METHOD FOR CONSOLIDATING A FIBROUS MATERIAL WITH A BIO-BASED BINDER POLYMER, A CONSOLIDATED FIBROUS MATERIAL AND AN AQUEOUS BINDER SOLUTION

Abstract

A method for consolidating a fibrous material of plant-based fibers, such as cellulose fibers and/or poly-lactic acid fibers, the method including: applying to the fibrous material an aqueous solution including a cellulose derivative, and/or a salt thereof, and an acid, the aqueous solution having a pH within the range of from 3 to 7, optionally within the range of from 3 to 6, optionally within the range of from 3 to 4.5; and drying the bonded fibrous material, optionally at 100° C. or higher. Also, a fibrous material formed by the method, an aqueous binder solution including a cellulose derivative, and/or a salt thereof, and an acid, and a nonwoven material including airlaid plant-based fibers being consolidated by a bio-based binder in the presence of a carboxylic acid, the bio-based binder being a cellulose derivative, and/or a salt thereof.

Claims

1. A method for consolidating a fibrous material comprising plant-based fibers, the method comprising the steps of: applying to the fibrous material an aqueous solution comprising a cellulose derivative, and/or a salt thereof, and an acid, the aqueous solution having a pH within the range of from 3 to 7; and drying the bonded fibrous material.

2. The method according to claim 1, wherein the cellulose derivative, and/or a salt thereof, is carboxymethyl cellulose and/or sodium carboxymethyl cellulose.

3. The method according to claim 1, where the fibrous material is an airlaid, wetlaid, foam formed or carded nonwoven material comprising plant-based fibers.

4. The method according to claim 1, wherein the acid is a monoprotic acid.

5. The method according claim 1, wherein the aqueous solution furthermore comprises a pH control agent.

6. The method according to claim 1, wherein the acid is carboxylic acid.

7. The method according to claim 6, wherein the carboxylic acid is a monocarboxylic acid.

8. The method according to claim 6, wherein the carboxylic acid is a polycarboxylic acid.

9. The method according claim 1, wherein the method comprises the step of adding a bio-based plasticizer to the fibrous material.

10. The method according to claim 1, wherein a ratio of the cellulose derivative, and/or a salt thereof, and the acid is from 1.2:1.

11. The method according to claim 1, wherein the amount of acid is within the range of from 0.01 wt-% to 3 wt-% of the aqueous binder solutions total mass.

12. The method according to claim 1, wherein the amount of cellulose derivative, and/or a salt thereof, is within the range of from 0.4 wt-% to 6 wt-% of the aqueous binder solutions total mass.

13. The method according to claim 1, wherein the cellulose derivative, and/or a salt thereof, has a degree of substitution of from 0.65 to 1.

14. The method according to claim 1, wherein the aqueous solution is applied by spraying or coating.

15. A fibrous material obtained by the method according to claim 1.

16. An aqueous binder solution comprising a cellulose derivative, and/or a salt thereof, and an acid, the aqueous solution having a pH within the range of from 3 to 7.

17. The aqueous binder solution according to claim 16, wherein the cellulose derivative, and/or a salt thereof, is carboxymethyl cellulose and/or sodium carboxymethyl cellulose.

18. The aqueous binder solution according to claim 16, wherein the acid is a carboxylic acid.

19. The aqueous binder solution according to claim 16, wherein the aqueous solution furthermore comprises a pH control agent.

20. The aqueous binder solution according to claim 16, wherein a ratio of the cellulose derivative, and/or a salt thereof, and the acid is from 1.2:1.

21. The aqueous binder solution according to claim 16, wherein the amount of acid is within the range of from 0.2 wt-% to 3 wt-% of the aqueous binder solution total mass.

22. A nonwoven material comprising plant-based fibers, the plant-based fibers being consolidated together by a bio-based binder in presence of a carboxylic acid, the bio-based binder being a cellulose derivative, and/or a salt thereof, wherein the nonwoven has a pH within the range of from 3.5 to 5.5, as measured with the method as disclosed herein.

23. A nonwoven material comprising plant-based fibers, the plant-based fibers being consolidated together by a bio-based binder in presence of a carboxylic acid, the bio-based binder being a cellulose derivative, and/or a salt thereof, the nonwoven having a wet maximum tensile strength in machine direction (MD) of 100 N/m or more, and wet maximum tensile strength in cross direction (CD) of 100 N/m or more, as measured according to NWSP 110.4R0 (15).

24. The nonwoven material according to claim 22, wherein the plant-based fibers are cellulosic fibers and/or polylactic acid fibers.

