Preparation method of composite particles of water-soluble polyurethane coated metal powder and composite particles

Abstract

The invention discloses a preparation method of composite particles of water-soluble polyurethane coated metal powder and the composite particles, and belongs to the technical field of preparation of composite metal particles. The preparation method of the water-soluble polyurethane coated metal powder composite particles comprises the following steps: (1) mixing metal powder, a polyurethane chain extender and an organic solvent in an inert atmosphere, and reacting to obtain hydroxyl or amino modified metal powder slurry; the polyurethane chain extender contains carboxyl and hydroxyl, or contains carboxyl and amino; and (2) mixing diisocyanate, water-soluble oligomer dihydric alcohol, a polymerization catalyst, an organic solvent and the hydroxyl or amino modified metal powder slurry in an inert atmosphere, and carrying out heating reaction to prepare the composite particles. A water-soluble polyurethane coating layer is generated on the surface of the metal powder in situ through a condensation polymerization method, so that the composite particle effectively keeps the activity of the metal powder, the storage stability is improved, and the metal powder can release energy directly in water due to the excellent water solubility of the composite particle.

Description

Technical Field

[0001] This invention relates to the field of composite metal particle preparation technology, and in particular to a method for preparing composite microparticles of water-soluble polyurethane-coated metal powder and the composite microparticles themselves. Background Technology

[0002] The reaction between metals and water releases a large amount of heat, making it a promising propulsion system for underwater use. Since it doesn't require carrying water during underwater propulsion, it boasts a very high volumetric energy density. Among metallic materials, excluding highly reactive lithium and beryllium, magnesium and aluminum are relatively suitable for water reactions, as are aluminum alloy powders. The energy density of the aluminum-water reaction is higher than that of the magnesium-water reaction. However, due to the highly activated state of these metallic surfaces, they readily react with gaseous and liquid molecules in the surrounding environment, leading to significant oxidation and loss of activity upon exposure to air. This severely impacts their energy release and may even cause spontaneous combustion, posing challenges to their stability during storage and use.

[0003] Appropriate surface treatment of metal particles to maintain their activity and improve storage performance is an important means of enhancing their performance. By coating the surface of metal particles with a protective film, the surface properties of the particles are changed, effectively isolating the active metal particles from the surrounding environment, thereby protecting the active metal core from further oxidation. Taking aluminum powder as an example, there are passivation treatment methods and surface coating methods. Passivation treatment forms an oxide layer on the surface. Surface coating methods include carbon coating, metal coating, organic acid coating, and polymer coating. Among them, polymer coating technology forms a thin film on the surface of aluminum powder with a polymer, which can effectively protect the activity of nano-aluminum powder and change its surface properties. For example, patent CN 111484382 A discloses a fluorinated polyurethane-coated micron or nano-aluminum powder composite microparticle, which effectively maintains the activity of micron or nano-aluminum powder. When applied to modern solid rocket engines, it can improve the high-temperature oxidation rate and heat release rate of micron or nano-aluminum powder, improve the combustion efficiency of aluminum powder, reduce the mass of combustion residue, and improve the specific impulse of propellant. However, the above methods all result in a protective layer on the surface of metal particles that does not react with or dissolve in water, thus isolating the metal from water and making them unsuitable for metal-water reaction systems. Summary of the Invention

[0004] In view of this, the technical problem to be solved by the present invention is to provide a method for preparing composite microparticles of water-soluble polyurethane-coated metal powder and the composite microparticles themselves. The composite microparticles prepared by the method have excellent water solubility in the coating layer, allowing the composite microparticles to be directly used in water to realize the energy release reaction of the metal powder, effectively maintaining the activity of the metal powder and improving the storage stability of the composite microparticles.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] This invention provides a method for preparing composite microparticles of water-soluble polyurethane-coated metal powder, comprising the following steps:

[0007] (1) Under an inert atmosphere, metal powder, polyurethane chain extender and organic solvent are mixed and reacted to obtain hydroxyl or amino modified metal powder slurry; wherein the polyurethane chain extender contains carboxyl and hydroxyl groups, or contains carboxyl and amino groups;

[0008] (2) Under an inert atmosphere, diisocyanate, water-soluble oligomer diol, polymerization catalyst, organic solvent and hydroxyl or amino modified metal powder slurry obtained in step (1) are mixed and heated to prepare the composite microparticles.

