A pulp composition and a method

Abstract

According to an example aspect of the present invention, there is provided a pulp composition comprising: cellulosic fibres and hemicelluloses originating from paper-grade pulp; wherein the amount of hemicelluloses is 5 to 20 wt-%, calculated from the dry weight of the pulp composition, wherein the amount of xylan is less than 7 wt-%, calculated from the dry weight of the pulp composition, wherein the intrinsic viscosity of the pulp composition is less than 650 ml / g.

Description

TITLEA pulp composition and a methodFIELD

[0001] The present application relates to treatment of cellulosic materials, particularly to make them spinnable to textile fibres in an industrial process.BACKGROUND

[0002] A good pulp for a textile fibre manufacturing process, such as the NMMO- based Lyocell process, has a good reactivity, meaning that the pulp dissolves entirely and there is no burden for spinning solution filtration process. Partially or incompletely dissolved pulp forms gels that can go through the filtration, but show as spinning instabilities (sticks and glues). Inorganic particles can also burden the filterability and small enough particles can come through in to the final product. Inorganic particles may become implemented to the fibre and make the fibre brittle. In processes involving a closed chemical cycle, the inorganic compounds burden the chemical recycling, as do the pulp and solvent degradation products. These typically originate from pulp impurities. All accumulating impurities and degradation products generally need to be removed from the chemical cycle. Pulp degradation products are typically from polymer ends and thus the hemicelluloses are seen as a risk. Soluble inorganics and degradation products are removed via an ion exchanger in the NMMO process. Ion exchange can be a bottle neck for the textile fibre manufacturing process, as well as the dope filtration.

[0003] At least in some embodiments, the present invention aims at providing an improved pulp for textile fibre manufacturing processes.SUMMARY OF THE INVENTION

[0004] The invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims.

[0005] According to a first aspect of the present invention, there is provided a pulp composition comprising: cellulosic fibres and hemicelluloses originating from paper-grade pulp; wherein the amount of hemicelluloses is 5 to 20 wt-%, calculated from the dry weight of the pulp composition, wherein the amount of xylan is less than 7 wt-%, calculated from the dry weight of the pulp composition, wherein the intrinsic viscosity of the pulp composition is less than 650 ml / g.

[0006] Various embodiments of the first aspect may comprise one or more features from the following bulleted list:• The cellulosic fibres originate from or comprise alkaline-extracted paper-grade pulp, such as alkaline-extracted kraft pulp.• The cellulosic fibres originate from or comprise paper-grade pulp which has been treated by cold caustic extraction (CCE) by using white liquor or at least partially oxidized white liquor as alkali.• The pulp composition comprises xylan in an amount of less than 5 wt-%, calculated from the dry weight of the pulp composition.• The pulp composition comprises glucomannan in an amount of at least 5 wt-%, such as at least 6 wt-%, such as at least 7 wt-%, or less than 10 wt-%, calculated from the dry weight of the pulp composition.• In the pulp composition, the weight ratio of glucomannan / hemicellulose is at least 0.5, such as at least 0.6, such as at least 0.7.• The pulp composition comprises less than 15 wt-%, such as less than 10 wt-% hemicelluloses, calculated from the dry weight of the pulp composition.• The pulp composition comprises at least 80 wt-%, such as at least 85 wt-%, such as at least 90 wt-% cellulosic fibres, calculated from the dry weight of the pulp composition.• The pulp composition comprises less than 5 wt-%, such as less than 3 wt-%, such as less than 1 wt-% lignin, calculated from the dry weight of pulp composition.• The pulp composition comprises less than 30 ppm of Fe, such as less than 25 ppm, such as less than 20 ppm, such as less than 10 ppm, for example less than 5 ppm.• The pulp composition comprises less than 30 ppm of Cu, such as less than 25 ppm, such as less than 20 ppm, such as less than 10 ppm, for example less than 5 ppm.• The amount of ash is less than 0.1 wt-%, calculated from the dry weight of the pulp composition.• The pulp composition comprises less than 20 ppm of Ca.• The pulp composition comprises less than 70 ppm of Mg.• The cellulose in the pulp composition comprises less than 30 umol / g of carbonyl groups, per gram of dry fibres.• The cellulose in the pulp composition comprises less than 20 umol / g of carboxyl groups, per gram of dry fibres.• The intrinsic viscosity of the pulp composition is less than 500 ml / g, such as less than 450 ml / g, such as less than 400 ml / g, such as less than 300 ml / g.

