Porous particle and water-absorbing material using same
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Filing Date
- 2026-03-10
- Publication Date
- 2026-06-22
Abstract
Description
Porous particles and water-absorbent material using the same
[0001] The present invention relates to porous particles and a water-absorbent material using the same, and more particularly to porous particles that can exhibit good water-absorbing performance and a water-absorbent material using the same.
[0002] Superabsorbent polymers (SAPs) are widely used in the sanitary field, such as disposable diapers, sanitary products, and incontinence pads, and in the agricultural field, such as water-retaining materials. Representative examples of such SAPs include chemically crosslinked polymers having a polyacrylate skeleton.
[0003] Disposable diapers contain a large amount of liquid excrement, including urine, after use, making their disposal a social issue. In particular, large amounts of adult (elderly) disposable diaper waste are generated in facilities, and with the arrival of an aging society, the amount of waste is expected to increase further in the future.
[0004] However, currently, the disposal of such waste inevitably places an environmental burden on the environment.
[0005] Many parts of disposable diapers are made up of various polymer materials, but the parts that absorb urine and other liquids are made up of SAP and pulp. While pulp is biodegradable, current SAP is not. For this reason, incineration is currently considered the only option for disposable diaper waste.
[0006] On the other hand, an approach has been proposed to reduce the environmental burden associated with waste disposal by using biodegradable materials for the entire disposable diaper, thereby treating the waste through composting. Under this proposal, there is a strong social demand for the development of a high-performance biodegradable SAP that can be produced efficiently.
[0007] For example, Patent Document 1 discloses an SAP that uses diethylenetriamine as a crosslinking agent for the base polymer polyglutamic acid. However, in the SAP of Patent Document 1, γ-glutamic acid used as a material for polyglutamic acid is very expensive, and there is a risk that the crosslinking agent will remain in the resulting SAP. For these reasons, there is a demand for the development of a biodegradable SAP that can withstand practical use.
[0008] Patent No. 6234358
[0009] The present invention is directed to solving the above-mentioned problems, and an object of the present invention is to provide porous particles that can be used as superabsorbent polymers (SAPs) and that can reduce the impact on the environment when disposed of, and a water-absorbent material using the same.
[0010] The present invention relates to porous particles containing starches modified with organic acids, wherein the organic acids are polycarboxylic acids having at least three carboxylic acid groups in one molecule or salts thereof.
[0011] In one embodiment, the organic acid is a polycarboxylic acid having three carboxylic acid groups or a salt thereof.
[0012] In one embodiment, the organic acid is at least one compound selected from the group consisting of citric acid and citrate salts.
[0013] In one embodiment, the porous particles of the present invention have a density of 0.1 to 0.8 g / cm ３ It has a specific gravity of
[0014] In one embodiment, the porous particles of the present invention have an average particle size of 0.1 to 8 mm.
[0015] The present invention also relates to a water-absorbing material containing the porous particles.
[0016] In one embodiment, the swelling degree when standard artificial urine is used and 3 minutes have passed since the start of water absorption is 3 to 100.
[0017] The present invention also provides a method for producing porous particles, comprising the steps of: combining unmodified starches and organic acids to obtain a mixture; adding water to the mixture to obtain a deliquescent mixture; and heating the deliquescent mixture at 105 to 140°C, wherein the organic acids are polycarboxylic acids having at least three carboxylic acid groups in one molecule or salts thereof.
[0018] In one embodiment, the deliquescent mixture is prepared using water having a mass of 0.02 to 0.2 times the total mass of the organic acid salt.
[0019] In one embodiment, the unmodified starches contain 15 to 30% by weight of amylose based on the total weight.
[0020] According to the present invention, a superabsorbent polymer (SAP) with excellent water absorption properties can be provided. The porous particles of the present invention are biodegradable, and the environmental impact can be reduced by composting them when they are disposed of. Furthermore, the porous particles of the present invention can be easily produced from widely used materials and are suitable for mass production.
[0021] 1 is a graph showing the results of IR spectra measured for sample particles (E1), (E3), and (E4) obtained in Examples 1, 3, and 4, and for untreated products (unmodified starches). 2 is an SEM photograph of the surface and cross section of sample particle (E1) obtained in Example 1.
