A method for preparing a phase change material that can store energy for a long time and can intermittently crystallize and release heat

Abstract

The application relates to a preparation method of a phase change material which can store energy for a long time and release heat in intermittent crystallization, and relates to a preparation method of the phase change material. The application solves the problem that the existing phase change material can only release all stored energy once, and cannot release part of the stored energy in intermittent multiple times. The method is as follows: a melted sodium acetate trihydrate, a polymer monomer, a crosslinking agent and a stabilizer are heated and mixed to obtain a reaction system, an initiator is added into the reaction system, and heat preservation is carried out. The application is used for the preparation of the phase change material which can store energy for a long time and release heat in intermittent crystallization.

Description

TECHNICAL FIELD

[0001] The present application relates to a preparation method of a phase change material. BACKGROUND

[0002] At present, energy storage and conversion mainly focuses on electrochemical batteries. However, heat is the most basic energy type in industrial production, human thermal environment and building thermal environment. The heat battery which can store heat for a long time and release stored energy as needed has attracted wide attention. Since the phase change material can reversibly store and release energy in the reversible phase change process, it can be used as a kind of heat battery. However, the phase change material can only release all the stored energy at one time, but cannot intermittently release part of the stored energy for multiple times, which causes great inconvenience and a large amount of energy waste. SUMMARY

[0003] The present application aims to solve the problem that the existing phase change material can only release all the stored energy at one time, but cannot intermittently release part of the stored energy for multiple times, and further provides a preparation method of a phase change material which can both store energy for a long time and release heat intermittently.

[0004] A preparation method of a phase change material which can both store energy for a long time and release heat intermittently, which is carried out according to the following steps:

[0005] The sodium acetate trihydrate crystal is heated and melted to obtain molten sodium acetate trihydrate, the molten sodium acetate trihydrate, polymer monomer, crosslinking agent and stabilizer are heated and mixed for 10-30 minutes to obtain a reaction system, an initiator is added to the reaction system and kept warm to obtain the phase change material which can both store energy for a long time and release heat intermittently.

[0006] The mass ratio of the sodium acetate trihydrate crystal to the polymer monomer is 1:(0.1-0.5); the mass ratio of the sodium acetate trihydrate crystal to the crosslinking agent is 1:(0.002-0.02); the mass of the sodium acetate trihydrate crystal to the volume of the stabilizer is 1g:(0.002-0.3)mL; the mass ratio of the sodium acetate trihydrate crystal to the initiator is 1:(0.002-0.015);

[0007] The stabilizer is cellulose suspension with a concentration of 0.001g / mL-0.2g / mL or whiskered wood powder dispersion liquid with a concentration of 0.05g / mL-0.2g / mL.

[0008] The present application has the following beneficial effects:

[0009] In order to obtain the intermittent heat release phase change material, the crystal growth must be able to quickly stop. The process of crystal growth refers to the continuous growth of the crystal nucleus or seed after the crystal nucleus or seed appears in the supersaturated solution, and the supersaturation is the driving force of the crystal growth. The three stages of crystal growth are: (1) the adsorption of solute molecules from the solution phase to the crystal surface; (2) the solute reaching the crystal surface grows to the crystal surface, making the crystal larger, while releasing the crystallization heat; (3) the crystallization heat is transferred back to the solution. If the path between the solute molecules and the crystal surface is cut off during the crystal growth process, the solute molecules can be prevented from adhering to the crystal surface, thereby preventing the crystal growth. In the sodium acetate trihydrate gel, the supercooled sodium acetate trihydrate has a high energy barrier, and it is not easy to nucleate in the matrix of the present application, so it can store energy for a long time. However, after the sodium acetate trihydrate gel is contacted with foreign matter (seed, plastic, wood, metal, glass, etc.), the contacted part will quickly form a crystal nucleus, and the sodium acetate trihydrate crystal will quickly grow and release heat. There is a very obvious boundary between the crystallization zone and the non-crystallization zone, and as the crystal continues to grow, the crystallization zone continues to expand. At this time, the crystallization can be stopped by quickly cutting the crystallization zone and the non-crystallization zone with a wet scissors. This is because water converts the saturated solution in the contact area between the salt gel and the scissors into an unsaturated solution, preventing the formation of new crystal nuclei in the part contacted with foreign matter, thereby stopping the crystallization without inducing nucleation crystallization. And the remaining uncrystallized sodium acetate trihydrate gel will continue to remain in a supercooled state (store energy) until the next use. In addition, when the crosslinking agent is starch, a large number of hydrogen bonds generated during the gelatinization of starch endow the sodium acetate trihydrate gel with good self-healing properties, thereby ensuring that the sodium acetate trihydrate gel can be recycled multiple times; when the crosslinking agent is N,N-methylene bisacrylamide and ferric chloride, a large number of ionic coordination bonds are formed between metal ions and the polymer system, thereby endowing the gel with self-healing properties.

