMP without impairing the properties of the pulp.

Abstract: A method of controlling micro-organisms during peroxide bleaching of cellulose pulp comprising adding to the pulp an effective micro-organism controlling amount of

Abstract: A process for applying chemicals, such as an alkaline peroxide pretreatment (1) to lignocellulosic material before chemical refining and at the primary refiner (3). The preferred embodiment comprises (i) preconditioning at temperatures below 95° C., especially below 80° C., (ii) limiting the time and/or temperature in the refiner, (iii) reaction quench to maintain temperatures below 80° C., and (iv) subsequent high consistency bleaching (4).

Abstract: Disclosed is a method for pulp bleaching. The method comprises the steps of providing a pulp sample for bleaching, the pulp sample stemming from a pulp producing process, providing a bleaching liquor comprising water and an organic component as solvent components constituting a bleaching medium, dissolved within are at least a bleaching agent, and a basic agent; and subjecting the pulp sample to the bleaching liquor for a predefined amount of time at predefined bleaching conditions. A preferred bleaching agent is hydrogen peroxide. The organic component amounts to at least 5% in weight of the bleaching medium.

Abstract: Chemical cellulose pulp produced by alkaline delignification and having a kappa number of under 24 (e.g. 14 or below) having hexenuronic acid is treated to remove at least 50% of the hexenuronic acid (e.g. 90-97%) such as by treating the pulp at a temperature over 85° C. (e.g. about 90-180° C., preferably about 90-110° C.) at a pH between about 2-5 (e.g. about 2.5-4), which also results in a reduction of kappa number by at least two units (e.g. about 2-9 units, preferably about 3-6 units). The treatment time t, in minutes, is at least 0.5 exp(10517/(T+273)−24), where T is the treatment temperature in degrees C. The chemical cellulose pulp is bleached in at least one bleaching stage; where the bleaching stage is a chlorine dioxide, ozone, or peracid, treatment takes place before bleaching. Under some other circumstances treatment can take place simultaneous with bleaching or after bleaching.

Abstract: The present invention aims firstly to provide a novel technique capable of preparing bleached pulp having high brightness from materials having low bleachability containing high levels of extractives and secondly to provide a technique capable of reducing the amount of bleaching agents used in processes for preparing bleached mechanical pulps.

Abstract: Methods of bleaching mechanical pulp under alkaline conditions with hydrogen peroxide. The methods include introducing a source of magnesium ions and hydroxyl ions to a refiner. The wood particulates are refined into a pulp in the presence of the magnesium ions and hydroxyl ions, and optionally perhydroxyl ions to simultaneously refine and bleach the pulp in a refiner.

Abstract: The present invention discloses methods of bleaching chemical pulp that combine xylanase enzymes with hydrogen peroxide, peracids, or a mixture. The method comprises the steps of carrying out a chemical pulping operation, optionally followed by delignifying the pulp with oxygen, then combining xylanase enzymes with hydrogen peroxide, peracids, or a mixture to bleach the pulp. The method allows the mill to use both xylanase and peracids in a single bleaching tower to decrease the usage of chlorine dioxide and other bleaching chemicals. The pulp bleaching method of the present invention may be performed in a pulp mill as part of a complex pulp bleaching process.

Abstract: A method in bleaching of pulp is described, in which the pulp is subjected to a peroxide bleaching step, whereupon the pulp is washed and the washing liquid from the washing is separated from the pulp in the form of a filtrate. The method is characterised in that the filtrate is treated with an aluminium compound, such as aluminium sulphate or polyaluminium sulphate, for precipitation of interfering substances, such as oxygen-demanding organic material and metals, that the precipitated material is removed from the filtrate, that the aluminium content of the filtrate after precipitation of interfering substances is adjusted to at most 20 ppm, and that the filtrate is then recirculated to the peroxide bleaching step. By the method, a reduced consumption of hydrogen peroxide in the peroxide bleaching step is achieved.

