Method for modifying fibrous materials

Abstract

According to the present invention, there is provided a method for modifying fibrous materials using a polymer. Likewise, the invention describes the materials thus obtained, and the use of said materials in the manufacture of paper or board products, wood-plastic composites, moisture-absorbing sheets, or fibrous insulation products.

Description

METHOD FOR MODIFYING FIBROUS MATERIAESFIEED

[0001] The present invention relates to a method for modifying fibrous materials using one or more polymers, to the materials thus obtained, and to the use of said materials in the manufacture of paper or board products, wood-plastic composites, moisture-transfer sheets, or fibrous insulation products.BACKGROUND

[0002] In common processes for manufacturing paper and board products, the fibres are mixed with the required additives and fillers into an aqueous suspension. The water of the suspension causes the fibres to swell, and thus absorb large amounts of water.

[0003] When the obtained pulp is wet-pressed and dried, high energy consumption is typically required to remove the moisture from the fibre web and also from within the fibre structure. The drying causes the largest share of the energy consumption of the overall process, and is thus also the cause of a high share of the costs of the process.

[0004] Wet-strength agents have been used in the past to increase the strength of the product by forming water resistant inter-fiber chemical bonds. These wet-strength agents typically form fiber bound crosslinked polymeric network on the fiber surfaces and between the fibers. Also chemical cross-linkers have been used, such as dialdehydes and polycarboxylic acids. These chemical cross-linkers are typically absorbed in to the fiber wall, and react between adjacent cellulosic chains

[0005] However, chemical cross-linkers require high temperatures, such as 130-150 °C, for efficient cross-linking. The high temperatures will cause yellowing of the fibre due to the formation of side-products, and will require a high energy consumption. Further, many of these cross-linkers make the fibres more fragile, and some are suspected to be health hazards. In their conventional use, they also prolong the biodegrading process of the fibre materials.

[0006] Polyamideamine epichlorohydrin (PAE) is an example of a wet strength additive (Ozaki et al. 2006) used in paper manufacture, and not requiring the same high temperatures as chemical cross-linkers. However, they are ineffective in reducing fiber water absorption, as they are used in the conventional manner, by adding to ready-made fibre pulp in a conventional papermaking process, just before pressing and drying the web, and typically already before forming the web. Thus, in a conventional process, they are added after the fibres have already swollen, whereby they are not capable of effectively preventing the swelling of the fibres.

[0007] Thus, the energy consumption of the manufacture of paper or board products is still high, despite the known use of wet-strength agents, and would benefit from further improvements of the process.SUMMARY OF THE INVENTION

[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 a method for modifying the surfaces of individual fibres in a fibrous material, thus reducing the swelling capacity of the fibres.

[0010] According to a second aspect of the invention, there is provided the modified fibre material that can be prepared using said method.

[0011] According to a third aspect, there is provided a method for preparing fibre products with decreased water retention, whereby the preparation can be carried out with reduced energy consumption.

[0012] According to a further aspect, there is provided a novel use of the mentioned modified fibre materials, utilizing the changed characteristics of the materials.

[0013] The present invention thus relates to a method for modifying fibrous materials using one or more polymers, to reduce the water-induced swelling of the individual fibres thereof, to the materials thus obtained, and to the use of said materials in the manufacture of paper or board products, wood-plastic composites, moisture-absorbingsheets, or fibrous insulation products. The method of the invention can thus be considered as a form of pre-treatment method for the fibres to be used in a paper or board manufacturing process.

[0014] The invention is based on a reduction of the amount of swelling of fibres in the aqueous suspensions used e.g. in manufacturing paper or board products. Further, the invention utilizes the well-known tendency of fibres and chemicals (herein polymers) of different charge characteristics to absorb and bind to one another. Thus, it is preferred to utilize e.g. cationically charged polymers with the anionically charged fibres.

