A method for shaping and cold encapsulating phase change materials based on polymer crosslinking

Abstract

This invention provides a method for cold encapsulation of phase change materials (PCMs) based on polymer crosslinking, belonging to the field of PCM molding and encapsulation technology. The method includes the following steps: paraffin powder and premixed epoxy resin are mixed uniformly in a vacuum environment at a mass ratio of (7~6):(3~4), cured to obtain a substrate of the PCM composite material; UV-curable adhesive is uniformly coated onto the surface of the substrate; then the substrate is placed under ultraviolet light to form a film, completing the encapsulation and obtaining the PCM composite material. This invention uses a specific polymer matrix material to efficiently cold encapsulate low-temperature powdered PCMs. The resulting PCM composite material has a low leakage rate, excellent thermal management performance and mechanical strength, and can be directly fabricated into complex structural components, solving the problems of complex encapsulation, high leakage rate, poor mechanical properties, and difficulty in processing into structural components in existing technologies.

Description

Technical Field

[0001] This invention relates to the field of phase change material molding and packaging technology, specifically to a method for shaping and cold packaging phase change materials based on polymer cross-linking. Background Technology

[0002] Phase change materials (PCMs) possess immense application potential, particularly in thermal management and energy conservation, due to their ability to effectively store and release thermal energy through a phase change process. However, existing PCMs often suffer from technical problems during use, such as phase change medium leakage, insufficient thermal cycling stability, low mechanical strength, and poor thermal conductivity. These issues hinder the long-term stable operation of PCMs in practical applications and severely limit their widespread use in industry, construction, and other fields.

[0003] To suppress leakage of phase change media (PCMs), PCMs are typically encapsulated to maintain their shape and strength while preventing leakage. Current PCM encapsulation technologies mainly include capsule encapsulation, porous carrier encapsulation, and polymer matrix encapsulation. Capsule encapsulation encapsulates the PCM into a core-shell capsule. While this method can achieve some encapsulation, the shell is prone to rupture under significant thermal stress, leading to leakage. Furthermore, capsule encapsulation increases the overall volume of the material, posing significant limitations in applications requiring high-power heat dissipation, limited volume, and stringent environmental regulations. Porous carrier encapsulation uses porous adsorption or physical blending to load materials with microporous structures or large specific surface areas, such as mixtures of hexagonal mesoporous silicates (HMS) and olefin block copolymers (OBCs), into the PCM, forming multifunctional composite PCMs. This method shows promise in certain thermal comfort applications, such as personal thermoregulation in textiles and infrared radiation heating fabrics. However, despite the mechanical flexibility and shape memory recovery capabilities offered by the matrix material, these encapsulation methods still suffer from shortcomings in mechanical strength and long-term stability. Polymer matrix encapsulation shape stabilization technology achieves shape stabilization by grafting phase change materials (PCMs) onto a polymer backbone. This method can address the leakage problem of PCMs to some extent, but it typically requires sacrificing the effective proportion of PCMs, leading to a reduction in energy storage density. Furthermore, polymer matrix-based encapsulation technologies usually require complex fabrication processes, which increases manufacturing costs and process complexity.

[0004] The low mechanical strength of phase change materials (PCMs) is also a major bottleneck hindering their application. PCMs are typically waxes or salts, which have low mechanical strength in the solid state, making them difficult to use directly as structural components. Furthermore, the volume change during the phase transition affects the encapsulation of the material and the stability of the overall structure. To enhance the mechanical strength of PCMs, a common approach is to combine them with reinforcing materials, but this often introduces additional process complexity and cost, and the reinforcement effect is affected by many factors. In addition, with the development of modern industrial and building systems towards integration and lightweighting, more and more applications demand multifunctional materials, requiring not only thermal management capabilities but also a certain level of mechanical strength, and even the ability to be used directly as structural components. However, current PCM encapsulation technologies struggle to meet these requirements simultaneously. Traditional encapsulation methods simply add PCMs to the system, failing to replace existing structural components and instead increasing the weight and complexity of the entire system. Therefore, effectively integrating PCMs into structures without increasing system complexity while improving overall thermal management capabilities has become an important research direction.