25. The nonwoven material according to claim 22, wherein the nonwoven material is an airlaid nonwoven material.

26. The nonwoven material according to claim 22, wherein the carboxylic acid is any one of lactic acid, salicylic acid and/or citric acid.

27. The nonwoven material according to claim 22, wherein the carboxylic acid is a monocarboxylic acid.

28. The nonwoven material according t claim 22, wherein the nonwoven material has a wet elongation in machine direction (MD) of at least 6%, and a wet elongation in cross direction (CD) of at least 6%, as measured by a tensile tester according to NWSP 110.4R0 (15).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0056] FIG. 1 shows a graph comparing the wet and dry tensile strength of a consolidated fibrous material according to the present invention with different ratios of CMC and acid;

[0057] FIG. 2 shows a graph comparing the wet tensile strength of a consolidated fibrous material according to the present invention with different pH;

[0058] FIG. 3 shows a graph comparing the wet tensile strength of a consolidated fibrous material according to the present invention with different pH reached by CMC/acid ratio;

[0059] FIG. 4 shows a graph comparing the wet tensile strength of a consolidated fibrous material according to the present invention with different pH reached by pH adjustment by HCl or NaOH;

[0060] FIG. 5 shows a graph comparing surface pH measured on consolidated fibrous materials according to the present invention;

[0061] FIG. 6 shows a graph illustrating a comparison of dry and wet tensile strength of a fibrous material consolidated with hydroxyethyl cellulose (HEC) and citric acid (CA) in two different HEC/CA ratio's;

[0062] FIG. 7 shows a graph illustrating a comparison of dry and wet elongation of a fibrous material consolidated with HEC and citric acid in two different HEC/CA ratio's;

[0063] FIG. 8 shows a graph illustrating a comparison of dry and wet tensile strength of a fibrous material consolidated with two different cellulose derivatives and an acid and with different cellulose derivatives/acid ratio's;

[0064] FIG. 9 shows a graph illustrating a comparison of dry and wet elongation of a fibrous material consolidated with different cellulose derivatives and with different cellulose derivative/acid ratio's; and

[0065] FIG. 10 shows a graph illustrating a comparison of dry and wet tensile strength of a fibrous material consolidated with CMC and CA with different CMC/CA ratio's.

DETAILED DESCRIPTION

Experimental Section

[0066] Following section will describe the experimental part including equipment, chemicals and laboratory methods. A detailed description of physical testing on material properties will be included as well.

Equipment and Material

[0067] The equipment used for laboratory testing is listed below; [0068] A pH meter of the brand VWR sympHony was used for measuring the pH of the binder solutions. [0069] A manual spray equipment of the brand Walther Pilot was used for spraying of the binder solutions. [0070] For measuring the thickness of the materials, a thickness gauge of the brand Mitutoyo was used. [0071] A tensile tester of the brand LLOYD LS1 was used for measuring wet and dry tensile strength.

Materials and Chemicals

[0072] The CMC material used as binder in the nonwoven materials is from Sigma Aldrich and is sodium CMC, supplier reference C9481. It has a viscosity within the range of from 400 cps to 800 cps, a DS of from 0.65 to 0.9 and a sodium content of from 6.5% to 9.5%.

[0073] EVA; Ethylene-Vinyl Acetate; aqueous copolymer dispersion based on vinyl acetate and ethylene; grade name; Vinamul Elite 25; supplier: Celanese.

[0074] HEC; Hydroxy-Ethyl-Cellulose; grade name; Natrasol™ 250LR; supplier Ashland.

[0075] Glycerol (purity>=99%); Analytical reagent grade; CAS Number 56-81-5; supplier; Fisher Scientific.

[0076] CA; Citric Acid; CAS Number 77-92-9; supplier Alfa Aesar.

[0077] Lactic Acid, 85%, ACS reagent ACROS Organics, (2-hydroxypropionic acid, DL-Lactic acid); CAS Number 50-21-5, supplier Fisher scientific

[0078] SA; Salicylic acid (2-Hydroxybenzoic acid), >=99.0%; CAS Number 69-72-7, Sigma Aldrich (product number 84210)

[0079] HCl; Hydrochloric acid; CAS Number 7647-01-0; 32-38% solution; supplier Fisher Scientific

[0080] NaOH; Sodium hydroxide; CAS Number 1310-73-2; supplier Fisher Scientific

Nonwoven Material

[0081] Throughout the description all testing will be performed on a nonwoven cloth based on cellulose fibers derived from wood. The nonwoven cloths are produced by airlaid web formation and have no additives beyond the basic cellulosic fibres. The size of each unbonded airlaid nonwoven cloth is 250×340 mm.

