INCREASED ABSORPTION CAPACITY OF SUPERABSORBENT MATERIAL WITH THE USE OF SELECTED SALTS

Abstract

The present invention describes a method for increasing the absorption capacity of a superabsorbent material (SAM) by treating the SAM with a selected salt or a combination of such salts. The selected salt(s) may interact with the polymer chain of the SAM through one or more absorption capacity enhancement mechanisms. The absorption capacity enhancement mechanism(s) between the selected salt(s) and the SAM may lead to an increased absorption capacity of the SAM.

Description

INCREASED ABSORPTION CAPACITY OF SUPERABSORBENT MATERIAL WITH THE USE OF SELECTED SALTS BACKGROUND OF THE INVENTION In recent years, superabsorbent materials (SAMs) have been developed that are capable of absorbing many times their own weight in liquid. SAMs, also known as water-insoluble hydrogels, are polymeric materials that have been used to increase the absorbency of sanitary products such as diapers, incontinence pads, and underwear. SAMs are often provided in the form of particulate powders, granules, or fibers that are distributed throughout absorbent cellulosic products to increase the product's absorbency. SAMs are described, for example, in U.S. Patent No. 4,160,059; U.S. Patent No. 4,676,784; U.S. Patent No. 4,673,402; and U.S. Patent No. 5,002,814. and United States Patent No. 5,057,166. Products such as diapers incorporating absorbent hydrogels are shown in United States Patent No.3,669,103 and United States Patent No. 3,670,731. More specifically, ionic gel-based superabsorbents, or polyelectrolytes, have been widely used in personal care products. They are special because of κρζίτηη / ζζηζ / Ε / γίΛΐ Ref. 333357, its unique ability to absorb liquids containing water. The impressive absorption and swelling powers of these materials come from both the electrostatic repulsion between negative charges in the main polymer chain, such as a carboxylate -COO⁻, and the osmotic pressure of positive counterions, such as sodium Na⁺. However, the water absorption and swelling capacities of ionic superabsorbents (SAMs) can be greatly reduced in salt-containing solutions such as physiological fluids like urine and blood. This salt sensitivity is due to the fact that excess ions, such as sodium ions (Na+) in physiological fluids, can effectively screen the charges of the main polymer chain. This can lead to reduced counterion numbers and repulsive forces, resulting in less swelling. In some cases, absorption and swelling capacities can be completely lost, as the ionic gels can screen into non-ionic gels. Therefore, to compensate for the salt sensitivity of SAMs, more SAM will be needed. This increased use can result in bulkier absorbent products, uncomfortable user experiences, and higher product costs.Consequently, there is still a need to improve the absorption capacity of SAMs. Rozfrnn / zznz / E / YiAi BRIEF DESCRIPTION OF THE INVENTION Rozfrnn / zznz / E / YiAi The present invention relates to a method for increasing the absorption capacity of a superabsorbent material (SAM) by treating the SAM with a selected salt or a combination of selected salts. More specifically, the method for increasing the absorption capacity includes providing a SAM comprising repeating units that carry an anion and a cation. The cation is a monometallic cation or a combination of a monometallic cation and a proton cation. The method also provides for treating the SAM with a selected salt or a combination of salts thereof. The selected salt(s) has / have the following structure: NRiaR?a X Z+ The X- in the tetrahedral structure of the selected salt of Formula (I) is -COO-, SO3-, or -OSO3-. The Z+ includes a monovalent cation. The NRiaR2ase selects from a primary, secondary, and tertiary amino group. The Riay R2a in Formula (I) are -H, -Me, -Et, or -Bu. The Rsa in Formula (I) includes H, -Me, -Et, or -Bu. The Ria in the tetrahedral structure of Formula (I) can be an alkyl chain with 8 or fewer carbons. An amino group (-N) can be attached to one or more carbons in the alkyl chain. Alternatively, the Ria can be an -H or an alkyl group. The alkyl group is preferably -Me, -Et, or -Bu. In a further embodiment, the present invention relates to a method for increasing the absorption capacity of SAM with an additional selected salt or a combination of salts thereof. The selected salt(s) has / have the following structure: Rozfrnn / zznz / E / YiAi (II) · The X- group in the tetrahedral structure of Formula (II) is C00~, -SOa, or -OSO3·. The Z+ group includes a monovalent cation. The Rib group includes -H, -Me, -Et, or -Bu. -H or -Me are the most preferred for Rib. The R2b group can include -H, -Me, -Et, or -Bu. -H or -Me are the most preferred for Rcu·. The Rsb in the tetrahedral structure of Formula (II) can be an alkyl chain with 8 or fewer carbons. An amino group (-N) can be attached to one or more carbons in the alkyl chain. Alternatively, R.3b can be an -H or an alkyl group. The alkyl group is preferably -Me, -Et, or -Bu. BRIEF DESCRIPTION OF THE FIGURES Figure 1 shows a functional group of a selected salt forming a complex with sodium ions from a SAM such that the sodium ions are moved away from the polymer chain. Figure 2 shows a functional group of a selected salt that forms bulky ions after deprotonating unneutralized acrylic acid units. Figure 3 shows a functional group of a selected salt forming bulky ions by ion exchange with unneutralized acrylic acid units in SAM. Figure 4 shows secondary dissociations of bulky ions to allow more free counterions. Figure 5 is a schematic view of a forced fluid distribution when treating a desired zone(s) in an absorbent article with increased and decreased absorption capacity of selected salts. Figure 6 is a schematic view of a laboratory screening procedure to determine whether the absorption capacity of SAM can be increased or decreased by treating the Rozfrnn / zznz / E / YiAi SAM with selected salts. DETAILED DESCRIPTION OF THE INVENTION When introducing elements of this description or the preferred modality(ies) thereof, the articles a, an, and the when used in this description are intended to mean that there is one or more of the elements. The terms comprising, including, and having when used in this description are intended to be inclusive and mean that there may be additional items other than those listed. The term superabsorbent material or SAM, as used herein, refers to a superabsorbent polymer, which can absorb and retain extremely large quantities of a liquid relative to its own mass. The ability of a SAM to absorb water depends on the ionic concentration of the aqueous solution, such as urine or blood. The term absorbent article, as used in this description, refers to devices that absorb and contain bodily exudates and, more specifically, to devices that are placed against or in close proximity to the wearer's body to absorb and contain the various exudates secreted from the body. Absorbent articles may include diapers, diaper-type pull-ups, open diapers, diaper covers having fastening means for securing the diaper, training pants, Rozfrnn / zznz / E / YiAi adult incontinence underwear, feminine hygiene products, breast pads, care mats, bibs, dressing products, and the like. As used herein, the term body exudates includes, but is not limited to, urine, blood, vaginal secretions, breast milk, sweat, and fecal matter. The term "basic in nature," when used in the present description, refers to a selected salt that has a functional group that can deprotonate a weak acid below pH 7. The term secondary dissociation when used in the present description refers to a charged or uncharged chemical fragment that is formed after selected salts interact with a SAM (e.g., bulky ions) from which a monocounterion can further dissociate to become a fully dissociated free ion, which will further help to increase the osmotic pressure of the SAM and thus swelling. The term superabsorbent particle, as used in this description, refers to the form of discrete units. Discrete units may include flakes, fibers, agglomerates, granules, powders, spheres, pulverized materials, or similar materials, as well as combinations thereof. The particles of superabsorbent material may have any desired shape: for example, cubic, rod-like polyhedral, spherical or hemispherical, rounded or semi-rounded, angular, irregular, etc. Superabsorbent materials (SAMs) are well known for being highly sensitive to salt screening during swelling in aqueous solutions such as urine or other bodily exudates. Consequently, the traditional view is that salts used in SAMs should be avoided, eliminated, filtered, or reduced. However, it has been surprisingly and unexpectedly discovered that treating SAMs with selected salts from Formulas (I) and (II), which are described in detail herein, can significantly increase the swelling capacity of SAMs. The SAM treated with a selected salt includes polyelectrolytes that generally consist of repeating units of negative:positive ion pairs along their polymer chains (e.g., carboxylates, phosphates, sulfates, sulfonates, and similar structures). More specifically, the SAMs used in the present invention are polyelectrolytes made from polymerization mixtures of 30% acrylic acid monomer and 70% sodium acrylic acid salt. However, the polymerization mixtures of acrylic acid monomer and sodium acrylic acid salt can be described in any desired percentage ratio. Rozfrnn / zznz / E / YiAi In one embodiment of the invention, the selected salt described herein for treating SAMs can be used alone or combined with one or more additional selected salts to achieve maximum increases in absorption capacity. More specifically, the selected salt(s) for