Nitrocellulose Degradation – an Important Factor
to Assess Ageing / Stability of Gun Propellants
Beat Vogelsanger, Ruth Sopranetti
© Nitrochemie 2012
Nitrocellulose Degradation
Introduction / Goal
This short presentation should demonstrate that nitrocellulose
degradation plays an important role in the understanding of
propellant ageing
2012 NC Symp Spiez _ Pres Vogelsanger et al 2 _ NC Degradation.ppt
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Nitrocellulose Degradation
Chemical Ageing of Propellants
Phenomenological Description
NO / NO2
("fumes")
Weight Loss
Diffusion
out of Grain
Thermolysis
of NC / NG
incl. Secondary
Reactions
Nitrogen
Oxides
and
Acids
Reaction with
Stabiliser
Reaction with
NC / NG
NOx
2012 NC Symp Spiez _ Pres Vogelsanger et al 2 _ NC Degradation.ppt
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StabiliserDepletion
+
Heat
H
N
NC-MolecularMass Reduction
+
Heat
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Nitrocellulose Degradation
Chemical Ageing of Propellants
Preference for Certain Stability Tests
Some institutes / testing laboratories have developed a strong preference for (or even addiction to) one single stability testing method
This is very dangerous !
Chemical ageing of propellants involves many different physicalchemical processes
Most stability tests only regard one of these processes
There are cases in which
NO
NO/ /NO
NO22
certain stability tests fail
("fumes")
("fumes")
Diffusion
out of Grain
Thermolysis
of NC / NGL
incl. Secondary
Reactions
Nitrogen
Oxides
and
Acids
Reaction with
Stabiliser
Reaction with
NC / NGL
NOx
2012 NC Symp Spiez _ Pres Vogelsanger et al 2 _ NC Degradation.ppt
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© Nitrochemie 2012
Weight
WeightLoss
Loss
StabiliserStabiliserDepletion
Depletion
++
Heat
Heat
H
N
NC-MolecularNC-MolecularMass
MassReduction
Reduction
++
Heat
Heat
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Nitrocellulose Degradation
Chemical Ageing of Propellants
Example: Relative Ageing Rates at 71°°C
18
8
7
6
5
7.5
6.8
Stabiliser Deplet.
NC Degradation
NOx Evolution
Heat Flow
5.4
4.1
4
2.6
3
2
1.9
1.8
Reference
all factors = 1.0
0.7
1
0.4
0
0
Single Base
[DPA]
Double Base
[Akardite-2]
2012 NC Symp Spiez _ Pres Vogelsanger et al 2 _ NC Degradation.ppt
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Double Base
[EC]
© Nitrochemie 2012
≈0
Triple Base
[no Stabiliser]
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Nitrocellulose Degradation
Chemical Ageing of Propellants
Influence of Stabiliser Type on Ageing
Propellant with efficient
stabiliser (DPA or Akardite)
Propellant with inefficient
stabiliser (Centralite)
NO / NO2
"fumes"
Thermolysis
of NC / NG
incl. secondary
Reactions
NO2
NO
other
Nitrogen
Oxides /
Acids
NO / NO2
"fumes"
Diffusion
out of Grain
StabiliserDepletion
+
Heat
Reaction with
Stabiliser
Reaction with
NC / NG
NOx
Thermolysis
of NC / NG
incl. secondary
Reactions
NC-MolecularMass Reduction
+
Heat
NO2
NO
other
Nitrogen
Oxides /
Acids
Diffusion
out of Grain
Reaction with
Stabiliser
Reaction with
NC / NG
NOx
StabiliserDepletion
+
Heat
NC-MolecularMass Reduction
+
Heat
Slowly depleting stabilisers are often inefficient an thus promote
other ageing reactions (mainly nitrocellulose degradation) !
Therefore, different ageing processes have to be investigated in
order to obtain a complete picture of the propellant ageing !
2012 NC Symp Spiez _ Pres Vogelsanger et al 2 _ NC Degradation.ppt
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© Nitrochemie 2012
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Nitrocellulose Degradation
Temperature Dependence of NC Molecular Mass Reduction
Arrhenius Diagram
-26
-27
40°°C
80
-28
80°°C
40
60°°C
70°°C
Activation Energy
EA = 121 kJ/mol
80°°C
50°°C
60
ln (kn)
Rel. NC Molecular Mass [%]
Nitrocellulose Molecular Mass Reduction
100
-29
-30
70°°C
60°°C
-31
50°°C
20
Result of Extrapolation: 40% NC
Depletion after 65 Years at 25°°C
-32
0
0
5
10
15
20
25
30
Ageing Tim e [w eeks]
35
40
-33
0.0028
40°°C
0.0030
0.0032
0.0034
1 / Tem perature [1/K]
Temperature dependence of NC molecular mass reduction can easily be analysed
using nth order kinetics + Arrhenius (such as for stabiliser depletion; see AOP-48 Ed. 2)
2012 NC Symp Spiez _ Pres Vogelsanger et al 2 _ NC Degradation.ppt
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Nitrocellulose Degradation
Summary and Conclusions
Nitrocellulose degradation
is a very robust indicator for chemical ageing of propellants
produces plausible results even in cases where the other test
methods fail
A sufficient understanding of chemical ageing of propellants requires
investigation of different ageing processes, including nitrocellulose
degradation
(apart from stabiliser depletion, heat production and gas / NOx production)
2012 NC Symp Spiez _ Pres Vogelsanger et al 2 _ NC Degradation.ppt
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Nitrocellulose Degradation
Thanks very much for your attention !
Wimmis, Switzerland
2012 NC Symp Spiez _ Pres Vogelsanger et al 2 _ NC Degradation.ppt
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Aschau, Germany
© Nitrochemie 2012
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