[0082] The combinations of substances, dry content in solution, pH of spraying solution and add-on are presented in the tables below. As reference binder an EVA binder is used.

Preparation of the Aqueous Solutions

[0083] The aqueous solutions were prepared according to details in the tables below. To enable dissolution of the cellulose derivative, the solutions were stirred in a magnetic stirrer for at least 4 hours. The glycerol and the acid are added before the spraying. The pH of the aqueous solutions was measured. Some of the aqueous solutions were thereafter adjusted by either HCl or NaOH to reach a specified pH as illustrated in the tables.

Spraying and Drying of the Aqueous Solution

[0084] The mixed final aqueous solutions are added to a manual spraying equipment. 20 g of the mixed aqueous solution is added per nonwoven cloth. The nonwoven cloth is placed on a steel tray with cavities which is placed in a fume cupboard. The cloth and the tray may be angled or leaned against the wall of the fume cupboard to provide optimum spraying range. Thus, it is of importance to ensure that the cloth is properly fixed to the tray, perhaps with help of clamps or the like. The cloth is then evenly sprayed with binder solution at one side on a distance of about 10 cm, and dried in an oven directly afterwards for 15 minutes at 150° C. After drying for 15 minutes the procedure is repeated for the remaining side of the cloth. The mass of spraying solution should be approximately 10 g per side of each cloth.

Measurement of pH-Level in the Aqueous Solution

[0085] The pH-levels of selected samples of binder combinations are measured with a pH-meter of the brand VWR SympHony. An electrode is rinsed with de-ionized water and then placed in a small beaker containing the binder mixture. The electrode is kept still until the display stops blinking and the final pH-value is logged.

Measurement of pH Level on Nonwoven Sample

[0086] Nonwoven materials of the same type as used in all experiments were cut in pieces of 5×5 cm. The material piece to be tested was placed on a plate. Then, 1 ml of 0.9% NaCl was added onto the nonwoven material. The pH was then measured directly on the nonwoven surface with a flat pH electrode. The pH value was measured at three different points and later reported as an average of the three points.

Thickness and Basis Weight

[0087] The basis weight is measured by weighing the cloth on a scale giving the results in gram. The results are then recalculated by adding the dimensions of the cloth and presented in g/m2. This is done on all cloths from each sample. The thickness is measured by means of a measuring foot with a fixed load which is lowered onto the sample. The thickness is read off at the digital thickness gauge. The pressure plate gives a static load of 0.5 kPa. These measurements are repeated 5 times for different part of each cloth and the results are given in millimeters.

Dry and Wet Tensile Strength

[0088] The EDANA standard method NWSP 110.4R0 (15) “Breaking Force and Elongation of Nonwoven Materials” (Strip Method) is used for measuring tensile strength and elongation. The type of specimen is according to Option B—50 mm strip tensile and with the Style of tensile testing machine option a) i.e. a Constant-rate-of-extension (CRE). The clamping distance is 100 mm, instead of 200 mm according to the standard method.

[0089] Measurements are performed on 5 dry pieces of each sample in machine direction (MD) and 5 pieces of each sample in cross direction (CD). Furthermore, measurements are also conducted on wet samples as well. For the wet testing one sample is soaked in water just before stretching to rupture/break at a constant rate of elongation. The tensile strength will record as a function of the elongation at this measurement as well. From received data, the parameters are calculated. As for dry testing, wet testing is conducted for 5 pieces of each samples in both MD and CD direction.

Water Absorption Time and Capacity

[0090] To determine the water absorption time and the water absorption capacity of the nonwoven, a basket immersion method is used. Measurements were performed according to ISO EN 12625-8. A test piece of defined width and total mass is placed in a cylindrical basket which is dropped from 2.5+/−0.5 cm above a water surface. The time is measured from when the basket is dropped until the test piece has been fully wetted and the results serve as water absorption time. The amount of absorbed water is determined from the dry and wet weight of the test piece.

Binder Add-on

[0091] The binder solutions (aqueous solutions) are prepared and sprayed upon the nonwoven fabric as described above. The binder add-on is shown both as the mass of the CMC and the carboxylic acid in the binder solution, as well as the percentage these components represent of the total weight of the treated nonwoven.

[0092] The add-on in percentage is calculated through the equation below.

[00002]$a=\frac{d_1\mathrm{or}{d}_2}{m_{\mathrm{dry}}+d_1+d_2}\times 100$

[0093] Where a is the add-on of the respective component, d.sub.1 represents the dry add-on of cellulose derivative and d.sub.2 represents the dry add-on of carboxylic acid and m.sub.dry is the mass of the dry samples before spraying.