treating SAMs to increase absorption capacity are generally categorized into two different structural formulas, Formula (I) and Formula (II). Formulas (I) and (II) generally have one or more functional groups that can interact with the positive-negative ion pairs of the SAMs along the SAM polymer chains, enabling sodium counterions to be displaced from the SAM polymer chains. More specifically, the structures of the selected salts of Formula (I) and (II) are described below. In one embodiment of the present invention, the selected salts of Formula (I) can be illustrated as a tetrahedral structure with four different functional groups: Rozfrnn / zznz / E / YiAi (I) 10 The X- in the salt functional group X-Z+ of the tetrahedral formula (I) is -COO-, -SO3-, -OSO3-, or similar structures thereof. The Z+ includes monovalent metal ions or organic ions. Examples of monovalent metal ions are Na+, K+, Li+, or similar ions thereof. Examples of monovalent organic ions include ammonium cations NH4+, tetramethylammonium Me4N+, tetraethylammonium Et4N+, tetrabutylammonium Et4N+, and similar structures thereof. Rozfrnn / zznz / E / YiAi The NRiaR2a group is selected from a primary, secondary, and tertiary amino group, and the Ria in the NRiaR2a group of Formula (I) includes -H, -Me, -Et, or -Bu, and the R2a group in Formula (I) includes -H, -Me, -Et, or -Bu. The R3a group in Formula (I) includes -H, -Me, -Et, or -Bu. The R4a group of Formula (I) may include an alkyl chain of 8 or fewer carbons. The R4a group may include an amino group (-N) attached to one or more of the eight carbons (-C) in the alkyl chain. Alternatively, the R4a group may not contain an alkyl chain, but may only include -H, -Me, -Et, or -Bu. In another embodiment of the present invention, the salts selected to treat the SAMs to increase the absorption capacity of the SAMs also include another tetrahedral structure with four different functional groups as shown in Formula (II): Rozfrnn / zznz / E / YiAi The X in the salt functionality group X-Z+ of Formula (II) includes -COO, -SOa, and -OSOa and similar structures thereof. The Z+ includes monovalent metal ions or monovalent organic ions. Examples of monovalent metal ions are Na+, K+, Li+, or similar ions thereof. Monovalent organic ions may include ammonium cations NH4+, tetramethylammonium Me4N+, tetraethylammonium Et4N+, tetrabutylammonium Bu4N+, and similar structures thereof. The second group, Rib in Formula (II), includes -H, -Me, -Et, or -Bu. -H or -Me are the most preferred for Rib. The third group, R2b, in Formula (II), includes -H, -Me, -Et, and -Bu. -H or -Me are the most preferred for R2b. The fourth group, Rab, in Formula (II), includes an alkyl chain having eight or fewer carbons. Additionally, an amino group (-N) may be attached to one or more carbons in the alkyl chain. Alternatively, the Rab group may not include an alkyl chain but may be -H, -Me, -Et, or -Bu. In one aspect of the present invention, one or more selected salts can be used to treat the SAM after the SAM has been made. In another aspect of the invention, one or more selected salts can be combined with prepared SAM. The selected salt(s) will then begin to interact with the polymer chain(s) of the SAM as soon as the SAM and the selected salt(s) come into contact with a swelling liquid such as urine or other bodily exudates. In another aspect of the invention, the selected salt(s) can be introduced into the prepared SAM during the surface crosslinking stage during SAM manufacturing. In an additional aspect, the selected salt(s) can be introduced in the initial polymerization stage of SAM manufacturing so that the interactions between the selected salt(s) and the polymer chain(s) can be fully accessed. In another embodiment of the invention, the amount of the selected salt(s) used to treat the SAM can be controlled so as not to exceed 25% of the total weight of the SAM. Excessive weight loading of the selected salt(s) may be undesirable since it can not only saturate the interaction sites of the SAM but also increase the likelihood that the selected salts may be converted into other salts, such as sodium chloride, which will lead to reduced absorption capacity due to load screening. Additionally, excessive weight loading of the selected salt(s) may be cost-prohibitive and will not be an efficient means of increasing absorption capacity. In a further aspect of the invention, improving the absorption capacity of the SAM with the selected salts of Formula (I) and (II) can be achieved by at least one or a combination of a plurality of the following mechanisms: a) the formation of complexes with SAM counterions, which can detach from the polymer chain; b) the deprotonation of an unneutralized acrylic acid group by one or more amino groups of the selected salt(s); c) the secondary dissociation of the large ions that are formed