1. A preparation method of a modified graphene oxide/HTPB polyurethane composite material is characterized by comprising the following steps:

s1, performing surface functional modification on graphene oxide by utilizing isophorone diisocyanate to obtain modified graphene oxide with free-NCO on the surface;

s2, reacting the modified graphene oxide with hydroxyl-terminated hyperbranched polyester to obtain modified graphene oxide with a large amount of free-OH on the surface;

s3, preparing the modified graphene oxide/HTPB polyurethane composite material by using the modified graphene oxide with a large amount of free-OH on the surface as a reinforcing agent and isophorone diisocyanate as a curing agent.

2. The method for preparing the modified graphene oxide/HTPB polyurethane composite material according to claim 1, wherein: the specific preparation process of the step S1 is as follows:

s11, dispersing graphene oxide in DMF, and performing rapid mechanical stirring and ultrasonic dispersion for 3 hours to obtain a graphene oxide suspension with higher stripping degree;

s12, slowly adding excessive isophorone diisocyanate and a catalyst dropwise into the graphene oxide suspension, slowly stirring, and placing the mixed solution in a water bath at 80 ℃ for reacting for 3 hours;

and S13, carrying out solid-liquid separation on the mixed solution after the reaction is finished, and drying the separated solid in a vacuum drying oven at 60 ℃ to obtain the modified graphene oxide with-NCO groups on the surface.

3. The method for preparing the modified graphene oxide/HTPB polyurethane composite material according to claim 2, wherein:

in the step S11, the weight-to-volume ratio of graphene oxide to DMF is 1 mg: 0.2ml to 0.3 ml;

in the step S12, the weight-to-volume ratio of the graphene oxide to the isophorone diisocyanate is 1 mg: 0.03ml to 4 ml; the catalyst is any one of triphenyl bismuth, stannous octoate or dibutyltin dilaurate, and the adding mass of the catalyst is 0.05-0.1 wt% of the mass of the graphene oxide;

in the step S13, solid-liquid separation is performed by adopting a centrifugal machine, wherein the rotating speed of the centrifugal machine is 1000 r/min-1200 r/min, and the centrifugal time is 10 min-15 min; and washing the separated precipitate with DMF and then drying.

4. The preparation method of the modified graphene oxide/HTPB polyurethane composite material of claim 1, wherein the specific preparation process of the step S2 is as follows:

s21, dispersing the modified graphene oxide with-NCO groups on the surface in DMF, and performing rapid mechanical stirring and ultrasonic dispersion for 2-3 h to obtain a modified graphene oxide suspension with higher stripping degree;

s22, mixing the modified graphene oxide suspension with a DMF (dimethyl formamide) solution of hydroxyl-terminated hyperbranched polyester, adding a catalyst triphenyl bismuth, and reacting for 2-3 hours in a water bath at 80 ℃ under the protection of nitrogen;

and S23, carrying out solid-liquid separation on the mixed solution after the reaction is finished, and drying the separated solid in a vacuum drying oven at 60 ℃ to obtain the modified graphene oxide with-OH groups on the surface.

5. The method for preparing the modified graphene oxide/HTPB polyurethane composite material according to claim 4, wherein:

in the step S21, the mass-to-volume ratio of the modified graphene oxide having-NCO groups on the surface to DMF is 1 mg: 0.2mL to 0.4 mL;

in the step S22, the mass-to-volume ratio of the hydroxyl-terminated hyperbranched polyester to DMF in the DMF solution of the hydroxyl-terminated hyperbranched polyester is 3 g: 20ml to 30ml, wherein the mass of the catalyst triphenyl bismuth is 0.05wt percent to 0.1wt percent of the sum of the mass of the modified graphene oxide and the mass of the hydroxyl-terminated hyperbranched polyester;

in the step S23, solid-liquid separation is performed by adopting a centrifugal machine, wherein the rotating speed of the centrifugal machine is 1000 r/min-1200 r/min, and the centrifugal time is 10 min-15 min; the bottom precipitate after separation was washed with DMF and then dried.

