A multi-level structure carbon fiber, toughened and reinforced PBX and its preparation method

Abstract

The present invention discloses a multi - level structure carbon fiber, a reinforced and toughened PBX and a preparation method thereof. The multi - level structure carbon fiber is composed of carbon fiber, polyurethane and graphene oxide. Polyurethane and graphene oxide are grafted onto the surface of the carbon fiber in the form of chemical bonds. The reinforced and toughened PBX is composed of 55% - 96% by mass of explosive, 3.7% - 6% of polymer binder, 0% - 35% of high - calorific - value metal powder, 0% - 3% of functional additives and 0.3% - 1% of the multi - level structure carbon fiber. The PBX shaping powder is prepared by means of water suspension granulation or kneading granulation, and after drying, it is pressed into a grain to obtain the reinforced and toughened PBX with enhanced mechanical properties. The process of the multi - level structure carbon fiber of the present invention is simple, and the raw materials are easy to obtain. It can significantly improve the interfacial action between the carbon fiber and the polymer binder solution, efficiently reinforce and toughen the PBX, and solve the problem of the weak mechanical properties of the current PBX explosives.

Description

Technical Field

[0001] The present invention relates to the technical field of composite energetic materials, specifically, to multi-stage structured carbon fibers, reinforced and toughened PBX and its preparation method. Background Art

[0002] Polymer bonded explosives (PBX) are high particle-filled composite materials composed of explosive crystals and a small amount of polymer binders (mass fraction less than 10%). They not only maintain the detonation energy of explosives but also have the advantage of easy molding of polymers, and are widely used in various weaponry. With the development of modern weaponry, during transportation, training, and combat use of PBX components, they will be subjected to the combined effects of various external stresses, vibration shocks, environmental thermal stresses, and penetration overloading, and are required to have good mechanical strength and toughness. However, as a typical high-filled polymer matrix composite material, PBX exhibits typical brittle and low-strength mechanical properties.

[0003] One-dimensional carbon fibers (CFs) are a kind of polycrystalline inorganic material with a carbon content higher than 90%, and the incomplete graphite crystals are arranged along the fiber axis. They have characteristics such as high specific strength, high specific modulus, low linear expansion coefficient, high temperature resistance, excellent thermal and electrical conductivity, etc., and are widely used as reinforcing materials for high-performance resin matrix composites. To improve the mechanical properties of explosives, short carbon fibers were used to mechanically reinforce RDX / TNT cast explosives in the literature (Energetic Materials, 2013, 21, 786 - 790). It was reported in the literature (Initiators & Pyrotechnics, 2014, 3, 35 - 37) that adding carbon fibers can improve the compressive and tensile strengths of PBX explosives. However, the surface energy of carbon fibers is low, the surface is relatively smooth and chemically inert, resulting in a weak interfacial strength between carbon fibers and polymer matrices, and it is difficult to fully exhibit the expected performance, and it is difficult to efficiently reinforce and toughen PBX.

[0004] To overcome the above problems, Patent CN107190512A grafted polymer PEI on the surface of carbon fibers to increase the mechanical meshing between carbon fibers and the matrix resin, thereby enhancing the interfacial shear strength of carbon fibers. Patent CN114456412A disclosed a method for grafting multi-walled carbon nanotubes (MWCNT) on the surface of carbon fibers to improve the fiber-matrix interfacial interaction. Patent CN113293605A deposited GO (graphene oxide) on the surface of carbon fibers, which helped to increase the interaction with the resin matrix and improve the mechanical properties of the composite. The above research results show that surface modification of carbon fibers is the main means to effectively modify the fiber-polymer matrix interface and the mechanical properties of composites. At present, the main problems of this technology are reflected in the limited improvement in the interfacial interaction between carbon fibers and the matrix, the poor mechanical enhancement effect of composites, the mostly physical interaction between the surface modifier and carbon fibers, the weak strength and easy shedding, the complex preparation process of modified carbon fibers, and the need to use expensive equipment, etc., which cannot achieve efficient reinforcement and toughening of PBX. Therefore, developing a surface modification method for carbon fibers with more excellent interfacial properties is of great significance for improving the mechanical properties of PBX, which can solve the bottleneck problem of low carbon fiber reinforcement efficiency and can be widely applied to the field of high-performance carbon fiber composites as a general technology. Summary of the Invention

