A core-shell structure anti-hygroscopic ammonium dinitroamide composite material, a preparation method and application thereof

Abstract

This invention discloses a core-shell structured moisture-resistant ammonium dinitramide composite material, its preparation method, and its applications. The composite material uses ammonium dinitramide (ADN) as the core and methyl methacrylate-butyl acrylate copolymer (PMMA-BA) as the shell. A solvent-non-solvent method is used to precipitate and coat the PMMA-BA copolymer onto the ADN surface, resulting in the ADN@PMMA-BA core-shell structured composite material. This invention effectively shields the polar ionic sites on the ADN surface by constructing a dense hydrophobic polymer shell, significantly reducing its adsorption and permeation of water molecules. While maintaining the original thermal stability and energy performance of ADN, this material exhibits reduced moisture absorption and increased water contact angle, demonstrating excellent moisture-resistant properties. It is suitable for applications in humidity-sensitive explosives, propellants, and blasting agents, effectively extending the storage stability and safety of ADN-containing materials.

Description

Technical Field

[0001] This invention belongs to the field of energetic materials and moisture-proof technology, specifically relating to a core-shell structure, high moisture-proof properties of dinitramide ammonium composite material and its preparation method, as well as the application of this material in the fields of explosives, propellants and so on. Background Technology

[0002] Ammonium dinitramide (ADN) is an important industrial oxidant, widely used in solid propellants and industrial explosives due to its high oxygen content, low cost, and clean decomposition products. However, the dinitramide group (N(NO2)2) in the ADN molecule... - Due to its high electronegativity, ADN readily forms hydrogen bonds with water molecules, making it extremely hygroscopic. After absorbing moisture, ADN deliquesces and clumps, severely damaging its physical morphology and flowability. This not only affects its performance (such as mixing uniformity and combustion rate) but also significantly reduces its energy density. More dangerously, moisture absorption can lead to uncontrollable crystal transformations, posing safety hazards. Therefore, improving the moisture resistance of ADN is crucial for expanding its application range and ensuring safe storage and use.

[0003] Currently, research on moisture-resistant modification of ADN mainly focuses on physical coating and eutectic modification. Physical coating involves constructing a hydrophobic barrier on the surface of ADN particles to isolate water molecules; commonly used coating materials include paraffin and polymers. However, traditional coating methods often suffer from uneven coating, weak bonding with the ADN matrix, or significant impact on energy performance. While eutectic modification can improve hygroscopicity, the introduced eutectic agent usually alters the oxygen balance of ADN, leading to a decline in its performance as an oxidant. Therefore, developing a surface modification technique that is simple to process, produces uniform and dense coating, and can maximally preserve the intrinsic properties of ADN is of significant practical importance. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a core-shell structured, moisture-resistant ammonium dinitramide composite material. This material effectively blocks water molecules by constructing a uniform and dense polymer shell, significantly reducing the moisture absorption rate of ADN while maintaining its good thermal stability and energy properties.

[0005] Another objective of this invention is to provide a method for preparing the above-mentioned core-shell structured moisture-resistant dinitramide ammonium composite material. This method is simple, operates under mild conditions, produces uniform coating, and is easily scalable for mass production.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a core-shell structured moisture-resistant dinitramide ammonium composite material, which uses dinitramide ammonium particles as the core and methyl methacrylate-butyl acrylate copolymer as the shell to form an ADN@PMMA-BA core-shell structure.

[0008] Secondly, the present invention provides a method for preparing the above-mentioned core-shell structured moisture-resistant dinitramide ammonium composite material, comprising the following steps:

[0009] 1) Coating agent preparation: MMA and BA are dissolved in a solvent in a certain proportion, an initiator is added, and a copolymerization reaction is carried out at a certain temperature to obtain PMMA-BA copolymer.

[0010] 2) Core-shell composite: Dissolve the above PMMA-BA copolymer in the first solvent, add the sieved ADN particles, and stir to fully disperse them.

[0011] 3) Precipitation and Coating: The above mixture is placed in a constant temperature water bath, and the second solvent is slowly added dropwise while stirring. With the addition of the precipitant, PMMA-BA gradually precipitates on the surface of the ADN particles and forms a coating layer.

[0012] 4) Post-processing: After coating is completed, the system is cooled and filtered. The resulting solid product is dried under vacuum to obtain ADN@PMMA-BA core-shell composite material.

