THERMOPLASTIC COMPOSITE SOLID PROPELLANT AND PREPARATION METHOD THEREFOR

Description

TECHNICAL FIELD

The present invention relates to the field of composite solid propellant technology, and in particular to a thermoplastic composite solid propellant and a preparation method thereof.

BACKGROUND

Composite solid propellant is composed of a solid filler such as an oxidizing agent, a metal fuel, a small component functional auxiliary agent, and a polymeric adhesive. By mixing the solid filler with the polymeric adhesive uniformly, the adhesive can bind the solid filler of the composite solid propellant and other components such as combustion catalyst, bonding agent, anti-aging agent and other functional additives to each other, while imparting an ideal configuration and structural integrity to the propellant.

The adhesive matrix network structure of a thermosetting composite solid propellant is typically formed by chemical crosslinking reaction between a macromolecular prepolymer and a curing agent, such as, the condensation of hydroxyl-terminated polybutadiene and bifunctional isocyanate to generate an urethane, and the cycloaddition of a monosubstituted alkyne and an organic azide compound to yield a 1,2,3-triazole. The chemically crosslinked network formed by covalent bond has many advantages, such as structural regularity, fewer dangling chains, and controllable curing parameters. However, due to the limitation of “pot life” of the thermosetting propellant slurry, the slurry in which the mixing has been done or the curing agent has been added has to be poured into the engine combustion chamber as soon as possible. The temperature and humidity need to be strictly controlled for a long period of time to complete the curing crosslinking reaction, and the requirements for the related facilities in the curing site are harsh. Also, the chemically crosslinked network formed by non-reversible covalent bonds makes the thermosetting composite solid propellant unable to be re-processed and formed. Once the propellant has quality problems or expires, it can only be destroyed by burning, causing waste of resources and environmental pollution.

In order to overcome the above shortcomings, a class of curing agent-free, reusable thermoplastic elastomer (TPE) materials that avoid the limitation for the “pot life” of propellant slurry are used as the adhesive in the composite solid propellants. The thermoplastic composite solid propellant has plastic-like repeatable molding characteristic and environmental stability, which can be prepared by small-scale continuous mixing, and does not require to produce the propellant massively and intensively. It is less dependent on the production conditions and environment such as mixing equipment and site, and can achieve a solvent-free, continuous processing. Thus, it is widely valued and studied as a green propellant variety.

In the thermoplastic composite solid propellants, a thermoplastic elastomer is typically used as adhesive. The thermoplastic elastomer is generally a linear block polymer formed by copolymerization of linear soft segments and linear hard segments. Among them, a reversible physical crystalline network formed by hydrogen bonds between the hard segments achieves the solid-liquid conversion of the propellant. However, because neither a reactive curing agent nor a bonding agent is used, the bulk structural characteristic of microphase separation in the elastomer determines the mechanical property of the thermoplastic composite solid propellant, that is, a weak interfacial effect between the thermoplastic adhesive matrix and the solid filler, so that a “dehumidification” phenomenon is very prone to occur in the propellant during the tensile failure process. Therefore, there is an urgent need to develop a thermoplastic composite solid propellant with enhanced interfacial effect, while seeking a safer and more efficient method for preparing a thermoplastic composite solid propellant in a slurry-free mixing manner.

SUMMARY OF THE INVENTION

In response to the above problems, a first object of the present invention is to provide a thermoplastic composite solid propellant. In the thermoplastic composite solid propellant, a thermoplastic elastomer grafted or copolymerized with a bonding functional group is used as adhesive so that the adhesive matrix has a strong interaction with the solid filler, which can enhance the interfacial effect, and slow down the occurrence of “dehumidification” phenomenon in the tensile failure process.

A second object of the present invention is to provide a method for preparing the above-described thermoplastic composite solid propellant. This method overcomes the shortcomings of the existing technology, and safely and efficiently prepares the thermoplastic composite solid propellant by means of acoustic resonance mixing, meeting the requirement for rapid charging of solid engines.

