Post on 03-Feb-2022
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
National Aeronautics and Space Administration
Improvements to the synthesis of polyimide aerogelsp y g
Mary Ann B. Meador, Baochau N. Nguyen, Haiquan Guo Stephanie Vivod Zuhui He ErickaHaiquan Guo, Stephanie Vivod, Zuhui He, Ericka
Malow and Rebecca Silva
NASA Glenn Research CenterCleveland, OH 44135
Maryann.meador@nasa.gov
www.nasa.gov 1
National Aeronautics and Space Administration
What are aerogels?
Sol Gel Aerogel• Highly porous solids made by drying a wet gel
without shrinking• Pore sizes extremely small (typically 10-40
g
Pore sizes extremely small (typically 10-40 nm)—makes for very good insulation
• 2-4 times better insulator than fiberglass under ambient pressure 10-15 times better in light
Typical monolithic silica aerogels
ambient pressure, 10 15 times better in light vacuum
• Invented in 1930’s by Prof. Samuel Kistler of the College of the Pacific
www.nasa.gov 2
the College of the Pacific
National Aeronautics and Space Administration
Examples of current commercial aerogel productsproducts• Cabot
– Pellets, composite– Oil and gas pipeline insulation– Cryo-insulation– Day-lighting applications
• Aspen Aerogels– Flexible blanket insulation– Oil and gas pipeline– Construction materials
Aerospace apparel– Aerospace, apparel• Nanopore
– Vacuum insulation panelsShipping containers– Shipping containers
– Refrigeration– Apparel
www.nasa.gov 3
National Aeronautics and Space Administration
Monolithic silica aerogels out-perform particulate forms as insulation
…but are extremely fragile and
forms as insulation
fragile and moisture sensitive
and limited to a few
Doug Smith, Aerogel Conference, 2007
…and limited to a few exotic applications
www.nasa.gov 4
Cosmic dust collector –Stardust Program Insulation on rovers
National Aeronautics and Space Administration
Potential applications for durable aerogels in aeronautics and space explorationaeronautics and space exploration
Cryotank Insulation Air revitalizationFan engine containment(Ballistic protection)
Sandwich structures
Ultra-lightweight, multifunctional structures for habitats, rovers
Insulation for EVA suitsHeat shielding
www.nasa.gov 5
Insulation for EVA suits, habitats and rovers
Heat shieldingPropellant tanks Inflatable aerodynamic
decelerators
National Aeronautics and Space Administration
Durable aerogels by reinforcing with polymersg y g p y
Native Cross-linked
• Polymer reinforcement doubles the density
• Results in two order of• Results in two order of magnitude increase in strength
• Reduces surface area by yonly 30-50%
• Leventis, Meador, Johnston, Fabrizio, and Ilhan, US Patent No. 7,732,496; June 8, 2010
www.nasa.gov 6
7,73 , 96; June 8, • Jason P. Randall, Mary Ann B. Meador, and Sadhan C. Jana,
ACS Appl. Mater. Interfaces, 2011, 3 (3), pp 613–626
National Aeronautics and Space Administration
Typical Aerogel Cross-linking ProcessSilanes
in solventH2O/solvent
/catalyst
Wash (water, l h l )
15 min
SOL GEL alcohols)
Soak in monomer
bath
Crosslinked Aerogel
heat
SCF d i Wash
( SCF drying (CO2)
(excess polymer)
www.nasa.gov 7
Cross-linked
National Aeronautics and Space Administration
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
www.nasa.gov 8
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
6
8
Modulus = 89 MPaDensity = 0 403 g/cm3Pore structure
Stre
ss, M
Pa
2
4
6
Test 1Test 2
Density 0.403 g/cmPore structure influenced by
bonding
• Use of MTMS instead of TMOS givesStrain
0.00 0.05 0.10 0.15 0.20 0.250
• 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
www.nasa.gov 9
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
www.nasa.gov
– 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
www.nasa.gov 18
• 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
aerogels of similar density
Pore
vol
ume,
c
1
2
3
30Polyimide0.24 g/cm3Epoxy reinforced
Pore diameter, nm
0 20 40 60 80 1000
Stre
ss, M
Pa
20
Epoxy reinforced0.23 g/cm3
NMP: 0 27 g/cm3; 410 m2/g DMF: 0 07 g/cm3; 356 m2/g
0 20 40 60 800
10NMP: 0.27 g/cm ; 410 m /g DMF: 0.07 g/cm ; 356 m /g
www.nasa.gov 19
Strain, %
DMAC: 0.09 g/cm3; 410 m2/g
National Aeronautics and Space Administration
A better approach: chemical imidization with pyridine and acetic anhydridepyridine and acetic anhydride
• Pyridine catalyzes imidization O
O
O
O O
OH2N NH2+
• Acetic anhydride reacts with water by-product
P t h d l i f
O
O
On + 1 eq. n eq.
