Phase change compound, phase change material and preparation method thereof

Abstract

The invention belongs to the technical field of phase change materials, and discloses a phase change compound, a phase change material and a preparation method thereof.The phase change compound comprises 40-60 wt% of organic modified boron nitride and 40-60 wt% of biomass porous carbon, and the organic modified boron nitride is polydopamine modified hydroxylated boron nitride. Through polydopamine modified hydroxylated boron nitride and biomass porous carbon, the effect of synergistically improving the heat conduction performance of paraffin can be achieved, the fluidity of paraffin can be further inhibited, and the overall stability and heat conduction performance of the phase change material are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of phase change materials, in particular to a phase change composite, a phase change material and a preparation method thereof. BACKGROUND

[0002] As the core unit of thermal energy storage, the research and development of phase change materials are crucial to the improvement of the heat storage capacity of thermal energy storage system. There are still significant defects in the practical application of phase change materials, which affect their working time and efficiency. The core problem is the insufficient thermal conductivity, and most organic PCMs (such as paraffin, fatty acid) have low thermal conductivity coefficients (usually <0.5 W / m·K), which leads to slow phase change process and limited energy storage / release efficiency.

[0003] The above problems have been solved by the background technology of prior art 1: Chinese patent application 200810154238.4, and new technical problems have been brought about: the reported preparation of shaped phase change materials has a high mass percentage of additives and a low percentage of paraffin-based heat storage materials, which inevitably reduces the phase change enthalpy and increases the proportion of support materials and additives. The use of complex preparation processes such as grafting or microencapsulation increases the cost.

[0004] Prior art 1 uses paraffin as a heat storage material and a spatial network structure formed by small molecule gelators as a support material for paraffin to solve the technical problem, but based on the development of technology, the technology that simply relies on paraffin for phase change has produced new problems. Paraffin has poor thermal conductivity and is prone to melting and spilling, which can cause a sharp decline in the working time and efficiency of the phase change material after long-term use. Therefore, it is necessary to develop a phase change material that can effectively improve the thermal conductivity of paraffin and effectively prevent paraffin from leaking, thereby improving the performance of the phase change material. SUMMARY

[0005] One of the purposes of the present application is to provide a phase change composite that effectively improves the thermal conductivity of paraffin while effectively preventing paraffin from melting and spilling by compounding organic modified boron nitride with biomass porous carbon.

[0006] Another purpose of the present application is to provide a phase change material that uses two types of paraffin with different phase change temperatures to construct a dual-control temperature binary system through the synergy of the phase change composite of the present application.

[0007] To achieve the above purpose, the present application provides a phase change composite, which comprises 40-60wt% organic modified boron nitride and 40-60wt% biomass porous carbon, and the organic modified boron nitride is polydopamine modified hydroxylated boron nitride.

[0008] Further, the preparation method of the organic modified boron nitride is as follows:

[0009] Step 1: hydroxylated boron nitride is obtained by hydroxylating boron nitride;

[0010] Step 2: the hydroxylated boron nitride is dispersed in a mixture of water and anhydrous ethanol, and a Tris buffer solution with pH = 8.5 is added to adjust the pH to 8.3-8.7;

[0011] Step 3: the mixture is ultrasonically treated, dopamine hydrochloride is added and fully reacted, and after the reaction is completed, it is cooled to room temperature, and then centrifuged to obtain a precipitate, which is washed with anhydrous ethanol and ultrapure water alternately for at least 3 times.

[0012] Preferably, the specific operation of step 1 is as follows: 1 g of boron nitride powder is weighed, 50 ml of mixed acid (HNO3:H2SO4 = 1:3, v / v) is added, and it is placed in a three-necked flask with a condenser, the oil bath temperature is controlled at 80-120℃, and it is refluxed and stirred for 4-24 h; after the reaction, it is cooled to room temperature, diluted with 100 ml of deionized water, and centrifuged to obtain a precipitate; the precipitate is repeatedly washed with deionized water until the supernatant pH = 6-7, and then washed with anhydrous ethanol; vacuum drying at 60-80℃ for 12-24 h to obtain hydroxylated boron nitride.

