Improvements to the Synthesis of Polyimide Aerogels Cross-linked polyimide aerogels are viable approach to higher temperature, flexible insulation for inflatable decelerators. Results indicate that the all- polyimide aerogels are as strong or stronger than polymer reinforced silica aerogels at the same density. Currently, examining use of carbon nanofiber and clay nanoparticles to improve performance. Flexible, polyimide aerogels have potential utility in other applications such as space suits, habitats, shelter applications, etc. where low dusting is desired https://ntrs.nasa.gov/search.jsp?R=20110011361 2019-01-28T15:56:06+00:00Z
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Improvements to the Synthesis of Polyimide Aerogels
Cross-linked polyimide aerogels are viable approach to higher temperature, flexible insulation for inflatable decelerators. Results indicate that the all-polyimide aerogels are as strong or stronger than polymer reinforced silica aerogels at the same density. Currently, examining use of carbon nanofiber and clay nanoparticles to improve performance. Flexible, polyimide aerogels have potential utility in other applications such as space suits, habitats, shelter applications, etc. where low dusting is desired
Process/property optimization of di-isocyanate cross linked aerogelscross-linked aerogels
Empirical models… Low density...
10000
1000
e
0 010.1
1
10
100
1000
Mod
ulus
, MP
a
1
10
100
No.
hex
amet
hyle
ne re
peat
uni
ts
sed for predictions of optima
0.01
0.40.8
1.21.6
2.0
46
810
12
Total silane, mol/lH
2 O, mol/l
1
0.40.8
1.21.6
2.0
46
810
1214
Total silane, mol/lH
2 O, mol/l
0 washes2 washes4 washes
…used for predictions of optima
…to high density… MP
a 10
100MeasuredPredicted
t uni
ts
20
25
30MeasuredPredicted
g yand everything
in-between
29 30 31 32 33 34 35 36 37
Mod
ulus
,
0.01
0.1
1
29 30 31 32 33 34 3 36 3
HD
I rep
eat
0
5
10
15
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Meador et al, Chemistry of Materials, 2007, 19, 2247-2260Run
29 30 31 32 33 34 35 36 37Run
29 30 31 32 33 34 35 36 37
National Aeronautics and Space Administration
Reduced bonding in silica backbone leads to excellent elastic recovery over modulus range of 0 01 to 100 MPaelastic recovery over modulus range of 0.01 to 100 MPa
• Use of MTMS instead of TMOS gives 25 % reduction in Si-O-Si bonding
• Almost all length is recovered after two compressions to 25% M
Pa
0.06
0.08
0.10
Modulus = 0.12 MPaDensity = 0.093 g/cm3
p• Polymer cross-linking provides
increased modulus/maximum stress at break
Stre
ss,
0 00
0.02
0.04Test 1
Test 2
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Strain
0.00 0.05 0.10 0.15 0.20 0.250.00
Nguyen et al, ACS Applied Materials and Interfaces, 2010, 2, 1430–1443
National Aeronautics and Space Administration
One pot process streamlines aerogel fabricationfabrication
Four Washes
SCEne P
ot • Eliminating diffusion Shortens process
Sol with epoxy Gel with epoxy Epoxy reinforced gel
Epoxy reinforcedaerogel
SCE
Two
Mul
On – Shortens process
– Cross-linking more efficient
– Aerogels are more uniform
SolGel
Monomer diffusion
Two washes
ltistep • Properties are the same as multistep when 15 mol % APTES used
400
• Higher APTES leads to much higher density, lower surface area 100
200
300
400
1.0Surfa
ce a
rea,
m2 /g
– Diffusion not a factor– Amount of polymer cross-
linking much higher
0 1.2
1.4
1.6
5 10 15 20 25 30 35 40
S
Total S
i, mol/
l
BTMSH, mol %
APTES = 15 mol %APTES = 30 mol %
www.nasa.gov 10
Meador et al, ACS Applied Materials and Interfaces, 2010, 2, 2162-2168
APTES = 45 mol %
National Aeronautics and Space Administration
www.nasa.gov 11
National Aeronautics and Space Administration
Improved insulation for inflatable p o ed su a o o a ab ere-entry vehicles
B li i l ti i A A l• Baseline insulation is Aspen Aerogels Pyrogel 3350
• Needs to be more flexible foldable lessNeeds to be more flexible, foldable, less dusty, thermally stable
• Target: thin film aerogels with nanofiberreinforcement– Silica aerogels with PDMS flexible linking groups – Silica aerogels reinforced with polyimideg p y– Cross-linked polyimide aerogels– Manufacture into thin film form
Electrospun fibers in film for added
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– Electrospun fibers in film for added durability/flexibility
12
National Aeronautics and Space Administration
Collaboration with University of Akron—thin film aerogels reinforced with electrospun nanofiberaerogels reinforced with electrospun nanofiber
• Sol cast into thin film• Electrospun fibers of PDMS/PU
Solution A
Solution B
Sol with desired
viscosity
mixFilm cast Nanofiber
Electrospinning
deposited into film• Flexible nanofibers bridge
cracks/hold structure together
Solution B y
Gelation
Aging
SolventExc.Reinforced Silica
Aerogel Thin Film SCF Drying
FanMULTINOZZLE ELECTROSPINNING PLATFORM
