Preparation method and application of moisture-absorbing micro-nano composite refrigeration hydrogel

Abstract

The application relates to a preparation method of a moisture-absorbing micro-nano composite refrigeration hydrogel, which is prepared by a free radical polymerization reaction with acrylamide as a monomer, methylene bisacrylamide as a crosslinking agent, zirconium dioxide micro-nano particles as a spectral modifier, ammonium persulfate as an initiator and tetramethyl ethylenediamine as a catalyst, and has a highly entangled structure by adjusting the molar ratio of the monomer and the crosslinking agent. The micro-nano composite hydrogel is soaked in a lithium bromide solution until swelling equilibrium. The application also relates to the application of the moisture-absorbing micro-nano composite refrigeration hydrogel to non-electricity-dependent cold chain transportation of fruits or biological agents. The application has the coupling effect of daytime radiation refrigeration and evaporation refrigeration, has the function of capturing environmental moisture at night to realize cold source replenishment, has the highly entangled structure to realize the strong and tough characteristics at a high water content, realizes passive high-efficiency refrigeration with zero energy consumption and zero emission, and belongs to the field of passive refrigeration technology.

Description

Technical Field

[0001] This invention relates to the field of passive refrigeration technology, specifically to a method for preparing a hygroscopic micro / nano composite refrigeration hydrogel and its application. Background Technology

[0002] Rapid industrialization and rising living standards have created a huge demand for refrigeration. Currently, the mainstream refrigeration technology is the vapor compression refrigeration cycle, which has permeated various fields such as industry, agriculture, construction, medicine, and logistics. However, this active refrigeration technology has a drawback: high power consumption. Under an energy model dominated by thermal power generation, high electricity consumption means high carbon dioxide emissions. Carbon dioxide is one of the main greenhouse gases causing global warming and the heat island effect, posing a significant threat to the global climate, environment, and economy. Therefore, developing new zero-energy, zero-emission refrigeration technologies is particularly urgent and important.

[0003] Compared to active cooling technology, passive cooling technology can achieve cooling without power input, but its low cooling power limits its application. Among these, daytime radiative cooling, a novel passive cooling technology, can achieve cooling under high-intensity solar radiation, but its cooling power is relatively low. Meanwhile, evaporative cooling technology based on hydrogel platforms, while possessing higher cooling power, is susceptible to the infrared thermal effect of solar radiation, resulting in low net cooling power. Therefore, coupling daytime radiative cooling with evaporative cooling, complementing each other's advantages and disadvantages, can reduce the impact of solar radiation on cooling power and increase the overall cooling power, potentially overcoming the low power limitation of daytime passive cooling.

[0004] Although previous patents have achieved the technology of coupling daytime radiative cooling and evaporative cooling, this technology mainly relies on the adhesion of an upper layer of polymer with radiative cooling properties and a lower layer of hydrogel with evaporative cooling properties to obtain a double-layer cooling material. Its drawbacks are: (1) During use, the water loss and shrinkage characteristics of the lower layer hydrogel will not match the shape of the upper layer polymer, which will eventually destroy the structure of the upper layer polymer or cause the upper and lower layers of materials to separate; (2) Two materials need to be prepared separately, which increases the preparation cost and process complexity; (3) During the evaporation process, the hydrogel has a limited amount of cold source (pure water) and there is a problem of unsustainable cooling; (4) After the hydrogel absorbs water, its mechanical properties decrease significantly due to the swelling and weakening effect, which is not conducive to practical application. Summary of the Invention

[0005] To address the technical problems existing in the prior art, the purpose of this invention is to provide a method for preparing a hygroscopic micro / nano composite cooling hydrogel with low preparation cost and which can achieve cooling through the synergistic effect of radiation cooling and evaporation cooling, as well as its application.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing a hygroscopic micro / nano composite cooling hydrogel, comprising the following steps:

[0007] S1, Acrylamide, zirconium dioxide, methylenebisacrylamide, ammonium persulfate and water are mixed to obtain a mixture;

[0008] S2, homogenize the mixture until the particles are evenly dispersed to obtain a uniform hydrogel precursor;

[0009] S3, add tetramethylethylenediamine as a catalyst to the hydrogel precursor and stir thoroughly with a glass rod, then inject it into a mold and carry out the polymerization reaction at room temperature to obtain micro-nano composite hydrogel, and then peel the micro-nano composite hydrogel off the mold.

[0010] S4. The micro-nano composite hydrogel is immersed in lithium bromide solution until swelling equilibrium is reached to obtain a hygroscopic micro-nano composite cooling hydrogel.