Abstract: A method of making bleached mechanical pulps is disclosed for pulping mills having a primary and a secondary refiner. A first step is to provide cellulosic materials, such as wood chips to refine into the pulp; the wood chips have an initial brightness level. A second step is to provide a bleaching liquor to the refining system of the pulp mill, wherein the liquor comprises an amount of hydrogen peroxide and an amount of alkali having greater than 0% to 100% magnesium hydroxide or soda ash or a combination thereof. A third step is to hold the pulp with the bleaching liquor at a temperature in the range of about 85° to about 160° C. and for about 2 to about 180 minutes. The components of the bleach liquor can be added at the first refiner or interstage between refiners.

Abstract: The present invention relates to a method of pretreating, by acidification and chelation, of pulp to be bleached with peroxide. Especially, the invention relates to intensifying, and at the same time simplifying the pretreatment required by peroxide bleaching. It is characteristic of the invention to introduce pulp into an acid tower (14, 112) where the pressure is 0 to 20 bar, preferably 1 to 10 bar, and the temperature 75 to 130° C. preferably 80 to 110° C., to treat the pulp in acid tower (14, 112) at a pH of 2 to 6, preferably 3 to 4, for 20 to 240 minutes, for decreasing the kappa number by 1-9, preferably 2-6 kappa units, to transfer the pulp from acid tower (14, 112) to a tower (24) of a second treatment stage, to treat the pulp with either a complexing agent at a pH of 4 to 9, preferably 5 to 6, or with an oxidizing chemical such as chlorine dioxide, Caro's acid, peracids or equivalent, and to wash and/or press the pulp.

Abstract: In a method for the production of fiber pulp for subsequent use in the production of a fiber web, especially a paper or cardboard web, the fiber pulp that was produced in a pulp production process is first loaded with an additive by way of a chemical precipitation reaction. The loaded pulp is then dried and available for subsequent utilization or formulated into a suitable form for shipment.

Abstract: The present invention discloses methods of bleaching chemical pulp with xylanase after chemical bleaching. The method comprises the steps of treating chemical pulp with a first xylanase in a first enzyme treatment stage to produce an enzyme treated pulp, exposing the enzyme treated pulp to a chemical bleaching stage to produce a partially bleached pulp, and treating the partially bleached pulp with a second xylanase in a second enzyme treatment stage at a pH of about 3 to about 8. Further, there is disclosed a method of bleaching pulp comprising the steps of exposing chemical pulp to a chlorine dioxide bleaching stage to produce a partially bleached pulp, treating the partially bleached pulp with a xylanase in an enzyme treatment stage at a pH of about 3 to about 8, then carrying out an alkaline extraction of the pulp. The pulp bleaching method of the present invention may be performed in a pulp mill as part of a complex pulp bleaching process.

Abstract: The invention combines the step of adding chemicals such as alkaline peroxide to an intermediate line after refining, with the step of applying chemicals such as alkaline peroxide as a pre-treatment before primary refining and/or applying chemicals such as alkaline peroxide at the primary refiner. This is implemented in the preferred embodiment, by pre-treating feed material, refining the materials into a pulp in a superatmospheric refiner, and adding chemicals in the post refining blow-line.

Abstract: Paper is formed from typically cellulose fibres which have a tendency to become discoloured during processing. Thus, in order to provide good quality white paper, it is necessary to bleach that paper to limit biological activity and remove discolouration. Of concern with respect to this particular invention is also the requirement to add so-called optical brightness agents (OBA). These optical brightness agents essentially fluoresce in daylight in order to give the impression of pure white colour even though the underlying fibres are still yellow white after bleaching. Optical brightness agents are expensive and therefore the present invention provides a composition which reduces the proportion of OBA agent necessary to achieve desired base point increases in paper quality.

Abstract: The invention relates to methods for reducing the amount of halogenated organics produced during a halogen bleaching process for lignocellulosic pulp fibers. According to the disclosed invention, it has been discovered that the use of a chelating agent prior to a non-halogen containing bleaching stage of a pulp bleaching process is effective to increase the brightness of the resulting bleached pulp without the need to increase the amount of halogen compounds required to obtain the same pulp brightness and without adversely affecting the pulp viscosity and yield.

