A composite phase-change hydrogel and preparation method thereof

Abstract

A composite phase-change hydrogel and its preparation method belong to the field of phase-change material technology, overcoming the defect in the prior art that the high addition amount of inorganic hydrated salts can cause hydrogel dehydration. The composite phase-change hydrogel of the present invention comprises, in terms of raw materials by mass percentage, 0.5-5% inorganic hydrated salts, 85-89.5% water, 5-6% polyvinyl alcohol-1799, 2.5-3% borax, and 0.1-1% molecular sieves. Molecular sieves are added to the system of the present invention to confine the inorganic hydrated salts within the molecular sieve pores, so that the inorganic hydrated salts do not directly contact the hydrogel, thereby avoiding hydrogel dehydration. At the same time, a large number of pores can accommodate more inorganic hydrated salts, thereby increasing the amount of inorganic hydrated salts added, thereby increasing the insulation time of the composite phase-change hydrogel material. Polyvinyl alcohol-1799 and borax form a three-dimensional network structure, which can effectively prevent sodium sulfate decahydrate from phase separation with the hydrogel after melting, thereby improving the stability of the composite phase-change hydrogel.

Description

Technical Field

[0001] The present invention belongs to the technical field of phase change materials, and in particular relates to a composite phase change hydrogel and a preparation method thereof. Background Art

[0002] Overexploitation of traditional fossil fuels and large-scale carbon emissions have led to a series of problems, including global warming and sea level rise, severely restricting socioeconomic development. Renewable energy, due to its clean and sustainable nature, has garnered significant attention. However, the development and application of sustainable energy sources such as solar and wind power are hampered by time and space constraints, hindering their availability around the clock and preventing efficient energy utilization and timely storage. Therefore, finding efficient energy storage materials is crucial to addressing the energy supply and demand mismatch.

[0003] Phase change energy storage materials, as a functional material with high energy storage and high energy saving, have attracted the attention of relevant researchers. The heat storage technology of phase change energy storage materials includes sensible heat storage, chemical energy storage and latent heat storage. The small system scale of sensible heat storage and the complex reaction process of chemical energy storage limit its large-scale application. The heat storage capacity of latent heat storage mainly depends on the latent heat value of the phase change material itself, and energy conversion is carried out by utilizing the absorption and release of energy during the physical state transformation. In addition, phase change materials can maintain a constant temperature during the phase change process, have a high heat storage density, high safety, easy design, and convenient use. They can achieve efficient use of energy, and therefore have broad application prospects in the fields of solar thermal utilization, waste heat recovery, electricity "peak shifting and valley filling", thermal management systems and building energy conservation.

[0004] Phase change energy storage materials can be divided into low-temperature (<100°C), medium-temperature (100-300°C), and high-temperature (>300°C) phase change materials according to the phase change temperature of the material. According to the composition of the material, it can be divided into organic (paraffin, fatty acids, esters, etc.) and inorganic (salt metals and alloys, hydrated salts) phase change materials. Compared with organic phase change energy storage technology, inorganic hydrated salt phase change energy storage technology utilizes the latent heat of medium and low-temperature phase change materials to store and release energy through heat absorption and heat release during melting and crystallization. It has the advantages of high energy storage density, wide energy storage temperature range, low cost, and stable performance.

[0005] However, single-component inorganic hydrated salts as phase change energy storage materials have high phase transition temperatures, all above 40°C, which often cannot meet the target wide temperature range refrigeration requirements. Furthermore, when inorganic hydrated salts are combined with other materials to prepare composite phase change hydrogel materials, the compatibility of inorganic hydrated salts with other phase change materials is poor. High additions of inorganic hydrated salts can lead to hydrogel dehydration, resulting in a low content of inorganic hydrated salt phase change variants per unit mass of the composite phase change material. This, in turn, results in a low energy storage capacity of the composite phase change material, limiting its practical application. Summary of the Invention

[0006] Therefore, the technical problem to be solved by the present invention is to overcome the defect in the prior art that a high amount of inorganic hydrated salt added will lead to dehydration of the hydrogel, thereby providing a composite phase change hydrogel and a preparation method thereof.

[0007] To this end, the present invention provides the following technical solutions.

