KR20150062959A - Measuring method of gel strength of super absorbent resin - Google Patents
Measuring method of gel strength of super absorbent resin Download PDFInfo
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- KR20150062959A KR20150062959A KR1020140163514A KR20140163514A KR20150062959A KR 20150062959 A KR20150062959 A KR 20150062959A KR 1020140163514 A KR1020140163514 A KR 1020140163514A KR 20140163514 A KR20140163514 A KR 20140163514A KR 20150062959 A KR20150062959 A KR 20150062959A
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- superabsorbent resin
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
- G01N3/14—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces generated by dead weight, e.g. pendulum; generated by springs tension
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/24—Investigating strength properties of solid materials by application of mechanical stress by applying steady shearing forces
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
- G01N33/44—Resins; rubber; leather
- G01N33/442—Resins, plastics
Abstract
Description
And a method of measuring a new gel strength of a superabsorbent resin capable of accurately reflecting and predicting physical properties of a superabsorbent resin under an actual use environment.
Super Absorbent Polymer (SAP) is a water-soluble ethylenically unsaturated monomer having at least partially neutralized acidic groups, typically a cross-linked polymer obtained by surface-crosslinking a base resin in powder form obtained by polymerizing at least partially neutralized acrylic acid And is known as a synthetic polymer material having a function capable of absorbing moisture several tens to several hundreds of its own weight.
Such superabsorbent resins have begun to be put to practical use as physiological tools and nowadays, besides sanitary articles such as diapers for children, there are currently used soil repair agents for horticultural use, index materials for civil engineering and construction, sheets for seedling exploration, freshness- And the like.
In most cases, such a superabsorbent resin is widely used in the field of sanitary materials such as diapers and sanitary napkins. In addition to exhibiting a certain level of water absorption capacity for such use, it is necessary to use an external pressure, for example, It is necessary to exhibit a property that once the absorbed moisture is not released again, despite the pressure due to the weight and the like. Therefore, the superabsorbent resin should contain a crosslinked structure of a network formed of a hydrophilic group at a certain level or more, and it is necessary to exhibit excellent gel strength in order to maintain the absorbing power and the water holding power in spite of the external pressure. Furthermore, when the gel strength of the superabsorbent resin is improved, the superabsorbent resin can maintain a good shape even after moisture absorption to exhibit excellent liquid permeability, and it is possible to provide a sanitary material with improved performance.
Therefore, the measurement of the gel strength of the superabsorbent resin is very important for evaluating and predicting its excellent physical properties, particularly, physical properties such as absorption power when used in sanitary materials, water-holding capacity under pressure and liquid permeability.
Conventionally, a superabsorbent resin that absorbs moisture and is swollen is disposed between two vertically disposed plates. Then, the normal force is measured while pressing the superabsorbent resin through the upper plate, The gel strength of the resin was measured. However, in the environment where the super absorbency resin is included in the sanitary material such as the diaper, the external pressure acts not only in the vertical direction but also in the horizontal direction of the super absorbency resin, and in spite of the force applied in the horizontal direction, It has been confirmed that the degree of relevance is determined depending on whether or not the strength is represented by the absorbency of the superabsorbent resin or the degree of physical properties such as liquid permeability.
However, a method for measuring the gel strength in the horizontal direction of the superabsorbent resin with high reliability has not yet been proposed.
Accordingly, the present invention provides a gel strength measuring method that reliably measures the gel strength in the horizontal direction of a superabsorbent resin so as to help reflect and predict properties of a superabsorbent resin under actual use environment.
The present invention relates to a method of absorbing and swelling a physiological saline solution (0.9 wt% aqueous sodium chloride solution) into a superabsorbent resin for a time of about 2 hours or less; Placing the swollen superabsorbent resin between plates of a rheometer having a predetermined gap; A linear viscoelastic regime section having a constant storage modulus and a loss modulus while increasing a shear strain using a rheometer under vibration at a speed of about 5 to 20 rad / Confirming the shear strain; And measuring the storage elastic modulus and the loss elastic modulus of the swollen superabsorbent resin under the identified shear deformation and measuring the average value of the storage elastic modulus as the horizontal gel strength of the superabsorbent resin. Of the gel strength.
