High-enthalpy-value phase-change gel material for cold-chain transportation and preparation method of high-enthalpy-value phase-change gel material

Abstract

The invention discloses a high-enthalpy-value phase-change gel material for cold-chain transportation. The high-enthalpy-value phase-change gel material is prepared from 25-30% by weight of n-alkane, 1-3% by weight of a surfactant, 3-4% by weight of polyvinyl alcohol, 1-3% by weight of a cross-linking agent, 0.05-0.1% by weight of a nano-material coordination agent and the balance of water through a gel method. The surfactant is one or a mixture of more of span 80, Tween 80, triton X-100, OP-10, SP-60 and monostearin; the surfactant is one or a mixture of more of the span 80, the Tween 80, the triton X-100, the OP-10, the SP-60 and the monostearin; the invention further discloses a preparation method of the high-enthalpy-value phase-change gel material for cold-chain transportation, the high-enthalpy-value phase-change gel material is prepared through emulsion preparation, polyvinyl alcohol dissolution, nanometer material coordination agent dispersion, initial phase-change gel forming and mold shaping, and the preparation process is simple. The phase-change gel material is high in enthalpy value, good in thermal cycling stability, not prone to leakage, high in supercooling degree, nonflammable and wide in phase-change temperature range, can be subjected to phase-change regulation and control at any temperature within the range of-20 DEG C to 60 DEG C, is suitable for cold-chain transportation and can also be used in the fields of medical temperature control and other industrial thermal management.

Description

Technical Field

[0001] The present invention belongs to the technical field of phase change materials, and in particular relates to a high enthalpy phase change gel material for cold chain transportation and a preparation method thereof. Background Art

[0002] Phase change energy storage materials enable transported goods such as food, medicine, and biological products to maintain a stable low-temperature environment throughout the entire process, and are key materials for cold chain transportation. Phase change energy storage materials mainly include inorganic salt hydrates and organic phase change materials. Among them, the phase change enthalpy of inorganic salt hydrates (such as calcium chloride hexahydrate and sodium sulfate decahydrate) is less than 200 J / g. During cold chain transportation, multiple melt-solidification cycles cause their structure to be destroyed or phase separated, resulting in the decay of phase change enthalpy and thermal stability, which directly affects cold chain transportation; for example, the patent with publication number CN103756645A, entitled Cold Chain Transportation Phase Change Material and Preparation Method thereof, discloses a cold chain transportation phase change material based on sodium sulfate, water, ammonium chloride and other components, whose phase change enthalpy is only 193.4 J / g, and the performance decays after multiple thermal cycles, which cannot meet the requirements of long-term efficient energy storage and cold chain transportation. The enthalpy value of organic phase change materials is relatively high, generally greater than 250J / g. During use, the phase change enthalpy value decreases due to the volatilization of low molecular weight components, or incomplete crystallization occurs in an overcooled environment, resulting in unstable phase change temperature, which affects the temperature control in cold chain transportation. In addition, leakage is prone to occur when melted, increasing the packaging and use costs. Flammability is also a safety hazard of organic phase change materials in cold chain transportation. For example, a patent with publication number CN1657587A, entitled "A Method for Preparing Microencapsulated Shaped Phase Change Materials", discloses a phase change material using paraffin and two resins, polystyrene and polyethylene, as supporting materials for mixed encapsulation by heating and melting. The phase change temperature of the material is adjustable from 0°C to 70°C, but due to the use of microencapsulation technology, the maximum phase change enthalpy is 138kJ / kg, and there are low packaging efficiency and insufficient mechanical strength during long-term use, resulting in leakage. In addition, different cold chain application scenarios have different temperature requirements for phase change materials, and the temperature control range of organic phase change materials is limited. For example, vaccine and blood transportation requires a stable temperature zone of 2 to 8°C, while special drugs or biological preparations require a phase change temperature close to 37°C. Summary of the invention

[0003] In view of the shortcomings of existing cold chain phase change energy storage materials, the present invention provides a high enthalpy phase change gel material for cold chain transportation, which has high enthalpy value, good thermal cycle stability, is not easy to leak, has a high degree of supercooling, is not flammable, and has a wide phase change temperature (-20°C to 60°C), and a preparation method thereof.

[0004] The present invention adopts the following technical solutions: A high enthalpy phase change gel material for cold chain transportation is prepared by a gel method, comprising 25-30%wt of normal alkanes, 1-3%wt of surfactants, 3-4%wt of polyvinyl alcohol, 1-3%wt of cross-linking agents, 0.05-0.1%wt of nanomaterial ligands, and the remainder being water; the surfactant is one or a mixture of several of Span 80, Tween 80, Triton X-100, OP-10, SP-60, and monoglycerides.