6. The preparation method of the modified graphene oxide/HTPB polyurethane composite material of claim 1, wherein the specific preparation process of the step S3 is as follows:

s31, fully dispersing the modified graphene oxide with-OH groups on the surface in a DMF solution under an ultrasonic condition, and carrying out ultrasonic treatment for 1-1.5 h to ensure that the content of the modified graphene oxide with-OH groups on the surface in the mixed solution is 3 mg/ml; then mixing the mixture with hydroxyl-terminated polybutadiene, dibutyl phthalate and catalyst triphenyl bismuth, and stirring the mixture for 6 hours at 50 ℃ to completely volatilize the solvent;

and S32, adding a curing agent isophorone diisocyanate into the reaction liquid, uniformly mixing, pouring into a mold, and curing at a constant temperature of 60 ℃ for 36 hours to obtain the modified graphene oxide/HTPB polyurethane composite material.

7. The method for preparing the modified graphene oxide/HTPB polyurethane composite material according to claim 6,

in the step S31, the mass-to-volume ratio of the modified graphene oxide with-OH groups on the surface to DMF is 1 mg: 0.2-0.4 mL, wherein the mass ratio of the modified graphene oxide with-OH groups on the surface to the hydroxyl-terminated polybutadiene is 0.05%: 1-0.2 percent of 1, wherein the adding weight of the dibutyl phthalate is 13-15 percent of the weight of the hydroxyl-terminated polybutadiene, and the adding weight of the catalyst triphenyl bismuth is 0.05-0.1 percent of the sum of the weight of the modified graphene oxide with-OH groups on the surface and the weight of the hydroxyl-terminated polybutadiene;

in the step S32, the adding amount of the curing agent isophorone diisocyanate is determined by an R value; the R value is the ratio of isocyanic acid radical to hydroxyl, and is selected from 0.7-0.8.

Background

The solid propellant plays an important role in the development of missiles and aerospace technologies, is an energy source of rocket and missile engines, and the comprehensive performance of the solid propellant is directly related to the accurate striking, high-energy damage and survival capability of modern weapon equipment systems. The good burning speed and energy characteristics are important directions and technical bases for developing solid propellants and weapon systems thereof. The composite solid propellant is widely applied to missile systems of various countries in recent years due to high specific impulse and good mechanical property, and is a mainstream engine design scheme adopted at present. The composite solid propellant is a multi-component filling type composite material taking a high molecular polymer as a matrix, consists of a binder, a solid oxidant, a metal combustion agent and a small amount of other components, and is widely applied to the conventional solid rocket charge. However, the composite solid propellant is inevitably subjected to extreme conditions such as complex load and temperature impact during production, storage, transportation and use, and is very easy to damage such as microcracks, which seriously jeopardizes the stability and safety of weapon systems. The adhesive is a polymer matrix of the propellant, and mainly has the function of bonding inorganic oxidizing agent and metal combustion particles distributed in the composite solid propellant, so that the mechanical property of the composite solid propellant is greatly dependent on the mechanical property of the adhesive, and the targeted reinforcement design of the composite solid propellant from the adhesive layer is a feasible way for solving the problems. Common methods of reinforcing adhesives are: chemical modification, nanoparticle filling, cross-linked network strengthening, and the like. One of the more currently used methods is nanoparticle filling, which can achieve this better.

Graphene, as an emerging lightweight nanomaterial, also known as "black gold," has extremely excellent physical and chemical properties. The method is widely applied to the traditional fields of aerospace, war industry, electronics, energy, environmental protection and the like and the strategic emerging industrial field. In recent years, applications of graphene in the field of energy-containing materials are increasing, but the main focus is on improving the thermal decomposition and combustion characteristics of the energy-containing materials by utilizing the catalytic characteristics of graphene. Meanwhile, the graphene has the highest material strength and an ultra-large specific surface area known at present, and can generate an effective mechanical enhancement effect in a polymer, so that the mechanical enhancement is taken as an important direction for the graphene to make application breakthrough in the field of propellants. Research shows that the addition of a small amount of graphene can significantly improve many important properties of the matrix material or endow new specific functions. However, the relatively strong pi-pi van der waals attraction between sheets of perfect defect-free graphene makes the graphene easy to be stacked or aggregated with each other and difficult to be uniformly dispersed in a matrix, thereby reducing the enhancement effect of the graphene and being difficult to form a firm bonding interface.

Graphene oxide itself has excellent properties as an oxygen-containing derivative of graphene, and at the same time, the surface of graphene oxide also has a large number of oxygen-containing functional groups, such as hydroxyl, carboxyl, epoxy, and the like. In fact, if it is simply filled into a polymer, the advantage of having a large number of active groups on its surface is not exerted, and thus the desired reinforcing effect is not achieved. Therefore, the surface modification of graphene oxide by utilizing the reactivity of the graphene oxide and the surface modification of the graphene oxide to adjust the interfacial property of the graphene oxide and the polymer and the dispersibility of the graphene oxide and the polymer in a matrix are common means for preparing graphene/polymer composite materials at present.

