Method for improving strength properties of nonwoven materials,

Abstract

The invention relates to a method for improving the strength properties of a nonwoven material. The method includes forming a nonwoven web comprising cellulose-based fibers, and optionally drying the nonwoven web. A strength composition is applied to the nonwoven web. The strength composition comprises (i) a glyoxalated polyacrylamide and (ii) a natural polymer selected from the group consisting of non-charged and cationically charged polysaccharides, non-charged and cationically charged polysaccharide derivatives, and any mixture thereof. The invention also relates to the nonwoven material obtained and to the use of the strength composition.

Description

Technical Field

[0001] This invention relates to a method for improving the strength properties of nonwoven materials according to the preamble of the following independent claims. The invention also relates to the use of nonwoven materials obtained by this method and strength compositions thereof. Background Technology

[0002] Nonwoven materials are now used in a wide range of applications, from hygiene products to agriculture and the automotive industry. They are particularly useful for industrial and household cleaning, personal hygiene, beauty care, and medical care. With increasing environmental awareness among industry and consumers, there is growing focus on reducing the environmental impact of nonwoven production and the materials themselves. Due to the large production volumes and wide range of applications, even small improvements can have a significant impact.

[0003] Nonwoven webs can be manufactured using a wet-laid process, in which an aqueous fiber dispersion is deposited onto a screen (i.e., a metal mesh), and water is drained through the screen, forming a nonwoven web on the screen. Alternatively, nonwoven webs can be manufactured using an air-laid process, in which fibers are dispersed in an airflow and deposited onto a permeable belt, forming a nonwoven web of randomly oriented fibers on the permeable belt. The strength properties of both wet-laid and air-laid nonwoven webs can be improved by incorporating synthetic polymer fibers into the fiber dispersion. Alternatively or additionally, a bonding agent can be applied to the nonwoven web after its formation. The bonding agent used is a synthetic polymer made from petroleum-based raw materials. The most common polymers used at this time are acrylate polymers and copolymers, styrene-butadiene copolymers, and vinyl acetate copolymers. Therefore, the nonwoven industry currently uses a significant amount of synthetic fibers and synthetic bonding agents, i.e., non-renewable raw materials. Therefore, nonwoven wipes (wipes, cloths, paper towels), for example, are considered among the most contaminated single-use items and among the most problematic plastic-containing products. Consequently, there is an urgent need to reduce the use of synthetic fibers and / or synthetic adhesives in the production of nonwoven materials. Given the vast quantities of nonwoven materials produced, used, and discarded, even a small reduction in the use of synthetic fibers and / or synthetic adhesives will have a significant impact. However, the properties of nonwoven materials—namely, their strength, liquid absorption capacity, and flushability—should be maintained at appropriate levels. Summary of the Invention

[0004] The purpose of this invention is to reduce or even eliminate the aforementioned problems in the prior art.

[0005] The object of this invention is to provide a new method for improving the wet and / or dry strength properties of nonwoven materials, particularly the dry tensile strength of nonwoven materials.

[0006] Another object of the present invention is to provide a nonwoven material with enhanced strength properties.

[0007] To achieve the purposes presented above and other objectives, the present invention is characterized by the content presented in the characterizing portion of the appended independent claims. Detailed Implementation

[0008] The embodiments and advantages mentioned herein, where applicable, relate to products, methods, and uses according to the invention, even if not always specifically mentioned.

[0009] Typical methods for improving the strength properties of nonwoven materials according to the present invention include: - Form a nonwoven material web containing cellulose-based fibers. -Optionally, dry the nonwoven mesh. The strength composition is applied to the formed nonwoven web, the strength composition comprising (i) glyoxalized polyacrylamide and (ii) a natural polymer selected from non-charged and cationically charged polysaccharides, non-charged and cationically charged polysaccharide derivatives, and any mixture thereof.

[0010] Typical nonwoven materials according to the invention are obtained by the method according to the invention, and have a fibrous matrix comprising cellulose-based fibers.

[0011] Typical use of the strength composition according to the invention is for improving the strength properties of nonwoven materials containing cellulose-based fibers, the strength composition comprising (i) glyoxalized polyacrylamide and (ii) a natural polymer selected from non-charged and / or cationic charged polysaccharides, non-charged and cationic charged polysaccharide derivatives, and any mixture thereof.

