Highly efficient and stable heat pack based on modification of MOFs and preparation method thereof

Abstract

This application discloses a highly efficient and stable hand warmer based on MOFs modification and its preparation method, belonging to the field of hand warmers. The hand warmer of this application comprises the following raw materials in the indicated mass percentages: 40-60% reduced iron powder, 5-10% MOFs material, 3-8% multifunctional composite stabilizer, 1-3% polyvinylpyrrolidone, 2-5% electrolyte, 15-20% heat-insulating agent, 0.1-1% water-retaining agent, and the remainder being deionized water. The preparation method includes raw material pretreatment and a stepwise mixing process. This application innovatively designs a synergistic system of "MOFs-multifunctional composite stabilizer-polyvinylpyrrolidone," specifically addressing the stability and compatibility issues of MOFs in formulations, and fully releasing the performance advantages of MOFs.

Description

Technical Field

[0001] This application relates to the field of hand warmer technology, specifically to a highly efficient and stable hand warmer based on metal-organic frameworks (MOFs) modification and its preparation method. Background Technology

[0002] Hand warmers, a commonly used instant heating product, utilize the exothermic oxidation reaction of iron (4Fe + 3O₂ + 6H₂O = 4Fe(OH)₃ + Q) as their core heating mechanism. Traditional hand warmer formulas mainly consist of iron powder, activated carbon, vermiculite, salts, and water. Activated carbon adsorbs oxygen and moisture, vermiculite provides insulation, and salts act as electrolytes to accelerate the oxidation reaction. However, traditional formulas have significant drawbacks: unstable heating efficiency, prone to localized overheating or insufficient heating time; slow start-up heating in low-temperature and low-humidity environments; and the formula is susceptible to moisture absorption and deterioration during long-term storage, affecting product reliability.

[0003] Metal-organic frameworks (MOFs), as a novel type of porous material with ultra-high specific surface area and controllable pore structure, are being explored for application in hand warmer formulations. The aim is to leverage their ability to precisely adsorb and control the release of oxygen and water vapor through their pores, thereby optimizing the oxidation-exothermic process and improving the uniformity and duration of heating. Simultaneously, the metal nodes of some MOFs may act as catalysts to accelerate iron oxidation reactions, improving low-temperature start-up performance. However, modifying hand warmer formulations with MOFs still faces key technical challenges: First, MOFs are prone to structural collapse in humid environments, leading to a decline in adsorption and catalytic performance and affecting the long-term stability of the formulation; second, MOFs have poor compatibility with traditional formulation components (such as iron powder and salts), easily resulting in agglomeration and reducing the consistency of heating efficiency; and third, the performance of the formulation fluctuates significantly during storage, transportation, and use, making it difficult to guarantee reliability.

[0004] Therefore, there is an urgent need to develop a MOF-modified hand warmer technology that can solve the aforementioned stability and reliability problems. Summary of the Invention

[0005] To address the aforementioned problems in the existing technology, this application provides a MOF-modified high-efficiency and stable hand warmer and its preparation method. By introducing a multifunctional composite stabilizer and polyvinylpyrrolidone, the problems of formulation storage stability, reaction stability, and performance consistency are solved simultaneously.

[0006] To solve the above problems, the technical solution adopted in this application is as follows:

[0007] The hand warmer contains the following raw materials in the following weight percentages: reduced iron powder 40-60%, MOF material 5-10%, multifunctional composite stabilizer 3-8%, polyvinylpyrrolidone 1-3%, electrolyte 2-5%, heat preservation agent 15-20%, water retention agent (water-absorbing resin) 0.1-1%, and the remaining components are deionized water.

[0008] Preferably, the MOF material is MIL-101(Fe) or ZIF-8.

[0009] Preferably, the multifunctional composite stabilizer is a hydroxylated graphene / chitosan composite microsphere.

[0010] Preferably, the polyvinylpyrrolidone is PVP-K30.

[0011] Preferably, the electrolyte is a mixture of calcium chloride and sodium chloride.

[0012] Preferably, the heat-insulating agent is vermiculite.

[0013] Preferably, the deionized water has a mass percentage of 15-25%.

[0014] The aforementioned method for preparing hand warmers involves mixing MOF materials and hydroxylated graphene / chitosan composite microspheres evenly, then adding other raw materials, mixing evenly, packing into a packaging bag and sealing it, wherein one side of the packaging bag is a breathable layer and the other side is either a breathable layer or an impermeable layer.