[0013] Further, the preparation method of the biomass porous carbon is as follows: the biomass is washed, dried, crushed, sieved to obtain biomass powder, a chemical activator is added, and carbonization activation is carried out under nitrogen protection, then it is taken out after cooling, washed and dried to obtain biomass porous carbon.

[0014] Preferably, the biomass is one of straw or sawdust.

[0015] Preferably, the preparation method of the biomass porous carbon comprises the following specific steps: the biomass is stirred and washed with anhydrous ethanol and deionized water until the washing liquid is not obviously turbid; then it is dried at 60-80℃ for 12-24 h; after drying, it is crushed by a high-speed universal crusher at a crushing speed of 8000-12000 rpm for 5-10 min, sieved through a 80-200 mesh sieve to obtain biomass powder; the chemical activator is added to the biomass powder at a mass ratio of 1:1-4, and reacted at 500-800℃ for 1-3 h, washed with deionized water for 2-3 times, and vacuum dried at 60-80℃ for 8-12 h to obtain biomass porous carbon.

[0016] Further, the chemical activator comprises one of sodium hydroxide, potassium hydroxide and zinc chloride.

[0017] The application also provides a phase change material, which comprises two or more paraffins with different phase change temperatures and the phase change composite described above, and the content of the phase change composite is 10-20wt%.

[0018] Preferably, the phase change material comprises 40-45wt% paraffin wax with a phase change temperature of 37℃, 40-45wt% paraffin wax with a phase change temperature of 46℃ and 10-20wt% of the phase change composite.

[0019] The application also provides a preparation method of the phase change material, comprising the following steps:

[0020] Step a: melt paraffin wax with a phase change temperature of 37℃ and paraffin wax with a phase change temperature of 46℃ at 80℃, and then add organic modified boron nitride to the mixture to obtain a mixture;

[0021] Step b: maintain 80℃, add biomass porous carbon to the mixture and stir until uniform, and then cool to room temperature to obtain the phase change material.

[0022] Advantages

[0023] Compared with the prior art, the application provides a phase change composite, which can produce a synergistic effect of improving the heat conduction performance of paraffin wax by using hydroxylated boron nitride modified by polydopamine and biomass porous carbon, and can further inhibit the flowability of paraffin wax, so as to improve the overall stability and heat conductivity of the phase change material. DETAILED DESCRIPTION

[0024] The application will be further described below in combination with examples, but does not constitute any limitation on the application, and any limited modification made within the scope of the claims of the application is still within the scope of the claims of the application.

[0025] In order to illustrate the technical content of the application, the following further illustrates the application in combination with the embodiments.

[0026] In the following examples and comparative examples, the hydroxylated boron nitride is prepared by the following steps:

[0027] 1 g of boron nitride powder is weighed, 50 ml of mixed acid (HNO3: H2SO4 = 1: 3, v / v) is added, and the three-necked flask is placed in an oil bath with a condenser, the temperature is controlled at 100±5 ℃, and the reflux is stirred for 14 h; after the reaction, it is cooled to room temperature, and 100 ml of deionized water is slowly added for dilution, and the precipitate is centrifuged; the precipitate is washed repeatedly with deionized water until the pH of the supernatant is 6.5±0.1, and then washed with anhydrous ethanol; vacuum drying at 60-80 ℃ for 18 h to obtain hydroxylated boron nitride.

[0028] Unless otherwise specified, the parts in the following examples and comparative examples are weight parts, and the % is weight percent.

[0029] Example 1

[0030] A phase change composite, consisting of 40 parts of organic modified boron nitride and 60 parts of biomass porous carbon;

[0031] The organic modified boron nitride is prepared by the following steps:

[0032] The hydroxylated boron nitride is dispersed in a mixture of water and anhydrous ethanol, and a Tris buffer solution with pH = 8.5 is added to adjust the pH to 8.5 ± 0.2;

[0033] Step 3: The mixture is ultrasonically treated, and dopamine hydrochloride is added for sufficient reaction (reaction in a constant temperature shaking bed at 37°C in the dark for 24 h to form a polydopamine coating layer), and after the reaction is completed, it is cooled to room temperature, and then centrifuged to obtain a precipitate, which is washed with anhydrous ethanol and ultrapure water alternately for 3 times;