[0008] On the one hand, the present invention provides a composite phase change hydrogel, the raw materials of which are calculated by mass percentage and include: inorganic hydrated salt: 0.5-5%, water: 85-89.5%, polyvinyl alcohol-1799: 5-6%, borax: 2.5-3%, and molecular sieve: 0.1-1%.

[0009] Furthermore, the inorganic hydrated salt includes at least one of sodium sulfate decahydrate, disodium hydrogen sulfate dodecahydrate, and ferric chloride hexahydrate.

[0010] Furthermore, the molecular sieve is at least one of Silicalite-1 molecular sieve, SBA-15 molecular sieve and ZSM-5 molecular sieve.

[0011] Furthermore, the preparation method of the Silicalite-1 molecular sieve comprises:

[0012] A. Mix the template, silicon source and water;

[0013] B. heating the solution obtained in step A to crystallize and separate the solid and liquid;

[0014] C. calcining the solid obtained in step B to obtain Silicalite-1 molecular sieve.

[0015] Furthermore, the template includes tetrapropylammonium hydroxide and tetrapropylammonium bromide, and the mass ratio thereof is (0.12-0.16): (0.05-0.12).

[0016] Furthermore, the silicon source includes gas-phase SiO2, white carbon black and ethyl orthosilicate, and the mass ratio thereof is (0.8-1.2): (0-0.1): (0.1-0.2);

[0017] Furthermore, the temperature for heating and crystallization in step B is 175-180° C. and the time is 24-26 hours;

[0018] Furthermore, in step C, the calcination temperature is 520-550° C., and the calcination time is 5.5-6 h.

[0019] In a second aspect, the present invention provides a method for preparing a composite phase change hydrogel, comprising the following steps:

[0020] Step 1, mixing an inorganic hydrated salt, polyvinyl alcohol-1799, molecular sieves and water to obtain a solution A;

[0021] Step 2, mixing borax and water to obtain solution B;

[0022] Step 3: adding solution B to solution A to react and obtain the composite phase change hydrogel.

[0023] Furthermore, the step 1 comprises: mixing an inorganic hydrated salt, polyvinyl alcohol-1799, molecular sieves and water, stirring the mixture at room temperature for 25 to 30 minutes, and then heating and stirring the mixture at 92 to 98° C. for 1.5 to 2 hours to obtain solution A.

[0024] Furthermore, step 2 includes mixing borax and water and stirring at 60-65° C. for 1-1.2 hours to obtain solution B;

[0025] and / or

[0026] The step 3 comprises adding solution B into solution A, stirring for 0.5-1 min, and then standing at 90-100° C. for 3-6 h to remove air bubbles, thereby obtaining the composite phase change hydrogel.

[0027] The technical solution of the present invention has the following advantages:

[0028] 1. The composite phase change hydrogel provided by the present invention comprises, by weight percentage, the following raw materials: inorganic hydrated salt: 0.5-5%, water: 85-89.5%, polyvinyl alcohol-1799: 5-6%, borax: 2.5-3%, and molecular sieve: 0.1-1%.

[0029] The system of the present invention incorporates molecular sieves, which confine inorganic hydrated salts within the pores of the molecular sieves. This prevents direct contact between the inorganic hydrated salts and the hydrogel, thus preventing hydrogel dehydration when high levels of inorganic water and salt are added. Furthermore, the large number of pores can accommodate more inorganic hydrated salts, thereby increasing the amount of inorganic hydrated salt added, thereby increasing the latent heat of the composite phase-change hydrogel material and extending the heat retention time.

[0030] Polyvinyl alcohol-1799 and borax form a three-dimensional network structure with a large number of voids, which allows the addition of a higher content of molecular sieves. The formed hydrogel can be structurally optimized so that a higher content of molecular sieves can be added to the composite system, thereby achieving a stronger ability to absorb molten inorganic hydrated salts. In addition, its network structure can effectively prevent sodium sulfate decahydrate from phase separation from the hydrogel after melting, thereby improving the stability of the composite phase change hydrogel. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0032] Figure 1 DSC curves of Control Example 1 and Examples 1 to 3;

[0033] Figure 2 This is the DSC curve of Example 3. DETAILED DESCRIPTION

[0034] The following examples are provided for a better understanding of the present invention and are not intended to limit the best mode of implementation. They do not limit the content and scope of protection of the present invention. Any product identical or similar to the present invention obtained by anyone under the guidance of the present invention or by combining the features of the present invention with other prior arts shall fall within the scope of protection of the present invention.