[0010] The present application is a preparation method for a phase change material that can both store energy for a long time and release heat intermittently. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 The actual pictures of the sodium acetate trihydrate gel prepared in Example 1 in the melted state, the supercooled state (kept for 10 days) and the crystallized state;

[0012] Figure 2 The supercooling phenomenon of the sodium acetate trihydrate gel prepared in Example 1 was determined by using a differential scanning calorimeter;

[0013] Figure 3 The crystallization process of the supercooled sodium acetate trihydrate gel in Example 1 after being touched by different foreign matter (seed, rubber, glass, metal);

[0014] Figure 4The picture of cutting the supercooled sodium acetate trihydrate gel of Example 1 with water-dipped scissors and non-water-dipped scissors, respectively;

[0015] Figure 5 The highest temperature-time curve of the continuous exothermic process of the supercooled sodium acetate trihydrate gel of Example 1;

[0016] Figure 6 The highest temperature-time curve of the intermittent exothermic process of the supercooled sodium acetate trihydrate gel of Example 1;

[0017] Figure 7 The intermittent exothermic process of the supercooled sodium acetate trihydrate gel of Example 1 recorded by photos and infrared thermal imager (for example, the intermittent exothermic process for three times);

[0018] Figure 8 The self-healing performance of the sodium acetate trihydrate gel prepared in Example 1 observed by optical microscope, a1 is to heat the two broken crystalline sodium acetate trihydrate gels to melting and contact, a2 is to supercool for 1 min, a3 is to supercool for 5 min, and a4 is to supercool for 10 min;

[0019] Figure 9 The self-healing performance of the sodium acetate trihydrate gel prepared in Example 1, a is to splice the three broken crystalline sodium acetate trihydrate gels, b is to heat the three broken crystalline sodium acetate trihydrate gels to melting and then place at room temperature, and c is to stretch the gel in b to 1.5 times of the length of itself;

[0020] Figure 10 The pictures of the melting state, supercooled state (kept for 10 days) and crystalline state of the sodium acetate trihydrate gel prepared in Example 2;

[0021] Figure 11 The supercooling phenomenon of the sodium acetate trihydrate gel prepared in Example 2 determined by differential calorimetric scanning;

[0022] Figure 12 The crystallization process of the supercooled sodium acetate trihydrate gel of Example 2 after touching different foreign matters (crystal seed, rubber, glass and metal);

[0023] Figure 13 The picture of cutting the supercooled sodium acetate trihydrate gel of Example 2 with water-dipped scissors and non-water-dipped scissors, respectively;

[0024] Figure 14 The highest temperature-time curve of the continuous exothermic process of the supercooled sodium acetate trihydrate gel of Example 2;

[0025] Figure 15 The highest temperature-time curve of the intermittent exothermic process of the supercooled sodium acetate trihydrate gel of Example 2;

[0026] Figure 16 Intermittent exothermic process of the supercooled sodium acetate trihydrate gel of Example 2 recorded by photo and infrared thermal imager (take the example of intermittent exothermic three times);

[0027] Figure 17 Self-healing performance of the sodium acetate trihydrate gel prepared in Example 2 observed by optical microscope, a1 is to heat the two broken pieces of crystalline sodium acetate trihydrate gel to melt and contact, a2 is supercooled for 1 min, a3 is supercooled for 3 min, a4 is supercooled for 5 min;

[0028] Figure 18 Self-healing performance of the sodium acetate trihydrate gel prepared in Example 2 observed by optical microscope, a is to splice the three broken pieces of crystalline sodium acetate trihydrate gel, b is to heat the three broken pieces of crystalline sodium acetate trihydrate gel to melt and then place at room temperature, c is to stretch the gel in figure b to 1.5 times of its own length;

[0029] Figure 19 Crystal growth rate of the sodium acetate trihydrate gel prepared in Example 1 (0 times) and crystal growth rate of the gel self-healing at the same site for 1-5 times recorded by optical microscope;

[0030] Figure 20 Crystal growth process diagram of the sodium acetate trihydrate gel prepared in Example 1 before and after healing observed by optical microscope, a1 is crystal growth 0s before healing, a2 is crystal growth 2s before healing, a3 is crystal growth 3s before healing, a4 is crystal growth 4s before healing, b1 is crystal growth 0s after healing, b2 is crystal growth 2s after healing, b3 is crystal growth 3s after healing, b4 is crystal growth 4s after healing;

[0031] Figure 21 Crystal growth rate of the sodium acetate trihydrate gel prepared in Example 2 (0 times) and crystal growth rate of the gel self-healing at the same site for 1-5 times recorded by optical microscope;

[0032] Figure 22 Crystal growth process diagram of the sodium acetate trihydrate gel prepared in Example 2 before and after healing observed by optical microscope, a1 is crystal growth 0s before healing, a2 is crystal growth 2s before healing, a3 is crystal growth 3s before healing, a4 is crystal growth 4s before healing, b1 is crystal growth 0s after healing, b2 is crystal growth 2s after healing, b3 is crystal growth 3s after healing, b4 is crystal growth 4s after healing. DETAILED DESCRIPTION

[0033] The technical solution of the present application is not limited to the following specific embodiments, but also includes any combination of the specific embodiments.

