A method of producing an aqueous suspension for manufacturing a fibrous monofilament, a method of manufacturing a fibrous monofilament, and a system for manufacturing a fibrous monofilament

Abstract

The specification relates to an improved method for producing an aqueous suspension for manufacturing a fibrous monofilament. The method comprises mixing water, natural fibrous material and dispersing agent so as to form a mixture, and exposing the mixture to homogenization in a homogenizer so as to form the aqueous suspension. Further, a method and a system for manufacturing a fibrous monofilament are provided.

Description

[0001] A method of producing an aqueous suspension for manufacturing a fibrous monofilament, a method of manufacturing a fibrous monofilament, and a system for manufacturing a fibrous monofilament

[0002] Technical field

[0003] This specification relates to a method of producing an aqueous suspension for manufacturing a fibrous monofilament. The specification also relates to a method and a system for manufacturing a fibrous monofilament.

[0004] Background

[0005] Conventionally, the process for producing a suspension for manufacturing fibrous monofilaments by extrusion takes long time, even up to 20 hours. Furthermore, with conventional process the suspension can only be produced batchwise.

[0006] Thus, there is a need for an improved process for producing the suspension, wherein the production time can be significantly reduced.

[0007] Summary

[0008] An improved method for producing an aqueous suspension for manufacturing fibrous monofilaments is provided. By the method disclosed herein the time for producing the aqueous suspension can be significantly reduced. Further, the process for preparing the aqueous suspension is simplified. Moreover, the disclosed method is shown to be more energy-efficient when compared to the conventional process for producing the aqueous suspension. The fibrous monofilaments produced from the aqueous suspension have improved mechanical properties and more uniform quality when compared to those produced by using the conventional process for preparing the aqueous suspension. According to an embodiment, a method of producing an aqueous suspension for manufacturing a fibrous monofilament is provided. The method comprises the following steps:

[0009] - mixing water, natural fibrous material and dispersing agent so as to form a mixture, and

[0010] - exposing the mixture to homogenization in a homogenizer so as to form the aqueous suspension.

[0011] According to another embodiment, a method of manufacturing a fibrous monofilament is provided. The method comprises the following steps:

[0012] - producing an aqueous suspension by the method defined herein,

[0013] - extruding the aqueous suspension into a monofilament, and

[0014] - drying the monofilament.

[0015] According to yet another embodiment, a system for manufacturing a fibrous monofilament is provided. The system comprises a vessel for forming a mixture comprising water, natural fibrous material and dispersing agent; a homogenizer for homogenizing the mixture so as to form an aqueous suspension; and an arrangement for extruding the aqueous suspension into a monofilament and drying the monofilament.

[0016] Brief description of the drawings

[0017] Fig. 1 illustrates, by way of an example, a schematic overview of the conventional process of producing an aqueous suspension for manufacturing a fibrous monofilament,

[0018] Fig. 2 illustrates, by way of an example, a schematic overview of a batchwise process of producing an aqueous suspension for manufacturing a fibrous monofilament according to an embodiment,

[0019] Fig. 3 illustrates, by way of an example, a schematic overview of a continuous process of producing an aqueous suspension for manufacturing a fibrous monofilament according to an embodiment, Fig.4 illustrates, by way of an example, a schematic overview of a method of manufacturing a fibrous monofilament.

[0020] The figures are schematic. The figures are not on any particular scale.

[0021] Detailed description

[0022] The solution is described in the following in more detail with reference to some embodiments, which shall not be regarded as limiting.

[0023] Unit of temperature expressed as degrees C corresponds to °C. The following reference numbers are used in this specification:

[0024] 101 , 201 , 301 (first) mixing tank

[0025] 102, 202 (first) recirculation line

[0026] 103, 203, 207 inline mixer

[0027] 204, 304 homogenizer

[0028] 205, 305 second mixing tank

[0029] 206 second recirculation line

[0030] 310 storage tank

[0031] 311 line

[0032] 312 arrangement for extruding the aqueous suspension into a monofilament and drying the monofilament

[0033] 420 step of mixing

[0034] 421 step of homogenizing

[0035] 422 step of extruding

[0036] 423 step of drying

[0037] The features recited in the embodiments of the description and in the claims are mutually freely combinable unless otherwise explicitly stated.