[0013] Thirdly, the present invention provides the application of the above-mentioned core-shell structure moisture-proof dinitramide ammonium composite material as a moisture-proof oxidizer in the fields of energetic materials, solid propellants, and civil explosives.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0015] 1) Significant moisture-proof effect: This invention constructs a dense polymer shell on the surface of ammonium dinitramide particles to form a core-shell structured composite material. The prepared composite material exhibits excellent moisture-proof ability in humid environments, effectively preventing problems such as deliquescence and agglomeration caused by ADN moisture absorption.

[0016] 2) Significantly improved surface properties: This invention uses PMMA-BA copolymer as the shell material, successfully transforming the original strongly hydrophilic surface of ADN into a hydrophobic surface. The surface hydrophobicity of the composite material is significantly improved, which can effectively inhibit the initial adsorption and spreading of water, reducing the possibility of water intrusion from the source.

[0017] 3) Enhanced thermal stability: The preparation process of this invention is mild, and the shell material is uniformly coated on the surface of ADN in a physical manner. The resulting dense shell also has a certain thermal barrier function, which helps to delay the thermal decomposition process of ADN and enhance its thermal stability.

[0018] 4) Simple and controllable preparation process: The solvent-non-solvent method used in this invention is simple. By adjusting parameters such as solvent ratio, reaction temperature, and amount of coating agent, the thickness and density of the coating layer can be effectively controlled. It has good reproducibility and is suitable for industrial production. Attached Figure Description

[0019] Figure 1 The infrared spectrum of the PMMA-BA copolymer shell material prepared in Example 1 is shown.

[0020] Figure 2 The image shows a scanning electron microscope (SEM) image of composite material 1 prepared in Example 1.

[0021] Figure 3 This is a high-resolution scanning electron microscope image of composite material 1 prepared in Example 1.

[0022] Figure 4 This is a photograph of the water contact angle of composite material 1 prepared in Example 1.

[0023] Figure 5 Photographs showing the water contact angle of composite material 2 prepared in Example 2.

[0024] Figure 6 This is a photograph of the water contact angle of composite material 3 prepared in Example 3.

[0025] Figure 7 This is a photograph of the water contact angle of composite material 4 prepared in Example 4.

[0026] Figure 8 This is a photograph of the water contact angle of composite material 6 prepared in Comparative Example 1.

[0027] Figure 9 This is a photograph of the water contact angle of composite material 7 prepared in Comparative Example 2.

[0028] Figure 10 The graph shows the DVS test data of composite material 3 prepared in Example 3.

[0029] Figure 11 This is a graph showing the DVS test data of the raw material ADN.

[0030] Figure 12 The graph shows the thermal stability test data of composite materials 3, 5, and 6 with the raw material ADN. Detailed Implementation

[0031] The present application will be further described below with reference to specific embodiments.

[0032] It should be noted that terms such as "upper", "lower", "left", "right", and "middle" used in this specification are only for clarity of description and are not intended to limit the scope of implementation. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered as within the scope of this application.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the term “and / or” as used herein includes any and all combinations of one or more of the associated listed items.

[0034] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0035] As used herein, the term “about” is used to provide for the flexibility and imprecision associated with a given term, measure, or value. Those skilled in the art can readily determine the degree of flexibility for a particular variable.

[0036] As used herein, the term “at least one of…” is intended to be synonymous with “one or more of…”. For example, “at least one of A, B, and C” explicitly includes only A, only B, only C, and combinations thereof.

[0037] The ADN@PMMA-BA composite materials in the following embodiments were prepared by the following steps:

[0038] 1) Preparation of PMMA-BA copolymer: Add 30 mL of chloroform, a mixture of MMA and BA monomers, and AIBN initiator to a four-necked flask. Stir magnetically for 8 hours. After the reaction is complete, cool the solution and pour it into a petri dish. After the solvent evaporates naturally, a transparent PMMA-BA film is obtained.

[0039] 2) Preparation of core-shell structured dinitramide ammonium composite material: Add 5 mL of chloroform to a 100 mL round-bottom flask and dissolve 0.004–0.1 g (0.2%–5.0% of ADN mass) of PMMA-BA. Add 2.0 g of ADN particles and stir in a water bath at a reaction temperature of 10–40 °C. Using a constant-pressure dropping funnel, add 25–50 mL of n-hexane (chloroform:n-hexane = 1:5–1:10) dropwise to the system at a rate of approximately 1–3 drops / second. After the addition is complete, continue stirring and allow to cool naturally to room temperature.