[0034] Specific implementation one: the preparation method of the phase change material which can store energy for a long time and release heat intermittently, is carried out according to the following steps:

[0035] The sodium acetate trihydrate crystal is heated and melted to obtain molten sodium acetate trihydrate, the molten sodium acetate trihydrate, polymer monomer, crosslinking agent and stabilizer are heated and mixed for 10-30 minutes to obtain a reaction system, an initiator is added to the reaction system and kept warm to obtain the phase change material which can store energy for a long time and release heat intermittently;

[0036] The mass ratio of the sodium acetate trihydrate crystal to the polymer monomer is 1:(0.1-0.5); the mass ratio of the sodium acetate trihydrate crystal to the crosslinking agent is 1:(0.002-0.02); the mass of the sodium acetate trihydrate crystal to the volume of the stabilizer is 1g:(0.002-0.3)mL; the mass ratio of the sodium acetate trihydrate crystal to the initiator is 1:(0.002-0.015);

[0037] The stabilizer is cellulose suspension with a concentration of 0.001g / mL-0.2g / mL or whiskered wood powder dispersion liquid with a concentration of 0.05g / mL-0.2g / mL.

[0038] The beneficial effects of the present embodiment are:

[0039] In order to obtain the intermittent heat release phase change material, the crystal growth must be able to be quickly stopped. The process of crystal growth refers to the continuous growth of the crystal nucleus or seed after the crystal nucleus or seed appears in the supersaturated solution, and the supersaturation is the driving force of the crystal growth. The three stages of the crystal growth are: (1) the adsorption of solute molecules from the solution phase to the crystal surface; (2) the growth of the solute reaching the crystal surface to the crystal surface, so as to make the crystal larger, and meanwhile release the crystallization heat; (3) the crystallization heat is transferred back to the solution. If the path between the solute molecules and the crystal surface is cut off during the crystal growth, the solute molecules can be prevented from adhering to the crystal surface, so as to stop the crystal growth. In the sodium acetate trihydrate gel, the supercooled sodium acetate trihydrate has a high energy barrier, and it is not easy to nucleate in the matrix of the embodiment, so that the energy can be stored for a long time. However, after the sodium acetate trihydrate gel is contacted with a foreign object (seed, plastic, wood, metal, glass, etc.), the contacted part will quickly form a crystal nucleus, and the sodium acetate trihydrate crystal will quickly grow and release heat. There is a very obvious boundary between the crystallization zone and the non-crystallization zone, and with the continuous growth of the crystal, the crystallization zone is continuously expanded. At this time, the crystallization can be stopped by quickly cutting the crystallization zone and the non-crystallization zone with a wet scissors. This is because the water will convert the saturated solution in the contact area between the salt gel and the scissors into an unsaturated solution, prevent the formation of new crystal nucleus in the part contacted with the foreign object, and thus stop the crystallization without inducing nucleation crystallization. And the remaining uncrystallized sodium acetate trihydrate gel will continue to remain in the supercooled state (store energy) until the next use. In addition, when the crosslinking agent is starch, a large number of hydrogen bonds generated during the gelatinization of starch endow the sodium acetate trihydrate gel with good self-healing performance, so as to ensure that the sodium acetate trihydrate gel can be used repeatedly; when the crosslinking agent is N,N-methylene bisacrylamide and ferric chloride, a large number of ionic coordination bonds are formed between the metal ions and the polymer system, so as to endow the gel with self-healing performance.

[0040] Specific embodiment two: the cellulose suspension is prepared by the following steps: the cellulose is added to the deionized water, and is homogenized at a rotation speed of 500 r / min to 10000 r / min for 5 min to 30 min to obtain the cellulose suspension. The other aspects are the same as those in the specific embodiment one.

[0041] Specific embodiment three: the cellulose is wood cellulose, cotton cellulose or bacterial cellulose, which is different from the specific embodiment one or two. The other aspects are the same as those in the specific embodiment one or two.

