Superabsorbent fiber for a paper diaper and method for producing the same

Abstract

The application provides a kind of high water-absorbing fiber for paper diaper and its preparation method, which comprises the following steps: S1: polyvinyl alcohol, first unsaturated hydrophilic monomer, first crosslinking agent and persulfate are dispersed in water to obtain spinning solution;Wherein, the first unsaturated hydrophilic monomer includes unsaturated carboxylic acid monomer;S2: the spinning solution is treated by wet spinning process to obtain nascent fiber;S3: the nascent fiber is immersed in the modification liquid including second unsaturated hydrophilic monomer, second crosslinking agent and photoinitiator, and then treated by ultraviolet light to obtain composite fiber as high water-absorbing fiber;Wherein, the second unsaturated hydrophilic monomer includes unsaturated zwitterionic monomer.The high water-absorbing fiber obtained by the method can significantly improve the absorption and retention performance in salt solution and pressure condition, so that the fiber is not easy to collapse in the actual use environment of paper diaper, and can maintain a high load absorption capacity.

Description

Technical Field

[0001] This application relates to the field of absorbent fiber technology, specifically to a superabsorbent fiber for diapers and its preparation method. Background Technology

[0002] Disposable diapers are a typical type of disposable hygiene product. Their core function is to quickly absorb and store bodily fluids, keeping the user dry and comfortable during use. The absorbent core of common diapers is usually composed of a combination of superabsorbent polymer (SAP) and absorbent fibers. The absorbent fibers are mainly responsible for the rapid absorption and diversion of liquids, while also providing dispersion support for the SAP particles to prevent uneven absorption and clumping.

[0003] In existing technologies, absorbent fibers are mostly made of wood pulp fibers or modified hydrophilic fibers, and their absorbency can meet certain absorption needs in a free state (without external force). However, when diapers are subjected to the weight or positional pressure of an infant during actual use, the fiber absorbent structure is prone to collapse, causing liquid to be squeezed out, thus significantly reducing the pressure absorption ratio (loaded absorbency). In this case, even if the free absorbency ratio is high, it is difficult to guarantee the absorption retention capacity under actual wearing conditions, which can easily lead to leakage and backflow, affecting comfort and safety.

[0004] To address these issues, some technologies attempt to improve absorbency by introducing hydrophilic groups or grafting acrylate monomers onto the fiber surface, or by adding cross-linked networks to enhance swelling stability. However, while existing carboxylate-based absorbent fibers (such as acrylate-modified fibers) achieve high free absorption rates in deionized water, in simulated urine saline solutions, electrolytes shield the charge repulsion of carboxylate groups, leading to a decrease in osmotic pressure and a significant reduction in fiber swelling capacity. Under pressure, the absorbed liquid is easily squeezed out, resulting in a significant decrease in pressure-bearing absorption rate. Furthermore, most existing cross-linking modifications are uniformly distributed throughout the fiber, making them prone to collapse under external forces, leading to liquid release and backflow problems.

[0005] Therefore, how to improve the absorption and retention performance of fibers under salt solutions and pressure conditions remains a problem that needs to be solved by existing technologies. Summary of the Invention

[0006] This application provides a superabsorbent fiber for diapers and a method for preparing the same, aiming to improve the problem that the absorbency of existing absorbent fibers is significantly reduced under salt solutions and pressure conditions.

[0007] In a first aspect, this application provides a method for preparing superabsorbent fibers for diapers, comprising the following steps:

[0008] S1: Polyvinyl alcohol, a first unsaturated hydrophilic monomer, a first crosslinking agent, and persulfate are dispersed in water to obtain a spinning solution; wherein, the first unsaturated hydrophilic monomer includes unsaturated carboxylic acid monomers;

[0009] S2: The spinning solution is treated by wet spinning to desolvent polyvinyl alcohol to form a fiber skeleton, and the unsaturated hydrophilic monomers are cross-linked in the fiber skeleton under the action of cross-linking agent and initiator to obtain nascent fiber.

[0010] S3: The nascent fiber is immersed in a modified solution containing a second unsaturated hydrophilic monomer, a second crosslinking agent and a photoinitiator, and then treated with ultraviolet light to crosslink the second unsaturated hydrophilic monomer on the surface of the nascent fiber under the action of the second crosslinking agent and the photoinitiator, thereby obtaining a composite fiber as a super absorbent fiber; wherein, the second unsaturated hydrophilic monomer includes an unsaturated zwitterionic monomer.

[0011] According to this application, the superabsorbent fiber obtained by the method can significantly improve the absorption and retention performance under salt solution and pressure conditions, making the fiber less prone to collapse in the actual use environment of diapers and able to maintain a high load absorption capacity.

[0012] Specifically, in steps S1 and S2, polyvinyl alcohol forms a crystalline fiber skeleton through solvent extraction, providing the fiber with the necessary mechanical strength and formability; unsaturated carboxylic acid monomers undergo cross-linking reactions within the skeleton, constructing an inner network capable of rapidly absorbing moisture and providing a high free absorption rate. The presence of this inner network allows the fiber to expand rapidly upon contact with liquid and achieve a high liquid storage capacity.

