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Nghiên cứu ảnh hưởng của một số yếu tố đến các đặc trưng của thuốc nổ nhiệt dẻo PBX trên cơ sở hexogen và pentrit tt tiếng anh

MINISTRY OF EDUCATION AND TRAINING

MINISTRY OF DEFENCE

ACADEMY OF MILITARY SCIENCE AND TECHNOLOGY

NGUYEN TRUNG TOAN

STUDY ON THE EFFECT OF SEVERAL FACTORS ON THE
CHARACTERISTICS OF THERMOPLASTIC POLYMERBONDED EXPLOSIVES BASED ON HEXOGEN AND PENTRIT

Specialization: Chemical engineering
Code: 9 52 03 01

SUMMARY OF DOCTORAL THESIS IN CHEMISTRY

HA NOI - 2019


THE WORK WAS COMPLETED AT
ACADEMY OF MILITARY SCIENCE AND TECHNOLOGY


Scientific Supervisor:
1. Assoc. Prof. Dr. Phan Duc Nhan
2. Dr. Vo Hoang Phuong
Reviewer 1:

Assoc. Prof. Dr. Tran Van Chung
Academy of Military Science and Technology

Reviewer 2:

Assoc. Prof. Dr. Dam Quang Sang
Military Technical Academy

Reviewer 3:

Dr. Dao Thanh Viet
General Department of Defence Industry

The thesis was defended before the doctoral admission Board of
Academy of Military Science and Technology at 8:30 AM,

The thesis can be found at:
- Library of Academy of Military Science and Technology
- Vietnam National Library


1

INTRODUCTION
1. The urgency of the Ph.D. thesis
Hexogen (RDX) and Pentrit (PETN) are two of the most widely used
explosives in military and civilian applications because of its high energetic
properties. However, RDX and PETN exhibit several notable drawbacks
including high sensitivity to mechanical shock, low compressibility, and
decomposition when melted. In order to overcome these drawbacks, RDX
and PETN – based composite explosives were made by three methods: 1combined with an explosive which has low sensitivity to mechanical shock
and molding properties such as TNT; 2- phlegmatized explosive; 3combined with a binder system (polymer bonded explosives - PBXs).
Compared to other types of composite explosives, thermoplastic PBX
has several key advantages. Firstly, the binder layer in PBX can absorb
impact impulse, reducing the sensitivity of explosives to mechanical shocks.
In addition, PBXs can be compressed into any special shapes at room
temperature with low compression force. Last but not least, unused or expired
explosive charges based on PBXs can be recycled with the least processing.
In Vietnam, the demand of thermoplastic PBX explosives for military and
civilian purposes is very large, such as in the manufacture of weapons for
infantry and tanks, in the manufacture of the explosive charges for the Special
Force, etc… Meanwhile, the import of thermoplastic PBXs has not been
implemented yet. The basic research of thermoplastic PBX explosives based on
RDX and PETN will contribute to overcoming the above limitations and clarify
the scientific basis for PBX production. Therefore, the Ph.D. thesis topic "Study
on the effect of several factors on the characteristics of thermoplastic
polymer-bonded explosives based on hexogen and pentrit" is urgent, with high
scientific and practical significance.
2. Research objectives of the thesis
- Select suitable binder systems for both RDX and PETN and assess the
adhesive possibility of explosive with the binder systems;
- Determining the law effecting of the content and the composition on
the characteristics of PBX explosives, propose suitable components to
manufacture thermoplastic PBX explosives with different explosive and
binder systems.


2

- Determining some kinetic parameters of the thermal decomposition
of PBX explosives, thereby predicting the shelf-life of explosive.
3. Research scopes of the thesis
Study to manufacture and evaluate the effects of several factors such as
explosives content, the binder composition, adhesion ... to the characteristics
of thermoplastic PBX based on hexogen and pentrit with the polystyrene
(PS) and nitrocellulose (NC)-based binder system at the laboratory scale.
4. Experimental methods
Method of manufacturing thermoplastic PBXs; methods of evaluating
the compatibility of explosives and polymers; methods of assessing the
adhesion of explosives and the binders; methods of determining several
technical-energy characteristics of thermoplastic PBX (such as ignition
temperature, chemical stability, impact sensitivity, compressibility,
plasticity, detonation velocity, brisance by Hess and strength of explosive);
method of determining kinetic parameters of thermal decomposition process
of explosives; method of calculating the shelf-life of explosives.
5. The thesis structure
The thesis includes the introduction, 3 chapters, conclusions, lists of
published articles, and references. Specific content as follows:
Chapter 1. Overview of PBX explosives: an overview of thermoplastic
PBX explosives; evaluating domestic and foreign research situation;
interpretation of research issues to be solved by the thesis.
Chapter 2. Subjects and experimental methods: presenting research objects;
chemicals, equipment and experimental methods.
Chapter 3. Results and discussion: present, evaluate and discuss the research
results achieved.
THESIS CONTENT
Chapter 1. OVERVIEW OF THERMOPLASTIC PBX
Present an overview of thermoplastic PBX explosives: the appearance
and advantages of thermoplastic PBX; components of thermoplastic PBX;
energy-technical characteristics; manufacturing methods; domestic and
foreign research situation, and the thesis has explained the selection of
components of thermoplastic PBX. On this basis, the thesis should focus on
solving the following main contents:



3

- Study on the component selection of thermoplastic PBX, including
assessing the compatibility of explosives with polymers and the adhesion of
explosives with the binder systems.
- Study the law of the effect of explosives content, component of the
binders to the technical-energy characteristics of thermoplastic PBX. From
there, propose the appropriate composition for each PBX system.
- Study the thermal decomposition characteristics of thermoplastic
PBX, determine thermal kinematic parameters, thereby predicting their
shelf-life.
Chapter 2. SUBJECTS AND EXPERIMENTAL METHODS
2.1. Subjects of research
Subjects: thermoplastic PBX based on two explosives (e.g. RDX and
PETN) with several binders (based on polystyrene and nitrocellulose).
Research content: manufacturing thermoplastic PBX explosives and
assessing the effect of several factors on the characteristics of explosives.
Besides, the thesis also studies the thermal decomposition process of
manufactured explosives, as a basis to predict the shelf-life of thermoplastic
PBX explosives.
2.2. Chemicals and equipment
2.2.1. Chemicals:
RDX (i.e. Class-1 with melting temperature ≥ 202.5 ºC) was imported
from Korea and PETN (i.e. Class-1 with melting temperature ≥ 139.0 ºC)
was imported from India. Polystyrene (PS) prepared in our laboratory, the
average molecular weight of 80,000 u. Three types of nitrocellulose,
including NC-3, NC-NB and NC-1 with a nitrogen content of 11.96%,
12.20% and 13.39%, respectively, were obtained from a factory in Vietnam.
Dioctyl phthalate (DOP) from Merk was used as a plasticizer to prepare the
binder from PS and NC.
2.2.2. Equipment and devices:
Equipment for manufacturing PBX explosives by block method; device for
determine static contact angle and surface tension CAM-200; Nikon YS-100
optical microscope; plasticity determination device; device for determining
compression capability; device for determine the ignition temperature DT-400;