[0022] The present invention will be described in detail below.
[0023] (Porous Particles) The porous particles of the present invention contain starches that have been modified with organic acids.
[0024] The starches modified with organic acids are obtained by treating unmodified (i.e., native) starches with the organic acids described below. Here, the term "modified" as used herein means to describe the "state" of the surface and / or interior of porous particles. On the other hand, the term "modified / modified" as used herein means that the surface and / or interior of unmodified starches that have not been subjected to a modification treatment (i.e., before the modification treatment) have undergone a process of modification (modification treatment), and is clearly distinguished from the above-mentioned "modified."
[0025] The starches modified with organic acids may be modified starches obtained by using organic acids and then neutralized by alkali treatment, which will be described later.
[0026] Unmodified starch is a carbohydrate (polysaccharide) containing amylose, amylopectin, glycogen, and combinations thereof as components. In the present invention, the unmodified starch contains, for example, 0% to 90% by mass, 5% to 70% by mass, or 15% to 30% by mass of amylose based on the total mass, because this allows for the production of porous particles with superior water absorption. In particular, by having the unmodified starch contain 15% to 30% by mass of amylose based on the total mass, an increase in viscosity during modification can be suppressed, enabling more uniform modification, and preventing a decrease in the water absorption rate of the resulting porous particles.
[0027] Examples of unmodified starches include raw starches such as tapioca starch, rice starch, wheat starch, corn starch (corn starch, corn starch), potato starch, sweet potato starch, and sago starch; pregelatinized starch; heat-treated starch; low-viscosity starch; and modified starches such as hydroxypropyl starch; and combinations thereof. Tapioca starch and corn starch, and combinations thereof, are preferred because of their versatility.
[0028] The organic acids are polycarboxylic acids or salts thereof.
[0029] The polycarboxylic acid used has at least three carboxylic acid groups in one molecule because it is highly reactive with the hydroxyl groups constituting the unmodified starch. Examples of polycarboxylic acids having at least three carboxylic acid groups in one molecule include citric acid, trimellitic acid, 1,2,3-propanetricarboxylic acid, 1,2,3-butanetricarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,3,4-butanetetracarboxylic acid, aconitic acid, and benzenetetracarboxylic acid, as well as combinations thereof.
[0030] Examples of the polycarboxylic acid salts include alkali metal salts (e.g., sodium salts and potassium salts, and combinations thereof) and alkaline earth metal salts (e.g., magnesium salts and calcium salts, and combinations thereof) of the above polycarboxylic acids, and combinations thereof. Specific examples of the polycarboxylic acid salts include sodium citrate and potassium citrate, and combinations thereof.
[0031] In the present invention, citric acid, citrates, and combinations thereof are preferred as organic acids because they are readily available and have excellent reactivity with unmodified starch.
[0032] The porous particles of the present invention can also be clearly distinguished from unmodified starch in that they preferably have a lower specific gravity than the unmodified starch. The specific gravity of the porous particles of the present invention is preferably 0.1 g / cm ３ ~0.8g / cm ３ , more preferably 0.2 g / cm ３ ~0.6g / cm ３ The specific gravity of the resulting porous particles is 0.1 g / cm ３ If the specific gravity of the resulting porous particles is less than 0.8 g / cm, the strength of the powder will decrease and handling may become difficult. ３ Above this value, the particles may lose their porous properties, which may affect the water absorption rate and water absorption speed.
[0033] The porous particles of the present invention also preferably have a predetermined average particle size so that they can provide uniform water absorption when used, for example, as a water-absorbent material. The average particle size of the porous particles of the present invention is preferably 0.1 mm to 8 mm, more preferably 0.2 mm to 5 mm. If the average particle size of the resulting porous particles is less than 0.1 mm, they may be too fine and difficult to handle as particles. If the average particle size of the resulting porous particles is more than 8 mm, the voids between adjacent particles will be large, and the overall water absorption efficiency may be reduced when such a particle group is used as a water-absorbent material.
[0034] The porous particles of the present invention have a morphology resembling an aggregation of multiple small particles, and a porous structure with numerous fine irregularities is formed on the surface and inside of the particles. When such porous particles come into contact with water, urine, etc., the particles can absorb the water on the surface or inside of the particles and swell on the fine irregularities. As a result, the porous particles of the present invention have excellent water absorption properties and can be used as a water-absorbing material as described below.
