A method for preventing moisture absorption of dinitramide ammonium by coating modification

Abstract

The application discloses a kind of anti-hygroscopic coating modification methods of dinitramide, belong to the field of anti-hygroscopic of energetic oxidizer.The method of the present application uses polyvinyl butyral and fatty acid surfactant as mixed coating agent, and forms polymer-surfactant synergistic anti-hygroscopic coating layer on the surface of dinitramide particles by liquid phase surface coating method;The fatty acid surfactant is octadecanoic acid or eicosanoic acid.Compared with prior art, the present application uses specific polymer and fatty acid surfactant synergistic coating strategy, improves the anti-hygroscopic property of dinitramide without changing its crystal structure and crystal form, realizes the improvement of the anti-hygroscopic property of dinitramide while improving its mechanical safety.The process of the present application is simple, mild, can effectively improve the hygroscopicity of dinitramide, and provides technical support for the practical application of dinitramide in the field of high-energy energetic materials.

Description

Technical Field

[0001] This invention relates to the field of moisture-proofing oxidants, specifically providing a method for moisture-proofing coating modification of dinitramide ammonium. Background Technology

[0002] Ammonium dinitramide (ADN) is a high-energy oxidant with advantages such as high oxygen content, high energy density, low characteristic signal, and environmental friendliness, showing broad application prospects in solid propellants, gas generators, and civilian energetic materials. However, ADN is extremely hygroscopic, with a low critical hygroscopic point. Under normal temperature and humidity conditions, it readily adsorbs moisture from the environment, leading to deliquescence and agglomeration on the particle surface, severely affecting its storage stability, processability, and safety in use.

[0003] Currently, research on moisture-wicking modification of ADN mainly employs methods such as paraffin physical coating, surfactant coating, polymer film coating, coupling agent coating, and inorganic nanomaterial coating. However, single coating methods have significant limitations in practical applications: although surfactants can form an adsorption layer on the ADN surface with their amphiphilic structure, reducing the moisture absorption rate to some extent, their coating layer lacks density and is difficult to effectively block moisture for a long time; although polymer coating can form a relatively continuous physical barrier through film-forming properties, due to the strong polarity of the ADN surface, single polymer films often suffer from weak interfacial bonding and unsatisfactory hydrophobicity, thus limiting the protective effect.

[0004] Theoretically, combining polymers and surfactants could potentially combine the advantages of both: surfactants can improve the wettability and interfacial compatibility of ADN surfaces, providing a favorable foundation for polymer film formation; while polymers can form a continuous and dense hydrophobic film layer based on the surfactant adsorption layer. However, simply mixing the two directly for coating often faces significant technical barriers: on the one hand, the phase behavior of polymers and surfactants in solution is complex, and poor compatibility can easily lead to uneven coating layer structure, or even damage to their respective film-forming properties; on the other hand, the long-chain alkyl groups of surfactants may compete with polymer segments for adsorption, interfering with the orderly arrangement of the polymer and reducing the density and hydrophobic effect of the coating layer. Therefore, how to achieve orderly synergy between the two and construct a composite coating layer with controllable structure is a key challenge that urgently needs to be overcome in current research on ADN moisture-wicking modification. Summary of the Invention

[0005] This invention addresses the shortcomings of existing technologies by providing a method for modifying ammonium dinitramide (ADN) through a moisture-resistant coating. This method employs a synergistic coating strategy of a specific polymer and a fatty acid surfactant, improving the moisture-resistant properties of ADN without altering its crystal structure and form. This achieves both enhanced moisture-resistant properties and improved mechanical safety of ADN.

[0006] The technical solution adopted by the present invention to solve its technical problem is: a method for modifying dinitramide ammonium with anti-hygroscopic coating, characterized by using polyvinyl butyral and fatty acid surfactants as mixed coating agents, and forming a polymer-surfactant synergistic anti-hygroscopic coating layer on the surface of dinitramide ammonium particles by liquid phase surface coating method.