[0005] Aiming at the problem of poor enhancement effect in the existing surface modification of carbon fibers, the present invention provides a carbon fiber with a multi-level structure on the surface, a reinforced and toughened PBX containing the carbon fiber with a multi-level structure, and a preparation method thereof. By grafting a cross-linked structure of polyurethane and graphene oxide on the surface of carbon fibers through in-situ chemical reactions, not only the infiltration and chemical affinity between carbon fibers and the binder are enhanced, and the surface rough physical anchor points are increased, but also the mechanical strength of the surface modification layer is improved by using high-strength graphene oxide, thereby efficiently improving the strength and toughness of the PBX composite.

[0006] The present invention solves the above problems through the following technical solutions:

[0007] A multi-level structure carbon fiber is composed of carbon fibers, polyurethane, and graphene oxide, and the polyurethane and graphene oxide are grafted onto the surface of the carbon fibers in a chemical bond form.

[0008] As a further improvement, the carbon fiber is a short-cut micron-sized carbon fiber with a length of 0.5 - 2 mm;

[0009] The polyurethane is formed by in-situ polymerization of a diisocyanate monomer and a hydroxyl-terminated polymer;

[0010] The graphene oxide is a single-layer structure with a lateral sheet diameter of 50 - 300 nm.

[0011] The present invention also solves the above problems through the following technical solutions:

[0012] A preparation method of a multi - level structure carbon fiber, comprising:

[0013] Step A: Add carbon fiber rovings into a mixed acid of concentrated nitric acid and concentrated sulfuric acid, mechanically stir, acidify the carbon fiber at a certain water bath temperature, then wash until neutral and dry to obtain oxidized carbon fiber;

[0014] Step B: Disperse the oxidized carbon fiber obtained in Step A in an organic solvent, raise the temperature, add a diisocyanate monomer, a catalyst dibutyltin dilaurate (DBTDL) and graphene oxide, react for 1 - 2 h, then add a hydroxyl - terminated polymer for cross - linking reaction for 1 h, wash 3 - 5 times, filter by suction and dry to obtain the multi - level structure carbon fiber in the present invention.

[0015] As a further improvement, in Step A, the volume ratio of concentrated nitric acid to concentrated sulfuric acid is 1:4 - 1:3, the acidification time is 2 h, and the temperature is 55 - 65 °C.

[0016] As a further improvement, in Step B,

[0017] The organic solvent is any one of DMF, tetrahydrofuran, and butyl acetate, and the reaction temperature is 60 - 80 °C; the diisocyanate monomer is any one of toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), and 4,4′ - diphenylmethane diisocyanate (MDI); the hydroxyl - terminated polymer is any one of polyethylene glycol (PEG, average molecular weight Mn 300 - 1000) and polytetrahydrofuran (PTMEG, Mn 850 - 1000). By mass, the dosage of the diisocyanate monomer is 0.06 - 0.1 of the carbon fiber, the dosage of graphene oxide is 0.02 - 0.07 of the carbon fiber, and the dosage of the hydroxyl - terminated polymer is 0.04 - 0.07 of the carbon fiber.

[0018] In addition, the present invention also solves the above problems through the following technical solutions:

[0019] An enhanced and toughened PBX, comprising:

[0020] 55% - 96% of explosive, 3.7% - 6% of binder, 0% - 35% of high - calorific - value metal powder, 0% - 3% of functional additive, and 0.3% - 1% of multi - level structure carbon fiber.

[0021] As a further improvement, the explosive is one or any combination of 1,3,5 - triamino - 2,4,6 - trinitrobenzene, HMX, RDX, CL - 20, FOX - 7, and 1 - oxo - diaminodinitropyrazine.

[0022] As a further improvement thereof, the binder is one of fluoropolymer, polyurethane, cellulose acetate, ethylene-vinyl acetate copolymer; the high calorific value metal powder is aluminum powder.

[0023] As a further improvement thereof, the functional auxiliary agent is one or both of desensitizing graphite and wax.