[0042] Specific embodiment four: the difference between this embodiment and one of the specific embodiments one to three is that the whiskered wood powder dispersion liquid is prepared by the following steps: the wood powder is immersed in a mixed aqueous solution of sodium chlorite and acetic acid, then etched at a temperature of 80-100°C for 1-12 hours, and finally washed with deionized water and dried to obtain whiskered wood powder, which is dispersed in water to obtain a whiskered wood powder dispersion liquid. The rest is the same as specific embodiments one to three.

[0043] Specific embodiment five: the difference between this embodiment and one of the specific embodiments one to four is that the mass percentage of sodium chlorite in the mixed aqueous solution of sodium chlorite and acetic acid is 1-5%, and the mass percentage of acetic acid is 0.1-1%. The rest is the same as specific embodiments one to four.

[0044] Specific embodiment six: the difference between this embodiment and one of the specific embodiments one to five is that the polymer monomer is acrylamide or a mixture of acrylamide and acrylic acid. The rest is the same as specific embodiments one to five.

[0045] Specific embodiment seven: the difference between this embodiment and one of the specific embodiments one to six is that the crosslinking agent is one or a mixture of several of N,N-methylene bisacrylamide, ferric chloride and starch. The rest is the same as specific embodiments one to six.

[0046] Specific embodiment eight: the difference between this embodiment and one of the specific embodiments one to seven is that the initiator is ammonium persulfate. The rest is the same as specific embodiments one to seven.

[0047] Specific embodiment nine: the difference between this embodiment and one of the specific embodiments one to eight is that the melted sodium acetate trihydrate, polymer monomer, crosslinking agent and stabilizer are heated and mixed at a temperature of 65-85°C for 5-30 minutes to obtain a reaction system. The rest is the same as specific embodiments one to eight.

[0048] Specific embodiment ten: the difference between this embodiment and one of the specific embodiments one to nine is that the initiator is added to the reaction system under magnetic stirring and at a temperature of 65-85°C, and after stopping stirring, it is kept for 5 minutes to 3 hours. The rest is the same as specific embodiments one to nine.

[0049] The following examples are used to verify the beneficial effects of the present application:

[0050] Example one:

[0051] A preparation method of a phase change material that can both store energy for a long time and intermittently crystallize and release heat, which is carried out according to the following steps:

[0052] 20.0 g of sodium acetate trihydrate crystals were melted at 75 °C to obtain molten sodium acetate trihydrate. The molten sodium acetate trihydrate, 4.0 g of acrylamide, 0.2 g of starch and 3.8 mL of cellulose suspension were heated and mixed for 15 min at 65 °C to obtain a reaction system. 0.23 g of ammonium persulfate was added to the reaction system under magnetic stirring at 1000 r / min and 65 °C. After stopping the stirring, the sodium acetate trihydrate gel was obtained by keeping for 2 h. The sodium acetate trihydrate gel can store energy for a long time and release heat intermittently.

[0053] The cellulose suspension is prepared by the following steps: 0.8 g of cellulose is added to 100 mL of deionized water, and homogenized at 10000 r / min for 10 min to obtain the cellulose suspension. The cellulose is cotton cellulose.

[0054] The starch is potato starch.

[0055] Figure 1 The actual pictures of the sodium acetate trihydrate gel prepared in Example 1 in the molten state, supercooled state (kept for 10 days) and crystalline state. The sodium acetate trihydrate gel prepared in Example 1 is heated to complete melting at 80 °C in an oven to obtain the molten state. The molten sodium acetate trihydrate gel is placed at room temperature, and the gel does not crystallize to reach the supercooled state, which can be kept for up to 10 days. A small amount of crystal seed is added to the supercooled sodium acetate trihydrate (kept for 10 days), and the gel begins to crystallize and releases a large amount of heat to reach the crystalline state. It is shown that the sodium acetate trihydrate gel can store energy for a long time in the supercooled state.

[0056] The supercooling phenomenon of the sodium acetate trihydrate gel prepared in Example 1 is determined by using a differential scanning calorimeter. The temperature rising and falling rates are both 5 °C / min. The temperature is first raised from 25 °C to 85 °C, then lowered from 85 °C to -30 °C, and then raised from -30 °C to 25 °C under N2 atmosphere. Figure 2 The supercooling phenomenon of the sodium acetate trihydrate gel prepared in Example 1 is determined by using a differential scanning calorimeter. The temperature rising and falling rates are both 5 °C / min. The temperature is first raised from 25 °C to 85 °C, then lowered from 85 °C to -30 °C, and then raised from -30 °C to 25 °C under N2 atmosphere. The sodium acetate trihydrate gel prepared in Example 1 has a clear endothermic peak in the heating 1 (from room temperature 25 °C to 85 °C) step, indicating that the sodium acetate trihydrate is melted and absorbs a large amount of heat. The sodium acetate trihydrate gel has no exothermic peak in the cooling 1 step, even at -35 °C, indicating that the sodium acetate trihydrate gel does not release heat, but continues to store energy in the supercooled state. The sodium acetate trihydrate gel has no exothermic peak even when heated to room temperature (25 °C) in the heating 2 step, indicating that the sodium acetate trihydrate gel can stably store energy in the supercooled state. Therefore, it can be proved that the sodium acetate trihydrate gel prepared in Example 1 is in the supercooled state at room temperature after melting by heating, rather than crystallizing, thereby storing energy for a long time.