[0038] Fibrous monofilaments for fibrous materials, such as woven, knitted or nonwoven materials, or for use in composite materials, can be produced by preparing an aqueous suspension comprising dry matter including natural fibrous material, extruding the aqueous suspension into a monofilament, and drying the monofilament.

[0039] Conventional process of producing the aqueous suspension is illustrated in Figure 1 . The aqueous suspension is prepared in a batch-wise manner in a mixing tank 101. Water, natural fibrous material and dispersing agent are mixed in the mixing tank 101 so as to form a mixture. When the mixture is homogeneous enough, the mixture is pumped into a recirculation line 102. In the recirculation line 102 optional additional component(s) are added into the mixture one at a time, such that duration of dosing of each additional component corresponds with the recirculation time of the contents of the mixing tank. The recirculation line 102 comprises an in-line mixer 103 for mixing the additional component into the mixture prior to supplying the mixture back into the mixing tank 101. Once the additional component(s) is / are added to the mixture, the thus formed aqueous suspension is mixed in the mixing tank 101 by a tank mixer until the suspension is homogeneous. Typically, about 15 to 25 recirculation rounds are needed and the process takes even up to 20 hours.

[0040] It is an aim of this disclosure to provide an improved method of producing an aqueous suspension for manufacturing fibrous monofilaments. The method according to this disclosure can be implemented as a batch process or as a continuous process.

[0041] The method according to this disclosure comprises mixing water, natural fibrous material and dispersing agent, as well as optional additional component(s) so as to form a mixture. The method comprises exposing the thus formed mixture to homogenization in a homogenizer so as to form an aqueous suspension.

[0042] Optional additional component(s) may include a wet strength agent, a hydrophobic agent, a crosslinking agent, a rheology modifier, or any mixture thereof.

[0043] The method can be implemented as a batch process or as a continuous process. In an exemplary batch process, as illustrated in Figure 2, water, natural fibrous material, dispersing agent and optional additional component(s) are mixed in a first mixing tank 201 so as to form a mixture. From the first mixing tank, the mixture is pumped into a first recirculation line 202. The first recirculation line 202 comprises an in-line mixer 203 for further mixing the mixture prior to supplying the mixture back into the first mixing tank 201 . For example, one to three recirculation rounds may be sufficient. From the first mixing tank the recirculated mixture is pumped into a homogenizer 204. In the homogenizer the mixture is exposed to homogenization so as to form an aqueous suspension. The aqueous suspension may be transferred from the homogenizer 204 to a second mixing tank 205. The aqueous suspension is mixed in second mixing tank 205 and pumped into a second recirculation line 206. In the second recirculation line 206 (optional) rheology modifier, particularly aPAM, is added into the aqueous suspension. The second recirculation line 206 comprises an in-line mixer 207 for mixing the rheology modifier into the aqueous suspension prior to supplying it back into the second mixing tank. Once the rheology modifier is added to the aqueous suspension, the aqueous suspension is mixed in the second mixing tank 205 by a tank mixer until the suspension is homogeneous.

[0044] In an exemplary continuous process, as illustrated in Figure 3, water, natural fibrous material and dispersing agent are mixed in a storage tank 310 so as to form a mixture. From the storage tank 310 the mixture is pumped into a line 311 , to which the optional additional component(s) can be added. After addition of the optional additional component(s) the mixture comprising water, natural fibrous material, dispersing agent and optional additional component(s) is supplied into a first mixing tank 301 for mixing. From the first mixing tank 301 the mixture is pumped into a homogenizer 304. In the homogenizer 304 the mixture is exposed to homogenization so as to form an aqueous suspension. Rheology modifier (optional), particularly aPAM, may be added to the aqueous suspension after exposing the mixture to homogenization. After addition of the rheology modifier, the aqueous suspension is transferred to a second mixing tank 305 for mixing. The aqueous suspension is mixed in the second mixing tank 305 by a tank mixer until the suspension is homogeneous. From the second mixing tank 305 the aqueous suspension may be transferred to a fiber line comprising an arrangement for extruding the aqueous suspension into a monofilament and drying the monofilament 312.

[0045] It is to be noted that when no aPAM as the rheology modifier (or any other component susceptible to high shear forces caused by the homogenizer) is used, there may not be a need for mixing the aqueous suspension in the second mixing tank. In that case, the aqueous suspension may be transferred from the homogenizer directly to the fiber line for producing the fibrous monofilament.

