Dried non-derivatized cellulosic fibrous material and method for producing the same

Abstract

According to an example aspect of the present invention, there is provided a dried non-derivatized cellulosic fibrous material, comprising non-derivatized cellulosic fibres having a water retention value of at least 1.0 g water / g pulp, curl-% less than 20 % and curl-% / width ratio less than 1.0.

Description

TITLEDried non-derivatized cellulosic fibrous material and method for producing the sameFIELD

[0001] The present invention relates to cellulosic fibres. Particularly, the present invention relates to a dried non-derivatized cellulosic fibrous material and a method for treating a cellulosic fibrous material with a deep eutectic solvent (DES), and use of a deep eutectic solvent as an aid in a pulp manufacturing process.BACKGROUND

[0002] Dry kraft pulp is an excellent starting material for production of various wood fibre-based products. Drying of pulp enables its cost-efficient transportation and long storage time. Pulp fibres have, however, a tendency to aggregate and lose fibre wall porosity or openness upon drying. This is explained for instance by homification (Stone, J.E.; Scallan A.M.). Changes are (partially) irreversible, with each rewetting-drying cycle causing more closing of the fibre.

[0003] Mechanical refining is the most used industrial process to recover the fibre wall porosity. The more closed the fibre structure is, the more difficult and energy-intensive the refining is. Closed fibre structure also decreases accessibility and ability of the fibres to absorb water. The accessibility of monomeric or polymeric chemicals into fibres is also decreased by closed fibre structure.

[0004] Treatment with an alkali, such as NaOH, swells the pulp fibre wall structure as the increased osmotic pressure disrupts the hydrogen bonding between fibrils forming the fibre wall. Simultaneously, hemicellulose that keeps the fibre wall open due to its charge is extracted from the fibres in the alkaline treatment. The content of charged groups in hemicellulose is the dominant factor of the swelling behaviour of the fibres (Laine, J.; Stenius, P.). Thus, removal of hemicellulose from pulp results in increased homification of fibres during drying, and when rewetted, the swelling of the fibre wall is clearly lower than in never-dried pulp or in dried hemicellulose-retaining pulp fibres (Lund et al.). Alkaline treatment also increases the curliness of pulp fibres and thus reduces the length of pulp fibres.

[0005] Hence, methods that keep the fibre structure open over a drying cycle would be beneficial in many respects. Potential applications benefitting from open fibre structureinclude e.g. paper and paperboard making, 3D molding, man-made cellulose fibre production, and cellulose derivate synthesis.

[0006] It is an aim of embodiments of the present invention to overcome at least some of the disadvantages of the prior art.SUMMARY OF THE INVENTION

[0007] An aim of the present invention is to provide a dried cellulosic fibrous material, which is energy-efficient to refine. A further aim is to provide a dried cellulosic fibrous material, which has straighter fibres having more open cell wall structure when redispersed in water, as compared with pulp fibres from typical pulping processes.

[0008] The invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims.

[0009] According to a first aspect of the present invention, there is provided dried cellulosic fibrous material comprising non-derivatized cellulosic fibres having a water retention value of at least 1.0 g water / g pulp, curl-% less than 20 % and curl-% / width ratio less than 1.0.

[0010] One or more embodiments may comprise one or more features from the following itemized list:- the water retention value is at least 1.5 g water / g pulp, such at least 2.0 g water / g pulp- curl-% / length ratio is less than 11.0, such as less than 10.5- the non-derivatized cellulosic fibres have a length of more than 0.5 mm- the non-derivatized cellulosic fibres have a width of more than 5 pm- the non-derivatized cellulosic fibres have a tensile index of at least 80 Nm / g, such as at least 130 Nm / g- the curl-% is determined according ISO 16065-2 standard- the non-derivatized cellulosic fibres are capable of being refined according to EN ISO 5264-2: 12 by revolutions of 2000 to a tensile index of at least 80 Nm / g

[0011] According to a second aspect of the present invention, there is provided a method comprising:- providing a cellulosic fibrous material in the form of an aqueous suspension;- adding an amount of a deep eutectic solvent in non-derivatizing conditions to the aqueous suspension, to obtain a mixture comprising the cellulosic fibrous material, water and the deep eutectic solvent; and- drying the obtained mixture.