after the interactions between the SAM ion pairs and the selected salts; d) Bulky ions that form from interactions between the ion pairs of the SAM chain and the selected salts. The formation of bulky ions can decrease the charge density of the counterions so that their tendency to bind to a polymer chain can be reduced; e) the ion exchange between ion pairs in a polymer chain of SAM and salts Rozfrnn / zznz / E / YiAi selected so that more counterions can be added to the polymer chain; and f) Forced charge-charge separation after the formation of large ions, which can occur after interactions between SAM ion pairs and selected salts. Forced charge separation can increase the negative charge density of the polymer chain and, therefore, the charge-charge repulsion along the polymer chain, thus increasing lynching. In light of the mechanisms for enhancing absorption capacity described above, Figures 1-4 illustrate these mechanisms through various structural interactions. For example, Figure 1 shows a functional group of a selected salt that can form a complex with sodium ions from a SAM, where the sodium ions are diverted from the polymer chain. Figure 2 shows a functional group of a selected salt that can form bulky ions after deprotonating unneutralized acrylic acid units. Bulk ion formation can force charge-charge separation between a polymer chain and its counterions. Figure 3 shows a functional group of a selected salt that can form bulky ions through ion exchange with unneutralized acrylic acid units in the current SAM. Deprotonation can add more counterions. Rozfrnn / zznz / E / YiAi to the polymer chain. Figure 4 shows secondary dissociations of bulky ions that can allow more free counterions. In another aspect of the present invention, the discovery of selected salts for SAM capacity enhancements may allow a personal care manufacturer to use a SAM to produce an absorbent article (i.e., diaper) with different capacity zones for forced fluid redistribution. For example, as shown in Figure 5, capacity-enhancing salts, as described in this invention, can be applied to desired areas in an absorbent article that may require increased absorbency for leak prevention, while salts with lower absorbency (i.e., sodium chloride) can be applied to areas where excess urine is redistributed. Such forced fluid redistribution can improve the wearer's comfort and reduce potential skin dryness. To further demonstrate the uniqueness of the selected salts from Formulas (I) and (II), various other salts were tested under the same test conditions and found to significantly decrease the absorption capacity. Such examples include ordinary inorganic salts, which are known to sieve the charges of SAM polymer chains, such as chlorides, halides, Rozfrnn / zznz / E / YiAi nitrates, phosphates, sulfates, zwitterionic salts, such as glycine sulfate salts, quinidine sulfate, higher order di- and trio carboxylate, sulfate, sulfonate, and spherically rigid salts with aromatic rings. Testing methods Absorption Capacity The absorption capacity of the superabsorbent material (SAM) can be measured using a test of Absorbance Under Load (AUL) is a well-known test for measuring the ability of superabsorbent particles to absorb a 0.9 wt% sodium chloride solution in distilled water at room temperature (test solution) while the particle is under load. For example, 0.16 grams of superabsorbent particles can be confined within a 5.07 cm² area of ​​an Absorbance Under Load (AUL) cylinder under a nominal pressure of 0.01 psi, 0.3 psi, 0.6 psi, or 0.9 psi. The sample is allowed to absorb the test solution from a dish containing excess fluid. At predetermined time intervals, a sample is weighed after a vacuum apparatus has removed any excess interstitial fluid within the cylinder. This weight-versus-time data is then used to determine the Absorption Rates at various time intervals. Rozfrnn / zznz / E / YiAi The AUL test apparatus is measured according to the EDANA-recommended test method WSP 242.3, which is similar to a GATS (Gravimetric Absorbance Test System) marketed by M / K Systems, as well as the system described by Lichstein on pages 129-142 of the INDA Technological Symposium Proceedings, March 1974. A portded disc is also used, with ports confined within an area 2.5 centimeters in diameter. The resulting AUL is reported as grams of liquid retained per gram of sample weight (g / g). To carry out the test, the following steps can be performed: (1) Clean the inside of the AUL cylinder with an antistatic cloth, and weigh the cylinder, weight and piston; (2) Record the weight as CONTAINER WEIGHT in grams to the nearest milligram; (3) Slowly pour the 0.16 ± 0.005 gram sample of the superabsorbent particles into the cylinder so that the particles do not make contact with the sides of the cylinder or they may adhere to the walls of the AUL