[0005] Furthermore, the normal alkane is one or a mixture of n-dodecane, n-tetradecane, n-hexadecane, n-octadecane and n-eicosane.

[0006] Furthermore, the cross-linking agent is one or a mixture of sodium borate decahydrate, maleic acid, silicon dioxide, trisodium trimetaphosphate or xanthan gum.

[0007] Furthermore, the average molecular weight of the polyvinyl alcohol is 600-800.

[0008] Furthermore, the nano material complexing agent is a compound of one or more of graphene oxide, graphene, carbon nanotubes, boron nitride, boron carbide, titanium carbide, aluminum oxide, and magnesium oxide.

[0009] The present invention also provides a method for preparing a high enthalpy phase change gel material for cold chain transportation, comprising the following steps: (1) Preparation of emulsion: Place water in a reactor, add surfactant and stir until completely dissolved, gradually add n-alkane while continuously stirring, heat to 30°C~70°C, and stir at high speed until the emulsion is evenly dispersed; (2) Dissolving polyvinyl alcohol: gradually add polyvinyl alcohol to the emulsion of step (1), heat to 80-95° C., and stir at 400-600 rpm until completely dissolved; (3) Dispersing the nanomaterial ligand: gradually add the nanomaterial ligand to the polyvinyl alcohol solution in step (2) and stir at high speed for 10 to 20 minutes; (4) Initial phase change gel formation: The solution of step (3) was cooled to 50°C, and the cross-linking agent was gradually added and stirred at 400-600 rpm for 10 minutes; (5) Mold shaping: Pour the initial phase change gel from step (4) into a mold and let it stand at 0°C to -10°C for shaping.

[0010] Furthermore, the high-speed stirring in step (1) and step (3) of the present invention is 8000-10000 rpm.

[0011] Beneficial effects of the present invention: (1) The present invention improves the latent heat storage efficiency and melting enthalpy of the phase change material by optimizing the emulsion preparation, the synergistic effect of normal alkanes and polyvinyl alcohol, the gel cross-linking and low-temperature setting processes; (2) The alkane emulsion of the present invention and polyvinyl alcohol synergistically form a stable eutectic system, which maintains dynamic equilibrium during the phase change process, effectively reduces internal stress, reduces structural damage, and significantly improves the stability of the phase change material; (3) The alkane emulsion in the eutectic system of the present invention has good compatibility with the water phase, and the phase change material is evenly distributed in the gel network to form a dense and stable solid microstructure, which not only effectively encapsulates the phase change substrate to prevent leakage, but also optimizes the thermal conductivity. The phase change gel material can still maintain stable phase change latent heat and phase change temperature in multiple melting-solidification cycles, and maintain good thermal stability throughout the cold chain transportation process; (4) The present invention reduces the supercooling of the phase change material by adding a nanomaterial ligand, and the supercooling is reduced from 20°C to 4°C, which effectively improves the crystallization nucleation rate and promotes the stable crystallization of the phase change material in a low temperature environment. Through DSC (differential scanning calorimetry) testing, the optimized material melting enthalpy value is 280 J / g~310J / g, and after 100 freeze-thaw cycles, its phase change temperature does not change by more than 3°C, which enhances the temperature control stability and reusability during cold chain transportation.

[0012] (5) The phase change gel material of the present invention can be controlled at any temperature within the range of -20°C to 60°C, which is suitable for cold chain transportation, and can also be used in medical temperature control and other industrial thermal management fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 is a flow chart of the preparation process of the present invention; Figure 2 This is a physical picture of the phase change gel material of Example 1 of the present invention; Figure 3 This is a graph showing the morphological stability of the phase change gel material of Example 1 of the present invention at 25°C; Figure 4 This is a SEM electron microscope image of the phase change gel material after low temperature drying in Example 3 of the present invention; Figure 5 This is a diagram of the enthalpy value of the thermal performance of the phase change gel material of Example 3 of the present invention; Figure 6 This is a flame retardancy test diagram of the phase change gel material of Example 1 of the present invention; Figure 7 The figure is a diagram showing the influence of different normal alkanes on the melting phase transition enthalpy and melting phase transition temperature used in the present invention; Figure 8 This is a diagram showing the effect of adding nanomaterials (graphene oxide) on the supercooling of phase change gel; Fig. 9 The melting phase change enthalpy and melting phase change temperature diagram of the phase change gel materials of Examples 1 to 4; Fig.10 Graphs showing the crystallization phase change enthalpy and crystallization phase change temperature of the phase change gel materials of Examples 1 to 4. DETAILED DESCRIPTION