[0005] In summary, there is an urgent need to develop a novel encapsulation technology for phase change energy storage materials. This technology should enable the phase change material to be effectively encapsulated to prevent leakage, while also achieving good bonding with the matrix material to form a composite structure with high mechanical strength. This would allow for a high degree of integration between thermal management and structural functionality. This new material should possess excellent formability, allowing it to be molded into complex shapes to adapt to various application scenarios. Furthermore, it should have a simple manufacturing process to reduce production costs and environmental impact. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for shaping and cold-packing phase change materials (PCMs) based on polymer crosslinking. By selecting a suitable polymer matrix material and mixing it with the PCM in a specific ratio under specific conditions and then curing it, a composite PCM with excellent mechanical and thermal management properties is prepared. This material not only effectively solves the leakage problem of PCMs but also replaces some traditional structural components, achieving material multifunctionality and system integration, thereby significantly expanding the application scenarios of PCMs in industry, construction, and other thermal management-related fields.

[0007] To achieve the above objectives, the specific technical solution of the present invention is as follows:

[0008] A method for shaping and cold-packing phase change materials based on polymer crosslinking includes the following steps:

[0009] (1) The paraffin wax is subjected to ultra-low temperature solidification treatment. The solidified paraffin wax is ground in an environment below the phase change temperature of paraffin wax to obtain paraffin wax powder. Before grinding the paraffin wax, it is necessary to solidify the paraffin wax at -80 ℃ to avoid the paraffin wax melting due to heat during the grinding process.

[0010] (2) Premix epoxy resin with curing agent to obtain premixed epoxy resin; mix paraffin powder and premixed epoxy resin in a vacuum environment at a mass ratio of (7~6):(3~4) and cure to obtain the substrate of phase change composite material.

[0011] (3) The substrate surface is rinsed with plasma flow, and then a waterproof coating film is prepared on the substrate surface to obtain a phase change composite material based on polymer crosslinking.

[0012] Furthermore, the phase transition temperature of the paraffin is 18~30 ℃.

[0013] To address the issues of low phase change material content and low latent heat and heat capacity per unit mass in existing phase change composite materials, this invention directly mixes and cures paraffin powder with a polymer matrix material at a mass ratio of (7~6):(3~4) under specific conditions. Then, a UV-curable adhesive is coated onto the surface of the formed substrate, and after curing into a film, a phase change composite material based on polymer crosslinking is obtained. This invention offers low cost, simple operation, and eliminates the need for individual coating of each powder particle. While significantly increasing the proportion of phase change material in the phase change composite material, the resulting composite material also possesses excellent mechanical properties and anti-leakage performance. This invention selects paraffin wax with a phase change temperature of 18~30 ℃ as the phase change material, enabling the prepared phase change composite material to be widely used in scenarios such as building energy conservation and building thermal management. The phase change temperature of 18~30 ℃ is exactly within the human body's comfortable temperature range, which helps to reduce the energy consumption of air conditioning and heating. In addition, paraffin wax has the advantages of low cost and high latent heat of phase change (200 J / g), and also has good cycle stability. After multiple phase change cycles, it can still maintain good thermal performance without significant thermal performance degradation.

[0014] Paraffin wax, with a phase change temperature of 18-30°C, becomes liquid at slightly higher temperatures, thus requiring more stringent encapsulation techniques. In the preparation of the phase change composite material, this invention first subjectes paraffin wax to ultra-low temperature (below -80°C) solidification treatment. The solidified paraffin wax is then ground into micron-sized powder particles in an environment below the phase change temperature. These micron-sized paraffin wax powders are then thoroughly mixed with a high-viscosity premixed epoxy resin under vacuum, allowing the epoxy resin to penetrate into the gaps between the paraffin wax powder particles. Through a chemical cross-linking reaction, a three-dimensional porous network structure containing numerous microcavities is formed. These microcavities effectively limit the volatilization and leakage of paraffin wax during the encapsulation process. A coating is then applied to the surface of the cured substrate to give the phase change composite material excellent waterproof and moisture-proof properties, further effectively preventing leakage of the phase change material.