[0012] It has been unexpectedly discovered that strength compositions comprising glyoxalized polyacrylamide and mixtures of specific non-charged natural polymers and / or cationic charged natural polymers improve the wet and / or dry strength properties of the nonwoven material. Strength compositions comprising bio-based natural polymers can replace at least a portion of fully synthetic adhesives and / or synthetic fibers, which are conventionally used in nonwoven materials to provide desired strength properties. The present invention thus provides at least similar or even enhanced strength properties for nonwoven materials while reducing the amount of synthetic polymer-based raw materials used. In particular, the present invention improves the dry tensile strength of the nonwoven web. An unexpected improvement in dry tensile strength is visible in both the machine direction (longitudinal) and cross-direction of the nonwoven web. Therefore, the present invention enables the production of nonwoven webs exhibiting uniform dry strength properties independent of the measurement direction. It is assumed that the application of the strength compositions of the present invention effectively improves the interbonding of cellulose-based fibers in the nonwoven web with each other or with other components of the nonwoven web. Surprisingly, even though the application of the strength composition improves the dry and / or wet strength properties of the nonwoven web, it generally retains its scattering properties.

[0013] According to one embodiment of the invention, the strength composition comprises: (i) glyoxalized polyacrylamide and (ii) a natural polymer selected from non-charged and cationic charged polysaccharides, non-charged and cationic charged polysaccharide derivatives, and any mixture thereof.

[0014] In this context, the term "nonwoven material" is understood as an engineered assemblies of fibers, primarily planar, that have been endowed with a predetermined degree of structural integrity, i.e., a measurable level of tensile strength, and excludes materials that can be obtained through weaving, knitting, or papermaking. Cellulose-based fibers and optional other fibers are engineered to a certain degree of structural integrity primarily through physical and / or chemical means other than hydrogen bonding between fibers.

[0015] The nonwoven web according to the invention can be formed from randomly oriented cellulose-based fibers by wet spinning or air-forming. In wet spinning, an aqueous fiber dispersion comprising cellulose-based fibers and possibly other fibers is supplied onto a filter screen, and water is discharged through the filter screen, thereby forming a fiber nonwoven web on the filter screen. In air-forming, cellulose-based fibers and possibly other fibers are fed to a forming head by an airflow, the forming head providing a homogeneous fiber mixture. A controlled portion of the fiber mixture is removed from the forming head, propelled by air, and deposited onto a moving belt, forming a randomly oriented nonwoven web on the moving belt. The methods of manufacturing nonwoven webs using wet spinning or air-forming are known to those skilled in the art.

[0016] After the nonwoven web is formed, a strength composition is applied to the web as a post-treatment. In the case of nonwoven web formation by wet spinning, it is preferable to dry the web before applying the strength composition. In addition to applying the strength composition, the nonwoven web may also undergo mechanical bonding, such as hydroentangling or needle punching. In hydroentangling, the web is bonded using a pressurized water jet, and in needle punching, the web is bonded by pushing and pulling needles through. Mechanical bonding can be performed before and / or after applying the strength composition, but is preferably performed before applying the strength composition.

[0017] The strength composition is applied to the surface of the nonwoven web. Preferably, the strength composition is added to the surface of the unsizing or uncoated nonwoven web such that the components of the strength composition are in direct contact with the cellulose-based fibers of the nonwoven web.

[0018] The strength composition can be applied to the formed nonwoven fabric web by any suitable application method. According to one embodiment of the invention, the strength composition can be applied to the nonwoven fabric web by spraying, surface sizing, coating, or bath immersion, preferably by spraying, surface sizing, or coating. For example, the application method can be selected based on the desired application amount or the available operating equipment. An advantage of the invention is that existing application equipment used for applying conventional adhesives can be used to apply the strength composition according to the invention.

[0019] The strength composition can be applied to one large surface or two large surfaces of the nonwoven web, preferably to both large surfaces of the nonwoven web.