[0007] According to a second aspect of the present invention, there is provided a method, typically for preparing a pulp composition, the method comprising: providing a pulp comprising or consisting of paper-grade pulp; providing white liquor or at least partially oxidized white liquor; subjecting the pulp to alkaline extraction wherein said white liquor or said at least partially oxidized white liquor is used as an alkali, to obtain an alkaline-extracted pulp; and thereafter subjecting the alkaline-extracted pulp to a heat treatment in the presence of oxygen, to decrease the intrinsic viscosity of the alkaline-extracted pulp to less than 650 ml / g.

[0008] Various embodiments of the second aspect may comprise one or more features from the following bulleted list:• White liquor is used as an alkali in the alkaline extraction, and said white liquor originates from a pulp mill.• The effective alkali of said white liquor is at least 70 g NaOH / L.• At least partially oxidized white liquor is used as an alkali in the alkaline extraction, and said at least partially oxidized white liquor is obtained by oxidizing white liquor that originates from a pulp mill.• The effective alkali of said at least partially oxidized white liquor is at least 85 g NaOH / L, such as at least 90 g NaOH / L, or 85 to 95 g NaOH / L.• The method comprising removing solid matter from said white liquor or from said at least partially oxidized white liquor before using said white liquor or said at least partially oxidized white liquor as an alkali in the alkaline extraction, wherein said removing step comprises filtering and / or clarifying.• As a result of said removing, the amount of heavy metals, such as iron and copper, in said white liquor or said at least partially oxidized white liquor is decreased.• The alkaline extraction comprises cold caustic extraction, and preferably during said cold caustic extraction step the temperature of said white liquor or said at least partially oxidized white liquor is in the range 0 to 60 °C, such as 5 to 50 °C, such as 10 to 30 °C.• NaOH is used as a further alkali in the alkaline extraction, for example to increase the effective alkali to at least 85 g NaOH / L, such as at least 90 g NaOH / L, or to 85 to 150 g NaOH / L, such as 85 to 95 g NaOH / L, particularly when using at least partially oxidized white liquor.• The cellulose in the pulp does not substantially become derivatized, such as converted to alkali cellulose, during the alkaline extraction.• The method comprising, before said heat treatment, removing at least part of the alkali from the alkaline-extracted pulp, for example by pressing.• The heat-treatment is carried out in a temperature of at least 30 °C, such as at least 40 °C, such as at least 50 °C, such as at least 60 °C, for example at least 70 °C, typically in a temperature below 80 °C.• During the heat treatment step maintaining the number of carboxyl groups in cellulose at a level of less than 20 umol / g, such as less than 15 umol / g of carboxyl groups, per gram of dry fibres.• During the heat treatment step, maintaining the number of carbonyl groups in cellulose at a level of less than 30 umol / g, such as less than 25 umol / g, such as less than 20 umol / g of carbonyl groups, per gram of dry fibres.• Immediately after the alkaline extraction, the viscosity of the alkaline-extracted pulp is at least 700 ml / g, such as 750 to 1200 ml / g, such as 800 to 1100 ml / g.• Before said heat treatment, the viscosity of the alkaline-extracted pulp is at least 700 ml / g, such as 750 to 1200 ml / g, such as 800 to 1100 ml / g.• As a result of said heat treatment, the viscosity of the alkaline-extracted pulp becomes lowered to less than 600 ml / g, such as to the range 350 to 550 ml / g, typically as a result of degradation of cellulose.• After said heat treatment, the viscosity of the alkaline-extracted pulp is less than 600 ml / g, such as in the range 350 to 550 ml / g, typically as a result of degradation of cellulose.• The method further comprises washing the alkaline-extracted and heat-treated pulp with an acidic solution, typically to remove at least a part of the metals present in the alkaline-extracted and heat-treated pulp .• The method comprises directing the used white liquor or the used oxidized white liquor to an industrial process selected from the following group: pulping, papermaking, waste water treatment, textile waste treatment, other industrial waste treatment.• The method further comprises using the purified and heat-treated pulp as a cellulosic starting material in a process for manufacturing regenerated filaments or staple fibres, said process comprising dry jet- wet spinning or wet spinning..• The purified and heat-treated pulp is capable of being converted to regenerated products selected from the following group: textile fibres, non-woven fibres, filaments, films or other fully or partially regenerated products.• The method is for preparing a pulp composition according to the first aspect.