[0015] Preferably, the breathable layer is a breathable membrane or a composite breathable membrane nonwoven fabric, and the impermeable layer is an impermeable membrane or an impermeable composite membrane nonwoven fabric.

[0016] Compared to existing technologies, the core innovation of this application lies in using MOFs materials as the core functional component of the hand warmer formula, breaking through the inherent mode of "activated carbon adsorption + salt catalysis" in traditional formulas. It utilizes the ultra-high specific surface area and controllable pore structure of MOFs to regulate the release and diffusion of oxygen and moisture, and leverages their metal nodes to achieve highly efficient catalysis, fundamentally solving the performance pain points of traditional hand warmers. Simultaneously, it innovatively designs a "MOFs-multifunctional composite stabilizer-polyvinylpyrrolidone" synergistic system, specifically addressing the stability and compatibility issues of MOFs in the formula, fully releasing the performance advantages of MOFs. Specifically: (1) The hand warmer of this application has high reaction stability: the porous structure of MOFs can regulate the diffusion behavior of oxygen and moisture in the system, the graphene component of the multifunctional composite stabilizer conducts heat uniformly, and polyvinylpyrrolidone optimizes the dispersion of the components. The three work together to avoid local overheating, so that the heating temperature is stable at 45-55℃ with a fluctuation range of ≤2℃.

[0017] (2) The hand warmer of this application has high reliability: through raw material pretreatment, step-by-step mixing process, and the dispersion effect of polyvinylpyrrolidone, the components are ensured to be evenly dispersed, avoiding the difference in heating caused by uneven moisture distribution; the performance consistency error is ≤3%.

[0018] (3) The hand warmer of this application has strong environmental adaptability: the hydrophilicity of chitosan in the multifunctional composite stabilizer and the moisture regulation function of polyvinylpyrrolidone work together, combined with the catalytic effect of MOFs and electrolytes, so that the product can start heating time ≤5min in a low temperature flexible environment of 0℃ and 30% relative humidity, which is far better than the 20min of traditional products.

[0019] (4) All raw materials of the hand warmer in this application are industrially available products. The addition of polyvinylpyrrolidone does not require additional complex processes. The step-by-step mixing process can achieve large-scale production, which has both technical advantages and market application prospects. Detailed Implementation

[0020] The core technical solution of this application is: designing a five-element core formulation system of "iron powder-MOFs-multifunctional composite stabilizer-polyvinylpyrrolidone-auxiliary components", wherein the multifunctional composite stabilizer is a specially prepared hydroxylated graphene / chitosan composite microsphere, and polyvinylpyrrolidone (PVP-K30) is an innovative functional component. The two work synergistically to improve the stability of the formulation and optimize the heating performance. The specific formulation composition is as follows: The hand warmer of this application comprises the following raw materials in the following weight percentages: 40-60% reduced iron powder, 5-10% MOF material, 3-8% multifunctional composite stabilizer, 1-3% polyvinylpyrrolidone, 2-5% electrolyte, 15-20% heat preservation agent, 0.1-1% water retention agent, and the remaining component is water.

[0021] Among them, reduced iron powder is the core heating material, providing an iron source for oxidation and exothermic reactions.

[0022] MOF materials, as the core inventive component of this application, are selected from MIL-101 (Fe) or ZIF-8, and have the following functions: 1. Adsorption-controlled release function: Utilizing their ultra-high specific surface area and precisely controlled pore structure, they selectively adsorb and slowly release oxygen and water vapor, providing a stable and continuous supply of reactants for the iron oxidation reaction, fundamentally avoiding the uneven heating problem caused by fluctuations in oxygen and moisture supply in traditional formulations; 2. Catalytic function: Their metal nodes (Fe... 3+ or Zn 2+) It can serve as a highly efficient catalyst for iron oxidation reaction, reducing the activation energy of the reaction and ensuring rapid start-up and heating in low temperature and low humidity environments; 3. Structural adaptability: The selected MOFs materials have good hydrothermal stability and can be adapted to the humid formula environment of hand warmers. Combined with multifunctional composite stabilizers, the structural stability is further improved.

[0023] The multifunctional composite stabilizer is a hydroxylated graphene / chitosan composite microsphere, which has the following functions: 1. Stabilizing effect: inhibits the collapse of MOF structure and prevents iron powder agglomeration; 2. Assisted temperature control: utilizes the high thermal conductivity of graphene to dissipate heat evenly and avoid local overheating; 3. Synergistic effect: chitosan hydroxyl groups coordinate with the metal nodes of MOF to improve adsorption performance; 4. Moisturizing effect: the hydrophilicity of chitosan maintains the appropriate humidity of the formulation and ensures low-temperature start-up.