[0034] The biomass porous carbon is prepared by the following steps:

[0035] The biomass (purchased from Binzhou Huoyue Grass Co., Ltd.) is sequentially washed with anhydrous ethanol and deionized water until the washing liquid is not obviously turbid; then dried at 70 ± 5°C for 18h; after drying, the biomass powder is obtained by crushing treatment with a high-speed universal crusher at a crushing speed of 10000rpm for 10min, and sieving through a 100 mesh sieve; according to the mass ratio of biomass powder to chemical activator sodium hydroxide (purchased from Foshan Sanzhong Environmental Protection Technology Co., Ltd.) of 1:1, the chemical activator sodium hydroxide is added to the biomass powder, and reacted at 700°C for 2h, washed with deionized water for 3 times, and vacuum dried at 70 ± 5°C for 10h to obtain the biomass porous carbon.

[0036] Example 2

[0037] Generally the same as Example 1, except that it consists of 50 parts of organic modified boron nitride and 50 parts of biomass porous carbon.

[0038] Example 3

[0039] Generally the same as Example 1, except that it consists of 60 parts of organic modified boron nitride and 40 parts of biomass porous carbon.

[0040] Comparative Example 1

[0041] Generally the same as Example 2, except that the organic modified boron nitride is prepared by the following steps:

[0042] The boron nitride is dispersed in a mixture of water and anhydrous ethanol, and a Tris buffer solution with pH = 8.5 is added to adjust the pH to 8.5 ± 0.2;

[0043] Step 3: ultrasonic treatment of the mixed solution, addition of dopamine hydrochloride for sufficient reaction, cooling to room temperature after completion of the reaction, and then centrifugation to obtain a precipitate, which is washed with anhydrous ethanol and ultrapure water alternately for 3 times.

[0044] Comparative Example 2

[0045] The same as Example 2, except that the organic modified boron nitride is replaced by hydroxylated boron nitride.

[0046] Comparative Example 3

[0047] The same as Example 2, except that the biomass porous carbon is replaced by porous carbon (purchased from Suzhou Kefan New Material Technology Co., Ltd., porous carbon powder series, model BK2020120205, specific surface area 200 m 2 / g).

[0048] Comparative Example 4

[0049] The same as Example 2, except that the organic modified boron nitride is replaced by boron nitride.

[0050] Application Example

[0051] The phase change composites of Examples 1-3 and Comparative Examples 1-3 are prepared into phase change materials, and the amount of the phase change composite is 10wt%, and the preparation method is as follows:

[0052] Step a: 45wt% paraffin with a phase change temperature of 37℃ and 45wt% paraffin with a phase change temperature of 46℃ are subjected to 80℃ melting treatment, and after complete melting, organic modified boron nitride or hydroxylated boron nitride is added for mixing to obtain a mixture;

[0053] Step b: maintain 80℃ and add biomass porous carbon or porous carbon to the mixture and stir uniformly, and then cool to room temperature to obtain the phase change material.

[0054] Performance Test

[0055] I. Thermal conductivity

[0056] The obtained phase change material is poured into a mold to obtain a block-shaped phase change material under the action of a 3 MP press. A thermal conductivity measuring instrument based on the transient hot wire method is used to test the sample. Two samples with uniform thickness, a thickness of not less than 0.3 mm and a smooth surface are prepared. At room temperature, the sample is completely attached to the upper and lower surfaces of the hot wire chip, and the sample is pressed against the hot wire chip with a weight. The hot wire chip is heated using a step constant heat flow, and the temperature rise of the hot wire chip and the sample is generated. The thermal conductivity value of the sample can be obtained by the temperature rise of the hot wire chip (reference Yang Hongwei, Hu Yuxia, Chen Ming. Method for measuring thermal conductivity of composite material by transient hot wire method [J]. High-tech fibers and applications, 2018, 43(02): 45-51.).

[0057] The phase change materials prepared from Examples 1-3 and Comparative Examples 1-3 are tested according to the above method, and the results are shown in Table 1.

