Polymer bonded explosive capable of mildly self-healing damage, polyamidosemicarbazide binder and preparation method of polymer bonded explosive and polyamidosemicarbazide binder

Abstract

The invention discloses a high polymer bonded explosive with mild and self-healing damage, a polyamidosemicarbazide binder and a preparation method of the high polymer bonded explosive. The high polymer bonded explosive with mild and self-healing damage comprises the following components: (a) a high-energy explosive; and (b) a polyamidosemicarbazide binder, the polyamidosemicarbazide binder has a disulfide bond structure and also contains multiple hydrogen bonds, and can be subjected to reversible exchange or reconstruction reaction under a mild heating condition, and a polymer molecular chain has sufficient movement ability at a damaged part of the high polymer bonded explosive, flows and fills a damaged interface, so that the damage of the high polymer bonded explosive to the damaged part is avoided. The disulfide bond and the hydrogen bond can be formed again, so that the microstructure and the strength of the explosive are recovered.

Description

Technical Field

[0001] The present invention belongs to the field of energetic materials, and in particular relates to a polymer bonded explosive capable of mild self-healing of damage, a polyamidourea binder and a preparation method thereof. Background Art

[0002] Polymer-bonded explosives are energetic composite materials composed of a continuous polymer binder and a large number of explosive particles. Due to their excellent molding, mechanical, and safety properties, they are widely used in defense and national economy fields. The preparation process of polymer-bonded explosives often results in initial damage. Subsequent processing, transportation, storage, and use can also lead to further damage within the polymer-bonded explosives, which can further develop during processing, transportation, storage, and use. These damages can further develop into macroscopic defects, leading to mechanical failure and compromising the safety and reliability of the polymer-bonded explosives. Therefore, imparting self-healing properties to polymer-bonded explosives, enabling them to heal under certain conditions and maintain their structural and functional integrity, has become a critical issue in the field of energetic materials.

[0003] Because the groups in explosive molecules are relatively stable, it is difficult to impart self-healing capabilities simply by modifying their structure. Therefore, the only approach is to modify the molecular structure of the polymer binder to impart self-healing properties to polymer-bonded explosives. Currently, methods for improving the healing properties of polymer materials primarily include adding fillers that promote healing, introducing non-covalent supramolecular interactions, and introducing dynamic covalent bonds. To date, self-healing technologies involving polymers have been extensively reported in the research and engineering of materials such as hydrogels, concrete, asphalt, and coatings. However, these existing technologies struggle to achieve a good balance between self-healing and mechanical properties. To achieve good mechanical properties, strong dynamic bonds are necessary. However, excessively strong bond energies weaken the mobility of chain segments, resulting in reduced self-healing ability. Conversely, strong chain mobility requires low dynamic bond energies, which in turn results in insufficient chain rigidity and reduced mechanical properties. Utilizing non-covalent aggregates as dynamic crosslinking structures has emerged as an effective strategy for simultaneously strengthening and toughening self-healing materials.

[0004] Patent CN 10415103A discloses a self-healing polyurethane hydrogel and its preparation method. Specifically, a hydrophilic polyurethane macromonomer terminated with an acrylic monomer is first prepared, and then free radical copolymerized with a methacrylic acid functional monomer containing a 2-ureido-4-pyrimidinone unit (UPy) in the presence of a photoinitiator. The resulting hydrogel can form multiple hydrogen bonds and can heal itself without any healing agents or specific environmental requirements. It can also achieve repeated healing of the same area. However, the strength of the hydrogel material is very low (<2MPa). Patent CN 108329184A discloses a method for preparing a self-healing polyurethane bonded explosive based on a DA reaction with high bonding strength. The method involves first preparing a polyurethane prepolymer with furan groups at both ends, then chain-extending it with bismaleimide to produce a self-healing polyurethane with a reversible DA structure, achieving a strength of up to 13.5 MPa. Using this polyurethane as a binder, a self-healing polymer bonded explosive can be prepared. When the polymer bonded explosive is damaged, it can be treated at 125°C for 6 hours to allow the binder molecules at the damaged area to undergo a full reverse DA reaction. It can then be treated at 60°C for approximately 12 hours to allow the broken furan groups to reconnect with the maleimide groups via the DA reaction, thus repairing the damage. However, the repair method provided by this invention requires two different temperatures, resulting in a complex process and certain limitations in practical application. Clearly, improving the ease with which polymer materials can heal is of greater practical value.