[0014] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. It should be understood that the present application is not limited to the example embodiments disclosed herein. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present application. Example 1

[0015] like Figure 1 As shown, a method for preparing a high enthalpy phase change gel material for cold chain transportation comprises the following steps: (1) Preparation of emulsion: 67 g of water was placed in a reaction vessel, 2 g of Span 60 and 1 g of Triton X-100 were gradually added and stirred until completely dissolved, the mixture was heated to 50°C, 30 g of n-tetradecane was gradually added under continuous stirring, the mixture was heated to 50°C, and the mixture was stirred at 8000 rpm for 20 min to obtain a stable emulsion; (2) Dissolving polyvinyl alcohol: gradually add 4 g of PVA 1799 to the emulsion of step (1), heat to 85°C, and stir at 500 rpm until completely dissolved; (3) Phase change gel formation: The solution of step (2) was cooled to 50°C, 1.5 g of sodium borate decahydrate was gradually added, and the system was stirred at 400 rpm for 10 min to crosslink and form a gel; (4) Mold shaping: Pour the obtained gel into a mold and let it stand at -5°C for 24 h to obtain the following Figure 2 Phase change gel material shown.

[0016] like Figure 3As shown in the figure, the phase change gel material prepared by the present invention is placed on a heating table at 25°C. After 24 hours, it still maintains good gel stability and no liquid leakage. The thermal imaging image on the right further verifies the thermal response process of the material. The temperature in the initial state (0 min) is relatively low. As time goes by (1 min, 5 min, 10 min, 20 min, 40 min), the gel gradually heats up to 25°C, but still maintains good stability in its original morphology and no liquefaction flow occurs (the phase change temperature of the phase change gel material is 0°C, and theoretically it is in a completely melted state at 25°C). The phase change gel material of this embodiment still maintains a stable solid morphology in an environment far higher than the phase change temperature, and no liquid leakage occurs. It is suitable for applications such as cold chain transportation that have strict requirements on leakage control of phase change materials. Figure 6 As shown in the flame retardancy test of the phase change gel material of the present invention, under the action of open flame, the material did not burn violently within 0s to 20s, only slightly carbonized, and had no obvious flame spread phenomenon. The flame retardant performance is excellent and the safety is high, which effectively reduces the fire risk of the phase change material during use; Figure 7 As shown in the figure, compared with pure alkanes, the phase change enthalpy of the phase change gel material after gelation is high, among which the phase change enthalpy of n-tetradecane gel and n-octadecane gel are both higher than their corresponding pure alkanes, reaching up to more than 300 J / g. Example 2

[0017] like Figure 1 As shown, a method for preparing a high enthalpy phase change gel material for cold chain transportation comprises the following steps: (1) Preparation of emulsion: Place 67 g of water in a reaction vessel, gradually add 2 g of Span 60 and 1 g of Triton X-100, and stir until completely dissolved. Heat to 50°C, gradually add 30 g of n-octadecane while stirring continuously, heat to 50°C, and stir at 8000 rpm for 20 min to obtain a stable emulsion.

[0018] (2) Dissolution of polyvinyl alcohol: gradually add 4 g of PVA 1799 to the emulsion of step (1), heat to 85°C, and stir at 500 rpm until completely dissolved.

[0019] (3) Phase change gel formation: The solution of step (2) was cooled to 50°C, 1.5 g of sodium borate decahydrate was gradually added, and the system was stirred at 400 rpm for 10 min to crosslink and form a gel.

[0020] (4) Mold shaping: Pour the obtained gel into the mold and let it stand at -5°C for 24 h to shape; Example 3

[0021] like Figure 1As shown, a method for preparing a high enthalpy phase change gel material for cold chain transportation comprises the following steps: (1) Preparation of emulsion: Place 67 g of water in a reaction vessel, gradually add 2 g of Span 60 and 1 g of Triton X-100, and stir until completely dissolved. Heat to 50°C, gradually add 30 g of n-tetradecane under continuous stirring, heat to 50°C, and stir at 8000 rpm for 20 min to obtain a stable emulsion.

[0022] (2) Dissolution of polyvinyl alcohol: gradually add 4 g of PVA 1799 to the emulsion of step (1), heat to 85°C, and stir at 500 rpm until completely dissolved.