[0009] According to a third aspect of the present invention, there is provided a pulp composition obtained by the method according to the second aspect.

[0010] Advantages of the invention

[0011] Some embodiments of the present invention may provide treatment sequences in order to achieve a pulp composition that has intrinsic viscosity on the level of less than 500 ml / g.

[0012] Some embodiments of the present invention may provide treatment sequences in order to achieve a pulp composition that has a high alpha cellulose content.

[0013] Some embodiments of the present invention may provide treatment sequences in order to achieve a pulp composition that contains a limited amount of carbonyl and carboxyl groups.

[0014] Some embodiments of the present invention may provide treatment sequences in order to achieve a pulp composition that has a balanced molar mass distribution.

[0015] Some embodiments of the present invention may provide treatment sequences in order to achieve a pulp composition that has a high purity in terms of short pulp polymers and inorganic content.EMBODIMENTS

[0016] DEFINITIONS

[0017] In the present context, the term “cold caustic extraction” (CCE) refers to a process in which a pulp is purified by extraction with a strongly alkaline solution in a temperature below 60 °C, such as below 40 °C.

[0018] In the present context, the term “white liquor” (WL) refers to an alkaline cooking media comprising mainly NaOH and Na2S typically as the main delignification chemicals.

[0019] In the present context, the term “oxidized white liquor” (OWL) comprises white liquor which has been oxidized at least partially. Typically, oxidized white liquor comprises the following compounds: NaOH, Na2S and oxidized sulphur compounds, such as sodium thiosulphate and / or sodium sulphate.

[0020] Typically, the term “at least partially oxidized white liquor” covers partially oxidized white liquor and fully oxidized white liquor.

[0021] In the present context, the term “viscosity” typically refers to intrinsic viscosity.

[0022] Intrinsic viscosity [ |] is a measure of a solute’s contribution to the viscosity | of a solution. Intrinsic viscosity can be measured according to the standard ISO 5351.

[0023] In the present context, the term “Lyocell process” comprises dry jet wet spinning technology in which a direct cellulose solvent, such as NMMO or an ionic liquid, is used as the solvent.

[0024] In the present context, the term “viscose process” comprises a wet spinning process in which cellulose is dissolved by derivatizing the cellulose with substances such as CS2 or urea.

[0025] In the present context, “effective alkali” (EA, g / L) describes white liquor sodium hydroxide (NaOH) and half of the sodium sulphide (Na2S) concentrations. Effective alkali is a measure of the alkali content in the white liquor, taking into account the ratio ofsodium hydroxide to sodium sulphide. The formula for effective alkali (EA) is often expressed as follows:EA = c(NaOH) + 0.5 • c(Na2S) , wherein c denotes concentration (g / L).

[0026] This equation takes into account the fact that sodium sulphide contributes half of its molar weight as effective alkali.

[0027] The inventors have observed that by treating paper-grade pulp by cold caustic extraction and subsequently heat-treating the extracted pulp, it is possible to achieve a new kind of pulp composition with properties that make it particularly suitable for certain applications, such as textile fibre manufacturing.

[0028] The method comprises providing a pulp comprising or consisting of papergrade pulp; providing white liquor or at least partially oxidized white liquor; subjecting the pulp to alkaline extraction wherein said white liquor and / or said at least partially oxidized white liquor is used as an alkali, to obtain an alkaline-extracted pulp; and thereafter subjecting the alkaline-extracted pulp to a heat treatment in the presence of oxygen, to decrease the intrinsic viscosity of the alkaline-extracted pulp to less than 650 ml / g, for example less than 500 ml / g.

[0029] The starting material, the pulp, preferably comprises or consists of paper-grade pulp. The pulp may comprise at least 50 wt-%, such as at least 80 wt-% of paper-grade pulp, calculated from dry weight of the pulp.

[0030] Preferably, the starting material pulp does not comprise any substantial amount of dissolving pulp. For example, the pulp may comprise less than 10 wt-%, such as less than 5 wt-% of dissolving pulp, calculated from dry weight of the pulp.

[0031] The pulp, such as the paper-grade pulp, may be selected from the following group: kraft pulp, sulphite pulp, chemi-thermomechanical pulp, thermomechanical pulp, mechanical pulp, and any combinations thereof.

[0032] In some embodiments, the pulp, such as the paper-grade pulp, is selected from the following group: kraft pulp, sulphite pulp, chemi-thermomechanical pulp, and any combinations thereof.