[0015] This invention utilizes cold grinding of paraffin wax under fixed pressure and time. By adjusting the grinding pressure and time, the particle size distribution of the paraffin wax powder can be controlled, ensuring high consistency in particle size across different batches. When the paraffin wax powder particle size is too large, the three-dimensional network porous structure formed by the epoxy resin and curing agent has large pores, resulting in high leakage rate and poor mechanical properties. Conversely, when the paraffin wax powder particle size is too small, the high-viscosity epoxy resin cannot fully penetrate into the powder gaps, increasing paraffin wax powder agglomeration and similarly leading to poor mechanical properties. Therefore, maintaining the paraffin wax powder particle size within a suitable range is crucial for the final performance of the phase change composite material.

[0016] Furthermore, the grinding method is mortar grinding; the paraffin wax put into grinding needs to be pre-cooled to a specific temperature and ground in an environment below the phase transition temperature of paraffin wax to avoid the paraffin wax from melting due to heat during the grinding process; in addition, the mortar grinding has a fast discharge time (60 s), avoiding the long grinding time in grinding methods such as ball mills that cause the paraffin wax to melt. The ground paraffin wax powder is placed in a refrigerator for storage for later use.

[0017] Furthermore, the curing temperature is higher than that of epoxy resin but lower than that of paraffin wax. The curing of this invention is carried out at a lower temperature to avoid melting and leakage of paraffin wax caused by slow heat release during the curing process.

[0018] Furthermore, the curing temperature is 5~10 ℃.

[0019] Furthermore, the mass ratio of the epoxy resin to the curing agent is (1.5~3):1.

[0020] Furthermore, the mass ratio of the epoxy resin to the curing agent is 2.5:1.

[0021] Furthermore, the epoxy resin is a bisphenol F type epoxy resin, and the curing agent is a phenolic amine curing agent; the epoxy resin can be cured at low temperature, and the mechanical compressive strength of the cured epoxy resin can reach 20 MPa, which can ensure that the phase change composite material has excellent mechanical properties.

[0022] Furthermore, the paraffin powder and premixed epoxy resin are mixed by vacuum planetary gravity stirring. The small-particle-size paraffin powder and the high-viscosity epoxy resin are fully mixed by utilizing the coupling effect of the centrifugal force of the mixture's revolution and the gravity of its rotation, while avoiding the introduction of air bubbles.

[0023] Furthermore, the waterproof coating film is a UV-curable adhesive coating film; the preparation of the waterproof coating film is as follows: the UV-curable adhesive is evenly applied to the surface of the molded phase change material using a roller or spraying tool, with a suitable thickness, and the coated part is placed under a UV lamp, which usually cures rapidly into a film in just a few seconds to tens of seconds. The UV-curable adhesive includes epoxy-based UV-curable adhesives, the main component of which is epoxy acrylate; the epoxy-based UV-curable adhesive undergoes a cationic polymerization reaction under UV irradiation, forming a highly cross-linked three-dimensional network structure. This structure significantly reduces the intermolecular gaps and can effectively prevent the penetration of phase change materials, water molecules, and other impurities; the present invention uses plasma flow treatment on the surface of the molded phase change material, which can not only improve adhesion but also introduce oxygen-containing groups (e.g., C=O, -OH, and -COOH). The oxygen-containing groups form chemical bonds with the active monomers in the UV-curable adhesive, which can strengthen the interfacial bonding and further reduce the waterproof and moisture-proof performance and leakage rate.

[0024] The present invention also provides a phase change composite material based on cross-linking of polymer materials obtained by the aforementioned shaping and cold encapsulation method.