[0057] The sodium acetate trihydrate gel prepared in Example One was heated in an oven at 80°C until completely melted to obtain a molten state. After the molten state of the sodium acetate trihydrate gel was placed at room temperature, the gel did not crystallize and reached a supercooled state to obtain a supercooled sodium acetate trihydrate gel. Figure 3 The crystallization process of the supercooled sodium acetate trihydrate gel of Example One after touching different foreign objects (crystal seeds, rubber, glass, metal). Note: 1. The supercooled sodium acetate trihydrate gel on one side will quickly produce crystal nuclei after contacting foreign objects, and the crystals will continuously grow to the other side; 2. There is a clear boundary between the crystallization zone and the non-crystallization zone during crystal growth, thereby laying the foundation for separating the crystallization zone and the non-crystallization zone with a water-wetted scissors.

[0058] Figure 4 The actual picture of the supercooled sodium acetate trihydrate gel of Example One being cut open with a water-wetted scissors and a non-water-wetted scissors, respectively; the gel cut open with the water-wetted scissors still maintains a supercooled state, while the gel cut open with the non-water-wetted scissors crystallizes due to contact-induced nucleation. It is shown that the water-wetted scissors indeed can separate the crystallization zone and the non-crystallization zone without inducing new crystallization, thereby laying the foundation for intermittent heat release. At the same time, since the water-wetted scissors has very little water on the surface, only a small part of the sodium acetate trihydrate in contact with the scissors changes from supersaturation to unsaturation, while the state and total amount of sodium acetate trihydrate do not change, so intermittent heat release only divides the continuous heat release into multiple intermittent releases, without changing the total amount of heat.

[0059] Figure 5 The highest temperature-time curve of the continuous heat release of the supercooled sodium acetate trihydrate gel of Example One. Figure 6 The highest temperature-time curve of the intermittent heat release of the supercooled sodium acetate trihydrate gel of Example One. Compared with Figure 5 Continuous heat release will continue until all the heat is released, while intermittent heat release (taking three intermittent releases as an example) will start to release heat after nucleation, with the temperature gradually increasing, but when the heat release is stopped (crystallization is stopped), the temperature will gradually decrease to room temperature, and the remaining heat will continue to be stored until the next use, repeated multiple times until all the heat is released.

[0060] Figure 7The intermittent exothermic process of the sodium acetate trihydrate gel of Example 1 was recorded by a camera and an infrared thermal imager (as an example, the intermittent exothermic process was repeated three times). First, the sodium acetate trihydrate gel in the supercooled state was rapidly crystallized and exothermed under the contact of the crystal seeds (one side of the gel was contacted with the crystal seeds), and the crystals grew from the side contacted with the crystal seeds to the other side and continued to release heat. When the exothermic process needed to be stopped, the crystallized area and the non-crystallized area were only needed to be separated by a pair of scissors dipped in water, and the crystals would not continue to grow and release heat. The remaining uncrystallized sodium acetate trihydrate gel would continue to remain in the stable supercooled state to continue to store the remaining energy. After the gel was completely crystallized after multiple intermittent exothermic processes, the gel could be reused multiple times not only because the energy could be stored again, but also because the large number of hydrogen bonds generated by the gelatinization of starch endowed the gel with good self-healing properties.

[0061] Figure 8 The self-healing properties of the sodium acetate trihydrate gel prepared in Example 1 were observed by an optical microscope, a1 is that two pieces of broken crystallized sodium acetate trihydrate gel were heated to melt and contacted, a2 is supercooled for 1 min, a3 is supercooled for 5 min, and a4 is supercooled for 10 min; the two pieces of broken crystallized sodium acetate trihydrate gel were heated to melt and contacted, and it could be seen that the two pieces of gel began to self-heal, and the wound was obvious at this time. After the melted gel was placed at room temperature and reached the supercooled state for 1 min, the wound became obviously lighter. After being supercooled for 5 min, the wound continued to fade. After being supercooled for 10 min, the wound was almost invisible, indicating that the large number of hydrogen bonds generated by the gelatinization of starch endowed the gel with good self-healing properties.