[0033] Typically, the pulp, such as the paper-grade pulp, comprises or consists of kraft pulp.

[0034] The pulp may comprise or consist of wet pulp or never-dried pulp.

[0035] The paper-grade pulp may comprise never-dried paper-grade pulp.

[0036] The paper-grade pulp may comprise wet paper-grade pulp, for example wet and never-dried paper-grade pulp.

[0037] The pulp, such as the paper-grade pulp, may be bleached, such as ECF- bleached or TCF-bleached, or non-bleached.

[0038] The pulp, such as the paper-grade pulp, may comprise hardwood pulp and / or softwood pulp.

[0039] In some embodiments, the pulp, such as the paper-grade pulp, may be made from any broad-leaved tree such as a tree from the betulaceae family, for example birch or aspen, from the salicaceae family, from eucalyptus, mixed tropical hardwood or pines or from any combination of the aforementioned. The pulp may be also made from any conifer, such as spruce or pine or from any combination thereof. The pulp may be also made from a combination of broad-leaved trees and conifers.

[0040] In some embodiments, the pulp may be made from any annual, such as straw, common reed, reed canary grass, bamboo, sugarcane, bagasse or any grass plant.

[0041] In some embodiments, the pulp may comprise recycled fibres, such as textile waste fibres.

[0042] In an embodiment, the pulp comprises paper-grade pulp and textile waste fibres.

[0043] In some embodiments, the treatment of the pulp, particularly the paper grade pulp, involves two steps: at least partial hemicellulose removal and intrinsic viscosity adjustment.

[0044] At least a part of hemicelluloses in the pulp may be removed by alkaline extraction. Typically, five-carbon sugars, such as xylan, and degraded pulp polymers, dissolve from the pulp to alkali. By contrast, glucomannan typically stays mainly intact, i.e.it does not dissolve in alkali. Presence of moderate amounts of glucomannan, for example together with other six-carbon sugars, is generally tolerated in the end product, i.e. in the alkaline-extracted and heat-treated pulp. Therefore removal of glucomannan from the starting material pulp may not be necessary.

[0045] In the present invention it has been observed that use of white liquor and / or at least partially oxidized white liquor, optionally in combination with added NaOH, as the alkali may bring many advantages.

[0046] Preferably, the alkaline extraction comprises cold caustic extraction (CCE), typically performed with one or more of the following as alkali source: white liquor, partially oxidized white liquor, fully oxidized white liquor, and any combinations thereof. NaOH may be used (added) as a further alkali. Thus, additional NaOH may be added to the other alkali source(s).

[0047] White liquor is a chemical mixture used in sulphate pulping containing mainly NaOH and Na2S. The concentration of NaOH and Na2S in white liquor are expressed as active alkali (AA) or effective alkali (EA). As white liquor and oxidized white liquor may be available at a sulphate pulp mill or an integrated facility connected to a sulphate pulp mill, the use of white liquor or oxidized white liquor in a CCE stage may bring substantial savings.

[0048] In an embodiment, white liquor is used as an alkali in the alkaline extraction, and said white liquor typically originates from a pulp mill.

[0049] The effective alkali of said white liquor may be at least 65 g NaOH / L, such as at least 70 g NaOH / L, such as at least 80 g NaOH / L.

[0050] In an embodiment, at least partially oxidized white liquor is used as an alkali in the alkaline extraction, and said at least partially oxidized white liquor is typically obtained by oxidizing white liquor that originates from a pulp mill.

[0051] In an embodiment, fully oxidized white liquor is used as an alkali in the alkaline extraction.

[0052] The effective alkali of said at least partially oxidized white liquor or said fully oxidized white liquor may be at least 85 g NaOH / L, such as at least 90 g NaOH / L, or 85 to 95 g NaOH / L.

[0053] The oxidized white liquor to be used as an alkali in the present method may be obtained from a pulp mill. Before using the white liquor and / or the oxidized white liquor obtained from a pulp mill, it may be pre-treated by for example cooling, filtering and / or clarifying.

[0054] It is also possible to use a combination of white liquor and oxidized white liquor as an alkali in the alkaline extraction.

[0055] Solid matter may be removed from the white liquor or the oxidized white liquor before using the white liquor or the oxidized white liquor as an alkali in the alkaline extraction. Said removing step may comprise filtering and / or clarifying.

[0056] As a result of said removing, the amount of heavy metals, such as iron and copper, in said white liquor or said oxidized white liquor may be decreased.