4

device for determine chemical stability Vacuum Stabil tester (VST); device for
determine impact sensitivity CAST; differential thermal analysis equipment
DSC, TGA; devices for determine energy characteristics (such as device for
determining explosion speed FO-2000, devices for determine the brisance by
Hess, and equipment for determining the strength of explosive).
2.3. Experimental methods:

2.3.1. Chemical compatibility test
Compatibility of explosives and polymers was assessed by VST and
DSC thermal analysis methods based on STANAG 4147:
- VST method: The volume of gas generated when the mixture of
explosives and polymers is heated in vacuum conditions (100 ºC/40 hours) is
compared with the volume of gas produced when testing explosives and
polymers in the same thing. to sue. Compatibility is assessed by the difference
in the volume of gas produced (VR) due to the interaction between explosives
and polymers:
𝑉𝑅 = 𝑀 − (𝐸 + 𝑆), 𝑚𝑙 .
(2.1)
where M is the gas volume released of 5.0 g of mixture; E and S are the
gas volumes released of 2.5g of explosives and 2.5g of a polymer,
respectively. According to STANAG 4147 standard, if VR ≤ 5 ml, two
materials are considered compatible, if VR> 5 ml - incompatible.
- DSC method: Evaluate by a shift in peak temperature on DSC curves
with a heating speed of 5 ºC / min:
TP = TPS − TPM , ºC
(2.2)
where TPS and TPM are the temperature of decomposition peaks of the substrate
and the mixture, respectively. If ΔTP ≤ 4ºC, the system will be compatible; ΔTP>
20 ºC - incompatible; ΔTP from 4 ÷ 20 ºC, another method should be used.

2.3.2. Surface parameters calculation
The surface tensions of explosives and the binders are calculated based
on measuring the static contact angles of standard solvents on the material
surface. Then, the interfacial tension and the work of adhesion between
explosives and the binder are calculated. When energetic material and the
binder have adhered, the smaller the interfacial tension and the greater the
work of adhesion will be, the better the adhesion between them will be.


5

2.3.3. Method of manufacturing thermoplastic PBX
- Prepare the original materials;
- Prepare the binder systems: Polymer, plasticizer and other additives
are quantified, mixed and dissolved in solvent (DOP/PS system uses
benzene or toluene, DOP/NC systems use ethyl acetate). The dissolving
polymers process is carried out in a stirring mixer.
- Explosives (e.g. RDX and PETN) are added to the above binder
solution. The mixing process is carried out by stirring, mixing and heating
(about 65 ÷ 70 °C) to remove the solvents. Then, the mixture was transferred
to a water bath, and continue mixing to make sure the mixture is well mixed.
- the mixture was dried at 90 ÷ 95 ºC for about 5 hours (either at 65 ÷
70 °C for 3 hours in a vacuum oven). Then, the product was collected and
compressed to form a charge.
2.3.4. Methods for determining technical-energy characteristics
- The plasticity: according to the MIL-STD-650-211 standard:
+ Using a mold to produce a molded pellet of PBX with a diameter of
50.80 mm, a height of 19.05 mm and a mass of 50 g, and accurately
determining the initial height of the PBX pellet (H0, mm); Carefully allow the
upper plate of the press to fall until the gage of the press has the same reading
as the reading recorded on the gage used to measure the thickness (Figure 2.3);

Figure 2.3. The diagram to determine the plasticity of PBX
+ After 20 minutes, remove the upper steel plate and determine the height
of the PBX pellet (H1, mm). The plasticity of PBX is determined as follow:
Plasticity =

lg H 0 − lg H1
1,3

(2.13)

- Compression capability: evaluate the density of PBX explosives at
different pressures. Compression equipment is a hydraulic compressor with
a pressure gauge and cylindrical compression mold (with a diameter of 24.5
mm; PBX mass of 15.0 g).


6

- The ignition temperature was measured by DT-400 (Germany): SP1~190
C, SP2~ 250 C; sample mass of 150 mg and heating rate of 5 C.min−1.
- Impact sensitivity studies were carried out using Cast Hammer Impact
Test with 10 kg drop hammer according to the TCVN/QS 1837:2017
(powder sample of about 0,05 g; the height of impact, 250 mm).
- Chemical stability: The thermal vacuum stability was conducted by the
vacuum stability test (VST) using a STABIL apparatus (Czech Republic)
following the STANAG 4556-2A standard. The sample mass was 2 g. Tests
were performed at 100 ºC for 48 hours. The released gas volume (V) was
recorded using a pressure transducer connected to a computer.
- The brisance by Hess was measured according to the TCVN/QS
6421:1998 (with sample mass, 25 g and 50 g; density, 1.0 g.cm-3).
- The strength of explosive was measured by ballistic mortar according
to the TCVN/QS 6424:1998 (sample mass, 10g; density, 1.0 g.cm-3).
- Detonation velocity: Determined by FO-2000 device, PBX charges
are prepared according to the TCVN 6421:1998 standard, charge diameter
of 24 mm, charge length of 320 mm, the distance of two sensors is 250 mm.