[0040] 3) Post-processing: The reaction mixture was transferred to a sand core funnel for filtration. The filter cake was placed in a petri dish and dried in a vacuum drying oven to constant weight to obtain a white powdery core-shell structured ADN@PMMA-BA composite material.

[0041] Example 1

[0042] 1) Preparation of PMMA-BA copolymer: 30 mL of chloroform, a mixture of MMA and BA monomers, and AIBN initiator were added to a four-necked flask. The mixture was magnetically stirred for 8 hours. After the reaction was completed, the solution was cooled and poured into a petri dish. After the solvent evaporated naturally, a transparent PMMA-BA film was obtained.

[0043] 2) Preparation of core-shell structured ammonium dinitramide composite material: Add 5 mL of chloroform to a 100 mL round-bottom flask to dissolve 0.02 g (1.0% of ADN mass) of PMMA-BA. Add 2.0 g of pretreated ADN particles and stir in a water bath at 15 °C. Using a constant-pressure dropping funnel, add 40 mL of n-hexane (chloroform:n-hexane = 1:8) to the system at a rate of approximately 2 drops / second. After the addition is complete, continue stirring and allow to cool naturally to room temperature.

[0044] 3) Post-processing: The reaction mixture was transferred to a sand core funnel for filtration. The filter cake was placed in a petri dish and dried in a vacuum drying oven to constant weight to obtain a white powdery core-shell structured ADN@PMMA-BA composite material, which was named composite material 1.

[0045] Example 2

[0046] The other processes are the same as in Example 1, except that the reaction temperature is controlled at 20 °C in this example to obtain a core-shell structured ADN@PMMA-BA composite material, which is named Composite Material 2.

[0047] Example 3

[0048] The other processes are the same as in Example 1, except that the reaction temperature is controlled at 30 °C in this example to obtain a core-shell structured ADN@PMMA-BA composite material, which is named Composite Material 3.

[0049] Example 4

[0050] The other processes are the same as in Example 1, except that the reaction temperature is controlled at 40 °C in this example to obtain a core-shell structured ADN@PMMA-BA composite material, which is named Composite Material 4.

[0051] Comparative Example 1

[0052] 1) Preparation of PMMA homopolymer: Add 30 mL of chloroform, MMA monomer, and AIBN initiator to a four-necked flask. Stir magnetically for 8 hours. After the reaction is complete, cool the solution and pour it into a petri dish. After the solvent evaporates naturally, a transparent PMMA film is obtained.

[0053] 2) Preparation of core-shell structured ammonium dinitramide composite material: Add 5 mL of chloroform to a 100 mL round-bottom flask to dissolve 0.02 g (1.0% of ADN mass) of PMMA. Add 2.0 g of pretreated ADN particles and stir in a water bath at 30 °C. Using a constant-pressure dropping funnel, add 40 mL of n-hexane (chloroform:n-hexane = 1:8) to the system at a rate of approximately 2 drops / second. After the addition is complete, continue stirring and allow to cool naturally to room temperature.

[0054] 3) Post-processing: The reaction mixture was transferred to a sand core funnel for filtration. The filter cake was placed in a petri dish and dried in a vacuum drying oven to constant weight to obtain a white powdery core-shell structured ADN@PMMA composite material, which was named composite material 5.

[0055] Comparative Example 2

[0056] 1) Preparation of PBA homopolymer: Add 30 mL of chloroform, BA monomer, and AIBN initiator to a four-necked flask. Stir magnetically for 8 hours. After the reaction is complete, cool the solution and pour it into a petri dish. After the solvent evaporates naturally, a transparent PBA film is obtained.

[0057] 2) Preparation of core-shell structured dinitramide ammonium composite material: Add 5 mL of chloroform to a 100 mL round-bottom flask to dissolve 0.02 g (1.0% of ADN mass) of PBA. Add 2.0 g of pretreated ADN particles and stir in a water bath at 30 °C. Using a constant-pressure dropping funnel, add 40 mL of n-hexane (chloroform:n-hexane = 1:8) to the system at a rate of approximately 2 drops / second. After the addition is complete, continue stirring and allow to cool naturally to room temperature.