[0012] One or more embodiments may comprise one or more features from the following itemized list:- the cellulosic fibrous material originates from a pulp production process- the cellulosic fibrous material comprises a never-dried pulp- said providing step comprises suspending dry cellulosic fibres or dry pulp to water, to obtain an aqueous suspension- the consistency of said aqueous suspension is at least 0.5 %, such as 1 to 40 %, such as 2 to 20 %- the deep eutectic solvent is not capable of derivatizing cellulose- the deep eutectic solvent consists of a non-derivatizing deep eutectic solvent- the deep eutectic solvent preferably consists of a mixture of choline chloride and urea, choline chloride and imidazole, ammonium thiocyanate and urea, guanidine hydrochloride and urea or choline chloride and dimethylurea- the obtained mixture comprises at least 0.1 %, such as at least 1 %, for example 5 to 50 % of the deep eutectic solvent calculated from the total volume of water- the obtained mixture comprises less than 70 %, such as less than 50 %, such as less than 30 %, of the deep eutectic solvent calculated from the total volume of water- the consistency of the obtained mixture is 0.5-30 %, such as 2-10 %- the method further comprises dewatering the mixture, for example by filtering, pressing, or a combination thereof, to obtain a dewatered mixture- said drying is carried out in a temperature of at least 50 °C, such as 50 to 100 °C, preferably in ambient pressure- said adding and drying steps are carried out in a temperature of less than 120 °C- after said drying, the water content of the mixture is less than 15 wt-%, calculated from the total weight of the mixture- after said drying, the fibres are non-derivatized- after said drying and after subsequent redispersing in water, the water retention value of the fibres is at least 1.0 g water / g pulp, for example, at least 1.2 or at least 1.5 g water / g pulp- after said drying, the tensile index of the fibres is at least 15 Nm / g, preferably at least 20 Nm / g- as a result of the method, refinability of the fibres of the pulp is improved- as a result of the method, the fibres are capable of being refined according to EN ISO 5264-2:12 by revolutions of 2000 to a tensile index of at least 80 Nm / g

[0013] According to a third aspect of the present invention, there is provided a dried cellulosic fibrous material, obtained by the said method.

[0014] According to a fourth aspect of the present invention, there is provided use of a deep eutectic solvent as an aid in a pulp manufacturing process, particularly in a drying step of a pulp manufacturing process, wherein the pulp is destined to be used as a raw material in a paperboard manufacturing process or in a nanocellulose manufacturing process.

[0015] Advantages of embodiments

[0016] A dried and structurally open fibre may have potential for various applications.

[0017] For instance, some embodiments may reduce consumption of energy that is needed for refining the fibres, typically in paperboard and tissue paper applications. With the same consumption of refining energy and defined for example, as revolutions in Papirindustriens forskningsinstitut (PFI) refining according to EN ISO 5264-2:12, a higher strength can be obtained without excess increase in fines content or in density.

[0018] The present dried fibres with an open fibre structure may offer benefits for subsequent chemical modification through improved accessibility of fibres for modification chemicals.

[0019] The present dried fibres may be suitable as such for certain hygiene products where high absorption capacity is needed.

[0020] The present dried fibres may even allow feasible production of nanocellulose by using the dried fibres as the starting material.

[0021] In some embodiments, the present method may open the fibre structure by internal fibrillation as measured by water retention values (WRV). The fibres obtained by the method may even retain their open structure over drying.

[0022] The fibres obtained by the method may be straighter than untreated fibres and thus may have fewer kinks, i.e. their curl-% is lower.

[0023] The fibres obtained by the method may simultaneously be, after drying, straight and have an open structure and good refinability.EMBODIMENTS

[0024] In the present context, the term “deep eutectic solvent” (DES) refers to solutions of Lewis or Bronsted acids and bases, which form a eutectic mixture having a complex hydrogen-bonding network having a hydrogen bond donor and a hydrogen bond acceptor. The DES is waterless and inert.

[0025] In the present context, the term “non-derivatizing condition” refers to a condition, wherein there is no chemical bonds, such as ester bonds, between a deep eutectic solvent or its components and a fibre.

[0026] In the present context, the term “dried” refers to material, which has a water content less than 20 wt-%, preferably less than 15 wt-%, more preferably less than 10 wt-%, calculated from the total weight of the material.