[0005] Patent CN 105482065B discloses a self-healing polyurethane resin containing disulfide bonds and its preparation method. When the polyurethane resin of this invention is heated to 80°C, scratches can disappear within 5 minutes, and the healing speed is relatively fast. Patent CN118255964 A discloses a polyurethane elastomer that can quickly self-repair at room temperature. By introducing multiple hydrogen bonds and dynamic disulfide bonds, the material is given self-repairing properties. The repair efficiency is about 100% within a short time (2h) at room temperature, but its strength is still very low (less than 0.1MPa). Patent CN 116003730 A discloses a self-healing polyurethane with a main chain containing a ureidopyrimidone structure. It has multiple physical cross-linking structures, which enable the polyurethane to have both good mechanical strength and self-healing ability. Its mechanical strength is about 3.5MPa, and the damage can recover about 80% of its strength after heating at 60°C for 48h.

[0006] While these inventions offer some valuable insights into the preparation of self-healing polymer-bonded explosives, publicly available data suggests that the primary challenge facing current self-healing technology remains the conflict between repair efficiency and mechanical performance. Materials with superior mechanical properties typically require harsh repair conditions or long repair times, while materials capable of repair at room temperature typically have very low mechanical strength. Multiple hydrogen bonds, as a highly binding non-covalent interaction, can impart sufficient elasticity to the material, and this structure is dynamically reversible. However, if the effects of multiple hydrogen bonds exceed a certain level, they constrain chain motion, requiring harsh, high temperatures and long periods of time to achieve self-healing. Therefore, the strength of multiple hydrogen bonds needs to be regulated through molecular chain structure. Since most materials are typically used under ambient conditions, the development of polymer-based composite materials that facilitate self-healing damage, particularly those potentially applicable to polymer-bonded explosives, requires significant research. Summary of the Invention

[0007] To address the aforementioned issues, the present invention provides a polyamide urea elastomer for polymer-bonded explosives that can readily self-heal under mild conditions, and a method for preparing the same. The core of the invention involves introducing a amide urea structure capable of forming numerous hydrogen bonds into a polyurethane elastomer, forming a dynamic network of multiple hydrogen bonds through multi-level hydrogen crosslinking, and introducing aromatic disulfide bonds with room-temperature dynamic exchange properties into the backbone. By regulating the molecular structure of the soft and hard segments and coordinating the ratio of multiple hydrogen bonds to disulfide bonds, the resulting elastomer material exhibits both high stretchability and self-healing properties under mild temperature conditions. The reconstructed hydrogen and disulfide bonds accelerate initial adhesion of fracture surfaces, rapidly completing self-repair of damage.

[0008] In order to achieve the above object of the invention, the present invention provides the following technical solutions:

[0009] The present invention provides a polymer-bonded explosive capable of mild self-healing damage, comprising an explosive and a self-healing polyamidourea binder having both disulfide bonds and multiple hydrogen bonds. The explosive can be a high-energy explosive such as 1,3,5-triamino-2,4,6-trinitrobenzene (TATB), cyclotetramethylenetetranitramine (HMX), cyclotrimethylenetrinitramine (RDX), or hexanitrohexaazaisopentazolidine (CL-20).

[0010] Furthermore, the mildly self-healing polyamidourea binder possesses both an amidourea and disulfide bond structure. By adjusting the hard segment molecular structure and the ratio of dihydrazide to disulfide, the hard segment size and the multiple hydrogen bond array between hard segment molecular chains can be regulated. This allows the multiple hydrogen bonds and disulfide bonds to undergo dissociation-reconstruction or dynamic exchange reactions under mild heating conditions. This, in turn, gives the binder molecular segments excellent mobility, allowing them to flow and fill damaged interfaces of polymer-bonded explosives, reforming a network microstructure composed of multiple hydrogen bonds and disulfide bonds, thereby conveniently repairing damage to the explosives.

[0011] Furthermore, a method for preparing the polyamidourea for polymer-bonded explosives with mild self-healing damage comprises the following steps: A. first reacting an excess of structurally flexible diisocyanate with polyether diol under nitrogen protection to generate a prepolymer with -NCO groups at both ends; and B. then reacting the prepolymer with dihydrazide and a diamine with a disulfide bond under the catalysis of dibutyltin dilaurate to generate a polymer with amidourea and disulfide bonds.

