Method for treating pulp, a pulp composition and products thereof

Abstract

According to an example aspect of the present invention, there is provided a method comprising treating a composition comprising paper-grade pulp with ozone to adjust intrinsic viscosity of the paper-grade pulp to below 550 ml / g The paper grade-pulp comprises at least 10 wt-% of hemicellulose of the dry weight of the paper-grade pulp, and the pH of the composition is at least 5.5 at the beginning of the treatment.

Description

Method for treating pulp, a pulp composition and products thereofFIELD

[0001] The present invention relates to methods for treating pulp and pulp compositions. Further, the present invention relates to products produced from the pulp composition.BACKGROUND

[0002] Intrinsic viscosity of pulp must in many cases be adjusted before the pulp is suitable for applications. Various methods exist for adjusting the intrinsic viscosity of pulp but these methods typically depend on the use of viscosity-regulating chemicals or catalysts. When using such chemicals conditions must be optimized for the chemical, which is not necessarily optimal for the subsequent use of the treated pulp. Further, the chemicals added to the pulp must in many cases be removed and recycled before the pulp can be used in different applications. Common issues with the known methods include high chemical consumption, long delay times, the need for a separate catalyst, and unresolved scalability to industrial scale.SUMMARY OF THE INVENTION

[0003] The invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims.

[0004] According to a first aspect, there is provided a method comprising treating a composition comprising paper-grade pulp with ozone to adjust intrinsic viscosity of the paper-grade pulp to below 550 ml / g, wherein the paper grade-pulp comprises at least 10 wt-% of hemicellulose of the dry weight of the paper-grade pulp, and the pH of the composition is at least 5.5 at the beginning of the treatment.

[0005] According to a second aspect, there is provided pulp obtained by the method according to the first aspect.

[0006] According to a third aspect, there is provided a pulp composition comprising at least 10 wt-% of hemicellulose of the dry weight of the pulp, wherein the intrinsic viscosity of the pulp is below 550 ml / g, the pulp comprises at least 5 wt-% of glucomannan, and the poly dispersity index of the pulp is in the range of 3 to 7.

[0007] According to a fourth aspect, there is provided textile fibres produced from the pulp or pulp composition according to the second or the third aspect.

[0008] According to a fifth aspect, there is provided a textile product comprising textile fibres according to the fourth aspect.

[0009] Various embodiments of the first aspect may comprise one or more features from the following bulleted list:• the temperature during the ozone treatment is in the range of 10 to 80 °C, preferably in the range of 15 to 60 °C, most preferably in the range of 20 to 40 °C.• the consistency of the composition comprising paper-grade pulp is adjusted to 8- 14 %, preferably to 9-13 %, most preferably to 10-12 %, prior to treating the composition with ozone.• the paper-grade pulp is pulp from kraft process.• the paper-grade pulp comprises at least 15 %, preferably at least 17 % of hemicellulose of the dry weight of the paper-grade pulp.• the pH of the composition at the beginning of the treatment is at least 7, preferably to at least 9.• the intrinsic viscosity of the paper-grade pulp is adjusted to below 500 ml / g, such as to 200-500 ml / g.• the amount of ozone during the treatment is in the range of 3 to 10 kg of ozone per 1000 kg of pulp dry weight.• the ozone treatment is performed within 30 seconds, preferably within 10 seconds, most preferably within 5 seconds.• the ozone treatment is performed multiple times, for example 2 to 5 times.• the ozone treatment is performed at a pressure below 10 bars, such as at a pressure in the range of 4 to 7 bar.• the paper-grade pulp is dissolved after the ozone treatment, preferably the pulp is dissolved in an ionic liquid, N-methylmorpholine N-oxide (NMMO), in another non-derivatizing cellulose solvent or mixtures thereof.• the method further comprises treating the paper-grade pulp with an alkaline compound or solution after the ozone treatment.• the paper-grade pulp is treated with or in a solution comprising 1 to 40 g / L, preferably 20 to 30 g / L, of an alkaline compound, such as sodium hydroxide, white liquor and / or oxidized white liquor, after the ozone treatment.• the paper-grade pulp is subjected to cold caustic extraction or mercerization after the ozone treatment.• the paper-grade pulp is directed to a process for manufacturing man-made cellulosic fibres, such as to a lyocell process or a viscose process after the ozone treatment.• the ozone treated pulp is directed to a process for manufacturing cellulose derivatives, such as carboxy methyl cellulose (CMC) or methyl hydroxyethyl cellulose (MHEC) or ethyl hydroxyethyl cellulose (EHEC), or cellulose acetate.EMBODIMENTS

[0010] DEFINITIONS

[0011] Unless otherwise stated herein or clear from the context, any percentages referred to herein are expressed as percent by weight based on a total weight of the respective composition.

[0012] Unless otherwise stated, properties that have been experimentally measured or determined herein have been measured or determined at room temperature. Unless otherwise indicated, room temperature is 25 °C.

[0013] Unless otherwise stated, properties that have been experimentally measured or determined herein have been measured or determined at atmospheric pressure.

[0014] In the present context, the term “intrinsic viscosity” is a measure of a solute’s contribution to the viscosity r| of a solution. Intrinsic viscosity is measured according to the standard ISO 5351.

[0015] In the present context, the term “paper-grade pulp” refers to pulp that is suitable for production of paper. It is lignocellulosic fibrous material prepared by chemically or mechanically separating cellulose fibres from wood, fibre crops or waste paper. Paper-grade pulp may be manufactured by a pulping process that aims at removing lignin and preserving cellulose fibres and hemicellulose in the cooking stage.

[0016] 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.

[0017] 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.

[0018] 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 Na2SOa and / or Na2SO4. Oxidized white liquor may be partially oxidized white liquor or fully oxidized white liquor.

