Jessica Gwyther
Characterisation of Plasticised
Nitrocellulose using NMR and
Rheology
2
Project Aims
• Prepare 5 inert PBX binder formulations using
nitrocellulose polymer and a series of nitroaromatic
plasticiser
• Characterisation of formulations that form gels
• Investigation of the molecular dynamics of the small
plasticiser molecules in the NC matrix using NMR
• Characterisation of bulk physical properties of the
binders using rheological measurements.
Binder Formulations
3
NC + a) ethylbenzene (EB)
b) mononitroethylbenzene (MNEB)
c) dinitroethylbenzene (DNEB)
d) trinitroethylbenzene (TNEB)
e) K10 (DNEB (65%) TNEB (35%))
Film
Gel
Gel
Solid
Gel
O NO 2
O
*
O 2 NO
O 2 NO
O NO 2
O
*
O
O
O NO 2
O NO 2
n
NC
EB
MNEB
DNEB
65%
35%
K10
TNEB
4
Binder Formulations
EB + NC
MNEB + NC
K10 + NC
TNEB + NC
DNEB + NC
Rheology – Amplitude Sweep
•
Oscillation expt. Stress sweep at constant frequency to find
linear viscoelastic region and good signal.
K10 G'
K10 G"
MENB G'
MNEB G"
100000
DNEB G'
DNEB G"
Modulus / Pa
5
10000
1000
100
0.01
0.1
1
10
100
Stress / Pa
•
•
G’ greater than G” for each gel – more Elastic than viscous.
Relative ‘rigidity’ of gels:
DNEB + NC < K10 + NC < MNEB + NC
rigidity
Rheology – Oscillation at Elevated Temperatures
G' 25oC
10000
G' 25oC
1000000
G" 25oC
G'' 25oC
G' 60oC
G' 80oC
G" 60oC
G" 80oC
Modulus / Pa
100000
10000
1000
1000
100
0.001
0.01
0.1
1
10
100
0.001
100
0.01
0.1
1
Freq / Hz
Freq / Hz
DNEB + NC binder
MNEB + NC binder
100000
G' 25oC
G'' 25oC
G' 80oC
G" 80oC
Modulus / Pa
Modulus / Pa
6
10000
1000
100
0.001
0.010
0.100
Freq / Hz
K10 + NC binder
1.000
10.000
100.000
10
100
Rheology – Oscillation at Sub-ambient Temperatures
G' 25oC
1000000
G'' 25oC
G' 25oC
100000
G" 25oC
G' -20oC
G" -20oC
Modulus / Pa
Modulus / Pa
G' -20oC
G" -20oC
100000
10000
10000
1000
1000
100
0.00
0.01
0.10
1.00
10.00
100
0.001
100.00
0.01
0.1
1
10
100
Freq / Hz
Freq / Hz
MNEB binder
Modulus / Pa
7
DNEB binder
1.00E+09
G' 25oC
G'' 25oC
1.00E+08
G' -10oC
G" -10oC
1.00E+07
G' -20oC
G" -20oC
•
Large G’ and G” at
-20oC for K10 binder.
•
Possible phase
transition.
1.00E+06
1.00E+05
1.00E+04
1.00E+03
1.00E+02
0.001
0.010
0.100
1.000
Freq / Hz
K10 binder
10.000
100.000
8
Modulus versus Temperature Plot at 0.01 Hz
MNEB binder G'
1.00E+08
MNEB binder G"
DNEB binder G'
DNEB binder G"
K10 Binder G'
1.00E+07
K10 Binder G"
Modulus / Pa
1.00E+06
1.00E+05
1.00E+04
1.00E+03
1.00E+02
-20
-10
0
10
20
30
T / oC
40
50
60
70
80
Time-temperature Superposition
80oC
5.0
60oC
40oC
4.5
25oC
4.0
Log G'
9
10oC
3.5
0oC
3.0
-10oC
2.5
2.0
1.5
-4.0
-2.0
0.0
2.0
4.0
6.0
Log reduced freq
•Good overlay of oscillation data for all
gels
M Doi and S. F. Edwards, The Theory of Polymer Dynamics
•Rheology dominated by NC not small
molecule plasticiser
•Evidence of highly concentrated solution of entangled polymer,
not cross linked gel
Creep Recovery
•
Stress applied to sample and strain measured.
•
Stress is removed after being applied for a time.
•
If no flow has occurred = strain gradually recovers to zero.
•
If some flow has occurred = strain does not recover to zero.
8.0E-02
25oC
35oC
Minimum viscosity:
7.0E-02
η=
σ
∂γ / ∂t
40oC
50oC
60oC
70oC
80oC
T / oC
Min. η x 105 / Pas
25
13.1
35
9.57
40
7.37
3.0E-02
50
3.93
2.0E-02
60
1.63
70
0.78
80
0.25
6.0E-02
5.0E-02
γ/ Pa-1
10
4.0E-02
1.0E-02
0.0E+00
0
100
200
300
400
Time / s
Creep recovery plot for K10 binder
500
600
700
11
NMR – T2 of Gels
T2 is a time constant which is related to molecular dynamics by:
τc
1
=A
+ Bτ c
2
T2
1 + ω 2τ c
τc = Molecular Correlation Time
ω is the Larmor frequency and
A and B are constants.
Liquids ω2 τc2 <<1
Solids ω2 τc2 >>1
Aromatic
protons
Aliphatic
and NC
protons
1
= ( A + B )τ c
T2
1
= Bτ c
T2
Spectrum K10 + NC gel
K10 (DNEB + TNEB) < DNEB ≤ MNEB
Molecular Mobility
12
NMR – Diffusion of Gels
•
Pulse Field Gradient (PFG) NMR used to find translational
diffusion co-efficient
ω = γBo
•
Larmor equation:
•
Bo spatially homogeneous, ω same throughout sample
•
However, if in addition to Bo magnetic field gradient applied…
…Larmor frequency varies with position and becomes a
spatial label.
NMR – Diffusion Gels
•
Whole molecule has same
diffusion coefficient
•
Relative ordering of gels
according to D:
K10 (DNEB + TNEB) < DNEB < MNEB
Stack plot of
(consistent with T2)
14
-21.00
2.80E-03 2.90E-03 3.00E-03 3.10E-03 3.20E-03 3.30E-03 3.40E-03
-21.50
-22.00
K10 + NC
MNEB + NC
DNEB + NC
•
12
10
8
6
4
2
0
-2
-4
ppm
between 25oC – 80oC
R2 = 0.9987
-23.00
R2 = 0.9959
-23.50
-24.00
R2 = 0.9981
-24.50
-25.00
1/T / K-1
K10 + NC binder
Diffusion expt’s repeated
-22.50
ln D
13
•
Arrhenius plots
14
Conclusions
•
Three formulations formed gels.
•
Bulk Properties:
- Rheological properties of the gels dominated by NC polymer
•
Molecular Dynamics:
- T2 and diffusion coefficients of small molecules within gels.
- Increasing molecular mobility with decreasing molecular
size.
- Molecular dynamics dominated by small molecule
plasticisers.
•
Evidence that gels are concentrated solutions of entangled
polymer, not cross linked gels.
15
Acknowledgements
•
AWE – Dr. Paul Deacon
•
Prof. Terence Cosgrove and Dr. Roy Hughes
•
Polymers at Interfaces Group – Dr. Youssef Espidel
•
Bristol Colloid Centre – Dr. Cheryl Flynn

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