[0012] Furthermore, in the step A, the diisocyanate is preferably an aliphatic or alicyclic molecule with good structural flexibility, preferably isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, hexamethylene diisocyanate, etc.; the polyether diol can be polytetramethylene glycol-1000, polytetramethylene glycol-2000, polypropylene glycol-1000, polypropylene glycol-2000, etc.; the molar ratio of diisocyanate to polyether / ester diol (-NCO / -OH) is 2:1, and the reaction is stirred at 75°C for 3 hours under nitrogen atmosphere to generate a prepolymer with -NCO end groups at both ends.

[0013] Furthermore, in step B, an appropriate amount of N,N-dimethylformamide is added to completely dissolve the terminal NCO prepolymer. A dihydrazide / diamine containing disulfide bonds at a (-NCO / -NH2) molar ratio of 2:1 (adjusting the ratio can control the density of multiple hydrogen bonds) is then slowly added dropwise to the prepolymer solution. Three to five drops of dibutyltin dilaurate catalyst are added, and the reaction is continued at 55°C for 3 hours to obtain a polyamide preform containing amide and disulfide bonds. The dihydrazide can be selected from dihydrazides such as hexadiazide, sebacic dihydrazide, isophthalic dihydrazide, and terephthalic dihydrazide. The molar ratio of the dihydrazide to the diamine containing disulfide bonds ranges from 1:0 to 5. The preform is then poured into a polytetrafluoroethylene mold and baked in a forced air oven at 60°C for 48 hours to obtain a thermally reversible, self-healing polyamide urea (MHPAU).

[0014] The preparation method of the polymer bonded explosive with mild self-healing damage comprises the following steps: preparing a dilute solution of thermoplastic polyamide semicarbazide, adding explosive and water in a measured ratio, stirring to allow the polyamide semicarbazide molecules to fully infiltrate and spread on the surface of the explosive; heating to volatilize the solvent, allowing the polyamide semicarbazide to gradually precipitate and coat the surface of the explosive; filtering and drying to obtain a polymer bonded explosive product with self-healing function.

[0015] Furthermore, the polyamide semicarbazide dilute solution has a concentration of 3% to 8%, the explosive to polymer ratio can be 95 / 5 to 80 / 20, and the heating temperature for preparing the molding powder is 40°C to 85°C. After coating, the explosive molding powder is dried at 60°C for 8 to 12 hours to obtain a polymer-bonded explosive product. The self-healing properties of the polymer-bonded explosive can be verified by compressing mechanical test pieces, inducing damage through force and temperature loading, and then healing the damage through heat treatment.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] The present invention innovatively provides a polymer binder with a unique amidourea and disulfide bond structure. By adjusting the hard segment molecular structure and the ratio of dihydrazide to disulfide, the dynamic bond energy can be regulated, coordinating the toughness of the polymer network with the mobility of the chain segments. After damage occurs within the material, mild heat treatment conditions are used to re-entangle the molecular segments at the damaged site to form a cross-linked grid structure through the dissociation and reconstruction of multi-level hydrogen bonds and the dynamic exchange mechanism of disulfide bonds, achieving automatic healing of the damage and restoring excellent mechanical properties. This has important practical significance for maintaining the charge stability of composite energetic materials and extending the life of energetic material components. It has important application prospects in the field of energetic materials for weapons such as hybrid explosives and solid propellants. The present invention has a simple preparation process, high mechanical strength of the product, mild self-healing conditions, and strong universality. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The following is a flow chart showing the preparation of the damage self-healing polymer bonded explosive according to the present invention;

[0019] Figure 2 Optical microscope images of the polymer before and after scratch healing according to Example 1 of the present invention;

[0020] Figure 3 The mechanical property curves of the polymer dumbbell sample in its original state and the scratch repaired sample at different times according to Example 1 of the present invention are shown;

[0021] Figure 4 These are photos of the initial sample, damaged sample and healed sample of the polymer bonded explosive mechanical property test piece according to Example 1 of the present invention. DETAILED DESCRIPTION