[0023] (3) Nanomaterial dispersion: Add 0.1 g of graphene oxide to the solution in step (2) and stir at 10,000 rpm for 15 min to uniformly disperse it.

[0024] (4) Phase change gel formation: The solution of step (3) was cooled to 50°C, 1.5 g of sodium borate decahydrate was gradually added, and the system was stirred at 400 rpm for 10 min to cross-link and form a gel.

[0025] (5) Mold shaping: Pour the obtained gel into a mold and let it stand at -5°C for 24 h to shape.

[0026] like Figure 4 As shown, after graphene oxide (GO) is added to the gel material prepared by the present invention, the gel network becomes more dense and uniform, forming a stable three-dimensional cross-linked structure, improving the packaging ability of the phase change substrate, enhancing the morphological stability and anti-leakage ability of the material, and maintaining good structural integrity during multiple phase change cycles, and having high safety and reliability in cold chain transportation; Figure 5 The phase change behavior of the gel prepared in the present invention during the heating (black) and cooling (red) processes. After adding graphene oxide (GO), the melting temperature and crystallization temperature of the phase change material are consistent, which improves the temperature control accuracy, cycle stability and long-term usability of the phase change material in cold chain transportation; Figure 8 As shown in the figure, the material without GO (black) shows a large supercooling phenomenon during the cooling process, and the crystallization temperature is significantly lower than the melting temperature. After adding GO (red), the supercooling is significantly reduced. The addition of GO promotes the nucleation process, accelerates the crystallization rate, and makes the phase transition temperature more stable. Example 4

[0027] like Figure 1 As shown, a method for preparing a high enthalpy phase change gel material for cold chain transportation comprises the following steps: (1) Preparation of emulsion: Place 67 g of water in a reaction vessel, gradually add 2 g of Span 60 and 1 g of Triton X-100, and stir until completely dissolved. Heat to 50°C, gradually add 30 g of n-octadecane while stirring continuously, heat to 50°C, and stir at 8000 rpm for 20 min to obtain a stable emulsion.

[0028] (2) Dissolution of polyvinyl alcohol: gradually add 4 g of PVA 1799 to the emulsion of step (1), heat to 85°C, and stir at 500 rpm until completely dissolved.

[0029] (3) Nanomaterial dispersion: Add 0.1 g of graphene oxide to the solution obtained in step (2) and stir at 10,000 rpm for 15 min to uniformly disperse it.

[0030] (4) Phase change gel formation: The solution of step (3) was cooled to 50°C, 1.5 g of sodium borate decahydrate was gradually added, and the mixture was stirred at 400 rpm for 10 min to allow the system to crosslink and form a gel.

[0031] (5) Mold shaping: Pour the obtained gel into a mold and let it stand at -5°C for 24 h to shape. Comparative Example 1

[0032] A method for preparing a PVA phase change gel material comprises the following steps: (1) Dissolution of polyvinyl alcohol: Place 100 g of water in a reaction vessel, gradually add 3 g of PVA 1799, heat to 85 °C, and stir at 500 rpm until completely dissolved; (2) Phase change gel formation: The obtained solution was cooled to 50 °C, 1.5 g of sodium borate decahydrate was gradually added, and the mixture was stirred at 400 rpm for 10 min to cross-link and form a gel; (3) Mold shaping: Pour the obtained gel into a mold and let it stand at -5°C for 24 h to shape. Comparative Example 2

[0033] A method for preparing a n-tetradecane phase change emulsion material for cold chain transportation comprises the following steps: Place 67 g of water in a reaction vessel, gradually add 2 g of Span 60 and 1 g of Triton X-100, and stir until completely dissolved. Heat to 50°C, gradually add 30 g of n-tetradecane under continuous stirring, heat to 50°C, and stir at 8000 rpm for 20 min to obtain a stable phase change emulsion. Comparative Example 3

[0034] A method for preparing a n-tetradecane phase change emulsion material for cold chain transportation comprises the following steps: Place 67 g of water in a reaction vessel, gradually add 2 g of Span 60 and 1 g of Triton X-100, and stir until completely dissolved. Heat to 50°C, gradually add 30 g of n-octadecane under continuous stirring, heat to 50°C, and stir at 8000 rpm for 20 min to obtain a stable emulsion.