[0046] By the method disclosed herein the time for producing the aqueous suspension can be significantly reduced. The process comprising the step of homogenizing the mixture is about ten times faster than the conventional process. Thus, with the method according to this disclosure the time needed for producing the aqueous suspension may be about 90 % less, in any case about 50 to 66% less, when compared to the time needed using the conventional process. Further, the process for preparing the aqueous suspension is simplified. Moreover, the disclosed method is shown to be more energy-efficient when compared to the conventional process for producing the aqueous suspension. Energy savings from about 25 to about 60% have been demonstrated.

[0047] Use of the homogenizer enables a more uniform and even suspension to be formed. In the homogenizer the mixture comprising water, natural fibrous material, dispersing agent and optional additional component(s) is homogenized by applying shear forces to the components of the mixture. In the homogenization, size of the particles of the mixture are reduced by the shear forces. In homogenization the mixture is forced, at high pressure, through a narrow orifice or gap. Shear forces are generated by applying pressure loss via guiding the components of the mixture through the orifice / gap, where an opening of the orifice / gap and thus the homogenization of the homogenized mixture, is controllable by adjusting the opening of the orifice / gap. The amount of the pressure loss applied may be for example from 50 to 1500 bar. The homogenizer may comprise a conduit and a limiter. The opening of the orifice / gap may be adjusted by moving the limiter in the conduit. For example, the limiter may be a needle valve and the opening of the orifice / gap may be adjusted by moving the needle valve in the conduit. The limiter may also be a homogenizer valve comprising valve seat, valve, and impact ring. Homogenizer works by breaking the components / particles of the mixture and evenly distributing them throughout the mixture.

[0048] Presence of the homogenizer may even allow use of lower grade raw materials. Use of the homogenizer enables production of more homogenized aqueous suspension, even with lower grade raw materials. With lower quality raw materials the conventional method may not be able to produce an aqueous suspension that fulfils the needs placed by the subsequent extrusion process. If the natural fibrous material comprises particles of varying size, homogenizer may be responsible for refining the bigger particles into smaller ones, thereby increasing fibrillation of the material. Increased fibrillation and decreased presence of flocs enables the natural fibrous material to be open for the optional additional component(s) to bind to the fibrils. This is demonstrated as improved mechanical properties of the fibrous monofilaments produced. Furthermore, the produced fibrous monofilaments are shown to be more uniform in quality. This is shown by the improved linear density standard deviation values of the fibrous monofilaments when compared to the reference filaments. When necessary, the process may comprise several, such as two or three, homogenizing steps. In other words, the same mixture may be exposed for example from one to three homogenizing steps. Share of fibrils / fibers having a shorter length typically gets higher when the number of the homogenizing steps is increased, for example from one to two and from two to three. The analysis on the length-weighted proportions of fibers / fibrils may be performed with ABB Fiber Tester Plus according to an ISO 16065-2 standard method.

[0049] A method of manufacturing a fibrous monofilament is also provided. A schematic overview of the method is presented in Figure 4. The method comprises producing an aqueous suspension. As described above, the aqueous suspension is produced by mixing water, natural fibrous material and dispersing agent, as well as optional additional component(s) so as to form a mixture (step of mixing, 420), and exposing the thus formed mixture to homogenization in a homogenizer so as to form an aqueous suspension (step of homogenizing, 421 ). The method of manufacturing a fibrous monofilament further comprises extruding the aqueous suspension into a monofilament (step of extruding, 422) and drying the monofilament (step of drying, 423).

[0050] The aqueous suspension is directed through a small nozzle (extruded) where fibers align (orient) well with the flow. The nozzle feeds the aqueous suspension to a solid surface which is followed by drying to obtain the fibrous monofilament.

[0051] Initial fibril orientation of the fibrous monofilament may be achieved during the extrusion phase. A nozzle having an outer diameter smaller than or equal to the maximum fibril length of the fibers causes the fibrils to orientate substantially in the longitudinal direction of the suspension exiting the nozzle. Fibril orientation along the longitudinal direction of the fibrous monofilament provides strength to the filament.