Fan
www.nasa.gov 13
Li et al, ACS Applied Materials and Interfaces, 2009, 1, 2491–2501
National Aeronautics and Space Administration
Polyimide reinforced silica aerogels
O
O
O
N
CF3F3C O
O
O NN
O
O
O
CF3F3C O
O
Polyimide cross-link reacted with APTES amine O O O O
n
0 15
0.18
n = 1 4
5
0.03
0.06
0.09
0.12
0.15
0.8
Den
sity
, g/c
m3
M
n = 1n = 3
0
1
2
3
4
0.8Mod
ulus
, MP
a
0.00
0.4
0.5
0.60.7
2530
35404550
Total
Si, M
Co-reactant, %
-1
0.4
0.5
0.60.7
2530
35404550
Total
Si, M
Co-reactant, %
• Low water to silane ratio (~3) used to make gels• Gels prepared in acetonitrile
– Solvent exchanged to NMP for cross-linking
www.nasa.gov
– Solvent exchanged to ethanol for drying
• Shrinkage <5%14
National Aeronautics and Space Administration
Surface areas, morphology of PI reinforced aerogels similar to other polymer reinforementaerogels similar to other polymer reinforement
0.8 M Si, 25 mol% APTES 0.44 M Si, 57 mol% APTES
400
440
m2
n = 1
240
280
320
360
0.70.8
BET
, g/m
3 240
0.4
0.5
0.6
2530
3540
4550
Total
Si, M
Co-reactant, %
n = 3
• PI oligomers with n = 3 produced core-shell structures with gels at low silane concentration
• All n = 1 samples appear uniform
www.nasa.gov
• All n = 1 samples appear uniform• Hence, diffusion into the gel was a problem for larger oligomers
15
National Aeronautics and Space Administration
Linear polyimide (PI) aerogels made by Aspen AerogelsAspen Aerogels
Wet gelNN
O
OO
O
O
• High MW polyimide gels made from PMDA and ODA
A l
OO
• Supercritical drying produced aerogels
• Onset of decomposition >560 oC
Aerogel
Onset of decomposition 560 C• As strong or stronger than
polymer reinforced silica aerogel• But much shrinkage on• But much shrinkage on
preparation
www.nasa.gov 16
Rhine, Wang and Begag, US Patent 7,074,880 B2, July 11, 2006
National Aeronautics and Space Administration
Cross-linked PI aerogels using branchingg g g• Use of triamines, or other
multifunctional groups to form +
Diamine Dianhydride
network structure• Gelled polyamic acid network is
imidizedn
imidized• Solvent exchange to acetone
then supercritical drying to
Triamine
produce aerogel
Monomers Polyamic Polyimide Polyimide
www.nasa.gov 17
yAcid Gel
yGel
yAerogel
Meador, US Patent application filed 9-30-2009
National Aeronautics and Space Administration
First example of PI aerogels from TAB/BTDA/ODA n=1TAB/BTDA/ODA, n 1
O
O O
O
O
O
O
OH2N NH2+
n + 1 eq. n eq.
O OOOO O
O
O
H2N
NH2
O HN
OO
O
O OHN
O
OO OH OHOn
NMP
O NH2
O
NH
OO
O
O
HN
O O
OO OH OHOO
HO
HN O
O
O
NH
NH
NHOH
n
heat
DMF
DMACO
N N
O
O
O
O
O
O
N N
O
O
O
O
O
O
O
N
N
O
O
OO
n
• Three solvents tried; gelation very fast• Thermally imidized
Gels liquefied during heating re
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• Gels liquefied during heating, re-gelled on cooling DMAC NMP
National Aeronautics and Space Administration
Properties of thermally imidized PI aerogels with TAB n=1 oligomerswith TAB, n=1 oligomers
• Aerogels made in NMP shrink about 30 %
cm3 /g
4
5
6
DMACNMPDMF
• Low shrinkage from DMF and DMAC• 5 times stronger than epoxy reinforced
• About 5-6 layers equals one layer of Pyrogel 3350
Test temperature, oC
20 60 100 140 180 2200
layer of Pyrogel 3350• Much more flexible, foldable
www.nasa.gov 30
National Aeronautics and Space Administration
Testing of PI-POSS aerogels under high heat flux
• Laser Hardened Materials Experimental Lab, Wright Pat
• Heat flux 20 W/cm2, 8 torr N2 2 layers BF-2011 l PI POSS (BAX)• 90 sec duration
• Bottom layer only darkened, no hole, no cracks
11 layers PI-POSS (BAX)(6.75 mm)
1400
1600
1800
2000
C)
Surface Temperature
TC1
TC2
TC3
600
800
1000
1200
Surf
ace
Tem
pera
ture
(Deg
TC3
TC4
0
200
400
600
0 20 40 60 80 100 120 140 160
S
www.nasa.gov31
Time (Sec)
National Aeronautics and Space Administration
Conclusions
• Cross-linked polyimide aerogels are viable approach to higher temperature, flexible insulation for inflatable decelerators
• Results indicate that the all-polyimide aerogels are as strong or stronger than polymer reinforced silica aerogels atstrong or stronger than polymer reinforced silica aerogels at the same density
• Currently, examining use of carbon nanofiber (Poster 334) and clay nanoparticles to improve performance
• Flexible, polyimide aerogels have potential utility in other applications such as space suits habitats shelterapplications such as space suits, habitats, shelter applications, etc. where low dusting is desired
www.nasa.gov 32
National Aeronautics and Space Administration
Acknowledgments
PersonnelNASA D k Q d St h i Vi dNASA: Derek Quade, Stephanie Vivod,
Anna Palczer OAI: Linda McCorkle, Dr. Baochau Nguyen, Dr. Heidi Guo
ARSC: Dan SchiemanStudent Interns: Ericka Malow, Joe He, Rebecca Silva,
Guilhermo Sprowl, Sarah ErcegovicUniversity of Akron: Dr. Miko Cakmak, Dr. Lichun Li,
Dr. Jiao Guo
Funding: NASA Fundamental Aeronautics Program (Hypersonics)