[0020] The strength composition according to the invention comprises a combination of glyoxalized polyacrylamide and a natural polymer selected from non-charged polysaccharides, cationic charged polysaccharides, non-charged polysaccharide derivatives, cationic charged polysaccharide derivatives, and any mixtures thereof. The glyoxalized polyacrylamide and the natural polymer are mixed together before being applied to the nonwoven fabric web. According to embodiments of the invention, the strength composition is a premix or preform formed by mixing before applying the strength composition to the nonwoven fabric web. Typically, the strength composition is applied to the nonwoven fabric web as a diluted aqueous solution. The pH of the aqueous solution of the strength composition can be in the range of 2.5-10, typically 3-9, or 4-9. When applied to the nonwoven fabric web, the dry solids content of the aqueous solution of the strength composition can be in the range of 1-50 wt%, preferably 1-20 wt%, based on the total weight of the aqueous solution. The dry solids content and viscosity of the aqueous solution containing the strength composition can be adjusted depending on the application method used.

[0021] The strength composition includes glyoxalized polyacrylamide as one of its components. According to one embodiment of the invention, the strength composition may comprise glyoxalized polyacrylamide and a natural polymer in a weight ratio from 40:60 to 1:99, preferably from 45:55 to 3:97, more preferably from 30:70 to 5:95. This means that a large portion, even the main portion, of the strength composition may comprise a natural polymer, while still providing the desired strength properties for the nonwoven material.

[0022] Glyoxal-modified polyacrylamide can be produced based on the principle of biomass balance, in which most or all of the fossil-based raw materials are replaced by bio-based and renewable mass-balanced raw materials.

[0023] Glyoxalized polyacrylamide can be obtained by reacting linear polyacrylamide (the base polymer) with glyoxal, thereby obtaining a polyacrylamide polymer with side-attached glyoxalized groups. Preferably, the glyoxalized polyacrylamide is a glyoxalized cationic polyacrylamide. The cationic polyacrylamide used as the base polymer can be a copolymer obtained by polymerizing acrylamide or a primary amine-containing monomer with at least one cationic monomer. The primary amine-containing monomer can be selected from methacrylamide, ethylacrylamide, N-ethylmethacrylamide, N-butylmethacrylamide, or N-ethylmethacrylamide, and any combination thereof. The cationic monomer can be selected from diallyl dimethylammonium chloride (DADMAC), [3-(acrylamido)propyl]trimethylammonium chloride (APTAC), and [3-(methacrylamido)propyl]trimethylammonium chloride (MAPTAC), and any combination thereof. The cationic polyacrylamide used as the base polymer, and thus the glyoxalized polyacrylamide, can each contain only one type of cationic monomer, or they can contain two or more types of cationic monomers. Preferably, the cationic monomer may be diallyl dimethyl ammonium chloride (DADMAC).

[0024] Polyacrylamide used as the base polymer for glyoxalized polyacrylamide can be obtained by polymerization of acrylamide or a primary amine-containing monomer with at least 5 mol%, preferably at least 7 mol%, more preferably at least 10 mol%, of at least one cationic monomer as defined above. According to embodiments of the invention, cationic polyacrylamide polymers can be obtained by polymerization of acrylamide or a primary amine-containing monomer with 5-40 mol%, preferably 7-30 mol%, more preferably 10-25 mol%, sometimes 10-20 mol%, of at least one cationic monomer as defined above. The percentages are calculated based on the total molar amount of polymerizable monomers in the polymerization.

[0025] Aqueous solutions of glyoxalized polyacrylamide can have a pH range of 2.7–4.0.

[0026] According to one embodiment of the invention, the strength composition may comprise glyoxalized cationic polyacrylamide having a charge density in the range of 0.5-2.5 meq / g or 0.5-2 meq / g, preferably 0.75-1.9 meq / g, more preferably 1-1.8 meq / g at pH 4.3. The charge density can be determined, for example, by using polyelectrolyte titration. The defined charge density value enables effective interaction between the strength composition and the negatively charged groups on the surface of the cellulose-based fibers.

[0027] The weight-average molecular weight of the glyoxalized polyacrylamide used in the strength composition can be in the range of 100,000-1,000,000 g / mol, preferably 200,000-700,000 g / mol, and more preferably 250,000-550,000 g / mol. The weight-average molecular weight is determined by size exclusion chromatography and calibrated using polyethylene oxide (PEO) calibration standards.