[0015] When a suitable polymer is added to the fibre in suitable media, preferably in aqueous suspensions containing no fillers or further retention aids, the polymer will absorb to the fibres. Upon drying the formed pulp suspension, the fibre structures will collapse, and the absorbed polymer will form a flexible, typically fiber-bound, coating of selfcrosslinked polymer molecules on the fibre surfaces, resulting in a fibre material with a modified fibre surface. The bonds formed between the polymer molecules, and generally between the polymer molecules and the fibres, are stable in aqueous solutions, whereby the fibre coating will remain intact even when the fibre is resuspended, thus preventing swelling of the modified fibre.As shown, among others, in the enclosed drawings (see e.g. Fig. 3), the polymer of the present material is added to the fibre pulp in connection with the pulping, before the pulp is dried, whereby some curing will take place already during this drying step, and further drying can take place in the warm and dry pulp.

[0017] Significant advantages are achieved using the present invention. Among others, a reduced swelling, and more generally reduced water absorption, of the fibres of a fibre material is achieved. Further, the dewatering in the paper machine forming sections and drying in the paper machine drying section will be faster, and less energy is needed for the dewatering and drying of the paper, when the dried and resuspended modified fibres of the invention are used instead of a common fibre pulp. This is a significant advantage, since the dewatering and drying steps on the paper machine typically represent around half of the energy consumption of the whole papermaking process. This will further cause an increase in the paper, board and tissue production speed. Since the coated fibres will absorb smaller amounts of water compared to uncoated fibres, and decrease water retention, the invention will also cause improved filler retention in the wet pressing stage,as smaller amounts of water will need to be removed from any fibrous products utilizing this modified fibre, and cause smaller losses of filler.

[0018] Since inter-fiber chemical crosslinking is not required in the preparation of fibrous end-products from the modified material of the invention, the flexibility and formability of the individual fibres will be maintained, as well as their biodegradability.

[0019] Due to the polymer coating on the individual fibres, the hydroxyl groups on the fibres will be partly masked, which will cause also an increased bulk of the fibrous product.

[0020] When using this fibrous material of dried coated fibres to prepare fibre products, such as paper or board products, the decreased water absorption of the fibres will result in reduced energy consumption during the manufacture. For example, the energy consumption during steps, such as web forming, wet pressing, and particularly drying, will be significantly reduced.

[0021] A reduced energy consumption during product manufacture will clearly also reduce the overall costs of manufacture. However, a reduced water absorption of the fibres in paper or board manufacture will also make it possible to increase the running speed of the paper or board machine.

[0022] Further, when requiring only a film-like protective network on the fibre, and no intrusion of the modifying agent into the cavities of the fibre structure, it will be sufficient to use smaller amounts of polymer, and the polymer will not cause embrittlement of the fibres as in chemical crosslinking treatments.

[0023] Compared to chemical cross-linking, the invention offers the further advantage that the cationic polymer binds fibrous fines to the fibres, whereby the modified pulp (dried and redispersed) has a lower content of fines compared to conventional fibre pulp. This will provide also an improved water removal at the forming section of the paper machine. No such binding capability exists for chemical cross-linkers, such as dialdehydes or polycarboxylic acids. Instead, these chemical cross-linkers function by forming interfiber non-ionic chemical crosslinks between the adjacent cellulose molecules.

[0024] Further, when using the small dosages of polymer that have been found sufficient in the present invention, the fibres of the dried pulp will be easier to re-disperse in water before manufacturing paper sheets from the fibre pulp.BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIGURE 1 illustrates the interactions taking place on the surface of the modified fibre material of the invention in an aqueous environment, having a cross-linked polymer coating bound to the individual fibres, thus preventing the fibre-water absorption and swelling (see right-hand drawing), as compared to the interactions in conventional cellulosic fibre, with wetting and swelling of the dried fibre upon adding to water (see lefthand drawing).

[0026] FIGURE 2 shows a configuration of a method according to some embodiments of the present invention, a method for modifying fibre materials shown on the left side of the Figure, the optional steps for manufacturing a fibrous sheet shown on the right side of the Figure, and examples of some further potential applications mentioned in the ends of the dotted arrows.

[0027] FIGURE 3 illustrates an embodiment of the invention, showing a preferred process scheme suitable for use in preparing a paper or board product using the modified fibre material of the invention, the general embodiment involving the choice of polymer from a broad selection of polymers, although illustrated in the figure by mentioning PAE as an example of suitable polymers.