[0035] Furthermore, since the porous particles of the present invention are mainly composed of starches modified with the organic acids, they have excellent biodegradability. Therefore, when disposing of these porous particles, they can be composted by burying them in the ground, in addition to or instead of incineration, as is the case with conventional SAP disposal. This reduces the environmental impact of waste disposal.
[0036] (Method for Producing Porous Particles) The porous particles of the present invention can be produced, for example, as follows.
[0037] In the production method of the present invention, first, unmodified starches and organic acids are mixed together.
[0038] The mixing ratio of unmodified starches to organic acids is not particularly limited, but is preferably 50 to 500 parts by mass, more preferably 100 to 500 parts by mass, per 100 parts by mass of unmodified starches. If the amount of organic acids is less than 50 parts by mass per 100 parts by mass of unmodified starches, the unmodified starches cannot be uniformly modified with the organic acids, and some unmodified starches may remain, making it difficult to obtain porous particles with sufficient water absorption performance. If the amount of organic acids exceeds 500 parts by mass per 100 parts by mass of unmodified starches, the unmodified starches have already been almost entirely modified with the organic acids, and not only is no further improvement in effect achieved, but productivity may actually decrease.
[0039] The unmodified starches and organic acids may be mixed manually or using a mixing means known to those skilled in the art (e.g., a Henschel mixer, a kneader, a Panbury mixer, etc.) or a grinding means (e.g., a jet mill, a vibration mill, a ball mill, a bead mill, a pot mill, a pin mill, a roller mill, a hammer mill, a rotary mill, a planetary mill, a stone grinder, etc.).
[0040] In this way, a mixture containing unmodified starches and organic acids is prepared.
[0041] Water is then added to this mixture to create a deliquescent mixture.
[0042] The term "deliquescent" used herein refers to a state in which water actively added to a mixture is incorporated into the crystalline surface of organic acid particles constituting the mixture, with some of the water dissolving out, forming a deliquescent surface state. In this sense, it is clearly distinguished from "deliquescence," in which water vapor from the air is incorporated into the crystalline surface and some of the water dissolves out.
[0043] The type of water to be added is not particularly limited. For example, any of pure water, ion-exchanged water, RO water, and tap water may be used.
[0044] In the present invention, the deliquescent mixture is preferably prepared by adjusting the amount of water added to the mixture containing the unmodified starches and organic acids. For example, in the present invention, the deliquescent mixture can be prepared by adding water in an amount preferably 0.02 to 0.2 times, more preferably 0.05 to 0.18 times, the total mass of the organic acids in the mixture containing the unmodified starches and organic acids. If the amount of water added is less than 0.02 times the total mass of the organic acids, it becomes difficult for the added water to uniformly incorporate into the crystalline surfaces of the organic acids, resulting in a non-homogeneous (i.e., uneven) deliquescent mixture. If the amount of water added is more than 0.2 times the total mass of the organic acids, more of the added water will be incorporated into the crystalline surfaces of the organic acids, resulting in the dissolution of more of the organic acids than will be sufficient to dissolve a portion of the organic acids, making it difficult to form the desired porous structure in the resulting particles.
[0045] The preparation of the deliquescent mixture is preferably carried out in the above-mentioned mixing means or grinding means known to those skilled in the art, in which water is added to a mixture containing the unmodified starches and organic acids, thereby obtaining a deliquescent mixture with a more uniform particle size (e.g., a relatively suppressed spread in the particle size distribution).
[0046] The deliquescent mixture is then heated.
[0047] The heating temperature of the deliquescent mixture is set to, for example, a temperature exceeding 100°C. Such a heating temperature is preferably 105°C to 140°C, more preferably 108°C to 135°C. If the heating temperature of the deliquescent mixture is below 105°C, water may remain in the reaction mixture, resulting in a decrease in the reaction rate. If the heating temperature of the deliquescent mixture is above 140°C, the unmodified starch may be modified in an undesired manner, causing discoloration, a decrease in molecular weight, and a decrease in water absorption.