[0009] This invention generates a water-soluble polyurethane coating layer in situ on the surface of metal powder through condensation polymerization, resulting in composite microparticles of water-soluble polyurethane-coated metal powder with a core-shell structure.

[0010] In the preparation method, the specific reaction involves the reaction of the carboxyl groups in the polyurethane chain extender with the metal powder to obtain a hydroxyl- or amino-modified metal powder slurry. Then, the hydroxyl or amino groups in the modified metal powder further undergo a condensation polymerization reaction with diisocyanate and water-soluble oligomer diol, thereby generating a dense water-soluble polyurethane coating layer in situ on the surface of the metal powder, resulting in the composite microparticles.

[0011] In the composite microparticles, the water-soluble polyurethane coating layer is uniform, dense, and not easily detached, effectively maintaining the activity of the metal powder and improving its stability during transportation and storage. Furthermore, due to the good water solubility of the coating layer, the composite microparticles require no special treatment and can directly react with water or acid solutions to release energy.

[0012] Preferably, the metal powder is selected from one or more of aluminum powder, magnesium powder, aluminum-magnesium alloy powder, magnesium alloy powder, and aluminum alloy powder; more preferably, it is aluminum powder or magnesium powder. The metal powder includes metal powders ranging from micron to nanometer scale.

[0013] Preferably, the polyurethane chain extender is selected from one or more of dimethylolpropionic acid, dimethylolbutyric acid, tartaric acid, N,N-dihydroxyethylglycine, N-[tris(hydroxymethyl)methyl]glycine, lysine, 2,4-diaminobutyric acid, and 2,5-diaminovaleric acid; more preferably, it is dimethylolpropionic acid or dimethylolbutyric acid.

[0014] If the amount of polyurethane chain extender described in this invention is too low, the metal powder may not be completely coated, resulting in poor coating effect; if the amount is too high, a large amount of polyurethane chain extender (containing carboxyl and hydroxyl groups, or containing carboxyl and amino groups) may be free in the reaction solvent, thereby affecting the in-situ synthesis of water-soluble polyurethane.

[0015] Preferably, the molar ratio of the metal powder to the polyurethane chain extender is 1:(0.0001-0.1); more preferably, it is 1:(0.001-0.005); and even more preferably, it is 1:0.002 or 1:0.004.

[0016] Preferably, the mass ratio of the metal powder to the organic solvent is 1:(1-100).

[0017] Preferably, the polymerization catalyst is selected from one or more of dibutyltin dilaurate, triphenylbismuth, triethoxyphenylbismuth, and stannous octoate; more preferably, it is dibutyltin dilaurate.

[0018] Preferably, the diisocyanate is selected from one or more of 4,4′-diisocyanate dicyclohexylmethane (HMDI), isophorone diisocyanate (IPDI), toluene diisocyanate (TDI), 1,6-hexanediisocyanate (HDI), 1,8-diisocyanate, trimethylhexanediisocyanate, diphenylmethane 4,4′-diisocyanate (MDI), and dimer acid diisocyanate; more preferably, it is 4,4′-diisocyanate dicyclohexylmethane (HMDI) or 1,6-hexanediisocyanate (HDI).

[0019] Preferably, the water-soluble oligomer diol is selected from one or more of polyethylene glycol, polypropylene glycol, and polytetrahydrofuran ether diol.

[0020] The present invention does not impose any particular limitation on the molecular weight of the water-soluble oligomeric diol.

[0021] In the preparation method described in this invention, step (2) can be divided into two cases:

[0022] The first method involves adding diisocyanate, water-soluble oligomer diol, and polymerization catalyst to the hydroxyl or amino modified metal powder slurry obtained in step (1) under an inert atmosphere, mixing, and heating to react, thereby preparing the composite microparticles.

[0023] The second method involves preparing an OCN-R-NCO type polyurethane prepolymer by mixing diisocyanate, oligomeric diol, and polymerization catalyst under an inert atmosphere; then, mixing it with the hydroxyl or amino modified metal powder slurry obtained in step (1) and polymerization catalyst, and heating the mixture to prepare the composite microparticles.