[0013] In step S3, unsaturated zwitterionic monomers are introduced into the outer layer of the fiber, and a cross-linking reaction occurs under ultraviolet light initiation, forming a cross-linked network distributed on the outer layer of the fiber. The zwitterionic groups can maintain a stable hydration layer in a salt solution environment, and some monomers exhibit "anomalous expansion" characteristics. Therefore, even under conditions of external salt solution or pressure, the outer network can still maintain strong expansion capacity. Simultaneously, the outer cross-linked network structurally provides a "shell-like" support framework for the fiber, effectively preventing fiber collapse under external force and avoiding the extrusion of absorbed liquid.

[0014] The fiber is constructed by partitioning an inner layer of unsaturated carboxylic acid monomer crosslinking network and an outer layer of unsaturated zwitterionic monomer crosslinking network. The inner layer has a strong liquid absorption driving force, which can quickly absorb and diffuse the liquid into the fiber at the initial stage of liquid contact, providing a basis for large-capacity water absorption. The outer network provides additional wetting channels during the process of liquid diffusion inward, and at the same time maintains the overall morphological stability of the fiber under the action of salt solution and external force, so that the liquid absorbed by the inner layer is not easily squeezed out.

[0015] Therefore, the superabsorbent fiber prepared in this application can maintain a high load absorption rate under simulated urine saline solution and pressure conditions, thus exhibiting stronger liquid retention and leak-proof performance during diaper use.

[0016] In some embodiments, step S1 includes:

[0017] 100 parts of polyvinyl alcohol, 80-100 parts of the first unsaturated hydrophilic monomer, 0.5-2 parts of the first crosslinking agent and 2-4 parts of persulfate are dispersed in 800-1000 parts of water, and the pH is adjusted to 3.0-3.5 to obtain the spinning solution.

[0018] In some of the above embodiments, based on 100 parts of polyvinyl alcohol, the amount of the first unsaturated hydrophilic monomer is controlled at 80-100 parts, which can match the content of the cross-linking network inside the fiber with the polyvinyl alcohol skeleton. This ensures that there are enough hydrophilic groups in the network to obtain a high free absorption rate, while avoiding the reduction of spinnability of the spinning solution due to an excessively high monomer ratio. The amount of cross-linking agent is controlled at 0.5-2 parts, which can form an appropriate cross-linking density inside the fiber. The amount of persulfate is controlled at 2-4 parts, which is beneficial to the full polymerization of monomers inside the fiber during the subsequent spinning process. Through the setting of the above ratios and conditions, the bond between the polyvinyl alcohol skeleton and the internal cross-linking network is tighter, and the fiber is less prone to interfacial separation when it absorbs water and swells, thus better balancing the spinnability of the spinning solution and the liquid absorption performance of the fiber.

[0019] In some embodiments, in step S1, the first unsaturated hydrophilic monomer further includes an unsaturated sulfonic acid monomer, wherein the mass ratio of the unsaturated carboxylic acid monomer to the unsaturated sulfonic acid monomer is 1:0.4~0.6.

[0020] In some of the above embodiments, unsaturated sulfonic acid monomers can provide stable, strongly acidic ionic groups to the fibers after polymerization. These groups remain fully ionized under almost all salt solution conditions, forming a stable hydrated layer. Compared to systems containing only carboxylate groups, it can maintain higher osmotic pressure and water absorption capacity in salt solution environments, thus significantly improving the salt resistance of the fibers. Simultaneously, controlling the mass ratio of the unsaturated carboxylic acid monomers to the unsaturated sulfonic acid monomers at 1:0.4~0.6 allows the carboxylic acid groups to provide a high free absorption rate while the sulfonic acid groups can suppress the attenuation of absorption performance caused by the salt ion shielding effect. This ratio range achieves an optimal balance between free absorption performance and salt environment stability. Furthermore, under pressure conditions, because the sulfonic acid groups can form a stable and incompressible hydrated layer, while simultaneously enhancing the ionic strength maintenance of the fiber's internal network, the fibers can maintain their expanded structure under external forces, making them less prone to pore collapse and water extrusion.

[0021] Through the above design, the resulting fiber maintains a high free absorption rate in a deionized water environment, still achieves a high water absorption rate in a 0.9% sodium chloride solution, and exhibits better load absorption under pressure conditions.

[0022] In some embodiments, the conditions for the wet spinning process in step S2 include: extruding the spinning solution through a spinneret into a coagulation solution for spinning; wherein the coagulation solution contains 20% to 25% sodium sulfate, 3% to 5% sulfuric acid, and 0.1% to 0.3% sodium metabisulfite by mass.