[0024] The preparation method of hydroxylated graphene / chitosan composite microspheres is as follows: (1) Preparation of chitosan solution: Weigh chitosan, add acetic acid solution, and prepare 2-3 wt% chitosan solution; (2) Preparation of hydroxylated graphene / chitosan composite sol: Hydroxylated graphene and composite structure regulator are added sequentially to the chitosan solution, wherein the mass ratio of chitosan to hydroxylated graphene is 1:0.01–0.03, the mass ratio of sodium β-glycerophosphate to trehalose in the composite structure regulator is 1:0.3–0.5, and the amount of the composite structure regulator added is 5–10 wt% of the mass of chitosan, to form a stable hydroxylated graphene / chitosan composite sol; (3) Microsphere droplet formation: The composite sol is slowly dripped into an ethanol / water coagulation bath, so that the droplets form spherical particles in the coagulation bath; (4) Gradient curing: The microspheres formed by dripping are further subjected to gradient curing in the coagulation bath. After curing, the microspheres are removed and cleaned to remove residual solvent and unreacted components. (5) Freeze-drying to form pores yields the multifunctional composite stabilizer.

[0025] The specific method of gradient curing treatment is as follows: In the first stage, the chitosan outer layer is allowed to stand at 4℃ for 2-3 hours to rapidly gel and form a stable shell; in the second stage, the temperature is then raised to 25℃ and cured for another 8-10 hours to further stabilize the internal structure of the microspheres and complete the composite cross-linking.

[0026] Polyvinylpyrrolidone (PVP-K30) is selected for its following functions: 1. Compatibility optimization: It reduces the interfacial tension between MOFs and iron powder particles, prevents MOFs from agglomerating, ensures their uniform dispersion in the formulation, fully exposes the high specific surface area, and maximizes the adsorption-controlled release and catalytic functions; 2. Low-temperature start-up synergistic effect: The hydrophilic groups regulate the moisture distribution, providing a sufficient moisture environment for the MOFs to catalyze the iron oxidation reaction, and improving the low-temperature start-up efficiency; 3. MOFs catalytic enhancement effect: It forms weak coordination bonds with the metal nodes of MOFs, optimizes the electronic structure of MOFs, and further enhances their catalytic activity for the iron oxidation reaction; 4. Storage stabilization aid effect: It forms a thin molecular film on the material surface, helps to isolate air, reduces the premature contact between MOFs and oxygen, and delays the premature oxidation of iron powder.

[0027] The electrolyte is a mixture of calcium chloride and sodium chloride, which can accelerate the iron oxidation reaction and increase the heating rate.

[0028] The purpose of thermal insulation agents is to improve the heat preservation effect.

[0029] Water-retaining agents (i.e., water-absorbing resins) can absorb and store moisture, and are used to regulate the water content and distribution of the system, and maintain the humidity environment required for the reaction through water absorption and release.

[0030] The role of deionized water is to provide the moisture needed for oxidation reactions.

[0031] The present application will be further described below with reference to specific embodiments.

[0032] In the following embodiments and comparative examples, the sources of the raw materials are as follows: Reduced iron powder: Wuxi Sairui Metal Powder Manufacturing Co., Ltd., reduced iron content ≥85%; MIL-101(Fe): Guangdong Carbon Language New Materials Co., Ltd., Product No.: KAR-F49; ZIF-8: Guangdong Carbon Language New Materials Co., Ltd., Product No.: KAR-F02; Calcium chloride: Zhenjiang Dingrun Chemical Co., Ltd.; Sodium chloride: China Salt Yangtze River Salt Chemical Co., Ltd.; PVP-K30: Lianyungang Ronghe New Material Technology Co., Ltd.; Water-absorbing resin: Qingdao Shouke New Materials Co., Ltd., Model: SNN810s; Hydroxylated graphene: Suzhou Beike Nanotechnology Co., Ltd.; Chitosan powder: Xi'an Ruien Biotechnology Co., Ltd.; Sodium β-glycerophosphate: Nantong Zhonghe Chemical New Materials Co., Ltd.; Trehalose: Jiangsu Peptize Biotechnology Co., Ltd.; The rest are all regular commercially available products.