[0024] Meanwhile, the present invention also solves the above problems through the following technical solutions:

[0025] A preparation method of an enhanced and toughened PBX, dispersing a multi-stage structure carbon fiber prepared by the preparation method of a multi-stage structure carbon fiber as described above into a polymer binder solution to form a carbon fiber-binder system, and preparing the enhanced and toughened PBX of the multi-stage structure carbon fiber by using one of water suspension granulation and kneading granulation.

[0026] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0027] (1). The multi-stage structure carbon fiber of the present invention, the rich functional groups in the grafted multi-stage structure on the surface can significantly enhance the surface free energy of the inert carbon fiber, and enhance the infiltration and chemical affinity between the carbon fiber and the binder; the grafted multi-stage structure on the surface has a rough physical undulating structure, which can provide physical anchor points for embedding with the matrix and enhance the interfacial action strength between the carbon fiber and the binder; the high-strength GO crosslinked to polyurethane on the surface can also enhance the mechanical strength and toughness of the carbon fiber surface modification layer itself;

[0028] (2). The preparation method of the multi-stage structure carbon fiber of the present invention, through in-situ chemical reaction, grafts a crosslinked structure of polyurethane and GO, the preparation process is simple, the cost is low, the reaction equipment is a general jacketed glass stirring kettle, and no other special equipment is required;

[0029] (3). Using the multi-stage structure carbon fiber of the present invention, dispersed in a polymer binder, can achieve efficient enhancement and toughening of PBX at a lower dosage. Description of the Drawings

[0030] Figure 1 It is a flow chart of the preparation method of the multi-stage structure carbon fiber of the present invention;

[0031] Figure 2 It is a scanning electron microscope schematic diagram of the multi-stage structure carbon fiber of the present invention;

[0032] Figure 3 It is a schematic diagram of the tensile and compressive strengths of the comparative example of the present invention and carbon fiber, oxidized carbon fiber, carbon fiber grafted polymer, and multi-stage structure carbon fiber. Detailed Embodiments

[0033] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0034] Referring to the attached Figures 1-3 , a multi-level structure carbon fiber is composed of carbon fiber, polyurethane, and graphene oxide. Polyurethane and graphene oxide are grafted onto the surface of the carbon fiber through chemical bonding. Specifically, the carbon fiber is a short-cut micron-sized carbon fiber commonly used in the composite material field, with a length of 0.5 - 2 mm; the polyurethane is formed by in-situ polymerization of diisocyanate monomers and hydroxyl-terminated polymers; the graphene oxide is a single-layer structure, and the lateral sheet diameter is 50 - 300 nm.

[0035] The preparation method of the multi-level structure carbon fiber is as follows:

[0036] Step A: Add the carbon fiber raw wire to a mixed acid of concentrated nitric acid and concentrated sulfuric acid, mechanically stir, acidify the carbon fiber at a certain water bath temperature, and then wash it to neutral and dry to obtain oxidized carbon fiber;

[0037] Among them, the volume ratio of concentrated nitric acid to concentrated sulfuric acid is 1:4 - 1:3, the acidification time is 2 h, and the temperature is 55 - 65 °C.

[0038] Step B: Disperse the oxidized carbon fiber obtained in Step A in an organic solvent, raise the temperature, add diisocyanate monomers, the catalyst dibutyltin dilaurate (DBTDL), and graphene oxide, react for 1 - 2 h, then add the hydroxyl-terminated polymer for cross-linking reaction for 1 h, wash 3 - 5 times, filter by suction and dry to obtain the multi-level structure carbon fiber in the present invention.

[0039] Among them, the organic solvent is any one of DMF, tetrahydrofuran, and butyl acetate, preferably DMF; the isocyanate monomer is any one of toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), and 4,4'-diphenylmethane diisocyanate (MDI); the hydroxyl-terminated polymer is polyethylene glycol (PEG, average molecular weight M n 300 - 1000), polytetrahydrofuran (PTMEG, M n 850 - 1000).

[0040] By mass, the dosage of the diisocyanate monomer is 0.06 - 0.1 of the carbon fiber, the dosage of the graphene oxide is 0.02 - 0.07 of the carbon fiber, and the dosage of the hydroxyl-terminated polymer is 0.04 - 0.07 of the carbon fiber.