[0019] 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.

[0020] 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.

[0021] It is an aim of the present invention to overcome at least some of the problems associated with the prior art and provide a simple and quick method for adjusting the intrinsic viscosity of paper-grade pulp. It has been observed that by the method disclosed herein, cellulose fibres may be broken even when the cellulose fibres are contained in a composition comprising hemicellulose. This allows adjusting intrinsic viscosity of paper-grade pulp without a need to remove hemicelluloses from the pulp. The pulp composition can be directly used for spinning textile fibres after adjustment of intrinsic viscosity without removing hemicelluloses from the composition. One advantage of the herein disclosed process is that it can be performed without addition of typicalchemicals for adjusting the intrinsic viscosity of cellulose, such as acids, or enzymes, that are cumbersome to be removed and recycled after the adjustment step.

[0022] The method comprises treating paper-grade pulp with ozone to adjust the intrinsic viscosity of the paper-grade pulp. The intrinsic viscosity of the paper-grade pulp is adjusted to below 550 ml / g. The pulp is paper grade-pulp comprising at least 10 wt-% of hemicellulose of the dry weight of the pulp. The pulp is provided as a composition comprising pulp, wherein the pH of the composition is at least 5.5 at the beginning of the treatment.

[0023] It has been discovered that ozone treatment prior to removal of hemicellulose or other impurities, such as residual lignin, from the pulp may be advantageous. Especially residual lignin may be problematic in many applications, for example in production of textile fibres. Without wishing to be bound by theory, it is thought that at least in some embodiments the adjustment of intrinsic viscosity loosens the cellulose structure such that impurities bound within the cellulose structure are released and can be thus easier removed. The ozone treatment may thus also lead to whitening of the pulp because many of the impurities within the pulp cause discoloration. By treating the pulp with ozone, such impurities can be removed more efficiently leading to formation of pulp with lighter colour.

[0024] The pulp may be obtained from any process producing paper-grade pulp. In some embodiments, the paper-grade pulp is pulp from a kraft process. The pulp may be for example alkaline hardwood pulp, alkaline softwood pulp, kraft pulp, hardwood kraft pulp, softwood kraft pulp, soda pulp, hardwood soda pulp, softwood soda pulp, or any mixture thereof. In some embodiments, softwood kraft pulp may be especially well suited for the herein disclosed method. The pulp maybe un-bleached, partially bleached or bleached pulp. The pulp may be provided in solution, or as dry pulp. In some embodiments, the paper-grade pulp is dry pulp.

[0025] A composition comprising paper-grade pulp may be produced by addition of water, mild effluents produced in pulp mills, for example condensate from an evaporation plant, filtrate from a bleach plant, or mill hot water, and / or alkaline solution to dry papergrade pulp. Preferably the consistency of the composition is adjusted to mediumconsistency as explained below, e.g. the consistency may be adjusted to 10-12 %. In some embodiments, the pH of the composition does not need to be adjusted after producing thecomposition comprising paper-grade pulp. For example, dry kraft pulp may be mixed with water, and the composition may be then directly used in the method disclosed herein.

[0026] The consistency of the composition comprising pulp may vary. The composition comprising the paper-grade pulp may in some embodiments be low- consistency pulp, or medium-consistency pulp. For example, the consistency of the composition comprising paper-grade pulp may be in the range of 8-14 %, or in the range of 10-12 %. In some embodiments, the consistency of the paper-grade pulp may be or be adjusted to 8-14 %, preferably to 9-13 %, most preferably to 10-12 %, prior to treating the composition with ozone. The adjustment of consistency may be performed by addition of water, or mild effluents produced in pulp mills, for example condensate from an evaporation plant, filtrate from a bleach plant, mill hot water, or filtrate obtained from the herein disclosed ozone treatment. In some embodiments the adjustment of consistency may be performed by using an alkaline effluent, for example an effluent produced in alkaline treatment of pulp or in cold caustic extraction. One advantage related to using an alkaline effluent for adjusting the consistency is that the pH of the composition may be simultaneously adjusted to a desired pH level.

[0027] In some embodiments, the paper-grade pulp may comprise at least 15 wt-%, preferably at least 17 wt-% of hemicellulose of the dry weight of the pulp. In some examples, the paper-grade pulp may comprise for example 13 wt-%, 20 wt-% or 25 wt-% of hemicellulose of the dry weight of the pulp The term “hemicellulose” refers to group of polysaccharides that may be branched, are shorter in length than cellulose (typically 500 to 3000 sugar units), and also show a propensity to crystallize. Hemicelluloses are composed of diverse sugars, and can include for example xylose, arabinose, glucose, mannose, galactose, and / or rhamnose. Examples of hemicelluloses include for example xylan, glucuronoxylan, arabinoxylan, glucomannan and xyloglucan.

[0028] In some embodiments, the composition comprises at least 50 wt-%, such as at least 70 wt-%, at least 80 wt-%, or at least 90-wt% of paper-grade pulp.

[0029] In some embodiments, the intrinsic viscosity of the paper grade pulp is at least 700 mL / g, such as in the range of 700 - 1 200 mL / g, or 800 - 1 000 mL / g, prior to the treatment with ozone.

[0030] It has been observed, that the intrinsic viscosity of paper-grade pulp may be adjusted by using the herein disclosed ozone treatment even in slightly acidic conditions, such as at a pH range from 5.5 to 7. This is surprising because ozone typically quickly forms radicals and brakes down rapidly in alkaline solutions and thus it has been believed that ozone treatments must be performed at strongly acidic pHs. In fact, it has now been discovered that it is actually possible to use even alkaline pH during the adjustment of intrinsic viscosity. Thus, in some embodiments, the pH of the composition comprising paper-grade pulp may be at least 7, preferably at least 9, at the beginning of the treatment. For example, the pH of the composition comprising paper-grade pulp may be in the range of 7 to 11, such as in the range of 8 to 10 at the beginning of the treatment. In some embodiments, the intrinsic viscosity is adjusted at a pH in the range from 5.5 to 7, i.e. the pH during adjustment of the intrinsic viscosity is in the range of 5.5 to 7.