[0024] Preferably, a hydrophilic chain extender may be added in step (2) of this invention;

[0025] The hydrophilic chain extender applicable to this invention contains carboxyl, sulfonic acid, or tertiary amine groups.

[0026] Preferably, the hydrophilic chain extender is selected from one or more of dimethylolpropionic acid (DMPA), dimethylolbutyric acid, tartaric acid, N,N-dihydroxyethylglycine, sodium ethylenediaminoethanesulfonate, sodium 2-(diethanolamino)ethanesulfonate, sodium 1,4-butanediol-2-sulfonate, di(hydroxyethyl)methylamine, and 2-[(dimethylamino)methyl]-1,3-propanediol; more preferably, it is di(hydroxyethyl)methylamine or dimethylolbutyric acid.

[0027] If, in the above preparation method, a hydrophilic chain extender is added in step (2) to participate in the condensation polymerization reaction, after the heating reaction is completed, a neutralizing agent needs to be added to make the hydrophilic chain extender fragments in the polyurethane form salts, thereby improving the overall hydrophilic properties of the polyurethane.

[0028] When the water-soluble polyurethane contains carboxyl and sulfonic acid groups, the neutralizing agent includes, but is not limited to, triethylamine, tripropylamine, tributylamine, ammonia, sodium hydroxide, etc.

[0029] When the water-soluble polyurethane contains tertiary amino groups, the neutralizing agent includes, but is not limited to, dimethyl sulfate, methyl trifluoromethanesulfonate, propanesulfonate lactone, iodomethane, iodoethane, bromoethane, bromobutane, etc.

[0030] The preparation method of the present invention further includes post-treatment such as washing and drying of the obtained product after the heating reaction is completed.

[0031] The present invention does not impose any particular limitation on the solvent used for washing and the method of drying; any solvent or method known to those skilled in the art is acceptable.

[0032] In some specific embodiments of the present invention, the washing solvent is preferably acetone.

[0033] The preferred drying method is vacuum drying.

[0034] The vacuum drying temperature is preferably 30℃~100℃; more preferably 40℃~60℃.

[0035] The vacuum drying time is preferably ≥12 h.

[0036] In the preparation method described in this invention, the organic solvents in steps (1) and (2) include, but are not limited to, acetone, tetrahydrofuran, 1,4-dioxane, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone or dimethyl sulfoxide, etc.

[0037] Preferably, the molar ratio of the diisocyanate to the water-soluble oligomeric diol is 1:(0.01-2.0); more preferably, it is 1:(0.5-1.0).

[0038] Preferably, the molar ratio of the diisocyanate to the hydrophilic chain extender is 1:(0.01 to 1.0); more preferably, it is 1:(0.1 to 0.5).

[0039] Preferably, the molar ratio of the diisocyanate to the polymerization catalyst is 1:(0.0001~0.01).

[0040] Preferably, the temperature of the heating reaction is 40℃~100℃; more preferably, it is 60℃~90℃.

[0041] The preferred heating reaction time is 0.5 to 48 hours.

[0042] The present invention also provides composite microparticles of water-soluble polyurethane-coated metal powder prepared by the above preparation method.

[0043] The composite microparticles have a core-shell structure and are composed of metal powder and water-soluble polyurethane coated on their surface.

[0044] The metal powder and water-soluble polyurethane are connected by covalent bonds, making the water-soluble polyurethane coating layer stable and not easy to fall off.

[0045] The present invention also provides the application of the above-mentioned water-soluble polyurethane-coated metal powder composite particles in a metal-water reaction energy release system.

[0046] The metal-water reaction energy release system includes, but is not limited to, metal-water reaction hydrogen production, water jet power system, and chemical de-icing system in cold environments.