The hyperbranched polymer is a polymer with a highly branched and non-entangled structure and a large number of terminal active groups, has low solution viscosity and high solubility compared with linear analogues thereof, has better compatibility with a polymer matrix, and is widely used for reinforcing and toughening epoxy resin. Considering that the active group of the HTPB (hydroxyl-terminated polybutadiene) adhesive molecule commonly used in the composite solid propellant is hydroxyl, the curing process is to perform curing crosslinking reaction with the polyurethane curing agent isophorone diisocyanate (IPDI), and the hydroxyl-terminated hyperbranched polyester (HBP) and the IPDI can be used to perform surface modification on the graphene oxide, and the mechanical property of the HTPB adhesive is enhanced by the hydroxyl-terminated hyperbranched polyester (HBP) and the IPDI.

Disclosure of Invention

The invention provides a method for preparing a modified graphene oxide/HTPB polyurethane composite material by using isophorone diisocyanate and hydroxyl-terminated hyperbranched polyester to perform surface modification on graphene oxide and using the graphene oxide as a reinforcing agent, wherein the mechanical property of the polyurethane composite material prepared by the method is greatly enhanced.

The technical scheme of the invention is as follows:

a preparation method of a modified graphene oxide/HTPB polyurethane composite material comprises the following steps:

s1, performing surface functional modification on graphene oxide by utilizing isophorone diisocyanate (IPDI) to obtain modified graphene oxide (GO-NCO) with free-NCO on the surface;

s2, reacting the modified graphene oxide (GO-NCO) with hydroxyl-terminated hyperbranched polyester (HBP) to obtain modified graphene oxide (GO-HBP) with a large amount of free-OH on the surface;

s3, preparing the modified graphene oxide/HTPB polyurethane composite material by using modified graphene oxide (GO-HBP) with a large amount of free-OH on the surface as a reinforcing agent and isophorone diisocyanate (IPDI) as a curing agent.

The specific preparation process of the step S1 is as follows:

s11, dispersing graphene oxide in DMF, and performing rapid mechanical stirring and ultrasonic dispersion for 3 hours to obtain a graphene oxide suspension with higher stripping degree;

s12, slowly adding excessive isophorone diisocyanate (IPDI) and a catalyst dropwise into the graphene oxide suspension, slowly stirring, and placing the mixed solution in a water bath at 80 ℃ for reacting for 3 hours;

and S13, carrying out solid-liquid separation on the mixed solution after the reaction is finished, and drying the separated solid in a vacuum drying oven at 60 ℃ to obtain the modified graphene oxide with-NCO groups on the surface.

In step S11, the weight-to-volume ratio of graphene oxide to DMF is 1 mg: 0.2ml to 0.3 ml;

in the step S12, the weight-to-volume ratio of the graphene oxide to isophorone diisocyanate (IPDI) is 1 mg: 0.03ml to 4 ml; the catalyst is any one of triphenyl bismuth, stannous octoate or dibutyltin dilaurate, and triphenyl bismuth is preferred; the adding mass of the catalyst is 0.05 wt% -0.1 wt% of the mass of the graphene oxide;

in the step S13, solid-liquid separation is performed by adopting a centrifugal machine, wherein the rotating speed of the centrifugal machine is 1000 r/min-1200 r/min, and the centrifugal time is 10 min-15 min; and washing the separated precipitate with DMF and then drying.

The specific preparation process of the step S2 is as follows:

s21, dispersing modified graphene oxide (GO-NCO) with-NCO groups on the surface in DMF, and performing rapid mechanical stirring and ultrasonic dispersion for 2-3 h to obtain a modified graphene oxide suspension with higher stripping degree;

s22, mixing the modified graphene oxide suspension with a DMF (dimethyl formamide) solution of hydroxyl-terminated hyperbranched polyester (HBP), adding a catalyst triphenyl bismuth, and reacting for 2-3 hours in a water bath at 80 ℃ under the protection of nitrogen;

and S23, carrying out solid-liquid separation on the mixed solution after the reaction is finished, and drying the separated solid in a vacuum drying oven at 60 ℃ to obtain the modified graphene oxide with-OH groups on the surface.