2.3.5. Methods of determining kinetic parameters
TG/DTG curves of the samples were established using A NETZSCH STA
409 PC/PG. The TG analysis was conducted at various heating rates (e.g. 4, 6, 8,
and 10 K.min-1). Nitrogen was circulated through the heating chamber at a flow
rate of 20 ml.min-1. Based on the results of the TG/DTG curves, applying
Kissinger and Ozawa methods to calculate the activation energy Ea and the
exponential factor A of the kinetic equation for thermal decomposition reaction.
2.3.6. Method of evaluating the shelf-life of PBX explosive
The shelf-life of an explosive is defined as a duration (i.e. at the temperature
of 25 ºC (i.e. 298 K)), within which the explosion properties and safety (e.g.
stability, strength, and sensitivity) of the explosive remain in acceptable ranges.
In this study, the VST method was used to determine the thermal vacuum
stability and hence to estimate shelf-life of the explosives. According to the
experience of material degradation, especially for brisance explosives, the shelflife of explosive is defined by the length of time for 5% decomposition:
t5% =

0, 0513
k298

(2.26)


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Chapter 3. RESULTS AND DISCUSSION
3.1. Study on the selection of PBX components
3.1.1. Chemical compatibility of explosives and polymers
3.1.1.1. According to VST method: The volume of gas generated by the
interaction between explosives and polymers (VR), calculated according to the
formula (2.1), is presented in Table 3.1.
Table 3.1. The VR values determined by VST method.
VR, mL
Polymer
Pentrit
Hexogen
PS
0.05
0.03
NC-3
0.20
0.13
NC-NB
0.42
0.27
NC-1
1.00
0.90

All VR values are much smaller than the minimum standard values
according to STANAG 4147 (5 mL), demonstrate explosives (e.g. RDX and
PETN) and polymers are compatible with each other. Therefore, they can be
used to manufacture thermoplastic PBX explosives in subsequent studies.
3.1.1.2. According to the DSC method: The difference temperature ( TP ) of the DSC
curve of single material compared to the mixture is presented in Table 3.2 and 3.3.
Table 3.2. DSC results determine the compatibility of RDX and polymers
Materials
The exothermic temperature peak, °C
∆TP
TPS
TPM
Single
Mixtures
RDX
RDX/PS
231.2
230.7
0.5
NC-1
RDX/NC-1
202.6
203.9
-1.3
NC-NB
RDX/NC-NB
203.5
204.3
-0.8
NC-3
RDX/NC-3
203.7
204.9
-1.2

Where the single system is the component with its exothermic peak
temperature lower than another component in the mixture system, and there
was not the exothermic peak in the DSC curves of PS.
Table 3.3. DSC results determine the compatibility of PETN and polymers
Materials
The exothermic temperature peak, °C
∆TP
TPS
TPM
Single
Single
PETN
PETN/PS
194.5
193.9
0.6
PETN
PETN/NC-1
194.5
194.3
0.2
PETN
PETN/NC-NB
194.5
194.8
-0.3
PETN
PETN/NC-3
194.5
195.0
-0.5


8

If ∆TP is negative (i.e. the mixture has higher temperature
decomposition than that of single energetic material), the mixture is
compatible. If ∆TP is positive, the compatibility of the mixture would be
evaluated according to the STANAG 4147. By this standard, RDX and
PETN are considered compatible with investigated polymers.
3.1.2. Evaluate the interfacial parameters
Based on the static contact measurement results of several standard
solvents (water, glycerol, ethylene glycol, chloroform), surface tension (γS)
of explosive (e.g. RDX, PETN) and the binders are calculated (Table 3.6).
Table 3.6. Surface tensions of explosives and the binders
 S = D +
Materials
αS
βS
γD
γP
RDX
5.90
1.99
34.81
3.96
38.77
PETN
4.92
2.77
24.20
7.67
31.88
DOP/PS (2/1)
5.11
1.94
26.11
3.76
29.88
DOP/PS (1.5/1)
5.22
2.08
27.25
4.32
31.57
DOP/NC (3/1)
5.06
1.44
25.60
2.07
27.67
DOP/NC (2/1)
5.07
1.83
25.70
3.35
29.05

P

From the surface tension values, the interfacial tensions, the works of
adhesion and the spreading coefficients between energetic materials and the
binders are calculated and expressed in Table 3.7.
Table 3.7. Interfacial surface parameters of explosives and several binders.
Interfacial tension,
Work of adhesion,
Spreading
-2
-2
mJ.m
mJ.m
coefficient
The binders
RDX
PETN RDX
PETN
RDX PETN
DOP/PS (2/1)
0.63
0.73
68.02
61.03
8.27
1.27
DOP/PS (1.5/1)
0.47
0.57
69.87
62.89
6.72 -0.26
DOP/NC (3/1)
1.00
1.79
65.44
57.77
10.08 2.41
DOP/NC (2/1)
0.71
0.90
67.10
60.03
9.00
1.92

When energetic material and the binder have adhered, the smaller the
interfacial tension and the greater the work of adhesion will be, the better
the adhesion between them will be. Besides that, the greater the spreading
coefficient will be, the larger the contact area of the binder with an energetic
material will be. As shown in Table 3.7, the adhesion of RDX to the binder
is better than that of PETN. In addition, the interfacial tension and the work
of adhesion results demonstrated that the adhesion of the binder based on
DOP/PS to explosives is better than that the binder based on DOP/NC.


9

3.2. Effect of the content and the composition on the characteristics of
thermoplastic PBX based on hexogen (PBX-H)
3.2.1. Select the content and the particle size of hexogen
The PBX-H samples with the proportion of RDX higher than 91 wt.% will
have poor adhesion, low plasticity, and high sensitivity to the mechanical
pulses. If the proportion of RDX was less than 80 wt.%, the PBX-H had low
energy characteristics. Therefore, the thesis has researched and manufactured
PBX-H with the content of RDX of (80-91) wt.%.
- Particle size: In order to make PBX explosives, main explosives are
often used in a mixture of different particle sizes, to ensure a high density
of the block. Based on the particle size standards of RDX used to make C-4
explosives, the author selected the explosive RDX as a mixture of particle
size segments smaller than 63 µm and particle size segmented from 150 ÷
300 µm with a ratio of 1: 4 in mass, respectively.
3.2.2. Effect of the content and the composition on the plasticity and
compression capability of PBX-H explosives
3.2.2.1. PBX based on RDX and PS (PBX-HP)
a. The plasticity: The PBX-HP samples were made with the content of
RDX were from 80 ÷ 91%, the DOP/PS ratio in the range of 1/1 to 2/1.
However, for PBX-HP sample containing 91% RDX, there has been a
discrete between RDX particles, which does not ensure the complete
adhesion. The plasticity of PBX-HP samples is determined according to
MIL-STD-650 standard and presented in Figure 3.5.
0.18