[0035] DSC performance test: Using NETZSCH DSC3500 equipment, in a nitrogen atmosphere, the heating / cooling cycle was tested at a rate of 10°C / min for phase change enthalpy; Morphological stability test: Place the material in a constant temperature environment of 30°C for 24 hours and observe the changes in the material structure; Cyclic stability test: Place the material in a high and low temperature cycle box and set the program to cycle 100 times from -30℃ to 50℃. After the program is completed, take samples for DSC testing.

[0036] Table 1 Test results of various properties of phase change gel materials of Examples 1 to 4 and Comparative Examples 1 to 3

[0037] From Table 1 and Fig. 9 It can be seen that the high enthalpy phase change gel material of the present invention significantly improves the morphological stability and avoids liquid phase leakage compared with the traditional emulsion system (Comparative Example 2, Comparative Example 3), and is suitable for cold chain transportation to maintain stability for a long time; compared with the traditional PVA gel (Comparative Example 1), the synergistic effect of the alkane emulsion and PVA increases the phase change enthalpy value, and the phase change enthalpy value is increased by more than 20% (from 260 J / g to 314 J / g). The present invention can also flexibly adjust the phase change temperature by adjusting the type and amount of alkane, and adjust it from 0°C (suitable for cold chain) to 26°C (suitable for human body temperature control) to meet different application requirements.

[0038] Depend on Fig. 9 and Fig.10 It can be seen that the gel material with added graphene oxide (GO) (Example 3, Example 4) effectively reduced the supercooling. Compared with the system without GO addition (19°C, 26°C), GO reduced the supercooling to 4°C and 8°C, improved the crystallization process, and improved the thermal cycle stability. GO optimized the phase change process, reduced the supercooling, improved the thermal cycle stability and enhanced the morphological stability, making the phase change gel material more suitable for application scenarios with high reliability requirements such as cold chain transportation.

[0039] The high enthalpy phase change gel material of the present invention is suitable for cold chain transportation, medical temperature control, industrial heat dissipation and electronic equipment thermal management and other fields. The phase change temperature is adjustable in the temperature range of -20°C to 60°C, and the adjustment range is wide.

[0040] The above embodiments are merely descriptions of preferred implementation modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A high enthalpy phase change gel material for cold chain transportation, characterized in that: The invention is prepared by a gel method from 25-30%wt normal alkane, 1-3%wt surfactant, 3-4%wt polyvinyl alcohol, 1-3%wt cross-linking agent, 0.05-0.1%wt nano material ligand and the balance water; the surfactant is one or a mixture of several of Span 80, Tween 80, Triton X-100, OP-10, SP-60 and monoglyceride.

2. The high enthalpy phase change gel material for cold chain transportation according to claim 1, characterized in that: The normal alkane is one or a mixture of n-dodecane, n-tetradecane, n-hexadecane, n-octadecane and n-eicosane.

3. The high enthalpy phase change gel material for cold chain transportation according to claim 1, characterized in that: The cross-linking agent is one or a mixture of sodium borate decahydrate, maleic acid, silicon dioxide, trisodium trimetaphosphate or xanthan gum.

4. The high enthalpy phase change gel material for cold chain transportation according to claim 1, characterized in that: The average molecular weight of the polyvinyl alcohol is 600-800.

5. The high enthalpy phase change gel material for cold chain transportation according to claim 1, characterized in that: The nano material ligand is a compound of one or more of graphene oxide, graphene, carbon nanotubes, boron nitride, boron carbide, titanium carbide, aluminum oxide, and magnesium oxide.

6. The method for preparing a high enthalpy phase change gel material for cold chain transportation according to any one of claims 1 to 5, characterized in that: The following steps are involved: (1) Preparation of emulsion: Place water in a reactor, add surfactant and stir until completely dissolved, gradually add n-alkane while continuously stirring, heat to 30°C~70°C, and stir at high speed until the emulsion is evenly dispersed; (2) Dissolving polyvinyl alcohol: gradually add polyvinyl alcohol to the emulsion of step (1), heat to 80-95° C., and stir at 400-600 rpm until completely dissolved; (3) Dispersing the nanomaterial ligand: gradually add the nanomaterial ligand to the polyvinyl alcohol solution in step (2) and stir at high speed for 10 to 20 minutes; (4) Initial phase change gel formation: The solution of step (3) was cooled to 50°C, and the cross-linking agent was gradually added and stirred at 400-600 rpm for 10 minutes; (5) Mold shaping: Pour the initial phase change gel from step (4) into a mold and let it stand at 0°C to -10°C for shaping.

7. The preparation method according to claim 6, characterized in that: The high-speed stirring in step (1) and step (3) is 8000-10000 rpm.

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