A first technical solution adopted by the present invention is: a thermoplastic composite solid propellant, which comprises, in percentages by mass:

• • 5% to 16% of a bonding functional thermoplastic elastomer;
  • 5% to 25% of a plasticizer;
  • 5% to 18% of a metal fuel;
  • 50% to 70% of an oxidizing agent; and
  • 0.4% to 5% of a functional auxiliary agent.

Preferably, the bonding functional group or block in the bonding functional thermoplastic elastomer comprises one or more of maleic anhydride, styrene, glycidyl methacrylate, butyl acrylate, hydroxyethyl acrylate, acrylic acid and methacrylic acid.

Preferably, the bonding functional group or block in the bonding functional thermoplastic elastomer has a mass percentage of 0.1 wt % to 5 wt %.

Preferably, the plasticizer comprises one or more of naphthenic oil, dioctyl sebacate, liquid paraffin and dioctyl phthalate.

Preferably, the oxidizing agent comprises one or more of ammonium perchlorate, ammonium nitrate, phase-stable ammonium nitrate, hexogen, octogen and 5,5′-bistetrazole-1,1′-dioxodihydroxylammonium salt.

Preferably, the functional auxiliary agent comprises a stabilizing agent and a combustion catalyst, wherein the stabilizing agent comprises one or more of N,N-dimethylaniline, N-methylaniline and diphenylamine; and the combustion catalyst comprises one or more of n-octylferrocene, ferric oxide and copper chromite.

A second technical solution adopted by the present invention is: a method for preparing a thermoplastic composite solid propellant comprising the steps of:

• • S1: heating and melting a bonding functional thermoplastic elastomer and a plasticizer, adding a functional auxiliary agent, and mixing them uniformly;
  • S2: adding a metal fuel and mix them uniformly by means of acoustic resonance;
  • S3: adding an oxidizing agent in batches and mixing them uniformly by means of acoustic resonance to prepare the thermoplastic composite solid propellant.

Preferably, the method for preparing the thermoplastic composite solid propellant further comprises: pouring the prepared thermoplastic composite solid propellant into a mold, which is naturally cooled and cured for shaping.

Preferably, the step S1 has a melting temperature of 85° C. to 95° C.

Preferably, the step S2 has a mixing temperature of 85° C. to 95° C., an acoustic resonance strength of 30 g to 70 g, and a resonance time of 5 min to 10 min.

The above technical solutions have the following beneficial effects:

• • (1) Currently, there is no effective bonding agent for the thermoplastic composite solid propellants. Therefore, there is a weak interfacial effect between the adhesive matrix and the solid filler, and a “dehumidification” phenomenon is prone to occur during the tensile failure process. Based on the theory of Neutral Polymeric Bonding Agent (NPBA), the thermoplastic composite solid propellant disclosed in the present invention utilizes a thermoplastic elastomer grafted or copolymerized with a bonding functional group as adhesive, so that the adhesive matrix has a strong interaction with the solid filler, which can enhance the interfacial effect, and slow down the occurrence of “dehumidification” phenomenon, improving the mechanical properties of the propellant.
  • (2) The method for preparing the thermoplastic composite solid propellant disclosed in the present invention utilizes an acoustic resonance mixer to prepare the thermoplastic composite solid propellant. It is a brand-new slurry-free mixing technology, which breaks the material mixing boundary conditions with minimum energy by the principle of mechanical resonance and stimulates the materials to mix rapidly by self-vibration, greatly improving the preparation efficiency while increasing the process safety.
  • (3) The thermosetting composite solid propellant forms a chemically crosslinked network by a irreversible reaction between a macromolecular prepolymer and a curing agent, in which the temperature and humidity need to be strictly controlled to complete the curing crosslinking reaction, and the requirements for the related facilities in the curing site are harsh. However, the thermoplastic composite solid propellant prepared in the present invention achieves the solid-liquid conversion by a reversible physical crystalline network formed by hydrogen bonds between the elastomer hard segments, which has repeatable molding characteristic. The residual materials generated during the processing can be recycled for reuse, and the expired or scrapped grain can also be post-processed via green process for reuse, meeting the green and environmental friendly concept.
  • (4) In the method for preparing the thermoplastic composite solid propellant disclosed in the present invention, the thermoplastic adhesive and the propellant have a softening point temperature of 85° C. to 95° C., and has a repeatable processability.
  • (5) In the method for preparing the thermoplastic composite solid propellant disclosed in the present invention, the acoustic resonance mixer is used to prepare the thermoplastic propellant; the slurry-free mixing greatly improves the mixing and preparation efficiency while improving the process safety; and the thermoplastic propellant slurry is not limited by the “pot life”, and the mixing and pouring processes are completely independent. The propellant has good application prospects in the fields such as rapid charging of solid engines and controllable energy release.