DOP/PS = 1/1
DOP/PS = 1.5/1
DOP/PS = 2/1

0.16
0.14

Plasticity

0.12
0.10
0.08
0.06
0.04
0.02
0.00
80

85

90

Content of RDX, %

Figure 3.5. Effect of the RDX content and the DOP/PS ratio on the plasticity of
PBX-HP explosives


10

1.65
1.60
1.55
1.50
1.45
1.40
1.35
PBX-HP-8001
PBX-HP-8002
PBX-HP-8003

1.30
1.25
0

50

100
150
200
250
300
Compression pressure, kG.cm-2

350

Density of the explosive charge, g.cm-3

Density of the explosive charge, g.cm-3

When increasing the content of RDX (from 80 to 90%) or when
reducing the DOP / PS ratio (from 2/1 to 1/1), the plasticity of PBX-HP
explosive drops quite a lot, but with a different reduction level. Specifically,
when the RDX content increased from 80 to 90%, the PBX-HP (DOP/PS
ratio of 2/1) has the highest level reduction of plasticity (from 0.179 to
0.078); the PBX-HP samples have a DOP/PS ratio of 1.5/1 (plasticity
decreases from 0.130 to 0.038); the PBX-HP (DOP/PS ratio of 1/1) has the
lowest level reduction of plasticity (from 0.084 to 0.013). This can be
explained by the fact that the PBX-HP samples with higher DOP/PS ratios
are more flexible, so according to the method of determining the plasticity
shown in section 2.3.4, the height differences of the PBX pellet before and
after the compression (the samples with different RDX content) are higher,
leads to the level reduction of the plasticity of PBX-HP are higher.
Most of the PBX-HP samples have met the requirements, except for
PBX-HP-8001 sample (80% RDX, DOP/PS = 2/1) has high plasticity,
difficult to shape, and PBX-HP-9003 sample (90% RDX, DOP/PS = 1/1)
has low plasticity, poor adhesion.
b. Compression capability (Figure 3.6)
1.65
1.60
1.55
1.50
1.45
1.40
PBX-HP-8501
PBX-HP-8502
PBX-HP-8503
PBX-HP-9001
PBX-HP-9002

1.35
1.30
1.25
0

50

100
150
200
250
300
Compression pressure, kG.cm-2

350

Figure 3.6. Relationship between the density of PBX-HP and compression pressure

The density of PBX-HP sample increases when increased compression
pressure but this relationship is not linear. Specifically, when the compression
pressure is in the range of 20 ÷ 150 kG.cm-2, the density of the PBX block
increases due to the consolidation of the explosive and the binder to fill the
gaps; when the compression pressure is in the range of 150 ÷ 320 kG.cm-2, the
density increases non-significant because the PBX block is in a compacted


11

state, the adhesive acts as an uncompressed fluid. If the compression pressure
continues to increase, the adhesive system will be squeezed out of the block.
Because the density of RDX is quite high (about 1.816 g.cm-3), when
increasing the content of RDX, the density of PBX-HP blocks also increases.
Compared to TNT (explosive with good compression capability, the density
of 1.57 g.cm-3 at 1200 kG.cm-2), compression capability of PBX-HP is much
better. PBX-HP-90 samples reach a density of 1.57 g.cm-3 at 150 kG.cm-2.
Therefore, most PBX -HP samples have good compression capability.
3.2.2.2. PBX based on RDX and NC (PBX-HN)
Because NC is a rigid polymer, so when using the binder with the low
ratio of DOP/NC, the PBX-HN will have high hardness, and result in the
increased sensitivity of PBX-HN. Therefore, thesis using the binder system
with the ratio of DOP/NC in the range of 2/1 to 3/1.
a. Plasticity (Figure 3.7).
0.012
DOP/NC-1 = 2/1
DOP/NC-NB = 2/1
DOP/NC-3 = 2/1
DOP/NC-1 = 3/1
DOP/NC-NB = 3/1
DOP/NC-3 = 3/1

0.010

Plasticity

0.008
0.006
0.004
0.002
0.000
80

85
Content of RDX, %

90

Figure 3.7. Effect of the RDX content and the DOP/NC ratio
on the plasticity of PBX-HN explosives.

The plasticity of PBX-HN samples also tends to decrease when increasing
the RDX content, with different levels of reduction, depending on the physical
state of the binder based on DOP/NC. The PBX-HN samples used NC-1 as the
binder has much lower plasticity than the PBX-HN samples use NC-3 or NCNB as a binder. This is explained because the nitrogen content of NC-1
(13.39% N) is much higher than that of NC-NB (12.20% N) and NC-3
(11.96% N), so NC-1 has a higher crystal level, leading to an increase in the
stiffness of the circuit. In addition, because NC-NB and NC-3 have similar
nitrogen content, viscosity and grinding properties, the plasticity of the PBXHN samples using NC-NB and NC-3 is similar.


12

1.65

1.65

1.60

1.60

1.55
1.50
1.45

DOP/NC - 2/1

1.40

PBX-HN-8001 (NC-1)
PBX-HN-8001 (NC-NB)
PBX-HN-8501 (NC-1)
PBX-HN-8501 (NC-NB)
PBX-HN-9001 (NC-1)
PBX-HN-9001 (NC-NB)

1.35
1.30
1.25

Density of explosive charge, g.cm-3

Density of explosive charge, g.cm-3

According to the plastic explosive standards used to manufacture US
explosive charge such as M5A1 block (plasticity ≤0.03), PBX-HN explosives
can be used to make a similar explosive charge. However, it is necessary to
investigate the compression capability of PBX-HN (Figure 3.8).