[0022] Example 1

[0023] See also Figure 1 Under nitrogen protection and mechanical stirring, the dehydrated polytetramethylene glycol-2000 (40.00 g, 0.02 mol), isophorone diisocyanate (8.90 g, 0.04 mol) and 20 mL of N,N-dimethylformamide were fully mixed; the temperature was raised to 75°C and the reaction was kept at this temperature for 3 hours; then the temperature was lowered to room temperature to obtain a prepolymer solution with isocyanate at both ends. Sebacic acid dihydrazide (2.23 g, 0.01 mol) and 4,4'-diaminodiphenyl disulfide (2.49 g, 0.01 mol) were slowly added dropwise to the prepolymer solution, followed by 3 drops of dibutyltin dilaurate (DBTDL). The temperature was raised to 55°C and the reaction was allowed to proceed for 3 hours to obtain a reaction preform with amide urea and disulfide bonds. The reaction preform was poured into a polytetrafluoroethylene mold and baked in a forced air oven at 60°C for 48 hours to produce 53.50 g of self-healing polyamide urea (MHPAU-A). An optical micrograph of the healing of the scratched MHPAU-A film showed that the surface scratches had essentially disappeared after treatment at 80°C for 30 minutes (see attached). Figure 2 The mechanical properties curve of MHPAU-A elastomer is shown in the attached figure. Figure 3 As shown in the figure, the tensile strength reaches 20MPa and the elongation at break is 1800%. The scratched sample can be repaired at 80℃ for 8h and the strength can be restored by more than 90%.

[0024] 10.0 g of thermally reversible, self-healing polyamide urea (MHPAU-A) was dissolved in 160.0 g of dichloromethane to prepare a 3.03% dilute solution. 90.0 g of TATB and 70 mL of deionized water were added and stirred thoroughly. The dichloromethane solvent was gradually evaporated at 40°C, and the MHPAU-A precipitated and coated on the TATB particles. The mixture was filtered and dried in a 60°C oil bath oven for 12 hours to obtain MHPAU-A-bonded TATB explosive molding powder. Mechanical test pieces (Φ20 mm × 6 mm) were prepared by molding and their mechanical strength was tested by mechanical loading. The damaged samples were heat treated at 80°C for 8 hours to heal the damaged areas. Optical images of the initial, damaged, and healed mechanical test pieces are shown in the attached figure. Figure 4 Compared to the initial sample, the mechanical properties of the polymer-bonded explosive can be restored to 87% of the initial sample. When the treatment time is extended to 16 hours, the mechanical properties can be restored to 99% of the initial sample.

[0025] Example 2

[0026] Under nitrogen protection and mechanical stirring, dehydrated polytetrahydrofuran diol-1000 (30.00 g, 0.03 mol), hexamethylene diisocyanate (10.09 g, 0.06 mol), and 20 mL of N,N-dimethylformamide were thoroughly mixed. The mixture was heated to 80°C and allowed to react for 3 hours before being cooled to room temperature to obtain a prepolymer solution with isocyanate bonds at both ends. Isophthalic dihydrazide (1.96 g, 0.01 mol) and 4,4'-diaminodiphenyl disulfide (4.97 g, 0.02 mol) were slowly added dropwise to the prepolymer solution, followed by 4 drops of DBTDL. The mixture was heated to 55°C and allowed to react for 3 hours to obtain a polyurethane preform with disulfide bonds. The preform was poured into a polytetrafluoroethylene mold and dried in a forced-air oven at 60°C for 48 hours to remove the solvent, yielding 47.00 g of a self-healing polyamidourea (MHPAU-B).

[0027] 10.0 g of thermally reversible, self-healing polyamidourea (MHPAU-B) was dissolved in 190.0 g of 1,2-dichloroethane to prepare a 5% dilute solution. 40.0 g of LLM-105 and 30 mL of deionized water were added and stirred thoroughly. The solvent was gradually evaporated at 65°C, allowing the MHPAU-B to precipitate and coat the LLM-105 particles. The mixture was then filtered and dried in an oil-bath oven at 60°C for 12 hours to obtain an LLM-105-based polymer-bonded explosive with self-healing damage. Compared to the initial sample, the mechanical strength of the polymer-bonded explosive recovered to 92% of the initial sample after heat treatment at 80°C for 8 hours after loading damage.

[0028] Example 3

[0029] Under nitrogen protection and mechanical stirring, dehydrated polypropylene glycol-1000 (20.00 g, 0.02 mol), 4,4'-dicyclohexylmethane diisocyanate (10.50 g, 0.04 mol), and 25 mL of N,N-dimethylformamide were thoroughly mixed. The mixture was heated to 70°C and allowed to react for 3 hours. The mixture was then cooled to room temperature to obtain a prepolymer solution with isocyanate groups at both ends. Sebacic acid dihydrazide (2.23 g, 0.01 mol) and 4,4'-diaminodiphenyl disulfide (2.49 g, 0.01 mol) were slowly added dropwise to the prepolymer solution, followed by 4 drops of DBTDL. The mixture was heated to 50°C and allowed to react for 3 hours to obtain the desired product. The product was poured into a polytetrafluoroethylene mold and dried in a forced-air oven at 60°C for 48 hours to remove the solvent, yielding 35.10 g of self-healing polyamidourea (MHPAU-C).