[0028] In addition to glyoxalized polyacrylamide, the strength compositions according to the invention also comprise natural polymers selected from non-charged and / or cationic charged polysaccharides, and / or non-charged and / or cationic charged polysaccharide derivatives. The strength compositions may comprise only one type of polysaccharide or polysaccharide derivative, or they may comprise two or more different non-charged and / or cationic charged polysaccharides, and / or non-charged and / or cationic charged polysaccharide derivatives. In this context, "derivative" means a polysaccharide that has been chemically modified by incorporating additional substituents into its structure.

[0029] According to one embodiment of the invention, the natural polymer can be a polysaccharide derivative selected from non-charged cellulose esters, cationic cellulose esters, non-charged cellulose ethers, cationic cellulose ethers, and any mixtures thereof. Cellulose esters and cellulose ethers are preferably polysaccharide derivatives because they are structurally similar to the cellulose-based fibers of nonwoven materials and are therefore well compatible with them. Cellulose esters and cellulose ethers are also renewable and potentially even biodegradable materials, and their use in improving the strength properties of nonwoven materials can significantly reduce the environmental impact of the resulting nonwoven materials.

[0030] The polysaccharide derivative may be selected from alkyl cellulose, hydroxyalkyl alkyl cellulose, hydroxyalkyl cellulose, and any mixture thereof. For example, non-charged or cationic cellulose ethers suitable for use in the strength compositions of the present invention may be selected from alkyl cellulose, hydroxyalkyl alkyl cellulose, hydroxyalkyl cellulose, and any mixture thereof. In particular, the cellulose ether may be selected from C1-C4 alkyl cellulose, C1-C4 hydroxyalkyl cellulose, and any mixture thereof. For example, the natural polymer of the strength composition may comprise or consist of a polysaccharide derivative selected from methylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxybutylcellulose, (hydroxyethyl)methylcellulose and (hydroxypropyl)methylcellulose, and any mixture thereof.

[0031] According to a preferred embodiment of the invention, the strength composition comprises a polysaccharide derivative comprising or consisting of hydroxyethyl cellulose.

[0032] The cellulose ester suitable for use in the strength compositions of the present invention may be selected from short-side-chain (C1-C6) cellulose esters, such as cellulose acetate, cellulose propionate acetate, cellulose butyrate acetate, cellulose valerate acetate, cellulose hexanoate, and any mixture thereof.

[0033] The polysaccharide derivative used in the strength composition may have a number-average molecular weight Mn in the range of 50,000-400,000 g / mol, preferably 70,000-120,000 g / mol, more preferably 80,000-100,000 g / mol. The number-average molecular weight can be determined by size exclusion chromatography and calibrated using polyethylene oxide (PEO) calibration standards.

[0034] According to one embodiment, the strength composition comprises a natural polymer, which is a non-charged or cationic charged polysaccharide selected from starch, modified starch, starch derivatives, and any mixture thereof. Suitable starch derivatives include, for example, alkali-modified starch; bleached starch; oxidized starch; enzyme-treated starch; acetylated starch; hydroxyalkyl starch, such as hydroxyethyl starch, hydroxypropyl starch; octenyl succinate starch, such as sodium octenyl succinate starch, aluminum octenyl succinate starch; maltodextrin; cyclodextrin; starch phosphates, such as monostarch phosphate, distarch phosphate; cationic starch; dextran; pullulan; glycogen, carboxymethylated starch, and any mixture thereof.

[0035] According to a preferred embodiment, the natural polymer comprises cationic starch. In embodiments according to the invention, the cationic starch has a degree of substitution in the range of 0.1-1.0, preferably 0.2-1.0, more preferably 0.3-0.9, and even more preferably 0.4-0.8. The charge density of the cationic starch can be freely selected according to the degree of substitution and the pH used. The charge density of the cationic starch can be from 0.1 meq / g to 3 meq / g. Cationic starch is widely available in large quantities and can be used as a mixture with other non-charged or cationicly charged polysaccharides or polysaccharide derivatives.

[0036] According to a preferred embodiment of the invention, the strength composition comprises a natural polymer selected from hydroxyethyl cellulose, cationic starch, or any mixture thereof, more preferably hydroxyethyl cellulose or cationic starch.

[0037] When natural polymers are dissolved in water, the resulting aqueous solution can have a pH in the range of 5-10, for example, 6-8.5.