[0035] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in this field can be used. If the manufacturer of the reagents or instruments is not specified, they are all commercially available conventional reagents.

[0036] The preparation method of the Silicalite-1 molecular sieve used in the Examples and Comparative Examples comprises the following steps:

[0037] Step A: 0.15 g of tetrapropylammonium hydroxide, 0.1 g of tetrapropylammonium bromide and 90 g of deionized water were mixed and the solution was stirred until uniform. A silicon source (1 g of fumed SiO2, 0.1 g of white carbon black and 0.15 g of ethyl orthosilicate) was then added to the solution and magnetically stirred at room temperature for 6 hours.

[0038] Step B: Place the solution obtained in step A into a stainless steel autoclave, set the drying oven temperature to 180°C, and crystallize for 24 hours. After the autoclave cools to room temperature, remove the reaction solution and centrifuge it at 10,000 rpm for 10 minutes until the pH value of the solution reaches neutral;

[0039] Step C: Dry the sample after centrifugal washing in step B at 120° C. for 5 hours, and then calcine it in a muffle furnace at 550° C. for 6 hours to obtain Silicalite-1 molecular sieve.

[0040] Example 1

[0041] This embodiment provides a method for preparing a composite phase-change hydrogel material, comprising the following steps:

[0042] 0.5 g of sodium sulfate decahydrate, 6 g of polyvinyl alcohol-1799, 1 g of Silicalite-1 molecular sieve, and 66 g of water were placed in a beaker and stirred at room temperature for 30 minutes until the polyvinyl alcohol-1799 was fully swollen. The mixture was then placed in a water bath, heated to 95° C., and heated and stirred at 95° C. for 2 hours until the polyvinyl alcohol-1799 was completely dissolved, to obtain solution A. Solution A now contained a large number of small bubbles and appeared to be in a flowing gel-like state.

[0043] Put 3g of borax and 23.5g of water into a beaker, then place the beaker in a water bath, heat to 60℃ and stir at 60℃ for 1 hour to dissolve all the borax to obtain solution B. At this time, solution B is a milky white liquid;

[0044] Solution B was added to Solution A, producing a milky white substance. Stirring with a glass rod for one minute resulted in the solution losing its fluidity and becoming a transparent, jelly-like substance containing numerous small bubbles. The solution was then placed in a 100°C water bath and allowed to stand for six hours. The bubbles were eliminated, resulting in a transparent, flowable gel, the final product. The prepared hydrogel was transparent above 20°C and milky white below 20°C.

[0045] Example 2

[0046] This embodiment provides a method for preparing a composite phase-change hydrogel material, comprising the following steps:

[0047] 3 g of sodium sulfate decahydrate, 6 g of polyvinyl alcohol-1799, 1 g of Silicalite-1 molecular sieve, and 63.5 g of water were placed in a beaker and stirred at room temperature for 30 minutes until the polyvinyl alcohol-1799 was fully swollen. The mixture was then placed in a water bath, heated to 95° C., and heated and stirred at 95° C. for 2 hours until the polyvinyl alcohol-1799 was completely dissolved, to obtain solution A. Solution A now contained a large number of small bubbles and appeared to be in a flowing gel-like state.

[0048] Put 3g of borax and 23.5g of water into a beaker, then place the beaker in a water bath, heat to 60℃ and stir at 60℃ for 1 hour to dissolve all the borax to obtain solution B. At this time, solution B is a milky white liquid;

[0049] Solution B was added to Solution A, producing a milky white substance. Stirring with a glass rod for one minute resulted in the solution losing its fluidity and becoming a transparent, jelly-like substance containing numerous small bubbles. The solution was then placed in a 100°C water bath and allowed to stand for six hours. The bubbles were then eliminated, resulting in a transparent, flowable gel, the final product. The prepared hydrogel was transparent above 50°C and milky white below 50°C.

