Preparation method of environment-friendly ultra-thin full-water foamed polyurethane thermal insulation material for cold storage

Abstract

This invention belongs to the field of thermal insulation materials, specifically relating to a method for preparing an environmentally friendly, ultra-thin, all-water-foamed polyurethane insulation material for refrigerators. The method comprises the following steps: nickel nitrate hexahydrate, trimesic acid, and polyvinylpyrrolidone are added to a mixed solvent of DMF and water, reacted under vacuum, and then washed and dried to obtain spherical nickel-based MOF materials; the obtained spherical nickel-based MOF materials are calcined under nitrogen and then naturally cooled to obtain spherical porous derived carbon materials; polyol, water, resin, triethanolamine, and the obtained spherical porous derived carbon materials are mixed and ultrasonically dispersed to form component A; stannous octoate and isocyanate are mixed to form component B; and component A and component B are mixed to obtain the desired product. This invention does not pollute the environment, improves thermal insulation performance, increases compressive strength, and is less prone to core burning and cracking.

Description

Technical Field

[0001] This invention belongs to the field of thermal insulation materials, specifically relating to a method for preparing an environmentally friendly, ultra-thin, all-water-foamed polyurethane thermal insulation material for refrigerators. Background Technology

[0002] With consumers becoming increasingly aware of food safety and the refrigeration industry booming, the demand for large-capacity, compact, and odor-free refrigeration equipment is growing daily, placing increasingly stringent requirements on insulation materials. This has directly driven the development of refrigeration insulation materials towards environmental friendliness, high thermal insulation performance, and high reliability. To meet these development needs, new materials and technologies are striving for leapfrog development, with high performance and composite materials being the most important development directions for insulation materials.

[0003] As a traditional thermal insulation material, polymer foam materials possess excellent properties such as low density, high porosity, low thermal conductivity, and high impact resistance due to their porous structure. Polyurethane foam (PUF), in particular, is an important thermal insulation material due to its ease of preparation, low cost, high compressive strength, and good flame retardant properties. The thermal insulation performance of polymer foam materials is mainly determined by the thermal conductivity of the cell walls, the thermal conductivity of the gas inside the cells, refractive and radiative thermal conductivity, and the convective thermal conductivity of the gas inside the cells. For PUF, due to the very small pore diameter, the convective and radiative thermal conductivity inside the cells can be ignored. The thermal conductivity of the gas inside the cells has the greatest impact on the thermal insulation performance of PUF. The main gas inside intact cells is carbon dioxide; therefore, with the same foaming agent, an intact cell structure is more conducive to improving thermal insulation performance. Controlling the cell structure by optimizing the foaming process, reducing the thermal conductivity of the cell walls, and preparing small and intact cells are effective ways to improve the thermal insulation performance of PUF.

[0004] Under the stringent environmental and ultra-thin requirements of the freezer industry, and based on mature foaming processes and production, the use of materials with excellent thermal insulation properties to composite with PUF (polyurethane foam) to prepare low-density, high-insulation foam materials has gained consensus in the thermal insulation materials industry. Common fillers in PUF composite materials include silica aerogel, hollow glass microspheres, and graphene. When these fillers are added to the polyurethane system, their inherent good thermal insulation properties reduce the thermal conductivity of the cell walls and improve the microstructure of the cells by increasing the number of nucleation sites. However, these common fillers suffer from problems such as cumbersome preparation, difficult addition, and limited performance improvement. Summary of the Invention

[0005] The present invention aims to overcome the shortcomings of the prior art and provide a simple, green and environmentally friendly method for preparing an environmentally friendly ultra-thin water-foamed polyurethane insulation material for refrigerators, which has ideal thermal insulation performance, high compressive strength and is not prone to core burning and cracking.

[0006] To solve the above-mentioned technical problems, the present invention is implemented as follows: A method for preparing an environmentally friendly, ultra-thin, water-foamed polyurethane insulation material for refrigerators is implemented according to the following steps: (1) Preparation of spherical nickel-based MOFs Nickel nitrate hexahydrate, trimesic acid, and polyvinylpyrrolidone were added to a mixed solvent of DMF and water, reacted under vacuum, and then washed and dried to obtain spherical nickel-based MOF materials. (2) Preparation of spherical porous derived carbon materials The spherical nickel-based MOFs material obtained in step (1) was calcined in a nitrogen atmosphere and then naturally cooled to obtain spherical porous derived carbon material. (3) Preparation of the target product Polyol, water, resin, triethanolamine and the spherical porous derived carbon material obtained in step (2) are mixed and ultrasonically dispersed to form component A; stannous octoate and isocyanate are mixed to form component B; component A and component B are mixed to obtain the target product.

[0007] Further, in step (1), the mass ratio of nickel nitrate hexahydrate, trimesic acid and polyvinylpyrrolidone is 2.5-2.6:0.9-1:3-15.