[0030] 5.0 g of thermally reversible, self-healing polyamidourea (MHPAU-C) was dissolved in 57.5 g of N,N-dimethylformamide to prepare an 8.0% dilute solution. 95.0 g of HMX and 75 mL of deionized water were added and stirred thoroughly. The solvent was gradually evaporated at 80°C, allowing the MHPAU-C to precipitate and coat the HMX particles. The mixture was then filtered and dried in an oil-bath oven at 60°C for 12 hours to obtain an MHPAU-C-bonded HMX explosive. Compared to the initial sample, the mechanical properties of this polymer-bonded explosive recovered to 83% of the initial sample after being damaged and then healed at 80°C for 8 hours.

[0031] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A polymer bonded explosive with mild self-healing damage, characterized in that: Includes the following components: (a) high explosives; as well as (b) A polyamidourea binder having both a disulfide bond structure and multiple hydrogen bonds, which can undergo a reversible exchange or reconstruction reaction under mild heating conditions. At damaged areas of polymer-bonded explosives, the polymer molecular chains have sufficient mobility to flow and fill the damaged interfaces, reforming disulfide bonds and hydrogen bonds, thereby restoring the microstructure and strength of the explosive.

2. The polymer bonded explosive according to claim 1, characterized in that The high-energy explosive is selected from at least one of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB), cyclotetramethylene tetranitramine (HMX), 2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105), cyclotrimethylene trinitramine (RDX) or hexanitrohexaazaisopentazolidine (CL-20).

3. A method for preparing a polyamidourea binder for polymer-bonded explosives with mild self-healing damage, characterized in that: The following steps are involved: A: Under nitrogen protection, first react excess diisocyanate with polyether diol to generate a polyurethane prepolymer with -NCO groups at both ends; B: Then, under the catalysis of dibutyltin dilaurate, a dihydrazide compound with an -NH2 group and a diamine with a disulfide bond are reacted with it to generate a polyamidourea elastomer with multiple hydrogen bonds and disulfide bonds.

4. The method for preparing a polyamidourea binder for polymer-bonded explosives capable of mild self-healing damage according to claim 3, characterized in that: In step A, the diisocyanate is one of isophorone diisocyanate, 4,4'-diphenylmethane diisocyanate, and hexamethylene diisocyanate; the polyether diol is one of polytetramethylene glycol-1000, polytetramethylene glycol-2000, polypropylene glycol-1000, and polypropylene glycol-2000; the molar ratio of the diisocyanate to the polyether / ester diol (-NCO / -OH) is 2:1, and the reaction is stirred at (70-80)°C for 3-4 hours under nitrogen atmosphere protection; and the reaction system is cooled to room temperature to generate a prepolymer with -NCO end groups at both ends.

5. The method for preparing a polyamidourea binder for polymer-bonded explosives capable of mild self-healing damage according to claim 3, characterized in that: In step B, an appropriate amount of N,N-dimethylformamide is added to completely dissolve the terminal-NCO prepolymer, and then a dihydrazide / diamine solution containing a disulfide bond having an equal molar ratio of diisocyanate is slowly added to the prepolymer solution. The solution is then heated to (50-60)°C and reacted for 3-4 hours under the catalysis of dibutyltin dilaurate to obtain a polyamidourea reactant containing an amidourea and a disulfide bond structure. The reaction product is poured into a polytetrafluoroethylene mold and baked in a blast oven for 48-60 hours to obtain a self-healing polyamidourea adhesive (MHPAU).

6. A method for preparing a polymer bonded explosive capable of mild self-healing damage, characterized in that: The thermoplastic polyamide semicarbazide binder is prepared into a dilute solution, explosive and water in a measured ratio are added, stirred to form a slurry, and heated to volatilize the solvent therein, so that the polyamide semicarbazide is precipitated and coated on the surface of the explosive. After filtering and drying, a polymer-bonded explosive molding powder with a self-healing function can be obtained.

7. The method for preparing a self-healing polymer bonded explosive according to claim 6, characterized in that: The concentration of the polyamidourea dilute solution is 3% to 8%, the ratio of explosive to polymer is 95 / 5 to 80 / 20, and the heating temperature is 40-90°C; the coated explosive is dried at (60-70)°C for 6-8 hours to obtain a polymer-bonded explosive product with damage self-healing function.

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