[0031] The pH of a composition comprising paper-grade pulp may be adjusted to the desired pH value by addition of an alkaline compound and / or solution. In some examples, the pH of the composition comprising paper-grade pulp may be adjusted by using alkaline effluent produced in a paper mill, such as effluent from alkaline wash of pulp or from cold caustic extraction of pulp.

[0032] Typically, the pH of the composition comprising paper-grade pulp will reduce during the ozone treatment. Thus, it may be advantageous to add alkaline compound and / or solution to the composition comprising paper-grade pulp during the treatment with ozone. Such addition may allow maintaining an alkaline pH of the composition during the ozone treatment or at least help maintaining the pH above a desired pH level. In at least some embodiments, the pH of the composition is kept above pH 3 throughout the treatment.

[0033] Treating pulp with ozone as disclosed herein may be performed in the absence of catalysts, such as manganese or cobalt, or chemical compounds, such as chlorine dioxide, peroxides or magnesium, typically used for paper whitening or adjusting the intrinsic viscosity of the pulp. In some embodiments, the ozone treatment is performed in the absence of a catalyst, such as in the absence of a metal catalyst. Not using a catalyst or chemical compounds is advantageous because use of catalysts or chemical compounds increases expenses and complicates the process because the catalyst must be removed prior to subsequent processing steps. Such complicated processes are not needed with the hereindisclosed method. Unreacted ozone may be separated from the composition comprising pulp by venting and / or degassing the composition after the treatment. No complex separation strategies are needed and the amount of produced waste is small. Further, the process does not produce complex waste that would require special disposal strategies. The process mainly produces oxygen, and in some cases other common gases, such as carbon dioxide and / or water vapor, as waste. After degassing and / or venting the composition, the pulp may be dewatered, for example by pressing, before directing the pulp to further treatments, such as washing. The residual solution produced during dewatering may be used in some embodiments for diluting the paper-grade pulp prior to ozone treatment.

[0034] One advantage of the herein disclosed method is that the adjustment of intrinsic viscosity with ozone is fast. Typically, the treatment may be performed in less than a minute. In some embodiments, the ozone treatment may be performed within 30 seconds, preferably within 10 seconds, most preferably within 5 seconds. One advantage related to the fast treatment time is that it may help controlling any unwanted side reactions and radical formation during the treatment. Further, fast adjustment of intrinsic viscosity of paper-grade pulp improves the overall process throughput. In some examples, the pulp may be provided as a stream, which is lead through a mixer, where it is mixed directly with an amount of ozone. One example of a suitable mixer is an in-line high-shear mixer comprising housing and a fast-rotating rotor element typically used with medium consistency pulp. In some embodiments, the ozone treatment may be performed in at least one medium consistency loop.

[0035] The amount of used ozone should preferably be close to the needed amount for adjusting the intrinsic viscosity of the pulp composition to the desired level. Ideally, a small residual amount of ozone remains in the composition after the treatment as an indication that the amount of ozone was sufficient for treating all pulp in the composition. In some embodiments, the amount of ozone may be in the range of 3 to 10 kg of ozone per 1000 kg of pulp dry weight.

[0036] In some embodiments, temperature during the ozone treatment may be in the range of 10 to 80 °C, preferably in the range of 15 to 60 °C, most preferably in the range of 20 to 40 °C. In such temperatures, ozone may dissolve better than at high temperatures. In addition, ozone may be more stable and have lower volume of gas thus allowing efficient treatment of the paper-grade pulp. Temperatures near room temperature also improve theoverall economy of the process both by reducing the need for heating of the composition prior to the treatment, and cooling of the composition after the treatment.

[0037] The ozone treatment may be performed at an elevated pressure. In some embodiments, ozone treatment may be performed at a pressure below 10 bars, such as at a pressure in the range of 4 to 7 bar. An elevated pressure may assist in proper mixing of the ozone with the composition comprising pulp. Thus, in some preferred embodiments, the pressure during the ozone treatment is at least 1 bar, such as at least 2 bars.

[0038] In some embodiments, the ozone treatment may be performed multiple times, for example 2 to 5 times. Each treatment may be performed within 30 seconds, preferably within 10 seconds, most preferably within 5 seconds. In some embodiments, the total treatment time is less than a minute. The ozone treatment may be performed for example by passing the composition comprising paper-grade pulp multiple times through separate treatment areas or the composition comprising paper-grade pulp may be circulated through one treatment area. For example, the treatment may be performed by using a mixing station to which an amount of ozone is injected together with the composition comprising paper-grade pulp. A process-line may include for example 1 to 5 of such mixing stations. In other embodiments, the composition comprising paper-grade pulp may be circulated through one mixing station multiple times, such as 2 to 5 times, and an amount of ozone may be injected to the composition each time.

[0039] The aim of the method is to lower the intrinsic viscosity of paper-grade pulp. In some embodiments, the intrinsic viscosity of the pulp may be adjusted to below 500 ml / g, such as to a range of 200 -500 ml / g.

[0040] In some embodiments, the intrinsic viscosity of the composition comprising paper-grade pulp is at least 700 ml / g prior to the adjustment. In some examples, the composition comprising paper-grade pulp has an intrinsic viscosity of at least 700 mL / g prior to the ozone treatment and during the ozone treatment, the intrinsic viscosity is reduced from at least 700 mL / g to below 550 mL / g, such as to below 500 mL / g, or to 200- 500 mL / g.