[0062] Figure 9 The self-healing properties of the sodium acetate trihydrate gel prepared in Example 1 were observed by an optical microscope, a1 is that two pieces of broken crystallized sodium acetate trihydrate gel were heated to melt and contacted, a2 is supercooled for 1 min, a3 is supercooled for 5 min, and a4 is supercooled for 10 min; the two pieces of broken crystallized sodium acetate trihydrate gel were heated to melt and contacted, and it could be seen that the two pieces of gel began to self-heal, and the wound was obvious at this time. After the melted gel was placed at room temperature and reached the supercooled state for 1 min, the wound became obviously lighter. After being supercooled for 5 min, the wound continued to fade. After being supercooled for 10 min, the wound was almost invisible, indicating that the large number of hydrogen bonds generated by the gelatinization of starch endowed the gel with good self-healing properties.

[0063] The crystallization rate of the gel was recorded by an optical microscope, and the crystallization growth rate of the gel after self-healing at the same site for 1-5 times was recorded, and each time of self-healing was 85°C heating to gel melting, and then the gel was placed at room temperature (supercooled) for 10 min; Figure 19The crystallization rate of the sodium acetate trihydrate gel prepared in Example One was recorded by optical microscope (0 times) and the crystallization growth rate of the gel after self-healing for 1-5 times at the same site was recorded; the crystallization rates were 0.065 mm / s (0 times), 0.064 mm / s, 0.057 mm / s, 0.071 mm / s, 0.068 mm / s and 0.066 mm / s, respectively. The self-healing effect was good and had little influence on the crystallization rate, as the crystallization rate did not suddenly decrease but fluctuated within a normal range. Figure 20 Figures a1, a2, a3 and a4 show the crystal growth process of the sodium acetate trihydrate gel prepared in Example One before self-healing, and figures b1, b2, b3 and b4 show the crystal growth process of the sodium acetate trihydrate gel prepared in Example One after self-healing. The crystal growth rate and morphology were not affected, although the crystal growth path needed to pass through the cutting area after self-healing. This shows that self-healing has little influence on the crystal growth.

[0064] Example Two

[0065] A preparation method of a phase change material which can store energy for a long time and release heat intermittently in crystallization, is carried out according to the following steps:

[0066] At a temperature of 75℃, 20.0 g of sodium acetate trihydrate crystals were melted to obtain molten sodium acetate trihydrate. At a temperature of 65℃, the molten sodium acetate trihydrate, 2.1 g of acrylamide, 0.8 g of acrylic acid, 0.015 g of N,N-methylene bisacrylamide, 0.08 g of ferric trichloride and 1.7 mL of whiskered wood powder dispersion liquid were heated and mixed for 15 min to obtain a reaction system. At a magnetic stirring speed of 1000 r / min and a temperature of 65℃, 0.05 g of ammonium persulfate was added to the reaction system. After stopping stirring, the system was kept at the temperature for 2 h to obtain a sodium acetate trihydrate gel, which is a phase change material which can store energy for a long time and release heat intermittently in crystallization.

[0067] The whiskered wood powder dispersion liquid is prepared according to the following steps: 60-mesh poplar wood powder was immersed in a mixed aqueous solution of sodium chlorite and acetic acid, then etched at a temperature of 60℃ for 8 h, and finally washed with deionized water and dried to obtain whiskered wood powder. 0.1 g of the whiskered wood powder was dispersed in 1.6 mL of water to obtain a whiskered wood powder dispersion liquid. The mass percentage of sodium chlorite in the mixed aqueous solution of sodium chlorite and acetic acid was 1%, and the mass percentage of acetic acid was 0.02%.

[0068] Figure 10The real photos of the molten state, supercooled state (kept for 10 days) and crystallized state of the sodium acetate trihydrate gel prepared in Example 2. The sodium acetate trihydrate gel prepared in Example 2 was heated in an oven at 80°C until completely molten to obtain the molten state. The molten sodium acetate trihydrate gel was placed at room temperature, and the gel did not crystallize, reaching the supercooled state, which can be kept for up to 10 days. A small amount of crystal seeds was added to the supercooled sodium acetate trihydrate gel (kept for 10 days), and the gel began to crystallize and released a large amount of heat to reach the crystallized state. It is shown that the sodium acetate trihydrate gel can be stored in the supercooled state for a long time to store energy.

[0069] The supercooling phenomenon of the sodium acetate trihydrate gel prepared in Example 2 was determined by using a differential scanning calorimeter. The heating and cooling rates were both 5°C / min. The sodium acetate trihydrate gel was first heated from 25°C to 85°C, then cooled from 85°C to -30°C, and then heated from -30°C to 25°C under N2 atmosphere. Figure 11 The supercooling phenomenon of the sodium acetate trihydrate gel prepared in Example 2 was determined by using a differential scanning calorimeter. The heating and cooling rates were both 5°C / min. The sodium acetate trihydrate gel was first heated from 25°C to 85°C, then cooled from 85°C to -30°C, and then heated from -30°C to 25°C under N2 atmosphere.