Abstract: A method for brightening chemical pulps with less than 18% lignin utilizing a magnesium compound in a sodium silicate solution to form a higher percentage of high molecular weight silicates. Such high molecular weight silicates preferentially adsorb transition metal impurities, which, if left in solution, would tend to decompose hydrogen peroxide and organic peroxides. Hydrogen peroxide is added to peroxide and peroxide/oxygen stages, while it is generated, along with organic peroxides during an oxygen stage.

Abstract: Various types of paper pulp are bleached in two steps at atmospheric pressure and at a temperature of less than or equal to 100° C. The first step is carried out by bringing the raw pulp into contact with a mixture of peracetic acid and performic acid. The second step is carried out by treating the bleached pulp obtained from the first step, with a solution of sodium hydroxide and hydrogen peroxide. The pulps obtained have a high brightness value and a degree of polymerization close to the raw pulps. The method is ecological and nonpolluting.

Abstract: An environmentally friendly (ECF), yet commercially viable, process produces fully bleached (typically having a brightness of over 89 or 90% ISO) cellulose pulp using a (ZEND) treatment. Typically pulp is produced in an essentially sulphur-free pulping process (such as an soda/AQ process), and is then treated by a D-EO-, D-EP-, or D-EOP-sequence before the (ZEND) treatment. Optional oxygen delignification may also be used, and subsequent elemental-chlorine-free bleaching sequences may also be employed, although normally not necessary since the pulp after the (ZEND) treatment has high brightness and good viscosity (e.g. over 21 cP).

Abstract: In the production of pulp and paper from starch-containing paper, the deinking effect can be improved by including treatment with both a starch-degrading enzyme and a pectate lyase. The process comprises enzyme treatment during or after disintegration of the paper to produce pulp, followed by separation of ink particles.

Abstract: The present invention relates to an environment friendly, safe, and efficient four-step method of bio-bleaching Kraft pulp using bacterial strains of accession no. MTCC 5096, MTCC 5094, MTCC 5095, and MTCC 5098, a microbial consortium comprising a synergistic mixture of ligninolytic bacterial isolates of accession no. MTCC 5094, MTCC 5095, and MTCC 5098, bacterial strains of accession Nos. MTCC 5096, MTCC 5094, MTCC 5095, and MTCC 5098, and a process of preparing an inoculum of the bacterial isolate of accession no. MTCC 5096, further, a process for the preparation of a consortium comprising the ligninolytic bacterial isolates of accession nos. MTCC 5094, MTCC 5095, and MTCC 5098, in addition, a process for the preparation of pulp suspension for the bio-bleaching.

Abstract: A process for the bleaching of lignin present in pulp fibers in an aqueous environment such as a pulp suspension. The invention also relates to a process for producing paper or board from pulp containing bleached lignin. According to the invention carbon dioxide is used for the bleaching of lignin.

Abstract: A method for selectively delignifying lignocellulosic materials and bleaching of pulp and dyes using a combination of an oxidative enzyme and a metal complex. More specifically, the process involves the oxidation of a transition metal redox complex by a phenol oxidizing enzyme such as laccase or peroxidase to mediate the catalytic delignification of chemical pulp and bleaching of textile dye. This process is unique in that only a catalytic amount of metal complex mediator is required on softwood or hardwood kraft pulp, and that recycling or regeneration of the mediator for further pulp delignification is possible. The redox mediator is characterized in that it contains a transition metal ion coordinated with molecules or ions in such a way that the complexes have a formal redox potential between 0.5 and 1.2 volt measured against a normal hydrogen electrode.

Abstract: A method of producing a high quality paper pulp slurry from high silica content lignocellulosic agricultural waste materials is provided. The method includes combining the agricultural waste materials with a chemical composition to form a mixture, sautéing the mixture, and grinding the sautéed mixture to provide the pulp slurry. The method results in greater than 55 percent solids recovery in the pulp slurry relative to the starting lignocellulosic agricultural waste materials, and removes substantially none of the lignin from the agricultural waste materials.

Abstract: A method for bleaching unbleached softwood or hardwood pulps using hydrogen peroxide without added alkali for activation is described. The aqueous hydrogen peroxide solution contains an alkaline earth metal carbonate, preferably magnesium carbonate and can be used at elevated temperatures. Bleached hardwood or softwood mechanical pulps with high brightness, low yellowness (b*) and reduced reversion properties are produced.