In the step S21, the mass-to-volume ratio of the modified graphene oxide with-NCO groups on the surface to DMF is 1 mg: 0.2mL to 0.4 mL;

in the step S22, the mass-to-volume ratio of the hydroxyl-terminated hyperbranched polyester to DMF in the DMF solution of the hydroxyl-terminated hyperbranched polyester is 3 g: 20ml to 30ml, wherein the mass of the catalyst triphenyl bismuth is 0.05wt percent to 0.1wt percent of the sum of the mass of the modified graphene oxide and the mass of the hydroxyl-terminated hyperbranched polyester;

in the step S23, solid-liquid separation is performed by adopting a centrifugal machine, wherein the rotating speed of the centrifugal machine is 1000 r/min-1200 r/min, and the centrifugal time is 10 min-15 min; the bottom precipitate after separation was washed with DMF and then dried.

The specific preparation process of the step S3 is as follows:

s31, fully dispersing the modified graphene oxide (GO-HBP) with-OH groups on the surface in a DMF solution under an ultrasonic condition, and carrying out ultrasonic treatment for 1-1.5 h to ensure that the content of the modified graphene oxide with-OH groups on the surface in the suspension is 3 mg/ml; then mixing with hydroxyl-terminated polybutadiene (HTPB), dibutyl phthalate (DBP) and catalyst triphenyl bismuth, and stirring for 6 hours at 50 ℃ to completely volatilize the solvent;

s32, adding a curing agent isophorone diisocyanate (IPDI) into the reaction liquid, uniformly mixing, pouring into a mold, and curing at a constant temperature of 60 ℃ for 36 hours to obtain the modified graphene oxide/HTPB polyurethane composite material.

Wherein, in the step S31,

the mass-volume ratio of the modified graphene oxide (GO-HBP) with-OH groups on the surface to DMF is 1 mg: 0.2mL to 0.4 mL;

the mass ratio of the modified graphene oxide with the-OH groups on the surface to hydroxyl-terminated polybutadiene (HTPB) is 0.05%: 1-0.2%: 1;

the adding weight of the dibutyl phthalate (DBP) is 13-15 wt% of the weight of the hydroxyl-terminated polybutadiene (HTPB);

the addition weight of the catalyst triphenyl bismuth is 0.05-0.1 wt% of the sum of the weight of modified graphene oxide (GO-HBP) with-OH groups on the surface and hydroxyl-terminated polybutadiene (HTPB);

in the step S32, the adding amount of a curing agent isophorone diisocyanate (IPDI) is determined by an R value; the R value is the ratio of isocyanic acid radical to hydroxyl, and is 0.7-0.8, preferably 0.75.

Due to the adoption of the technical scheme, the invention has the technical progress that:

the invention provides a preparation method of a modified graphene oxide/HTPB polyurethane composite material, which is characterized in that hydroxyl-terminated hyperbranched polyester is used for modifying graphene oxide, so that the dispersibility of graphene oxide sheets in a matrix is improved, and the components of the composite material are uniformly distributed; meanwhile, hydroxyl-terminated hyperbranched polyester is introduced into the matrix, so that the crosslinking degree of the composite material is improved, and the modified graphene oxide/HTPB polyurethane composite material with better mechanical properties such as tensile strength and flexibility is obtained. The modified graphene oxide/HTPB polyurethane composite material can be used as an adhesive for preparing a composite solid propellant, so that the mechanical property of the composite solid propellant is obviously enhanced. The modified graphene oxide/HTPB polyurethane composite material prepared by the method can be widely applied to the national defense and military fields of carrier rockets, missile weapon systems and the like.

Drawings

FIG. 1 is a process flow diagram of the present invention;

FIG. 2 is a schematic view of a graphene oxide microstructure;

FIG. 3 is a microscopic view of a modified graphene oxide structure with-NCO on the surface;

FIG. 4 is a schematic structural view of a hydroxyl-terminated hyperbranched polyester;

FIG. 5 is a microscopic view of a graphene oxide structure with hydroxyl-terminated hyperbranched polyester groups on the surface;

FIG. 6 is a microscopic view of a modified graphene oxide/polyurethane structure;

fig. 7 is an SEM image of graphene oxide;

FIG. 8 is an SEM image of hyperbranched polyester-modified graphene oxide;

fig. 9 is a 2-fold magnified SEM image of fig. 8.