[0027] In the present context, the term “water retention value” (WRV) refers to an ability of a sample of wood fibre or pulp mass to retain water. The value can be determined according to ISO 23714:2014. It is a ratio of a mass (weight) of water retained after centrifugation under specified conditions by a wet pulp sample to the oven dry mass (weight) of the same pulp sample. The WRV-value increases with increasing beating because of internal fibrillation, a widening of the small internal pores and delamination, which has been called ’’swelling” and which occurs concurrently with the development of external fibrils, which also serve to hold additional water (Scandinavian Pulp, Paper and Board Testing Committee).

[0028] In the present context, the term “curl-%” refers to a curl index, which is a length-weighted average fibre curl percentage. Curl-% of fibres can be determined by FS5 analysis carried out in compliance with ISO 16065-2 standard.

[0029] In the present context, the term “never-dried pulp” refers to a pulp, which has not been dried to a dry-matter content higher than 50 wt-% after pulping, such as the chemical cooking.

[0030] The present embodiments describe dried non-derivatized cellulosic fibres with an open structure, their preparation with a treatment in water containing deep eutectic solvent preceding drying, and potential applications.

[0031] According to an aspect, there is provided a dried non-derivatized cellulosic fibrous material, comprising non-derivatized cellulosic fibres having a water retention value (WRV) of at least 1.0 g water / g pulp, curl-% less than 20 % and curl-% / width ratio less than 1.0.

[0032] The present cellulosic fibrous material preferably has an open fibre structure. This is indicated by the higher WRV level compared with pulp fibres from typical pulping processes. So, the present fibres may have a higher degree of internal fibrillation than the pulp fibres from typical pulping processes. Thus, a consumption of energy that is needed for refining the fibres, typically in paperboard and tissue paper applications, is reduced. With the same consumption of refining energy, higher strength can be obtained without excess increase in fines or density. The fibres are typically straighter than the pulp fibres from typical pulping processes and thus may have fewer kinks, i.e. their curl-% is lower. Surprisingly, openness in the fibre structure, straightness of the fibres and higher refinability was not lost upon drying, but all these features can be maintained at the same time. The obtained cellulosic fibrous material may offer benefits for chemical modification through improved accessibility and may be suitable as such for certain hygiene products where absorption is needed.

[0033] The water retention value (WRV) can be at least 1.5 g water / g pulp, such as 2.0 g water / g pulp.

[0034] The non-derivatized cellulosic fibres can have a length of more than 0.5 mm. By “length” it is meant the greatest dimension of the fibre. The length can be measured for example, by optical methods, such as by FS5 fibre analyser in compliance with ISO 16065- 2 standard.

[0035] The non-derivatized cellulosic fibres can have a width of more than 5 pm. By “width” it is meant the dimension perpendicular to the greatest dimension, i.e. the length. The width can be measured for example by optical methods, such as by FS5 fibre analyser in compliance with ISO 16065-2 standard.

[0036] Curl-% / width ratio can be determined by curl-% of the non-derivatized cellulosic fibres and width of the said non-derivatized cellulosic fibres.

[0037] Curl-% / length ratio can be less than 11.0, such as less than 10.5.

[0038] Curl-% / length ratio can be determined by curl-% of the non-derivatized cellulosic fibres and width of the said non-derivatized cellulosic fibres.

[0039] The non-derivatized cellulosic fibres of the dried non-derivatized cellulosic fibrous material can have a tensile index of at least 80 Nm / g, such as at least 130 Nm / g.

[0040] The non-derivatized cellulosic fibres of the dried non-derivatized cellulosic fibrous material can have Scott Bond value of at least 80 Nm / g, such as at least 130 Nm / g.

[0041] Tensile index and Scott Bond can be measured using standard methods ISO 1924-2 and TAPPI T569.

[0042] The cellulosic fibre of the dried non-derivatized cellulosic fibrous material can be capable of being refined according to EN ISO 5264-2:12 by revolutions of 2000 to a tensile index of at least 80 Nm / g.