[0011] This preparation method uses acrylamide as a monomer, methylenebisacrylamide as a crosslinking agent, zirconium dioxide micro / nanoparticles as a spectral modifier, ammonium persulfate as an initiator, and tetramethylethylenediamine as a catalyst to prepare a micro / nano composite cooling hydrogel with a coupling effect of daytime radiative cooling and evaporative cooling via free radical polymerization. By adjusting the molar ratio of monomer to crosslinking agent to achieve a highly entangled structure, the micro / nano composite hydrogel is then immersed in lithium bromide solution until swelling equilibrium is reached, yielding a hygroscopic micro / nano composite cooling hydrogel. This hydrogel exhibits high solar reflectivity, high atmospheric window emissivity, and high atmospheric water capture rate. After absorbing water and swelling, it retains strong mechanical properties and can effectively reflect sunlight under daytime solar radiation. Through the synergistic effect of radiative and evaporative cooling, it can effectively cool food containers or medicine bottles, reducing the impact of solar radiation and ambient temperature on fruits or biological preparations. Furthermore, this hydrogel can capture moisture from the ambient air under high humidity conditions at night, providing a cold source replenishment for the next evaporative cooling cycle, enabling sustainable non-electric cold chain transportation of fruits or biological preparations.

[0012] As a preferred embodiment, in step S1, the molar ratio of acrylamide to water is 1:2-1:5, and the molar ratio of methylenebisacrylamide to acrylamide is 10. -5 -10 -3 The molar ratio of ammonium persulfate to acrylamide is 2.0 × 10⁻⁶. -4 -2.5×10 -4 .

[0013] As a preferred embodiment, in step S1, the zirconium dioxide has a particle size of 100-1000 nm and an addition amount of 20-60 wt%.

[0014] As a preferred option, in step S2, the homogenization process is performed using an ultrasonic cleaner with a power of 80-300W for 5 minutes.

[0015] As a preferred embodiment, in step S3, the molar ratio of tetramethylethylenediamine to acrylamide is 1.0 × 10⁻⁶. -3 -3.0×10 -3 The room temperature is 25-30℃, and the reaction time is 5-10 min.

[0016] As a preferred embodiment, in step S3, the mold is provided with several grooves, and tetramethylethylenediamine and the hydrogel precursor are thoroughly mixed and then injected into the grooves. The shape of the grooves is one or more of the following: square, circle, cylinder, square prism, hexagonal prism, and octagonal prism.

[0017] As a preferred embodiment, in step S4, the concentration of the lithium bromide solution is 30-45 wt%.

[0018] In step S4, the swelling equilibrium is reached when the hydrogel absorbs water until its mass no longer changes.

[0019] In step S4, pure water is used.

[0020] The hygroscopic micro-nano composite cooling hydrogel obtained by the above preparation method is used for non-electric cold chain transportation of fruits or biological agents. The hygroscopic micro-nano composite cooling hydrogel is adhered to the surface of the container carrying the fruits or biological agents. The hygroscopic micro-nano composite cooling hydrogel cools during the day and captures water at night.

[0021] As a preferred option, a waterproof adhesive is used to bond the moisture-absorbing micro-nano composite cooling hydrogel to the container surface.

[0022] The container is either a cylindrical food storage box or a cube food storage box.

[0023] The aforementioned hygroscopic micro / nano composite cooling hydrogel is suitable for use in high-temperature, low-humidity daytime environments and low-temperature, high-humidity nighttime environments. The daytime conditions are: ambient temperature 25-40℃, relative humidity 0-60% RH; the nighttime conditions are: ambient temperature 15-25℃, relative humidity 60-100% RH. The principle is as follows: under the high-temperature, low-humidity daytime environment, evaporative cooling and daytime radiative cooling technologies are coupled for cooling; under the low-temperature, high-humidity nighttime environment, environmental moisture capture and daytime radiative cooling technologies are coupled for replenishing the cold source (pure water). The moisture captured at night can meet the needs of daytime evaporative cooling, achieving a sustainable passive cooling system that combines daytime cooling with nighttime water capture.

[0024] In summary, the present invention has the following advantages:

[0025] (1) The method for preparing a hygroscopic micro-nano composite cooling hydrogel of the present invention is simple, does not require toxic or harmful organic solvents, does not require complex instruments and equipment, has low cost, and is expected to be used for industrial production.

[0026] (2) The present invention provides a hygroscopic micro-nano composite cooling hydrogel with an integrated composite structure, which eliminates the need to prepare two different materials in batches to couple daytime radiation cooling and evaporative cooling technologies.