[0070] The sodium acetate trihydrate gel prepared in Example 2 was heated in an oven at 80°C until completely molten to obtain the molten state. The molten sodium acetate trihydrate gel was placed at room temperature, and the gel did not crystallize, reaching the supercooled state. Figure 12 The crystallization process of the supercooled sodium acetate trihydrate gel prepared in Example 2 after touching different foreign objects (crystal seeds, rubber, glass, metal). It is shown that: 1. After the side of the supercooled sodium acetate trihydrate gel touches a foreign object, the part in contact with the foreign object will quickly produce a crystal nucleus, and the crystal will continuously grow to the other side; 2. There is a clear boundary between the crystallized area and the non-crystallized area during the crystal growth process (the crystallized area is lighter in color than the non-crystallized area), thereby laying the foundation for separating the crystallized area and the non-crystallized area with a wetted scissors.

[0071] Figure 13The photographs of the sodium acetate trihydrate gel of Example 2 being cut by the wet scissors and the dry scissors, respectively. The gel cut by the wet scissors still keeps the supercooled state, while the gel cut by the dry scissors crystallizes due to the contact-induced nucleation. It is proved that the wet scissors can separate the crystalline region and the non-crystalline region without inducing new crystallization, which lays the foundation for the intermittent heat release. At the same time, since the water on the surface of the wet scissors is very small, only a small part of the sodium acetate trihydrate in contact with the scissors changes from supersaturation to unsaturation, while the state and total amount of sodium acetate trihydrate do not change, so the intermittent heat release only divides the continuous heat release into multiple intermittent releases, without changing the total amount of heat.

[0072] Figure 14 The highest temperature-time curve of the continuous heat release of the sodium acetate trihydrate gel of Example 2. Figure 15 The highest temperature-time curve of the intermittent heat release of the sodium acetate trihydrate gel of Example 2. Compared with Figure 14 The continuous heat release will continue until all the heat is released, while the intermittent heat release (taking three intermittent heat releases as an example) will start to release heat after nucleation, and the temperature will gradually rise as the crystal grows. However, when the heat release is stopped (crystallization is stopped), the temperature will gradually decrease to room temperature, and the remaining heat will continue to be stored until the next use, repeated multiple times until all the heat is released.

[0073] Figure 16 The intermittent heat release process (taking three intermittent heat releases as an example) of the sodium acetate trihydrate gel of Example 2 recorded by photographs and infrared thermal imaging instrument. First, the supercooled sodium acetate trihydrate gel crystallizes and releases heat rapidly under the contact of the crystal seed (contacting one side of the gel), and the crystal grows from the side of the crystal seed contact to the other side, and continues to release heat. When the heat release needs to be stopped, the crystalline region and the non-crystalline region are separated by the wet scissors, and the crystal will not continue to grow and release heat. The remaining uncrystallized sodium acetate trihydrate gel will continue to maintain a stable supercooled state to continue to store the remaining energy. After multiple intermittent heat releases, the gel is completely crystallized. After heating again, not only can the energy be stored again, but also the large number of hydrogen bonds of the gelatinized starch endow the gel with good self-healing property, so that the gel can be repeatedly used multiple times.

[0074] Figure 17To observe the self-healing performance of the sodium acetate trihydrate gel prepared in Example 2 by optical microscope, a1 is to heat the two broken pieces of crystalline sodium acetate trihydrate gel to melt and contact, a2 is to supercool for 1 min, a3 is to supercool for 3 min, and a4 is to supercool for 5 min. The two broken pieces of crystalline sodium acetate trihydrate gel are heated to melt and contact, and it can be seen that the two pieces of gel begin to self-heal, and at this time the wound is more obvious. After the melted gel is placed at room temperature and reaches the supercool state for 1 min, the wound becomes obviously lighter. After 3 min of supercooling, the wound continues to fade. After 5 min of supercooling, the wound is almost invisible.

[0075] Figure 18 The actual picture of the self-healing performance of the sodium acetate trihydrate gel prepared in Example 2, a is to splice the three broken pieces of crystalline sodium acetate trihydrate gel, b is to heat the three broken pieces of crystalline sodium acetate trihydrate gel to melt and then place at room temperature, and c is to stretch the gel in b to 1.5 times the length of itself. The three broken pieces of crystalline sodium acetate trihydrate gel are spliced and heated to melt and then placed at room temperature, and almost no self-healing wound can be seen. The self-healing gel is stretched to 1.5 times the length of itself, and the gel does not break, indicating that the large number of hydrogen bonds generated by starch gelatinization endow the gel with good self-healing properties.