BRIEF SUMMARY OF THE DRAWINGS

FIG. 1 is a process flow chart of a method for preparing a thermoplastic composite solid propellant of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter the present invention is further described by specific embodiments. It should be noted that several variations and improvements can be made by persons of ordinary skills in the art without departing from the principles of the present invention, which should be considered to fall within the protection scope of the present invention.

The contents which are not described in detail in the specification of the present invention belong to well-known techniques of those skilled in the art.

The present invention discloses a thermoplastic composite solid propellant, which comprises in percentages by mass: 5% to 16% of a bonding functional thermoplastic elastomer; 5% to 25% of a plasticizer; 5% to 18% of a metal fuel; 50% to 70% of an oxidizing agent; and 0.4% to 5% of a functional auxiliary agent; wherein a sum of the mass percentages of various materials in the thermoplastic composite solid propellant is 100%.

The bonding functional thermoplastic elastomer (Bonding Functional TPE) of the present invention is obtained by grafting or copolymerizing a bonding functional group or block onto a thermoplastic elastomer, wherein the bonding functional group or block comprises one or more of maleic anhydride (MAH), styrene (St), glycidyl methacrylate (GMA), butyl acrylate (BA), hydroxyethyl acrylate (HEA), acrylic acid (AA) and methyl methacrylate (MMA), and the bonding functional group or block in the bonding functional thermoplastic elastomer has a mass percentage of 0.1 wt % to 5 wt %.

The bonding functional thermoplastic elastomer is, e.g., a maleic anhydride-grafted ethylene-vinyl acetate copolymer; and the bonding functional thermoplastic elastomer has a relative molecular mass of 21,000 to 40,000, a softening point temperature as adhesive of 85° C. to 95° C., a maximum tensile strength at 20° C. of 0.7 MPa to 4.9 MPa, and a maximum elongation at break of 485% to 1330%.

The plasticizer comprises one or more of naphthenic oil (KN), dioctyl sebacate (DOS), liquid paraffin and dioctyl phthalate; and a mass ratio of the plasticizer to the bonding functional thermoplastic elastomer is (0.6-1.55):1.

The metal fuel comprises, but is not limited to, aluminum powder (Al).

The oxidizing agent comprises one or more of ammonium perchlorate (AP), ammonium nitrate (AN), phase-stable ammonium nitrate (PSAN), hexogen (RDX), octogen (HMX) and 5,5′-bistetrazole-1,1′-dioxodihydroxylammonium salt (TKX-50).

The functional auxiliary agent comprises, but is not limited to, a stabilizing agent and a combustion catalyst, wherein the stabilizing agent comprises one or more of N,N-dimethylaniline (NN), N-methylaniline (NMA) and diphenylamine (NPA); and the combustion catalyst comprises one or more of n-octylferrocene, ferric oxide and copper chromite.

As shown in FIG. 1, the thermoplastic composite solid propellant is prepared by the steps of:

• • S1: heating the bonding functional thermoplastic elastomer and the plasticizer in a high-shear dispersing emulsifier (but not limited hereto) to 85° C. to 95° C. for melting, adding a functional auxiliary agent, and then mixing them uniformly;
  • S2: transferring the uniformly mixed materials to an acoustic resonance mixer, adding a metal fuel, and mixing them uniformly by means of acoustic resonance for 5 min to 10 min at a mixing temperature of 85° C. to 95° C. and a resonance strength of 30 g to 70 g; and
  • S3: adding a certain amount oxidizing agent in batches to the above materials, and mixing them uniformly by means of acoustic resonance to give the thermoplastic composite solid propellant.