[0008] Further, in step (1), nickel nitrate hexahydrate, trimesic acid and polyvinylpyrrolidone are added to a mixed solvent of DMF and water and ultrasonicated for 1 to 1.5 hours to disperse them evenly.

[0009] Furthermore, in step (1), the reaction is carried out under vacuum conditions at 120-180°C for 8-12 hours.

[0010] Further, in step (1), after the reaction is complete, the powder sample is washed 4 to 8 times with DMF and anhydrous ethanol and then dried to obtain spherical nickel-based MOF material.

[0011] Further, in step (2), the spherical nickel-based MOFs material obtained in step (1) is calcined at 200-400°C for 3 hours in a nitrogen atmosphere, and then naturally cooled in a nitrogen atmosphere to obtain spherical porous derived carbon material.

[0012] Further, in step (3), polyol, water, resin, triethanolamine and the spherical porous derived carbon material obtained in step (2) are mixed and ultrasonically dispersed for 30-40 minutes to form component A.

[0013] Further, in step (3), the mass ratio of the polyol, water, resin, triethanolamine and spherical porous derived carbon material is 59-63:1.5-2:0.6-1:0.2-0.4:0.3-1.2 respectively.

[0014] As typical three-dimensional porous materials, metal-organic frame materials (MOFs) are formed by the self-assembly of inorganic metal centers and bridging organic ligands. They possess high designability and structural diversity, allowing for structural design and control at the molecular scale. The derived carbon materials obtained after calcination of MOFs exhibit richer hierarchical structures, uniformly distributed porosity, and good stability. Modifying PUFs with MOFs can significantly improve their thermal insulation and mechanical properties, offering numerous potential applications. Considering the environmental protection and high-performance requirements of the freezer industry, this invention employs a one-step method to incorporate MOFs into a polyurethane system for all-water foaming. Simultaneously, a solvothermal method is used to synthesize spherical nickel-based metal framework materials. After high-temperature calcination under nitrogen conditions, spherical porous derived carbon materials with nickel-based metal framework materials as precursors are obtained. These derived carbon microspheres are used as fillers to prepare PUF composite materials. Due to its unique porous structure, the composite material exhibits reduced thermal conductivity of the cell walls. Simultaneously, the microspheres act as nucleation sites within the system, effectively regulating the cell structure and reducing both the thermal conductivity of the gas within the cells and its radiative thermal conductivity, thereby improving the insulation performance of the foam material. This invention improves the performance of the foam material while employing a simple and environmentally friendly preparation process, enabling industrial-scale production. Compared to existing technologies, this invention offers a simple method that yields ultra-thin polyurethane insulation material for refrigerators with excellent thermal insulation properties. It also enhances compressive strength and reduces the likelihood of core burning and cracking. Using water as the foaming agent avoids environmental pollution, ensuring a green and environmentally friendly process and eliminating odors during foaming and refrigerator use. Attached Figure Description

[0015] The present invention will now be described in detail through specific embodiments. These embodiments are provided to enable a more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art. As used throughout the specification and claims, the terms "comprising" or "including" are open-ended and are interpreted as "comprising but not limited to". The following description is a preferred embodiment for carrying out the invention; however, this description is intended to illustrate the general principles of the specification and is not intended to limit the scope of the invention. The scope of protection of the invention is determined by the appended claims. Unless otherwise specified, all reagents and materials used in the present invention are commercially available.

[0016] Figure 1 This is a schematic diagram of the preparation process of the low thermal conductivity PUF composite material of the present invention; Figure 2 This is a finished product image of the low thermal conductivity PUF composite material of the present invention; Figure 3The images shown are electron microscope images of the present invention; wherein, (a) is a scanning electron microscope image of nickel-based MOF microspheres; (b) is a scanning electron microscope image of nickel-based MOF microsphere-derived carbon material; (c) is a transmission electron microscope image of nickel-based MOF microspheres; (d) is a transmission electron microscope image of nickel-based MOF microsphere-derived carbon material; (e) is an unmodified PUF composite material; and (f) is a PUF composite material modified with nickel-based MOF microsphere-derived carbon material. Figure 4 The diagram shows the thermal conductivity, specific heat capacity, and compressive strength of PUF composite materials with different components according to the present invention; wherein, a) thermal conductivity of PUF composite materials with different components; b) specific heat capacity of PUF composite materials with different components; c) compressive strength of PUF composite materials with different components. Detailed Implementation

[0017] Example 1 The preparation method of environmentally friendly ultra-thin water-based polyurethane foam insulation material for refrigerators is carried out according to the following steps: (1) Preparation of spherical nickel-based MOFs: 2.5 g of nickel nitrate hexahydrate, 0.95 g of trimesic acid, and 10 g of polyvinylpyrrolidone were dispersed in a mixed solvent of DMF and water, and sonicated for 1.2 h to ensure uniform dispersion. After being placed in a tetrafluoroethylene liner, the mixture was placed in a reaction vessel and reacted at 160 °C under vacuum for 11 h. After the reaction was completed, the powder sample was washed 6 times with DMF and anhydrous ethanol, and then dried to obtain spherical nickel-based MOF materials.