[0047] Compared with the prior art, the method for preparing the composite microparticles of water-soluble polyurethane-coated metal powder provided by the present invention includes the following steps: (1) Under an inert atmosphere, metal powder, polyurethane chain extender and organic solvent are mixed and reacted to obtain hydroxyl or amino modified metal powder slurry; the polyurethane chain extender contains carboxyl and hydroxyl groups, or contains carboxyl and amino groups; (2) Under an inert atmosphere, diisocyanate, water-soluble oligomeric diol, polymerization catalyst, organic solvent and the hydroxyl or amino modified metal powder slurry are mixed and heated to prepare the composite microparticles. The present invention generates a water-soluble polyurethane coating layer on the surface of metal powder in situ through condensation polymerization, which effectively maintains the activity of metal powder, improves storage stability, and, due to its excellent water solubility, allows the metal powder to release energy directly in water. Attached Figure Description

[0048] Figure 1SEM image of the water-soluble polyurethane-coated aluminum powder composite microparticles prepared in Example 1;

[0049] Figure 2 EDS image of the water-soluble polyurethane-coated aluminum powder composite microparticles prepared in Example 1;

[0050] Figure 3 Thermogravimetric analysis curves of the water-soluble polyurethane-coated aluminum powder composite particles prepared in Example 1. Detailed Implementation

[0051] To further illustrate the present invention, the preparation method of water-soluble polyurethane-coated metal powder composite microparticles and the composite microparticles provided by the present invention will be described in detail below with reference to embodiments.

[0052] Example 1

[0053] Step 1: Under an inert atmosphere, aluminum powder (5.0 g, 0.185 mol), dimethylolbutyric acid (0.059 g, 0.0004 mol), and 20 mL of anhydrous N,N-dimethylacetamide were added to a three-necked flask and stirred thoroughly for 4 hours to obtain a modified aluminum powder slurry.

[0054] Step 2: Under an inert atmosphere, add 0.331 g (0.0013 mol) of 4,4′-diisocyanate dicyclohexylmethane and two drops of dibutyltin dilaurate to the slurry from Step 1. After heating to 80°C and reacting for 2 hours, add (1.601 g (0.0008 mol) of polyethylene glycol 2000 and continue heating for 8 hours. Then, lower the reaction temperature to room temperature, filter the reaction solution, wash the obtained composite aluminum powder with acetone, and dry it in a vacuum oven to obtain water-soluble polyurethane-coated aluminum powder composite particles.

[0055] Figure 1 and Figure 2 The images shown are SEM and EDS images of the aluminum powder composite particles coated with water-soluble polyurethane in Example 1. The EDS results show that the aluminum powder surface contains carbon elements (red area in the figure), which indirectly indicates that the present invention achieves the coating of aluminum powder with water-soluble polyurethane. Figure 3 The thermogravimetric analysis curves of the aluminum powder composite particles coated with water-soluble polyurethane in Example 1 are shown. The results indicate that, within 800°C, the weight loss of the water-soluble polyurethane in the aluminum powder composite particles coated with water-soluble polyurethane is approximately 30% as the temperature increases.

[0056] Example 2

[0057] Step 1: Under an inert atmosphere, aluminum powder (5.0 g, 0.185 mol), 2,2-dimethylolpropionic acid (0.1080 g, 0.0008 mol), and 20 mL of anhydrous N,N-dimethylformamide were added to a three-necked flask and stirred thoroughly for 6 hours to obtain a modified aluminum powder slurry.

[0058] Step 2: Under an inert atmosphere, add (0.318 g, 0.0019 mol) 1,6-hexamethylene diisocyanate, (0.801 g, 0.0008 mol) polypropylene glycol 1000, (0.024 g, 0.0002 mol) di(hydroxyethyl)methylamine and two drops of dibutyltin dilaurate to the slurry from Step 1. Heat the mixed solution to 80°C, stir and react for 8 hours, then cool to room temperature. Add (0.0303 g, 0.00024 mol) dimethyl sulfate and stir and react for another 4 hours to form a salt of di(hydroxyethyl)methylamine. Then filter the reaction solution to obtain composite aluminum powder, wash with acetone, and dry in a vacuum oven at 40°C to obtain water-soluble polyurethane-coated aluminum powder composite particles.

[0059] Example 3

[0060] Step 1: Under an inert atmosphere, aluminum powder (5.0 g, 0.185 mol), 2,2-dimethylolpropionic acid (0.1080 g, 0.0008 mol), and 20 mL of anhydrous N,N-dimethylformamide were added to a three-necked flask and stirred thoroughly for 6 hours to obtain a modified aluminum powder slurry.