[0028] FIGURE 4 provides the test results carried out on HW fibres of the invention, pre-modified by using a dosage of 0.25% or 0.5% PAE, Fig. 4A showing the results for the SR number, Fig. 4B showing the results for the water retention value (WRV), Fig. 4C showing the results for the fines content, Fig. 4D showing the results for the drainage time in sheet making, Fig. 4E showing the results for the dry matter content after wet pressing, when the modified pulp has been used in sheet making, Fig. 4F showing the results for the bulk, Fig. 4G showing the results for the Z-strength, Fig. 4H showing the results for the tensile index, and Fig. 41 showing the results for the tear index.EMBODIMENTS

[0029] The present invention relates to a method for modifying fibre materials, wherein one or more polymers is added to an aqueous fibre pulp, and a film-like protective polymer network is created on the surface of the fibres of the pulp by allowing the polymer to absorb to the fibres, followed by drying the pulp to cause the polymer to attach to the fibre surface, and form a film-like network thereon. The product of the method is thus a dried modified fibre material.

[0030] In an embodiment, the fibres are selected from natural wood fibres, such as the fibres of pine, fir, spruce, hemlock, birch, aspen, eucalyptus, acacia, or oak trees, or from artificial or regenerated fibres, such as viscose (e.g. Rayon) or lyocel. Particularly, the fibres are selected from natural virgin or recycled wood fibres or from cellulosic recycled fibres.

[0031] Either softwood or hardwood fibres can be used.

[0032] The pulp made from these fibres can have the characteristics of an ordinary wood pulp used for the manufacture of paper or board products. Typically, the pulp has a consistency of 0.2-2 % by weight of dry matter.

[0033] In an embodiment the pulp from these fibres is foamed by air using surface active agents to assist the foaming.

[0034] In an embodiment the pulp from these fibres are used as dry in an air-laying process, whereby the fines will be attached to the fibre, thus reducing the dust formation in the fibre material, while also reducing the water absorption of the material, further accelerating the drying process.

[0035] In an embodiment, the polymer network is formed from one or more natural or synthetic polymeric wet strength agents, preferably selected from polyamideamine epichlorohydrin (PAE), cationic starch, melamine formaldehyde resin (MF resin), polyacrylamide (PAM), glyoxylated polyacrylamide (GPAM), polyethyleneimine (PEI), polyvinylamine (PVAm), lignin, and soy protein. A particularly preferred polymer is polyamideamine epichlorohydrin (PAE), which has been shown to readily absorb to fibres at room temperature, the absorption thus not requiring heating. PAE is a safe chemical thathas been approved for use in e.g. food packages, and is safe for use also in hygiene products.

[0036] When requiring only a film-like protective network on the fibre, without intrusion of the modifying agent into the cavities of the fibre structure, it will be sufficient to use smaller amounts of polymer. Preferably, the amount of polymer added to the fibre pulp in the herein described method is < 2% by weight of the dry fibre, preferably 0.2- 1.8%, most suitably 0.4-0.8%.

[0037] In another embodiment, contents of polymer modifying agent as low as <0.5% by weight can be used, or 0.1-0.5% by weight, particularly 0.2-0.4% by weight, most suitably about 0.25% by weight. Already these low contents of polymer will cause a significant improvement in, among others, the drainability and bulking properties of the fibers.

[0038] The absorption of the polymer to the fibre takes place already at ambient conditions, immediately after mixing the polymer and the fibre into the aqueous suspension. However, an increased temperature, such as a temperature extending from 25 °C to below 100 °C, preferably a temperature between 60 and 95 °C, can be used to facilitate bonding or cross-linking of the polymer, which takes place after wet pressing and drying, particularly covalent bonding of the polymer to the fibres and self-crosslinking of the polymer. Typically ambient pressure is still used, or a slightly elevated pressure.

[0039] In an embodiment, the absorption step of the method is allowed to proceed for a period of at least 10 seconds, preferably 0.5-5 minutes.

[0040] The following optional wet pressing step typically takes place by spreading the modified fibre material onto a porous support and using mild suction from underneath the support and / or gentle pressing from above the support.

[0041] In an embodiment the modified fibres are dried using flash drying method.

[0042] The drying step is preferably accomplished by heating, e.g. to a temperature of 50-130 °C, preferably to 70-95 °C.