1.55
1.50
1.45

DOP/NC - 3/1

1.40

PBX-HN-8002 (NC-1)
PBX-HN-8002 (NC-NB)
PBX-HN-8502 (NC-1)
PBX-HN-8502 (NC-NB)
PBX-HN-9002 (NC-1)
PBX-HN-9002 (NC-NB)

1.35
1.30
1.25

0

50
100
150
200
250
Compression pressure, kG.cm-2

300

350

0

50
100
150
200
250
Compression pressure, kG.cm-2

300

350

Figure 3.8. Relationship between the density of PBX-HN and compression pressure

214

217.0

212

216.5

210

Ignition temperature, C

217.5

o

Ignition temperature, oC

When the compression pressure increases from 20 ÷ 200 kG.cm-2, the
density increases very quickly; when the compression pressure increases
from 200 ÷ 320 kG.cm-2, the density increases but is not significant. In the
compression pressure range, PBX-HN samples using the DOP/NC ratio of
3/1 reached higher density in the initial compression pressure range (from
50 ÷ 100 kG.cm-2), but at higher compression pressures, this density is lower
than that of PBX-HN samples using DOP/NC ratio of 2/1.
3.2.3. Effect of the content and the composition on the ignition
temperature and the chemical stability of PBX-H explosives
3.2.3.1. Ignition temperature Ti (Figure 3.10 and 3.11)

216.0
215.5
215.0
214.5
PBX-HP-80
PBX-HP-85
PBX-HP-90

214.0
213.5

206
204
DOP/NC-1 = 2/1
DOP/NC-NB = 2/1
DOP/NC-3 = 2/1
DOP/NC-1 = 3/1
DOP/NC-NB = 3/1
DOP/NC-3 = 3/1

202
200
198

213.0
1.0

208

1.5
Ratio of DOP/PS

3.10

2.0

80

85
Content of RDX, %

90

3.11

Figure 3.10-3.11. Effect of the RDX content and the DOP/polymer ratio
on the ignition temperature of 3.10) PBX-HP and 3.11) PBX-HN.


13

a. PBX-HP: The ignition temperatures of all PBX-HP samples are lower
than that of RDX. This can be attributed to the physical interaction between
components rendering the systems less thermally stable. On the other hand, the
thermal decomposition conditions of RDX and PBX are different. While the
heating process of RDX is considered in isobaric conditions, the heating process
of RDX crystals in PBX-HP occurred under isometric conditions. Therefore,
when the RDX crystals in PBX-HP have been partially decomposed, the
generated gas increases the internal pressure. In turn, the increased internal gas
pressure accelerated the decomposition process of PBX-HP samples.
b. PBX-HN: PBX-HN samples have a much lower temperature than pure
RDX. Besides the interaction between the components in PBX-HN
composition and the differences in thermal decomposition conditions, the most
important cause is the presence of NC types (lowest thermal stability). Because
of this reason, when the content of RDX increasing (reducing the content of
NC), the ignition temperature of PBX-HN explosives tends to increase.
Ignition temperatures of PBX-HN increased when using NC-1, NC-NB
and NC-3 as binders, respectively (PBX-HN using NC-1-based binder has
significantly lower Ti), due to the nitrogen content of NC-1 (13.39%) is much
higher than NC-NB and NC-3 (12.20% and 11.96%, respectively).
3.2.3.2. Chemical stability of PBX-H (Figure 3.12 and 3.13)
0.34
0.32

0.15
0.14
0.13
0.12
DOP/PS = 2/1
DOP/PS = 1,5/1
DOP/PS = 1/1

0.11

Chemical stability, cm3.g-1

Chemical stability, cm3.g-1

0.16

0.30
0.28
0.26
0.24

DOP/NC-1 = 2/1
DOP/NC-1 = 3/1
DOP/NC-NB = 2/1
DOP/NC-NB = 3/1
DOP/NC-3 = 2/1
DOP/NC-3 = 3/1

0.22
0.20
0.18
0.16

0.10
80

85
Content of RDX, %

3.12

90

80

85
Content of RDX, %

90

3.13

Figure 3.12-3.13. Effect of the RDX content and the DOP/polymer ratio
on the chemical stability of 3.12) PBX-HP and 3.13) PBX-HN.

a. PBX-HP samples: PBX-HP samples (RDX content of 80% and 85%)
have a higher chemical stability than pure RDX (0.15 mL.g-1), while HPPBX (RDX content of 90%) have similar chemical stability due to two


14

opposite effect factors: Firstly, the physico-chemical interaction between
the binder and the explosive makes the stability decrease; secondly, RDX
has the lowest chemical stability, deciding to the general chemical stability
of PBX-HP. Therefore, the chemical stability of PBX-HP samples tends to
decrease when the content of RDX increases. However, according to
STANAG 4556, all of the PBX-HP samples have high chemical stability.
b. PBX-HN: Chemical stability of PBX-HN is lower than that of pure
RDX due to the presence of NC. When increasing the content of RDX,
chemical stability tends to increase. On the other hand, the PBX-HN samples
using a higher DOP/NC ratio will have higher chemical stability.
Because the nitrogen content of NC-1 is much higher than that of NCNB and NC-3, so PBX-HN samples (use NC-1 as a binder) have much lower
chemical stability. Therefore, NC-1 was not selected to manufacture PBXHN in continues studies.
3.2.4. Effect of several factors on the impact sensitivity (Table 3.16, 3.17)
No.
1
2
3
4
5
6
7
8
9

Table 3.16. Impact sensitivity of PBX-HP sample
Content of RDX,
Impact
Samples
DOP/PS ratio
%
sensitivity, %
PBX-HP-8001
80
2/1
8
PBX-HP-8501
85
2/1
18
PBX-HP-8503
85
1/1
36
PBX-HP-9001
90
2/1
28
PBX-HP-9002
90
1.5/1
48
A-IX-1
94
--25-35
RDX
72
C-4 (USA): 91% RDX, 9% binder
40
C-4 VN
28
Table 3.17. Impact sensitivity of PBX-HN sample