[0041] In the present invention, a toughened and reinforced PBX with a multi-stage structure carbon fiber, based on 100% of its total weight, comprises the following components in parts by weight: 55% - 96% of an explosive, 3.7% - 6% of a binder, 0% - 35% of a high calorific value metal powder, 0% - 3% of a functional additive, and 0.3% - 1% of a multi-stage structure carbon fiber.

[0042] Among them, the explosive is one or any combination of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB), octogen (HMX), cyclotrimethylenetrinitramine (RDX), hexanitrohexaazaisowurtzitane (CL-20), 1,1-diamino-2,2-dinitroethylene (FOX-7), 1-oxo-diamino-3,5-dinitropyrazine (LLM-105). The binder is one of a fluoropolymer, polyurethane, cellulose acetate, ethylene-vinyl acetate copolymer. The high calorific value metal powder can also be replaced by boron powder, and the high calorific value metal powder is preferably aluminum powder. The functional additive is one or any combination of desensitized graphite and wax.

[0043] In the present invention, a preparation method of a toughened and reinforced PBX containing a multi-stage structure carbon fiber disperses a multi-stage structure carbon fiber prepared by a preparation method of a multi-stage structure carbon fiber into a polymer binder solution to form a carbon fiber-binder system, and uses one of water suspension granulation and kneading granulation to prepare a toughened and reinforced PBX with a multi-stage structure carbon fiber.

[0044] Example 1

[0045] Step 1: Add 1 mm long chopped carbon fiber filaments to a mixed acid of concentrated nitric acid and concentrated sulfuric acid with a volume ratio of 1:4, mechanically stir, the water bath temperature is 60 °C, the reaction time is 2 h, and then wash until neutral and dry to obtain oxidized carbon fiber;

[0046] Step 2: Weigh 5 g of the oxidized carbon fiber obtained in Step 1 and disperse it in DMF, heat up to 65 °C, sequentially add 0.4 g of MDI, 1 drop of catalyst DBTDL, and 20 mg of graphene oxide, react for 2 h, then add 0.3 g of PEG for cross-linking reaction for 1 h, and finally wash 3 - 5 times, filter by suction and dry to obtain 1 mm long multi-stage structure carbon fiber (CFsO-MDI-GO) in the present invention.

[0047] Step 3: Stir and dissolve 2.35 g of fluorine-containing polymer F2313 in ethyl acetate solvent to prepare a binder solution with a concentration of 8 wt%. Weigh 0.15 g of 1 mm long multi-structured carbon fiber (CFsO-MDI-GO) in Step 2, add it to the binder solution for uniform dispersion to form a carbon fiber-binder system, and then slowly drop it into the water suspension solution composed of 43.5 g of HMX and 4 g of TATB. After that, prepare shaped powder by water suspension granulation, dry it, and press it into explosive charges of various sizes to obtain PBX modified with multi-structured carbon fiber. As Figure 3 The mechanical test results of the CFsO-MDI-GO sample shown in the figure indicate that the Brazilian tensile fracture strength is 7.93 MPa, the fracture strain is 0.40%, the compressive strength is 54.83 MPa, and the fracture strain is 2.48%.

[0048] Example 2

[0049] In this example, the preparation method of the multi-structured carbon fiber is the same as that in Example 1, only replacing the 1 mm long chopped carbon fiber with 2 mm long chopped carbon fiber. Through Step 1 and Step 2 in Example 1, 2 mm long multi-structured carbon fiber is prepared.

[0050] Stir and dissolve 2.35 g of fluorine-containing polymer F2313 in ethyl acetate solvent to prepare a binder solution with a concentration of 8 wt%. Weigh 0.15 g of 2 mm long multi-structured carbon fiber, add it to the binder solution for uniform dispersion to form a carbon fiber-binder system, and then slowly drop it into the water suspension solution composed of 43.5 g of HMX and 4 g of TATB. After that, prepare shaped powder by water suspension granulation, dry it, and press it into explosive charges of various sizes to obtain PBX modified with multi-structured carbon fiber. The mechanical test results indicate that the Brazilian tensile fracture strength is 8.51 MPa, the fracture strain is 0.42%, the compressive strength is 57.27 MPa, and the fracture strain is 2.51%.