[0052] Manufactured fibrous monofilament is continuous but it may be postprocessed into shorter lengths by any of suitable methods known in the art. Thickness of the fibrous monofilament may be affected at least in part by adapting manufacturing speed, aqueous suspension concentration and nozzle geometry. Chemical post-treatment, such as dyeing or introduction of a surface finishing agent is possible.

[0053] The term “fibrous monofilament” as used herein refers to a continuous length of individual fibrils grouped and extending generally along the longitudinal dimension of the monofilament. The fibrils interact chemically and / or mechanically in order to form a permanent monofilament structure. Disintegration of fibrous monofilament yields only individual fibrils. The fibrous monofilament may comprise continuous length of several meters or kilometers. Individual fibrils of the fibrous monofilament are mainly oriented along length of the fibrous monofilament. Term “monofilament” refers to a single strand filament produced by extruding a polymer suspension. Fibrous monofilament may also be called a monofilament fiber. The manufacturing method of the fibrous monofilament is an environmentally friendly one, utilizing mild conditions and not employing any harmful substances. This is a significant benefit when compared to other natural fiberbased textile fibers, such as viscose and Lyocell. The method is free of organic solvents. The sole solvent used in the method is water.

[0054] As shown in the Examples section, the fibrous monofilaments produced from the aqueous suspension prepared according to the method disclosed herein have improved mechanical properties (tenacity and elongation) when compared to those fibrous monofilaments produced from aqueous suspension prepared according to conventional method.

[0055] Tenacity is a customary measure of strength of a fiber or yarn. It is usually defined as the ultimate (breaking) force of the fiber / yarn (in gram-force units) divided by the linear density. Tenacity is often expressed as cN / (d)tex. Linear density is a value expressing the fiber / yarn weight in grams per 1 000 meters of fiber / yarn (tex) or grams per 10 000 meters of fiber / yarn (dtex).

[0056] A system for manufacturing a fibrous monofilament is provided. The system comprises a vessel for forming a mixture comprising water, natural fibrous material and dispersing agent, and a homogenizer for homogenizing the mixture so as to form an aqueous suspension. The system further comprises an arrangement for extruding the aqueous suspension into a monofilament and drying the monofilament.

[0057] The vessel may be any kind of container suitable for receiving water, natural fibrous material and dispersing agent. For example, the vessel may be a tank, such as a mixing tank or a storage tank.

[0058] The arrangement for extruding the aqueous suspension into a monofilament and drying the monofilament may comprise a nozzle for extruding the aqueous suspension into a monofilament. Further, said arrangement may comprise a solid surface for receiving the monofilament. Still further, the arrangement may comprise means for drying the monofilament. Within context of this disclosure, the natural fibrous material comprises fibrous material derived from cellulosic material, textile waste fibers, protein material, or any mixture thereof.

[0059] Textile waste fibers may comprise recycled fibers derived from textile waste. The textile waste fibers may comprise for example cotton, SPINNOVA®, Lyocell, viscose, modal, acetate, rayon, wool or silk fibers, or any mixture thereof.

[0060] Protein materials include for example wool, silk, and fibers derived from leather waste material. Fibers derived from leather waste material may include for example collagen fibers.

[0061] Cellulosic material may originate from any plant-based material. Plant-based raw material may be wood material or non-wood material. The wood material can be based on softwood tree, such as spruce, pine, fir, larch, Douglas-fir or hemlock, or on hardwood tree, such as birch, aspen, poplar, alder, eucalyptus or acacia, or on any mixture of above. The non-wood material may be as cotton, hemp, flax, sisal, jute, kenaf, bamboo, peat, or coconut. Non-wood based natural cellulose fibers may also be derived from agricultural residues, grasses, or other plant substances such as straw, leaves, bark, seeds, hulls, flowers, vegetables, or fruits. Woody plants have a good availability, small environmental burden and the quality of fiber is good. The above applies both to non-regenerated cellulose and also regenerated and processed forms of cellulose.