[0023] In some of the above embodiments, the addition of sodium sulfate can rapidly desolvate and precipitate polyvinyl alcohol under high ionic strength conditions, forming a dense fiber skeleton, thereby ensuring rapid molding of the spinning solution in the coagulation bath; sulfuric acid can further reduce the pH difference between the spinning solution and the coagulation solution, keeping the system in an acidic environment, thereby delaying the premature decomposition of persulfate, reducing the generation of free radicals before spinning, and promoting the monomers to gradually enter the polymerization state after the fiber enters the coagulation bath, ensuring the uniform formation of the internal network; sodium metabisulfite, as a mild reducing agent, can form an initiation system together with persulfate in the spinning solution, enabling the fiber to quickly trigger the generation of free radicals after molding, accelerating the cross-linking polymerization process of monomers inside the fiber.

[0024] By setting the above coagulation liquid conditions, the polyvinyl alcohol skeleton and the internal monomer cross-linking network can be constructed simultaneously during the spinning process. The resulting fiber has both good formability and uniformity of the internal network, making the nascent fiber structure more stable. It is not easy for pores to collapse during subsequent water absorption and expansion, thus exhibiting high absorption and retention performance under both salt solution and pressure conditions.

[0025] In some embodiments, the spinneret has an aperture of 80-120 μm, the extrusion speed is 2-4 m / s, the coagulation liquid temperature is 15-25°C, and the extruded fiber stays in the coagulation liquid for 10-20 s.

[0026] In some of the above embodiments, the spinneret orifice diameter is controlled at 80~120μm, which ensures that the fiber diameter is moderate. This ensures that the fiber has sufficient pore structure to facilitate water absorption and expansion, while reducing fiber breakage and forming difficulties caused by excessively fine fibers. The extrusion speed is controlled at 2~4m / s, which helps the spinning solution maintain a stable flow state when entering the coagulation solution, and at the same time promotes full contact between the spinning solution and the coagulation solution, which is conducive to the rapid desolvation of the polyvinyl alcohol skeleton. The coagulation solution temperature is maintained at 15~25℃, which can ensure rapid solidification of the spinning solution while avoiding excessively low temperature which would lead to excessively fast desolvation rate and uneven internal network, or excessively high temperature which would cause skeleton collapse. The residence time of the extruded fiber in the coagulation solution is 10~20s, which allows the polyvinyl alcohol segments to fully crystallize and the internal hydrophilic monomers to complete the initial cross-linking polymerization, thereby obtaining nascent fibers with stable structure and uniform network distribution.

[0027] Through the optimization of the above conditions, the resulting fibers have both good formability and uniform internal structure, thus exhibiting higher free absorption ratio and better pressure absorption performance.

[0028] In some embodiments, in step S3, the modified solution contains 8%–12% by mass of the second unsaturated hydrophilic monomer, 0.1%–0.3% by mass of the second crosslinking agent, and 0.05%–0.15% by mass of the photoinitiator; the pH of the modified solution is 6.5–7.5; the conditions for the post-impregnation UV irradiation treatment include: immersing the nascent fibers in the modified solution for 15–30 seconds, and then using 30–60 mW / cm² UV light. 2 Expose to ultraviolet light for 10-20 seconds.

[0029] In some of the above embodiments, the concentration of the second unsaturated hydrophilic monomer is controlled at 8%~12%, which can introduce uniform and sufficient hydrophilic groups into the outer layer of the fiber, thereby giving the fiber stronger liquid absorption and retention capabilities; the content of the second crosslinking agent is in the range of 0.1%~0.3%, which helps to form a moderate three-dimensional crosslinking structure in the outer layer, so that the outer network has both stability and good expansion capacity. The concentration of the photoinitiator is 0.05%~0.15%, which can efficiently generate free radicals under ultraviolet light, ensuring that the outer monomer is rapidly cured and uniformly crosslinked; the pH of the modified liquid is adjusted to 6.5~7.5, so that the zwitterionic monomer is in a better reaction state, which is conducive to the formation of a continuous and dense hydrophilic network on the fiber surface; the impregnation time of 15~30s can ensure that the monomer is fully penetrated on the fiber surface, and the subsequent 30~60mW / cm 2 Exposure to ultraviolet light for 10-20 seconds can achieve rapid curing, forming a dense and stable cross-linked structure on the outer layer.

[0030] By setting the above conditions, the resulting outer cross-linked network is uniform and of moderate thickness, which can maintain a strong hydration effect in a salt solution environment and provide a support similar to an "outer shell" under pressure conditions, thereby effectively preventing the fiber from collapsing after expansion and enabling the resulting fiber to maintain a higher absorption rate under load.

[0031] Furthermore, the outer and inner cross-linking networks work synergistically. Specifically, the unsaturated carboxylic acid monomer network of the inner layer imparts a high free absorption capacity to the fiber, but it is susceptible to collapse due to ion shielding under salt solutions and pressure conditions. The outer cross-linking network, constructed from zwitterionic groups, maintains a stable hydration layer in salt environments and provides a "support shell" on the fiber's outer surface. Therefore, when the fiber expands under external load, the inner layer ensures high liquid absorption, while the outer layer provides morphological stability. Together, they enable the fiber to maintain a higher load absorption capacity under salt solutions and pressure conditions, effectively reducing the risk of backflow.