[0027] (3) The method for preparing a hygroscopic micro-nano composite cooling hydrogel of the present invention is flexible. The casting method can be used to prepare the required shape and size according to the needs of the application scenario.

[0028] (4) The present invention provides a hygroscopic micro-nano composite cooling hydrogel with a highly entangled structure, which can still have strong mechanical properties at high water content. Its structure is not easily damaged by external forces and can be repeatedly recycled.

[0029] (5) The hygroscopic micro-nano composite cooling hydrogel of the present invention can achieve passive cooling that can sustainably cycle between daytime cooling and nighttime water capture, without requiring additional power input and with zero emissions. Attached Figure Description

[0030] Figure 1 This diagram illustrates the swelling and stretching processes of hygroscopic micro / nano composite cooling hydrogels, the passive cooling process of cycles, and the swelling and stretching processes of highly cross-linked hydrogels.

[0031] Figure 2 The tensile stress-strain characteristics of the hygroscopic micro / nano composite cooling hydrogel in Example 1 are shown in the figure.

[0032] Figure 3 The image shows the spectral characteristics of the hygroscopic micro / nano composite cooling hydrogel in Example 1.

[0033] Figure 4 The diagram shows the moisture absorption properties of the hygroscopic micro / nano composite cooling hydrogel in Example 1.

[0034] Figure 5 The temperature change graphs are shown for the hygroscopic micro / nano composite cooling hydrogel group and the blank group in Example 4. Detailed Implementation

[0035] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0036] Example 1

[0037] A method for preparing a hygroscopic micro / nano composite cooling hydrogel, comprising the following steps:

[0038] (1) Using water as a solvent, acrylamide, methylenebisacrylamide, ammonium persulfate, and zirconium dioxide are added and mixed to obtain a mixture, wherein the molar ratio of acrylamide to water is 1:2.9, and the molar ratio of methylenebisacrylamide to acrylamide is 10. -4 The molar ratio of ammonium persulfate to acrylamide is 2.25 × 10⁻⁶. -4 The amount of zirconium dioxide (particle size 200nm) added was 43wt%.

[0039] (2) The mixture was treated with ultrasound to obtain a uniform hydrogel precursor;

[0040] (3) Tetramethylethylenediamine was added to the hydrogel precursor, with a molar ratio of tetramethylethylenediamine to acrylamide of 2.0 × 10⁻⁶. -3 The mixture was quickly stirred with a glass rod and poured into a mold with a square groove (groove dimensions: side length 80mm, thickness 3mm). The mixture was reacted at room temperature (25-30℃) for 5 minutes to obtain a micro-nano composite hydrogel.

[0041] (4) The micro-nano composite hydrogel is then soaked in a solution containing 40wt% lithium bromide for 24h to obtain a hygroscopic micro-nano composite cooling hydrogel.

[0042] like Figure 1 As shown, traditional highly cross-linked hydrogels are stiff and brittle when stretched. However, the hygroscopic micro-nano composite cooling hydrogel obtained by the preparation method of this invention has a highly entangled structure formed by polyacrylamide chains, methylenebisacrylamide and zirconium dioxide particles. It retains its elasticity and toughness after stretching, and can achieve passive cooling that can be continuously circulated during the day and at night for water capture.

[0043] like Figure 2 As shown, compared to traditional hydrogels (acrylamide to water molar ratio of 1:10.0, methylenebisacrylamide to acrylamide molar ratio of 10), -3 The molar ratio of ammonium persulfate to acrylamide is 2.25 × 10⁻⁶. -4 The amount of zirconium dioxide (particle size 200nm) added is 43wt%, and the highly cross-linked hydrogel No. 1 (the molar ratio of acrylamide to water is 1:10.0, and the molar ratio of methylenebisacrylamide to acrylamide is 10) is also present. -2 The molar ratio of ammonium persulfate to acrylamide is 2.25 × 10⁻⁶. -4 The amount of zirconium dioxide (particle size 200nm) added is 43wt%, and the highly cross-linked hydrogel No. 2 (the molar ratio of acrylamide to water is 1:10.0, and the molar ratio of methylenebisacrylamide to acrylamide is 10) is also present. -2 The molar ratio of ammonium persulfate to acrylamide is 2.25 × 10⁻⁶. -4The addition of zirconium dioxide (particle size 200 nm) at 43 wt% significantly improved stress and strain. Figure 3 As shown, the obtained hygroscopic micro / nano composite cooling hydrogel exhibits high solar reflectivity and high atmospheric emissivity. Figure 4 As shown, the obtained hygroscopic micro-nano composite cooling hydrogel has a high ability to capture ambient water vapor under different environmental humidity conditions.