HN
O
O OHN
O O
OO OH OHO
O
O
O
O O
n– Prevents hydrolysis of amic acid
• Gel forms within 30
O
O
O
H2N
NH2
NH2
n
NH
OO
O HN
O O
HN O
O
NH
NHO O
Stir 1 hour to overnight
minutes; aged for 24 hours for n = 15 or greater 5-10 wt % solids
NH O HN
OO OH OHOO
HO
HN O
O
NH
NHOH
n
N N
OO
O N N
OO
O
O N
O
OO
O O
acetic anhydride, pyridine
greater, 5 10 wt % solids• Imidization proceeds
almost completely at
OOOO
O N
O
n
www.nasa.gov
room temperature
20
Vivod, et al, POLY Poster 334, Wed 9:30
National Aeronautics and Space Administration
Approaches to PI aerogels• Varying structure (connecting
groups) of diamine and dianhydrides provide means to
Diamines
PPDANH2H2N
dianhydrides provide means to tailor properties– Flexibility
O
NH2H2N
NH2
PPDA
ODA
BAX– Thermal oxidative stability– Mechanical properties– Thermal conductivity
H2N
O
H2N
O
NH2
BAX
BAPPy
• Longer chains between cross-links
Dianhydrides
OO O CF3O O
OO
O O
OO O
OO
O O
CF3
O O
O
O
O NH2
NH2
Triamine
BTDA HFDA
www.nasa.gov 21
OO
O O
O
O
O
O
H2N
BPDA OTDATAB
National Aeronautics and Space Administration
TAB cross-linked aerogels 550ghave different pore
structure depending on d
Sur
face
are
a, m
2 /g
400
450
500
BPDA/ODABTDA/ODABTDA/PPDA
BPDA/ODA
monomers used
BTDA/PPDA BTDA/ODAnumber of repeat units, n
15 20 25
S
300
350
BPDA/ODA BTDA/PPDA BTDA/ODA
3.5
15
14 3.5
15
Pore
vol
ume,
cm
3 /g
1.0
1.5
2.0
2.5
3.0 n=15n=20n=25
Por
e vo
lum
e, c
m3 /g
4
6
8
10
12 n=15n=20n=25
Pore
vol
ume,
cm
3 /g
0 5
1.0
1.5
2.0
2.5
3.0 n=15n=20n=25
www.nasa.gov 22
Pore diameter, nm1 10 100
0.0
0.5
Pore diameter, nm1 10 100
0
2
Pore diameter, nm1 10 100
0.0
0.5
National Aeronautics and Space Administration
Properties of the aerogels depend mostly on shrinkage during processingshrinkage during processing
%
50
60
BPDABTDA
cm3
0.3
0.4
BPDABTDA
Shrin
kage
,
20
30
40
Den
sity
, g/
0.2
100
DiamineODA PPDA
10
95Diamine
ODA PPDA0.1
odul
us, M
Pa
1
10
BPDA
Por
osity
, %
85
90
DiamineODA PPDA
M
0.1
1 BPDABTDA
DiamineODA PPDA
75
80 BPDABTDA
www.nasa.gov 23
DiamineDiamine
Number of repeat units between TAB cross-likes had no effect on any of the properties
National Aeronautics and Space Administration
Thin films cast from TAB cross-linked PI aerogels
• Collaboration with Prof. Miko Cakmak, University of AkronUniversity of Akron
• TAB/ODA/BPDA, n= 30– n = 25 too viscous to cast
• Density of film: 0.17 g/cm3
(shrinks a little more than thick part)• Tensile testing:• Tensile testing:
– 79 MPa modulus– Tensile stress at break = 4.5 MPa
3 000 000
3,500,000
4,000,000
4,500,000
5,000,000
ess (Pa
)
500 000
1,000,000
1,500,000
2,000,000
2,500,000
3,000,000
True
Stre
www.nasa.gov 24
0
500,000
0 0.02 0.04 0.06 0.08 0.1 0.12True strain (mm/mm)
Tensile specimen
National Aeronautics and Space Administration
Polyimide 3D network using T8-POSSy gO
Si
O
SSi
O
SiO
Si
OO
SiO O
NH2
NH2
NH2H2N
NH2
H2N
SiO
SO
SiO
SiO O
NH2H2N
H2N
NN
O
O
O
O
NNO
O
O
O
H2C
H2C *
• PI cross linked with POSS
O OO O
n