Abstract: A process for bleaching high bulk cellulosic fiber and producing a durable elevated curl index includes: (a) concurrently bleaching, heat treating and convolving cellulosic fiber pulp at elevated temperature and pressure at high consistency generally under conditions selected so as to preclude substantial fibrillation and attendant paper strength and fiber bonding development; and (b) recovering the pulp wherein the length weighted curl index of the treated fiber is at least about 20% higher than the length weighted curl index of the fiber prior to the heat treatment and convolving thereof. Preferably, the curl imparted to the fiber persists upon treatment for 30 minutes in a laboratory disintegrator at 3000 rpm at 1% consistency at a temperature of 125° F. Moreover, the curl may be imparted to the fiber in a disk refiner at very short residence times, on the order of several seconds or less.

Abstract: A method of bleaching chemical pulp, comprising two bleaching stages (D0 and, respectively, D1) with chlorine dioxide as dominating bleaching chemical and at least one intermediate alkaline bleaching stage (E). The ingoing pulp is dewatered to a concentration of 25-40% before the first chlorine dioxide stage (D0) and to 10-40% after the second chlorine dioxide stage (D1). Filtrate from the dewatering after the second chlorine dioxide stage (D1) is re-cycled and utilized for controlling the pulp concentration to 8-15% of the dewatered pulp to the first chlorine dioxide stage (D0).

Abstract: (Co)poly-&agr;-hydroxyacrylic-acid-based polymers (P), optionally in lactonized form or in salt form, optionally as Mg-complexes, and which are characterized by a content in carbohydrate units and 2-hydroxy-2-carboxyethylene-1,2 monomer units, are suitable as biologically degradable, alkali-resistant stabilizers for peroxide bleaching agents.

Abstract: A method and device for bleaching chemical paper pulp or dissolving wood pulp, which has been cooked and delignified without employing chlorine-containing chemicals, comprising a bleaching sequence which comprises optionally a first stage comprising a chelation treatment step; a second stage comprising a first peroxide treatment stage, wherein said first peroxide treatment stage is a delignifying peroxide treatment stage in which the amount of peroxide is less than 12 kilo/bone dry metric tons; a third stage comprising an acidic delignifying treatment stage, following said second stage and including a wash, and a fourth stage comprising a second peroxide treatment stage, following said third stage and including a wash, wherein said second peroxide treatment stage is a bleaching peroxide treatment, in which the amount of peroxide exceeds 3 kilo/bone dry metric tons and exceeds the amount of peroxide employed in said second step.

Abstract: A method of improving the brightness of calcium carbonate filled paper. The filled paper is dried and then bleached with an aqueous solution of a bleaching agent. The process may be used on all grades of paper that contain filler and is particularly useful in the bleaching of low brightness grade papers that are produced from mechanical pulp that contain calcium carbonate.

Abstract: In one embodiment of the invention is disclosed a process for the production of microcrystalline cellulose comprising

Abstract: The present invention relates to a method for bleaching mechanical and chemithermomechanical pulp including that an advancing pulp suspension obtained after that the fibres are laid free is prebleached by adding reductive bleaching agent to the pulp suspension in a location just after the fibres are laid free and that the bleaching is carried out under given conditions in the form of high temperature and minimized oxygen access in respect of said adding location and immediately downstream of said location, characterized in, that the in the described manner prebleached pulp is subjected to at least one further bleaching treatment including that the pulp is bleached with an oxidizing bleaching agent, preferably peroxide bleaching agent, reinforced with borohydride.

Abstract: The present invention comprises an improved method for refining cellulose that produces a highly refined cellulosic material. The method comprises soaking raw material in a mild NaOH using reduced temperatures and pressures, and refining the material with a plate refiner so that a waste water stream is reduced in volume and has a pH within a range of 8 to 9. The present invention also comprises a HRC gel having a lignin concentration of at least about one (1)% by weight, and a water retention capacity of about 25 to at least about 56 g H2O/g dry HRC.