[0043] According to another aspect, there is provided method comprising:- providing a cellulosic fibrous material in the form of an aqueous suspension;- adding an amount of a deep eutectic solvent in non-derivatizing conditions to the aqueous suspension, to obtain a mixture comprising the cellulosic fibrous material, water and the deep eutectic solvent; and- drying the obtained mixture.

[0044] The method enables achieving open and straight fibres by preparation the fibres with a treatment in water comprising a non-derivatizing deep eutectic solvent (DES) preceding drying. Thus, with the same consumption of refining energy, higher strength can be obtained without excess increase in fines or density. The fibres obtained by the method are typically straighter than the untreated fibres and thus may have fewer kinks, i.e. their curl-% is lower. Surprisingly, openness in the fibre structure, straightness of the fibres and high strength was not lost upon drying, but all these features are maintained at the same time. In addition, the fibres produced by the present method may offer benefits for chemical modification through improved accessibility and may be suitable as such for certain hygiene products where absorption is needed.

[0045] In some embodiments, the cellulosic fibrous material comprises cellulosic fibres from perennial plants, such as wood, for example 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 thereof. The cellulosic fibres may be also made from any conifer such as spruce or pine or from any combination thereof. The cellulosic fibres may be also made from a combination of broadleaved trees and conifers.

[0046] In some embodiments, the cellulosic fibrous material comprises at least 80 wt- %, such as at least 90 wt-%, cellulosic fibres from wood, calculated from the total dry weight of the material. The cellulosic fibrous material can comprise cellulosic fibres from annual plants, such as straw, common reed, reed canary grass, bamboo, sugarcane, bagasse or any other grass plant.

[0047] In some embodiments, the cellulosic fibrous material comprises pulp fibres from typical pulping processes.

[0048] The cellulosic fibrous material can originate from a pulp production process.

[0049] The cellulosic fibrous material can originate from a process in which a woodbased material, such as wood chips and / or sawdust, are treated with a conventional pulp production process to produce the cellulosic fibrous material.

[0050] The pulp production process can comprise cooking with a hot mixture of water, sodium hydroxide and sodium sulphide, washing, bleaching and optionally drying.

[0051] The cellulosic fibrous material may comprise pulp, such as paper-grade pulp. The cellulosic fibrous material may comprise at least 50 wt-%, such as at least 80 wt-%, such as at least 90 wt-% of pulp, such as paper-grade pulp, such as kraft pulp, calculated from the total dry weight of the material.

[0052] The pulp may be selected from the following group: kraft pulp, sulphite pulp, chemi-thermomechanical pulp, thermomechanical pulp, mechanical pulp, and any combinations thereof.

[0053] Preferably, the cellulosic fibrous material comprises kraft pulp.

[0054] In an embodiment, the cellulosic fibrous material does not substantially comprise any nanostructured or microstructured cellulose, such as microfibrillated cellulose, nanofibrillated cellulose, cellulose microfibrils and cellulose nanofibrils. In an embodiment, the cellulosic fibrous material comprises less than 5 wt-%, such as less than 1 wt-% of nanostructured or microstructured cellulose, calculated from the total dry weight of the material.

[0055] Preferably, the cellulosic fibrous material can comprise a never-dried pulp. The never-dried pulp has not been dried during or after the pulp production process and thus has a higher water content than a dried pulp. For example, the never-dried pulp can have a water content more than 10 wt-%. In an embodiment, the cellulosic fibrous material comprises at least 50 wt-%, such as at least 80 wt-%, such as at least 90 wt-% of never-dried pulp, calculated from the total dry weight of the material.

[0056] Alternatively or additionally, the cellulosic fibrous material can comprise a dried pulp. For example, the dried pulp can have a water content less than 10 wt-%. In an embodiment, the cellulosic fibrous material comprises less than 20 wt-%, such as less than 5 wt-% of dried pulp, calculated from the total dry weight of the material.

[0057] The never-dried pulp or the dried pulp can be a softwood or hardwood pulp.

[0058] The consistency of said aqueous suspension can be at least 0.5 %, such as 1 to40 %, such as 2 to 20 %.

[0059] In the present method, said providing step can comprise suspending dry cellulosic fibres or dry pulp to water, to obtain an aqueous suspension.

[0060] The method can comprise adding the deep eutectic solvent (DES) as liquid.