[0032] In some embodiments, in step S3, the second crosslinking agent comprises polyethylene glycol diacrylate with a weight-average molecular weight of 300-600.

[0033] In some of the above embodiments, the inventors found that when polyethylene glycol diacrylate with a weight-average molecular weight of 300-600 is selected as the second crosslinking agent in step S3, the resulting superabsorbent fiber exhibits higher load absorption under salt environment and load conditions. This may be because the polyethylene glycol diacrylate molecular chain segments are flexible and have active double bonds at both ends, allowing for rapid polymerization under ultraviolet light irradiation. The resulting network combines elasticity and stability. When its weight-average molecular weight is in the range of 300-600, the chain segment length is moderate, ensuring both good expansion capacity of the outer network and sufficient structural strength. Compared to commonly used small-molecule crosslinking agents (such as methylenebisacrylamide), the crosslinked network formed by polyethylene glycol diacrylate in the outer layer has better flexibility and is less prone to brittleness during pressure testing. Compared to polyacrylic acid multifunctional crosslinking agents with larger molecular weights, it has better solubility and dispersibility, enabling uniform distribution in the modified liquid and the formation of a stable crosslinked network on the fiber surface.

[0034] Therefore, when polyethylene glycol diacrylate with a weight-average molecular weight of 300-600 is used as the second crosslinking agent, the resulting outer network exhibits strong reversible stretchability during water absorption and swelling. It can maintain a stable hydrated layer in salt solutions and provide flexible support under pressure conditions, thereby effectively preventing the expanded fibers from collapsing. The inner unsaturated carboxylic acid monomer network provides a high free absorption rate, while the outer layer ensures the morphological stability of the fiber under salt environment and load conditions. The combination of the two enables the superabsorbent fiber to have a higher load absorption capacity under salt environment and load conditions.

[0035] In some embodiments, the method further includes: S4: mixing the composite fiber and 1~3wt% sodium carbonate aqueous solution at a solid-liquid mass ratio of 1:15~20, neutralizing for 1~3 minutes to obtain neutralized composite fiber as super absorbent fiber.

[0036] In some of the above embodiments, after the composite fiber undergoes cross-linking polymerization, some carboxylic acid groups in its internal and outer network are in a free acid state. By placing the composite fiber in a low-concentration sodium carbonate aqueous solution for neutralization, some carboxylic acid groups are converted into sodium carboxylate groups, thereby increasing hydrophilicity and ion concentration, and enabling the fiber to generate a higher osmotic pressure driving force during liquid absorption. The concentration of sodium carbonate solution is controlled at 1~3wt%, which can achieve relatively sufficient neutralization in a short time, while avoiding damage to the fiber skeleton caused by excessive alkalinity. The solid-liquid mass ratio is controlled at 1:15~20, which is conducive to sufficient contact between the neutralizing liquid and the fiber, ensuring uniform reaction. The neutralization time is 1~3 min, which can effectively complete the conversion of some carboxylic acid groups and obtain neutralized fibers with stable performance.

[0037] Through the above neutralization treatment, the degree of ionization of the internal network of the fiber is significantly improved, the water absorption ratio of the fiber in salt solution is enhanced, and it exhibits a higher load absorption capacity under pressure conditions.

[0038] In some embodiments, the polyvinyl alcohol has a weight-average molecular weight of 70,000 to 100,000 and a degree of hydrolysis of 95% or higher. Based on the above embodiments, the polyvinyl alcohol has a relatively long chain length and a high degree of hydrolysis, which enables the formation of a more crystalline skeletal structure during wet spinning, thereby giving the fiber better formability and mechanical strength. The high degree of hydrolysis ensures uniform distribution of hydroxyl groups and enhances the hydrogen bonding between hydroxyl groups and hydrophilic monomers, making the inner cross-linked network more tightly bonded to the skeleton, which is beneficial for maintaining structural stability when absorbing water and swelling.

[0039] In some embodiments, the first crosslinking agent comprises methylenebisacrylamide. Based on the above embodiments, methylenebisacrylamide has two highly reactive double bonds, which can initiate a relatively uniform three-dimensional crosslinking reaction within the fiber, forming a stable inner network structure.

[0040] In some embodiments, the persulfate includes at least one of sodium persulfate, potassium persulfate, and ammonium persulfate. Based on the above embodiments, this type of persulfate is stable in an acidic environment, but can efficiently decompose in the coagulation liquid to generate free radicals, thereby ensuring that the polymerization reaction occurs at the appropriate time, and that fiber forming and cross-linking network construction proceed simultaneously, resulting in a uniform and stable internal structure of the obtained fiber.