cylinder; (4) Weigh the cylinder, weight, piston, and superabsorbent particles and record the value on the balance as DRY WEIGHT in grams to the nearest milligram; (5) Gently tap the AUL cylinder until the superabsorbent particles are evenly distributed on the bottom of the cylinder; Rozfrnn / zznz / E / YiAi (6) Gently place the piston and weight in the cylinder; (7) Place the test fluid (0.9% by weight aqueous solution of sodium chloride) in a fluid bath with a large mesh sieve at the bottom; (8) Simultaneously start the timer and place the superabsorbent particles and the cylinder assembly on the sieve in the fluid bath for one hour. The level in the bath should be at a height to provide at least a positive height of 1 cm above the base of the cylinder; (9) Gently shake the sample to release any trapped air and ensure that the superabsorbent particles are in contact with the fluid. (10) Remove the cylinder from the fluid bath at a designated time interval and immediately place the cylinder in the vacuum apparatus (disc with ports on top of the AUL chamber) and remove excess interstitial fluid for 10 seconds; (11) Clean the outside of the cylinder with paper towels or tissue paper; (12) Weigh the AUL assembly (i.e., cylinder, piston, and weight), with the SAM and any absorbed test fluid immediately, and record the weight as WET WEIGHT in grams to the nearest milligram and the time interval; and Rozfrnn / zznz / E / YiAi The absorption capacity of the superabsorbent particle at a designated time interval is calculated in grams of liquid per gram of superabsorbent using the following formula: (Wet Weight-Dry Weight) / (Dry Weight-Container Weight) Laboratory screening procedure To determine whether the absorption capacity of a superabsorbent material (SAM) could be increased or decreased, a laboratory screening procedure was developed. In this procedure (Figure 6), the salt chemical was first introduced into the pre-made SAM in an aqueous solution in an AUL cup, and then the AUL test procedures were followed as described above. The AUL cup was exposed to an excess of 0.9% NaCl at a desired weight to see if the absorption capacity of the SAM would increase or decrease compared to the control, i.e., the sample without added salt. EXAMPLES Example 1 Example 1 demonstrates that the absorption capacity of SAM increases when a commercial SAM (i.e., Evonik 5630) is treated with a selected sodium glycine salt at different weight loading levels, following the test procedures described herein. The results are Rozfrnn / zznz / E / YiAi are listed in Table 1. As shown in Table 1, an increase in the absorption capacity of SAM of up to approximately 10% can be achieved by treating SAM with sodium glycine. Example 1 also demonstrates that excessive loading with selected salts may not be preferable, as excess salts can saturate the ion pairs of the polymer chain and induce charge screening, thereby reducing absorption capacity. κρζίτηη / ζζηζ / Ε / γίΛΐ Table 1 SAM Evonik 5 630 g Sodium Glycine g (% by Weight of SAM) AUL Capacity (0.6 PSI, 2 hours) g / g Change in Absorption Capacity (%) 0.16 0 (Control) 26.26 0 0.16 0.0064 (4%) 27.41 4.38 0.16 0.0128 (8%) 27.90 6.25 0.16 0.0256 (16%) 28.68 9.20 0.16 0.0512 (32%) 27.89 6.21 Example 2 Example 2 demonstrates that the absorption capacity of SAM increases when a commercial SAM (i.e., Evonik 5630) is treated with a selected potassium glycine salt at different weight loading levels following the test procedures described herein. The results are listed in Table 2. As shown in Table 2, an increase in the absorption capacity of SAM of 10.25% is achieved by treating SAM with the selected potassium glycine salt. Table 2 Rozfrnn / zznz / E / YiAi SAM Evonik 5630 g Potassium Glycine g (% by Weight of SAM) AUL Capacity (0.6 PSI, 2 hours) g / g Change in Absorption Capacity (%) 0.16 0 (Control) 26.34 Control 0.16 0.0064 (4%) 27.33 3.76 0.16 0.0128 (8%) 27.98 6.23 0.16 0.00256 (16%) 28.48 8.12 0.16 0.00512 (32%) 29.04 10.25 Example 3 Example 3 demonstrates that the absorption capacity of SAM increases when a commercial SAM (i.e., Evonik 5630) is treated with a selected tetramethylammonium glycine salt at different weight loading levels following the test procedures described herein. The results are listed in Table 3. As shown in Table 3, an increase in the absorption capacity of SAM of more than 16% can be achieved by treating SAM with the selected tetramethylammonium glycine salt. Rozfrnn / zznz / E / YiAi Table 3 SAM Evonik 5630 g Tetramethylammonium Glycine g (% by Weight of SAM) AUL Capacity (0.6 PSI, 2 hours) g / g Change in Absorption Capacity (%) 0.16 0 (Control) 26.34 Control 0.16 0.0064 (4%) 27.59 4.75 0.16 0.0128 (8%) 27.97 6.19 0.16 0.00256 (16%) 29.28 11.16 0.16 0.00512 (32%) 30.73 16.67 Example 4 Example 4 demonstrates that the absorption capacity of SAM increases when a commercial