[0062] Plant materials are built up by a matrix formed by cellulose fibers also containing lignin and hemicelluloses. The cellulosic fibers that form such a matrix are fibril bundles which in turn consist of microfibrils. Through a fibrillation process the cellulose fibers are separated into a three-dimensional network of microfibrils with a large surface area. These entangled fibrils are called microfibrillar cellulose (MFC). The width of entangled fibrils in MFC may be from 50 nanometers to 2 micrometers and length or longitudinal dimension may be from 100 nanometers to 500 micrometers, such as from 100 nanometers to 200 micrometers. In an example, the cellulosic material comprises of consists of MFC. Within context of this disclosure, the method of manufacturing MFC is not limited. MFC may be produced from cellulose fibers using methods known within the art through high pressure, high temperature and high velocity impact homogenization, for instance. The homogenization process is used to delaminate or disintegrate the cell walls of the fibers and to liberate their sub- structural fibrils and microfibrils. Enzymatic and / or mechanical pre-treatments of wood fibers may also be used.

[0063] The MFC used may be non-regenerated and / or regenerated. Expressions “non-regenerated cellulose” or “natural cellulose” refer to cellulose or cellulose fibrils or fibers that have not undergone chemical or physical modification of their macromolecular structure. Non-regenerated MFC is substantially nonregenerated and consists mainly of crystalline structure of cellulose I. Cellulose I may have structures laand Ip. Man-made cellulosic fibers commonly used in textile applications are regenerated and their crystalline structure is mainly other than cellulose I. Conversion of cellulose I to cellulose II (or other forms, like cellulose III or cellulose IV) is irreversible. Thus, these forms are stable and cannot be converted back to cellulose I.

[0064] Within context of this disclosure the natural fibrous material is provided through mechanical disintegration, i.e., fibrillation, of the raw material. Fibrillation may be carried out, for example, using a stone mill, refiner, grinder, homogenizer, colloider, ultrasound-sonicator, fluidizer, or any combination thereof.

[0065] In an example, the aqueous suspension comprises from 90 to 96 wt.% of water and from 4 to 10 wt.% of dry matter comprising natural fibrous material and dispersing agent.

[0066] Dry matter of the aqueous suspension comprises at least 50 wt.% of natural fibrous material. Preferably, the amount of the natural fibrous material is from 50 to 95 wt.%. For example, the amount of the natural fibrous material may be from 60 to 95 wt.%, from 70 to 95 wt.%, from 80 to 95 wt.%, from 80 to 90 wt.%, or from 80 to 85 wt.%. Purpose of the dispersing agent is to improve separation of the fibrils of the natural fibrous material and to prevent their settling or clumping in the manufacturing process. The dispersing agent can be any anionic hydrophilic polymer. In an example, the dispersing agent is carboxymethyl cellulose (CMC). Alternatively, the dispersing agent may be any of the following: hydroxyethyl cellulose (HEC), ethyl hydroxyethyl cellulose (EHEC), methyl cellulose (MC), hydroxypropyl methyl cellulose (HPMC), hydroxyethyl methyl cellulose (HEMC), methyl ethyl hydroxyethyl cellulose (MEHEC), hydroxypropyl cellulose (HPC), ethyl cellulose (EC) and starch, or any combination thereof. Dispersing agent may also have an effect on tensile strength of the fibrous monofilament.

[0067] The dispersing agent may be used in an amount of 0.5 to 25 wt.% of the dry matter of the aqueous suspension. For example, the amount of the dispersing agent may be from 5 to 25 wt.%, from 10 to 25 wt.%, from 13 to 20 wt.%, such as about 14 wt.% of the dry matter of the aqueous suspension.

[0068] As already mentioned, optional additional component(s) include a wet strength agent, a hydrophobic agent, a crosslinking agent, a rheology modifier, or any mixture thereof.

[0069] The amount of the wet strength agent, if present, may be from 1 to 6 wt.%, such as from 2 to 5 wt.% of the dry matter of the aqueous suspension. For example, the amount of the wet strength agent may be about 3 wt.% of the dry matter of the aqueous suspension. In an example, the wet strength agent is a polyamidoamine-epichlorohydrin (PAE) resin. PAE provides improved wet strength properties such as wet tenacity and elongation to the fibrous monofilament. PAE may also prevent shrinkage and improve wet abrasion resistance.

[0070] The hydrophobic agent may be alkyl ketene dimer (AKD, an alkaline or neutral sizing agent), alkenylsuccinic anhydride (ASA, sizing agent), rosin (acidic sizing agent), natural wax, and modified sunflower-based adhesive (MSOHO) or any mixture thereof. In an example, the aqueous suspension contains AKD as the hydrophobic adhesive. As a hydrophobic adhesive AKD reduces the absorption properties of the fibrous monofilament. AKD may also increase strength of the fibrous monofilament. Amount of AKD, when used, may be from 0.5 to 10 wt.%, such as from 0.5 to 5 wt.% of the dry matter of the aqueous suspension.