[0044] Example 2

[0045] The application of a hygroscopic micro / nano composite cooling hydrogel in non-electrically dependent cold chain transportation of fruits involves the following steps:

[0046] (1) Using water as a solvent, acrylamide, methylenebisacrylamide, ammonium persulfate, and zirconium dioxide were mixed to obtain a mixture, wherein the molar ratio of acrylamide to water was 1:2.9, and the molar ratio of methylenebisacrylamide to acrylamide was 10. -4 The molar ratio of ammonium persulfate to acrylamide is 2.25 × 10⁻⁶. -4 The amount of zirconium dioxide (particle size 200nm) added was 43wt%.

[0047] (2) The mixture was treated with ultrasound to obtain a uniform hydrogel precursor;

[0048] (3) Tetramethylethylenediamine was added to the hydrogel precursor, with a molar ratio of tetramethylethylenediamine to acrylamide of 2.0 × 10⁻⁶. -3 Stir quickly and evenly with a glass rod, then pour into a mold with a circular groove (groove size: diameter 8cm, thickness 3mm), and react at room temperature (25-30℃) for 5 minutes to obtain micro-nano composite cooling hydrogel;

[0049] (4) Then soak it in a solution containing 40wt% lithium bromide for 24h to obtain a hygroscopic micro-nano composite cooling hydrogel with a diameter of 14cm and a thickness of 5mm.

[0050] (5) Adhere the moisture-absorbing micro-nano composite cooling hydrogel to the lid of the food storage box (diameter: 14cm) with waterproof glue. The volume of the food storage box is 1L. After placing 3 Fuji apples inside, place the food storage box outdoors.

[0051] After half an hour of solar radiation (800W m) -2 Afterwards, the average temperature of apples in the control group reached 39.2℃, and the respiration rate reached 65 mg (CO2) kg. -1 h -1 Furthermore, the apples exhibited sunburn on their surface. The average temperature of the apples in the hygroscopic micro / nano composite cooling hydrogel group remained stable at 26.5℃, and the respiration rate was maintained at 30 mg (CO2) / kg. -1h -1 Furthermore, the surface of the apple is similar to that of fresh fruit.

[0052] Example 3

[0053] The application of a hygroscopic micro / nano composite cooling hydrogel in the non-electrically dependent cold chain transportation of biological agents involves the following steps:

[0054] (1) Using water as a solvent, acrylamide, methylenebisacrylamide, ammonium persulfate, and zirconium dioxide were mixed to obtain a mixture, wherein the molar ratio of acrylamide to water was 1:2.9, and the molar ratio of methylenebisacrylamide to acrylamide was 10. -4 The molar ratio of ammonium persulfate to acrylamide is 2.25 × 10⁻⁶. -4 The amount of zirconium dioxide (particle size 200nm) added was 43wt%.

[0055] (2) The mixture was treated with ultrasound to obtain a uniform hydrogel precursor;

[0056] (3) Tetramethylethylenediamine was added to the hydrogel precursor, with a molar ratio of tetramethylethylenediamine to acrylamide of 2.0 × 10⁻⁶. -3 Stir quickly and evenly with a glass rod, then pour into a mold with an octagonal prism groove (groove dimensions: outer diameter 34mm, inner diameter 14mm, height 69mm), and react at room temperature (25-30℃) for 5 minutes to obtain micro-nano composite cooling hydrogel.

[0057] (4) Then soak it in a solution containing 40wt% lithium bromide for 24h to obtain a hygroscopic micro-nano composite cooling hydrogel package with an outer diameter of 38mm, an inner diameter of 25mm and a height of 75mm.

[0058] (5) Place a 10ml vial into a hygroscopic micro-nano composite cooling hydrogel package, add 5ml of 2.0wt% anthocyanin solution to the vial, and place the package outdoors.

[0059] After half an hour of solar radiation (800W m) -2 Afterwards, the average temperature of the vials in the blank control group reached 48.7℃, and the anthocyanin content decreased from 20g / L. -1 Reduced to 7g / L -1 The average temperature of vials packaged with hygroscopic micro-nano composite cooling hydrogel remained stable at 26.6℃, and the anthocyanin content was maintained at 20g / L. -1 .

[0060] Example 4

[0061] A hygroscopic micro / nano composite cooling hydrogel with sustainable cyclic cooling process is described below:

[0062] (1) Using water as a solvent, acrylamide, methylenebisacrylamide, ammonium persulfate, and zirconium dioxide were mixed to obtain a mixture, wherein the molar ratio of acrylamide to water was 1:2.9, and the molar ratio of methylenebisacrylamide to acrylamide was 10. -4 The molar ratio of ammonium persulfate to acrylamide is 2.25 × 10⁻⁶. -4 The amount of zirconium dioxide (particle size 200nm) added was 43wt%.