[0058] 3) Post-processing: The reaction mixture was transferred to a sand core funnel for filtration. The filter cake was placed in a petri dish and dried in a vacuum drying oven to constant weight to obtain a white powdery core-shell structured ADN@PBA composite material, which was named composite material 6.

[0059] Characterization and test results

[0060] The core-shell structured ADN@PMMA-BA composite materials prepared in the above four examples have the same morphology, but their reaction temperatures are different. The reaction temperature in the comparative example is the same as that in example 3, but the shell material prepared in comparative example 1 is a PMMA homopolymer, and the shell material prepared in comparative example 2 is a PBA homopolymer.

[0061] Figure 1 The images show the infrared spectra of the PMMA-BA copolymers with the same shell material prepared in Examples 1-4. It can be seen from the images that the peak shapes of the PMMA-BA copolymers with the shell material are consistent.

[0062] Figure 2 The image shows a scanning electron microscope (SEM) image of the core-shell structured ADN@PMMA-BA composite material prepared in Example 1. As can be seen from the image, the prepared core-shell structured ADN@PMMA-BA composite material is granular and has a relatively uniform morphology.

[0063] Figure 3 The image shows a high-resolution scanning electron microscope (SEM) image of the core-shell structured ADN@PMMA-BA composite material prepared in Example 1. The image shows that the shell material, PMMA-BA copolymer, is uniformly and densely coated on the surface of the ADN particles.

[0064] Water contact angle tests were conducted on composite materials 1, 2, 3, 4, 5, and 6 prepared in Examples 1-4 and Comparative Examples 1-2, respectively. The results are as follows: Figures 4-9 As shown, the change in the contact angle can be used to reflect the moisture-wicking effect of the composite material. Generally speaking, the larger the contact angle, the better the moisture-wicking effect. From the image, it can be seen that the shell material is a PMMA homopolymer (…). Figure 8 ) and the shell material is PBA homopolymer ( Figure 9 The contact angles of the shell material are all relatively small, while the shell material is a PMMA-BA copolymer at a reaction temperature of 30 °C. Figure 6 The core-shell structured ADN@PMMA-BA composite material exhibits the best moisture-proof performance. The contact angle of the prepared ADN@PMMA-BA composite material reaches 61.3°, indicating that among the moisture-proof dinitramide ammonium composite materials, the copolymer shell material has the best moisture-proof effect for dinitramide ammonium compared to the single homopolymer material, and the protective effect is best when the reaction temperature is 30 °C.

[0065] Table 1. Moisture absorption data of different samples after 2 hours of constant temperature and humidity testing.

[0066] Sample Name Moisture absorption rate / % Moisture absorption rate reduction / % Raw material ADN 16.57 - Composite Material 1 5.94 64.15 Composite Material 2 5.21 68.53 Composite Material 3 4.66 71.87 Composite Material 4 4.97 70.02 Composite Material 5 12.48 24.71 Composite Material 6 13.07 21.14

[0067] Composite materials 1, 2, 3, 4, 5, and 6 prepared in Examples 1-4 and Comparative Examples 1-2 were subjected to constant temperature and humidity tests (25°C, 65% RH, 2h), and their moisture absorption data are shown in Table 1. Lower moisture absorption rates and greater reductions in moisture absorption indicate superior moisture-proof performance of the composite materials. As can be seen from the data in Table 1, the moisture absorption rates of all composite materials were significantly lower than the 16.57% of the raw material AND, indicating that the introduction of the PMMA-BA shell generally improved the moisture-proof capability of ADN. Among them, composite materials 5 and 6 showed relatively low reductions in moisture absorption rates, at 24.71% and 21.14% respectively, indicating relatively limited moisture-proof performance. In contrast, composite materials 1-4, prepared using PMMA-BA copolymer as the shell material, all had moisture absorption rates reduced to below 6%, with reductions exceeding 64%, demonstrating excellent moisture-proof performance. In particular, the composite material 3 prepared when the reaction temperature was controlled at 30°C had the lowest moisture absorption rate and the highest moisture absorption rate reduction, reaching 71.87%, indicating that under this optimized process condition, the PMMA-BA copolymer shell had the best moisture-proof effect on dinitramide ammonium.