In the method of measuring the gel strength of such a superabsorbent resin, the swelling step may be performed by immersing the superabsorbent resin in physiological saline solution for about 0.5 to 1 hour, and then removing the unabsorbed solvent.
In the gel strength measuring step, the storage elastic modulus of the swollen superabsorbent resin is measured in a rheometer under vibration at a speed of about 5 to 20 rad / s for about 60 seconds under a constant shear strain of the linear viscoelastic state section , And the average value of the storage elastic modulus having a value larger than the loss elastic modulus can be obtained and measured as the gel strength in the horizontal direction of the superabsorbent resin.
In the method of measuring the gel strength of the superabsorbent resin, the rheometer includes an upper plate and a lower plate each having a diameter of about 8 to 60 mm and arranged in parallel with each other, and the lower plate has a diameter of about 1 to 5 mm You can have a wall.
In the method of measuring the gel strength, in the step of positioning the swollen superabsorbent resin between plates of a rheometer having a predetermined gap,
After the swollen superabsorbent resin is positioned between the plates of the rheometer, the gap between the plates can be controlled to control packing of the swollen superabsorbent resin as a whole in the space between the plates. In a more specific example, after positioning the swollen superabsorbent resin between the plates of the rheometer, the distance between the plates may be adjusted to about 1 to 3 mm. At this time, in consideration of the degree of hardening or softening of the swollen superabsorbent resin, a force of about 3N or less may be applied, or the interval between the plates may be appropriately adjusted without applying a separate force.
Hereinafter, a method for measuring the gel strength of a superabsorbent resin according to a specific embodiment of the present invention will be described in more detail. It is to be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
In addition, throughout this specification, "comprising" or "containing ", unless specifically stated, refers to including any and all components (or components) Can not be interpreted as excluding.
According to one embodiment of the present invention, there is provided a method of absorbing saline (absorbing 0.9 wt% sodium chloride aqueous solution) into a superabsorbent resin for a time of about 2 hours or less and swelling the same; Placing the swollen superabsorbent resin between plates of a rheometer having a predetermined gap; A linear viscoelastic regime section having a constant storage modulus and a loss modulus while increasing a shear strain using a rheometer under vibration at a speed of about 5 to 20 rad / Confirming the shear strain; And measuring the storage elastic modulus and the loss elastic modulus of the swollen superabsorbent resin under the identified shear deformation and measuring the average value of the storage elastic modulus as the horizontal gel strength of the superabsorbent resin. A method for measuring the gel strength of the gel is provided.
That is, according to the gel strength measuring method of this embodiment, the swollen superabsorbent resin is placed in a plate of a rheometer having a predetermined interval, and a force is applied by using a plate under the vibration of the rheometer, The directional gel strength can be appropriately measured.
Particularly, as a result of experiments conducted by the inventors of the present invention, it has been found that, in a commercially available rheometer, a superabsorbent resin is placed between two plates arranged in parallel in a direction perpendicular to the direction of gravity, It has been confirmed that when the gel strength of the superabsorbent resin is measured (for example, while vibrating the rheometer), it is possible to measure the gel strength in the horizontal direction of the superabsorbent resin with high reliability.
More specifically, the superabsorbent resin is absorbed and swollen for about 2 hours or less, for example, for about 0.5 to 1 hour, using physiological saline, as in the method of one embodiment, and the absorbance of about 5 to 20 rad / s It was confirmed that the horizontal gel strength of the high water absorbent resin can be more reliably measured so that the physical properties under the actual use environment are better reflected by measuring the gel strength in the horizontal direction using the rheometer under the vibration at the speed.
On the other hand, when ordinary brine is used instead of physiological saline, absorption and swelling times are different, and the vibration speed of the rheometer is varied, the time required for measuring the gel strength may be excessively long, It is difficult to reliably measure the gel strength in the horizontal direction. From these measurement results, it has been confirmed that the physical properties of the superabsorbent resin under actual use environment are hardly predicted.