[0071] Anionic polyacrylamide (aPAM) may be used as a rheology modifier. Alternatively, polyethylene oxide (PEO) may be utilized as a rheology modifier. Amount of the rheology modifier, if present, may be from 0.5 to 5 wt.%, such as from 2 to 4 wt.% of the dry matter of the aqueous suspension.

[0072] It is essential, that when aPAM is used it is added into the aqueous suspension. Thus, aPAM is added after exposing the mixture to homogenization in a homogenizer. This is because aPAM cannot tolerate the high shear forces caused by the homogenizing step.

[0073] Polyurethane (Pll) may be used as a crosslinking agent.

[0074] In an example, the aqueous suspension comprises or consists of water, MFC, CMC as dispersing agent, PAE as wet strength agent, AKD as hydrophobic agent, Pll as crosslinking agent and aPAM as rheology modifier.

[0075] The fibrous monofilament according to this disclosure may have a density of between 500 and 2000 kg / m3, for example between 1000 and 1700 kg / m3, such as about 1500 kg / m3.

[0076] The fibrous monofilament prepared from the aqueous suspension may be biobased and / or biodegradable. Biodegradability of a material means that greater than 90 % of the original material is converted into CO2, water and minerals by biological processes within 6 months.

[0077] The fibrous monofilament according to this disclosure finds use in fibrous materials, such as woven, knitted or non-woven materials or as composite materials. The fibrous monofilaments may be utilized for producing fiber or yarn for fibrous materials. Particularly, the fibrous monofilaments disclosed herein are utilizable for producing fiber or yarn for woven or knitted materials. The manufacturing method disclosed herein is such that fibrous monofilaments with properties (e.g., linear density and tenacity) required from monofilaments suitable for producing fiber or yarn for woven or knitted materials are produced.

[0078] The fibrous materials may be manufactured by using any methods known in the art. Exemplary uses of the fibrous materials include for example non-woven fabrics. Non-woven fabrics are sheet or web structures formed from fibers bonded together via mechanical, thermal or chemical treatment. The fibrous monofilament disclosed herein may be used for providing non-woven fabric for use e.g. in medical applications, such as protective layers, surgical masks, face masks, wipes and in wound care products. Non-woven materials may also find use in thermal insulation materials for example in clothing. Further, the fibrous monofilament disclosed herein may be used in any woven or knitted fabric or textile.

[0079] Examples

[0080] Exemplary fibrous monofilaments were prepared from aqueous suspensions wherein the dry matter of the suspension comprised or consisted of MFC, CMC (14%), PAE (2%), AKD (1 .5%), PU (1 %) and aPAM (2%).

[0081] In reference example, the aqueous suspension was produced by following the conventional method. The aqueous suspension was prepared in a batch-wise manner in a mixing tank. Water, MFC and CMC were mixed in the mixing tank so as to form a mixture. When the mixture was homogeneous enough, the mixture was pumped into a recirculation line. In the recirculation line the additional components (PAE, AKD, PU and aPAM) were added into the mixture one at a time, such that duration of dosing of each additional component corresponded with the recirculation time of the contents of the mixing tank. The in-line mixer of the recirculation line was utilized for mixing each additional component into the mixture prior to supplying the mixture back into the mixing tank. Once the additional components were added to the mixture, the thus formed aqueous suspension was mixed in the mixing tank by a tank mixer until the suspension was homogeneous. The aqueous suspension was extruded into a fibrous monofilament (reference). In inventive example, the aqueous suspension was produced by following the batch process as illustrated in Fig. 2. Water, MFC, CMC and additional components PAE, AKD and Pll were mixed in a first mixing tank so as to form a mixture. From the first mixing tank, the mixture was pumped into a first recirculation line. The first recirculation line comprised an in-line mixer for further mixing the mixture prior to supplying the mixture back into the first mixing tank. One to three recirculation rounds were utilized. From the first mixing tank the recirculated mixture was pumped into a homogenizer. In the homogenizer the mixture was exposed to homogenization so as to form an aqueous suspension. The aqueous suspension was transferred from the homogenizer to a second mixing tank. The aqueous suspension was mixed in the second mixing tank and pumped into a second recirculation line. In the second recirculation line aPAM was added into the aqueous suspension. An in-line mixer of the second recirculation line was utilized for mixing aPAM into the aqueous suspension prior to supplying it back into the second mixing tank. Once the aPAM was added to the aqueous suspension, the aqueous suspension was mixed in the second mixing tank by a tank mixer until the suspension was homogeneous. The aqueous suspension was extruded into a fibrous monofilament (inventive).