[0041] In some embodiments, the unsaturated carboxylic acid monomer includes at least one of acrylic acid and methacrylic acid. Based on the above embodiments, acrylic acid or methacrylic acid can provide a large number of carboxyl sites for the inner network, thereby increasing the free uptake rate and osmotic pressure driving force.

[0042] In some embodiments, the unsaturated sulfonic acid monomer includes 2-acrylamido-2-methylpropanesulfonic acid. Based on the above embodiments, the sulfonic acid groups in 2-acrylamido-2-methylpropanesulfonic acid can remain fully ionized in salt solutions, providing a stable hydration layer, thereby improving the absorption performance of the fiber under salt solution conditions and reducing the decrease in absorption rate caused by the salt effect.

[0043] In some embodiments, the unsaturated zwitterionic monomer includes sulfobetaine methacrylate. Based on the above embodiments, sulfobetaine methacrylate molecules carry both positive and negative charges, enabling them to maintain an extended chain segment state in salt solutions. This results in the outer network exhibiting anomalous expansion characteristics, giving the fiber good structural stability and liquid retention under both salt environments and pressure conditions.

[0044] In some embodiments, the photoinitiator includes at least one of Irgacure 2959 and Irgacure 184. Based on the above embodiments, these photoinitiators can rapidly and efficiently generate free radicals under ultraviolet light irradiation, triggering uniform polymerization of the outer layer monomers, with fast curing rate, low residual amount, and the ability to obtain a structurally uniform and highly stable outer layer crosslinked network in a short time.

[0045] Secondly, this application provides a superabsorbent fiber for diapers, prepared according to the method described in any embodiment of the first aspect.

[0046] According to this application, the superabsorbent fiber contains a cross-linked network composed of carboxylic acid groups / sulfonic acid groups inside the fiber, and further constructs an outer network formed by cross-linking of zwitterionic monomers on the fiber surface. Through the synergistic effect of the inner and outer double-layer structure, the fiber not only has a high water absorption ratio under free absorption conditions, but also maintains a stable expansion state under salt solution environment and pressure conditions, significantly improving the load absorption capacity and reducing the risk of backflow, thereby meeting the comprehensive requirements of diapers for high-efficiency absorption and liquid retention performance.

[0047] Compared with the prior art, the beneficial effects of this application are at least as follows:

[0048] 1. By introducing a carboxylic acid / sulfonic acid group crosslinking network inside the fiber, the fiber has abundant hydrophilic sites and stable ion driving force, enabling it to quickly absorb water and maintain a high liquid absorption rate under free absorption conditions.

[0049] 2. The sulfonic acid groups remain completely ionized in the salt solution, and the outer zwitterionic groups exhibit an anomalous expansion effect, enabling the fiber to maintain the stability of the hydration layer and network even in a high-salt environment.

[0050] 3. The outer cross-linked network forms a flexible "support shell" that can disperse external forces and inhibit pore shrinkage after expansion. Together with the inner network, it enables the fiber to maintain a high load absorption capacity under pressure conditions and significantly reduces liquid backflow. Detailed Implementation

[0051] The various embodiments or implementation schemes in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments.

[0052] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with an embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0053] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0054] In this specification, unless otherwise specified, "parts" refers to "parts by weight".

[0055] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0056] Polyvinyl alcohol has a weight-average molecular weight of approximately 85,000 and a degree of hydrolysis of over 96%.

[0057] methyl methacrylate sulfobetaine, CAS number 3637-26-1;

[0058] Coagulation solution: 22 wt% sodium sulfate, 4 wt% sulfuric acid, and 0.2 wt% sodium metabisulfite, prepared in deionized water.

[0059] Example 1

[0060] Preparation of superabsorbent fibers for diapers:

[0061] S1: Add 100 parts of polyvinyl alcohol to 850 parts of deionized water and stir to dissolve in a 95°C water bath to obtain a clear PVA solution. Cool the solution to 35°C and add 60 parts of acrylic acid, 30 parts of 2-acrylamide-2-methylpropanesulfonic acid, 1 part of methylenebisacrylamide and 3 parts of potassium persulfate in sequence. Adjust the pH of the solution to 3.3 and stir evenly to obtain the spinning solution.

[0062] S2: The above spinning solution is extruded through a spinneret with a pore size of 100μm and the spinning speed is controlled at 3m / s. It is then sprayed into a coagulation solution at 20℃. The fiber stays in the coagulation solution for 15s to complete desolvation and preliminary cross-linking, forming nascent fiber.

[0063] S3: Immerse the nascent fibers in the modifying solution for 20 seconds, then remove the fibers and place them under a UV curing device (UV intensity 40 mW / cm²). 2 Irradiation with a wavelength of 365nm for 15 seconds causes the outer monomer to cross-link and solidify, resulting in composite fibers.