[0061] The DES can be formed by weighing DES components in a beaker, mixing theDES components and creating a DES mixture from the mixed DES components. The DES mixture can be created in an oven at a temperature of 100 °C. After that, the DES mixture can be heated. The DES mixture can be heated in an oil bath. The heating can be carried out at a temperature of 100 °C for 4 h.

[0062] Preferably, the deep eutectic solvent is not capable of derivatizing cellulose.

[0063] Preferably, the deep eutectic solvent consists of a non-derivatizing deep eutectic solvent.

[0064] For example, the DES can be a mixture of choline chloride and urea, choline chloride and imidazole, ammonium thiocyanate and urea, guanidine hydrochloride and urea, choline chloride and dimethylurea or other such non-derivatizing DES systems.

[0065] The obtained mixture can comprise at least 0.1 %, such as at least 1 %, for example 5 to 50 % of the deep eutectic solvent calculated from the total volume of water.

[0066] The obtained mixture comprises less than 70 %, such as less than 50 %, such as less than 30 % of the deep eutectic solvent calculated from the total volume of water.

[0067] The consistency of the obtained mixture can be 0.5-30 %, such as 2-10 %.

[0068] Said adding step can comprise mixing the cellulosic fibrous material, water and the DES. The mixing can be carried by using of a pump or a mixer, such as a static mixer or dynamic mixer. The cellulosic fibrous material, water and the DES can be mixed for example, up to 30 min. The mixing can be carried out in a temperature of less than 90 °C.

[0069] Before said drying step, the method can further comprise dewatering the mixture, for example by filtering, pressing, or a combination thereof, to obtain a dewatered mixture. By “dewatering”, it is meant removing at least some of the water from the mixture. Thus, most of the water can be removed by the filtering, and as a result the subsequent drying of the mixture takes less time.

[0070] After said dewatering and / or before said drying, the cellulosic fibrous material can be washed with deionized water. The washing can be carried out for example, three times.

[0071] Said drying can be carried out in a temperature of at least 50 °C, such as 50 to 100 °C, preferably in ambient pressure.

[0072] Said adding and drying steps can be carried out in a temperature of less than 120 °C.

[0073] After said drying, the water content of the mixture can be less than 15 wt-%, calculated from the total weight of the mixture.

[0074] After said drying, the fibres can be non-derivatized.

[0075] After said drying and after subsequent redispersing in water, the water retention value of the fibres can be at least 1.0 g water / g pulp, for example at least 1.2 g water / g pulp or at least 1.5 g water / g pulp.

[0076] After said drying, tensile index of the fibres can be at least 15 Nm / g, preferably at least 20 Nm / g.

[0077] After said drying, Scott Bond of the fibres can be at least 80 Nm / g’ such as at least 130 Nm / g.

[0078] As a result of the method, refinability of the fibres of the pulp can be improved.

[0079] As a result of the method, the fibres can be capable of being refined according to EN ISO 5264-2: 12 by revolutions of 2000 to a tensile index of at least 80 Nm / g.

[0080] The method can further comprise refining said fibres according to EN ISO 5264-2: 12 after said drying, preferably with revolutions of 2000 to a tensile index of at least 80 Nm / g.

[0081] According to another aspect, a dried cellulosic fibrous material is obtained by the method as described above.

[0082] According to another aspect, there is provided use of a deep eutectic solvent as an aid in a pulp manufacturing process, particularly in a drying step of a pulp manufacturing process, wherein the pulp is destined to be used as a raw material for example, in a paperboard manufacturing process or in a nanocellulose manufacturing process.

[0083] The DES can be used for improving water retention values of fibres of the pulp.EXAMPLESExample 1

[0084] In this example, never-dried bleached softwood kraft pulp was treated in aqueous system containing different DES-water ratios using a DES consisting of choline chloride and urea. Never-dried pulp was first dispersed to water. DES formed of choline chloride and urea with molar ratio of 2:1 was prepared by weighing choline chloride and urea (the DES components) in a beaker, mixing the DES components, and creating a DESmixture in an oven at 100 °C. The DES mixture was then heated in an oil bath at 100 °C for 4 h. A needed amount of DES was added to the pulp dispersion to obtain samples with DES- water volume ratios of 10:90, 30:70 and 70:30. Samples were thereafter mixed at 80 °C for 30 min. Reference sample was treated similarly but without DES addition. The treated samples were filtrated and thereafter dried at 80 °C overnight. The dried samples were disintegrated (redispersed) to water according to EN ISO 5264-2:12 and water retention value (WRV) was measured from the disintegrated pulp samples, see Table 1 below. FS5 analysis was carried out in compliance with ISO 16065-2 standard to determine curl-% of the fibres.Table 1. Water retention values (WRV) and curl-% of the disintegrated pulp samples.