[0033] Example 1 The specific preparation steps for hydroxylated graphene / chitosan composite microspheres are as follows: (1) Preparation of chitosan solution Weigh out chitosan (degree of deacetylation ≥ 85%) and add it to a 1-1.5 wt% acetic acid solution. Stir magnetically at room temperature (20-25℃) for 3-4 h to ensure complete dissolution, preparing a 2-3 wt% chitosan solution. Then filter through a 100-mesh filter to remove undissolved particles, obtaining a homogeneous and transparent chitosan solution.

[0034] (2) Preparation of composite mixture Hydroxylated graphene (chitosan:hydroxylated graphene mass ratio = 1:0.02) and a composite structure modifier (sodium β-glycerophosphate:trehalose = 1:0.4) were added sequentially to the above chitosan solution, wherein the amount of composite structure modifier added was 8 wt% of the chitosan mass. Subsequently, ultrasonic dispersion (power 200-300 W) was used for 20-30 min, with simultaneous magnetic stirring, to uniformly disperse the hydroxylated graphene in the chitosan system, forming a stable hydroxylated graphene / chitosan composite sol.

[0035] (3) Microsphere droplet molding The above mixture is loaded into a syringe or peristaltic pump titration device and dripped into an ethanol / water coagulation bath (volume ratio 1:1) at a flow rate of 0.8-1.0 mL / min through a 0.6-0.8 mm needle. The dripping process is carried out under gentle magnetic stirring (200 rpm) to allow the droplets to form spherical particles in the coagulation bath. In the presence of ethanol, chitosan rapidly desolvents to form a primary gel layer, and hydroxylated graphene gradually accumulates internally, thus forming primary core-shell structured microspheres.

[0036] (4) Gradient curing The microspheres formed by dripping were then subjected to a gradient solidification process in a coagulation bath: The first stage (low-temperature pre-curing) involves standing at 4 ℃ for 2-3 hours to allow the outer layer of chitosan to rapidly gel and form a stable shell.

[0037] The second stage (room temperature curing) is followed by curing at 25 ℃ for another 8-10 h to further stabilize the internal structure of the microspheres and complete the composite cross-linking.

[0038] After curing, remove the microspheres and wash them repeatedly with deionized water 3-5 times until the solution pH≈7 to remove residual solvent and unreacted components.

[0039] (5) Freeze-drying to form pores The cleaned microspheres were pre-frozen at -40 ℃ for 4-6 h, and then freeze-dried in a freeze dryer for 8-12 h.

[0040] Example 2 A hand warmer comprises the following raw materials in the indicated weight percentages: 50% reduced iron powder, 5% MIL-101 (Fe), 3% hydroxylated graphene / chitosan composite microspheres, 1% PVP-K30, 2% sodium chloride, 1% calcium chloride, 15% vermiculite, 1% absorbent resin, and the remainder being deionized water. The preparation method of the hand warmer is basically the same as that of commercially available traditional products, as detailed below: The hydroxylated graphene / chitosan composite microspheres were prepared using the product from Example 1. MIL-101(Fe) and the hydroxylated graphene / chitosan composite microspheres were mixed evenly, and then other raw materials were added. After being mixed evenly, the mixture was packaged into a bag.

[0041] One side of the package is a breathable layer, and the other side is either a breathable layer or an impermeable layer. The breathable layer is a breathable membrane or a composite breathable membrane nonwoven fabric, and the impermeable layer is an impermeable membrane or an impermeable composite membrane nonwoven fabric.

[0042] Example 3 A hand warmer comprises the following raw materials in the indicated weight percentages: 50% reduced iron powder, 8% MIL-101 (Fe), 3% hydroxylated graphene / chitosan composite microspheres, 2% PVP-K30, 2% sodium chloride, 1% calcium chloride, 15% vermiculite, 0.6% absorbent resin, and the remainder being deionized water. The preparation method of the hand warmer is the same as in Example 2.

[0043] Example 4 A hand warmer comprises the following raw materials in the indicated weight percentages: 50% reduced iron powder, 8% ZIF-8, 3% hydroxylated graphene / chitosan composite microspheres, 2% PVP-K30, 2% sodium chloride, 1% calcium chloride, 15% vermiculite, 0.6% absorbent resin, and the remainder being deionized water. The preparation method of the hand warmer is the same as in Example 2.