[0061] Step 2: Under an inert atmosphere, add 0.605 g (0.0036 mol) of 1,6-hexamethylene diisocyanate, 1.802 g (0.0018 mol) of polyethylene glycol 1000, and two drops of dibutyltin dilaurate to a three-necked flask. Heat to 70°C with stirring and react for 2 hours. Then add 0.1184 g (0.0008 mol) of dimethylolbutyric acid and continue the reaction for 4 hours. During the reaction, adjust the viscosity with 10 mL of anhydrous N,N-dimethylacetamide to obtain an OCN-R-NCO type polyurethane prepolymer solution. Then add 0.084 g (0.0002 mol) of triethylamine and stir the reaction solution for 4 hours to allow the carboxyl groups of dimethylolbutyric acid to form a salt. Add the obtained prepolymer solution to the slurry from Step 1, add two drops of dibutyltin dilaurate, and heat the mixture to 70°C to continue the reaction for 4 hours. After an hour, the reaction temperature was lowered to room temperature, the aluminum powder was filtered, washed with acetone, and dried in a vacuum oven at 40°C to obtain aluminum powder composite particles coated with water-soluble polyurethane.

[0062] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing composite microparticles of water-soluble polyurethane-coated metal powder, characterized in that, Includes the following steps: (1) Under an inert atmosphere, metal powder, polyurethane chain extender and organic solvent are mixed and reacted to obtain hydroxyl or amino modified metal powder slurry; wherein the polyurethane chain extender contains carboxyl and hydroxyl groups, or contains carboxyl and amino groups; (2) Under an inert atmosphere, diisocyanate, water-soluble oligomer diol, polymerization catalyst, organic solvent and hydroxyl or amino modified metal powder slurry obtained in step (1) are mixed and heated to prepare the composite microparticles.

2. The preparation method according to claim 1, characterized in that, The metal powder is selected from one or more of aluminum powder, magnesium powder, aluminum-magnesium alloy powder, magnesium alloy powder, and aluminum alloy powder; The polyurethane chain extender is selected from one or more of dimethylolpropionic acid, dimethylolbutyric acid, tartaric acid, N,N-dihydroxyethylglycine, N-[tris(hydroxymethyl)methyl]glycine, lysine, 2,4-diaminobutyric acid, and 2,5-diaminovaleric acid.

3. The preparation method according to claim 1 or 2, characterized in that, The molar ratio of the metal powder to the polyurethane chain extender is 1:(0.0001~0.1); The mass ratio of the metal powder to the organic solvent is 1:(1-100).

4. The preparation method according to claim 1, characterized in that, The polymerization catalyst is selected from one or more of dibutyltin dilaurate, triphenylbismuth, triethoxyphenylbismuth, and stannous octoate.

5. The preparation method according to claim 1, characterized in that, The diisocyanate is selected from one or more of 4,4′-diisocyanate dicyclohexylmethane, isophorone diisocyanate, toluene diisocyanate, 1,6-hexane diisocyanate, 1,8-diisocyanate, trimethylhexane diisocyanate, diphenylmethane 4,4′-diisocyanate, and dimer acid diisocyanate. The water-soluble oligomeric diol is selected from one or more of polyethylene glycol, polypropylene glycol, and polytetrahydrofuran ether diol.

6. The preparation method according to claim 1 or 5, characterized in that, A hydrophilic chain extender may also be added in step (2); The hydrophilic chain extender is selected from one or more of dimethylolpropionic acid, dimethylolbutyric acid, tartaric acid, N,N-dihydroxyethylglycine, sodium ethylenediaminoethanesulfonate, sodium 2-(diethanolamino)ethanesulfonate, sodium 1,4-butanediol-2-sulfonate, di(hydroxyethyl)methylamine, and 2-[(dimethylamino)methyl]-1,3-propanediol.

7. The preparation method according to claim 6, characterized in that, The molar ratio of the diisocyanate to the water-soluble oligomeric diol is 1:(0.01~2.0); The molar ratio of the diisocyanate to the hydrophilic chain extender is 1:(0.01~1.0); The molar ratio of the diisocyanate to the polymerization catalyst is 1:(0.0001~0.01).

8. The preparation method according to claim 1, characterized in that, The temperature of the heating reaction is 40℃~100℃.

9. Composite microparticles of water-soluble polyurethane-coated metal powder prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the composite microparticles of water-soluble polyurethane-coated metal powder as described in claim 9 as fuel in a metal-water reaction energy release system.

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