According to a more specific example, when the content of the surface cross-linking agent is controlled in the process of producing the superabsorbent resin and the surface cross-linking degree is varied, the horizontal direction gel strength is measured by the method of one embodiment described above. , The horizontal gel strength measured by the above method was found to be a value substantially proportional to the content of the surface cross-linking agent. This indicates that, in accordance with the method of one embodiment, the gel strength in the horizontal direction, which reflects the degree of crosslinking of the superabsorbent resin, can be reliably measured.
Thus, according to the method of one embodiment, the gel strength of the superabsorbent resin which can better predict the actual physical properties of the superabsorbent resin, particularly the actual physical properties of the superabsorbent resin under actual use environment in the sanitary material such as diapers, . Further, in the past, there has been practically no method for reliably measuring the gel strength in the horizontal direction of the superabsorbent resin, and thus it has been difficult to predict the liquid permeability and related properties of the superabsorbent resin. However, The gel strength in the horizontal direction of the resin can be measured with high reliability, so that the liquid permeability and related physical properties of the superabsorbent resin can be predicted and judged better.
Therefore, the gel strength measurement method of one embodiment can be greatly helpful in predicting and determining various physical properties such as liquid permeability of the superabsorbent resin and improving the physical properties thereof.
On the other hand, as described above, physiological saline (0.9 wt% aqueous solution of sodium chloride) is used in the swelling step of the superabsorbent resin in the gel strength measuring method of a superabsorbent resin according to an embodiment. Particularly, examples of the solvent that has been used for evaluating the physical properties of the superabsorbent resin include aqueous solutions of various inorganic salts such as water and sodium chloride aqueous solution, artificial urine, etc. In the gel strength measuring method of one embodiment, Use physiological saline.
By swelling the superabsorbent resin in the physiological saline solution and then measuring the gel strength in the horizontal direction of the swollen superabsorbent resin, it is possible to more easily judge the relationship between the measured gel strength and various physical properties of the superabsorbent resin which has been conventionally measured Thus, the physical properties of the superabsorbent resin can be predicted and determined more reliably.
In this swelling step, depending on the most typical conditions for measuring the physical properties of the superabsorbent resin, for example, the superabsorbent resin is impregnated with an excess amount of physiological saline solution at room temperature for about 0.5 to 1 hour, typically about 1 hour After swelling, the solvent remaining unabsorbed in the superabsorbent resin can be removed. In order to remove such solvent, an aspirator or the like can be used. The solvent on the surface of the swollen superabsorbent resin can be removed by using a filter paper or the like.
For the swollen superabsorbent resin, for example, a gel strength measurement step using a rheometer is carried out. As the rheometer, any known or commercially available rheometer may be used.
In the step of measuring the gel strength after the swelling step, the swollen superabsorbent resin is positioned between plates of a rheometer having a predetermined interval. A linear viscoelastic regime section having a constant storage modulus and a loss modulus while increasing a shear strain using a rheometer under vibration at a speed of about 5 to 20 rad / Confirming the shear strain; And measuring the storage elastic modulus and the loss elastic modulus of the swollen superabsorbent resin under the identified shear deformation and measuring the average value of the storage elastic modulus as the horizontal gel strength of the superabsorbent resin, The gel strength of the water absorbent resin is measured.
In the step of measuring the gel strength, in order to place the swollen superabsorbent resin between the plates of the rheometer, first, the superabsorbent resin is placed between two plates of a rheometer having a slightly wider gap, . In addition, there may be a wall between the two plates so that the superabsorbent resin sample does not escape. A more specific example of this is as follows.
First, the rheometers comprise a top plate and a bottom plate, each having a diameter of about 8 to 60 mm, or about 10 to 30 mm, or about 25 mm, and arranged in parallel one above the other, Lt; / RTI > This wall can serve to prevent the superabsorbent resin sample between the upper and lower plates from escaping.