[0085] Surprisingly, even the lowest addition of 10 % of choline chloride-urea DES to the aqueous pulp suspension treatment before drying increased the WRV of dried and redispersed pulp considerably. In unrefined pulps, both fibre porosity and fines content are contributing to WRV. As no increase of fines content was observed in the pulps treated with choline chloride-urea addition by FS5 analysis in compliance with ISO 16065-2 standard, it can be concluded that the fibres of these pulps were more open, or less homified, after the drying as compared with the reference pulp fibres.Example 2

[0086] The pulps prepared as explained in Example 1 were PFI refined and handsheets were prepared from the refined pulps according to EN ISO 5264-2:12. WRV was measured from the refined pulps. Tensile index and Scott Bond, which is a measure of internal bonding strength of paper, were measured from the handsheets using standard methods ISO 1924-2 and TAPPI T569.

[0087] Surprisingly, it was found that the DES-treated and subsequently dried pulps were easier to refine as compared with the reference pulp. Less refining, i.e. revolutions (revs), was needed to reach the same tensile index and Scott Bond levels as compared with the reference pulp. Ae higher WRV level was retained over the refining, which indicates that the openness of the fibres was retained.Table 2. Water retention value (WRV) of the refined pulps, and tensile index and Scott Bond of the handsheets.

[0088] 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.

[0089] Reference throughout this specification to “one embodiment” or “anembodiment” 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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 otherwiseexplicitly 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

[0094] The present invention is industrially applicable at least in manufacturing of fibrous compositions.ACRONYMS LISTDES deep eutectic solventCC1 choline chlorideWRV water retention valuePFI Papirindustriens forskningsinstitutCITATION LISTStone, J.E.; Scallan A.M. The Influence of Drying on the Pore Structure of the Cell Wall. 1965. Consolidation of the Paper Web, Trans, of the Hird Fund. Res. Symp. Cambridge, 1965, (F. Bolam, ed.), pp 145-166, FRC, Manchester, 2018.Joutsimo, O. 2004. Effect of Mechanical Treatment on Softwood Kraft Fibre Properties.Available: http: / / lib.tkk.fi / Diss / 2004 / isbn9512274450 / isbn9512274450.pdfScandinavian Pulp, Paper and Board Testing Committee. 2000. Water Retention Value. SCAN-C 62:00.Lund et al. J. Engineered Fibers and Fabrics, Vol 7, Issue 2 - 2012.Laine, J.; Stenius, P.; Effect of charge on the fiber and paper properties of bleached industrial kraft pulp, Paperi Puu 1997, 79, No 4, 257-266.

Claims

CLAIMS:

1. A dried non-derivatized cellulosic fibrous material, comprising non-derivatized cellulosic fibres having a water retention value of at least 1.0 g water / g pulp, curl-% less than 20 % and curl-% / width ratio less than 1.0.

2. The dried non-derivatized cellulosic fibrous material of claim 1, wherein the water retention value is at least 1.5 g water / g pulp, such as at least 2.0 g water / g pulp.

3. The dried non-derivatized cellulosic fibrous material of any one of the preceding claims, wherein curl-% / length ratio is less than 11.0, such as less than 10.5.

4. The dried non-derivatized cellulosic fibrous material of any one of the preceding claims, wherein the non-derivatized cellulosic fibres have a length of more than 0.5 mm.

5. The dried non-derivatized cellulosic fibrous material of any one of the preceding claims, wherein the non-derivatized cellulosic fibres have a width of more than 5 pm.

6. The dried non-derivatized cellulosic fibrous material of any one of the preceding claims, wherein the non-derivatized cellulosic fibres have a tensile index of at least 80 Nm / g, such as at least 130 Nm / g.

7. The dried non-derivatized cellulosic fibrous material of any one of the preceding claims, wherein the curl-% is determined according ISO 16065-2 standard.