[0007] Preferably, the coating modification method of the present invention employs a mixed coating process, comprising the following steps: Polyvinyl butyral and fatty acid surfactants are dissolved in a good solvent to form a coating agent solution; Add an appropriate amount of dried dinitramide ammonium granules to the coating agent solution, and after dispersing evenly under stirring at 40±3℃, slowly add a certain amount of unsuitable solvent, and react at a constant temperature for a certain period of time. The temperature was slowly lowered to 15±3℃, the solid was separated, and after drying, the modified dinitramide ammonium product was obtained.

[0008] Preferably, the fatty acid surfactant is octadecanoic acid or icosanoic acid.

[0009] Preferably, based on the mass of dinitramide ammonium, the mass fraction of polyvinyl butyral is 2.00%. wt %~3.00 wt %, with a preferred value of 2.25%. wt % ~2.75 wt The molecular weight of the polyvinyl butyral is 25,000 to 40,000.

[0010] Preferably, based on the mass of dinitramide ammonium, the mass fraction of the fatty acid surfactant is 1.00%. wt % ~2.00 wt %, with a particularly preferred value of 1.25%. wt % ~1.75 wt %.

[0011] Preferably, the good solvent is dichloromethane or trichloromethane, and dichloromethane is particularly preferred.

[0012] Preferably, the undesirable solvent is n-hexane or cyclohexane, with n-hexane being particularly preferred.

[0013] Preferably, the volume ratio of good solvent to poor solvent is 1:3 to 1:7, and particularly preferably 1:5 to 1:6, wherein the amount of good solvent is sufficient to dissolve the coating agent.

[0014] Preferably, the stirring speed is 200-300 r / min, and more preferably 240-280 r / min.

[0015] Preferably, the reaction is carried out at a constant temperature for 1.5 to 4 hours after adding a poor solvent, and more preferably for 1.5 to 2.5 hours.

[0016] Preferably, the isothermal reaction temperature is 40±1℃.

[0017] Preferably, the coating modification method of the present invention employs a step-by-step coating process, including: First, the dinitramide ammonium particles are coated with polyvinyl butyral. The dinitramide ammonium particles coated with polyvinyl butyral are then coated a second time with a fatty acid surfactant.

[0018] Preferably, the primary coating includes: Polyvinyl butyral is dissolved in a good solvent to form a coating agent solution; Add an appropriate amount of dried dinitramide ammonium granules to the coating agent solution, and after dispersing evenly under stirring at 40±3℃, slowly add a certain amount of unsuitable solvent, and react at a constant temperature for a certain period of time. The temperature was slowly lowered to 15±3℃, the solid was separated, and after drying, dinitramide ammonium particles coated with polyvinyl butyral were obtained. The secondary coating includes: Fatty acid surfactants were dissolved in a poor solvent and polyvinyl butyral-coated dinitramide ammonium particles were dispersed therein. The mixture was reacted at 40±3℃ under stirring for a certain period of time. The temperature was lowered to 15±3℃, the solid was separated, and after drying, the modified dinitramide ammonium product was obtained.

[0019] Compared with the prior art, the anti-hygroscopic coating modification method of dinitramide ammonium of the present invention has the following outstanding advantages: (1) Simple process: The operation conditions of this method are mild, the reaction temperature is only 40℃, no high temperature and high pressure equipment is required, and the coated sample can be prepared by one-time mixing, which saves time and cost and is suitable for industrial production; (2) The coating materials used are low in cost and widely available; (3) The polymer provides rigidity and density to the film layer, while the surfactant reduces surface polarity and enhances the dispersibility of the coating system. The synergistic use of the two can significantly improve the continuity and uniformity of the film layer, thereby improving the moisture-proof performance and mechanical safety of the modified dinitramide ammonium. Under optimal process conditions, the moisture absorption rate of modified ADN decreased from 28.97% to 14.63% after 2 hours at 25℃ and 75% RH, a reduction of 49.49%. The friction sensitivity of modified ADN increased from 72 N to 84 N, providing a basic guarantee for the safe production and storage application of ADN. Attached Figure Description

[0020] Figure 1 This is a schematic diagram illustrating the coating principle of ADN by mixing PVB and stearic acid in Example 1. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. In the following description, unless otherwise defined, the technical and scientific terms used will have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In the following description and drawings, descriptions relating to well-known functions and structures that may obscure the essence of the invention will be omitted.