[0050] Example 3

[0051] This embodiment provides a method for preparing a composite phase-change hydrogel material, comprising the following steps:

[0052] 5 g of sodium sulfate decahydrate, 6 g of polyvinyl alcohol-1799, 1 g of Silicalite-1 molecular sieve, and 61.5 g of water were placed in a beaker and stirred at room temperature for 30 minutes until the polyvinyl alcohol-1799 was fully swollen. The mixture was then placed in a water bath, heated to 95° C., and heated and stirred at 95° C. for 2 hours until the polyvinyl alcohol-1799 was completely dissolved, to obtain solution A. Solution A now contained a large number of small bubbles and appeared to be in a flowing gel-like state.

[0053] Put 3g of borax and 23.5g of water into a beaker, then place the beaker in a water bath, heat to 60℃ and stir at 60℃ for 1 hour to dissolve all the borax to obtain solution B. At this time, solution B is a milky white liquid;

[0054] Solution B was added to Solution A, producing a milky white substance. Stirring with a glass rod for one minute resulted in the solution losing its fluidity and becoming a transparent, jelly-like substance containing numerous small bubbles. The solution was then placed in a 100°C water bath and allowed to stand for six hours. The bubbles were then eliminated, resulting in a transparent, flowable gel, the final product. The prepared hydrogel was transparent above 70°C and milky white below 70°C.

[0055] Example 4

[0056] This embodiment provides a method for preparing a composite phase-change hydrogel material, comprising the following steps:

[0057] 5 g of sodium sulfate decahydrate, 6 g of polyvinyl alcohol-1799, 1 g of Silicalite-1 molecular sieve, and 61.5 g of water were placed in a beaker and stirred at room temperature for 30 minutes until the polyvinyl alcohol-1799 was fully swollen. The mixture was then placed in a water bath, heated to 95° C., and heated and stirred at 95° C. for 2 hours until the polyvinyl alcohol-1799 was completely dissolved, to obtain solution A. Solution A now contained a large number of small bubbles and appeared to be in a flowing gel-like state.

[0058] Put 3g of borax and 23.5g of water into a beaker, then place the beaker in a water bath, heat to 60℃ and stir at 60℃ for 1 hour to dissolve all the borax to obtain solution B. At this time, solution B is a milky white liquid;

[0059] Solution B was added to Solution A, producing a milky white substance. Stirring with a glass rod for one minute resulted in the solution losing its fluidity and becoming a transparent, jelly-like substance containing numerous small bubbles. The solution was then placed in a 100°C water bath and allowed to stand for three hours. The upper layer of the solution became covered with small bubbles, while the lower layer became a transparent, flowable gel, yielding the final product. The prepared hydrogel was transparent above 70°C and milky white below 70°C.

[0060] Example 5

[0061] This embodiment provides a method for preparing a composite phase-change hydrogel material, comprising the following steps:

[0062] 5 g of sodium sulfate decahydrate, 6 g of polyvinyl alcohol-1799, 1 g of Silicalite-1 molecular sieve, and 61.5 g of water were placed in a beaker and stirred at room temperature for 30 minutes until the polyvinyl alcohol-1799 was fully swollen. The mixture was then placed in a water bath, heated to 95° C., and heated and stirred at 95° C. for 2 hours until the polyvinyl alcohol-1799 was completely dissolved, to obtain solution A. Solution A now contained a large number of small bubbles and appeared to be in a flowing gel-like state.

[0063] Put 3g of borax and 23.5g of water into a beaker, then place the beaker in a water bath, heat to 60℃ and stir at 60℃ for 1 hour to dissolve all the borax to obtain solution B. At this time, solution B is a milky white liquid;

[0064] Solution B was added to Solution A, producing a milky white substance. Stirring with a glass rod for 30 seconds resulted in the solution losing its fluidity and becoming a transparent, jelly-like substance containing numerous small bubbles. The solution was then placed in a 100°C waterbath and allowed to stand for 6 hours, at which point the bubbles were eliminated, resulting in a transparent, flowable gel. The resulting hydrogel was transparent above 70°C, but partially milky white and transparent below 70°C.