[0051] Example 3

[0052] In this example, the preparation method of the multi-structured carbon fiber is the same as that in Example 2.

[0053] Weigh 2.25 g of fluoropolymer F2314 and dissolve it in a mixed solvent of ethyl acetate and butyl acetate to prepare a binder solution with a concentration of 8 wt%. Weigh 0.25 g of 2-mm-long multi-structured carbon fibers, add them to the binder solution and disperse them evenly to form a carbon fiber-binder system. Take 35 g of TATB and 12.5 g of pure aluminum powder and add them to the carbon fiber-binder system, stir and disperse. Then, prepare shaped powder by non-aqueous kneading granulation, dry it and press it into pellets of various sizes to obtain PBX modified with multi-structured carbon fibers. The mechanical test results show that the Brazilian tensile fracture strength is 9.26 MPa, the fracture strain is 0.32%, the compressive strength is 40.73 MPa, and the fracture strain is 2.85%.

[0054] Example 4

[0055] Example 4 is a blank control group, and only uses an explosive and a fluoropolymer binder solution to form a PBX preparation method.

[0056] Weigh 2.5 g of fluoropolymer F2313 and dissolve it in ethyl acetate to prepare a binder solution with a concentration of 8 wt%. Take 43.5 g of HMX and 4 g of TATB and add them to a pure water system for dispersion. Then, prepare shaped powder by water suspension granulation, dry it and press it into pellets of various sizes to obtain unmodified PBX. As Figure 3 shown by the mechanical test results of the PBX sample, the Brazilian tensile fracture strength is 4.86 MPa, the fracture strain is 0.19%, the compressive strength is 39.44 MPa, and the fracture strain is 2.31%.

[0057] Example 5

[0058] Example 5 is another blank control group, and only uses an explosive, metal powder and a fluoropolymer binder solution to form a PBX preparation method.

[0059] Weigh 2.5 g of fluoropolymer F2314 and dissolve it in a mixed solvent of ethyl acetate and butyl acetate to prepare a binder solution with a concentration of 8 wt%. Take 35 g of TATB and 12.5 g of pure aluminum powder and add them to the fluoropolymer solution, stir and disperse. Then, prepare shaped powder by non-aqueous kneading granulation, dry it and press it into pellets of various sizes to obtain unmodified PBX. The mechanical test results show that the Brazilian tensile fracture strength is 5.44 MPa, the fracture strain is 0.16%, the compressive strength is 26.78 MPa, and the fracture strain is 1.97%.

[0060] Example 6

[0061] Example 6 is another control group, and carbon fiber rovings (CFs) are added on the basis of Example 4.

[0062] 2.35 g of fluorine-containing polymer F2313 was stirred and dissolved in ethyl acetate solvent to prepare a binder solution with a concentration of 8 wt%. 0.15 g of 1 mm long and short carbon fiber filaments were weighed and added to the binder solution for uniform dispersion to form a carbon fiber-binder system, and then slowly dropped into a water suspension solution composed of 43.5 g of HMX and 4 g of TATB. After that, it was prepared into shaped powder by the method of water suspension granulation, and dried and pressed into explosive columns of various sizes to obtain carbon fiber-modified PBX. As Figure 3 The mechanical test results of the CFs samples showed that the Brazilian tensile fracture strength was 5.71 MPa, the fracture strain was 0.23%, the compressive strength was 44.43 MPa, and the fracture strain was 2.36%.

[0063] Example 7

[0064] Example 7 was the control group, and carbon fiber oxide (CFsO) was added on the basis of Example 4, and the preparation method was the same as Step 1 in Example 1.

[0065] 2.35 g of fluorine-containing polymer F2313 was stirred and dissolved in ethyl acetate solvent to prepare a binder solution with a concentration of 8 wt%. 0.15 g of 1 mm long oxidized short carbon fiber filaments were weighed and added to the binder solution for uniform dispersion to form a carbon fiber-binder system, and then slowly dropped into a water suspension solution composed of 43.5 g of HMX and 4 g of TATB. After that, it was prepared into shaped powder by the method of water suspension granulation, and dried and pressed into explosive columns of various sizes to obtain carbon fiber oxide-modified PBX. As Figure 3 The mechanical test results of the CFsO samples showed that the Brazilian tensile fracture strength was 6.14 MPa, the fracture strain was 0.23%, the compressive strength was 45.86 MPa, and the fracture strain was 2.37%.