[0082] Mechanical properties of the prepared fibrous monofilaments were studied and are shown in Table 1 .

[0083] Table 1 .

[0084] Linear density was measured following standard EN ISO 1973: 1995. Tenacity and elongation were determined following standard ASTM 3822 / D3822M-14. The measurements were performed at RH 65% (+ / - 2%) and temperature 20 degrees C (+ / - 2 degrees C). As can be seen from Table 1 , mechanical properties of the fibrous monofilaments prepared from the aqueous suspension undergone homogenization are generally better when compared to those of the fibrous monofilament produced from aqueous suspension prepared by the conventional process. Linear density values as such are comparable, but smaller standard deviation of the inventive monofilaments suggests that the inventive monofilaments are of more uniform quality.

[0085] Amount of energy consumed by the process according to the inventive example was shown to be from about 25 to about 60% lower when compared to the energy consumed by the conventional method. Further, the process according to the inventive example was shown to be from about 50 to about 66% faster than the conventional process.

[0086] In a further example, effect of the homogenizing step(s) to the MFC fibril / fiber size distribution was studied. The analysis was performed with ABB Fiber Tester Plus according to an ISO 16065-2 standard method. The analysis gave results defined as the length-weighted proportions of fibers / fibrils. Three experiments employing from one to three homogenizing steps were conducted and length-weighted proportions of fibers / fibrils in the resulting suspension were determined. Results are shown in Table 2. It can be seen that the share of fibrils / fibers having a length below 100 pm gets higher when the number of the homogenizing steps is increased from one to two and from two to three.

[0087] Table 2.

Claims

Claims:1 . A method of producing an aqueous suspension for manufacturing a fibrous monofilament, the method comprising the following steps:- mixing (420) water, natural fibrous material and dispersing agent so as to form a mixture, and- exposing the mixture to homogenization (421 ) in a homogenizer so as to form the aqueous suspension.

2. The method according to claim 1 , wherein the method further comprises adding additional component(s) into the mixture prior to exposing the mixture to homogenization.

3. The method according to claim 1 or 2, wherein the method comprises homogenizing the mixture by applying shear forces to the components of the mixture.

4. The method according to claim 3, wherein the shear forces are generated by applying pressure loss via guiding the components of the mixture through an orifice, where an opening of the orifice and thus the homogenization of the homogenized mixture, is controllable by adjusting the opening of the orifice.

5. The method according to any of the preceding claims, wherein the method is implemented as a batch process or as a continuous process.

6. The method according to any of the preceding claims, wherein the natural fibrous material comprises fibrous material derived from cellulosic material , textile waste fibers, protein material, or any mixture thereof.

7. The method according to any of the preceding claims, wherein the natural fibrous material comprises or consists of MFC.

8. The method according to any of the preceding claims, wherein the additional component(s) comprise a wet strength agent, a hydrophobic agent, a crosslinking agent, a rheology modifier, or any mixture thereof.

9. The method according to any of the preceding claims, wherein the aqueous suspension comprises from 90 to 96 wt.% of water and from 4 to 10 wt.% of dry matter comprising natural fibrous material and dispersing agent.

10. A method of manufacturing a fibrous monofilament, the method comprising the following steps:- producing an aqueous suspension by a method defined in any of the claims 1 -9,- extruding (422) the aqueous suspension into a monofilament, and- drying (423) the monofilament.

11. A system for manufacturing a fibrous monofilament, the system comprising- a vessel (101 , 201 , 301 , 310) for forming a mixture comprising water, natural fibrous material and dispersing agent;- a homogenizer (204, 304) for homogenizing the mixture so as to form an aqueous suspension; and- an arrangement for extruding the aqueous suspension into a monofilament and drying the monofilament (312).

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