Improvements to the Synthesis of Polyimide Aerogels · 2013-04-10 · Improvements to the Synthesis of Polyimide Aerogels Cross-linked polyimide aerogels are viable approach to higher

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 2020-03-08T13:32:12+00:00Z

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Typewritten Text

.

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

[email protected]

www.nasa.gov 1


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


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


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


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


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


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


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


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


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 %


www.nasa.gov 11


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


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


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


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


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


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


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


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


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


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


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


0

2


0.0

0.5


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


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


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


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


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


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


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)


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


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)


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


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

Documents

Improvements to the Synthesis of Polyimide Aerogels · 2013-04-10 · Improvements to the Synthesis of Polyimide Aerogels Cross-linked polyimide aerogels are viable approach to higher