In the figure, 1-graphene oxide sheet; 2-an oxygen-containing functional group; 3-an IPDI molecule; 4-hydroxy-terminated hyperbranched polyester; 5-hydrogen bond.

DETAILED DESCRIPTION OF EMBODIMENT (S) OF INVENTION

The present invention will be further illustrated with reference to the following examples, but the preparation method of the present invention is not limited to the following specific examples.

A preparation method of a modified graphene oxide/HTPB polyurethane composite material comprises the following steps:

s1, performing surface functional modification on graphene oxide by utilizing isophorone diisocyanate (IPDI) to obtain modified graphene oxide (GO-NCO) with free-NCO on the surface;

s2, reacting the modified graphene oxide (GO-NCO) with hydroxyl-terminated hyperbranched polyester (HBP) to obtain modified graphene oxide (GO-HBP) with a large amount of free-OH on the surface;

s3, preparing the modified graphene oxide/HTPB polyurethane composite material by using modified graphene oxide (GO-HBP) with a large amount of free-OH on the surface as a reinforcing agent and isophorone diisocyanate (IPDI) as a curing agent.

The specific preparation process of the step S1 is as follows:

s11, dispersing graphene oxide in DMF, and performing rapid mechanical stirring and ultrasonic dispersion for 3 hours to obtain a graphene oxide suspension with higher stripping degree;

s12, slowly adding excessive isophorone diisocyanate (IPDI) and a catalyst dropwise into the graphene oxide suspension, slowly stirring, and placing the mixed solution in a water bath at 80 ℃ for reacting for 3 hours;

and S13, carrying out solid-liquid separation on the mixed solution after the reaction is finished, and drying the separated solid in a vacuum drying oven at 60 ℃ to obtain the modified graphene oxide with-NCO groups on the surface.

In step S11, the weight-to-volume ratio of graphene oxide to DMF is 1 mg: 0.2ml to 0.3 ml;

in the step S12, the weight-to-volume ratio of the graphene oxide to isophorone diisocyanate (IPDI) is 1 mg: 0.03ml to 4ml, preferably 1 mg: 0.03ml to 0.1 ml; the catalyst is any one of triphenyl bismuth, stannous octoate or dibutyltin dilaurate, and triphenyl bismuth is preferred; the adding mass of the catalyst is 0.05 wt% -0.1 wt% of the mass of the graphene oxide;

in the step S13, solid-liquid separation is performed by adopting a centrifugal machine, wherein the rotating speed of the centrifugal machine is 1000 r/min-1200 r/min, and the centrifugal time is 10 min-15 min; and washing the separated precipitate with DMF and then drying.

The specific preparation process of the step S2 is as follows:

s21, dispersing modified graphene oxide (GO-NCO) with-NCO groups on the surface in DMF, and performing rapid mechanical stirring and ultrasonic dispersion for 2-3 h to obtain a modified graphene oxide suspension with higher stripping degree;

s22, mixing the modified graphene oxide suspension with a DMF (dimethyl formamide) solution of hydroxyl-terminated hyperbranched polyester (HBP), adding a catalyst triphenyl bismuth, and reacting for 2-3 hours in a water bath at 80 ℃ under the protection of nitrogen;

and S23, carrying out solid-liquid separation on the mixed solution after the reaction is finished, and drying the separated solid in a vacuum drying oven at 60 ℃ to obtain the modified graphene oxide with-OH groups on the surface.

In the step S21, the mass-to-volume ratio of the modified graphene oxide with-NCO groups on the surface to DMF is 1 mg: 0.2mL to 0.4 mL;

in the step S22, the mass-to-volume ratio of the hydroxyl-terminated hyperbranched polyester to DMF in the DMF solution of the hydroxyl-terminated hyperbranched polyester is 3 g: 20ml to 30ml, wherein the mass of the catalyst triphenyl bismuth is 0.05wt percent to 0.1wt percent of the sum of the mass of the modified graphene oxide and the mass of the hydroxyl-terminated hyperbranched polyester;

in the step S23, solid-liquid separation is performed by adopting a centrifugal machine, wherein the rotating speed of the centrifugal machine is 1000 r/min-1200 r/min, and the centrifugal time is 10 min-15 min; the bottom precipitate after separation was washed with DMF and then dried.