[0041] In some embodiments, the paper-grade pulp may be dewatered and / or dried after the ozone treatment, Dewatering and / or drying may be in some embodiments beperformed for example by filtration, pressing, centrifugation, multi-cylinder drying, web drying, and / or flash drying.

[0042] In some embodiments the paper-grade pulp may be dissolved after the ozone treatment. In some preferred embodiments, the treated pulp may be dissolved in a solvent, such as in an ionic liquid, or in N-m ethylmorpholine N-oxide (NMMO), or in another non- derivatizing cellulose solvent. The term “non-derivatizing cellulose solvent” refers to solvents that are capable of dissolving cellulose without covalent chemical modification, of its structure. Non-limiting examples of non-derivatizing cellulose solvents include sodium hydroxide (NaOH)-based systems, such as NaOH / thiourea, or NaOH / PEG, LiOH, LiOH / urea, and N,N-dimethylacetamide (DMAc) / lithium chloride (LiCl). The pulp may be in some embodiments dried and / or dewatered after the ozone treatment and prior to dissolving the cellulose as disclosed above. In some embodiments, the aim is to produce a composition comprising 50 to 60 wt-% of solvent, 20- 30 wt-% of aqueous solution, and 10-15 wt-% of treated pulp.

[0043] An advantage of the present invention is that the ozone treatment may allow easier removal of impurities and residual lignin from the treated pulp because the treatment loosens the fibrillar structure of cellulose and thus releasing impurities. Typically, impurities and residual lignin may be removed from the treated pulp by washing. Thus, in some embodiments the pulp is washed after the ozone treatment. In some examples, the solid matter remaining in the composition after the ozone treatment is separated from the liquid, and thereafter the solid matter may be washed. The separation maybe performed for example by filtration, pressing, or centrifugation. In some embodiments, the pulp is washed after the ozone treatment and before dissolving it as disclosed above.

[0044] Ozone treatment may lead to reduced pH of the treated pulp composition. Thus, the pulp may be, in some embodiments, treated with an alkaline compound or solution after ozone treatment. Such treatment allows adjusting the pH of the pulp to a desired level for example to a pH value that is needed in subsequent applications. Further, alkaline treatment may allow removal of at least part of hemicelluloses and other impurities of the pulp. Thus, an alkaline treatment of the pulp composition after the ozone treatment may be advantageous even in cases where the pH of the composition does not need to be increased for subsequent applications. In fact, performing the ozone treatment at pH of above 5, such as at neutral or alkaline pH, may be advantageous because the amountof alkaline needed to be added for removal of at least part of hemicelluloses and other impurities of the pulp is lower than when the pH is strongly acidic. The alkaline treatment may at least in some embodiments be an alkaline extraction or an alkaline wash, i.e. a wash or an extraction conducted at an alkaline pH. In some preferred embodiments the pulp does not substantially become derivatized, such as converted to alkali cellulose, during the treatment with an alkaline compound or solution. In some embodiments, the paper-grade pulp may be dried prior to the alkaline treatment.

[0045] It has been observed, that by adjusting the alkaline content during the alkaline treatment may allow controlling the amount of hemicellulose that is removed from the treated paper-grade pulp. Typically, five-carbon sugars, such as xylan, and degraded pulp polymers, dissolve from the pulp to alkali even at low alkaline concentrations. By contrast, glucomannan typically stays mainly intact, i.e. it does not dissolve in alkali at low alkaline concentrations. Presence of moderate amounts of glucomannan, for example together with other six-carbon sugars, is generally tolerated in the end product. It may even be advantageous to maximize the amount of glucomannan in the pulp composition for some applications. Glucomannan may at least in some cases behave similarly to cellulose during dissolving and / or regeneration steps in manufacturing of man-made cellulosic fibres, such as in lyocell process. Thus, using a paper-grade pulp comprising relatively high amounts of glucomannan may in some embodiments be preferable. In some embodiments, the paper-grade pulp may therefore be softwood kraft pulp. In some embodiments, the paper-grade pulp comprises at least 5 wt-%, preferably at least 6 wt-%, most preferably at least 6.5 wt-%, of glucomannan of the total amount of carbohydrates.

[0046] In some embodiments, the pulp may be treated in or with or in a solution comprising 1 to 40 g / L, preferably 20 to 30 g / L, of an alkaline compound, such as sodium hydroxide, white liquor and / or oxidized white liquor. In these conditions, a portion of hemicelluloses are removed while another portion remains in the treated pulp. In some embodiments, less than 30 wt-%, such as 2 to 25 wt-% or 5 to 20 wt-%, of hemicelluloses comprised in the treated pulp are removed during the alkaline treatment. This might be desired in some application, where a content of hemicelluloses within the pulp composition is desired or does not negatively affect the application. The alkaline treatment of pulp may be for example a wash with an alkaline solution comprising 1 to 40 g / L, preferably 20 to 30 g / L, of an alkaline compound.

[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 (or oxidized white liquor) are expressed as active alkali (AA, total amount of OH- and HS- ions) or effective alkali (EA, OH- ion concentration). As white liquor may be available at a kraft pulp mill or an integrated facility connected to a sulphate pulp mill the use of white liquor in the alkali treatment may bring substantial savings. The effective alkali of said white liquor or oxidized white liquor may be in the range of 1 to 40 g NaOH / L, preferably 20 to 30 g NaOH / L. Such effective alkali concentration may be obtained for example by diluting white liquor obtained from kraft pulp mill with a suitable solution, such as water.