In the step of positioning the swollen superabsorbent resin between the plates of the rheometer having a predetermined interval, after the swollen superabsorbent resin is positioned between the plates of the rheometer having a slightly wider gap, So that the swollen superabsorbent resin can be tightly packed in the space between the plates. To this end, the swollen superabsorbent resin may be positioned between the plates of the rheometer, for example, in an amount of about 2 g or more, and then the distance between the plates may be adjusted to about 1 to 3 mm.
At this time, the amount of the superabsorbent resin positioned between the plates may vary depending on the diameter of the plate. If the amount of the superabsorbent resin is excessively small in consideration of the diameter of the plate, or if the superabsorbent resin swelled in the space between the plates is not controlled so as to be packed tightly (for example, The gel strength may be measured to be lower than the actual value and the reliability of the measured value may be deteriorated.
In order to reduce the reliability of the measured values, the gap between the plates is adjusted. In this case, the swollen superabsorbent resin may be applied with a force of about 3N or less, It is possible to adjust the distance between the plates without applying the plate.
For example, relatively soft (superfluid) superabsorbent resin samples can be easily adjusted to a desired spacing and proceed to subsequent measurement steps, so that the spacing between the plates can be adjusted without applying any additional force. Conversely, a hard sample may be difficult to meet the desired desired spacing. Thus, a rigid sample can press the plate with a constant force (e.g., about 3N or less) on the plate to allow all the superabsorbent resin samples to contact the plate surface and to adjust the spacing between the appropriate plates.
After the swollen superabsorbent resin is positioned between the plates of the rheometer and the interval between the plates is adjusted, the superabsorbent resin to which the force is applied can be stabilized for a predetermined time. In a more specific example, in this stabilization step, the swollen superabsorbent resin located between the spaced plates is subjected to a shear strain check step and a gel strength measurement step for about 1 to 5 minutes, or It is allowed to stand for about 2 to 3 minutes to stabilize the superabsorbent resin. It has been confirmed that the progress of the stabilization step can more reliably measure the gel strength. If this stabilization step was not carried out, it was confirmed that a relatively large deviation or error could be observed in the measured gel strength value.
On the other hand, after proceeding to the above step, it is possible to increase the shear strain by applying a force to both plate surfaces while vibrating the rheometer at a speed of, for example, about 5 to 20 rad / s, or about 10 rad / The shear deformation of the linear viscoelastic regime, which has a constant storage modulus and loss modulus, can be confirmed by increasing the shear strain. In normally swollen superabsorbent resin samples, shear deformation of 0.1% can be seen to be within the linear viscoelastic state section.
After confirming the shear deformation of this linear viscoelastic regime section, it is possible to obtain a constant shear strain in a linear viscoelastic regime, for example, in a rheometer under vibration at a speed of about 5 to 20 rad / s, The storage modulus and the loss modulus of the swollen superabsorbent resin may be respectively measured for a predetermined period of time, for example, for about 60 seconds, and an average value of the storage modulus may be determined and measured as the horizontal gel strength of the superabsorbent resin. Usually, the storage elastic modulus may have a value much larger than the loss elastic modulus.
Through the above-described method, it is possible to measure the gel strength in the horizontal direction of the superabsorbent resin with high reliability, thereby making it possible to more effectively predict and determine the degree of crosslinking of the superabsorbent resin and the degree of physical property under the actual use environment.
According to the present invention, there is provided a gel strength measuring method capable of highly reliable measurement of the gel strength in the horizontal direction of a superabsorbent resin.
According to this gel strength measuring method, the horizontal direction gel strength of the superabsorbent resin, which has conventionally been difficult to measure, can be effectively measured in relation to the degree of crosslinking of the superabsorbent resin. Therefore, using these gel strength measurement results, the actual physical properties of the superabsorbent resin can be better predicted, particularly the actual physical properties of the superabsorbent resin under actual use environment in the sanitary material such as diaper.