[0022] As attached Figure 1 As shown, one aspect of the present invention relates to a method for moisture-resistant coating modification of dinitramide ammonium using a mixed coating, comprising: dissolving polyvinyl butyral (molecular weight range 25000~40000) and fatty acid surfactants in a good solvent to form a coating agent solution; adding an appropriate amount of dried dinitramide ammonium particles to the coating agent solution, dispersing at 40±3℃ and a stirring speed of 200~300r / min, and after uniform dispersion, slowly adding a certain amount of unsuitable solvent, and continuing the reaction at a constant temperature for 1.5~4h; slowly cooling to 15±3℃, separating the solid, and drying to obtain the modified dinitramide ammonium product.

[0023] This invention also relates to a method for moisture-resistant coating modification of ammonium dinitramide using stepwise coating, comprising: One-step coating: Polyvinyl butyral (molecular weight range 25,000~40,000) is dissolved in a good solvent to form a coating agent solution; an appropriate amount of dried dinitramide ammonium particles are added to the coating agent solution and dispersed at 40±3℃ and a stirring speed of 200~300r / min. After uniform dispersion, a certain amount of poor solvent is slowly added dropwise, and the reaction is carried out at a constant temperature for 1.5~4h; the temperature is slowly lowered to 15±3℃, the solid is separated, and after drying, polyvinyl butyral-coated dinitramide ammonium particles are obtained. Secondary coating: Fatty acid surfactants are dissolved in a poor solvent, and polyvinyl butyral-coated dinitramide ammonium particles are dispersed in it. The mixture is reacted at a constant temperature of 40±3℃ and a stirring speed of 200~300r / min for 1.5~4h. The temperature is then lowered to 15±3℃, the solid is separated, and the modified dinitramide ammonium product is obtained after drying.

[0024] Main reagents and instruments used in the embodiments and comparative examples of this invention: Ammonium dinitramide: 500 g, Xi'an Modern Chemistry Research Institute; Polyvinyl butyral: 500g, MW25000 ~ 40000, Nanjing Juyou Scientific Instruments Co., Ltd. Octadectin: 500g, 98%, Nanjing Wanqing Chemical Glassware Co., Ltd. Etiological acid: 5g, 98%, Nanjing Wanqing Chemical Glassware Co., Ltd.; Dichloromethane: 500mL, AR, 99%, Sinopharm Chemical Reagent Co., Ltd.; Chloroform: 500mL, AR, 99%, Sinopharm Chemical Reagent Co., Ltd.; n-Hexane: 500mL, AR, 99%, Nanjing Wanqing Chemical Glassware Co., Ltd.; Constant temperature and humidity chamber; GT-THS-22Z, Hubei Gaotian Test Equipment Co., Ltd.; BAM friction sensitivity meter: FST 20; Adiseon (Beijing) Technology Co., Ltd.

[0025] Example 1 (Preparation method of mixed coating, the coating agent is PVB and stearic acid) (1) Place the ADN raw material in a vacuum drying oven at 35℃ and dry it for 5 h until constant weight. Then seal and store it for later use.

[0026] (2) Weigh 0.05 g PVB and 0.03 g octadecanoic acid into a 100 mL three-necked flask, add 5 mL of dichloromethane, and after the coating agent dissolves, weigh 2 g of the above ADN particles and disperse them in the coating system. Place the apparatus in a water bath, adjust the temperature to 40℃, and the mechanical stirring speed is 250 r / min. After the system is evenly dispersed, slowly add 25 mL of n-hexane and react at a constant temperature for 2 h. The total volume of dichloromethane and n-hexane is 30 mL, and the volume ratio is 1:5.

[0027] (3) Stop heating and slowly cool down to 15°C. Place the solid product separated by vacuum filtration in a vacuum drying oven and dry at 35°C for 30 min to obtain a PVB / octadecanoic acid mixed coating modified ADN sample.

[0028] Example 2 (Preparation method of mixed coating, the coating agent is PVB and eicosanoic acid) Using the same process conditions as in Example 1, octadecanoic acid was replaced with an equal mass fraction (1.5%). wt% The remaining steps remain unchanged, and a PVB / eicosic acid mixed coating modified ADN sample is obtained.