SAM (i.e., Evonik 5630) is treated with a selected tetramethylammonium dimethylglycine salt at different weight loading levels, following the test procedures described herein. The results are listed in Table 4. As shown in Table 4, an increase in the absorption capacity of SAM of more than 14% can be achieved by treating SAM with the selected tetramethylammonium dimethylglycine salt. Table 4 SAM Evonik 5630 g Tetramethylammonium Dimethylglycine g (% by Weight of SAM) AUL Capacity (0.6 PSI, 2 hours) g / g Change in Absorption Capacity (%) 0.16 0 (Control) 26.34 Control 0.16 0.0064 (4%) 26.97 2.39 0.16 0.0128 (8%) 27.66 5.01 0.16 0.00256 (16%) 28.66 8.79 0.16 0.00512 (32%) 30.05 14.1 Rozfrnn / zznz / E / YiAi Example 5 Example 5 demonstrates that the absorption capacity of SAM increases when a commercial SAM (i.e., Evonik 5630) is treated with sodium aminomethanesulfonic acid at different weight loading levels following the test procedures described herein. The results are listed in Table 5. As shown in Table 5, an increase in the absorption capacity of SAM of more than 7% can be achieved by treating SAM with sodium aminomethanesulfonic acid. Table 5 SAM Evonik 5630 g Sodium Aminomethanesulfonic Acid g (% by Weight of SAM) AUL Capacity (0.6 PSI, 2 hours) g / g Change in Absorption Capacity (%) 0.16 0 (Control) 26.34 Control 0.16 0.0064 (4%) 27.09 2.83 0.16 0.0128 (8%) 27.32 3.72 0.16 0.00256 (16%) 28.25 7.25 0.16 0.00512 (32%) 28.21 7.10 Example 6 Example 6 demonstrates that the absorption capacity of SAM increases when a commercial SAM (i.e., Evonik 5630) is treated with a selected sodium salt at different weight loading levels following the test procedures described herein. The results are listed in Table 6. As shown in Table 6, an increase in the absorption capacity of SAM of more than 11% can be achieved by treating SAM with the selected sodium lysine salt. Rozfrnn / zznz / E / YiAi Table 6 SAM Evonik 5630 g Sodium Lysine g (% by Weight of SAM) AUL Capacity (0.6 PSI, 2 hours) g / g Change in Absorption Capacity (%) 0.16 0 (Control) 26.16 0 0.16 0.0064 (4%) 27.46 4.97 0.16 0.0128 (8%) 28.06 7.26 0.16 0.00256 (16%) 29.07 11.12 0.16 0.00512 (32%) 28.18 7.72 Examples 7–10 demonstrate that not all salts can increase the absorption capacity of the SAM at different weight loading levels. The same test procedures used to demonstrate the increases in absorption capacity in Examples 1–6 were used in Examples 7–10. Example 7 Example 7 demonstrates that the absorption capacity of SAM decreases with a sodium chloride salt. Table 7 shows that the absorption capacity decreases by about 30% when SAM is treated with approximately 30% by weight of sodium chloride. Rozfrnn / zznz / E / YiAi Table 7 SAM Evonik 5630 g Sodium Chloride g (% by Weight of SAM) AUL Capacity (0.6 PSI, 1 hour) g / g Change in Absorption Capacity (%) 0.16 0 (Control) 26.25 0 0.16 0.0064 (4%) 24.25 -7.60 0.16 0.00128 (8%) 23.84 -9.18 0.16 0.0256 (16%) 20.90 -20.38 0.16 0.0512 (32%) 17.78 -32.30 Example 8 Example 8 demonstrates that the absorption capacity of SAM decreases when SAM is treated with a selected aminosulfanilic tetramethylammonium salt. Table 8 shows that the absorption capacity decreases by about 7% when SAM is treated with approximately 30 wt% aminosulfanilic tetramethylammonium salt. Unlike the other salts mentioned in Examples 1–6, aminosulfanilic tetramethylammonium salt has a spherically rigid phenyl group. This spherically rigid phenyl group prevents the formation of absorption capacity mechanisms. Therefore, it decreases the absorption capacity of SAM. Rozfrnn / zznz / E / YiAi Table 8 SAM Evonik 5630 g Tetramethylammonium Aminosulfanilic acid g (% by Weight of SAM) AUL Capacity (0.6 PSI, 2 hours) g / g Change in Absorption Capacity (%) 0.16 0 (Control) 26.34 Control 0.16 0.0064 (4%) 25.74 -2.28 0.16 0.0128 (8%) 25.98 -1.37 0.16 0.00256 (16%) 25.21 -4.29 0.16 0.00512 (32%) 24.15 -8.31 Example 9 Example 9 demonstrates a decrease in the absorption capacity of SAM when it is treated with a selected zwitterionic guanidine sulfate salt. Table 9 shows that the decrease in absorption capacity for SAM treated with guanidine sulfate is approximately 17%. As shown in Table 9, guanidine sulfate can decrease the absorption capacity of SAM. Even though guanidine sulfate has similar functional groups to selected SAM salts that exhibit increased absorption capacity, it acts like sodium chloride. This is because guanidine sulfate may not interact with the SAM polymer chain, as its internal salt structure can significantly reduce the interaction forces between the ion pairs of the polymer chain and the zwitterionic salts. Rozfrnn / zznz / E / YiAi Table 9 SAM Evonik 5630 g Guanidine Sulfate g (% by Weight of SAM) AUL Capacity (0.6 PSI, 2 hours) g / g Change in Absorption Capacity (%) 0.16 0 (Control) 26.18 0 0.16 0.0064 (4%) 25.19 -3.80 0.16 0.0128 (8%) 24.64 -5.89 0.16 0.0256 (16%) 23.30 -11.0 0.16 0.0512 (32%) 21.64 -17.3 Example 10 Example 10 demonstrates a decrease (or lack of increase) in the absorption capacity of SAM if the SAM is treated with a salt, di-tetramethylammonium L-aspartic acid dicarboxylate. Table 10 shows that there is almost no impact on the absorption capacity of SAM. This is very surprising and unexpected since di-tetramethylammonium L-aspartic acid dicarboxylate has more functional and structural features than the selected salts described in Examples 1–6. The reason di-tetramethylammonium L-aspartic acid dicarboxylate cannot effectively increase the absorption capacity of SAM is because the second carboxylate salt can significantly prevent (or filter out) the increases in absorption capacity induced by the first carboxylate group. Consequently, there is only a minimal change in the absorption capacity of SAM treated with di-tetramethylammonium L-aspartic acid dicarboxylate. Table 10 Rozfrnn / zznz / E / YiAi SAM Evonik 5630 g Di-Tetramethylethylammonium L-Aspartic Acid g (% by Weight of SAM) AUL Capacity (0.6 PSI, 2 hours) g / g Change in Absorption Capacity (%) 0.16 0 (Control) 26.34 Control 0.16 0.0064 (4%) 26.36 - 0% 0.16 0.0128 (8%) 26.67 - 1% 0.16 0.00256 (16%) 26.78 - 1.5% 0.16 0.00512 (32%) 26.84 ~1.9% In summary, the results set out in Tables 1-6 surprisingly and unexpectedly demonstrate that by using the selected salt structures described herein, the absorption capacity of SAM increases. MODALITIES First Embodiment: In a first embodiment, the invention provides a method for increasing the absorption capacity of a superabsorbent material (SAM), the method comprising: provide a SAM comprising repeating units carrying an anion and a cation wherein the cation is a monometallic ion or a combination of a monometallic ion and a protonic ion; treat the SAM with a selected salt, wherein the selected salt has the following structure: Rozfrnn / zznz / E / YiAi where X~ is selected from -C00~, -SO3“ and -OSO3· and Z+ comprises a monovalent cation; where NRiaR2a is selected from a primary, secondary or tertiary amino group and Riase selects from -H, -Me, -Et, and -Bu and R2a is selected from -H, -Me, -Et and -Bu; where the Rsa is selected from: -H, -Me, -Et and -Bu; wherein R4a is an alkyl chain with 8 or fewer -C additionally wherein an amino group is attached to one or a plurality of the -C in the alkyl chain; or wherein R4a is selected from -H, -Me, -Et and -Bu. The method according to the previous modality, where the monometallic ion of the SAM is selected from Na+, K+ and Li+. The method in accordance with the above modalities, wherein the monovalent cation of the selected salt is selected from NH4+, Me4N+, Et4N+ and Bu4N+. The method in accordance with the above modalities, where the salt selected to treat the SAM is less than 25% of the weight of the SAM. The method in accordance with the above modalities, where the salt to treat SAM is incorporated into an absorbent article selected from diapers, training pants, feminine pads, interlabial pads, tampons, wound management products, and adult incontinence garments. The method according to the previous modalities, where a SAM is formed with a selected salt. Second Embodiment: In a second embodiment, the invention provides a method for increasing the absorption capacity of a SAM, wherein the method comprises: provide a SAM comprising an anion and a cation wherein the cation undergoes ion exchange with units of Rozfrnn / zznz / E / YiAi unneutralized acyl acid; and treating the SAM with a selected salt has the structure: R2h^'^X-Z+ where X is selected from -C00~, - where the salt SO3· and -OSO3· and the Z+ comprises a monovalent cation; where the Rib is selected from: -H, -Me, -Et and -Bu; where R2b is selected from: -H, -Me, -Et and -Bu; wherein the Rab is an alkyl chain with 8 or fewer carbons, wherein an amino group is attached to one or a plurality of the carbons in the alkyl chain; or wherein the Rab is selected from -H, -Me, -Et, and -Bu. The method according to the second modality above, where Z+ is selected from Na+, K+, Li+, Me4N+, Et4N+ and BU4N+. The method in accordance with the previous second modalities, where the salt selected to treat the SAM is less than 25% of the weight of the SAM. The method in accordance with the previous second modalities, where the salt to treat SAM is incorporated into an absorbent article selected from diapers, training pants, feminine pads, interlabial pads, pacifiers, wound management products, and adult incontinence garments. The method according to the previous second modalities, where a SAM is formed with a selected salt. It is hereby stated that, as of this date, the best method known to the applicant for putting the aforementioned invention into practice is the one that is clear from the present description of the invention.