[0048] The heating time for the deliquescent mixture is not particularly limited, and can be appropriately selected by those skilled in the art depending on the amount of the deliquescent mixture to be heated and the heating temperature.
[0049] The deliquescent mixture is preferably heated in a mixing or grinding means known to those skilled in the art, as described above, to obtain porous particles with a more uniform particle size (e.g., a relatively small particle size distribution).
[0050] After heating the deliquescent mixture, unreacted organic acids may remain in the resulting reaction product. In such cases, an appropriate amount of water may be added to the resulting reaction product to dissolve the unreacted organic acids in the water. The unreacted organic acids can then be easily removed by filtration. Furthermore, by repeatedly performing this filtration and confirming that the resulting filtrate is neutral, the unreacted organic acids can be more reliably removed from the resulting reaction product. After removing the unreacted organic acids, the residue (reaction product) is dried, if necessary, using a method known to those skilled in the art.
[0051] The particles thus obtained may then be subjected to a post-treatment, such as a surface treatment with an alkaline solution, to obtain neutralized particles. Examples of alkaline solutions that can be used include solutions containing sodium hydroxide and / or potassium hydroxide (e.g., a sodium hydroxide-methanol solution, a potassium hydroxide-methanol solution, and combinations thereof).
[0052] In this way, the porous particles of the present invention, which contain starches modified with organic acids, can be obtained.
[0053] (Water-Absorbent Material) The water-absorbent material of the present invention contains the porous particles. That is, the porous particles function as, for example, a superabsorbent polymer (SAP) and can be used as is as a constituent component of the water-absorbent material.
[0054] The water absorption performance of such a water-absorbing material can be evaluated, for example, by the degree of swelling after 3 minutes of water absorption using standard artificial urine. Here, the term "standard artificial urine" used in this specification refers to an aqueous solution having the composition shown in Table 1 below.
[0055]
[0056] The procedure for measuring the swelling degree is as follows.
[0057] First, 0.10 g of sample (dry mass: Mdry) is placed in a metal mesh (using a φ30 mm tea strainer) and immersed together with the mesh in a Petri dish (φ35 mm) containing 8 mL of pure water or the above-mentioned standard artificial urine. After leaving it as is for 3 minutes, the sample is removed and excess liquid on the mesh is wiped off with paper (e.g., Pro Wipe manufactured by Daio Paper Co., Ltd.), and the sample is weighed (wet mass (Mwet)). The swelling degree Q is then calculated according to the following formula (1):
[0058]
[0059] The water-absorbent material of the present invention may contain, in addition to the porous particles, other biodegradable materials known in the art. Examples of other biodegradable materials include polysaccharides other than the above-mentioned unmodified starches, such as polyglutamic acid, polyaspartic acid, polylysine, cellulose, pulp, plant fibers, silk, agarose, carrageenan, xanthan gum, curdlan, pullulan, hyaluronic acid, glucomannan, levan, alginic acid, and carboxymethylcellulose, as well as combinations thereof. The content of the other biodegradable resin in the water-absorbent material of the present invention can be selected by those skilled in the art in an appropriate amount as long as it does not inhibit the function of the porous particles as SAP.
[0060] The absorbent material of the present invention may also optionally contain other additive materials, such as clays, sugars (e.g., trehalose), fillers, and antioxidants, and combinations thereof.
[0061] Examples of clays include, but are not limited to, montmorillonite, beidellite, nontronite, and bentonite, and combinations thereof. Examples of fillers include, but are not limited to, carbon black, silica, talc, and titanium oxide, and combinations thereof. The antioxidant is not particularly limited, and commercially available antioxidants can be used, for example.
[0062] The content of the other additive materials is not particularly limited, and can be selected by a person skilled in the art in any amount taking into consideration the content of the porous particles.
[0063] The absorbent material of the present invention contains the starches modified with the organic acids as the main component, and thus can be used in various industrial products that require excellent water absorption, such as sanitary products such as disposable diapers and sanitary napkins, and agricultural materials such as water-retaining materials.
[0064] The absorbent material of the present invention can be easily produced from porous particles, which are the main components, using organic acids and unmodified starch as described above, and furthermore, when it is disposed of, it can be composted instead of the conventional incineration process, taking advantage of its biodegradability. Therefore, it is possible to reduce concerns about the environmental impact when disposing of the absorbent material after use.