[0043] After the fibres have obtained their polymer coating, using the steps described herein, the previously anionically charged fibres will typically have become cationically charged. Thus, in a further embodiment, one or more anionic additives can beadded to the pulp, in order to improve the capability of the cationic coated fibres to bind to each other and to other agents of the pulp, i.e. in order to improve the strength of the final product containing the modified fibres. These additives can be selected from anionic papermaking agents, preferably from anionic long-chained dry-strength adhesives, such as carboxymethyl cellulose (CMC), anionic polyacrylamide (APAM), or anionic nanocellulose, preferably being CMC. These additives can be added at any stage before, during or after the polymer absorption step, preferably after the polymer has been absorbed to the fibres.

[0044] The method described herein will result in a modified fibre material that contains polymer-coated fibres.

[0045] Said modified fibre material is obtained in dried form, as the polymer network is crosslinked only upon drying. Thus, the manufacture of fibrous end-products, such as paper or board products, using the modified fibre material requires a resuspension of the modified fibre.

[0046] Upon resuspension, the polymer-treated fibre material will have a reduced swelling capacity as compared to materials formed of native fibres.

[0047] It is also an alternative to mix the modified fibres with conventional fibres upon resuspension. The content of modified fibres in such a mixture is typically 10 - 85 weight-% of the total weight of fibres, preferably 20 - 50 weight-%., depending on the end-product.

[0048] Therefore, a method for manufacturing a fibrous sheet in accordance with at least some of the embodiments described above would include the steps of:- adding one or more polymers is to an aqueous fibre pulp,- allowing the polymer to absorb to the fibres,- drying the pulp to cause the polymer to attach to the fibre surface and form a network thereon, thus obtaining a modified fibre material,- resuspending the modified fibre material, optionally mixed with unmodified fibre material,- optionally, adding further papermaking additives to the resuspended material,- optionally, foaming of the fiber-water suspension by air,- typically, separately dewatering the resuspended material, andwet-pressing the resuspended material to form a web, and drying the wet-pressed web to form a fibrous sheet product.

[0049] In an embodiment, the method could include a step of forming an air-laid web from the modified dry fibres to form a fibrous sheet product.

[0050] Thus, the absorption of the polymer to the fibres takes place in the absence of further paper-making additives, and when preparing a paper or board product from the modified fibre material, a separate drying step is necessary before adding the papermaking additives and before forming the paper pulp into a web, e.g. by pressing, to allow the curing of the polymer.

[0051] In a preferred embodiment, debonders are added to the fibre-polymer pulp to facilitate resuspension of the modified fibre material.

[0052] In another embodiment, the modified fibre material of the invention is mixed with unmodified fibre before resuspension. A content of 20 w-% or more of the modified fibre material calculated from the total weight of fibre material is sufficient to provide the final paper product with the advantages mentioned herein, or a content of 20-100 w-%, although a content of 25-50 w-% of the modified fibre material is preferred.

[0053] The fibre materials that have been modified as herein described are useful for various purposes, including the use in the above described method for manufacturing a fibrous sheet. Thus, the invention also relates to the use of the modified materials in the manufacture of paper or board products, wood-plastic composites, moisture-transfer sheets, or fibrous insulation products.

[0054] The properties of the modified fibre material are different from the properties of conventional fibre materials. Among others, the charge characteristics of the product has changed. This could result in a weak strength of products prepared from this material. However, using suitable additives the strength can be restored, if so desired. A further alternative is to use the material in layers that have lower strength requirements, such as in the middle layer of boxboard, or as tissue paper. Further, the products have a density that is lower than for conventional paper products, and have a softer feel, thus further demonstrating their usefulness as moisture-transfer sheets in e.g. diapers. These characteristics can also be further improved e.g. by grinding.

[0055] In said applications, the modified material of the invention is typically used as a fibre raw material in the manufacture of the end-product, e.g. as suggested above for the fibrous sheet. In diapers and other similar products requiring moisture transfer characteristics, the material is used in the layer that is to be positioned against the skin, where the material, due to its low water absorption, transfers any moisture to the inner layers of the diaper, where the moisture absorbing materials are confined. In commercial products, chemically cross-linked fibres are used for this purpose. Thus, compared to commercial diapers, those incorporating the material described herein have the advantage of providing a softer feel of the layers placed against the skin, as well as providing an improved biodegradability.