[0065] Example 6

[0066] This embodiment provides a method for preparing a composite phase-change hydrogel material, comprising the following steps:

[0067] 5 g of sodium sulfate decahydrate, 6 g of polyvinyl alcohol-1799, 1 g of Silicalite-1 molecular sieve, and 61.5 g of water were placed in a beaker and stirred at room temperature for 30 minutes until the polyvinyl alcohol-1799 was fully swollen. The mixture was then placed in a water bath, heated to 95° C., and heated and stirred at 95° C. for 2 hours until the polyvinyl alcohol-1799 was completely dissolved, to obtain solution A. Solution A now contained a large number of small bubbles and appeared to be in a flowing gel-like state.

[0068] Put 3g of borax and 23.5g of water into a beaker, then place the beaker in a water bath, heat to 60℃ and stir at 60℃ for 1 hour to dissolve all the borax to obtain solution B. At this time, solution B is a milky white liquid;

[0069] Solution B was added to Solution A, producing a milky white substance. Stirring with a glass rod for one minute resulted in the solution losing its fluidity and becoming a transparent, jelly-like substance containing numerous small bubbles. The solution was then placed in a 90°C water bath and allowed to stand for six hours. The upper layer of the solution became covered with small bubbles, while the lower layer became a transparent, flowable gel, yielding the final product. The prepared hydrogel was transparent above 70°C and milky white below 70°C.

[0070] Example 7

[0071] This embodiment provides a method for preparing a composite phase-change hydrogel material, comprising the following steps:

[0072] 5 g of sodium sulfate decahydrate, 6 g of polyvinyl alcohol-1799, 1 g of Silicalite-1 molecular sieve, and 61.5 g of water were placed in a beaker, which was then placed in a water bath. The temperature was raised to 95° C. and heated and stirred at 95° C. for 2 hours until the polyvinyl alcohol-1799 was completely dissolved, to obtain solution A. Solution A contained white flocculent matter and appeared to be a flowing gel.

[0073] Put 3g of borax and 23.5g of water into a beaker, then place the beaker in a water bath, heat to 60℃ and stir at 60℃ for 1 hour to dissolve all the borax to obtain solution B. At this time, solution B is a milky white liquid;

[0074] Solution B was added to Solution A, producing a milky white substance. Stirring with a glass rod for one minute resulted in the solution losing its fluidity and becoming a translucent gel containing numerous small bubbles. The solution was then placed in a 100°C water bath and allowed to stand for six hours, at which point the bubbles were eliminated, resulting in a flowable, translucent gel. The resulting hydrogel was translucent above 70°C and partially milky white below 70°C.

[0075] Example 8

[0076] This embodiment provides a method for preparing a composite phase-change hydrogel material, comprising the following steps:

[0077] 3 g of sodium sulfate decahydrate, 6 g of polyvinyl alcohol-1799, 1 g of SBA-15 molecular sieve, and 63.5 g of water were placed in a beaker and stirred at room temperature for 30 minutes until the polyvinyl alcohol-1799 was fully swollen. The mixture was then placed in a water bath, heated to 95° C., and heated and stirred at 95° C. for 2 hours until the polyvinyl alcohol-1799 was completely dissolved, to obtain solution A. Solution A now contained a large number of small bubbles and appeared to be a flowing gel.

[0078] Put 3g of borax and 23.5g of water into a beaker, then place the beaker in a water bath, heat to 60℃ and stir at 60℃ for 1 hour to dissolve all the borax to obtain solution B. At this time, solution B is a milky white liquid;

[0079] Solution B was added to Solution A, producing a milky white substance. Stirring with a glass rod for one minute resulted in the solution losing its fluidity and becoming a transparent, jelly-like substance containing numerous small bubbles. The solution was then placed in a 100°C water bath and allowed to stand for six hours. The bubbles were then eliminated, resulting in a transparent, flowable gel, the final product. The prepared hydrogel was transparent above 50°C and milky white below 50°C.