[0048] In some cases, a considerable amount of hemicelluloses needs to be removed. This can be achieved by using higher alkaline amounts during the alkaline treatment. For example, in some embodiments the pulp may be subjected to cold caustic extraction or mercerization after the ozone treatment. Cold caustic extraction may be especially preferable treatment in some embodiments. The cold caustic extraction may be performed for example by treating the pulp with at least 40 g / L, such as at least 60 g / L of an alkaline compound, such as sodium hydroxide, white liquor, and / or oxidized white liquor. The effective alkali of said white liquor or oxidized white liquor may be at least 55 g NaOH / L, such as at least 70 g NaOH / L, such as at least 80 g NaOH / L. In some embodiments, the cold caustic extraction may be performed at a temperature of below 50 ° C, such as at a temperature of below 40 ° C or below 30 ° C. In some embodiments, the cold caustic extraction may be performed within 30 minutes, such as within 15 minutes. Cold caustic extraction may allow for example reducing the amount of short chain carbohydrates by dissolving them. At the high alkaline amounts used in CCE or mercerization considerable amount of hemicelluloses can be removed. In some embodiments, at least 30 wt-%, such as at least 40 wt-%, or at least 50 wt-%, of hemicelluloses comprised in the treated pulp are removed during the cold caustic extraction or mercerization.

[0049] In some embodiments, the paper-grade pulp may be washed with an acidic solution after the ozone treatment. A wash with an acidic solution may be needed for example to remove excess metal impurities from the paper-grade pulp. Removal of metal impurities may be especially important if the paper-grade pulp is subjected to a process for making man-made fibers. In some embodiments, the method disclosed herein comprises a step of washing the paper-grade pulp with an acidic solution after treatment with ozone, such as prior to dissolving the paper-grade pulp. Preferably, the pH of the acidic solution isbelow 2.5. In some embodiments, the paper-grade pulp is washed with an acidic solution until the paper-grade pulp comprises less than 5 ppm of iron, less than 2 ppm of copper and / or less than 2 ppm of manganese.

[0050] In some embodiments, the ozone treated pulp may be directed to a process for manufacturing man-made cellulosic fibres, such as to a lyocell process or a viscose process. Said process for manufacturing man-made cellulosic fibres may be a cellulose non-derivatizing process or a cellulose derivatizing process.

[0051] The process for manufacturing man-made cellulosic fibres may comprise cold caustic extraction or mercerisation of the treated fibres. Mercerisation may be especially advantageous if the process for manufacturing man-made cellulosic fibres is a viscose process.

[0052] In some embodiments process for manufacturing man-made cellulosic fibres may comprise dissolving the ozone treated pulp in an ionic liquid, in NMMO or in another non-derivatizing cellulose solvent. Examples of other non-derivatizing cellulose solvents have been given above.

[0053] In other embodiments, the treated pulp may be directed to a process for manufacturing cellulose derivatives. Cellulose derivates may include for example carboxy methyl cellulose (CMC), methyl hydroxyethyl cellulose (MHEC), ethyl hydroxyethyl cellulose (EHEC), cellulose acetate, hydroxy ethyl cellulose (HEC), hydroxypropyl methyl cellulose (HMCP), ethyl cellulose (EC), methyl cellulose, and cellulose acetate phthalate (CAP).

[0054] Another aspect of the present disclosure is pulp obtained by the method as disclosed herein. The intrinsic viscosity of the pulp is below 550 mL / g, for example in some embodiments the intrinsic viscosity of the pulp may be in the range of 200 to 500 mL / g.

[0055] In some embodiments, the poly dispersity index of the ozone treated pulp may be in the range of 3 to 7, such as in the range of 5.5 to 7. It may be possible to lower the poly dispersity index of the pulp by using an alkaline treatment as disclosed herein after the ozone treatment. This is because small carbohydrates may be removed from the pulp during the alkaline treatment. Thus, in some embodiments, the poly dispersity index of the pulp may be in the range of 3.5 to 5. Poly dispersity index (PDI) is used as a measure ofbroadness of molecular weight distribution. PDI of a polymer is calculated as the ratio of weight average by number average molecular weight. The ozone treatment disclosed herein allows producing pulp with a molecular weight distribution which is applicable for production of textile fibres. Both longer and shorter cellulosic fibres are typically needed for production of good quality textile fibres because longer fibres are stronger whereas shorter fibres dissolve easier and thus allow easier production of textile fibres.

[0056] In some embodiments, the ratio of glucomannan to xylan in the pulp obtained by the method disclosed herein may be in the range of 0.5 to 1.5. In some embodiments, the ratio of glucomannan to xylan may be larger than 0.9, such as larger than 1. The ratio of glucomannan to xylan may be affected for example by the initial amounts of these compounds in the paper-grade pulp and the selected treatment steps. For example, a mild alkaline treatment may selectively remove certain hemicelluloses from the ozone treated paper-grade pulp as explained above. Glucomannan may be at least in some embodiments be dissolved with similar solvents as cellulose and thus it does not cause issues in subsequent applications. For example, glucomannan may at least in some cases behave similarly to cellulose during dissolving and / or regeneration steps in manufacturing of manmade cellulosic fibres, such as in lyocell process. In some embodiments, the pulp may comprise at least 5.0 wt-% of glucomannan, preferably at least 6.0 wt-%, most preferred at least 6.5 wt-%. The amount of glucomannan in the pulp obtained by the method disclosed here may be in some embodiments at least 5.0 wt-%, preferably at least 6.0 wt-%, most preferred at least 6.5 wt-%. The glucomannan content can be calculated according to Janson, J (Calculation of the polysaccharide composition of wood and pulp. Pap Puu 1970, 52: 323-329). The sugar analysis, for example performed with a method based on sulfuric acid hydrolysis of the sample followed by chromatography (SCAN-CM 71 :09), only gives information on the constituent monosaccharides. Thus, to study quantitatively the behavior of polysaccharides during different processes, one may express the monosaccharides as polysaccharides. The suitable parameters for calculating the polysaccharide composition of the pulp from the sugar analysis can be selected as presented in the article by Janson, J., where the equation is named Poly 1. The equation is as follows:Pi = l-S / 100AA= 100-UNi=88(AR+XY) / AA+0.90(GA+GL+MA)Content of polysaccharides, % of sample:Xylan= 8800(AR+XY)Pi / (Ni*AA)Glucomannan=90(GA*M+MA*M+MA)Pi / (Ni*M) wherein:M= molar ratio of mannose: glucose in glucomannanGA=galactose content % of neutral sugarsGL=glucose content % of neutral sugarsMA=mannose content % of neutral sugarsXY=xylose content % of neutral sugarsAR=arabinose content % of neutral sugarsU= uronic acid in xylan, % of xylanS= Content of non-carbohydrates, extracts, lignin