Samples

Content of
RDX, %

DOP/NC
ratio

PBX-HN-8001
PBX-HN-8501
PBX-HN-9001
PBX-HN-9002
RDX

80
85
90
90
100

3/1
3/1
3/1
2/1
---

Impact sensitivity, %
Type of NC
NC-NB
NC-3
32
32
36
--48
----52
72


15

The impact sensitivities of PBX-HP and PBX-HN samples are much
lower than that of pure RDX, because: firstly, RDX particles are surrounded
by a layer of binder that absorbs and eliminates most of the impact pulse;
secondly, the surface of RDX particle dissolved when mixing in a binder
solution, eliminating sharp edges and surface defects, resulting in a
reduction in the impact sensitivity of the explosive.
When RDX content increases, the impact sensitivity of PBX-HP and
PBX-HN also increases. In addition, when the DOP/polymer ratio increases,
the impact sensitivity of PBX explosives tends to decrease due to the
increasing plasticity of explosives, and DOP/polymer ratio has more
influence on impact sensitivity than the content of RDX. On the other hand,
the impact sensitivity of PBX-HN explosives is higher than that of PBX-HP
and A-IX-1 due to the presence of NC.
3.2.5. Effect of several factors on the detonation characteristics
PBX-HP and PBX-HN samples have much higher energy
characteristics than TNT, and belonging to the high explosive group, similar
to some high explosive such as C-4, Comp- A, A-IX-1. PBX-HN samples
have higher energy characteristics than the HP-PBX samples (with the same
RDX content) by the presence of NC (which is the component that provides
more energy) in the composition (Table 3.18 and 3.19).
Table 3.18. Detonation charcteristics of PBX-HP samples
Content
Brisance by Hess
Strength of
Detonation
of
at 1.0 g.cm-3, [mm]
Samples
velocity, m.s-1, explosive,
RDX,
(1.50 g.cm-3)
25g
50g
% TNT
%
PBX-HP-8001
7115
122.6
17.0
24.8
80
PBX-HP-8002
7125
------PBX-HP-8501
7298
125.7
18.9
26.2
85
PBX-HP-8502
----18.9
26.3
PBX-HP-9001
7400
129.2
19.8
Be destroyed
90
PBX-HP-9002
----19.7
Be destroyed
TNT
0
6655
100
--15.6
Be destroyed
RDX
100
7700
140-150
21.5
Be destroyed
C-4 (US)
91
--130.0
18.5
Be destroyed
C-4 (VN)
91
7363 (1.45)
129.4
18.4


16

Table 3.19. Detonation charcteristics of PBX-HP samples
Brisance by Hess
Strength of
Content Detonation
at 1.0 g.cm-3, mm
Samples
of RDX, velocity, m.s-1, explosive,
%
(1.50 g.cm-3)
25g
50g
% TNT
PBX-HN-8001
7280
127.3
--25.8
80
PBX-HN-8002
7305
--17.2
26.1
PBX-HN-8501
7350
129.7
--26.6
85
PBX-HN-8502
7390
----27.2
PBX-HN-9001
90
7485
131.5
20.0
Be destroyed
Comp-A
91
--132.0
----A-IX-1
94-95
7420
120-139
≥15.0
---

Discussion: For the purpose of manufacturing PBX-HP and PBX-HN
samples with suitable plasticity, good compression capability, low impact
sensitivity, high chemical stability and high energy, PBX-HP-9001 sample
(90% RDX, 10% DOP/PS with ratio of 2/1) and PBX-HN-9001 sample
(90% RDX, 10% DOP/NC with ratio of 3/1, using NC-3 or NC-NB) are
appropriate compositions to met the requirements.
3.3. Effect of the content and the composition on the characteristics of
thermoplastic PBX based on pentrit (PBX-P)
3.3.1. Select the content and the particle size of pentrit
Through of the composition of PBX explosives based on PETN
explosives in the world such as Semtex-1A, Semtex-10 (Czech Republic),
Formex P1 (France), Sprangdeg m/46 (Sweden) and EPX- 1 (Egypt), the
content of PETN is in the range of 80 ÷ 85%, some types of PBX have PETN
content up to nearly 90%. Therefore, the thesis chooses to make PBX
explosives based on PETN and PS (PBX-PP) with the content of PETN from
80 to 90%.
For PBX-P samples based on PETN and NC (PBX-PN), the thesis
selected the PETN content from 75 to 85% due to: Firstly, because NC is
also a high-energy compound, it also plays contribute to the overall energy
of the PBX sample; Second, the ability to completely explode of PETN is
better than that of RDX; Third, the adhesion of PETN with the binder is
lower than that of RDX.
The particle size of PETN is chosen similar to the particle size of RDX.


17

3.3.2. Effect of the content and the composition on the plasticity and
compression capability of PBX-P explosives
3.3.2.1. PBX based on PETN and PS (PBX-PP)
- Plasticity (Figure 3.15): Most of PBX-PP samples have high plasticity
and easy to shape by hand. When the content of PETN increased, the plasticity
of PBX-PP samples tends to decrease because of the flexibility of the PBX
system is reduced. Except for PBX-PP-9003 sample (90% PETN, DOP/PS =
1/1) with low plasticity and PBX-PP-8001 sample (80% PETN, DOP/PS = 2/1)
with high plasticity, most of PBX-PP samples meet the plasticity requirements.
0.20

DOP/PS = 2/1
DOP/PS = 1.5/1
DOP/PS = 1/1

0.18
0.16

Plasticity

0.14
0.12
0.10
0.08
0.06
0.04
0.02
0.00
80

85
Content of PETN, %

90

Figure 3.15. Effect of the PETN content and the DOP/PS ratio
on the plasticity of PBX-PP explosives.

- Compression capability (Figure 3.16): When the compression pressure
increases from 20 ÷ 150 kG.cm-2, the density of the PBX blocks increases
rapidly; when the compression pressure increases from 150 ÷ 320 kG.cm-2, the
density of PBX blocks increases slowly, reaching the maximum value from
1.52 to 1.62 g.cm-3 (depending on the content of PETN).
1.60

Density of explosive charge, g.cm-3

Density of explosive charge, g.cm-3

1.60
1.55
1.50
1.45
1.40
1.35
1.30

PBX-PP-8001
PBX-PP-8002
PBX-PP-8003

1.25

1.55
1.50
1.45
1.40
PBX-PP-8501
PBX-PP-8502
PBX-PP-8503
PBX-PP-9001
PBX-PP-9002

1.35
1.30
1.25

0

50

100
150
200
250
300
Compression pressure, kG.cm-2

350

0

50

100
150
200
250
Compression pressure, kG.cm-2

300

350

Figure 3.16. Relationship between the density of PBX-PP and compression pressure

In general, the density of PBX-PP samples is smaller than the PBXHP samples (with the same explosive content and the same DOP/PS ratio),


18

due to the density of PETN (1.770 g.cm3) smaller than the density of RDX
(1.816 g.cm3). However, PBX-PP samples have good compression
capability (equivalent to PBX-HP samples), much better than TNT.
3.3.2.2. PBX based on PETN and NC (PBX-PN)
- Plasticity (Figure 3.18): PBX-PN samples have low plasticity and are
influenced by the DOP/NC ratio. The plasticity of PBX-PN decreases when
increasing the content of PETN or reducing the DOP/NC ratio. The level reduction
of the plasticity of PBX-PN with the DOP/NC ratio of 3/1 (from 0.180 to 0.008)
is greater than those with the DOP/NC ratio of 2/1 (from 0.010 to 0.005).
0.020
DOP/NC-NB = 2/1
DOP/NC-3 = 2/1
DOP/NC-NB = 3/1
DOP/NC-3 = 3/1

0.018
0.016

Plasticity

0.014
0.012
0.010
0.008
0.006
0.004
75

80
Content of PETN, %

85

Figure 3.18. Effect of the PETN content and the DOP/NC ratio
on the plasticity of PBX-PN explosives.