[0058] Table 1 Thermal conductivity performance results of phase change materials prepared from Examples 1-3 and Comparative Examples 1-3

[0059] Thermal conductivity (W / (m·K)) Example 1 7.80 Example 2 8.21 Example 3 8.55 Comparative Example 1 5.09 Comparative Example 2 4.43 Comparative Example 3 4.37 Comparative Example 4 3.22

[0060] According to the results in Table 1, it can be seen that:

[0061] The phase change composites prepared from Examples 1-3 can all exhibit excellent thermal conductivity performance, and the thermal conductivity performance of Example 3 is better, which is speculated to be due to the fact that the organic modified boron nitride plays a stronger role in improving the thermal conductivity performance of the entire composition.

[0062] According to the data comparison of Comparative Examples 1, 2 and 4, compared with the technical solution of Comparative Example 4 which simply uses boron nitride and biomass porous carbon, Comparative Examples 1 and 2 respectively modify boron nitride with hydrochloric acid dopamine and hydroxylation, which can improve the thermal conductivity performance of the phase change material to a certain extent. However, when the boron nitride is treated by organic modification and hydroxylation, the thermal conductivity performance generated when it is compounded with biomass porous carbon is significantly higher than that of Comparative Examples 1 and 2, which is speculated to be as follows:

[0063] (1) When the residual groups on the surface of the biomass porous carbon contact with the polar groups such as polydopamine and hydroxyl groups, the hydrogen bonds and electrostatic interactions between the groups make them tightly combined, so that the organic modified boron nitride is well anchored in the inner wall or surface of the porous carbon pores, rather than freely agglomerated in the paraffin, reducing the interfacial gap between "boron nitride-porous carbon" and "boron nitride-paraffin", and reducing the interfacial thermal resistance, laying a foundation for the subsequent continuous construction of the thermal conductivity network;

[0064] (2) In addition to the physical adsorption of paraffin wax by the porous carbon, the polydopamine has certain viscosity, which has a certain effect on preventing paraffin wax from leaking; and the partially hydroxylated boron nitride can form van der Waals force and covalent bond force with the inside and surface of the porous carbon skeleton, which can further inhibit the flowability of paraffin wax;

[0065] (3) The three-dimensional porous structure of biomass porous carbon is equivalent to a "skeleton", and the connected pores provide a uniform distribution of "channels" for the organic modified boron nitride, so that the boron nitride particles can be arranged continuously along the pore wall of the porous carbon; the polydopamine is a "bridge", which ensures that the boron nitride particles are tightly attached to the surface / pores of the porous carbon through the interfacial bonding of the polydopamine and the porous carbon, so as to avoid displacement and agglomeration of the boron nitride during stirring or paraffin wax melting; at the same time, the van der Waals force and covalent bond force formed by the combination of the hydroxyl groups of the boron nitride and the porous carbon skeleton, so as to build a continuous heat conduction network of "porous carbon (auxiliary heat conduction) - boron nitride (main heat conduction) - polydopamine (interfacial connection)", and form a stable paraffin phase change material, which synergistically improves the heat conduction performance.

[0066] According to the data comparison of Example 2 and Comparative Example 3, it can be seen that replacing the biomass porous carbon with ordinary porous carbon will reduce the heat conduction performance of the phase change material, and the reason may be as follows:

[0067] ① The biomass porous carbon is prepared from biomass, and its carbon skeleton retains the ordered microstructure of the biomass itself, and can form carbon domains with high graphitization degree during carbonization and activation, so it has high self-heat conductivity; the ordinary porous carbon has disordered amorphous carbon structure and low graphitization degree, so it has low self-heat conductivity;

[0068] ② The biomass porous carbon can form a high-connectivity porous structure, and the carbon skeleton can form a continuous "heat conduction path", so heat can be quickly conducted along the carbon skeleton; the pore structure of the ordinary porous carbon is disordered and has poor connectivity, so the conduction efficiency is greatly reduced; on this basis, the continuous heat conduction network formed by the organic modified boron nitride and the biomass porous carbon will be more unobstructed, thereby producing a synergistic effect of improving the thermal stability;