[0080] Example 9

[0081] This embodiment provides a method for preparing a composite phase-change hydrogel material, comprising the following steps:

[0082] 3 g of sodium sulfate decahydrate, 6 g of polyvinyl alcohol-1799, 1 g of ZSM-5 molecular sieve, and 63.5 g of water were placed in a beaker and stirred at room temperature for 30 minutes until the polyvinyl alcohol-1799 was fully swollen. The beaker was then placed in a water bath, heated to 95° C., and heated and stirred at 95° C. for 2 hours until the polyvinyl alcohol-1799 was completely dissolved, to obtain solution A. Solution A now contained a large number of small bubbles and appeared to be a flowing gel.

[0083] Put 3g of borax and 23.5g of water into a beaker, then place the beaker in a water bath, heat to 60℃ and stir at 60℃ for 1 hour to dissolve all the borax to obtain solution B. At this time, solution B is a milky white liquid;

[0084] Solution B was added to Solution A, producing a milky white substance. Stirring with a glass rod for one minute resulted in the solution losing its fluidity and becoming a transparent, jelly-like substance containing numerous small bubbles. The solution was then placed in a 100°C water bath and allowed to stand for six hours. The bubbles were then eliminated, resulting in a transparent, flowable gel, the final product. The prepared hydrogel was transparent above 50°C and milky white below 50°C.

[0085] Comparative Example 1

[0086] This comparative example provides a method for preparing a composite phase-change hydrogel material, comprising the following steps:

[0087] 6 g of polyvinyl alcohol-1799, 1 g of Silicalite-1 molecular sieve, and 66.5 g of water were placed in a beaker and stirred at room temperature for 30 minutes until the polyvinyl alcohol-1799 was fully swollen. The mixture was then placed in a water bath, heated to 95°C, and heated and stirred at 95°C for 2 hours until the polyvinyl alcohol-1799 was completely dissolved, to obtain solution A. Solution A contained a large number of small bubbles and appeared to be a flowing gel.

[0088] Put 3g of borax and 23.5g of water into a beaker, then place the beaker in a water bath, heat to 60℃ and stir at 60℃ for 1 hour to dissolve all the borax to obtain solution B. At this time, solution B is a milky white liquid;

[0089] Solution B was added to Solution A and stirred with a glass rod for 1 minute. The solution lost its fluidity and became a transparent gel containing numerous small bubbles. The solution was then placed in a 100°C water bath and allowed to stand for 6 hours. The bubbles were then removed from the solution, resulting in a flowable, transparent gel. This hydrogel remained transparent at any temperature.

[0090] Comparative Example 2

[0091] This comparative example provides a method for preparing a composite phase-change hydrogel material, comprising the following steps:

[0092] 5 g of sodium sulfate decahydrate, 6 g of polyvinyl alcohol-1799, and 61.5 g of water were placed in a beaker and stirred at room temperature for 30 minutes until the polyvinyl alcohol-1799 was fully swollen. The beaker was then placed in a water bath, heated to 95° C., and heated and stirred at 95° C. for 2 hours until the polyvinyl alcohol-1799 was completely dissolved, to obtain solution A. Solution A now contained a large number of small bubbles and appeared to be a flowing gel.

[0093] Put 3g of borax and 23.5g of water into a beaker, then place the beaker in a water bath, heat to 60℃ and stir at 60℃ for 1 hour to dissolve all the borax to obtain solution B. At this time, solution B is a milky white liquid;

[0094] Solution B was added to Solution A, producing a milky white substance. Stirring with a glass rod for one minute resulted in the solution losing its fluidity and becoming a translucent gel and water, containing numerous small bubbles. The solution was then placed in a 100°C waterbath and allowed to stand for six hours, at which point the bubbles disappeared, leaving the solution as a flowable, translucent gel and water, yielding the final product. The prepared hydrogel was translucent above 70°C, but below 70°C, it was partially milky white, partially transparent, and partially water.

[0095] Comparative Example 3

[0096] This comparative example provides a method for preparing a composite phase-change hydrogel material, comprising the following steps:

[0097] 5 g of sodium sulfate decahydrate, 6 g of polyvinyl alcohol-1788, 1 g of Silicalite-1 molecular sieve, and 61.5 g of water were placed in a beaker and stirred at room temperature for 30 minutes until the polyvinyl alcohol-1799 was fully swollen. The mixture was then placed in a water bath, heated to 95°C, and heated and stirred at 95°C for 2 hours until the polyvinyl alcohol-1799 was completely dissolved, to obtain solution A. Solution A now contained a large number of small bubbles and appeared to be in a flowing gel-like state.