Further, in an embodiment, the method further comprises pouring the thermoplastic composite solid propellant into a mold, which is naturally cooled, cured for shaping, and then stored. During charging, a square billet (shaped by curing of the thermoplastic composite solid propellant) is melted and poured into an engine shell for shaping, or loading the square billet into the engine shell and then melt and shaped, wherein a heating temperature during charging is 95° C. to 100° C.

The prepared thermoplastic composite solid propellant is characterized as follows:

• • 1) Mechanical properties: the maximum tensile strength, σ_b, and the elongation at break, ε_m, of the mechanical properties are measured under the testing conditions of 20° C. and 100 mm/min with reference to GJB 770B-2005;
  • 2) Density: the density is measured under the test conditions of 20° C., g/cm³ with reference to QJ 917A-97; and
  • 3) Theoretical specific impulse.

Example 1

Materials were weighed according to the formula in Table 1. The bonding functional thermoplastic elastomer (Bonding Functional TPE) and the plasticizer were put into a high-shear dispersing emulsifier and heated to 90° C. for melting. Then, a functional auxiliary agent was added and mixed uniformly. The materials were transferred to an acoustic resonance mixer, heated to 90° C., and Al was added and pre-mixed. The Al was mixed uniformly by means of acoustic resonance with a resonance strength of 50 g for a resonance time of 5 min. Then, a certain amount of oxidizing agent was added in batches, and mixed uniformly by means of acoustic resonance to give the thermoplastic composite solid propellant, which was poured into a mold, naturally cooled, and cured to give a propellant sample.

TABLE 1
Formula and Properties of The
Thermoplastic Composite Solid Propellant

Composition of Formula	Mass Percent/% wt
Bonding Functional TPE	8.55
KN	6
DOS	2
Al	18
AP	59
AN	/
PSAN	/
RDX	6
NPA	0.1
n-octylferrocene	0.35

			Maximum
			Tensile	Elongation
Sample	Test	Test	Strength	at Break
Properties	Standards	Conditions	σb/MPA	εm/%
Mechanical	GJB 770B-	20° C.,	1.62	25.5
Properties	2005	100 mm/min

Density

QJ 917A-97

20° C., g/cm3

1.71

Theoretical

20° C., 6.86 MPa, s

261.977

Specific
Impulse

Example 2

Various materials were weighed according to the formula in Table 2. The bonding functional thermoplastic elastomer (Bonding Functional TPE) and the plasticizer were put into a high-shear dispersing emulsifier and heated to 85° C. for melting. Then, a functional auxiliary agent was added and mixed uniformly. The materials were transferred to an acoustic resonance mixer, heated to 85° C., and Al was added and pre-mixed. The Al was mixed uniformly by means of acoustic resonance with a resonance strength of 30 g for a resonance time of 10 min. Then, a certain amount of oxidizing agent was added in batches, and mixed uniformly by means of acoustic resonance to give the thermoplastic composite solid propellant, which was poured into a mold, naturally cooled, and cured to give a propellant sample.

TABLE 2
Formula and Properties of The
Thermoplastic Composite Solid Propellant

Composition of Formula	Mass Percent/% wt
Bonding Functional TPE	7.6
KN	7.2
DOS	1.7
Al	17
AP	59
AN	7
PSAN	/
5,5′-bistetrazole-1,1′-	/
dioxodihydroxylammonium salt
RDX	/
NN	0.1
n-octylferrocene	0.4

Sample	Test	Test
Properties	Standards	Conditions	σb/MPA	εm/%
Mechanical	GJB 770B-	20° C.,	1.57	23.8
Properties	2005	100 mm/min