- Compression capability (Figure 3.19):
Density of explosive charge, g.cm-3

1.60
1.55
1.50
1.45
1.40
PBX-PN-7501
PBX-PN-7502
PBX-PN-8001
PBX-PN-8002
PBX-PN-8501
PBX-PN-8502

1.35
1.30
1.25
0

50

100
150
200
250
Compression pressure, kG.cm-2

300

350

Figure 3.19. Relationship between the density of PBX-PN and compression pressure.

The density of PBX-PN samples increases when increasing compression
pressure. Specifically, the density of PBX-PN samples increased rapidly when
the compression pressure increased from 20 ÷ 200 kG.cm-2; when the
compression pressure continues to increase from 220 ÷ 350 kG.cm-2, the
density of PBX-PN blocks increases not much (to about 1.57 g.cm-3), even if
several PBX-PN blocks remain the same density.


19

Compared to PBX-HN samples, PBX-PN samples have a significantly
lower density (density difference of 0.50 g.cm3), due to: (1) the content of
main explosives in the PBX-PN samples are lower and (2) RDX density is
higher than that of PETN.
3.3.2. Effect of the content and the composition on the ignition
temperature and the chemical stability of PBX-P explosives
3.3.2.1. Ignition temperature (Figure 3.20 and Figure 3.21)
184.5
182.0

Ignition temperature, oC

Ignition temperature, oC

184.0

183.5

183.0

PBX-PP-80
PBX-PP-85
PBX-PP-90

182.5

181.5

181.0

180.5
DOP/NC-NB = 2/1
DOP/NC-NB = 3/1
DOP/NC-3 = 2/1
DOP/NC-3 = 3/1

180.0

179.5

182.0
1.0

1.5
DOP/PS ratio

3.20

2.0

75

80
Content of PETN, %

85

3.21

Figure 3.20-3.21. Effect of the PETN content and the DOP/polymer ratio
on the ignition temperature of 3.20) PBX-PP and 3.21) PBX-PN.

Ignition temperatures of all PBX-PP and PBX-PN samples are lower
than pure PETN (185.7 °C), due to the interaction between explosive
components and the difference in thermal decomposition conditions of pure
PETN compared to PETN crystals in PBX explosives. Besides, with the
appearance of NC in the binder composition, ignition temperatures of PBXPN samples are also lower than the PBX-PP samples.
When PETN content increases, ignition temperatures of PBX-PP and
PBX-PN will decrease because PETN has the lowest ignition temperature. On
the other hand, because NC is poor thermal stability compound, so the PBXPN samples use a low DOP/NC ratio will have lower ignition temperatures.
3.3.2.2. Chemical stability (Figure 3.22 and 3.23)
The PBX-PP-80 and PBX-PP-85 samples have higher chemical
stability than pure PETN; while PBX-PP-90 samples have the same
chemical stability as PETN. The trend of changing the chemical stability of
PBX-PP samples is similar to the PBX-HP explosives (RDX/PS), due to the
interaction between components (explosive and polymer) of PBX-PP and
the effect of PETN content.


20
0.25

0.30
0.29

Chemical stability, ml.g-1

Chemical stability, ml.g-1

0.24
0.23
0.22
0.21
DOP/PS = 2/1
DOP/PS = 1,5/1
DOP/PS = 1/1

0.20
0.19

0.28
0.27
0.26
0.25
0.24
0.23

DOP/NC-NB = 2/1
DOP/NC-NB = 3/1
DOP/NC-3 = 2/1
DOP/NC-3 = 3/1

0.22
0.21
0.20

80

85
Content of PETN, %

3.22

90

75

80
Content of PETN, %

85

3.23

Hình 3.22-3.23. Effect of the PETN content and the DOP/polymer ratio
on the chemical stability of 3.22) PBX-PP and 3.23) PBX-PN.

Most of the PBX-PN samples have slightly lower chemical stability than
pure PETN. When the PETN content decreases (the content of NC-based
binder increases), the chemical stability of the PBX-PN tends to decrease. The
reasons are due to (1) the interaction between the components and (2) because
NC is the compound with the lowest chemical stability. According to
STANAG 4556, PBX-PP and PBX-PN samples have high chemical stability.
3.3.3. Effect of several factors on the impact sensitivity of PBX-P
(Table 3.28 and 3.29)
No.
1
2
3
4
5

Table 3.28. Impact sensitivity of several PBX-PP samples
Content of
DOP/PS
Impact
Sample
PETN, %
ratio
sensitivity, %
PBX-PP-8002
80
1.5/1
10
PBX-PP-8003
80
1/1
30
PBX-PP-8501
85
2/1
32
PBX-PP-8503
85
1/1
46
PETN
100
--100

The impact sensitivity of PBX-PP samples is much smaller than that
of pure PETN, even the impact sensitivity of the PBX-PP-8002 sample is
similar to TNT. The purpose of sensitivity reduction of the using the binder
for the PETN has been achieved by two reasons: the surround binder layer
of PETN crystals absorbs and eliminates most of the impact pulse, and the
surface defects PETN crystals have been removed when dissolved during
fabrication. On the other hand, the impact sensitivity of PBX-PP samples
depends a lot on the physical state of the binder system.