[0063] (2) The mixture was treated with ultrasound to obtain a uniform hydrogel precursor;

[0064] (3) Tetramethylethylenediamine was added to the hydrogel precursor, with a molar ratio of tetramethylethylenediamine to acrylamide of 2.0 × 10⁻⁶. -3 Stir quickly and evenly with a glass rod, then pour into a mold with a square groove (groove dimensions: side length 80mm, thickness 3mm), and react at room temperature (25-30℃) for 5 minutes to obtain micro-nano composite cooling hydrogel;

[0065] (4) The micro / nano composite cooling hydrogel was then immersed in a solution containing 40 wt% lithium bromide for 24 h to obtain a hygroscopic micro / nano composite cooling hydrogel. This hydrogel was then placed on a square copper sheet (80 mm side length, 2 mm thickness) and placed together with an analog light source (800 W m²). -2 ) for 8 hours, then place in a constant temperature and humidity chamber (27℃, 16h).

[0066] like Figure 5 As shown, with 24 hours as one cycle, after three cycles, under light, the average temperature of the blank group was 44.2-44.4℃, and the average temperature of the hygroscopic micro-nano composite cooling hydrogel group (treatment group) was 34.8-34.9℃. This indicates that the hygroscopic micro-nano composite cooling hydrogel can achieve passive cooling with a sustainable cycle of daytime cooling and nighttime water capture.

[0067] The above embodiments are preferred embodiments of the invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a hygroscopic micro / nano composite cooling hydrogel, characterized in that: Includes the following steps: S1, Acrylamide, zirconium dioxide, methylenebisacrylamide, ammonium persulfate and water are mixed to obtain a mixture; S2, homogenize the mixture until the particles are evenly dispersed to obtain a uniform hydrogel precursor; S3, add tetramethylethylenediamine as a catalyst to the hydrogel precursor and stir thoroughly with a glass rod, then inject it into a mold and carry out the polymerization reaction at room temperature to obtain micro-nano composite hydrogel, and then peel the micro-nano composite hydrogel off the mold. S4. The micro-nano composite hydrogel is immersed in lithium bromide solution until swelling equilibrium is reached to obtain a hygroscopic micro-nano composite cooling hydrogel. In step S1, the molar ratio of acrylamide to water is 1:2 to 1:5, and the molar ratio of methylenebisacrylamide to acrylamide is 10. -5 -10 -3 The molar ratio of ammonium persulfate to acrylamide is 2.0 × 10⁻⁶. -4 -2.5×10 -4 .

2. The method for preparing a hygroscopic micro / nano composite cooling hydrogel according to claim 1, characterized in that: In step S1, the zirconium dioxide has a particle size of 100-1000 nm and an addition amount of 20-60 wt%.

3. The method for preparing a hygroscopic micro / nano composite cooling hydrogel according to claim 1, characterized in that: In step S2, the homogenization process is performed using an ultrasonic cleaner with a power of 80-300W for 5 minutes.

4. The method for preparing a hygroscopic micro / nano composite cooling hydrogel according to claim 1, characterized in that: In step S3, the molar ratio of tetramethylethylenediamine to acrylamide is 1.0 × 10⁻⁶. -3 -3.0×10 -3 The room temperature is 25-30℃, and the reaction time is 5-10 min.

5. The method for preparing a hygroscopic micro / nano composite cooling hydrogel according to claim 1, characterized in that: In step S3, the mold is provided with several grooves. Tetramethylethylenediamine and the hydrogel precursor are thoroughly mixed and then injected into the grooves. The shape of the grooves is one or more of the following: square, circle, cylinder, square prism, hexagonal prism, and octagonal prism.

6. The method for preparing a hygroscopic micro / nano composite cooling hydrogel according to claim 1, characterized in that: In step S4, the concentration of the lithium bromide solution is 30-45 wt%.

7. The application of the hygroscopic micro / nano composite cooling hydrogel obtained by the preparation method according to any one of claims 1 to 6, characterized in that: For non-electric cold chain transportation of fruits or biological agents, a hygroscopic micro-nano composite cooling hydrogel is adhered to the surface of the container carrying the fruit or biological agent. The hygroscopic micro-nano composite cooling hydrogel cools during the day and captures water at night.

8. The application of the hygroscopic micro / nano composite cooling hydrogel according to claim 7, characterized in that: A moisture-absorbing micro-nano composite cooling hydrogel is adhered to the surface of the container using waterproof adhesive.

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