[0056] It is well-known that increasing polymer contents decrease the biodegradation rates of the products. Thus, it is of advantage that only small amounts of polymer are needed. Further, the effect on the biodegradation rates in the products of the present invention is not as strong as the effect of chemical cross-linking (as shown in Korpela et al. 2024).

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.EXAMPLESExample 1 - Preparation and re-dispersion of modified fibre material of the invention

[0063] Polyamide-epichlorohydrin (PAE), commonly used as a wet strength agent in paper making, was added into a dry matter content of 0 % by weight (Ref) and 2.0 % by weight (pulp + PAE) to non-dried non-ground bleached birch sulphate pulp having a consistency of 0.5% by weight, calculated from the dry matter. After mixing, the pulp wasfiltered in a Buchner funnel on a wire. The filter cakes were crumbled by hand, and dried at a temperature of 80 °C over night to provide the modified fibres or reference material.

[0064] The dried samples were added to water (into a consistency of 2.0%) and allowed to soak for 10 hours. Subsequently, the pulp was dispersed using a Waring Blender for 40 s at a consistency of 2.0 %. After dispersing, the Schopper-Riegler values (°SR) were measured from the pulps using the EN ISO 5267-1 : 99 method, and the WRV values (water retention value) using the ISO 23714:14 method. The results shown in the following Table 1 demonstrate that the addition of PAE improved the drainability of the birch sulphate pulp, as demonstrated by °SR measurements, and lowered the retention tendencies, as demonstrated by WRV measurements.Table 1.Example 2 - Preparation and re-dispersion of modified fibre material of the invention

[0065] Polyamide-epichlorohydrin (PAE), commonly used as a wet strength agent in paper making, was added into a dry matter content of 0 % by weight (Ref), and either 1.0 or 2.0 % by weight dosages (pulp + PAE) to non-dried non-ground bleached birch sulphate pulp having a consistency of 1.0% by weight, calculated from the dry matter. After mixing, the pulp was filtered in a Buchner funnel on a wire. The filter cakes were crumbled by hand, and dried at a temperature of 80 °C over night to provide the modified fibres or reference material.

[0066] The dried samples were redispersed into water using a wet pulper and a stick blender. After dispersing, the Schopper-Riegler values (°SR) were measured from the pulps using the EN ISO 5267-1 : 99 method, and the WRV values (water retention value) using the ISO 23714:14 method. The results shown in the following Table 2 demonstrate that the addition of PAE lowered the °SR values of the birch sulphate pulp, and also lowered its retention tendencies.Table 2.Example 3 - Preparation and re-dispersion of modified fibre material of the invention

[0067] Polyamide-epichlorohydrin (PAE), commonly used as a wet strength agent in paper making, was added into dosages providing a dry matter content of 0 % by weight (Ref), and either 0.25 %, 0.5 % or 1.0 % by weight (pulp + PAE) to non-dried non-ground bleached birch sulphate pulp having a consistency of 1.0% by weight, calculated from the dry matter. After mixing, the pulp was filtered in a Buchner funnel on a wire. The filter cakes were crumbled by hand, and dried at a temperature of 80 °C over night to provide the modified fibres or reference material.

[0068] The dried samples were redispersed into water using a wet pulper, and ground using a laboratory grinder with 0 rotations, 1000 rotations, and 4000 rotations. Subsequently, the Schopper-Riegler values (°SR) were measured from the pulps using the EN ISO 5267-1 : 99 method, and the WRV values (water retention value) using the ISO 23714:14 method. Further test methods are shown in the following Table 3.Table 3. Test methods

[0069] The results shown in the following Table 4 demonstrate that the addition of PAE lowered the °SR and WRV values of the birch sulphate pulp. The PAE bound onto the fibre surfaces, preventing the swelling of the fibres in water, also lowered the tensile strength, the elongation at break, the z-directional tensile strength, and the Young’s modulus, of the paper product prepared therefrom, but the strength can be improved by a mechanical grinding of the modified fibre pulp.Table 4.Example 4 - Comparison of softwood fibres to hardwood fibres

[0070] Never-dried unbeaten bleached softwood and bleached hardwood sulphate pulps (SW and HW) were obtained from a Finnish pulp mill. The consistency of the pulps was 10.2 wt-% and 8.9 wt-%, respectively. The used PAE was obtained from Solenis Finland Oy as a technical grade product. Ion-exchanged water was used for all dilutions.