Claims

1. A method for increasing the absorption capacity of a superabsorbent material, characterized in that it comprises: providing a superabsorbent material comprising repeating units carrying an anion and a cation, wherein the cation is a monometallic ion or a combination of a monometallic ion and a protonic ion; treating the superabsorbent material with a selected salt, wherein the selected salt has the structure: Rozfrnn / zznz / E / YiAi, wherein Xa is selected from -COO, -SOr, and -OSCg- and Z+ comprises a monovalent cation; wherein NRiaR2a is selected from a primary, secondary, or tertiary amino group and Ria is selected from -H, -Me, -Et, and -Bu, and R2a is selected from -H, -Me, -Et, and -Bu; wherein R3a is selected from: -H, -Me, -Et, and -Bu; wherein R4a is an alkyl chain with 8 or fewer -C additionally wherein an amino group is attached to one or a plurality of the -C in the alkyl chain; or wherein R4a is selected from -H, -Me, -Et and -Bu;and wherein the salt selected to treat the superabsorbent material is at least 16% and less than 25% of the weight of the superabsorbent material.

2. The method according to claim 1, characterized in that the monometallic ion of the superabsorbent material is selected from Na+, K+ and Li+.

3. The method according to claim 1, characterized in that the monovalent cation of the selected salt is selected from NH4+, Me4N+, Et4N+ and Bu4N+.

4. The method according to claim 1, characterized in that the salt for treating the superabsorbent material is incorporated into an absorbent article selected from diapers, training pants, feminine pads, interlabial pads, hams, wound management products, and adult incontinence garments.

5. A superabsorbent material with a selected salt, characterized in that it is formed according to the method of claim 1.

6. A method for increasing the absorption capacity of a superabsorbent material, characterized in that it comprises: providing a superabsorbent material comprising an anion and a cation wherein the cation undergoes ion exchange with unneutralized acrylic acid units; and treating the superabsorbent material with a selected salt, wherein the selected salt has the structure: Rozfrnn / zznz / E / YiAi wherein X is selected from -COO”, -SO3 and -OSO3” and Z+ comprises a monovalent cation; wherein Rib is selected from: -H, -Me, -Et and -Bu; wherein R2b is selected from: -H, -Me, -Et and -Bu; wherein R3b is an alkyl chain with 8 or fewer carbons wherein an amino group is attached to one or a plurality of the carbons in the alkyl chain; or wherein R3b is selected from -H, -Me, -Et and -Bu. where the salt selected to treat the superabsorbent material is less than 25% of the weight of the superabsorbent material.

7. The method according to claim 6, characterized in that Z+ is selected from Na+, K+, Li+, Me4N+, Et4N+ and Bu4N+.

8. The method according to claim 6, characterized in that the salt for treating the superabsorbent material is incorporated into an absorbent article selected from diapers, training pants, feminine pads, interlabial pads, hams, wound management products, and adult incontinence garments.

9. A superabsorbent material with a selected salt, characterized in that it is formed according to the method of claim 6.

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