8. The dried non-derivatized cellulosic fibrous material of any one of the preceding claims, wherein the non-derivatized cellulosic fibres are capable of being refined according to EN ISO 5264-2: 12 by revolutions of 2000 to a tensile index of at least 80 Nm / g.

9. A method comprising:- providing a cellulosic fibrous material in the form of an aqueous suspension;- adding an amount of a deep eutectic solvent in non-derivatizing conditions to the aqueous suspension, to obtain a mixture comprising the cellulosic fibrous material, water and the deep eutectic solvent; and- drying the obtained mixture, to obtain a dried non-derivatized cellulosic fibrous material.

10. The method of claim 9, wherein the cellulosic fibrous material originates from a pulp production process.

11. The method of any one of the preceding claims 9 to 10, wherein the cellulosic fibrous material comprises a never-dried pulp.

12. The method of any one of the preceding claims 9 to 11, wherein said providing step comprises suspending dry cellulosic fibres or dry pulp to water, to obtain an aqueous suspension.

13. The method of any one of the preceding claims 9 to 12, wherein the consistency of said aqueous suspension is at least 0.5 %, such as 1 to 40 %, such as 2 to 20 %.

14. The method of any one of the preceding claims 9 to 13, wherein the deep eutectic solvent is not capable of derivatizing cellulose.

15. The method of any one of the preceding claims 9 to 14, wherein the deep eutectic solvent consists of a non-derivatizing deep eutectic solvent, preferably one of the following mixtures: choline chloride and urea, choline chloride and imidazole, ammonium thiocyanate and urea, guanidine hydrochloride and urea, and choline chloride and dimethylurea.

16. The method of any one of the preceding claims 9 to 15, wherein the obtained mixture comprises at least 0.1 %, such as at least 1 %, for example 5 to 50 % of the deep eutectic solvent calculated from the total volume of water.

17. The method of any one of the preceding claims 9 to 16, wherein the obtained mixture comprises less than 70 %, such as less than 50 %, such as less than 30 % of the deep eutectic solvent calculated from the total volume of water.

18. The method of any one of the preceding claims 9 to 17, wherein the consistency of the obtained mixture is 0.5-30 %, such as 2-10 %.

19. The method of any one of the preceding claims 9 to 18, further comprising dewatering the mixture, for example by filtering, pressing, or a combination thereof, to obtain a dewatered mixture.

20. The method of any one of the preceding claims 9 to 19, wherein said drying is carried out in a temperature of at least 50 °C, such as 50 to 100 °C, preferably in ambient pressure.

21. The method of any one of the preceding claims 9 to 20, wherein said adding and drying steps are carried out in a temperature of less than 120 °C.

22. The method of any one of the preceding claims 9 to 21, wherein after said drying, the water content of the mixture is less than 15 wt-%, calculated from the total weight of the mixture.

23. The method of any one of the preceding claims 9 to 22, wherein after said drying, the cellulosic fibres are non-derivatized.

24. The method of any one of the preceding claims 9 to 23, wherein after said drying and after subsequent redispersing in water, the water retention value of the cellulosic fibres is at least 1.0 g water / g pulp, for example, at least 1.2 or at least 1.5 g water / g pulp.

25. The method of any one of the preceding claims 9 to 24, wherein after said drying, the tensile index of the cellulosic fibres is at least 15 Nm / g, preferably at least 20 Nm / g.

26. The method of any one of the preceding claims 9 to 25, wherein as a result of the method, refinability of the cellulosic fibres of the pulp is improved.

27. The method of any one of the preceding claims 9 to 26, wherein as a result of the method, the cellulosic fibres are capable of being refined according to EN ISO 5264-2:12 by revolutions of 2000 to a tensile index of at least 80 Nm / g.

28. A dried cellulosic fibrous material, obtained by the method according to any of the preceding claims 9 to 27.

29. Use of a deep eutectic solvent as an aid in a pulp manufacturing process, particularly in a drying step of a pulp manufacturing process, wherein the pulp is destined to be used as a raw material for example, in a paperboard manufacturing process or in a nanocellulose manufacturing process.

30. The use of claim 29, for improving water retention value of cellulosic fibres of the pulp.

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