[0064] The modified solution contains 10 wt% methacrylic acid sulfobetaine, 0.2 wt% polyethylene glycol diacrylate (weight average molecular weight 400), and 0.1 wt% Irgacure 2959, prepared in deionized water and adjusted to pH 7.0.

[0065] S4: Mix the composite fiber with a 2wt% sodium carbonate aqueous solution at a solid-liquid mass ratio of 1:18, stir for 2 minutes, remove the fiber, rinse it three times with deionized water, and vacuum dry it for 24 hours to obtain the final superabsorbent fiber.

[0066] Example 2

[0067] Preparation of superabsorbent fibers for diapers:

[0068] It is largely the same as Example 1, except that step S1 is different, which is as follows:

[0069] S1: Add 100 parts of polyvinyl alcohol to 850 parts of deionized water and stir to dissolve in a 95°C water bath to obtain a clear PVA solution. Cool down to 35°C and add 90 parts of acrylic acid, 1 part of methylenebisacrylamide and 3 parts of potassium persulfate in sequence. Adjust the pH of the solution to 3.3 and stir evenly to obtain the spinning solution.

[0070] Example 3

[0071] Preparation of superabsorbent fibers for diapers:

[0072] It is largely the same as Example 1, except that step S1 is different, which is as follows:

[0073] S1: Add 100 parts of polyvinyl alcohol to 850 parts of deionized water and stir to dissolve in a 95°C water bath to obtain a clear PVA solution. Cool the solution to 35°C and add 45 parts of acrylic acid, 45 parts of 2-acrylamide-2-methylpropanesulfonic acid, 1 part of methylenebisacrylamide and 3 parts of potassium persulfate in sequence. Adjust the pH of the solution to 3.3 and stir evenly to obtain the spinning solution.

[0074] Example 4

[0075] Preparation of superabsorbent fibers for diapers:

[0076] The process is largely the same as in Example 1, except that the modifying liquid in step S3 is different. Specifically:

[0077] The modified solution contained 10 wt% methacrylic acid sulfobetaine, 0.2 wt% methylenebisacrylamide, and 0.1 wt% Irgacure 2959, prepared in deionized water and adjusted to pH 7.0.

[0078] Example 5

[0079] Preparation of superabsorbent fibers for diapers:

[0080] The process is largely the same as in Example 1, except that the modifying liquid in step S3 is different. Specifically:

[0081] The modified solution contained 10 wt% methacrylate sulfobetaine, 0.2 wt% ethylene glycol diacrylate, and 0.1 wt% Irgacure 2959, prepared in deionized water and adjusted to pH 7.0.

[0082] Example 6

[0083] Preparation of superabsorbent fibers for diapers:

[0084] The process is largely the same as in Example 1, except that the modifying liquid in step S3 is different. Specifically:

[0085] The modified solution contains 10 wt% methacrylate sulfobetaine, 0.2 wt% polyethylene glycol diacrylate (weight average molecular weight 1000), and 0.1 wt% Irgacure 2959, prepared in deionized water and adjusted to pH 7.0.

[0086] Comparative Example 1

[0087] Preparation of superabsorbent fibers for diapers:

[0088] S1: Add 100 parts of polyvinyl alcohol to 850 parts of deionized water and stir to dissolve in a 95°C water bath to obtain a clear PVA solution. Cool the solution to 35°C and add 60 parts of acrylic acid, 30 parts of 2-acrylamide-2-methylpropanesulfonic acid, 1 part of methylenebisacrylamide and 3 parts of potassium persulfate in sequence. Adjust the pH of the solution to 3.3 and stir evenly to obtain the spinning solution.

[0089] S2: The above spinning solution is extruded through a spinneret with a pore size of 100μm and the spinning speed is controlled at 3m / s. It is then sprayed into a coagulation solution at 20℃. The fiber stays in the coagulation solution for 15s to complete desolvation and preliminary cross-linking, forming nascent fiber.

[0090] S3: Immerse the nascent fibers in the modifying solution for 20 seconds, then remove the fibers and place them under a UV curing device (UV intensity 40 mW / cm²). 2 Irradiation with a wavelength of 365nm for 15 seconds causes the outer monomer to cross-link and solidify, resulting in composite fibers.

[0091] The modified solution contains 6.7 wt% acrylic acid, 3.3 wt% 2-acrylamide-2-methylpropanesulfonic acid, 0.2 wt% polyethylene glycol diacrylate (weight average molecular weight 400), and 0.1 wt% Irgacure 2959, prepared in deionized water and adjusted to pH 7.0.

[0092] S4: Mix the composite fiber with a 2wt% sodium carbonate aqueous solution at a solid-liquid mass ratio of 1:18, stir for 2 minutes, remove the fiber, rinse it three times with deionized water, and vacuum dry it for 24 hours to obtain the final superabsorbent fiber.