[0094] FIGS. 1-4 illustrate comparisons of the wet and/or dry tensile strength of samples of nonwoven materials as disclosed above which have been consolidated according to the present disclosure. The specifics of the samples and measurements are given in table 1 below.

[0095] The aqueous solutions used for consolidating the samples are prepared by mixing the CMC and the carboxylic acid with water in specified amounts.

[0096] FIG. 1 illustrates a comparison of the wet and dry tensile strength measured on a sample fibrous material according to the present invention consolidated with different ratios of acid and CMC. A first aqueous solution added to a first fibrous material had a ratio of the CMC to the lactic acid being 0.2:1, a second aqueous solution added to a second fibrous material had a ratio of CMC to lactic acid being 1.8:1 and a third aqueous solution was added to a third fibrous material with the ratio of the CMC to the lactic acid being 10:1. The pH of the respective aqueous solutions was adjusted to 3.5 by HCl or NaOH.

[0097] As may be shown in the graph in FIG. 1, a ratio of 1.8:1 of the CMC and the lactic acid compared to a ratio of 0.2 shows more than 50% increase in the measured wet strength and more than 200% increase in dry strength. Comparing the ratios of 1.8:1 and 10:1 shows rather similar values. The best values for the wet strength could be seen at 1.8:1. This shows that it is beneficial to add the acid, here the lactic acid, in lower amounts compared to the CMC.

[0098] FIG. 2 illustrates a comparison made with nonwoven material samples consolidated with aqueous solutions with either CMC and lactic acid, CMC and citric acid or CMC and salicylic acid with respect to wet tensile strength. For each of the respective combinations, the pH was adjusted by adding different amount of the acids while keeping the CMC level at about 0.624 wt. % in the spraying solution (and the CMC add-on level at about 2.2 wt. %), giving a CMC/acid ratio of from 1.8:1 to 1.9:1. In one solution the pH was adjusted to 3, in a further solution to pH 3.5, in a still further solution the pH was adjusted to 4 and in one solution to pH 4.5. Consequently, twelve groups of fibrous material samples were consolidated with the twelve different types of aqueous solutions and then dried. The wet tensile strength of each of the resulting consolidated fibrous materials were measured and the comparison is illustrated in the graph in FIG. 2. As may be seen in the graph, each of the three combinations with lactic acid, citric acid and salicylic acid shows the highest wet strength at pH 3.5. However, each of the pH values pH 3, pH 4 and pH 4.5 shows satisfying wet strength results.

[0099] FIG. 3 illustrates further results from measurement of the wet tensile strength on nonwoven material samples having been consolidated according to the present disclosure by seven different aqueous solutions comprising CMC and citric acid or seven different aqueous solutions comprising CMC and lactic acid. For each of the respective combinations, the pH was adjusted by adding different amount of the carboxylic acids while keeping the CMC level at about 0.624 wt. % in the spraying solution (and the CMC add-on level at about 2.2 wt. %). It is clear from the results that the aqueous solutions pH values of between 3 and 4.5 have the optimal results in terms of wet tensile strength, both when the carboxylic acid is lactic acid and citric acid.

[0100] In FIG. 4, the results of a comparison of the wet tensile strength results measured for fibrous material samples having been consolidated according to the present disclosure by seven different aqueous solutions comprising CMC and citric acid or seven different aqueous solutions comprising CMC and lactic acid. The aqueous solutions used for each of the combination had a respective pH of 2.5, 3, 3.5, 4, 4.5, 5.5 or 6.5. The ratio of the CMC and the lactic acid/citric acid in each of the respective aqueous solutions were between 1.8:1-1.9:1 and the pH of the aqueous solution was instead reached by adding HCl or NaOH.

[0101] It is clear from the results that the aqueous solutions pH values of between 3 and 4.5 have the optimal results in terms of wet tensile strength, both when the carboxylic acid is the monocarboxylic acid, lactic acid and the multicarboxylic acid, citric acid. The results furthermore indicate that the presence of a crosslinking agent in form of carboxylic acid, in particular multicarboxylic acid, may not be as important as generally believed. This is supported by the fact that the wet strength decreases when the amount of carboxylic acid increases. The results furthermore clearly show that the pH is important in promoting/activating the bonding ability of the cellulose derivative, here CMC.