[0057] Another aspect of the present disclosure is a pulp composition comprising at least 10 wt-% of hemicellulose of the dry weight of the pulp, wherein the intrinsic viscosity of the pulp is below 550 ml / g, at least 5 wt-% of the total carbohydrates in the pulp composition is glucomannan, and the poly dispersity index of the pulp is in the range of 3 to 7. In some embodiments, the intrinsic viscosity of the pulp composition may be adjusted to below 500 ml / g, such as to 200 -500 ml / g. In some embodiments, the poly dispersity index of the pulp composition may be in the range of 3.5 to 5. In some embodiments, the pulp composition may comprise at least 6.0 wt-%, preferably at least 6.5 wt-% of glucomannan of the total carbohydrates in the pulp composition.

[0058] In some embodiments, the ratio of glucomannan to xylose in the pulp composition may be larger than 0.9, preferably larger than 1.

[0059] In some embodiments, the pulp composition comprises less than 5 ppm of iron, less than 2 ppm of copper and / or less than 2 ppm of manganese. Such low metal content is especially important in a spinning process that uses NMMO as solvent.

[0060] Another aspect of the present disclosure is textile fibres produced from the pulp or pulp composition disclosed herein. In some preferred examples, the textile fibres may be produced with a lyocell process.

[0061] Yet, another aspect of the present disclosure is a textile product comprising textile fibres disclosed herein.Examples

[0062] Example 1

[0063] Bleached softwood kraft pulp (intrinsic viscosity 915 ml / g) was provided by a kraft pulp mill in the form of dry sheets. Ozone treatments were carried out to this pulp in two separate test points, test point 1 and test point 2.

[0064] An aqueous, homogeneous suspension was prepared of the pulp in 5 % consistency. The pH of water was adjusted to pH=9.1 in test point 1 and pH=8.3 in test point 2 before the suspension preparation. The initial pH of the suspension before reaction with ozone was pH=5.9 in test point 1 and pH=5.6 in test point 2, due to the slight acidity of the kraft pulp. After pulping, consistency was increased from 5 % to 10 %, in order to operate in medium consistency in following ozone treatment stage.

[0065] The medium consistency pulp was fed to a laboratory size reactor where it was treated with ozone. Temperature was close to room temperature (24 °C) and ozone consumption was 5.7 kg / bone dry ton (BDt) of pulp in test point 1 and 4.4 kg / BDt of pulp in test point 2. Final pH after the ozone treatment was pH=3.4 in test point 1 and pH=3.3 in test point 2. Finally, the pulp was washed, and intrinsic viscosity was measured to be 451 ml / g in test point 1 and 479 ml / g in test point 2. The obtained viscosities are on appropriate level especially in test point 1 when considering using the pulp in textile fibre spinning processes where direct dissolving methods are utilized.

[0066] Conditions used in the ozone treatment are shown in Table 1.

[0067] Table 1. Conditions used in the ozone treatment for two different test points.

[0068] Example 2

[0069] Similar ozone treatment was carried out for the same bleached softwood kraft pulp than in Example 1. The carbohydrate and lignin contents of the pulp before and after ozone treatment, as well as lignin content of the filtrate obtained after the ozone treatment, were analyzed according to Sluiter, A. et al. Results are presented in Table 2.

[0070] Table 2. Carbohydrate and lignin content of the pulp and ozone treatment filtrate.

[0071] From Table 2 it can be seen that ozone treatment did not have a significant effect on the carbohydrate content of the pulp. However, the lignin content in pulp, both acid soluble and insoluble lignin, decreased due to the ozone treatment. This was further demonstrated by the filtrate after ozone treatment also containing some lignin. Ozone attacking and removing the residual lignin in bleached kraft pulp can for example facilitate the dissolution of pulp in spinning dope preparation.

[0072] The determination of the molecular weight distribution of cellulose for the sample was made by a size exclusion chromatography system equipped with a molecularweight sensitive detector which allowed the determination of the absolute molecular weight values. As a molecular weight sensitive detector a low angle light-scattering and a viscosity detector were used in combination. For the sample analysis the system calibration taken place with polystyrol standards. Results of size exclusion chromatography (SEC) characterization:Number average molecular weight (Mn): 60 668 DaltonsWeight average molecular weight (Mw): 363 088 DaltonsRatio of Mw / Mn: 6.0

[0073] Example 3

[0074] Similar ozone treatment was carried out for the same bleached softwood kraft pulp than in Example 1. The ozone treated pulp was further processed in cold caustic extraction (CCE) treatment step. The ozone treated pulp was brought to contact with a 70 g / L sodium hydroxide solution in 40 °C temperature. The pulp suspension was mixed in 4 % consistency for 30 minutes. Next, the filtrate was removed by centrifuge. Finally, pulp was washed.