[0076] The crystallization rate of the gel and the crystallization growth rate of the gel at the same site after self-healing 1-5 times are recorded by optical microscope, and each self-healing is heating at 85°C to melt the gel, and then placing the gel at room temperature (supercooling) for 10 min; Figure 21 The crystallization rate of the gel prepared in Example 2 (0 times) and the crystallization growth rate of the gel at the same site after self-healing 1-5 times are recorded by optical microscope; the crystallization rates are 0.30 mm / s (0 times), 0.30 mm / s, 0.29 mm / s, 0.31 mm / s, 0.31 mm / s and 0.29 mm / s, respectively. The crystallization rate does not suddenly drop, but fluctuates within a normal range, indicating that the self-healing effect is very good and almost has no impact on the crystallization rate. Figure 22 The picture of the crystal growth process of the sodium acetate trihydrate gel prepared in Example 2 before and after healing is observed by optical microscope, a1 is the crystal growth 0s before healing, a2 is the crystal growth 2s before healing, a3 is the crystal growth 3s before healing, a4 is the crystal growth 4s before healing, b1 is the crystal growth 0s after healing, b2 is the crystal growth 2s after healing, b3 is the crystal growth 3s after healing, and b4 is the crystal growth 4s after healing. Although the crystal growth path needs to pass through the cutting area after self-healing, the crystal growth rate and morphology are not affected. This indicates that self-healing has almost no impact on crystal growth.

Claims

1. A method for preparing a phase change material that can both store energy for a long time and release heat through intermittent crystallization, characterized in that... It is done in the following steps: Sodium acetate trihydrate crystals are heated and melted to obtain molten sodium acetate trihydrate. The molten sodium acetate trihydrate, polymer monomer, crosslinking agent and stabilizer are heated and mixed for 10 min to 30 min to obtain a reaction system. An initiator is added to the reaction system and the temperature is maintained to obtain a phase change material that can store energy for a long time and can intermittently crystallize and release heat. The mass ratio of sodium acetate trihydrate crystals to polymer monomers is 1:(0.1-0.5); the mass ratio of sodium acetate trihydrate crystals to crosslinking agent is 1:(0.002-0.02); the mass ratio of sodium acetate trihydrate crystals to stabilizer is 1g:(0.002-0.3)mL; and the mass ratio of sodium acetate trihydrate crystals to initiator is 1:(0.002-0.015). The stabilizer is a cellulose suspension with a concentration of 0.001 g / mL to 0.2 g / mL or a whisker-like wood powder dispersion with a concentration of 0.05 g / mL to 0.2 g / mL; The cellulose suspension is prepared by the following steps: cellulose is added to deionized water and homogenized for 5 min to 30 min at a rotation speed of 500 r / min to 10000 r / min to obtain the cellulose suspension. The whisker-like wood powder dispersion is prepared by the following steps: wood powder is immersed in a mixed aqueous solution of sodium chlorite and acetic acid, then etched at a temperature of 80℃~100℃ for 1h~12h, and finally washed and dried with deionized water to obtain whisker-like wood powder. The whisker-like wood powder is then dispersed in water to obtain the whisker-like wood powder dispersion. The crosslinking agent is ferric chloride or starch.

2. The method for preparing a phase change material that can both store energy for a long time and release heat through intermittent crystallization, as described in claim 1, is characterized in that... The cellulose mentioned is wood cellulose, cotton cellulose, or bacterial cellulose.

3. The method for preparing a phase change material that can both store energy for a long time and release heat through intermittent crystallization, as described in claim 1, is characterized in that... The sodium chlorite and acetic acid mixed aqueous solution contains 1% to 5% sodium chlorite by mass and 0.1% to 1% acetic acid by mass.

4. The method for preparing a phase change material that can both store energy for a long time and release heat through intermittent crystallization according to claim 1, characterized in that... The polymer monomer is acrylamide or a mixture of acrylamide and acrylic acid.

5. The method for preparing a phase change material that can both store energy for a long time and release heat through intermittent crystallization according to claim 1, characterized in that... The initiator is ammonium persulfate.

6. The method for preparing a phase change material that can both store energy for a long time and release heat through intermittent crystallization according to claim 1, characterized in that... Under conditions of 65℃~85℃, molten sodium acetate trihydrate, polymer monomer, crosslinking agent and stabilizer are heated and mixed for 5min~30min to obtain the reaction system.

7. The method for preparing a phase change material that can both store energy for a long time and release heat through intermittent crystallization according to claim 1, characterized in that... Under magnetic stirring and at a temperature of 65℃~85℃, an initiator is added to the reaction system, and the temperature is maintained for 5min~3h after stirring is stopped.

Images