[0038] The strength composition may be added to or applied to the nonwoven web in an amount of 1-60 wt%, preferably 5-20 wt%, calculated from the dry weight of the fibers in the nonwoven web.

[0039] The strength composition is applied to a nonwoven web comprising cellulose-based fibers. This nonwoven web may contain 80-100 wt%, preferably 90-100 wt%, more preferably 95-100 wt%, and sometimes even 96-100 wt% of cellulose-based fibers. According to a preferred embodiment, the nonwoven material is composed of cellulose-based fibers. The cellulose-based fibers may comprise or be selected from natural cellulose fibers, man-made cellulose fibers (i.e., cellulose-derived man-made fibers), and any mixture thereof.

[0040] Natural cellulose fibers can be selected from wood fibers, such as cork or hardwood fibers; seed and hair fibers, such as cotton, kapok, or milkgrass fibers; leaf fibers, such as sisal, abaca, or pineapple fibers; bast fibers, such as flax, hemp, jute, or kenaf fibers; and any combination thereof. Natural cellulose fibers may also include cellulose fibers of microbial origin. Natural cellulose fibers can have a fiber length in the range of 0.5–3.5 mm, preferably 1–3 mm.

[0041] Man-made cellulose fibers may include regenerated cellulose fibers, such as viscose, lyocell, modal, acetate, triacetate, cuprammonium, or any combination thereof. Man-made cellulose fibers may be or include Infinna™, Ioncell™, or Spinnova™ fibers, and are preferably short fibers. Man-made cellulose fibers may have a fiber length in the range of 3-15 mm, preferably 5-13 mm, and more preferably 5-12 mm.

[0042] Cellulose-based fibers (both natural and man-made cellulose fibers) may include virgin fibers, regenerated fibers, or a mixture of virgin and regenerated fibers. Fiber dispersions may also contain only virgin fibers and / or only regenerated fibers. Cellulose-based fibers may alternatively or additionally be fibers derived from agricultural waste or residues, or fibers derived from food processing and / or beverage industry waste, such as citrus industry waste.

[0043] According to one embodiment of the invention, the nonwoven web may comprise 50-100 wt%, preferably 60-99 wt%, more preferably 60-95 wt% of natural cellulose fibers, calculated on a dry weight basis. The nonwoven web may comprise 0-50 wt%, typically 1-40 wt%, more typically 5-40 wt% of synthetic cellulose fibers. The use of the strength composition makes it possible to increase the amount of natural cellulose fibers in the nonwoven web without impairing or reducing its strength properties. Increasing the amount of natural cellulose fibers makes the nonwoven material more sustainable and easier to deposit after use. Furthermore, natural cellulose fibers absorb moisture / water, and thus provide advantageous absorption properties for the nonwoven material.

[0044] In addition to cellulose-based fibers, the nonwoven material web may contain synthetic fibers, such as synthetic polymer fibers, carbon fibers, and / or glass fibers. Synthetic polymer fibers may be thermoplastic polymer fibers, such as polyolefin fibers, for example, polyethylene fibers, polypropylene fibers; polyamide fibers, such as aromatic polyamide fibers; polyester fibers; polylactide fibers; or any mixture thereof. The nonwoven material typically contains synthetic fibers in an amount of <10 wt%, preferably <5 wt%, more preferably <1 wt%. According to one embodiment, the nonwoven material does not contain synthetic fibers selected from synthetic polymer fibers, carbon fibers, and / or glass fibers, and especially does not contain synthetic polymer fibers. The strength composition according to the invention enables the production of nonwoven materials that provide sufficient strength properties without the use of synthetic fibers, particularly synthetic polymer fibers.

[0045] The nonwoven material of the present invention, obtained by the method according to the present invention, can have a content of 10-260 g / m². 2 Preferred concentration: 30-150 g / m 2 More preferably 40-70 g / m 2 Weight within a range. Nonwoven materials can have, for example, a weight of 30-100 g / m². 2 Preferred concentration: 45-90 g / m 2 More preferably 50-70 g / m 2 Weight within the specified range.

[0046] The nonwoven materials manufactured according to the present invention can be used, for example, as personal and industrial wiping products (personal / industrial wipes), household articles (e.g., tabletops), agricultural products, and geotextiles. The manufactured nonwoven materials can preferably be disposed of after use by flushing, composting, decomposition, recycling, or similar end-of-life disposal methods.