[0057] Typically, during the alkaline extraction the temperature of the alkali, such as the white liquor and / or the oxidized white liquor, is less than 60 °C, such as less than 50 °C, such as less than 45 °C, or 5 to 50 °C, such as 10 to 40 °C.

[0058] Typically, the alkaline extraction comprises cold caustic extraction, and preferably during said cold caustic extraction step the temperature of the alkali, such as the white liquor and / or the oxidized white liquor, is in the range 0 to 60 °C, such as 5 to 50 °C, such as 10 to 30 °C.

[0059] NaOH may be used as a further alkali in the alkaline extraction, to increase the effective alkali to at least 85 g NaOH / L, such as at least 90 g NaOH / L, or to 85 to 150 g NaOH / L, such as 85 to 95 g NaOH / L. It is particularly advantageous to use NaOH as a further alkali when using oxidized white liquor as an alkali.

[0060] Preferably, the cellulose in the pulp does not substantially become derivatized, such as converted to alkali cellulose, during the alkaline extraction.

[0061] The used white liquor and / or the used oxidized white liquor may be directed to an industrial process selected from the following group: pulping, papermaking, waste water treatment, textile waste treatment, other industrial waste treatment.

[0062] Heat-treatment of the pulp

[0063] In some embodiments, the intrinsic viscosity adjustment for the pulp may be carried out by heat-treatment of the pulp in the presence of oxygen.

[0064] The heat-treatment may comprise alkaline oxidation but the invention is not to be limited to any particular mechanism or chemical reaction during the heat treatment step.

[0065] In some embodiments, the pulp that has been treated with alkaline extraction is subsequently heat-treated in the presence of oxygen.

[0066] Alkaline oxidation is affected by of oxygen (accessibility), alkali (concentration), time and temperature. The reaction may be catalyzed by metals. An advantage of alkaline oxidation is that the pH of the alkaline-extracted pulp does not have to be varied over a wide range, such as from alkaline to acidic.

[0067] An advantage is that there is no need to wash the pulp after the CCE step, before carrying out the viscosity adjustment, i.e. the heat treatment, such as alkaline oxidation.

[0068] In an embodiment, the heat-treatment is carried out in a temperature of at least 30 °C, such as at least 40 °C, such as at least 50 °C, such as at least 60 °C, for example at least 70 °C. Preferably, the heat-treatment is carried out in a temperature below 80 °C, such as 60 to 80 °C. Advantageously, in these temperatures the cellulose fibres do not become degraded too excessively.

[0069] In some embodiments, during the heat treatment step, the number of carboxyl groups in cellulose is maintained at a level of less than 20 umol / g, such as less than 15 umol / g of carboxyl groups, per gram of dry fibres.

[0070] In some embodiments, during the heat treatment step, the number of carbonyl groups in cellulose is maintained at a level of less than 30 umol / g, such as less than 25 umol / g, such as less than 20 umol / g of carbonyl groups, per gram of dry fibres.

[0071] In an embodiment, before said heat treatment, the viscosity of the alkaline- extracted pulp is at least 700 ml / g, such as at least 750 ml / g, such as 750 to 1200 ml / g, such as 800 to 1100 ml / g.

[0072] In an embodiment, as a result of said heat treatment, the viscosity of the alkaline-extracted pulp becomes lowered to less than 600 ml / g, such as to the range 350 to 550 ml / g, typically as a result of degradation of cellulose.

[0073] Washing steps

[0074] Optionally, the heat-treated pulp may be washed with water. Such water washing may remove residual alkali, for example to be recycled or reused.

[0075] In some embodiments, after said heat treatment and after an optional step of washing with water, the pulp may be washed with an acidic solution, to remove at least a part of the metals present in the pulp.

[0076] In the acid washing step, the pH may be lowered to 2.5 or below, for example by sulphuric acid. The washing liquid may be removed by pressing, filtration or by centrifuge, resulting in a pulp with approximately 30-40 % dry matter content.

[0077] A further water washing may be carried out after the acid washing, to remove residual acid and salts.

[0078] In an aspect of the present invention, a pulp composition is provided.

[0079] The pulp composition may be obtained as the end product in some embodiments of the present method. Thus, in some embodiments, the pulp composition may be an alkaline-extracted and heat-treated pulp.