[0068] The above tests show that the copolymer PMMA-BA shell material exhibits the best moisture-resistant effect on dinitramide ammonium when the reaction temperature is controlled at 30 °C. To further verify the moisture-inhibiting effect of the copolymer PMMA-BA shell material on dinitramide ammonium, composite material 3 and raw material ADN were tested using a DVS instrument at 25 °C and 65% RH. The moisture absorption data are as follows: Figures 10-11 As shown. Due to the N(NO2)2 in the raw material ADN molecule. - Ions readily adsorb water molecules from the environment, exhibiting extremely high hygroscopicity. It was observed that the raw material ADN reached hygroscopic equilibrium in approximately 80 minutes, while the prepared core-shell structured ADN@PMMA-BA composite material reached equilibrium in 150 minutes, with a significantly reduced equilibrium moisture absorption. This indicates that the core-shell structured ADN@PMMA-BA composite material has a better anti-hygroscopic effect than the raw material ADN, confirming the effective inhibitory function of the PMMA-BA copolymer shell material on the moisture absorption of dinitramide ammonium.

[0069] Composite materials 3, 5, and 6, along with raw material ADN, were subjected to thermal stability tests to observe their effects on the thermal stability of dinitramide ammonium. The thermal performance data are as follows: Figure 12As shown, TG-DSC analysis revealed that the thermal decomposition temperature of the ADN@PMMA composite material was not significantly different from that of the raw material ADN, both decomposing at around 229 °C. However, the decomposition endothermic peak of ADN@PMMA-BA was delayed to 242 °C, confirming the enhancing effect of the PMMA-BA copolymer shell material on the thermal stability of dinitramide ammonium.

[0070] In summary, this invention successfully prepared an ADN@PMMA-BA core-shell composite material with excellent moisture-proof properties. The preparation process is simple, the conditions are mild, and the coating is uniform. This material significantly improves the moisture absorption defects of ADN while maintaining good intrinsic properties, making it of significant application value in the field of energetic materials.

[0071] The above embodiments are merely preferred embodiments of the present invention, but the implementation of the present invention is not limited to the above embodiments. Any changes, modifications, substitutions, or combinations made without departing from the spirit and principle of the present invention, such as various combinations of solutions in the embodiments, should be considered equivalent replacements and are all within the protection scope of the present invention.

Claims

1. A core-shell structured, moisture-resistant dinitramide ammonium composite material, characterized in that, A core-shell structure is formed with ammonium dinitramide particles as the core and methyl methacrylate-butyl acrylate copolymer as the shell.

2. The core-shell structured moisture-resistant dinitramide ammonium composite material as described in claim 1, characterized in that, The amount of methyl methacrylate-butyl acrylate copolymer added is 0.2% to 5.0% of the mass of dinitramide ammonium, preferably 1.0%.

3. A method for preparing a core-shell structured, moisture-resistant, dinitramide ammonium composite material as described in claim 1 or 2, characterized in that, Includes the following steps: Step 1: Copolymerize methyl methacrylate (MMA), butyl acrylate (BA), and an initiator in a solvent to prepare PMMA-BA copolymer; Step 2: Dissolve the obtained PMMA-BA copolymer in the first solvent, add dinitramide ammonium granules, and stir to disperse to form a uniform system; Step 3: Add the second solvent as a precipitant to the system obtained in Step 2, and control the reaction temperature to allow the PMMA-BA copolymer to precipitate and coat the surface of the dinitramide ammonium particles; Step 4: Filter and collect the solid product. After drying, the core-shell structured moisture-proof dinitramide ammonium composite material is obtained.

4. The preparation method according to claim 3, characterized in that, The molar ratio of MMA to BA is 1:

1.

5. The preparation method according to claim 3, characterized in that, The first solvent is chloroform; the second solvent is n-hexane; the volume ratio of the first solvent to the second solvent is 1:5 to 1:10, preferably 1:

8.

6. The preparation method according to claim 3, characterized in that, In step 3, the reaction temperature is 10°C to 40°C, preferably 30°C.

7. The preparation method according to claim 3, characterized in that, The dropping rate of the precipitant is 1-3 drops / second.

8. The application of a core-shell structured moisture-resistant dinitramide ammonium composite material as described in claim 1 or 2 in solid propellants or explosives.

9. The application of the core-shell structured moisture-resistant dinitramide ammonium composite material as described in claim 1 as a moisture-proof oxidant.

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