[0047] Nonwoven materials obtained by using the strength composition according to the invention can have

[0048] - At least 100%, preferably at least 200%, more preferably at least 300%, sometimes even at least 500%, higher dry tensile strength, and / or

[0049] -At least 50%, preferably at least 75%, more preferably at least 100%, higher wet strength The same nonwoven material is manufactured without applying any chemical composition to the nonwoven fabric web. Although both dry and wet strength properties are significantly improved, the nonwoven material according to the invention generally retains its scattering properties.

[0050] experiment

[0051] Some embodiments of the invention are described in the following non-limiting examples.

[0052] Preparation of strength composition

[0053] Prepare a strength composition comprising the following

[0054] 1) Glyoxal-modified polyacrylamide, GPAM1 (Kemira Oyj), and cationic starch (Hi-Cat 21370, Roquette); and

[0055] 2) Glyoxalized polyacrylamide, GPAM1 (Kemira Oyj) and hydroxyethyl cellulose, HEC (SigmaAldrich); For testing purposes. The strength composition comprises 30 wt% glyoxalized polyacrylamide and 70 wt% cationic starch or HEC. The strength composition is prepared at a total solids content of 1 wt% to provide the desired viscosity.

[0056] The glyoxal-modified polyacrylamide GPAM1 used has a weight-average molecular weight of approximately 400,000 g / mol and a charge density of approximately 1.6 meq / g. GPAM1 was diluted with deionized water to a 1 wt% solution.

[0057] Hydroxyethyl cellulose (HEC) was used as a 1 wt% solution, which was prepared by measuring cold deionized water into a beaker with a magnetic stirrer and gradually spraying hydroxyethyl cellulose into a vortex for 1.5 hours while mixing.

[0058] The cationic starch was used as a 1 wt% solution, which was prepared by mixing starch into deionized water at room temperature and heating the mixture to 94°C–98°C, wherein the mixture was boiled for 30 minutes. While mixing, the resulting starch solution was cooled to room temperature (approximately 22–25°C).

[0059] A strength composition is prepared by mixing appropriate portions of the components together. The strength composition is continuously mixed for 30 minutes using a magnetic stirrer.

[0060] The commercially available adhesive used as a reference was diluted with deionized water to a solids concentration of 3 wt%.

[0061] Manufacturing of nonwoven materials

[0062] Air-laid nonwoven fabrics were manufactured using a pilot-scale air-laid unit (Dan-Web, Denmark) and a fiber dispersion comprising commercially available fluff pulp (Golden isles fluff pulp, GP cellulose) with an average fiber length of 2 mm and viscose fibers (1.7 dtex, Kelheim fibers) with a fiber length of 10 mm. On a dry weight basis, the fiber dispersion contained 70 wt% fluff pulp and 30 wt% viscose fibers. The air-laid nonwoven fabrics were calendered at 100°C, a speed of 1 m / min, and a gap of 0.02 mm to reduce bulkiness and delamination.

[0063] Apply the strength composition in the desired amount using a spraying device (Campen, Denmark) and dry in a trough-air oven. Spray the strength composition onto both sides of the nonwoven fabric and dry in a trough-air oven at 140°C for 3 minutes after each spray.

[0064] The strength compositions tested and the amounts applied are given in Table 1. Commercially available rinseable wet wipes were used as references. Commercially available acrylic adhesives and commercially available bio-based adhesives were used as reference strength compositions.

[0065] Table 1. Strength test compositions and application amounts

[0066] Testing of nonwoven materials

[0067] Before testing, the nonwoven material prepared above was conditioned at 23°C and 50% relative humidity for 20 minutes.

[0068] The following properties were tested from samples of nonwoven materials using a defined test method / Nonwoven Standard Procedure (NWSP): Wet tensile strength: EDANA–NWSP 1104R0 (20), five parallel measurements Dry tensile strength: EDANA–NWSP 1104R0 (20), five parallel measurements Liquid absorbance capacity (LAC): EDANA–NWSP 0101R0 (20), five parallel measurements Washability: Evaluated based on decomposition in a drainage test. Place the sheet sample in 1 liter of water and agitate at 100 rpm for 3 hours. Change direction every 45 minutes. Pour the contents through a 12.5 mm sieve, and define the passing level as >50% passing. Perform two parallel measurements.