TABLE-US-00001 TABLE 1 Dry content in spraying Ratio solution [w-%] Add-on [%] Binder pH pH Mean tensile Mean Binder Polymer Polymer polymer/ control spraying Grammage Thickness strength [N/m] elongation Code system binder Acid binder Acid Acid agent solution [g/m2] [mm] Dry Wet Dry Wet Ref Elite 25 2.5 — 8.5 — — — 5.5 67.4 1.40 204 104 7.8 12.8 0.1 CMC 0.63 — 2.3 — — — 6.7 65.5 1.41 270 53 4.5 8.0 8.1 CMC + 0.625 3.13 2.0 9.8 0.2 NaOH 3.5 67.3 1.25 130 44 2.9 6.0 LA 8.2 CMC + 0.625 0.063 2.2 0.22 10 HCl 3.5 65.4 1.19 366 113 4.3 9.2 LA 9.1 CMC + 0.625 2.18 2.0 7.1 0.3 — 2.5 67.4 1.55 257 81 4.2 8.4 LA 9.2 CMC + 0.625 0.58 2.2 2.0 1.1 — 3.0 66.3 1.60 284 92 4.2 8.6 LA 9.3 CMC + 0.625 0.354 2.1 1.2 1.8 — 3.5 67.3 1.47 342 119 4.6 9.6 LA 9.4 CMC + 0.625 0.141 2.2 0.49 4.4 — 4.0 62.4 1.15 351 102 4.3 10.1 LA 9.5 CMC + 0.625 0.088 2.1 0.30 7.1 — 4.5 66.7 1.39 313 87 4.5 9.4 LA 9.6 CMC + 0.625 0.026 2.1 0.09 24 — 5.5 67.0 1.39 334 80 5.1 9.3 LA 9.7 CMC + 0.625 0.005 2.2 0.02 125 — 6.5 66.1 1.45 293 58 5.1 9.5 LA 10.1 CMC + 0.625 1.875 2.1 6.6 0.3 — 2.5 68.0 1.64 148 81 2.3 4.2 CA 10.2 CMC + 0.625 0.857 2.1 2.9 0.7 — 3.0 65.4 1.56 259 105 3.2 5.9 CA 10.3 CMC + 0.625 0.333 2.1 1.1 1.9 — 3.5 69.0 1.50 312 124 4.1 9.2 CA 10.4 CMC + 0.625 0.150 2.2 0.52 4.2 — 4.0 62.5 1.22 372 106 4.3 9.8 CA 10.5 CMC + 0.625 0.083 2.2 0.29 7.5 — 4.5 66.7 1.45 296 95 4.5 9.7 CA 10.6 CMC + 0.625 0.014 2.1 0.05 45 — 5.5 65.6 1.42 347 82 5.2 9.8 CA 10.7 CMC + 0.625 0.002 2.1 0.007 313 — 6.5 67.1 1.33 322 62 5.2 8.5 CA 11.1 CMC + 0.625 0.354 2.2 1.22 1.8 HCl 2.5 65.0 1.27 236 90 3.2 7.1 LA 11.2 CMC + 0.625 0.354 2.2 1.22 1.8 HCl 3.0 63.7 1.60 344 126 4.0 8.7 LA 11.3 CMC + 0.625 0.354 2.2 1.22 1.8 NaOH 4.0 60.8 1.35 315 96 4.8 9.6 LA 11.4 CMC + 0.625 0.354 2.2 1.22 1.8 NaOH 4.5 66.2 1.36 383 103 5.7 10.1 LA 11.5 CMC + 0.625 0.354 2.2 1.22 1.8 NaOH 5.5 67.1 1.39 365 56 6.1 8.0 LA 11.6 CMC + 0.625 0.354 2.2 1.22 1.8 NaOH 6.5 64.5 1.39 396 46 5.8 7.2 LA 12.1 CMC + 0.625 0.333 2.2 1.16 1.9 HCl 2.5 64.9 1.21 257 96 2.8 6.3 CA 12.2 CMC + 0.625 0.333 2.2 1.16 1.9 HCl 3.0 64.8 1.31 346 125 3.5 7.4 CA 12.3 CMC + 0.625 0.333 2.2 1.16 1.9 NaOH 4.0 62.6 1.38 339 102 4.7 10.4 CA 12.4 CMC + 0.625 0.333 2.2 1.16 1.9 NaOH 4.5 66.2 1.48 350 98 4.1 8.5 CA 12.5 CMC + 0.625 0.333 2.2 1.16 1.9 NaOH 5.5 65.3 1.63 327 63 4.7 8.4 CA 12.6 CMC + 0.625 0.333 2.2 1.16 1.9 NaOH 6.5 64.8 1.60 352 44 4.8 6.7 CA 14.1 CMC + 0.625 0.400 2.2 1.4 1.6 — 3.0 65.0 1.23 279 100 4.1 9.2 SA 14.3 CMC + 0.625 0.267 2.2 0.9 2.3 — 3.5 65.0 1.21 333 110 4.0 9.6 SA 14.4 CMC + 0.625 0.150 2.2 0.5 4.2 — 4.0 65.5 1.37 327 105 4.3 10.1 SA 14.5 CMC + 0.625 0.083 2.2 0.3 7.5 — 4.5 65.0 1.39 309 93 4.6 9.3 SA