[0066] Example 8

[0067] Example 8 was the control group, and carbon fiber grafted with polymer (CFsO-MDI) was added on the basis of Example 4.

[0068] Step 801: The same as Step 1 in Example 1;

[0069] Step 802: Weigh 5 g of carbon fiber oxide obtained in Step 801 and add it to DMF for dispersion, heat up to 65 °C, add 0.4 g of MDI and 1 drop of catalyst DBTDL, react for 2 h, wash 3 - 5 times, filter by suction and dry to obtain 1 mm long carbon fiber grafted with polymer in the present invention.

[0070] Step 803: Stir and dissolve 2.35 g of fluorine-containing polymer F2313 in ethyl acetate solvent to prepare a binder solution with a concentration of 8 wt%. Weigh 0.15 g of carbon fiber with 1 mm long grafted polymer, add it to the binder solution for uniform dispersion to form a carbon fiber-binder system, and then slowly drop it into a water suspension solution composed of 43.5 g of HMX and 4 g of TATB. After that, prepare shaped powder by the way of water suspension granulation, and press it into explosive charges of various sizes after drying, then the PBX modified by grafted polymer carbon fiber can be obtained. As Figure 3 The mechanical test results of CFsO-MDI show that the Brazilian tensile fracture strength is 7.02 MPa, the fracture strain is 0.40%, the compressive strength is 49.28 MPa, and the fracture strain is 2.40%.

[0071] Comparing with the above embodiments,

[0072] (1) For PBX without metal powder, in Example 4, the Brazilian tensile fracture strength of the blank control group PBX is 4.86 MPa, and the fracture strain is 0.19%; after introducing CFs, in Example 6, both the Brazilian tensile fracture and compressive strengths of PBX are improved, by 17% and 13% respectively; in Examples 7 and 8, the oxidation of the carbon fiber surface and the grafted polymer can further improve the mechanical properties on the basis of the addition of CFs. Among them, in Example 8, both the Brazilian tensile fracture and compressive strengths of PBX are improved, by 44% and 25% respectively; after using the multi-level structure carbon fiber prepared by the present invention, in Example 1, the enhancement effect of the mechanical properties of PBX is the best, the Brazilian tensile fracture strength is increased by 63%, the fracture strain is increased by 110%, and the compressive strength is increased by 39%; further, by using 2 mm multi-level structure carbon fiber, in Example 2, the Brazilian tensile fracture strength of PBX is increased by 75%, the fracture strain is increased by 121%, and the compressive strength is increased by 45%; comparing Examples 1-2, 6-8, it shows that the multi-level structure carbon fiber of the present invention has a significantly better mechanical enhancement effect on PBX than traditional carbon fiber, oxidized carbon fiber and carbon fiber grafted polymer, etc., and can efficiently enhance and toughen PBX with only 0.3% (mass fraction) addition amount;

[0073] (2) For PBX containing metal powder, comparing Example 3 and 5, by using the multi-level structure carbon fiber of the present invention, with only 0.5% mass fraction dosage, the Brazilian tensile fracture strength of PBX can be increased by 70%, the fracture strain is increased by 100%, and the compressive strength is increased by 52%; the improvement effect is very significant.

[0074] Although the present invention has been described herein with reference to illustrative embodiments of the present invention, the above embodiments are only preferred embodiments of the present invention, and the embodiments of the present invention are not limited by the above embodiments. It should be understood that those skilled in the art can design many other modifications and embodiments, which will fall within the scope and spirit of the principles disclosed in this application.