[0029] Example 3 (two-stage coating preparation method, coating agents are PVB and stearic acid) (1) ADN pretreatment is the same as in Example 1.

[0030] (2) First coating: Weigh 0.05 g of PVB into a 100 mL three-necked flask, add 5 mL of dichloromethane, and after the coating agent dissolves, weigh 2 g of dried ADN particles and disperse them in the coating system. Place the apparatus in a water bath, adjust the temperature to 40℃, and mechanically stir at 250 r / min. After the system is evenly dispersed, slowly add 25 mL of n-hexane and react at a constant temperature for 2 h. The total volume of dichloromethane and n-hexane is 30 mL, with a volume ratio of 1:5. After the reaction is complete, cool to 15℃, filter under reduced pressure, and dry at 35℃ for 30 min to obtain PVB-coated ADN particles.

[0031] (3) Second coating: 0.03 g of stearic acid was dissolved in 30 mL of n-hexane, and 2.0 g of the above PVB-coated ADN particles were dispersed in it. The mixture was mechanically stirred in a water bath at 40 °C at a stirring speed of 250 r / min and reacted at a constant temperature for 2 h. After the reaction was completed, the temperature was lowered to 15 °C, filtered and dried to obtain the PVB / stearic acid secondary coated ADN sample.

[0032] Example 4: (Preparation method of mixed coating, the coating agent is PVB and stearic acid) The only difference from Example 1 is the amount of PVB and stearic acid used, as follows:

[0033] Example 5 (Preparation method of mixed coating, the coating agent is PVB and stearic acid) The only difference from Example 1 is the volume ratio of the good solvent to the poor solvent, and the specific amounts are as follows:

[0034] Example 6 (Preparation method of mixed coating, the coating agent is PVB and stearic acid) The only difference from Example 1 is the solvent, as detailed below:

[0035] Comparative Example 1 (Blank Group) No ADN was coated, serving as a blank control group.

[0036] Comparative Example 2 (using PVB as the coating agent only) (1) ADN pretreatment is the same as in Example 1.

[0037] (2) Weigh 0.08 g of PVB into a 100 mL three-necked flask, add 5 mL of dichloromethane, and after the coating agent dissolves, weigh 2 g of dried ADN particles and disperse them in the coating system. Place the apparatus in a water bath, adjust the temperature to 40℃, and mechanically stir at 250 r / min. After the system is evenly dispersed, slowly add 25 mL of n-hexane and react at a constant temperature for 2 h. The total volume of dichloromethane and n-hexane is 30 mL, with a volume ratio of 1:5. After the reaction is complete, cool to 15℃, filter under reduced pressure, and dry at 35℃ for 30 min to obtain the PVB-coated ADN sample.

[0038] Comparative Example 3 (using only stearic acid as a coating agent) (1) ADN pretreatment is the same as in Example 1.

[0039] (2) Weigh 0.08 g of octadecanoic acid into a 100 mL three-necked flask, add 5 mL of dichloromethane, and after the coating agent dissolves, weigh 2 g of dried ADN particles and disperse them in the coating system. Place the apparatus in a water bath, adjust the temperature to 40℃, and mechanically stir at 250 r / min. After the system is evenly dispersed, slowly add a certain amount of n-hexane and react at a constant temperature for 2 h. The total volume of dichloromethane and n-hexane is 30 mL, with a volume ratio of 1:5. After the reaction is complete, cool to 15℃, filter under reduced pressure, and dry at 35℃ for 30 min to obtain the octadecanoic acid-coated ADN sample.

[0040] Comparative Example 4 (preparation method using a mixed coating agent: PVB and cetyl alcohol) (1) ADN pretreatment is the same as in Example 1.