Density

QJ 917A-97

20° C., g/cm3

1.696

Theoretical

20° C., 6.86 MPa, s

259.975

Specific
Impulse

Example 3

Materials were weighed according to the formula in Table 3. The bonding functional thermoplastic elastomer (Bonding Functional TPE) and the plasticizer were put into a high-shear dispersing emulsifier and heated to 85° C. for melting. Then, a functional auxiliary agent was added and mixed uniformly. The materials were transferred to an acoustic resonance mixer, heated to 90° C., and Al was added and pre-mixed. The Al was mixed uniformly by means of acoustic resonance with a resonance strength of 70 g for a resonance time of 5 min. Then, a certain amount of oxidizing agent was added in batches, and mixed uniformly by means of acoustic resonance to give the thermoplastic composite solid propellant, which was poured into a mold, naturally cooled, and cured to give a propellant sample.

TABLE 3
Formula and Properties of The
Thermoplastic Composite Solid Propellant

Composition of Formula	Mass Percent/% wt
Bonding Functional TPE	9.94
KN	9.5
Al	17
AP	51
AN	/
PSAN	8
5,5′-bistetrazole-1,1′-	/
dioxodihydroxylammonium salt
HMX	4
NMA	0.16
Fe2O3	0.4

Sample	Test	Test
Properties	Standards	Conditions	σb/MPA	εm/%
Mechanical	GJB 770B-	20° C.,	1.29	36.6
Properties	2005	100 mm/min

Density	QJ 917A-97 20° C., g/cm3	1.657
Theoretical	20° C., 6.86 MPa, s	253.397

Specific
Impulse

Example 4

Materials were weighed according to the formula in Table 4. The bonding functional thermoplastic elastomer (Bonding Functional TPE) and the plasticizer were put into a high-shear dispersing emulsifier and heated to 95° C. for melting. Then, a functional auxiliary agent was added and mixed uniformly. The materials were transferred to an acoustic resonance mixer, heated to 95° C., and Al was added and pre-mixed. The Al was mixed uniformly by means of acoustic resonance with a resonance strength of 50 g for a resonance time of 8 min. Then, a certain amount of oxidizing agent was added in batches, and mixed uniformly by means of acoustic resonance to give the thermoplastic composite solid propellant, which was poured into a mold, naturally cooled, and cured to give a propellant sample.

TABLE 4
Formula and Properties of The
Thermoplastic Composite Solid Propellant

Composition of Formula	Mass Percent/% wt
Bonding Functional TPE	6
DOS	5.5
Al	18
AP	49
AN	/
PSAN	/
5,5′-bistetrazole-1,1′-	/
dioxodihydroxylammonium salt
RDX	21
NN	0.15
Copper Chromite	0.5

Sample	Test	Test
Properties	Standards	Conditions	σb/MPA	εm/%
Mechanical	GJB 770B-	20° C.,	1.42	16.8
Properties	2005	100 mm/min

Density

QJ 917A-97

20° C., g/cm3

1.784

Theoretical

20° C., 6.86 MPa, s

266.391

Specific
Impulse

Example 5

Materials were weighed according to the formula in Table 5. The bonding functional thermoplastic elastomer (Bonding Functional TPE) and the plasticizer were put into a high-shear dispersing emulsifier and heated to 95° C. for melting. Then, a functional auxiliary agent was added and mixed uniformly. The materials were transferred to an acoustic resonance mixer, heated to 95° C., and Al was added and pre-mixed. The Al was mixed uniformly by means of acoustic resonance with a resonance strength of 50 g for a resonance time of 5 min. Then, a certain amount of oxidizing agent was added in batches, and mixed uniformly by means of acoustic resonance to give the thermoplastic composite solid propellant, which was poured into a mold, naturally cooled, and cured to give a propellant sample.