[0025] Compared with the prior art, the advantages of the present invention are:

[0026] 1. The shaping and cold encapsulation method provided by this invention is simple to operate and low in cost. By directly mixing and solidifying paraffin powder with shaping material at low temperature, it eliminates the need to individually encapsulate each piece of paraffin powder, which greatly increases the proportion of phase change material in phase change composite material. At the same time, the prepared phase change composite material has both thermal management function and mechanical strength. It can replace some original structural components without increasing the system complexity, improve the system integration, and has broad industrial application potential.

[0027] 2. The phase change composite material of the present invention can be prepared into structural components with complex shapes through a molding process similar to concrete, thereby greatly expanding the application scenarios of phase change materials in industry, construction and other fields.

[0028] 3. The epoxy resin and paraffin involved in the phase change composite material of the present invention are both non-toxic, odorless, and chemically stable environmentally friendly materials with low cost. They can be directly used for indoor cooling and heating, as well as thermal management of electronic equipment.

[0029] 4. The innovative coating strategy in the method of this invention further reduces the leakage rate of paraffin and significantly improves the service life of phase change composite materials. Attached Figure Description

[0030] Figure 1 This is a flowchart of the present invention regarding the shaping and cold encapsulation method of phase change materials based on polymer crosslinking;

[0031] Figure 2 These are stress-strain curves for different paraffin contents in the matrix of phase change composite materials.

[0032] Figure 3 These are the test results of the leakage rate of the phase change material in the phase change composite material of the present invention;

[0033] Figure 4 These are the leakage rate test results of phase change composite materials prepared with different waterproof coating films;

[0034] Figure 5 These are the leakage rate test results of phase change composite materials prepared from different phase change materials. Detailed Implementation

[0035] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] This invention provides a method for shaping and cold encapsulating phase change materials based on polymer crosslinking (flowchart shown). Figure 1 ), including the following steps:

[0037] (1) The paraffin wax is subjected to ultra-low temperature solidification treatment, and the solidified paraffin wax is ground in an environment below the phase transition temperature of paraffin wax to obtain paraffin wax powder.

[0038] (2) Premix epoxy resin and curing agent at a mass ratio of (1.5~3):1 to obtain premixed epoxy resin; mix paraffin powder and premixed epoxy resin at a mass ratio of (7~6):(3~4) in a vacuum environment, cure, and obtain the substrate of phase change composite material.

[0039] (3) The substrate surface is rinsed with plasma flow, and then a waterproof coating film is prepared on the substrate surface to obtain a phase change composite material based on polymer crosslinking.

[0040] In some examples, the phase transition temperature of the paraffin is 18~30 °C.

[0041] In some examples, the curing temperature is 5~10 °C.

[0042] Example 1

[0043] A phase change composite material based on crosslinking of polymer materials is prepared by the following method:

[0044] The first step is to prepare paraffin powder. Paraffin with a phase transition temperature of 30 ℃ is selected as the phase transition material. First, the paraffin is frozen to below -80 ℃, while ensuring that the ambient temperature for grinding is below 25 ℃. The amount of paraffin used is determined according to the size of the grinding instrument. In this embodiment, the mortar has a volume of approximately 700 mL, and about 80 g of paraffin is added each time. The pressure of the pestle is set to the maximum, and the grinding time is 1 minute. After grinding, the paraffin powder is stored in an environment of -80 ℃ for later use.

[0045] The second step is to prepare the premixed epoxy resin. Bisphenol F type epoxy resin (Nanya 170 bisphenol F type epoxy resin) and phenolic amine curing agent (593 phenolic amine curing agent) are placed in a vacuum planetary gravity mixer for premixing to obtain the premixed epoxy resin. The mixer speed is set to 900 RPM for 1 minute. Then, paraffin powder is placed in the vacuum planetary gravity mixer to mix with the premixed epoxy resin to obtain a mixture. Before mixing, the premixed epoxy resin and the mixing container need to be frozen to below -20 ℃. The mixing is carried out in three stages: the first stage is at 600 RPM for 1 minute; the second stage is at 900 RPM for 5 minutes; and the third stage is at 600 RPM for 1 minute.