• PI cross-linked with POSS• BPDA-(BAX-BPDA)n; n = 10 to 25• Low shrinkage (~10 %) • Density: ~0.1 g/cm3
• Porosity > 90 %
www.nasa.gov 25
Guo, et al, ACS Appl. Mater. Interfaces, 2011, 3 (2), 546–552 POLY Poster 327, Wed 9:30
National Aeronautics and Space Administration
Formulation study of PI-POSS aerogels with different dianhydrides and diaminesdifferent dianhydrides and diamines
• Differences in h i k b t
0.2525
shrinkage between different monomers affects density, D
ensi
ty, g
/cm
3
0.10
0.15
0.20
Shr
inka
ge, %
10
15
20
yother properties
BPDA/BAX BPDA/ODA BTDA/BAPP0.00
0.05
BPDA/BAX BPDA/ODA BTDA/BAPP0
5
www.nasa.gov 26
BPDA/BAX BPDA/ODA BTDA/BAPP
National Aeronautics and Space Administration
POSS/PI cast as thin film is flexible both before and after supercritical drying
• Collaboration with Miko Cakmak, University of Akron• Density of film is similar to molded cylinder
– 0.12 g/cm3
– 90 % porousp• Middle picture is 9” x 13” pan; film is folded multiple times
www.nasa.gov 27
As-cast wet films Dry aerogel
National Aeronautics and Space Administration
Mechanical properties: Tensile and icompression
• Slight decrease in5
6
BTDA/BAPP• Slight decrease in compressive modulus with increasing n
• Differences in modulus/stress2
3
4
Stre
ss (M
Pa)
BPDA/ODA
BTDA/BAPP
• Differences in modulus/stress at break probably mostly due to shrinkage
• Formulations which shrink the0 10 20 30 40 50 60 70 80
0
1
Strain (%)
BPDA/BAX
• Formulations which shrink the most have the highest density
• Mechanical properties track with density
( )
MP
a
100
1000
Compressive modulus Tensile modulus Tensile stress at break
with densityM
odul
us, M
1
10
www.nasa.gov 28
BPDA/BAX BPDA/ODA BTDA/BAPP0.1
National Aeronautics and Space Administration
Aging up to 500 oC in N2 for 24 hoursg g up o 500 C 2 o ou sBPDA/BAX BPDA/ODA BTDA/BAPP
95
100
95
100
300 95
100
)300oC 300oC
75
80
85
90
Wei
ght R
etai
ned
(%)
w300 w400 w500
75
80
85
90
Wei
ght r
etai
ned
%
400 500
75
80
85
90
Wei
ght R
etai
ned
(%)
w500 w400 w300
300oC400oC500oC 300oC
400oC500oC
300oC400oC500oC
0 200 400 600 800 1000 120065
70
time (min)0 200 400 600 800 1000
65
70
5
Temperature (oC)
0 200 400 600 800 1000 120065
70
W
time (min)
85
90
95
100
105
ed (%
)
Before heating
After 300 oC
TGA in N2
60
65
70
75
80
85
Wei
ght R
etai
ne
After 400 oC
After 500 oC
BPDA/BAXBPDA/ODABTDA/BAPP
www.nasa.gov
100 200 300 400 500 600 700
55
Temperature (oC)
National Aeronautics and Space Administration
PI-POSS aerogels—thermal conductivity
• n = 20 formulation measured at TPRL m
-K 35
40
at TPRL• Multiple layers 0.6 mm thick
measuredC bl t b li du
ctiv
ity, m
W/m
20
25
30
35
• Comparable to baseline insulation for inflatable decelerator (Pyrogel 3350) in both thermal conductivity and Th
erm
al C
ond
5
10
15BAX 760 torr BAX 0.01 torr ODA 760 torrODA 0.01 torr
both thermal conductivity and density
• 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)
Thank you!
www.nasa.gov 33