[0093] Comparative Example 2

[0094] Preparation of superabsorbent fibers for diapers:

[0095] S1: Add 100 parts of polyvinyl alcohol to 850 parts of deionized water and stir to dissolve in a 95°C water bath to obtain a clear PVA solution. Cool the solution to 35°C and add 54 parts of acrylic acid, 27 parts of 2-acrylamide-2-methylpropanesulfonic acid, 9 parts of methacrylic acid sulfobetaine, 1 part of methylenebisacrylamide and 3 parts of potassium persulfate in sequence. Adjust the pH of the solution to 3.3 and stir evenly to obtain the spinning solution.

[0096] S2: The above spinning solution is extruded through a spinneret with a pore size of 100μm and the spinning speed is controlled at 3m / s. It is then sprayed into a coagulation solution at 20℃. The fiber stays in the coagulation solution for 15s to complete desolvation and preliminary cross-linking, forming nascent fiber.

[0097] S3: Immerse the nascent fibers in the modifying solution for 20 seconds, then remove the fibers and place them under a UV curing device (UV intensity 40 mW / cm²). 2 Irradiation with a wavelength of 365nm for 15 seconds causes the outer monomer to cross-link and solidify, resulting in composite fibers.

[0098] The modified solution contains 6 wt% acrylic acid, 3 wt% 2-acrylamide-2-methylpropanesulfonic acid, 1 wt% methacrylic acid sulfobetaine, 0.2 wt% polyethylene glycol diacrylate (weight average molecular weight 400), and 0.1 wt% Irgacure 2959, prepared in deionized water and adjusted to pH 7.0.

[0099] S4: Mix the composite fiber with a 2wt% sodium carbonate aqueous solution at a solid-liquid mass ratio of 1:18, stir for 2 minutes, remove the fiber, rinse it three times with deionized water, and vacuum dry it for 24 hours to obtain the final superabsorbent fiber.

[0100] Test section

[0101] Salt solution absorption ratio (FAR) SA test:

[0102] Take 0.200 ± 0.001 g of dried fiber and put it into a mesh bag; record the mass m of the empty bag. bag Immerse the sample bag in a 0.9wt% NaCl aqueous solution and let it stand for 30 min; gently lift the bag three times during the process to release air; remove the sample bag and suspend it vertically on a drip rack for 10 s to remove surface water; quickly weigh to obtain m. w .

[0103] Calculate FAR SA =(m w -m bag -m) / m, the unit is g / g.

[0104] AUL pressure absorption ratio test:

[0105] Apparatus: AUL clamp (bottom 100-mesh sieve cup), total weight of weights generates 2.07 kPa pressure. Constant liquid level supply system (liquid level ≥ 5 mm above the sieve bottom).

[0106] Test solution: 0.9wt% NaCl aqueous solution, 23±2℃.

[0107] Evenly spread dry fiber m=0.900±0.001g in the sieve cup, and place weights on it to form a pressure of 2.07kPa;

[0108] Turn on the liquid supply and time for 60 minutes; stop the liquid supply, remove the clamp while maintaining the load and weigh it to obtain m (subtract the empty weight of the clamp m1).

[0109] Calculate AUL = (m w -m1-m) / m, the unit is g / g.

[0110] The test results are shown in Table 1.

[0111] Table 1

[0112]

[0113] According to Table 1, the free absorption ratio (FAR) of each embodiment relative to Comparative Example 1 and Comparative Example 2 for the salt solution is... SA Both the absorbency and pressure uptake ratio (AUL) are higher, indicating that the superabsorbent fiber provided in this application has a higher absorption capacity in a salt solution environment and can still maintain a high liquid storage capacity under pressure. The beneficial effect of this solution is that by constructing a partitioned cross-linked network inside and outside the fiber, the absorption retention is significantly improved. The possible reason is that in Comparative Example 1, the outer layer lacks a zwitterionic monomer cross-linked network, and the fiber is prone to osmotic pressure shielding effect in salt solution, resulting in easy collapse and water loss under pressure; in Comparative Example 2, the copolymerization of inner and outer monomers does not form a clear layer, the fiber has insufficient structural support when expanding, and is prone to water loss under pressure, resulting in a significant decrease in the pressure uptake ratio.

[0114] As demonstrated in Examples 1-3, adjusting the ratio of inner-layer acrylic acid to 2-acrylamide-2-methylpropanesulfonic acid significantly affects salt solution absorption and pressure absorption. When only acrylic acid is used (Example 2), the fiber's FAR... SA The lowest AUL indicates that the expansion of a single carboxylate group is limited in a salt environment, resulting in poor salt resistance; when the ratio of acrylic acid to 2-acrylamide-2-methylpropanesulfonic acid is 1:0.5 (Example 1), the fiber's FAR SA Both FAR and AUL reached their highest values, indicating that the moderate introduction of 2-acrylamido-2-methylpropanesulfonic acid can improve water absorption capacity under salt conditions while maintaining high pressure stability; when the proportion of 2-acrylamido-2-methylpropanesulfonic acid continued to increase (Example 3), although FAR SA It remains at a high level, but its pressure-bearing capacity has slightly decreased due to the network's excessive hydrophilicity.