[0046] The third step is to cure the phase change composite material substrate. The mixture is transferred to a mold, which in this embodiment is a cylindrical silicone mold with a diameter of 60 mm. It is cured at 5 ℃ for one day to obtain the phase change composite material substrates S1~S6. The details of the raw material mass ratio of S1~S6 are shown in Table 1. The substrate has a diameter of 60 mm, a thickness of 14 mm, and a weight of 50 g.

[0047] Table 1: Raw material mass ratio of S1 to S6

[0048]

[0049] Figure 2The figures show the stress-strain curves of the phase change composite material substrates S3 (α=70%), S5 (α=60%), and S6 (α=80%). As can be seen from the figures, compared with the material with 0% paraffin (cured from epoxy resin and curing agent at a mass ratio of 2.5:1), the maximum stress value of the substrate with paraffin is significantly reduced. Furthermore, as the proportion of paraffin increases, the maximum stress value of the substrate shows a decreasing trend. Different phase change composite materials can be selected according to the actual application scenario and requirements.

[0050] Step 4: Activate the substrate surface. Rinse the surface of substrate S3 for 1 minute in a vacuum environment using an oxygen molecular plasma stream; apply UV-curable adhesive (D-5604 UV-curable adhesive) and insulating conformal coating evenly and to a suitable thickness to the surface of substrate S3 using a spraying tool; place the coated part under a UV lamp to form a film, thus obtaining phase change composite materials S7 (coating is UV-curable adhesive) and S8 (coating is insulating conformal coating) based on polymer crosslinking.

[0051] Comparative Example 1

[0052] Epoxy resin and curing agent were premixed in a vacuum planetary gravity mixer at a mass ratio of 2.5:1. The mixer speed was set to 900 RPM for 1 minute to obtain premixed epoxy resin. Liquid paraffin with a phase change temperature of 30 ℃ was mixed with the premixed epoxy resin in a vacuum planetary gravity mixer at a mass ratio of 7:3 to obtain a mixture. The mixing was carried out in three stages: the first stage was at a speed of 600 RPM for 1 minute; the second stage was at a speed of 900 RPM for 5 minutes; and the third stage was at a speed of 600 RPM for 1 minute. The mixture was transferred to a mold, which in this embodiment was a 100 mm x 100 mm x 10 mm cuboid. It was cured at 5 ℃ for one day, but failed to cure completely.

[0053] Comparative Example 2

[0054] The inorganic phase change material hydrated salt was used to replace the paraffin in Example 1. The preparation steps are as follows: The hydrated salt (sodium sulfate decahydrate) was frozen to below -80 ℃, while ensuring that the ambient temperature for grinding was below 25 ℃. The amount of hydrated salt was determined according to the size of the grinding instrument; in this example, the volume of the mortar was approximately 700 mL, and 80 g of hydrated salt was added each time; the pressure of the pestle was set to the maximum, and the grinding time was 1 minute; the hydrated salt powder was then frozen at -80 ℃ for later use.

[0055] Epoxy resin and curing agent were placed in a vacuum planetary gravity mixer at a mass ratio of 2.5:1 for premixing. The mixer speed was set to 900 RPM and the time was 1 minute to obtain premixed epoxy resin. The premixed epoxy resin was then removed and stored at -20 ℃ for later use.

[0056] Hydrated salt powder stored at -80 °C and premixed epoxy resin were mixed in a vacuum planetary gravity mixer at a mass ratio of 7:3 to obtain a mixture. The mixing was carried out in three stages: the first stage was at a speed of 600 PRM for 1 minute; the second stage was at a speed of 900 PRM for 5 minutes; and the third stage was at a speed of 600 PRM for 1 minute. The mixture was then transferred to a mold, which in this embodiment was a 100 mm x 100 mm x 10 mm cuboid. The mixture was cured at 5 °C for one day to obtain the phase change composite material substrate S9.