The specific preparation process of the step S3 is as follows:

s31, fully dispersing the modified graphene oxide (GO-HBP) with-OH groups on the surface in a DMF solution under an ultrasonic condition, and carrying out ultrasonic treatment for 1-1.5 h to ensure that the content of the modified graphene oxide with-OH groups on the surface in the suspension is 3 mg/ml; then mixing with hydroxyl-terminated polybutadiene (HTPB), dibutyl phthalate (DBP) and catalyst triphenyl bismuth, and stirring for 6 hours at 50 ℃ to completely volatilize the solvent;

s32, adding a curing agent isophorone diisocyanate (IPDI) into the reaction liquid, uniformly mixing, pouring into a mold, and curing at a constant temperature of 60 ℃ for 36 hours to obtain the modified graphene oxide/HTPB polyurethane composite material.

Wherein, in the step S31,

the mass-volume ratio of the modified graphene oxide (GO-HBP) with-OH groups on the surface to DMF is 1 mg: 0.2mL to 0.4mL, preferably 1 mg: 0.3 mL;

the mass ratio of the modified graphene oxide with the-OH groups on the surface to hydroxyl-terminated polybutadiene (HTPB) is 0.05%: 1-0.2%: 1;

the adding weight of the dibutyl phthalate (DBP) is 13-15 wt% of the weight of the hydroxyl-terminated polybutadiene (HTPB);

the addition weight of the catalyst triphenyl bismuth is 0.05-0.1 wt% of the sum of the weight of modified graphene oxide (GO-HBP) with-OH groups on the surface and hydroxyl-terminated polybutadiene (HTPB);

in the step S32, the adding amount of a curing agent isophorone diisocyanate (IPDI) is determined by an R value; the R value is the ratio of isocyanic acid radical to hydroxyl, and is 0.7-0.8, preferably 0.75.

The R value is the ratio of isocyanic acid radical to hydroxyl, different R values can influence the cured crosslinking network, the R values can be different due to different structures of the crosslinking network required by the product, and when the R value is 0.7-0.8, the crosslinking network structure of the obtained product enables the mechanical property of the polyurethane composite material to be optimal. 1mol IPDI contains 2mol of isocyanic acid radical, and the adding amount of curing agent isophorone diisocyanate (IPDI) can be calculated through the total hydroxyl and R value.

The present invention is further illustrated by the following examples. The specifications and manufacturers of the raw materials used in the following examples were:

in the following examples and comparative examples, the R value was 0.75.

Example 1

A preparation method of a modified graphene oxide/HTPB polyurethane composite material comprises the following steps:

s1, performing surface functional modification on graphene oxide by utilizing isophorone diisocyanate to obtain modified graphene oxide with free-NCO on the surface;

s11, dispersing 250mg of graphene oxide in 50mLDMF, and performing rapid mechanical stirring and ultrasonic dispersion for 3 hours to obtain a graphene oxide suspension with higher stripping degree;

s12, slowly and dropwise adding excessive isophorone diisocyanate (7.5mL) and catalyst triphenyl bismuth (0.25mg) into the graphene oxide suspension, slowly stirring, and placing the mixed solution in a water bath at 80 ℃ for reacting for 3 hours;

s13, carrying out centrifugal separation on the mixed solution after the reaction, wherein the rotating speed of a centrifugal machine is 1000r/min, and the centrifugal time is 10 min; washing the bottom precipitate with DMF, and drying in a vacuum drying oven at 60 ℃ to obtain modified graphene oxide with-NCO groups on the surface;

s2, reacting the modified graphene oxide with hydroxyl-terminated hyperbranched polyester to obtain the modified graphene oxide with a large amount of free-OH on the surface.

S21, dispersing the modified graphene oxide with-NCO groups on the surface in (50mL) DMF, and rapidly mechanically stirring and ultrasonically dispersing for 3 hours to obtain a modified graphene oxide suspension with higher stripping degree; and (3g) hydroxyl-terminated hyperbranched polyester is dissolved in (20mL) DMF;

s22, mixing the modified graphene oxide suspension with the hydroxyl-terminated hyperbranched polyester solution, adding (1.63mg) catalyst triphenylbismuth, and reacting for 3 hours in a water bath at 80 ℃ under the protection of nitrogen;

s23, carrying out centrifugal separation on the mixed solution after the reaction, wherein the rotating speed of a centrifugal machine is 1000r/min, and the centrifugal time is 10 min; and (3) washing the bottom precipitate with DMF, and drying in a vacuum drying oven at 60 ℃ to obtain the modified graphene oxide with-OH groups on the surface.