21

Table 3.29. Impact sensitivity of several PBX-PN samples
Sample

Content of
PETN, %

DOP/NC
ratio

Impact sensitivity, %

Type of NC
NC-NB
NC-3
PBX-PN-7501
75
3/1
--44
PBX-PN-7502
75
2/1
52
48
PBX-PN-8001
80
3/1
52
52
PBX-PN-8501
85
3/1
68
64
PBX-PN-8502
85
2/1
--72
PETN
100
--100
The impact sensitivity of PBX-PN samples is much higher than that of
PBX-PP samples due to the existence of NC in the composition of explosives.
However, when compared to the impact sensitivity of pure PETN (100%), the
sensitivity reduction effect of the DOP/NC binder is relatively good.

3.3.4. Effect of several factors on the detonation characteristics of PBX-P
Table 3.30-3.31. Detonation characteristics of PBX-PP and PBX-PN samples
Brisance by
Strength of
Detonation
Hess, mm
Sample
velocity, m.s-1,
explosive,
-3
(density, g.cm )
% TNT
25g
50g
PBX-PP-8001
7100 (1.50)
--17.0
23.0
PBX-PP-8002
7129 (1.50)
119.3
16.8
22.6
PBX-PP-8502

7200 (1.50)

124.8

19.0

24.5

PBX-PN-7501

7163 (1.50)

125.7

---

24.5

PBX-PN-8001
PBX-PN-8501
TNT
PETN
Semtex-10 (85% PETN)
Sprangdeg (86% PETN)
EPX-1 (86% PETN)

7290 (1.50)
7353 (1.50)
6655 (1.50)
7500 (1.50)
7370 (1.52)
7232 (1.52)
7398 (1.55)

126.2
127.4
100
140 ÷ 150
-------

------20.1
-------

25.0
26.0
15.6
--22.0
-----

PBX-PP and PBX-PN samples have much higher energy characteristics
than TNT. The PBX-PP-8502 sample has the same energy characteristics as
the Semtex-10 sample (Czech Republic) and Sprangdeg m/46 sample
(Sweden). The energy characteristic of PBX-PN-8501 sample is slightly
higher due to the presence of NC in the composition which increases the


22

energy for the PBX system. Thus, it can be confirmed that PBX-PP and PBXPN samples (80 ÷ 85% PETN) belong to the high explosive group.
Discussion: The PBX-PP samples have high plasticity, can be easily
shaped by hand, with the PBX-PP-8501 sample (85% PETN, 15% DOP/PS
with a ratio of 2/1) is optimal. PBX-PN samples are not too high plasticity,
suitable for making an explosive charge by compression method, with PBXPN-8501 sample (85% PETN, 15% DOP/NC with a ratio of 3/1) is optimal.
3.4. Evaluate thermal decomposition behaviors and predict shelf-life of
thermoplastic PBX
3.4.1. Several thermal decomposition behaviors of thermoplastic PBX
Table 3.32-3.33. Composition of PBX-H and PBX-P samples
Content of material, %
Sample
RDX
PETN
DOP
NC-3
NC-NB
PBX-HN-80-1
80.0
--13.33
6.67
--PBX-HN-80-2
80.0
--13.33
--6.67
PBX-HN-85
85.0
--11.25
--3.75
PBX-HP-85
85.0
--10.00
----PBX-PP-8001
--80.0
13.33
----PBX-PN-8002
--80.0
13.33
--6.67

PS
------5.00
6.67
---

Table 3.34-3.37. The kinetic parameters of explosives
Kisinger method
Ozawa method
Sample
-1
-1
Ea, kJ.mol
logA, min
Ea, kJ.mol-1 logA, min-1
PBX-HN-80-1
150.72
15.45
151.19
15.50
PBX-HN-80-2
149.37
15.32
149.89
15.38
PBX-HN-85
153.33
15.70
153.70
15.74
PBX-HP-8501
212.35
21.84
209.86
21.58
RDX
206.35
21.23
204.14
21.00
PBX-PP-8001
141.43
15.51
141.87
15.56
PBX-PN-8002
126.54
13.81
127.54
13.92
PETN
132.59
14.50
133.45
14.60

The activation energy values (Ea) of PBX samples used NC-based binder
are lower than those of RDX or PETN, and the increase in NC content in the
binder composition leads to reduces the value of Ea. On the other hand, PBX
samples used PS-based binder have a slightly higher Ea than single explosives,
due to the low content of main explosives (thermal stability) in PBX
explosives is smaller. This confirms the effect of the binder system on the
thermal stability of the PBX system.


23

3.4.3. Predict shelf-life of thermoplastic PBX
The prediction of shelf life was carried out through the vacuum stability
test (VST). For single RDX and PBX-H samples, VST values are determined
at temperatures of 90, 100, 110 and 120 °C. For single PETN and PBX-P
samples, VST values are determined at temperatures of 80, 90, 100 and 110
°C. Based on VST results, the value of k298 is calculated according to the
equation (2.26), the shelf-life values of single explosives, PBX-H and PBX-P
samples were calculated and presented in Figure 3.28-3.29.
PBX-HP-8501
5

78.3
PBX-PN-8002

PBX-HN-80-2
4

38.7

41.6

PBX-HN-80-1
3

56.0

PBX-PP-8001

44.9

48.8

2
PBX-HN-85

PETN

47.6

70.2

1
RDX

0

10

20 30 40 50 60 70
Shelf-life of RDX and PBX-H, years

a)

80

90

0

10

20
30
40
50
60
70
Shelf-life of PETN and PBX-P, years

80

b)

Figure 3.28-3.29. The shelf-life of single explosives, PBX-H and PBX-P

The influence of the binder was evident over the shelf-life (estimated) of
single explosives and thermoplastic PBX explosives. While the shelf-life of
RDX and PBX-HP samples (about 70 ÷ 80 years), the shelf-life of PBX-HN
explosives is smaller (about 40 ÷ 50 years); similar values of explosives PETN
is about 48 years, PBX-PP explosives (about 56 years) and PBX-PN
explosives (about 38 years). On the other hand, due to the thermal stability of
RDX higher than PETN, so the shelf-life of PBX-P explosives is significantly
lower than that of PBX-H.
CONCLUSIONS
1. Single RDX and PETN are well chemical compatible with PS and
three types of NC, thereby orienting the use of PS and NC as binders to
make thermoplastic PBX explosives. In addition, RDX with PS and NCbased binder systems have smaller interfacial tension, greater work of
adhesion than those of PETN, so the adhesion of RDX to the binder is better
than that of PETN.


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