[0041] (2) Weigh 0.05 g PVB and 0.03 g cetyl alcohol into a 100 mL three-necked flask, add 5 mL of dichloromethane, and after the coating agent dissolves, weigh 2 g of dried ADN particles and disperse them in the coating system. Place the apparatus in a water bath, adjust the temperature to 40℃, and mechanically stir at 250 r / min. After the system is evenly dispersed, slowly add a certain amount of n-hexane and react at a constant temperature for 2 h. The total volume of dichloromethane and n-hexane is 30 mL, and the volume ratio is 1:5. After the reaction is complete, cool to 15℃, filter under reduced pressure, and dry at 35℃ for 30 min to obtain a PVB / cetyl alcohol mixed-coated modified ADN sample.

[0042] Comparative Example 5 (preparation method of mixed coating, the coating agent is polycarbonate PC and octadecanoic acid) (1) ADN pretreatment is the same as in Example 1.

[0043] (2) Weigh 0.05 g of PC and 0.08 g of octadecanoic acid into a 100 mL three-necked flask, add 5 mL of dichloromethane, and after the coating agent dissolves, weigh 2 g of dried ADN particles and disperse them in the coating system. Place the apparatus in a water bath, adjust the temperature to 40℃, and mechanically stir at 250 r / min. After the system is evenly dispersed, slowly add a certain amount of n-hexane and react at a constant temperature for 2 h. The total volume of dichloromethane and n-hexane is 30 mL, and the volume ratio is 1:5. After the reaction is complete, cool to 15℃, filter under reduced pressure, and dry at 35℃ for 30 min to obtain a PC / octadecanoic acid mixed-coated modified ADN sample.

[0044] Test examples (moisture absorption rate, friction sensitivity) The coated samples from each embodiment and comparative example were placed in a constant temperature and humidity chamber at 25°C and 75%RH for 2 hours to absorb moisture, and the moisture absorption rate and the decrease in moisture absorption rate were calculated (the test results are shown in Table 4).

[0045] Friction sensitivity tests were conducted on the coated sample from Example 1 and the sample from Comparative Example 1. Test conditions: drop weight 5 kg, drop height adjustable range (0 ~ 100 cm), ambient temperature and relative humidity 15℃ and 36% RH. The white porcelain plate dimensions were 25 × 25 × 5 mm (length × width × height), and the porcelain pressure column dimensions were 10 × 15 mm (diameter × height). 30 mg of the coated sample was placed on the white porcelain plate, the porcelain pressure column was adjusted to be directly above the sample, and the instrument was switched on for testing (test results are shown in Table 4).

[0046]

[0047] As shown in Table 4, the ADN coated with a mixture of PVB and octadecanoic acid (Example 1) exhibits the best moisture-wicking effect, with a moisture absorption rate reduction of 49.49%, slightly better than the PVB / eicosinate coating (Example 2). This may be because the carbon chain length of octadecanoic acid is moderate, resulting in good spreadability and no aggregation defects; while the carbon chain of eicosinate is too long, with strong intermolecular van der Waals forces, making it prone to self-aggregation and unable to be uniformly dispersed in the PVB membrane, leading to pores in the membrane layer and weakening its moisture barrier ability.

[0048] The hybrid coating method (Examples 1 and 2) has a better moisture-proof effect than the two-layer coating method (Example 3). This may be because PVB and octadecanoic acid are dissolved and precipitated together in the same solvent system during the hybrid coating process. The carbon chain length of octadecanoic acid is moderate and has good compatibility with the PVB molecular chain, so it can be uniformly dispersed in the PVB film to form a continuous hydrophobic layer. In contrast, the interfacial bonding force between the two layers in the two-layer coating is weak, which leads to a reduction in the overall protective effect of the coating layer.

[0049] As can be seen from the data in Examples 4.1 to 4.4 in Table 4 combined with Example 1, the moisture-wicking coating effect first increases and then decreases as the mass ratio of PVB to octadecanoic acid increases. This is because PVB provides the rigidity required for the coating layer, while octadecanoic acid fills the gap in PVB coating and reduces surface tension. If either component is too small, it may affect the coating process of ADN.