[0018] (2) Preparation of spherical porous derived carbon material: The obtained nickel-based MOF material was calcined at 350°C for three hours in a nitrogen atmosphere and then naturally cooled in a nitrogen atmosphere to obtain spherical porous derived carbon material.

[0019] (3) Preparation of low thermal conductivity PUF composite material: 61 parts of polyol, 0.9 parts of spherical porous derived carbon material, 1.8 parts of water, 0.9 parts of resin, and 0.35 parts of triethanolamine were ultrasonicated for 35 min as component A, and 0.14 parts of stannous octoate and 91.8 parts of isocyanate were used as component B. (4) Use a high-speed mixer to mix material A and material B for 10 seconds and then pour them into a free foaming mold. After curing for three days, a PUF composite material with good thermal insulation performance is obtained, namely an environmentally friendly ultra-thin freezer all-water foamed polyurethane insulation material.

[0020] Example 2 The preparation method of environmentally friendly ultra-thin water-based polyurethane foam insulation material for refrigerators is carried out according to the following steps: (1) Preparation of spherical nickel-based MOFs: 2.6 g of nickel nitrate hexahydrate, 0.98 g of trimesic acid, and 12 g of polyvinylpyrrolidone were dispersed in a mixed solvent of DMF and water, and sonicated for 1.3 h to ensure uniform dispersion. After being placed in a tetrafluoroethylene liner, the mixture was placed in a reaction vessel and reacted at 145 °C under vacuum for 12 h. After the reaction was completed, the powder sample was washed 7 times with DMF and anhydrous ethanol, and then dried to obtain spherical nickel-based MOF materials.

[0021] (2) Preparation of spherical porous derived carbon material: The obtained nickel-based MOF material was calcined at 280°C for three hours in a nitrogen atmosphere and then naturally cooled in a nitrogen atmosphere to obtain spherical porous derived carbon material.

[0022] (3) Preparation of low thermal conductivity PUF composite material: 62 parts of polyol, 1.1 parts of spherical porous derived carbon material, 2 parts of water, 0.7 parts of resin, and 0.28 parts of triethanolamine were ultrasonicated for 38 min as component A, and 0.15 parts of stannous octoate and 92 parts of isocyanate were used as component B. (4) Use a high-speed mixer to mix material A and material B for 10 seconds and then pour them into a free foaming mold. After curing for three days, a PUF composite material with good thermal insulation performance is obtained, namely an environmentally friendly ultra-thin freezer all-water foamed polyurethane insulation material.

[0023] Example 3 The preparation method of environmentally friendly ultra-thin water-based polyurethane foam insulation material for refrigerators is carried out according to the following steps: (1) Preparation of spherical nickel-based MOFs: 2.59 g of nickel nitrate hexahydrate, 0.90 g of trimesic acid, and 9 g of polyvinylpyrrolidone were dispersed in a mixed solvent of DMF and water and sonicated for 1 h to ensure uniform dispersion. The mixture was then placed in a reaction vessel with a tetrafluoroethylene liner and reacted under vacuum at 150 °C for 10 h. After the reaction was completed, the powder sample was washed 8 times with DMF and anhydrous ethanol and then dried to obtain spherical nickel-based MOF materials.

[0024] (2) Preparation of spherical porous derived carbon material: The obtained nickel-based MOF material was calcined at 300°C for three hours in a nitrogen atmosphere and then naturally cooled in a nitrogen atmosphere to obtain spherical porous derived carbon material.

[0025] (3) Preparation of low thermal conductivity PUF composite material: 60 parts of polyol, 0.9 parts of spherical porous derived carbon material, 1.6 parts of water, 0.8 parts of resin, and 0.3 parts of triethanolamine were ultrasonicated for 30 min as component A, and 0.13 parts of stannous octoate and 91.7 parts of isocyanate were used as component B; (4) Use a high-speed mixer to mix material A and material B for 10 seconds and then pour them into a free foaming mold. After curing for three days, a PUF composite material with good thermal insulation performance is obtained, namely an environmentally friendly ultra-thin freezer all-water foamed polyurethane insulation material.