[0102] FIG. 5 shows the results of pH measurements of samples of nonwoven materials produced according to the present disclosure. The samples are nonwoven materials formed by airlaid web formation as disclosed above. The samples were consolidated by aqueous solutions either comprising CIVIC and lactic acid or an aqueous solution comprising CIVIC and citric acid. Twelve aqueous solutions were prepared, with a first batch comprising six aqueous solutions comprising CMC and citric acid and a second batch comprising six solution comprising CMC and lactic acid. The pH was adjusted in each of the solutions by adding different amounts of carboxylic acid while keeping the CMC level at about 0.624 wt. % in the spraying solution (and the CMC add-on level constant at about 2.2 wt. %). The pH of the aqueous solutions was adjusted to 2.5, 3, 3.5, 4.5, 5.5 and 6.5, for each of the batches as illustrated in table 2 below.

[0103] Five to ten samples of nonwoven materials were consolidated using each aqueous solution and the surface pH was then measured for the respective sample as disclosed above. The value illustrated in the graph is the average value of the five to ten samples in each group.

[0104] As may be seen in FIG. 5 and Table 2, an aqueous solution having a pH of 2.5 and comprising citric acid provided a nonwoven sample having a surface pH of 3.34 while the aqueous solution comprising lactic acid provided a nonwoven sample having a pH of 3.07. The aqueous solution having a pH of 3.0 and comprising citric acid provided a nonwoven sample having a surface pH of 3.77 while the aqueous solution comprising lactic acid provided a nonwoven sample having a pH of 3.66. The aqueous solution having a pH of 3.5 and comprising citric acid provided a nonwoven sample having a surface pH of 4.33 while the aqueous solution comprising lactic acid provided a nonwoven sample having a pH of 3.95. The aqueous solution having a pH of 4.5 and comprising citric acid provided a nonwoven sample having a surface pH of 4.68 while the aqueous solution comprising lactic acid provided a nonwoven sample having a pH of 4.71. The aqueous solution having a pH of 5.5 and comprising citric acid provided a nonwoven sample having a surface pH of 5.33 while the aqueous solution comprising lactic acid provided a nonwoven sample having a pH of 5.23. The aqueous solution having a pH of 6.5 and comprising citric acid provided a nonwoven sample having a surface pH of 5.34 while the aqueous solution comprising lactic acid provided a nonwoven sample having a pH of 5.34. Thus, the surface pH measured on the nonwoven sample corresponds relatively well with the pH in the respective aqueous solution. Consequently, it may be concluded that the benefits which may be provided with a nonwoven material intended to be used in contact with the skin and having a pH controlling effect may be provided with a fibrous material produced according to the present disclosure.

TABLE-US-00002 TABLE 2 Ratio Binder system Add-on [w-%] Binder pH Binder Binder polymer/ spraying Measured surface pH Code polymer Acid polymer Acid Acid solution 1 2 3 4 5 6 7 8 9 10 Average Ref Elite 25 — 8.5 — — 5.5 3.95 3.92 3.98 3.94 3.97 3.94 3.97 3.95 0.1 CMC — 2.3 — — 6.7 5.08 5.06 5.20 5.21 5.17 5.15 5.13 5.14 9.1 CMC LA 2.1 6.6 0.3 2.5 3.12 3.07 3.09 3.07 3.05 3.03 3.05 3.07 9.2 CMC LA 2.1 2.9 1.1 3.0 3.65 3.62 3.70 3.74 3.60 3.72 3.61 3.66 9.3 CMC LA 2.1 1.1 1.8 3.5 3.92 3.85 3.89 3.95 3.91 4.13 4.07 3.93 3.91 3.95 9.5 CMC LA 2.2 0.29 7.1 4.5 4.72 4.74 4.73 4.68 4.63 4.62 4.73 4.76 4.81 4.68 4.71 9.6 CMC LA 2.1 0.05 24 5.5 5.24 5.27 5.29 5.24 5.31 5.25 5.23 5.01 5.14 5.27 5.23 9.7 CMC LA 2.1 0.007 125 6.5 5.36 5.32 5.29 5.37 5.42 5.32 5.32 5.34 10.1 CMC CA 2.0 7.1 0.3 2.5 3.35 3.39 3.36 3.30 3.32 3.33 3.36 3.34 10.2 CMC CA 2.2 2.0 0.7 3.0 3.65 3.76 3.80 3.78 3.78 3.81 3.80 3.77 10.3 CMC CA 2.1 1.2 1.9 3.5 4.27 4.34 4.33 4.38 4.24 4.38 4.35 4.33 10.5 CMC CA 2.1 0.30 7.5 4.5 4.68 4.66 4.65 4.69 4.69 4.72 4.70 4.68 10.6 CMC CA 2.1 0.09 45 5.5 5.31 5.34 5.32 5.36 5.29 5.32 5.34 5.33 10.7 CMC CA 2.2 0.02 313 6.5 5.35 5.40 5.07 5.26 5.39 5.32 5.41 5.40 5.38 5.40 5.34