[0069] Measurements were taken of the nonwoven material samples in the machine direction (MD) and machine transverse direction (CD). The measurement characteristics of the manufactured nonwoven materials are given in Table 2.

[0070] Table 2. Properties of the manufactured nonwoven materials.

[0071]

[0072] The results in Table 2 clearly show that the strength composition containing glyoxalized polyacrylamide and polysaccharide / polysaccharide derivatives significantly improves the strength properties of nonwoven materials, especially the dry tensile index. Simultaneously, the liquid absorption capacity and washability of the nonwoven materials are maintained. Therefore, this invention provides a more sustainable way to produce nonwoven materials without compromising their performance properties.

[0073] Although the invention has been described with reference to what now appears to be the most practical and preferred embodiment, it should be understood that the invention is not limited to the embodiments described above, but is intended to also cover various modifications and equivalents within the scope of the appended claims.

Claims

1. A method for improving the strength properties of nonwoven materials, the method comprising: - Form a nonwoven material web containing cellulose-based fibers. - Optionally, dry the nonwoven fabric web. Its features are, The strength composition is applied to the nonwoven fabric web, wherein the strength composition comprises (i) glyoxalized polyacrylamide and (ii) a natural polymer selected from non-charged and cationic charged polysaccharides, non-charged and cationic charged polysaccharide derivatives, and any mixture thereof.

2. The method according to claim 1, characterized in that, The strength composition is applied to the nonwoven fabric web by spraying, surface sizing, coating, or immersion.

3. The method according to claim 1 or 2, characterized in that, The nonwoven material web is formed by air-jet forming or wet forming.

4. The method according to claim 1, 2 or 3, characterized in that, The strength composition comprises the glyoxalized polyacrylamide and the natural polymer in a weight ratio of 40:60 to 1:99, preferably 30:70 to 5:

95.

5. The method according to any one of claims 1-4, characterized in that, The glyoxalized polyacrylamide has a charge density measured at pH 4.3 in the range of 0.5-2.5 meq / g or 0.5-2 meq / g, preferably 0.75-1.9 meq / g, more preferably 1-1.8 meq / g.

6. The method according to any one of claims 1-5, characterized in that, The glyoxalized polyacrylamide has a weight-average molecular weight in the range of 100,000-1,000,000 g / mol, preferably 200,000-700,000 g / mol, and more preferably 250,000-550,000 g / mol.

7. The method according to any one of claims 1-6, characterized in that, The natural polymer is a polysaccharide derivative selected from non-charged and cationic cellulose esters, non-charged and cationic cellulose ethers, and any mixture thereof.

8. The method according to claim 7, characterized in that, The polysaccharide derivative is selected from alkyl cellulose, hydroxyalkyl alkyl cellulose, hydroxyalkyl cellulose, and any mixture thereof.

9. The method according to claim 8, characterized in that, The polysaccharide derivative is selected from the group consisting of: methylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxybutylcellulose, (hydroxyethyl)methylcellulose, and (hydroxypropyl)methylcellulose, and any mixture thereof, preferably hydroxyethylcellulose.

10. The method according to any one of claims 1-9, characterized in that, The polysaccharide derivative has a number-average molecular weight Mn in the range of 50,000-400,000 g / mol, preferably 70,000-120,000 g / mol, and more preferably 80,000-100,000 g / mol.

11. The method according to any one of claims 1-10, characterized in that, The natural polymer includes cationic starch.

12. The method according to any one of claims 1-11, characterized in that, The resulting nonwoven material web contains 90-100 wt%, preferably 95-100 wt%, of cellulose-based fibers.

13. The method according to any one of claims 1-11, characterized in that, The resulting nonwoven web is subjected to mechanical bonding, such as hydroentangling or needle punching, which is performed before and / or after the strength composition is applied.

14. A nonwoven material obtained by the method according to any one of claims 1-13, having a fiber matrix comprising cellulose-based fibers.

15. Use of a strength composition for improving the strength properties of a nonwoven material comprising cellulose-based fibers, the strength composition comprising (i) glyoxalized polyacrylamide and (ii) a natural polymer selected from non-charged and / or cationic charged polysaccharides, non-charged and cationic charged polysaccharide derivatives, and any mixture thereof.

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