[0026] A schematic diagram of the preparation process of low thermal conductivity PUF composite materials is shown below. Figure 1 As shown in the diagram. A schematic diagram of the preparation process for low thermal conductivity PUF composite materials, as follows. Figure 1 As shown. A finished product image of the low thermal conductivity PUF composite material, as shown. Figure 2 As shown. Figure 3 (a) and (b) are scanning electron microscope (SEM) images of nickel-based MOF microspheres and nickel-based MOF microsphere-derived carbon materials, respectively. As can be seen from the images, the microparticles are spherical both before and after high-temperature calcination. Such regular and smooth spherical shapes can serve as excellent nucleation sites in polyurethane systems, regulating the pore structure of PUFs. Figure 3 Images (c) and (d) are transmission electron microscopy (TEM) images of nickel-based MOF microspheres and nickel-based MOF microsphere-derived carbon materials. It can be seen that the porous derived carbon materials formed by high-temperature calcination possess a core-shell structure. This structure can effectively block heat conduction, which is beneficial to the thermal insulation performance of PUF composites. The structure of the PUF composite modified with nickel-based MOF microsphere-derived carbon materials is shown below. Figure 3 As shown in (f), through with Figure 3 (e) Compared with the scanning electron microscope, the PUF composite material without modification is clearly observed to have more uniform pore size and more complete pore structure after the addition of spherical porous derived carbon material.

[0027] It can be seen that, compared with unmodified PU, the addition of nickel-based MOF-derived carbon materials to the polyurethane system reduced the thermal conductivity of the PUF composite by 23.13%, which is lower than that of nickel-based MOF-modified PUF. This is because the microsphere morphology of the derived carbon materials and nickel-based MOFs plays an advantageous role in the polyurethane system. Uniformly sized and smooth-surfaced microspheres act as nucleation sites, uniformly dispersing in the polyurethane system during foaming, resulting in a uniform distribution of pores and a more regular foam structure. Compared with nickel-based MOFs, nickel-based MOF microsphere-derived carbon materials have a richer pore structure, which also makes them more dispersed in the system. In addition, the special core-shell structure generated after calcination effectively hinders heat transfer, reducing the thermal conductivity of the pore walls. Figure 4 (b) Specific heat capacity of PUF composites with different components. It can be seen that the specific heat capacity of PUF modified with nickel-based MOF-derived carbon materials increased by 30.24% compared with that of unmodified PUF. Figure 4 (c) Compressive strength of PUF composites with different components. Compared with unmodified PUF, the compressive strength of PUF modified with nickel-based MOF-derived carbon material increased by 55.18%. In addition to the good cell structure brought about by the rich pore structure, the stable structure of the nickel-based MOF-derived carbon material itself plays an important supporting role in the cell walls, which is also a key factor in the enhanced compressive strength. The significant increase in compressive strength makes the PUF composite material less prone to core burning and cracking during use.

[0028] It is understood that the above specific description of the present invention is only for illustrating the present invention and is not limited to the technical solutions described in the embodiments of the present invention. Those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention to achieve the same technical effect; as long as the use needs are met, they are all within the protection scope of the present invention.

Claims

1. A method for preparing an environmentally friendly, ultra-thin, water-foamed polyurethane insulation material for refrigerators, characterized in that, Follow these steps to implement: (1) Preparation of spherical nickel-based MOFs Nickel nitrate hexahydrate, trimellitic acid, and polyvinylpyrrolidone were added to a mixed solvent of DMF and water and sonicated for 1–1.5 h to achieve uniform dispersion. After reacting under vacuum at 120–180 °C for 8–12 h, the powder sample was washed 4–8 times with DMF and anhydrous ethanol and then dried to obtain spherical nickel-based MOF material. The mass ratio of nickel nitrate hexahydrate, trimellitic acid, and polyvinylpyrrolidone was 2.5–2.6:0.9–1:3–15. (2) Preparation of spherical porous derived carbon materials After calcining the spherical nickel-based MOFs material obtained in step (1) at 200-400°C for 3 hours in a nitrogen atmosphere, it was then naturally cooled in a nitrogen atmosphere to obtain a spherical porous derived carbon material with a core-shell structure. (3) Preparation of the target product Polyol, water, resin, triethanolamine and the spherical porous derived carbon material obtained in step (2) are mixed and ultrasonically dispersed for 30-40 min to form component A; stannous octoate and isocyanate are mixed to form component B; the target product is obtained by mixing component A and component B. The mass ratio of the polyol, water, resin, triethanolamine and spherical porous derived carbon material is 59-63:1.5-2:0.6-1:0.2-0.4:0.3-1.2, respectively.

2. The preparation method of the environmentally friendly ultra-thin water-foamed polyurethane insulation material for refrigerators according to claim 1, characterized in that, The thermal conductivity of the environmentally friendly ultra-thin water-foamed polyurethane insulation material obtained in step (3) is 23.13% lower than that of unmodified polyurethane foam, and the compressive strength is 55.18% higher than that of unmodified polyurethane foam.

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