S3, preparing the modified graphene oxide/HTPB polyurethane composite material by using the modified graphene oxide with a large amount of free-OH on the surface as a reinforcing agent and isophorone diisocyanate as a curing agent.

S31, fully dispersing 0.0015g of modified graphene oxide with-OH groups on the surface in 0.5ml of DMF solution under the ultrasonic condition, and carrying out ultrasonic treatment for 60min to ensure that the content of the modified graphene oxide with-OH groups on the surface in the mixed solution is 3 mg/ml; then mixed with 3g of HTPB, 0.39g of DBP and 1.63mg of TPB and stirred for 6h at 50 ℃, mixed thoroughly and the solvent removed;

s32, adding 0.26g of curing agent IPDI into the reaction liquid, uniformly mixing, pouring into a mold, and curing at 60 ℃ for 36h to obtain the modified graphene oxide/HTPB polyurethane composite material.

Example 2

A preparation method of a modified graphene oxide/HTPB polyurethane composite material comprises the following steps:

s1, performing surface functional modification on graphene oxide by utilizing isophorone diisocyanate to obtain modified graphene oxide with free-NCO on the surface;

s11, dispersing 250mg of graphene oxide in 50mLDMF, and performing rapid mechanical stirring and ultrasonic dispersion for 3 hours to obtain a graphene oxide suspension with higher stripping degree;

s12, slowly and dropwise adding excessive isophorone diisocyanate (7.5mL) and catalyst triphenyl bismuth (0.25mg) into the graphene oxide suspension, slowly stirring, and placing the mixed solution in a water bath at 80 ℃ for reacting for 3 hours;

s13, carrying out centrifugal separation on the mixed solution after the reaction, wherein the rotating speed of a centrifugal machine is 1000r/min, and the centrifugal time is 10 min; washing the bottom precipitate with DMF, and drying in a vacuum drying oven at 60 ℃ to obtain modified graphene oxide with-NCO groups on the surface;

s2, reacting the modified graphene oxide with hydroxyl-terminated hyperbranched polyester to obtain the modified graphene oxide with a large amount of free-OH on the surface.

S21, dispersing the modified graphene oxide with-NCO groups on the surface in (50mL) DMF, and rapidly mechanically stirring and ultrasonically dispersing for 3 hours to obtain a modified graphene oxide suspension with higher stripping degree; and (3g) hydroxyl-terminated hyperbranched polyester is dissolved in (20mL) DMF;

s22, mixing the modified graphene oxide suspension with the hydroxyl-terminated hyperbranched polyester solution, adding (1.63mg) catalyst triphenylbismuth, and reacting for 3 hours in a water bath at 80 ℃ under the protection of nitrogen;

s23, carrying out centrifugal separation on the mixed solution after the reaction, wherein the rotating speed of a centrifugal machine is 1000r/min, and the centrifugal time is 10 min; and (3) washing the bottom precipitate with DMF, and drying in a vacuum drying oven at 60 ℃ to obtain the modified graphene oxide with-OH groups on the surface.

S3, preparing the modified graphene oxide/HTPB polyurethane composite material by using the modified graphene oxide with a large amount of free-OH on the surface as a reinforcing agent and isophorone diisocyanate as a curing agent.

S31, fully dispersing 0.003g of modified graphene oxide with-OH groups on the surface in a 1ml of DMF solution under an ultrasonic condition, wherein the ultrasonic time is 60min, and the content of the modified graphene oxide with-OH groups on the surface is 3 mg/ml; then mixed with 3g of HTPB, 0.39g of DBP and 1.64mg of TPB and stirred for 6h at 50 ℃, mixed thoroughly and the solvent removed;

s32, adding 0.28g of curing agent IPDI into the reaction liquid, uniformly mixing, pouring into a mold, and curing at 60 ℃ for 36h to obtain the modified graphene oxide/HTPB polyurethane composite material.