[0098] Put 3g of borax and 23.5g of water into a beaker, then place the beaker in a water bath, heat to 60℃ and stir at 60℃ for 1 hour to dissolve all the borax to obtain solution B. At this time, solution B is a milky white liquid;

[0099] Solution B was added to solution A and stirred with a glass rod for 1 minute. At this time, the solution was not gelled. Then it was placed in a 100°C water bath and allowed to stand for 6 hours. At this time, the small bubbles in the solution were drained out and the solution was transparent but did not form a gel.

[0100] Comparative Example 4

[0101] This comparative example provides a method for preparing a composite phase-change hydrogel material, comprising the following steps:

[0102] 5 g of sodium sulfate decahydrate, 6 g of polyethyleneimine (BASF, polymin SN), 1 g of Silicalite-1 molecular sieve, and 61.5 g of water were placed in a beaker and stirred at room temperature for 30 minutes until the polyvinyl alcohol-1799 was fully swollen. The mixture was then placed in a water bath, heated to 95° C., and heated and stirred at 95° C. for 2 hours until the polyvinyl alcohol-1799 was completely dissolved, to obtain solution A. Solution A now contained a large number of small bubbles and appeared to be in a flowing gel-like state.

[0103] Put 3g of borax and 23.5g of water into a beaker, then place the beaker in a water bath, heat to 60℃ and stir at 60℃ for 1 hour to dissolve all the borax to obtain solution B. At this time, solution B is a milky white liquid;

[0104] Solution B was added to solution A and stirred with a glass rod for 1 minute. At this time, the solution was not gelled. Then it was placed in a 100°C water bath and allowed to stand for 6 hours. At this time, the small bubbles in the solution were drained out and the solution was transparent but did not form a gel.

[0105] Comparative Example 5

[0106] This comparative example provides a method for preparing a composite phase-change hydrogel material, comprising the following steps:

[0107] 5 g of sodium sulfate decahydrate, 6 g of polyvinyl alcohol-1799, 1 g of Silicalite-1 molecular sieve, and 61.5 g of water were placed in a beaker and stirred at room temperature for 30 minutes until the polyvinyl alcohol-1799 was fully swollen. The mixture was then placed in a water bath, heated to 95° C., and heated and stirred at 95° C. for 2 hours until the polyvinyl alcohol-1799 was completely dissolved, to obtain solution A. Solution A now contained a large number of small bubbles and appeared to be in a flowing gel-like state.

[0108] Put 3g of glutaraldehyde and 23.5g of water into a beaker, then place the beaker in a water bath, heat to 60℃ and stir at 60℃ for 1 hour to dissolve all the borax to obtain solution B. At this time, solution B is a milky white liquid;

[0109] Add solution B to solution A and stir with a glass rod for 1 minute. The solution will be milky white and colloidal. Then place it in a 100°C water bath and let it stand for 6 hours. The small bubbles in the solution will be drained away, and the solution will be translucent but contain a large amount of water.

[0110] Performance Testing

[0111] The hydrogels prepared in the examples and control examples were subjected to DSC testing to analyze the phase change process. The instrument used for the DSC test of the hydrogel was a differential scanning calorimeter (DSC 204F1Phoenix 240-12-0246-L) produced by NETZSCH, Germany. The test procedure adopted for the DSC test of the hydrogel was as follows: under a nitrogen atmosphere, the sample was equilibrated at 50°C for 2 minutes, and then the temperature was raised and lowered in the order of 50°C, -50°C, 50°C, -50°C, and 50°C at a rate of 5°C / min, and the temperature was kept at that temperature for 2 minutes.

[0112] The test results are shown in Table 1.

[0113] Table 1 DSC test data analysis results of composite phase change hydrogel materials

[0114]

[0115] The DSC curves of Control Example 1, Example 1, Example 2 and Example 3 are shown in FIG. Figure 1-Figure 2 As shown in Table 1, the addition of sodium sulfate decahydrate is beneficial to increasing the latent heat value of the composite phase change hydrogel material, and as the content of sodium sulfate decahydrate increases, the latent heat value of the composite phase change hydrogel material increases.