Abstract: Bleaching device for pulp includes a container to which a supply of pulp and bleaching chemicals containing peroxide as well as discharge of bleached pulp are connected. The device comprises an oxygen measuring device a temperature measuring device and/or a carbon monoxide measuring device, which are arranged to measure oxygen concentration, temperature and/or carbon monoxide concentration, respectively, from the contents of the container such as from the gas volume of the same, or from a substance flow coming from the container, such as gas flow. The measuring device is connected to a data processing unit which is coupled to a controller for automatic control of the process. The process is especially a high consistency pulp bleaching of mechanical pulp, in which the consistency of pulp in the reaction area is at least 25%, advantageously at least 30%.

Abstract: Wood and non-wood pulp is bleached by: a) adding an aliquot of agglomerate from a bulk solids dispensing means, advantageously a hopper, to a dilute solution of hydrogen peroxide which is desirably agitated to keep the agglomerate in suspension, the agglomerate comprising: a bleach activator, advantageously tetraacetyl ethylene diamine (TAED); a peroxide soluble binder, preferably polyvinyl alcohol (PVOH); a dispersing system comprising a wetting agent which is a low foaming and does not discolour on exposure to temperatures of up to 120° C. and optionally a salt, preferably sodium acetate, which is highly soluble in hydrogen peroxide; and sequestrant which may additionally or alternatively be added directly to the hydrogen peroxide; b) allowing the TAED to substantially completely react with the hydrogen peroxide; c) adjusting the pH of the bleach solution by adding alkali, preferably caustic soda; and d) bleaching the pulp by contacting it with the bleaching solution under alkaline conditions.

Abstract: The specification discloses an improved bleaching sequence which provides significant reduction in filtrate volumes and amounts of absorbable organic halide (AOX), color, and chemical oxygen demand (COD) in the effluent. These reductions are achieved without adversely affecting the brightness and viscosity properties of the bleached pulp and without a high capital cost and operating cost penalty or impact on existing mill processes. The bleaching sequence according to the invention for reducing filtrate volumes is an EOD1EOPD2 or EOPD1EOPD2 bleaching sequence wherein substantially all of the filtrates from the later bleaching stages are recycled to earlier bleaching stages and eventually treated in the initial EO or EOP stage prior to discharge from the plant.

Abstract: A two-component mediator system is disclosed, wherein one component serves as a pro-oxidant and the other component serves as a pro-degradant and booster. When used in combination with a laccase, the two-component mediators enhance the bleaching of pulp. In addition, a composition comprising an oxidative enzyme, a pro-oxidant, and a pro-degradant, and a process for oxidizing a substrate that comprises treating the substrate with an oxidizing enzyme, a pro-oxidant, and a pro-degradant are disclosed. The pro-oxidant can be ascorbic acid, ascorbate, salicylic acid, salicylate, nicotinic acid, nicotinate, a hardwood black liquor, a softwood black liquor, ligno-organosolv, lignin sulfonate, or mixtures thereof. The pro-degradant can be urea, thiourea, sulfamic acid, sulfamide, guanidine, methylsulfonic acid, or mixtures thereof.

Abstract: A composition comprising an enzyme exhibiting laccase activity and an enzyme enhancing agent, also referred to as a mediator, is disclosed. A process for oxidizing a substrate that comprises treating the substrate with a composition comprising an enzyme exhibiting laccase activity and an enzyme enhancing agent is disclosed. The process when used on lignin-containing material bleaches the lignin-containing material. A process for enhancing the activity of an enzyme exhibiting laccase activity that comprises adding an enzyme enhancing agent to the enzyme is also disclosed.

Abstract: Pulping liquors used in the bleaching of pulps by hydrogen peroxide, and containing catalase-producing bacteria and/or catalase enzyme are treated with tris (hydroxymethyl) phosphine or a tetrakis (hydroxymethyl) phosphonium salt to kill the bacteria and destroy the enzyme.