[0071] The pulps were diluted by water to 1.5% consistency. The pHs of the pulp were adjusted to 6.5-7.5 using diluted HC1 and NaOH. Diluted PAE (1.0%) was added into the pulp suspension, and the pulp was mixed for one minute before filtering under a water jet vacuum pump connected to a Buchner funnel with a filter cloth. The pulp cakes were crumbled by hand and dried overnight in a ventilated oven at 80 °C. To ensure complete curing of the PAE, the pulps were heated additionally in 80 °C for 2 h. The dry matter content of the HW and SW pulps were around 99 ±0.5% after the drying and the heat treatment. The reference pulps were treated in a similar way but without a PAE addition.

[0072] The PAE dosages and the results of the analyses carried out on these pulps are shown in the following Table 5.

[0073] As the results show, the bulk is improved in all of these samples (both hardwood and softwood) following the treatment according to the invention, while the strength decreases.Table 5.Example 5 - Preparation and re-dispersion of CMC-containing modified fibre material of the invention

[0074] Anionic carboxymethyl cellulose (CMC, 0.2 % by weight) was added to the pulp treated as described in Example 3, in addition to the PAE (0.5 %).

[0075] As shown in the following Table 6, the addition of CMC improved the tensile strength and the Z-directional tensile strength of the pulp. These results demonstrate that the bonding ability of the fibres modified using cationic PAE can be improved by adding anionic dry-strength adhesive to the pulp, used to facilitate fibre bonding. The bulk, in turn, is not significantly reduced, even though the CMC addition improves the tensile and Z- directional strengths of the pulp.Table 6.Example 6 - Preparation and re-dispersion of modified fibre material of the invention, and use in pulp mixtures

[0076] Bleached refined hardwood (HW) fibres (EOK 50 kWh / t) obtained from a Finnish pulp mill as sulphate pulps were mixed with corresponding pre-modified HW fibres of the invention, pre-modified by using a dosage of 0% (Ref.), 0.25%, 0.5% and 0.75% PAE. The weight ratio of pre-modified / unmodified fibre in the mixtures was 25 / 75. The obtained pulp mixtures and hand sheets prepared therefrom were analyzed, and the results are shown in the enclosed Figs. 4 A-E

[0077] As shown in the results, already the lower PAE doses used for the premodification of the fibre (0.25% or 0.5%) result in a clear improvement of the water retention properties of the pulp, as well as an improvement in the bulk and tensile strength of the pulp, as only an insignificant change takes place in the tensile and Z-directional strengths. Surprisingly, the results show that increasing the dosage over 0.5% provides no significant further advantage. The small PAE dosages, however, provide the further advantage that the pre-modified pulp is easier to disperse in water (due to the smaller wet strength of the modified material of the invention as compared to conventional pulps) and causes lower chemical costs.

[0078] More specifically, Fig. 4A demonstrates that the SR number (the value indicating the drainage resistance on the wire section) is lowered significantly already using the 0.25% dosage of PAE in the 25 / 75 mixture of pre-modified fibre in unmodified fibres, Fig. 4B demonstrates that the water retention value (WRV, the value being comparable to the amount of water that needs to be removed by heating at the drying section of the paper machine) decreases significantly already with the same low 0.25% dosage in the 25 / 75 mixture described above, Fig. 4C demonstrates that the amount of fines decreases significantly already with the same low dosage as above, which is caused by the small amount of cationic PAE effectively binding anionic fines to the fibres, Fig. 4Ddemonstrates that the reduction in the retention time is significant with the same low dosage as above, whereas an increase in the dosage will cause an increase in the drainage time, Fig. 4E demonstrates that the addition of PAE-treated fibres to a fibre pulp will cause a significant increase in the dry-matter content of a wet-pressed paper product prepared from said mixed pulp, Fig. 4F surprisingly demonstrates that the increase in bulk is significant already using the low PAE dosage as above, while the effect is levelled off at higher dosages, Fig. 4G and 4H demonstrate that the expected decrease in the strength values is surprisingly insignificant using the low PAE dosage as above, and Fig. 41 demonstrates that the increase in the tear strength is significant already when using the low PAE dosage as above, and a further increase of the dosage causes no remarkable further improvement.INDUSTRIAL APPLICABILITY

[0079] The modified fibre materials of the present invention are useful for various purposes, including the use in manufacturing fibrous sheets.