[0075] In Table 3, conditions of CCE and the analysis results of the ozone + CCE treated pulp are shown. Carbohydrate and lignin contents of pulp were analyzed according to Sluiter, A. et al. CCE treatment effectively removed xylan and this removal was mainly responsible for the yield loss in the process. Xylan removal can be beneficial when treated pulp is used in textile fibre spinning processes where direct dissolving methods are utilized. Also, content of acid soluble lignin was slightly further decreased. Moreover, the obtained intrinsic viscosity 398 mL / g is still on good level for these kinds of spinning processes.

[0076] Table 3. Conditions of CCE and analysis results of Z+CCE treated pulp.Results of size exclusion chromatography (SEC) characterization performed as disclosed above:Number average molecular weight (Mn): 61 706 DaltonsWeight average molecular weight (Mw): 224 604 DaltonsRatio of Mw / Mn: 3.6

[0077] Example 4

[0078] In another trial, bleached softwood kraft pulp treated with ozone as described in Example 1 was brought to contact with a 50 g / 1 sodium hydroxide solution in 40 °C temperature for 30 minutes (CCE treatment). The removal of hemicelluloses was lower than in previous runs. There were 90.3 wt-% glucose, 3.4 % of xylose, 6.3 wt-% mannose, 0.1 wt-% of arabinose and 0.1 wt-% of galactose remaining in the pulp after the CCE treatment (SCAN-CM 71 :09). The polysaccharide content calculated from sugar analyses (Janson, J. pulp. Pap Puu 1970, 52: 323-329, described in more detail above) resulted in 3.5 wt-% of xylan and 7.8 wt-% of glucomannan.

[0079] Example 5

[0080] In another trial, ozone treatment was carried out for the same type of bleached softwood kraft pulp than in Example 1. The ozone treated pulp was brought to contact with a 20 g / L sodium hydroxide solution at 30 °C to bring pulp into neutral pH and to wash the pulp. The removal of hemicelluloses was low. There was 87.1 wt-% of glucose, 7.1 wt-% of xylose and 5.7 wt-% mannose remaining in the pulp after the lowalkali treatment (SCAN-CM 71 :09). The polysaccharide content calculated from sugar analyses according to Janson, J. resulted in 7.2 wt-% of xylan and 7.1 wt-% of glucomannan.

[0081] Example 6

[0082] Ozone treatment was carried out for the same type of bleached softwood kraft pulp than in Example 1 in a larger scale in a medium consistency loop (MC-loop). While in examples 1-3 ozone was fed in 2-3 dosages, in the MC-loop the ozone feed was continuous and extended on a longer period of time.

[0083] A pulp suspension in approximately 7.6 % consistency was prepared directly to the MC-loop. Initial pH of the pulp suspension before reaction with ozone was pH=6.67. No pH adjustment of water nor the pulp suspension was made. Ozone was fed to the pulp suspension directly prior to chemical mixer. Temperature at the beginning of reaction was 20.9 °C and at the end of reaction 42.7 °C. Moreover, the consistency decreased during the reaction, the final consistency being 5.1 %. pH at the end of reaction was pH=3.42.

[0084] In total, 7.5 kg / BDt of pulp of ozone was consumed and obtained intrinsic viscosity was 445 ml / g. Thus, it could be demonstrated that ozone can work in intrinsic viscosity adjustment of kraft pulp also in MC-loop.

[0085] Conditions used in the ozone treatment in MC-loop are shown in Table 4.

[0086] Table 4. Conditions used in the ozone treatment in MC-loop.

[0087] Example 7

[0088] Determined cellulose parameters of the cellulose sample from Example 6

[0089] Content of a-cellulose: 82.9 wt-%. The content of a-cellulose was determined as the residue of pulp that is not dissolvable in 17.5 wt-% NaOH at 20°C.

[0090] Content of carbonyl groups: 85.7 pmol / g. Measured using absorbance at 530 nm.

[0091] Content of carboxyl groups: 22.9 pmol / g. Determined by complexometric titration.

[0092] Content of heavy metal ions as determined according to DIN EN ISO 11885:4.2 ppm Fe / <0.3 ppm Cu / 0.47 ppm Mn / 0.31 ppm Cr, 0.3 ppm Ni

[0093] The determination of the molecular weight distribution of cellulose was made by a size exclusion chromatography system equipped with a molecular weight sensitive detector which allowed the determination of the absolute molecular weight values. As a molecular weight sensitive detector a low angle light-scattering and a viscosity detector were used in combination. For the sample analysis the system calibration taken place with polystyrol standards. Results of size exclusion chromatography (SEC) characterization:Number average molecular weight (Mn): 51 484 DaltonsWeight average molecular weight (Mw): 348 662 DaltonsRati o of Mw / Mn : 6.8

[0094] Example 8

[0095] Spinning tests were carried out using the sample from experiment 2. The sample was diluted with NNMO solvent to prepare cellulose dope for the spinning. The prepared cellulose dopes were transferred in the laboratory spinning equipment, degassed, tempered and then regenerated by means of a dry-wet spinning process to fibres with a target fineness of 1.7 dtex. Typical spinning conditions were used and spinning worked without spinning failures. The fibre properties of the obtained fibres were determined according to DIN EN ISO 1973: 1995-12 (linear density), DIN EN ISO 5079 (tenacity and elongation at break). The textile-physical properties of the prepared fibres from spinningtests were at a good level. Linear density was 1.58 dtex, tenacity was 32.0 cN / tex and elongation at break was 10.3 %.

[0096] 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 the purpose of describing particular embodiments only and is not intended to be limiting.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] The verbs “to comprise” and “to include” are used in this document as open limitations 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.