Example 3

A preparation method of a modified graphene oxide/HTPB polyurethane composite material comprises the following steps:

s1, performing surface functional modification on graphene oxide by utilizing isophorone diisocyanate to obtain modified graphene oxide with free-NCO on the surface;

s11, dispersing 250mg of graphene oxide in 50mLDMF, and performing rapid mechanical stirring and ultrasonic dispersion for 3 hours to obtain a graphene oxide suspension with higher stripping degree;

s12, slowly and dropwise adding excessive isophorone diisocyanate (7.5mL) and catalyst triphenyl bismuth (0.25mg) into the graphene oxide suspension, slowly stirring, and placing the mixed solution in a water bath at 80 ℃ for reacting for 3 hours;

s13, carrying out centrifugal separation on the mixed solution after the reaction, wherein the rotating speed of a centrifugal machine is 1000r/min, and the centrifugal time is 10 min; washing the bottom precipitate with DMF, and drying in a vacuum drying oven at 60 ℃ to obtain modified graphene oxide with-NCO groups on the surface;

s2, reacting the modified graphene oxide with hydroxyl-terminated hyperbranched polyester to obtain the modified graphene oxide with a large amount of free-OH on the surface.

S21, dispersing the modified graphene oxide with-NCO groups on the surface in (50mL) DMF, and rapidly mechanically stirring and ultrasonically dispersing for 3 hours to obtain a modified graphene oxide suspension with higher stripping degree; and (3g) hydroxyl-terminated hyperbranched polyester is dissolved in (20mL) DMF;

s22, mixing the modified graphene oxide suspension with the hydroxyl-terminated hyperbranched polyester solution, adding (1.63mg) catalyst triphenylbismuth, and reacting for 3 hours in a water bath at 80 ℃ under the protection of nitrogen;

s23, carrying out centrifugal separation on the mixed solution after the reaction, wherein the rotating speed of a centrifugal machine is 1000r/min, and the centrifugal time is 10 min; and (3) washing the bottom precipitate with DMF, and drying in a vacuum drying oven at 60 ℃ to obtain the modified graphene oxide with-OH groups on the surface.

S3, preparing the modified graphene oxide/HTPB polyurethane composite material by using the modified graphene oxide with a large amount of free-OH on the surface as a reinforcing agent and isophorone diisocyanate as a curing agent.

S31, fully dispersing 0.006g of modified graphene oxide with-OH groups on the surface in a 2ml of DMF solution under an ultrasonic condition, wherein the ultrasonic time is 60min, and the content of the modified graphene oxide with-OH groups on the surface is 3 mg/ml; then mixed with 3g of HTPB, 0.39g of DBP and 1.66mg of TPB and stirred at 50 ℃ for 6h, mixed thoroughly and the solvent removed;

s32, adding 0.31g of curing agent IPDI into the reaction liquid, uniformly mixing, pouring into a mold, and curing at 60 ℃ for 36h to obtain the modified graphene oxide/HTPB polyurethane composite material.

Comparative example 1

This comparative example is an HTPB polyurethane material without modified graphene oxide. The preparation method comprises the following steps:

weighing 3g of HTPB, adding 0.39g of DBP, 1.63mg of TPB and 0.25g of curing agent IPDI, mixing at 50 ℃, stirring for 6h, pouring into a mold after mixing uniformly, and curing at 60 ℃ for 36h to obtain the HTPB polyurethane composite material.

The composite materials prepared in examples 1-3 and comparative example 1 were subjected to mechanical property tests, and the data are as follows:

	comparative example 1	Example 1	Example 2	Example 3
					Modulus of elasticity	0.03733MPa	0.05042MPa	0.06219MPa	0.07039MPa
Breaking strength	0.25067MPa	0.33600MPa	0.39567MPa	0.27733MPa
					Elongation at break	1267.67％	1158％	1292.67％	972％

The data show that compared with comparative example 1, the elastic modulus and the breaking strength of the products in examples 1-3 are both obviously improved, the elastic modulus is improved by 35.07% -88.56% compared with comparative example 1, and the breaking strength is improved by 10.64% -57.84% compared with comparative example 1; compared with the comparative example 1, the elongation at break is basically equal, the higher level is kept, and the use requirement of the solid propellant can be met.

The composite materials prepared in the embodiments 1-3 and the comparative example 1 are taken as the binder to prepare the composite solid propellant, and experiments prove that compared with the conventional propellant prepared in the comparative example 1, the mechanical property of the products in the embodiments 1-3 at normal temperature is improved by 20-25%, and the effect is very obvious.

The preparation method provided by the invention is described by the detailed embodiment, and a person skilled in the art can understand that certain changes or modifications can be made to the invention without departing from the scope of the invention; not limited to the disclosure in the examples.