Therefore, the gel strength measuring method of the present invention can be greatly helpful in predicting and judging various properties such as liquid permeability of the superabsorbent resin and improving its physical properties.
Fig. 1 is a graph showing the results of measurement of gel strength for the superabsorbent resins of Production Examples 1 to 3 in Examples. Fig.
Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the scope of the present invention is not limited to the following examples.
Manufacturing example 1 to 3
100 g of acrylic acid, 0.5 g of polyethylene glycol diacrylate (Mw = 523) as a crosslinking agent, 83.3 g of 50% caustic soda (NaOH) and 89.8 g of water were mixed to obtain a monomer aqueous solution composition ratio of 45% .
Then, 810 g of the monomer aqueous solution was first added to 30 g of a 0.18% ascorbic acid solution and 30 g of a 1% sodium persulfate solution, followed by successive polymerization with 30.45 g of a 0.15% hydrogen peroxide solution, And the polymerization was carried out. At this time, the temperature of the polymerization reactor was kept at 80 ° C, the maximum temperature of polymerization was 110 ° C, and the polymerization time was 1 minute and 15 seconds. Thereafter, the kneading was continued and polymerization and kneading were carried out for 20 minutes. The size of the polymerizers produced was less than 0.2 cm. At this time, the water content of the finally formed hydrogel polymer was 51% by weight.
Then, the hydrogel polymer was dried for 30 minutes in a hot-air dryer at a temperature of 180 ° C, and the dried hydrogel polymer was pulverized with a pin mill. Then, a polymer having a particle diameter of less than about 150 탆 and a polymer having a particle diameter of about 150 탆 to 850 탆 were classified using a sieve.
Thereafter, a surface treatment solution containing 0.12 wt% (Production Example 1), 0.20 wt% (Preparation Example 2) and 0.33 wt% (Production Example 3) of 1,3-propanediol was sprayed onto the prepared base resin Surface cross-linking proceeded. Further, in the surface cross-linking step, the base resin was fed into one surface cross-linking reactor, and the surface cross-linking reaction was conducted at a temperature of about 180 캜 or more for about 40 minutes or more.
After the surface cross-linking step, a superabsorbent resin of Preparation Examples 1 to 3 was obtained, which was cross-linked with a particle diameter of about 150 to 850 탆 by using a sieve.
Example : Gel strength ( Come Strength )
For the superabsorbent resins of Examples 1 to 3, the horizontal direction gel strength (Gel Strength) was measured by the following method.
First, 1 g of a superabsorbent resin sample (30 to 50 Mesh) of Examples 1 to 3 was sieved and weighed. The weighed sample was sufficiently impregnated and swelled in 100 g of physiological saline for 1 hour. Thereafter, the unabsorbed solvent was removed with an aspirator for 4 minutes, and the solvent on the surface was evenly distributed on the filter paper and wiped off once.
2.5 g of the swollen superabsorbent resin sample is placed between a rheometer and two plates (25 mm in diameter, with a wall that prevents 2 mm of sample from escaping from the bottom), and the gap between the two plates is adjusted to 1 mm Respectively. (At this time, when the sample was hard and difficult to adjust at intervals of 1 mm, the gap between the plates was adjusted by pressing with a force of about 3 N so that the swollen superabsorbent resin sample contacted all the plate surfaces.
The superabsorbent resin sample between the plates was then stabilized for about 5 minutes.
Thereafter, the shear strain was increased at an oscillation frequency of 10 rad / s using the rheometer, and the shear strain was increased, and the shear modulus of the linear viscoelastic regime, which has a constant storage modulus and loss modulus, Strain was confirmed. In a generally swollen superabsorbent resin sample, a shear strain of 0.1% is in the linear viscoelastic state section.
The storage elastic modulus and the loss modulus of the superabsorbent resin swelled for 60 seconds at constant shear strain values of the linear viscoelastic state section were measured at a constant 10 rad / s oscillation frequency. The storage elastic modulus values obtained at this time were averaged to obtain the gel strength in the horizontal direction. For reference, the loss modulus is measured to be very small compared to the storage modulus.