[0116] It can be seen from Control Example 2 and Example 3 that adding Silicalite-1 molecular sieve to the composite phase change hydrogel material can increase the content of sodium sulfate decahydrate per unit mass of the composite phase change hydrogel material while avoiding dehydration, thereby improving the latent heat value of the composite phase change hydrogel material.

[0117] By comparing Examples 3-6, it can be seen that when solution B and solution A are mixed and cross-linked, the optimal stirring time is 1 minute, the optimal degassing temperature is 100° C., and the optimal degassing time is 6 hours.

[0118] It can be seen from Examples 3 and 7 that when preparing Solution A, it is necessary to stir in air for 30 minutes to allow the polyvinyl alcohol-1799 to fully swell and further increase the latent heat.

[0119] From Example 3 and Comparative Examples 3-5, it can be seen that polyvinyl alcohol-1799 solution is more sensitive to gelation induced by borax, polyethyleneimine or polyvinyl alcohol-1788 cannot form gel as a matrix, and glutaraldehyde as a coagulant still causes hydrogel dehydration.

[0120] Therefore, the best embodiment of the present invention is embodiment 3. The composite phase change hydrogel material prepared by embodiment 3 has good stability and the maximum phase change latent heat value.

[0121] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A composite phase change hydrogel, characterized in that: The raw materials, calculated by mass percentage, include: inorganic hydrated salt: 0.5-5%, water: 85-89.5%, polyvinyl alcohol-1799: 5-6%, borax: 2.5-3%, molecular sieve: 0.1-1%; The inorganic hydrated salt includes at least one of sodium sulfate decahydrate, disodium hydrogen sulfate dodecahydrate, and ferric chloride hexahydrate; The molecular sieve is at least one of Silicalite-1 molecular sieve, SBA-15 molecular sieve and ZSM-5 molecular sieve; The preparation method of the composite phase change hydrogel comprises the following steps: Step 1, mixing an inorganic hydrated salt, polyvinyl alcohol-1799, molecular sieves and water to obtain a solution A; Step 2, mixing borax and water to obtain solution B; Step 3: adding solution B to solution A to react and obtain the composite phase change hydrogel.

2. The composite phase change hydrogel according to claim 1, characterized in that The preparation method of the Silicalite-1 molecular sieve comprises: A. Mix the template, silicon source and water; B. heating the solution obtained in step A to crystallize and separate the solid and liquid; C. calcining the solid obtained in step B to obtain Silicalite-1 molecular sieve.

3. The composite phase change hydrogel according to claim 2, characterized in that: The template comprises tetrapropylammonium hydroxide and tetrapropylammonium bromide in a mass ratio of (0.12-0.16): (0.05-0.12); and / or The silicon source includes gas-phase SiO2, white carbon black and ethyl orthosilicate, and the mass ratio thereof is (0.8-1.2): (0-0.1): (0.1-0.2).

4. The composite phase change hydrogel according to claim 2, characterized in that: The temperature for heating and crystallization in step B is 175-180° C., and the time is 24-26 hours.

5. The composite phase-change hydrogel according to claim 2, characterized in that: In step C, the calcination temperature is 520-550° C. and the calcination time is 5.5-6 hours.

6. The composite phase-change hydrogel according to claim 1, characterized in that: The step 1 comprises: mixing an inorganic hydrated salt, polyvinyl alcohol-1799, molecular sieves and water, stirring the mixture at room temperature for 25 to 30 minutes, and then heating and stirring the mixture at 92 to 98° C. for 1.5 to 2 hours to obtain solution A.

7. The composite phase-change hydrogel according to claim 1, characterized in that: The step 2 comprises mixing borax and water and stirring the mixture at 60-65° C. for 1-1.2 hours to obtain a solution B; and / or The step 3 comprises adding solution B into solution A, stirring for 0.5-1 min, and then standing at 90-100° C. for 3-6 h to remove air bubbles, thereby obtaining the composite phase change hydrogel.

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