[0065] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.
[0066] 1. Preparation of Sample Particles (Example 1) Preparation of Citric Acid-Modified Tapioca Starch Sample Particles (E1) 40 g of tapioca starch (manufactured by Matsutani Chemical Industry Co., Ltd.; amylose content 17% by mass) and 120 g of citric acid were combined and thoroughly mixed to obtain a mixture. Next, 12 g of pure water (equivalent to 10% of the mass of the organic acid salt (citric acid) used) was added to the mixture so that it was evenly distributed throughout, and further mixed. The addition of this pure water caused some of the contents of the mixture to dissolve, as if deliquescing. By stirring appropriately, a spherical deliquescent mixture with a diameter of approximately 3 to 5 mm was obtained. This deliquescent mixture was spread as thinly as possible in a glass container, left overnight at room temperature, dried in a vacuum dryer for 8 hours, and then stored in a desiccator. It was further vacuum-dried for 1 hour before heating to remove moisture from the deliquescent mixture. The deliquescent mixture was then heated for 5 hours in a small thermostatic chamber set at 110°C to obtain a spherical thermally denatured product. The thermally denatured product was then removed from the chamber and allowed to cool. An appropriate amount of pure water was then added to swell the thermally denatured product, and the filtrate was filtered to remove unreacted citric acid. This process of adding pure water, swelling the thermally denatured product, and filtering was repeated until the pH of the filtrate, as confirmed with pH test paper, reached approximately 6-7, confirming that the resulting filtrate was neutral. Meanwhile, the residue was recovered, and the remaining water was replaced with methanol and acetone. The residue was then spread as thinly as possible in a glass container and vacuum-dried. This yielded sample particles (E1) composed of citric acid-modified tapioca starch.
[0067] A portion of the sample particles (E1) was taken and cut into 1 cm ３ The mass per unit area was measured and the specific gravity was calculated. The specific gravity of the obtained sample particles (E1) was 0.48 cm ３ The specific gravity of the tapioca starch (unmodified starch) used was 1.6 cm ３ It was significantly lower than the
[0068] Furthermore, the particle size distribution of the sample particles (E1) was measured using a digital macroscope (HRX-01 / RX-100 manufactured by Hirox Co., Ltd.), and the average particle diameter was calculated. The average particle diameter of the obtained sample particles (E1) was 1.86 mm.
[0069] (Example 2) Preparation of sample particles (E2) of citric acid-modified cornstarch Sample particles (E2) composed of citric acid-modified cornstarch were obtained in the same manner as in Example 1, except that 40 g of cornstarch (manufactured by Matsutani Chemical Industry Co., Ltd.; amylose content 28% by mass) was used instead of tapioca starch, and the resulting spherical deliquescent mixture was heated for 5 hours in a small thermostatic chamber set at 130°C.
[0070] Example 3: Preparation of Sample Particles (E3) of Alkali-Treated Citric Acid-Modified Tapioca Starch Sample particles (E1) composed of citric acid-modified tapioca starch obtained in Example 1 were immersed in a 0.1 M potassium hydroxide ethanol solution and slowly stirred. After reacting at room temperature for 1 hour, the alkali-treated material was removed from the solution, and an appropriate amount of pure water was added to swell the alkali-treated material. The filtrate was then filtered to remove any remaining potassium hydroxide. This procedure of adding pure water, swelling the alkali-treated material, and filtering was repeated three times, and the resulting filtrate was confirmed to be neutral. Meanwhile, the residue was recovered, and the remaining solution was replaced with methanol and acetone. The mixture was spread as thinly as possible in a glass container and vacuum-dried. This yielded sample particles (E3) composed of alkali-treated citric acid-modified tapioca starch.
[0071] (Example 4) Preparation of sample particles (E4) of alkali-treated citric acid-modified tapioca starch Sample particles (E4) composed of alkali-treated citric acid-modified tapioca starch were obtained in the same manner as in Example 3, except that the particles were immersed in a 0.1 M potassium hydroxide ethanol solution and then reacted at 40°C for 2 hours.