[0102] ACRONYMS LISTAR arabinose content % of neutral sugarsCAP cellulose acetate phthalateCMC carboxy methyl celluloseCCE Cold caustic extractionDABCO l,4-diazabicyclo[2.2. 2]octaneEC ethyl celluloseEHEC ethyl hydroxyethyl celluloseGA galactose content % of neutral sugarsGL glucose content % of neutral sugarsHEC hydroxy ethyl celluloseHMCP hydroxypropyl methyl celluloseM molar ratio of mannose: glucose in glucomannanMA mannose content % of neutral sugarsMC-loop medium consistency loopMHEC methyl hydroxyethyl celluloseNMMO N-methylmorpholine N-oxideOWL oxidized white liquor PDI Poly dispersity indexU uronic acid in xylan, % of xylanWL white liquorXY xylose content % of neutral sugars CITATION LISTNon Patent LiteratureJanson, J. Calculation of the polysaccharide composition of wood and pulp. Pap Puu 1970, 52: 323-329. Sluiter, A., Hames, B., Ruiz, R., Scarlata, C., Sluiter, J., Templeton, D., Crocker, D. (2012) Determination of Structural Carbohydrates and Lignin in Biomass Laboratory Analytical Procedure (LAP). NREL.

Claims

CLAIMS:

1. A method comprising treating a composition comprising paper-grade pulp with ozone to adjust intrinsic viscosity of the paper-grade pulp to below 550 ml / g, wherein the paper grade-pulp comprises at least 10 wt-% of hemicellulose of the dry weight of the papergrade pulp, and the pH of the composition is at least 5.5 at the beginning of the treatment.

2. The method according to claim 1, wherein the temperature during the ozone treatment is in the range of 10 to 80 °C, preferably in the range of 15 to 60 °C, most preferably in the range of 20 to 40 °C.

3. The method according to claim 1 or 2, wherein the consistency of the composition comprising paper-grade pulp is adjusted to 8-14 %, preferably to 9-13 %, most preferably to 10-12 %, prior to treating the composition with ozone.

4. The method according to any of the preceding claims, wherein the paper-grade pulp is pulp from kraft process.

5. The method according to any of the preceding claims, wherein the intrinsic viscosity of the composition comprising paper-grade pulp is at least 700 ml / g prior to the adjustment.

6. The method according to any of the preceding claims, wherein the paper-grade pulp comprises at least 15 wt-%, preferably at least 17 wt-% of hemicellulose of the dry weight of the paper-grade pulp.

7. The method according to any of the preceding claims, wherein the pH of the composition at the beginning of the treatment is at least 7, preferably to at least 9.

8. The method according to any of the preceding claims, wherein the intrinsic viscosity is adjusted at a pH in the range from 5.5 to 7.

9. The method according to any of the preceding claims, wherein the intrinsic viscosity of the paper-grade pulp is adjusted to below 500 ml / g, such as to 200-500 ml / g.

10. The method according to any of the preceding claims, wherein the amount of ozone during the treatment is in the range of 3 to 10 kg of ozone per 1000 kg of pulp dry weight.

11. The method according to any of the preceding claims, wherein the ozone treatment is performed within 30 seconds, preferably within 10 seconds, most preferably within 5 seconds.

12. The method according to any of the preceding claims, wherein the ozone treatment is performed multiple times, for example 2 to 5 times.

13. The method according to any of the preceding claims, wherein the ozone treatment is performed at a pressure below 10 bars, such as at a pressure in the range of 4 to 7 bar.

14. The method according to any of the preceding claims, wherein the paper-grade pulp is dissolved after the ozone treatment, preferably the pulp is dissolved in an ionic liquid, N- methylmorpholine N-oxide (NMMO), in another non-derivatizing cellulose solvent or mixtures thereof.

15. The method according to any of the preceding claims, wherein the method further comprises treating the paper-grade pulp with an alkaline compound or solution after the ozone treatment.

16. The method according to any of the preceding claims, wherein the paper-grade pulp is treated with or in a solution comprising 1 to 40 g / L, preferably 20 to 30 g / L, of an alkaline compound, such as sodium hydroxide, white liquor and / or oxidized white liquor, after the ozone treatment.

17. The method according to any of the claims 1-15, wherein the paper-grade pulp is subjected to cold caustic extraction or mercerization after the ozone treatment.

18. The method according to any of the preceding claims, wherein the paper-grade pulp is directed to a process for manufacturing man-made cellulosic fibres, such as to a lyocell process or a viscose process after the ozone treatment.

19. The method according to any of claims 1 to 17, wherein the ozone treated pulp is directed to a process for manufacturing cellulose derivatives, such as carboxy methyl cellulose (CMC) or methyl hydroxyethyl cellulose (MHEC) or ethyl hydroxyethyl cellulose (EHEC), or cellulose acetate.

20. Pulp obtained by the method according to any of the preceding claims.

21. The pulp according to claim 20, wherein the poly dispersity index of the pulp is in the range of 3 to 7, preferably in the range of 3.5 to 5.

22. A pulp composition comprising at least 10 wt-% of hemicellulose of the dry weight of the pulp, wherein the intrinsic viscosity of the pulp is below 550 ml / g, the pulp comprises at least 5 wt-% of glucomannan, and the poly dispersity index of the pulp is in the range of3 to 7.

23. The pulp composition according to claim 22, wherein the intrinsic viscosity of the pulp is below 500 ml / g, such as 200 -500 ml / g.

24. The pulp composition according to claim 22 or 23, wherein the ratio of glucomannan to xylose in the pulp is larger than 0.9, preferably larger than 1.

25. The pulp composition according to any of the claims 22 to 24, wherein the poly dispersity index of the pulp is in the range of 3.5 to 5.

26. Textile fibres produced from the pulp or pulp composition according to claim 20-25.

27. A textile product comprising textile fibres according to claim 26.

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