[0057] The surface of substrate S9 was rinsed in a vacuum environment for 1 minute using an oxygen molecular plasma stream; the surface of the UV-curable adhesive substrate S9 was coated evenly and with a moderate thickness using a spraying tool; the coated part was placed under a UV lamp to form a film, thus obtaining phase change composite material S10 based on polymer crosslinking.

[0058] The substrates of the phase change composite material S1~S6, S9, and the phase change composite materials based on polymer crosslinking S7, S8, S10 were placed in a drying oven at an ambient temperature of 50 ℃ and continuously heated. Their mass was measured again, and the ratio of the decrease in mass to the original mass is the leakage rate. The test results are as follows: Figures 3 to 5 As shown. By Figure 3 It can be seen that after continuous heating for 450 h, the leakage rate was lowest when the mass ratio of epoxy resin to curing agent was 2.5:1; the leakage rate was also lowest when the mass ratio of paraffin powder to premixed epoxy resin was 7:3; after preparing a waterproof coating film on the substrate surface, the leak-proof performance of the material was further enhanced (after continuous heating for 450 h, the leakage rate of S7 remained below 5%). Figure 4 It can be seen that the present invention uses VU light-curing adhesive as a waterproof coating film, and its leak-proof effect is superior to that of an insulating conformal coating film; by Figure 5 It can be seen that using paraffin as the phase change material provides superior leak-proof performance compared to hydrated salts. These results demonstrate that the phase change composite material obtained using the shaping and encapsulation method of this invention exhibits excellent leak-proof performance.

[0059] The above detailed embodiments describe the implementation of the present invention; however, the present invention is not limited to the specific details described in the above embodiments. Within the scope of the claims and technical concept of the present invention, various simple modifications and changes can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

Claims

1. A method for shaping and cold-packing phase change materials based on polymer cross-linking, characterized in that, Includes the following steps: (1) The paraffin wax is solidified at -80 ℃ or below, and the solidified paraffin wax is ground in an environment below the phase transition temperature of paraffin wax to obtain paraffin wax powder; the phase transition temperature of the paraffin wax is 18~30 ℃. (2) Premix epoxy resin with curing agent to obtain premixed epoxy resin; mix paraffin powder and premixed epoxy resin in a vacuum environment at a mass ratio of (7~6):(3~4) and cure to obtain a substrate of phase change composite material; the curing temperature is higher than the curing temperature of epoxy resin and lower than the phase change temperature of paraffin, and the curing temperature is 5~10℃. (3) The substrate surface is rinsed with plasma flow, and then a waterproof coating film is prepared on the substrate surface to obtain a phase change composite material based on polymer crosslinking.

2. The method for shaping and cold-packing phase change materials based on polymer crosslinking according to claim 1, characterized in that, The mass ratio of epoxy resin to curing agent is (1.5~3):

1.

3. The method for shaping and cold-packing phase change materials based on polymer crosslinking according to claim 1, characterized in that, The epoxy resin is a bisphenol F type epoxy resin; the curing agent is a phenolic amine curing agent.

4. The method for shaping and cold-packing phase change materials based on polymer crosslinking according to claim 1, characterized in that, The grinding method is mortar grinding.

5. The method for shaping and cold-packing phase change materials based on polymer crosslinking according to claim 1, characterized in that, The paraffin powder and premixed epoxy resin are mixed by vacuum planetary gravity stirring.

6. The method for shaping and cold-packing phase change materials based on polymer crosslinking according to claim 1, characterized in that, The waterproof coating film is a UV-curable adhesive coating film.

7. A phase change composite material based on polymer crosslinking obtained by using the phase change material shaping and cold encapsulation method as described in any one of claims 1 to 6.

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