[0072] 2. Evaluation of Sample Particles (1) IR Spectrum The obtained sample particles (E1), (E3), and (E4) were subjected to IR measurement using a Fourier transform infrared spectrophotometer (FT-IR) (NICOLET iS5, Thermo Fisher Scientific Co., Ltd.) together with the tapioca starch used (unmodified starches; untreated product). The results are shown in Figure 1.
[0073] As shown in FIG. 1, the sample particles (E1) obtained in Example 1 exhibited a peak at 1700 cm －１ It was confirmed that a peak due to a carboxylic acid group appeared around 1700 cm (see the open arrow). On the other hand, for sample particles (E3) and (E4) of Examples 3 and 4, －１ The peak around 1600 cm is significantly smaller, while －１ A peak corresponding to carboxylate appears nearby, and it is believed that the carboxylic acid group was neutralized by the alkali treatment.
[0074] (2) SEM Photograph The surface and cross section of the sample particle (E1) obtained in Example 1 were observed with a scanning electron microscope (SEM). The obtained SEM photograph is shown in FIG.
[0075] As shown in Figure 2, the sample particle (E1) obtained in Example 1 has numerous fine pores formed on its surface and inside (cross section) (60x magnification). Furthermore, at larger magnifications (500x and 1500x magnification), it can be seen that numerous fine irregularities have been formed on the surface and inside (cross section) of the sample particle (E1).
[0076] (3) Swelling Degree in Artificial Urine or Pure Water Standard artificial urine was prepared with the composition shown in Table 1 above. Next, 0.10 g (dry mass: Mdry) of sample particles (E1) to (E4) obtained in Examples 1 to 4 was placed in a metal mesh (using a φ30 mm tea strainer), and the mesh was immersed in a Petri dish (φ35 mm) containing 8 mL of the standard artificial urine. After leaving it as is for 3 minutes, it was removed and excess liquid on the mesh was wiped off with paper (e.g., Pro Wipe manufactured by Daio Paper Co., Ltd.), and each sample was weighed (wet mass (Mwet)). The swelling degree Q was then calculated according to the following formula (1). The results are shown in Table 2.
[0077]
[0078] Furthermore, the swelling degree Q was calculated in the same manner as above, except that pure water was used instead of the standard artificial urine. The results are shown in Table 2.
[0079]
[0080] As shown in Table 2, all of the sample particles (E1) to (E4) obtained in Examples 1 to 4 had a good degree of swelling within 3 minutes of starting to absorb standard artificial urine or pure water. These results indicate that it is possible to absorb a large amount of water in a short period of time, and it is clear that all of the sample particles (E1) to (E4) obtained in Examples 1 to 4 are useful as water-absorbing materials.
[0081] According to the present invention, the composition is useful as a material for sanitary products and agricultural materials, for example.
Claims
1. Porous particles containing starches modified with organic acids, Porous particles wherein the organic acids are polycarboxylic acids or salts thereof having at least three carboxylic acid groups in one molecule.
2. The porous particles according to claim 1, wherein the organic acids are polycarboxylic acids having three carboxylic acid groups or a salt thereof.
3. The porous particle according to claim 1, wherein the organic acids are at least one compound selected from the group consisting of citric acid and citrate salts.
4. 0.1~0.8g / cm ３ A porous particle according to claim 1, having the density of [value].
5. Porous particles according to claim 1, having an average particle diameter of 0.1 to 8 mm.
6. A water-absorbing material containing porous particles according to any one of claims 1 to 5.
7. The absorbent material according to claim 6, wherein the degree of swelling after 3 minutes from the start of water absorption using standard artificial urine is 3 to 100.
8. A method for producing porous particles, A step of obtaining a mixture by combining unmodified starches and organic acids. A step of adding water to the mixture to obtain a deliquescence-like mixture, A step of heating the deliquescent mixture at 105 to 140°C. It includes, A method wherein the organic acids are polycarboxylic acids having at least three carboxylic acid groups in one molecule or a salt thereof.
9. The method according to claim 8, wherein the deliquescent mixture is prepared using water having a mass of 0.02 to 0.2 times the total mass of the organic acid salt.
10. The method according to claim 8, wherein the unmodified starches contain 15 to 30% by mass of amylose based on the total mass.