[0050] The data from Examples 5.1 to 5.4, combined with those from Example 1, show that the coating modification effect initially increases and then decreases as the volume ratio of dichloromethane to n-hexane decreases. This is because when the solvent volume ratio is too high, there is too much good solvent, resulting in a high solubility of the mixed coating agent in the system, making it difficult for it to precipitate. However, as the proportion of poor solvent increases, the coating effect reaches its peak at a volume ratio of 1:5. Subsequently, due to the insufficient amount of good solvent, a solvent effect occurs, leading to an excessively rapid evaporation rate of the good solvent. This results in the coating agent precipitating too quickly, causing the coating layer to be discontinuous and not dense, thus reducing the moisture-proof effect.

[0051] Data from Examples 6.1-6.3, compared with those from Example 1, show that the mixed solvent system of dichloromethane and n-hexane yields the best results. This is likely because the solubility of the mixed coating agent in chloroform is too high, making it difficult to induce phase separation using n-hexane or cyclohexane. Therefore, the combination containing chloroform has the worst effect. Cyclohexane, with its similar structure to n-hexane, provides a reasonably good coating effect.

[0052] Comparing Examples 2, 3, 4, and 5 with Example 1, it can be seen that the effect of PVB mixed with stearic acid coating is significantly better than single coating and other combinations.

Claims

1. A method for modifying dinitramide ammonium with a moisture-resistant coating, characterized in that, Polyvinyl butyral and fatty acid surfactants are used as a mixed coating agent to form a polymer-surfactant synergistic moisture-proof coating layer on the surface of dinitramide ammonium particles by liquid phase surface coating method.

2. The method for moisture-resistant coating modification of ammonium dinitramide according to claim 1, characterized in that: Includes the following steps: Polyvinyl butyral and fatty acid surfactants are dissolved in a good solvent to form a coating agent solution; Add an appropriate amount of dried dinitramide ammonium granules to the coating agent solution, and after dispersing evenly under stirring at 40±3℃, slowly add a certain amount of unsuitable solvent, and react at a constant temperature for a certain period of time. The temperature was slowly lowered to 15±3℃, the solid was separated, and after drying, the modified dinitramide ammonium product was obtained.

3. The method for moisture-resistant coating modification of ammonium dinitramide according to claim 1 or 2, characterized in that: The fatty acid surfactant is octadecanoic acid or icosanoic acid.

4. The method for modifying dinitramide ammonium with anti-hygroscopic coating according to claim 3, characterized in that: Based on the mass of dinitramide ammonium, the mass fraction of polyvinyl butyral is 2.

00. wt % ~3.00 wt The fatty acid surfactant has a mass fraction of 1.00%. wt % ~2.00 wt %.

5. The method for moisture-resistant coating modification of ammonium dinitramide according to claim 2, characterized in that: The good solvent is dichloromethane or trichloromethane, and the bad solvent is n-hexane or cyclohexane; The volume ratio of good solvent to poor solvent is 1:3 to 1:7, wherein the amount of good solvent used is appropriate to dissolve the coating agent.

6. The method for moisture-resistant coating modification of ammonium dinitramide according to claim 2, characterized in that: The stirring speed is 200~300 r / min.

7. The method for modifying dinitramide ammonium with anti-hygroscopic coating according to claim 1, characterized in that, include: First, the dinitramide ammonium particles are coated with polyvinyl butyral. The dinitramide ammonium particles coated with polyvinyl butyral are then coated a second time with a fatty acid surfactant.

8. The method for modifying ammonium dinitramide with anti-hygroscopic coating according to claim 7, characterized in that, The single coating includes: Polyvinyl butyral is dissolved in a good solvent to form a coating agent solution; Add an appropriate amount of dried dinitramide ammonium granules to the coating agent solution, and after dispersing evenly under stirring at 40±3℃, slowly add a certain amount of unsuitable solvent, and react at a constant temperature for a certain period of time. The temperature was lowered to 15±3℃, the solid was separated, and after drying, dinitramide ammonium particles coated with polyvinyl butyral were obtained. The secondary coating includes: Fatty acid surfactants were dissolved in a poor solvent and polyvinyl butyral-coated dinitramide ammonium particles were dispersed therein. The mixture was reacted at 40±3℃ under stirring for a certain period of time. The temperature was lowered to 15±3℃, the solid was separated, and after drying, the modified dinitramide ammonium product was obtained.

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