[0069] ③ The surface of the biomass porous carbon has a certain amount of functional groups such as hydroxyl and carboxyl groups due to the characteristics of the biomass, and has better interface compatibility with paraffin wax, so the two are tightly combined and have small interface thermal resistance; in combination with the hydroxyl modification of the organic modified boron nitride, the interface compatibility is synergistically improved, and the heat conduction performance is further improved; the surface of the ordinary porous carbon has low hydrophobicity and low matching degree with paraffin wax, so the interface is prone to form gaps or weakly bonded layers, the interface thermal resistance is increased, and heat is difficult to transfer from the carbon skeleton to the inside of paraffin wax, so the combination of the ordinary porous carbon and paraffin wax can be effectively improved only by the combination of the polydopamine, and on this basis, it is difficult to form a continuous heat conduction network, so its heat conduction performance is weaker than that of Example 2.

[0070] II. Stability test

[0071] The comparative material is placed in an 80 ℃ constant temperature drying oven to test the leakage rate of the sample. Specifically, a certain mass of sample is placed on filter paper and placed in an 80 ℃ constant temperature drying oven for 12 h. After the end, the sample is taken out and weighed to measure the leakage rate of the sample by the mass loss rate of the sample, so as to evaluate the stability of the sample.

[0072] The phase change materials prepared from examples 1-3 and comparative examples 1-3 are tested according to the above method, and the results are shown in table 2.

[0073] Table 2 stability results of phase change materials prepared from examples 1-3 and comparative examples 1-3

[0074] Sample loss rate (%) Example 1 0.77 Example 2 1.25 Example 3 1.96 Comparative Example 1 8.52 Comparative Example 2 10.01 Comparative Example 3 13.74 Comparative Example 4 10.63

[0075] According to the results in table 2, it can be seen that:

[0076] Different from the results in table 1, the best stability in examples 1-3 is example 1, which proves that biomass porous carbon is the basis of stability in the whole combination of phase change materials; combined with the data in table 1 and table 2, example 2 is the best ratio of balancing the stability and thermal conductivity of phase change materials.

[0077] Approximately the same as the results in table 1, according to the data comparison of comparative example 1, comparative example 2 and comparative example 4, it can be seen that compared with comparative example 4 which simply uses the technical scheme of compounding boron nitride and biomass porous carbon, comparative example 1 and comparative example 2 respectively modify boron nitride with hydrochloric acid dopamine and hydroxylation, which can improve the stability of phase change materials to a certain extent; and on this basis, compared with example 2, it is found that when boron nitride is treated by organic modification and hydroxylation combination, the stability generated when it is compounded with biomass porous carbon is significantly higher than that of comparative example 1 and comparative example 2, which further verifies the rationality of the conclusion of table 1.

[0078] Similarly, the data comparison of Example 2 and Comparative Example 3 shows that replacing the biomass porous carbon with ordinary porous carbon can reduce the stability of the phase change material, and the reasons are as follows: ① Biomass porous carbon is a porous material that can form a highly connected porous structure, and has strong adsorption on paraffin as a carrier material, which can prevent paraffin from overflowing. In addition to the physical adsorption of paraffin by porous carbon, the polydopamine has certain viscosity, which can prevent paraffin from leaking to a certain extent. In addition, the partially hydroxylated boron nitride can form van der Waals force and covalent bond with the internal and surface of the porous carbon skeleton, which can further inhibit the flowability of paraffin. Ordinary porous carbon has problems such as uneven pore size and poor connectivity, which cannot effectively adsorb paraffin, resulting in more prone to leakage. ② The surface of biomass porous carbon contains a certain amount of functional groups such as hydroxyl and carboxyl groups due to the characteristics of biomass, which can form strong intermolecular forces with paraffin, further fixing paraffin. The surface of ordinary porous carbon is mostly inert, and the interaction between paraffin and ordinary porous carbon is weak, which makes paraffin more prone to leakage. In addition, the hydrophobic groups on the surface of ordinary porous carbon also weaken the binding force of the polydopamine and hydroxyl groups of the organically modified boron nitride to a certain extent, resulting in the stability of Comparative Example 3 being significantly weaker than that of Example 2.