[0080] The pulp composition typically comprises cellulosic fibres and hemicelluloses originating from paper-grade pulp. In the pulp composition, the amount of hemicelluloses is 5 to 20 wt-%, calculated from the dry weight of the pulp composition. Preferably the amount of xylan is less than 7 wt-%, calculated from the dry weight of the pulp composition. Typically the intrinsic viscosity of the pulp composition is less than 650 ml / g.

[0081] The pulp composition, as well as the starting material pulp, typically comprises hemicellulose-rich cellulosic fibres. The hemicelluloses are usually connected to or bound to the cellulosic fibres in the pulp composition.

[0082] The cellulosic fibres typically originate from alkaline-extracted paper-grade pulp, such as alkaline-extracted kraft pulp.

[0083] In some embodiments, the cellulosic fibres originate from paper-grade pulp which has been treated by cold caustic extraction (CCE) by using white liquor or at least partially oxidized white liquor as alkali.

[0084] The pulp composition may comprise less than 5 wt-% of xylan, calculated from the dry weight of pulp composition.

[0085] The pulp composition may comprise at least 5 wt-% of glucomannan, such as at least 6 wt-%, such as at least 7 wt-%, or less than 10 wt-%, calculated from the dry weight of pulp composition. In this case, the cellulosic fibres and the hemicelluloses may originate from softwood paper-grade pulp.

[0086] In the pulp composition, the weight ratio of glucomannan / hemicellulose is typically at least 0.5, such as at least 0.6, such as at least 0.7. In this case, the cellulosic fibres and the hemicelluloses may originate from softwood paper-grade pulp.

[0087] In some embodiments, the pulp composition comprises less than 15 wt-%, such as less than 10 wt-% hemicelluloses, calculated from the dry weight of the pulp composition.

[0088] In some embodiments, the pulp composition comprises at least 80 wt-% cellulosic fibres, calculated from the dry weight of the pulp composition.

[0089] In some embodiments, the pulp composition comprises less than 5 wt-%, such as less than 3 wt-%, such as less than 1 wt-% lignin, calculated from the dry weight of the pulp composition.

[0090] In an embodiment, the pulp composition comprises less than 30 ppm of Fe, such as less than 25 ppm, such as less than 20 ppm, such as less than 10 ppm, for example less than 5 ppm.

[0091] In an embodiment, the pulp composition comprises less than 30 ppm of Cu, such as less than 25 ppm, such as less than 20 ppm, such as less than 10 ppm, for example less than 5 ppm.

[0092] In an embodiment, the pulp composition comprises less than 0.1 wt-% of ash, calculated from the dry weight of the pulp composition.

[0093] In an embodiment, the pulp composition comprises less than 20 ppm of Ca.

[0094] In an embodiment, the pulp composition comprises less than 70 ppm of Mg.

[0095] Typically, the cellulose in the obtained pulp composition comprises less than 30 umol / g, such as less than 20 umol / g of carbonyl groups, and less than 20 umol / g of carboxyl groups, per gram of dry fibres.

[0096] Preferably, the viscosity of the obtained pulp composition is less than 500 ml / g, such as less than 450 ml / g, such as less than 400 ml / g, such as less than 300 ml / g.

[0097] The pulp composition may be capable of being converted to regenerated products selected from the following group: textile fibres, such as staple fibres, non-woven fibres, filaments, films or other fully or partially regenerated products.

[0098] The pulp composition may be capable of being dissolved in NMMO, to obtain a spinning dope which can be spun to produce regenerated textile fibres.

[0099] The pulp composition may be applicable as a cellulosic starting material in a process for manufacturing regenerated filaments or staple fibres, said process comprising dry jet- wet spinning or wet spinning.

[0100] The pulp composition may be applicable as a cellulosic starting material in a Lyocell or viscose manufacturing process.

[0101] Examples

[0102] Various treatment sequences comprising an alkaline extraction step and a heat treatment step were studied. The raw material (feed pulp) was fully bleached paper-grade softwood kraft pulp.

[0103] The first step comprised cold caustic extraction (CCE) with either NaOH or WL or OWL as the alkali.

[0104] The target consistency, after mixing the pulp with the alkaline suspension, was 4%. NaOH stock solution and WL were diluted with deionized water to reach target EA NaOH concentrations in CCE. OWL was strengthened with NaOH solution (50 wt-%) to reach target EA NaOH concentration in CCE.

[0105] In the NaOH test, Cobalt was charged as C0CI2 in HC1 solution. The Co charge was diluted in 500 ml water before charging, to ensure good mixing in pulp.