[0105] FIG. 6 illustrates the results from measurements of dry and wet strength with nonwoven material samples as described above being consolidated with a binder system of HEC and CA, the ratio of the HEC/CA being 0.3:1 and 3.0:1.

[0106] FIG. 7 illustrates the results of dry and wet elongations tests being performed on nonwoven samples materials as described for FIG. 6.

[0107] When using HEC, in contrast to the results when using CMC, the material seems to gain slightly higher mechanical strength if more citric acid is used, but lower elongation, see FIGS. 6 and 7. When preparing the binder solution with HEC and citric acid it was soon clear that the viscosity of the solution was very high. Due to the high viscosity of the mixture it was hard, impossible almost, to distribute it over the nonwoven material through spraying. The solution was therefore diluted with water to half the concentration

[0108] FIG. 8 illustrates the results from measurements of dry and wet strength performed on nonwoven samples as described above and with a binder system either CMC and CA or a combination of CMC and HEC in the presence of CA.

[0109] FIG. 9 illustrates the results from measurements of dry and wet elongation performed on the nonwoven samples where a comparison between HEC and HEC/CMC in combination with a high and low amount of carboxylic acid was made.

[0110] As shown in FIG. 9 and which may also be seen from the results presented in table 4 below, the elongation of the nonwoven material is surprisingly increased when the amount of carboxylic acid in the solution is decreased. This is contrary to what is seen for HEC in FIGS. 6-7 where a lower concentration of citric acid generates a higher elongation.

[0111] Details of the samples tested in FIGS. 6-9 are given in table 3 below.

TABLE-US-00003 TABLE 3 Dry content in spraying Ratio Binder system solution [w-%] Binder pH Add-on [wt-%] Binder Binder polymer/ spraying Binder Code polymer Acid polymer Acid Acid Additive solution polymer Acid Ref Elite 25 — 2.5 — — — 5.5 8.5 — 0.1 CMC — 0.625 — — — 6.7 2.3 — 1.1 CMC CA 1.25 2.5  0.5 — n.a. 4.1 8.1 1.2 CMC CA 1.25 0.625 2.0 — n.a. 4.3 2.2 1.3 CMC CA 0.625 1.875 0.3 — 2.5 2.2 6.6 1.4 CMC CA 0.625 1.250 0.5 — n.a. 2.3 4.7 1.5 CMC CA 0.625 0.625 1.0 — n.a. 2.4 2.4 1.6 CMC CA 0.625 0.313 2.0 — n.a. 2.4 1.2 1.7 CMC CA 0.625 0.210 3.0 — 3.9 2.3 0.8 1.8 CMC CA 0.625 1.875 0.3 GLY* n.a. 2.3 6.6 1.9 CMC CA 0.625 0.210 3.0 GLY* n.a. 2.4 0.8 1.10 CMC CA 0.625 0.210 3.0 GLY ** n.a. 2.4 0.8 3.1 HEC CA 0.313 0.938 0.3 — n.a. 1.1 3.3 3.2 HEC CA 0.313 0.105 3.0 — n.a. 1.2 0.4 4.1 CMC + HEC CA 0.42 + 0.21 1.875 0.3 — n.a. 1.4 + 0.7 6.4 4.2 CMC + HEC CA 0.42 + 0.21 0.210 3.0 — n.a. 1.4 + 0.7 0.7 6.1 CMC HCl 0.625 added to pH 3 — — 3.0 2.1 — 6.2 CMC HCl 0.625 added to pH 4 — — 4.0 2.2 — 6.3 CMC HCl 0.625 added to pH 5 — — 5.0 2.2 — 6.4 CMC HCl 0.625 added to pH 6 — — 6.0 2.2 — n.a. = not available

[0112] FIG. 10 illustrates the results from a comparison of dry and wet tensile strength of a fibrous material consolidated with CMV and CA with different CMC/CA ratios.