[0044] Comparative Example 1 A hand warmer, without added MOF materials, comprises the following raw materials in the following weight percentages: 50% reduced iron powder, 3% hydroxylated graphene / chitosan composite microspheres, 2% PVP-K30, 2% sodium chloride, 1% calcium chloride, 15% vermiculite, 0.6% superabsorbent polymer, and the remainder being deionized water. Its preparation method is the same as in Example 2.

[0045] Comparative Example 2 A type of hand warmer, without added polyvinylpyrrolidone, comprises the following raw materials in weight percentages: 50% reduced iron powder, 8% MIL-101 (Fe), 3% hydroxylated graphene / chitosan composite microspheres, 2% sodium chloride, 1% calcium chloride, 15% vermiculite, 0.6% water-absorbing resin, and the remainder being deionized water.

[0046] The preparation method is the same as in Example 2.

[0047] Comparative Example 3 A type of hand warmer, without added hydroxylated graphene / chitosan composite microspheres, comprises the following raw materials in the following weight percentages: 50% reduced iron powder, 8% MIL-101 (Fe), 2% PVP-K30, 2% sodium chloride, 1% calcium chloride, 15% vermiculite, 0.6% water-absorbing resin, and the remainder being deionized water.

[0048] The preparation method is the same as in Example 2.

[0049] Using commercially available traditional products (activated carbon adsorption + salt catalysis) as a reference, the hand warmer products of each embodiment and comparative example were tested using a temperature tester. The test results are shown in Table 1.

[0050] Table 1 Performance test results of hand warmers

[0051] As shown in Table 1, the heating temperatures of Examples 2-4 containing MOFs reached 45-55℃, significantly higher than the comparative examples (36-43℃) and the conventional product (36℃) without MOFs. Adding 8% MIL-101 (Fe) or ZIF-8 increased the peak temperature to 55℃, with a start-up time of only 3-4 minutes, much faster than the comparative examples (6-18 minutes) and the conventional product (20 minutes), indicating that MOFs can effectively accelerate the iron powder oxidation reaction and improve the start-up rate. The significantly prolonged start-up time in Comparative Example 2 indicates that PVP-K30, as a dispersant stabilizer, can prevent MOF aggregation and ensure rapid start-up. The consistency error in Comparative Example 3 increased to 10%, much higher than the 2%-3% of the examples, proving that hydroxylated graphene / chitosan composite microspheres can stabilize the heating process and reduce temperature fluctuations through uniform thermal conduction.

[0052] This application successfully developed a high-temperature, stable, rapid, and uniform iron powder heating composition by introducing MIL-101 (Fe) or ZIF-8 as a heating aid and combining it with the synergistic effect of PVP-K30 and hydroxylated graphene / chitosan composite microspheres. Its comprehensive performance is significantly better than that of traditional products and MOF-free comparative solutions.

Claims

1. A hand warmer, characterized in that, Its internal materials include the following raw materials in the following weight percentages: reduced iron powder 40-60%, MOFs material 5-10%, multifunctional composite stabilizer 3-8%, polyvinylpyrrolidone 1-3%, electrolyte 2-5%, heat preservation agent 15-20%, water retention agent 0.1-1%, and the remaining component is deionized water.

2. A hand warmer according to claim 1, characterized in that, The MOFs material is MIL-101(Fe) or ZIF-8.

3. A hand warmer according to claim 1, characterized in that, The multifunctional composite stabilizer is a hydroxylated graphene / chitosan composite microsphere.

4. A hand warmer according to claim 1, characterized in that, The polyvinylpyrrolidone is PVP-K30.

5. A hand warmer according to claim 1, characterized in that, The electrolyte is a mixture of calcium chloride and sodium chloride.

6. A hand warmer according to claim 1, characterized in that, The heat-insulating agent is vermiculite.

7. A hand warmer according to claim 1, characterized in that, The deionized water has a mass percentage of 15-25%.

8. The method for preparing the hand warmer as described in any one of claims 1 to 7, characterized in that, After the MOFs material and multifunctional composite stabilizer are mixed evenly, other raw materials are added. After being mixed evenly, the mixture is packed into a bag and sealed. One side of the bag is a breathable layer, and the other side is either a breathable layer or an impermeable layer.

9. The method for preparing the hand warmer as described in claim 8, characterized in that, The breathable layer is a breathable membrane or a composite breathable membrane nonwoven fabric, and the impermeable layer is an impermeable membrane or an impermeable composite membrane nonwoven fabric.

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