[0079] The examples presented herein are merely selected embodiments according to a combination of all possible embodiments. The appended claims should not be limited by the embodiments described in this application. Some numerical ranges used in the claims include sub-ranges within them, and variations in these ranges should also be covered by the appended claims.

Claims

1. A phase change composite, characterized in that, It comprises 40-60 wt% organically modified boron nitride and 40-60 wt% biomass porous carbon, wherein the organically modified boron nitride is polydopamine-modified hydroxylated boron nitride.

2. The phase change composite according to claim 1, characterized in that, The method for preparing the organically modified boron nitride is as follows: Step 1: Hydroxylating boron nitride to obtain hydroxylated boron nitride; Step 2: Disperse hydroxylated boron nitride in a mixture of water and anhydrous ethanol, and add Tris buffer solution with pH=8.5 to adjust the pH to 8.3-8.7; Step 3: Sonicate the mixture, add dopamine hydrochloride to react fully, cool to room temperature after the reaction is complete, and then centrifuge to obtain the precipitate. Wash the precipitate with anhydrous ethanol and ultrapure water alternately at least 3 times.

3. The phase change composite according to claim 2, characterized in that, The specific operation of step 1 is as follows: Weigh 1 g of boron nitride powder, add 50 ml of mixed acid (HNO3: H2SO4 = 1: 3, v / v), place it in a three-necked flask with a condenser, control the temperature in an oil bath at 80-120℃, and stir under reflux for 4-24 h; after the reaction, cool to room temperature, slowly add 100 ml of deionized water to dilute, and centrifuge to obtain the precipitate; wash the precipitate repeatedly with deionized water until the pH of the supernatant is 6-7, and then wash with anhydrous ethanol; vacuum dry at 60-80℃ for 12-24 h to obtain hydroxylated boron nitride.

4. The phase change composite according to claim 1, characterized in that, The method for preparing biomass porous carbon is as follows: the biomass is washed, dried, crushed, and sieved to obtain biomass powder. A chemical activator is added, and carbonization activation is carried out under nitrogen protection. After cooling, the carbon is removed, washed, and dried to obtain biomass porous carbon.

5. The phase change composite according to claim 4, characterized in that, The biomass is either straw or wood chips.

6. The phase change composite according to claim 4 or 5, characterized in that, The preparation method of the biomass porous carbon includes the following specific steps: Biomass is washed with anhydrous ethanol and deionized water until the rinsing solution is free of obvious turbidity; then dried at 60-80℃ for 12-24 hours; after drying, it is pulverized using a high-speed universal pulverizer at a speed of 8000-12000 rpm for 5-10 minutes, and then sieved through an 80-200 mesh screen to obtain biomass powder; a chemical activator is added to the biomass powder at a mass ratio of 1:1-4, and the mixture is reacted at 500-800℃ for 1-3 hours, washed with deionized water 2-3 times, and then vacuum dried at 60-80℃ for 8-12 hours to obtain biomass porous carbon.

7. The phase change composite according to claim 6, characterized in that, The chemical activator includes one of sodium hydroxide, potassium hydroxide, and zinc chloride.

8. A phase change material, characterized in that, It includes two or more paraffins with different phase transition temperatures and the phase transition complex according to any one of claims 1-7, wherein the content of the phase transition complex is 10-20 wt%.

9. The phase change material according to claim 8, characterized in that, The product comprises, by weight percentage, 40-45 wt% paraffin wax with a phase transition temperature of 37°C, 40-45 wt% paraffin wax with a phase transition temperature of 46°C, and 10-20 wt% of the phase transition composite.

10. A method for preparing a phase change material as described in claim 9, characterized in that, Includes the following steps: Step a: Melt paraffin with a phase change temperature of 37℃ and paraffin with a phase change temperature of 46℃ at 80℃. After complete melting, add organic modified boron nitride while stirring to obtain a mixture. Step b: Maintain 80°C and add biomass porous carbon to the mixture and stir until homogeneous, then cool to room temperature to obtain the phase change material.