[0113] A surprising result from table 4 and FIGS. 8 and 10 is that the mechanical strength, both dry and wet, of the material is increased as the level of carboxylic acid in the binder solution is decreased.

[0114] Table 4 below illustrates further characteristics of the samples illustrated in table 3 above. As may be seen in Table 4, the water absorption capacity and absorption time are less affected by the different ratios of CMC and citric acid than the mechanical strength. It is easy to obtain an acceptable level of capacity and an acceptable time, quite independent of the amount of citric acid in the binder.

TABLE-US-00004 TABLE 4 Ratio Binder system Add-on [wt-%] Binder Binder Binder polymer/ Grammage Thickness Code polymer Acid polymer Acid Acid Additive [g/m2] [mm] Ref Elite 25 — 8.5 — — — 67.4 1.40 0.1 CMC CA 2.3 — — — 65.5 1.41 1.1 CMC CA 4.1 8.1 0.5 — 60.4 1.75 1.2 CMC CA 4.3 2.2 2.0 — 58.6 1.99 1.3 CMC CA 2.2 6.6 0.3 — 59.6 1.68 1.4 CMC CA 2.3 4.7 0.5 — 61.1 1.59 1.5 CMC CA 2.4 2.4 1.0 — 60.0 1.55 1.6 CMC CA 2.4 0.2 2.0 — 60.0 1.72 1.7 CMC CA 2.3 0.8 3.0 — 58.1 1.83 1.8 CMC CA 2.3 6.6 0.3 GLY* 63.3 1.89 1.9 CMC CA 2.4 0.8 3.0 GLY* 58.5 1.96 1.10 CMC CA 2.4 0.8 3.0 GLY ** 66.1 1.57 3.1 HEC CA 1.1 3.3 0.3 — 57.9 1.74 3.2 HEC CA 1.2 0.4 3.0 — 60.9 1.77 4.1 CMC + HEC CA 1.4 + 0.7 6.4 0.3 — 71.1 1.71 4.2 CMC + HEC CA 1.4 + 0.7 0.7 3.0 — 65.6 1.65 6.1 CMC HCl 2.1 added to pH 3 — — 63.6 1.51 6.2 CMC HCl 2.2 added to pH 4 — — 62.0 1.45 6.3 CMC HCl 2.2 added to pH 5 — — 64.4 1.44 6.4 CMC HCl 2.2 added to pH 6 — — 63.5 1.44 Dry Dry Wet Wet strength elongation strength elongation Absorption Absorption Arithmetic Arithmetic Arithmetic Arithmetic Thickness time capacity Code mean [N/m] mean [%] mean [N/m] mean [%] [mm] [s] [g/g] Ref 204 7.8 104 12.8 1.40 3.0 15 0.1 270 4.5 53 8.0 1.41 1.6 14.0 1.1 283 2.3 150 4.0 1.75 3.3 15.0 1.2 567 4.5 227 7.8 1.99 2.1 14.6 1.3 117 2.2 56 3.6 1.68 2.6 17.9 1.4 215 2.5 87 4.2 1.59 1.9 15.9 1.5 217 3.2 98 5.5 1.55 1.9 14.7 1.6 335 3.8 114 7.5 1.72 1.8 16.6 1.7 395 4.7 126 9.0 1.83 1.6 17.5 1.8 143 2.4 74 4.9 1.89 3.7 16.8 1.9 461 5.0 184 10.1 1.96 1.7 16.3 1.10 359 4.5 120 8.9 1.57 1.6 14.0 3.1 130 2.4 53 5.0 1.74 1.7 16.0 3.2 96 4.5 36 8.7 1.77 2.0 16.0 4.1 185 2.1 80 4.4 1.71 1.4 15.0 4.2 325 3.9 111 7.0 1.65 1.4 14.5 6.1 279 4.4 90 8.6 1.51 1.6 14.2 6.2 310 4.8 80 10.0 1.45 1.6 14.6 6.3 354 5.2 85 9.9 1.44 1.7 14.6 6.4 543 5.7 89 8.5 1.44 1.5 14.4 n.a. = not available *The mass of glycerol in solution is 10% of the mass of CMC ** The mass of glycerol in solution is 40% of the mass of CMC