Abstract: A process is provided for preparing a commercially acceptable pharmaceutical grade microcrystalline cellulose which comprises: a) repulping a pulp, the pulp having a composition, b) pressing the pulp obtained in a; c) decompacting of the pulp obtained in b; d) feeding the pulp obtained in c) into a pre-heated reactor; e) cooking the pulp in the reactor until the pulp obtains a desired degree of polymerization, said cooking being performed at a temperature, a time, and a pressure which is a function of the desired degree of polymerization and the composition of the pulp, the cooked pulp being hydrolyzed cellulose; f) partially depressurizing the reactor; g) injecting water into the reactor; h) discharging the hydrolyzed cellulose from the reactor, i) filtrating the hydrolyzed cellulose; j) deaggregating the hydrolyzed cellulose of step i; and k) drying the hydrolyzed cellulose to form microcrystalline cellulose.

Abstract: A process for the delignification and bleaching of chemical paper pulps comprising one or more stage(s) of treatment with hydrogen peroxide, at a temperature greater than 100° C. and under high pressure, in the presence of a polymer and of a compound A chosen from potassium hydroxide, sodium hydroxide and alkali metal or alkaline-earth metal carbonates.

Abstract: There is provided a new and useful process for peroxide bleaching of mechanical or high yield pulp, the process comprising adding to a pulp slurry at least one stabilizer for stabilizing low valency states of transition metal ions in the slurry; subsequently adding caustic soda to said slurry simultaneously with or subsequent to adding said at least one stabilizer; adding hydrogen peroxide to the slurry at a preselected point; and subjecting the slurry to preselected conditions to complete the bleaching process.

Abstract: Methods for bleaching chemical pulps are disclosed including a final bleaching sequence of bleaching with chlorine dioxide, treating with a chelating agent, in which the bleaching and treating steps are carried out in sequence without an intermediate washing step, washing the bleached pulp, and bleaching with hydrogen peroxide.

Abstract: A process of oxidizing a substrate is disclosed. The process comprising the step of treating the substrate with an oxidizing enzyme, a mediator that enhances the oxidative activity of the enzyme, and a chain transfer agent. In one example, the substrate is a lignin-containing material and the process results in bleaching of the lignin-containing material. Examples of some useful enzymes are laccase, catechol oxidase, monophenol monooxygenase, and bilirubin oxidase. A composition comprising an oxidative enzyme, a mediator that enhances the oxidative activity of the enzyme, and a chain transfer agent is also disclosed.

Abstract: A process for peroxide bleaching of pulp using magnesium oxide or magnesium hydroxide as a substitute for caustic soda wherein the pulp is bleached in the presence of hydrogen peroxide characterized in that the concentration of ion present in the magnesium oxide or magnesium hydroxide and the pulp is maintained less than 20 ppm and/or the concentration of manganese is maintained less than 10 ppm.

Abstract: Composite panels and pulp, and paper products of the pulp, are produced from Arundo donax. In the fabrication of the composite panels, Arundo donax is comminuted to a suitable size, combined with a binder, and consolidated into panels that meet standards for construction and/or furniture grade panels. The Arundo donax particulates may be combined with wood particulates to produce a mixed furnish that can be used in the preparation of composite panels. Comminuted Arundo donax is treated, in conventional pulping processes, to produce a high tensile strength pulp that can be used in the production of paper. The pulp has a lighter color than wood pulp, and thereby uses less bleaching chemicals to achieve a desired whiteness. The pulp can be combined with wood pulp to produce a variety of products.

Abstract: The subject process comprises providing chemical pulp and an Eop and/or Ep aqueous bleaching solution. The Eop aqueous bleaching solution comprises a peroxide compound, an oxygen-containing material, sodium hydroxide and magnesium hydroxide, in the absence of magnesium sulfate. Alternatively, the Eop aqueous chemical solution for bleaching chemical pulp comprises an Eop aqueous bleaching solution consisting essentially of a peroxide compound, an oxygen-containing material, sodium hydroxide and magnesium hydroxide. In any case, the chemical pulp is bleached with the Eop aqueous bleaching solution to form a bleached chemical pulp. The Ep aqueous bleaching solution comprises a peroxide compound, sodium hydroxide and magnesium hydroxide, in the absence of magnesium sulfate. Alternatively, the Ep aqueous bleaching solution consists essentially of a peroxide compound, sodium hydroxide and magnesium hydroxide.