[0106] The high consistency feed pulp and chemicals were first preheated to 40 °C, then the pulp was submerged and mixed into the alkaline liquor in a temperature-controlled container (bucket) equipped with mechanical stirrer. In the NaOH test, pulp and NaOH solution were first thoroughly mixed, and diluted (preheated) Co was added last. The CCE container was open to atmosphere during the test. The calculation of CCE retention time (total 45 min) started from mixing pulp and alkaline liquor, and was stopped when pressing commenced.

[0107] Pressing was carried out in a temperature controlled cylindrical hydraulic press. The press was preheated to 40 °C before starting tests. Pressing program: 4 bar for 4 to 6 min, then 15 bar for 6 to 10 min. There was no more filtrate flow at the completion of the pressing. The pressed pulp cakes obtained were disintegrated by hand, the duplicate samples were combined, and the composite sample was fluffed (homogenized) three times.

[0108] After the CCE step, the pulp was heat-treated. The heat treatment was carried out in a 10 liter electrically heated, Teflon lined revolving autoclave. A considerable air volume remained in the reactor after charging the pulp. The treatment temperature was either 80 °C (for CCE-NaOH-treated pulp) or 62 °C (for CCE-WL-treated and CCE-OWL-treated pulps). The treatment time was 1 h.

[0109] After the heat treatment, the pulps were washed three times: first with water, then with acid, and finally with water.

[0110] In the first water washing step, washing was carried out as simple one step dilution concentration washing. The heat-treated pulp sample was suspended in a specified volume of deionized water preheated to 60 °C. The consistency target was 4%. After reaching a uniform suspension, the sample was transferred to the temperature controlled hydraulic press (60 °C) and pressed first at 4 bar and then 15 bar until dry. The pressing time required was typically 2 to 3 min in each step. The pressed pulp cake was disintegrated by hand and fluffed (homogenized) three times.

[0111] The acid washing step was similar to the first water washing, but diluted pulp suspension pH was adjusted to 2.5 using sulphuric acid and allowed to stabilize for 30 min before pressing.

[0112] The second water washing was similar to the first water washing.

[0113] The analysis results are shown in Tables 1 and 2.

[0114] Table 1. Hemicellulose and cellulose contents of pulps treated by alkaline extraction and heat-treatment (as wt-%, calculated from dry weight of the treated pulp).

[0115] Table 2. Viscosity (as ml / g) of the pulp in various stages.

[0116] It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for thepurpose of describing particular embodiments only and is not intended to be limiting.

[0117] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment.

[0118] As used herein, a plurality of items, structural elements, compositional elements, and / or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.

[0119] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

[0120] While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

[0121] The verbs “to comprise” and “to include” are used in this document as openlimitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of “a” or “an”, i.e. a singular form, throughout this document does not exclude a plurality.INDUSTRIAL APPLICABILITY

[0122] The present invention may be industrially applicable at least in manufacturing of a pulp composition that is suitable as a raw material in production of textile fibres, nonwoven products, filaments, films and other products from dissolved and regenerated pulp.ACRONYMS LISTCCE cold caustic extractionWL white liquorOWL oxidized white liquor AA active alkaliEA effective alkaliNMMO N-methylmorpholine N-oxide

Claims

CLAIMS:

1. A pulp composition comprising:- cellulosic fibres and hemicelluloses originating from paper-grade pulp; wherein in the pulp composition the amount of hemicelluloses is 5 to 20 wt-%, calculated from the dry weight of the pulp composition, wherein in the pulp composition the amount of xylan is less than 7 wt-%, calculated from the dry weight of the pulp composition, wherein the intrinsic viscosity of the pulp composition is less than 650 ml / g.

2. The pulp composition according to claim 1, wherein the cellulosic fibres originate from alkaline-extracted paper-grade pulp, such as alkaline-extracted kraft pulp.

3. The pulp composition according to any of the preceding claims, wherein the cellulosic fibres originate from paper-grade pulp which has been treated by cold caustic extraction (CCE) by using white liquor as alkali.

4. The pulp composition according to any of the preceding claims, wherein the cellulosic fibres originate from paper-grade pulp which has been treated by cold caustic extraction (CCE) by using at least partially oxidized white liquor as alkali.

5. The pulp composition according to any of the preceding claims, wherein in the pulp composition the amount of xylan is less than 5 wt-%, calculated from the dry weight of the pulp composition.

6. The pulp composition according to any of the preceding claims, comprising less than 15 wt-%, such as less than 10 wt-% hemicelluloses, calculated from the dry weight of the pulp composition.