Claims

1. An enhanced and toughened PBX, characterized in that, Comprising: 55% - 96% of explosive, 3.7% - 6% of binder, 0% - 35% of high - calorific - value metal powder, 0% - 3% of functional additive, and 0.3% - 1% of multi - structured carbon fiber; The multi - structured carbon fiber is composed of carbon fiber, polyurethane, and graphene oxide, and the polyurethane and graphene oxide are grafted onto the surface of the carbon fiber through chemical bonding; The preparation method of the multi - structured carbon fiber includes: Step A: Add carbon fiber precursor filaments into a mixed acid of concentrated nitric acid and concentrated sulfuric acid, mechanically stir, acidify the carbon fiber at a certain water - bath temperature, then wash until neutral and dry to obtain oxidized carbon fiber; Step B: Disperse the oxidized carbon fiber obtained in Step A in an organic solvent, raise the temperature, add diisocyanate monomers, catalyst dibutyltin dilaurate, and graphene oxide, after reacting for 1 - 2 h, add a hydroxyl - terminated polymer for cross - linking reaction for 1 h, wash 3 - 5 times, filter by suction and dry to obtain a multi - structured carbon fiber.

2. An enhanced and toughened PBX according to claim 1, wherein The carbon fiber is short - cut micron - sized carbon fiber with a length of 0.5 - 2 mm; The polyurethane is in - situ polymerized from diisocyanate monomers and hydroxyl - terminated polymers; The graphene oxide is a single - layer structure with a lateral sheet diameter of 50 - 300 nm.

3. An enhanced and toughened PBX according to claim 1, characterized in that, The explosive is one or any combination of 1,3,5 - triamino - 2,4,6 - trinitrobenzene, HMX, RDX, CL - 20, FOX - 7, 1 - oxo - diamin - 3,5 - dinitropyrazine.

4. An enhanced and toughened PBX according to claim 1, wherein The binder is one of fluorine - containing polymers, polyurethane, cellulose acetate vinyl, ethylene - vinyl acetate copolymer; The high - calorific - value metal powder is aluminum powder.

5. An enhanced and toughened PBX according to any one of claims 1-4, characterized in that, The functional additive is one or both of desensitized graphite and wax.

6. A preparation method for enhancing and toughening PBX, characterized in that, Comprising: Preparing a multi - structured carbon fiber; And dispersing the prepared multi - structured carbon fiber into a polymer binder solution to form a carbon fiber - binder system, and preparing an enhanced and toughened PBX of the multi - structured carbon fiber by using one of water suspension granulation and kneading granulation; Among them, the method for preparing a multi - structured carbon fiber includes: Step A: Add carbon fiber precursor filaments into a mixed acid of concentrated nitric acid and concentrated sulfuric acid, mechanically stir, acidify the carbon fiber at a certain water - bath temperature, then wash until neutral and dry to obtain oxidized carbon fiber; Step B: Disperse the oxidized carbon fiber obtained in Step A in an organic solvent, raise the temperature, add diisocyanate monomers, catalyst dibutyltin dilaurate, and graphene oxide, after reacting for 1 - 2 h, add a hydroxyl - terminated polymer for cross - linking reaction for 1 h, wash 3 - 5 times, filter by suction and dry to obtain a multi - structured carbon fiber; the multi - structured carbon fiber is composed of carbon fiber, polyurethane, and graphene oxide, and the polyurethane and graphene oxide are grafted onto the surface of the carbon fiber through chemical bonding.

7. According to claim 6, the preparation method of an enhanced and toughened PBX, wherein In the step A, the volume ratio of concentrated nitric acid to concentrated sulfuric acid is 1:4 to 1:3, the acidification time is 2 h, and the temperature is 55 to 65 °C.

8. The preparation method of an enhanced and toughened PBX according to claim 6 or 7, characterized in that In the step B The organic solvent is any one of DMF, tetrahydrofuran, and butyl acetate, and the reaction temperature is 60 to 80 °C; the diisocyanate monomer is any one of toluene diisocyanate, isophorone diisocyanate, and 4,4′-diphenylmethane diisocyanate; the hydroxyl-terminated polymer is any one of polyethylene glycol and polytetrahydrofuran; by mass, the dosage of the diisocyanate monomer is 0.06 to 0.1 of the carbon fiber, the dosage of graphene oxide is 0.02 to 0.07 of the carbon fiber, and the dosage of the hydroxyl-terminated polymer is 0.04 to 0.07 of the carbon fiber.

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