TABLE 5
Formula and Properties of
Thermoplastic Composite Solid Propellant

Composition of Formula	Mass Percent/% wt
Bonding Functional TPE	15.2
KN	6.2
DOS	3
Al	17
AP	48
AN	/
PSAN	4
HMX	6
NBA	0.15
Fe2O3	0.45

Sample	Test	Test
Properties	Standards	Conditions	σb/MPA	εm/%
Mechanical	GJB 770B-	20° C.,	0.86	48.3
Properties	2005	100 mm/min

Density

QJ 917A-97

20° C., g/cm3

1.597

Theoretical

20° C., 6.86 MPa, s

246.029

Specific
Impulse

Example 6

Materials were weighed according to the formula in Table 6. The bonding functional thermoplastic elastomer (Bonding Functional TPE) and the plasticizer were put into a high-shear dispersing emulsifier and heated to 95° C. for melting. Then, a functional auxiliary agent was added and mixed uniformly. The materials were transferred to an acoustic resonance mixer, heated to 95° C., and Al was added and pre-mixed. The Al was mixed uniformly by means of acoustic resonance with a resonance strength of 50 g for a resonance time of 5 min. Then, a certain amount of oxidizing agent was added in batches, and mixed uniformly by means of acoustic resonance to give the thermoplastic composite solid propellant, which was poured into a mold, naturally cooled, and cured to give a propellant sample.

TABLE 6
Formula and Properties of
Thermoplastic Composite Solid Propellant

Composition of Formula	Mass Percent/% wt
Bonding Functional TPE	15
KN	20
DOS	5
Al	5
AP	40
AN	/
PSAN	4
HMX	6
NBA	1
Fe2O3	4

Sample	Test	Test
Properties	Standards	Conditions	σb/MPA	εm/%
Mechanical	GJB 770B-	20° C.,	0.59	57.6%
Properties	2005	100 mm/min

Density

QJ 917A-97

20° C., g/cm3

1.382

Theoretical

20° C., 6.86 MPa, s

194.914

Specific
Impulse

Comparative Example 1

Materials were weighed according to the formula in Table 7. The thermoplastic elastomer (i.e., a non-Bonding Functional TPE) and the plasticizer were put into a high-shear dispersing emulsifier and heated to 90° C. for melting. Then, a functional auxiliary agent was added and mixed uniformly. The materials were transferred to an acoustic resonance mixer, heated to 90° C., and Al was added and pre-mixed. The Al was mixed uniformly by means of acoustic resonance with a resonance strength of 50 g for a resonance time of 5 min. Then, a certain amount of oxidizing agent was added in batches, and mixed uniformly by means of acoustic resonance to give the thermoplastic composite solid propellant, which was poured into a mold, naturally cooled, and cured to give a propellant sample.

TABLE 7
Formula and Properties of
Thermoplastic Composite Solid Propellant

Composition of Formula	Mass Percent/% wt
TPE	8.55
KN	6
DOS	2
Al	18
AP	59
AN	/
PSAN	/
RDX	6
NPA	0.1
n-octylferrocene	0.35

Sample	Test	Test
Properties	Standards	Conditions	σb/MPA	εm/%
Mechanical	GJB 770B-	20° C.,	0.43	12

Properties	2005	100 mm/min
Density	QJ 917A-97	20° C., g/cm3	1.69

Theoretical

20° C., 6.86 MPa, s

259.312

Specific
Impulse

It can be seen from the data in Example 1 and Comparative Example 1, the mechanical properties of the thermoplastic composite solid propellant prepared from the non-bonding functional thermoplastic elastomer (the maximum tensile strength σ_b is 0.43 MPa, and the elongation at break ε_m is 12%) are significantly lower than the mechanical properties of the thermoplastic composite solid propellant prepared from the bonding functional thermoplastic elastomer (σ_b is 1.62 MPa, and ε_m is 25.5%). That is, the present invention utilizes the bonding functional group-grafted or copolymerized thermoplastic elastomer as adhesive, so that the adhesive matrix has a strong interaction with the solid filler, which can enhance the interfacial effect and improve the mechanical properties of the propellant, thereby slowing down the occurrence of “dehumidification” phenomenon.

The present invention has been detailedly described as above with reference to the specific embodiments and exemplary examples. However, these descriptions should not be construed to limit the present invention. It is appreciated by those skilled in the art that various equivalent substitutions, modifications or improvements can be made to the technical solutions and embodiments of the invention without departing from the spirit and scope of the invention, all of which all fall within the scope of the invention. The scope of protection of the present invention is defined by the appended claims.