[0080] More precisely, the materials can be used in the manufacture of paper or board products, wood-plastic composites, moisture-transfer sheets, or fibrous insulation products.ACRONYMS LISTAPAM anionic polyacrylamideCMC carboxymethyl celluloseGPAM glyoxylated polyacrylamideMF melamine formaldehydePAE polyamideamine epichlorohydrinPAM polyacrylamidePEI polyethyleneiminePVAm polyvinylamine°SR Schopper-Riegler valueWRV water retention valueCITATION LISTNon Patent LiteratureKorpela, A., Tanaka, A., Asikainen, A.; Enhancing Subsequent Kraft Fiber Dewatering Properties by using Fiber Polyamide-epichlorohydrin (PAE) Treatment to Prepare a Dry Pulp Product; BioResources (2024); 19(3); 5227-5238Ozaki, Y., Bousfield, D. W., and Shaler, S. M.; The characterization of polyamide epichlorihydrin resin in paper - relationship between beating degree of pulp and wet strength; Appita Journal (2006); Vol 59; No 4; p. 326-330

Claims

Claims1. Method for modifying fibre materials, wherein an aqueous fibre pulp is provided, and one or more polymers is added to the pulp, characterized by- allowing the added polymer to absorb to the fibres of the pulp, and- drying the pulp to cause the polymer to attach to the fibre surface and form a network thereon, thus obtaining a modified fibre material.

2. The method of claim 1, wherein the fibres are selected from natural wood fibres, such as the fibres of pine, fir, spruce, hemlock, birch, aspen, eucalyptus, acacia, or oak trees, or from artificial or regenerated fibres, such as rayon, viscose or lyocell, or recycled paper, paperboard, or textile fibres.

3. The method of claim 1 or 2, wherein the polymer network is formed from one or more polymeric wet strength agents, preferably selected from polyamideamine epichlorohydrin (PAE), cationic starch, melamine formaldehyde resin (MF resin), polyacrylamide (PAM), glyoxylated polyacrylamide (GPAM), polyethyleneimine (PEI), polyvinylamine (PVAm), lignin, and soy protein, preferably being polyamideamine epichlorohydrin (PAE).

4. The method of any preceding claim, wherein the amount of polymer added to the fibre pulp is < 2% by weight of the fibre, preferably 0.2-1.8%, most suitably 0.4-0.8%.

5. The method of any of claims 1 to 3, wherein the amount of polymer added to the fibre pulp is <0.5% by weight of the fibre, preferably 0.1-0.5% by weight, particularly 0.2- 0.4% by weight, most suitably about 0.25% by weight.

6. The method of any preceding claim, wherein the absorption step is carried out at a temperature below 100 °C, preferably at 25-85 °C.

7. The method of any preceding claim, wherein one or more anionic additives are added to the pulp, such as carboxymethyl cellulose (CMC), anionic polyacrylamide (APAM), or anionic nanocellulose, preferably being CMC.

8. The method of claim 6, wherein the one or more additives are added before, during or after the polymer absorption step.

9. A modified fibre material, characterized in that is has been prepared using the method of any of claims 1 to 7, and contains polymer-coated fibres.

10. Use of the modified fibre materials of claim 8, or obtained using the method of any of claims 1 to 7, in the manufacture of paper or board products, wood-plastic composites, moisture-transfer sheets, or fibrous insulation products.

11. A method for manufacturing a fibrous sheet from the modified fibre material of claim 8, or obtained using the method of any of claims 1 to 7, characterized by:- resuspending the modified fibre material,- optionally, adding further papermaking additives to the resuspended material,- wet-pressing the resuspended material to form a web, and- drying the wet-pressed web to form a fibrous sheet product.

12. The method of claim 11 , wherein the modified fibre material of the invention is mixed with unmodified fibre before the resuspension, into a content of 20 w-% or more of the modified fibre material calculated from the total weight of fibre material, or into a content of 20-100 w-%, preferably a content of 25-50 w-%.

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