The gel strength measurement results of Production Examples 1 to 3 measured by the above-described method are shown in Fig.
Referring to FIG. 1, measurement results of the gel strength in the horizontal direction in proportion to the content of the crosslinking agent are shown, which indicates that the gel strength measured by the method of the embodiment reflects the degree of crosslinking of the superabsorbent resin very well. Therefore, it is expected that the degree of physical properties of the superabsorbent resin can be very well predicted from the gel strength measurement results.
Claims (7)
Placing the swollen superabsorbent resin between plates of a rheometer having a predetermined gap;
Shear strain is increased by using a rheometer under vibration at a speed of 5 to 20 rad / s, and the shear strain is increased, and the shear of the section of the linear viscoelastic regime in which the storage modulus and the loss modulus are constant Confirming the deformation; And
Measuring the storage elastic modulus and the loss elastic modulus of the swollen superabsorbent resin under the identified shear deformation respectively and measuring an average value of the storage elastic modulus as the horizontal gel strength of the superabsorbent resin Method of measuring gel strength.
The storage elastic modulus and the loss elastic modulus of the swollen superabsorbent resin are measured for 60 seconds under a certain shear strain of the linear viscoelastic state section in a rheometer under vibration at a speed of 5 to 20 rad /
A method for measuring the gel strength of a superabsorbent resin, wherein the average value of the storage elastic modulus having a value larger than the loss elastic modulus is determined and measured as the gel strength in the horizontal direction of the superabsorbent resin.
Absorbing resin is placed between the plates of the rheometer and the space between the plates is adjusted so that the swollen superabsorbent resin is entirely packed in the space between the plates, Method of measuring strength.
And allowing the swollen superabsorbent resin located between the plates to stand for 1 to 5 minutes to stabilize the gel strength of the superabsorbent resin.
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| KR1020130147847 | 2013-11-29 | ||
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Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2017061705A1 (en) * | 2015-10-07 | 2017-04-13 | 주식회사 엘지화학 | Method for measuring fracture strength of superabsorbent polymer single particle |
| WO2018030709A1 (en) * | 2016-08-11 | 2018-02-15 | 한국기초과학지원연구원 | Method for pretreatment of sample using superabsorbent polymer and device therefor |
| WO2019039916A1 (en) * | 2017-08-25 | 2019-02-28 | 주식회사 엘지화학 | Sap evaluation device |
| KR20200086167A (en) * | 2019-01-08 | 2020-07-16 | 주식회사 엘지화학 | Evaluation method for property of super absorbent polymer |
| KR20200116770A (en) * | 2019-04-02 | 2020-10-13 | 주식회사 엘지화학 | Method for predicting property of super absorbent polymer |
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2014
- 2014-11-21 KR KR1020140163514A patent/KR20150062959A/en not_active Application Discontinuation
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2017061705A1 (en) * | 2015-10-07 | 2017-04-13 | 주식회사 엘지화학 | Method for measuring fracture strength of superabsorbent polymer single particle |
| US10634595B2 (en) | 2015-10-07 | 2020-04-28 | Lg Chem, Ltd. | Method of measuring fracture strength of single particles of superabsorbent polymer |
| WO2018030709A1 (en) * | 2016-08-11 | 2018-02-15 | 한국기초과학지원연구원 | Method for pretreatment of sample using superabsorbent polymer and device therefor |
| WO2019039916A1 (en) * | 2017-08-25 | 2019-02-28 | 주식회사 엘지화학 | Sap evaluation device |
| US11635421B2 (en) | 2017-08-25 | 2023-04-25 | Lg Chem, Ltd. | SAP evaluation apparatus |
| KR20200086167A (en) * | 2019-01-08 | 2020-07-16 | 주식회사 엘지화학 | Evaluation method for property of super absorbent polymer |
| KR20200116770A (en) * | 2019-04-02 | 2020-10-13 | 주식회사 엘지화학 | Method for predicting property of super absorbent polymer |
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