[0115] As demonstrated in Examples 1, 4-6, the type and molecular weight of the outer crosslinking agent also affect performance. In Example 4, when methylenebisacrylamide was used as the outer crosslinking agent, the outer network was relatively rigid, resulting in decreased pressure absorption capacity. In Example 5, when ethylene glycol diacrylate was used, the pressure-bearing performance was improved compared to MBAA, but still worse than in Example 1. In Example 6, when PEGDA (approximately 1000), with a higher weight-average molecular weight, was used, the outer network may have become too porous, reducing its supporting effect and resulting in decreased pressure-bearing performance compared to Example 1. In contrast, Example 1, using ethylene glycol diacrylate with a suitable molecular weight, produced an outer network that was both flexible and provided effective support, exhibiting the best FAR (Flatness Absorption Rate). SA With AUL performance.

[0116] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for preparing superabsorbent fibers for diapers, characterized in that, Includes the following steps: S1: Polyvinyl alcohol, a first unsaturated hydrophilic monomer, a first crosslinking agent, and persulfate are dispersed in water to obtain a spinning solution; wherein, the first unsaturated hydrophilic monomer includes unsaturated carboxylic acid monomers and unsaturated sulfonic acid monomers; S2: The spinning solution is treated by wet spinning to desolvent polyvinyl alcohol to form a fiber skeleton, and the unsaturated hydrophilic monomers are cross-linked in the fiber skeleton under the action of cross-linking agent and initiator to obtain nascent fiber. S3: The nascent fiber is immersed in a modified solution containing a second unsaturated hydrophilic monomer, a second crosslinking agent, and a photoinitiator, and then treated with ultraviolet light to crosslink the second unsaturated hydrophilic monomer on the surface of the nascent fiber under the action of the second crosslinking agent and the photoinitiator, thereby obtaining a composite fiber; wherein, the second unsaturated hydrophilic monomer includes an unsaturated zwitterionic monomer, the unsaturated zwitterionic monomer includes methacrylate sulfobetaine, and the second crosslinking agent includes polyethylene glycol diacrylate with a weight average molecular weight of 300-600; S4: Mix the composite fiber with a 1-3 wt% sodium carbonate aqueous solution at a solid-liquid mass ratio of 1:15-20, and neutralize for 1-3 minutes to obtain the neutralized composite fiber, which is used as a super absorbent fiber.

2. The method according to claim 1, characterized in that, Step S1 includes: 100 parts of polyvinyl alcohol, 80-100 parts of the first unsaturated hydrophilic monomer, 0.5-2 parts of the first crosslinking agent and 2-4 parts of persulfate are dispersed in 800-1000 parts of water, and the pH is adjusted to 3.0-3.5 to obtain the spinning solution.

3. The method according to claim 1, characterized in that, In step S1 The mass ratio of the unsaturated carboxylic acid monomer to the unsaturated sulfonic acid monomer is 1:0.4~0.

6.

4. The method according to claim 1, characterized in that, In step S2, the conditions for the wet spinning process include: extruding the spinning solution through a spinneret into a coagulation solution for spinning; wherein the coagulation solution contains 20% to 25% sodium sulfate, 3% to 5% sulfuric acid, and 0.1% to 0.3% sodium metabisulfite by mass.

5. The method according to claim 4, characterized in that, The spinneret has an aperture of 80~120μm, an extrusion speed of 2~4m / s, a coagulation liquid temperature of 15~25℃, and an extruded fiber residence time in the coagulation liquid of 10~20s.

6. The method according to claim 1, characterized in that, In step S3, the modified liquid contains 8% to 12% by mass of the second unsaturated hydrophilic monomer, 0.1% to 0.3% by mass of the second crosslinking agent, and 0.05% to 0.15% by mass of the photoinitiator. The modified liquid has a pH of 6.5 to 7.

5. The conditions for the post-impregnation UV treatment include: impregnating the nascent fibers in the modified solution for 15-30 seconds, and then applying 30-60 mW / cm² UV light. 2 Expose to ultraviolet light for 10-20 seconds.

7. The method according to claim 3, characterized in that, The method satisfies at least one of the following conditions: 1) The polyvinyl alcohol has a weight-average molecular weight of 70,000 to 100,000 and a degree of hydrolysis of 95% or more; 2) The first crosslinking agent includes methylenebisacrylamide; 3) The persulfate includes at least one of sodium persulfate, potassium persulfate, and ammonium persulfate; 4) The unsaturated carboxylic acid monomers include at least one of acrylic acid and methacrylic acid; 5) The unsaturated sulfonic acid monomers include 2-acrylamido-2-methylpropanesulfonic acid; 6) The photoinitiator includes at least one of Irgacure 2959 and Irgacure 184.

8. A superabsorbent fiber for use in diapers, characterized in that, Prepared by the method according to any one of claims 1 to 7.

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