7. The pulp composition according to any of the preceding claims, comprising at least 80 wt-% cellulosic fibres, calculated from the dry weight of the pulp composition.

8. The pulp composition according to any of the preceding claims, wherein the cellulose in the pulp composition comprises less than 30 umol / g , such as less than 20 umol / g of carbonyl groups, per gram of dry fibres.

9. The pulp composition according to any of the preceding claims, wherein the cellulose in the pulp composition comprises less than 20 umol / g of carboxyl groups, per gram of dry fibres.

10. The pulp composition according to any of the preceding claims, wherein the intrinsic viscosity of the pulp composition is less than 500 ml / g, such as less than 450 ml / g, such as less than 400 ml / g, such as less than 300 ml / g.

11. A method comprising:- providing a pulp comprising or consisting of paper-grade pulp;- providing white liquor or at least partially oxidized white liquor;- subjecting the pulp to alkaline extraction wherein said white liquor or said at least partially oxidized white liquor is used as an alkali, to obtain an alkaline-extracted pulp; and thereafter- subjecting the alkaline-extracted pulp to a heat treatment in the presence of oxygen, to decrease the intrinsic viscosity of the alkaline-extracted pulp to less than 650 ml / g.

12. The method according to claim 11, wherein white liquor is used as an alkali in the alkaline extraction, and said white liquor originates from a pulp mill.

13. The method according to claim 12, wherein the effective alkali of said white liquor is at least 70 g NaOH / L.

14. The method according to claim 11, wherein at least partially oxidized white liquor is used as an alkali in the alkaline extraction, and said at least partially oxidized white liquor is obtained by oxidizing white liquor that originates from a pulp mill.

15. The method according to claim 14, wherein the effective alkali of said at least partially oxidized white liquor is at least 85 g NaOH / L, such as at least 90 g NaOH / L, or 85 to 95 g NaOH / L.

16. The method according to any of claims 11 to 15, wherein as a result of said removing, the amount of heavy metals, such as iron and copper, in said white liquor or said at least partially oxidized white liquor is decreased.

17. The method according to any of claims 11 to 16, wherein the alkaline extraction comprises cold caustic extraction, and preferably during said cold caustic extraction step the temperature of said white liquor or said at least partially oxidized white liquor is in the range 0 to 60 °C, such as 5 to 50 °C, such as 10 to 30 °C.

18. The method according to any of claims 14 to 17, wherein NaOH is added as a further alkali in the alkaline extraction, for example to increase the effective alkali to at least 85 g NaOH / L, such as at least 90 g NaOH / L, or to 85 to 150 g NaOH / L, such as 85 to 95 g NaOH / L.

19. The method according to any of claims 11 to 18, wherein the cellulose in the pulp does not substantially become derivatized, such as converted to alkali cellulose, during the alkaline extraction.

20. The method according to any of claims 11 to 19, wherein the heat-treatment is carried out in a temperature of at least 30 °C, such as at least 40 °C, such as at least 50 °C, such as at least 60 °C, for example at least 70 °C, typically in a temperature below 80 °C.

21. The method according to any of claims 11 to 20, wherein during the heat treatment step maintaining the number of carboxyl groups in cellulose at a level of less than 20 umol / g, such as less than 15 umol / g of carboxyl groups, per gram of dry fibres.

22. The method according to any of claims 11 to 21, wherein during the heat treatment step, maintaining the number of carbonyl groups in cellulose at a level of less than 30 umol / g,such as less than 25 umol / g , such as less than 20 umol / g of carbonyl groups, per gram of dry fibres.

23. The method according to any of claims 11 to 22, wherein immediately after said alkaline extraction, the intrinsic viscosity of the alkaline-extracted pulp is at least 700 ml / g, such as750 to 1200 ml / g, such as 800 to 1100 ml / g.

24. The method according to any of claims 11 to 23, wherein as a result of said heat treatment, the intrinsic viscosity of the alkaline-extracted pulp becomes lowered to less than 600 ml / g, such as to the range 350 to 550 ml / g, typically as a result of degradation of cellulose.

25. The method according to any of claims 11 to 24, the method further comprising using the purified and heat-treated pulp as a cellulosic starting material in a process for manufacturing regenerated filaments or staple fibres, said process comprising dry jet- wet spinning or wet spinning.

26. A pulp composition obtained by the method according to any of claims 11 to 25.

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