Electron beam curing of Polymer Matrix Composites (PMC's) is a nonthermal, nonautoclave curing process that has been demonstrated to be a cost effective and advantageous alternative to conventional thermal curing. Advantages of electron beam curing include: reduced manufacturing costs; significantly reduced curing times; improvements in part quality and performance; reduced environmental and health concerns; and improvement in material handling. In 1994 a Cooperative Research and Development Agreement (CRADA), sponsored by the Department of Energy Defense Programs and 10 industrial partners, was established to advance the electron beam curing of PMC technology. Over the last several years a significant amount of effort within the CRADA has been devoted to the development and optimization of resin systems and PMCs that match the performance of thermal cured composites. This highly successful materials development effort has resulted in a board family of high performance, electron beam curable cationic epoxy resin systems possessing a wide range of excellent processing and property profiles. Hundreds of resin systems, both toughened and untoughened, offering unlimited formulation and processing flexibility have been developed and evaluated in the CRADA program

Dorsey, George F.

Havens, Stephen J.

Janke, Christopher J.

Lopata, Vincent J.

Meador, Michael A.

English

NASA Technical Reports Server

ELECTRON BEAM CURED EPOXY RESIN COMPOSITES FOR HIGH
TEMPERATURE APPLICATIONS*
CHRISTOPHER J. JANK.E
Oak Ridge Centers for Manufacturing Technology
Oak Ridge National Laboratory**
Oak Ridge, TN 37831-8048
George F. Dorsey
Lockheed Martin Energy Systems, Inc.** *
Oak Ridge, TN 37831-8097
i
/
. )
,/
• y
Stephen J. Havens
Oak Ridge Institute for Science and Education,
Oak Ridge, TN 37831-0117
Vincent J. Lopata
Atomic Energy of Canada Ltd. - Whiteshell Laboratories,
Pinawa, Manitoba, Canada ROE 1LO
Michael A. Meador
NASA Lewis Research Center
Cleveland, OH 44135
Introduction
Electron beam curing of Polymer Matrix Composites (PMCs) is a nonthermal, nonautoclave curing
process that has been demonstrated to be a cost effective and advantageous alternative to
conventional thermal curing. Advantages of electron beam curing include: reduced manufacturing
costs; significantly reduced curing times; improvements in part quality and performance; reduced
environmental and health concerns; and improvement in material handling. In 1994 a Cooperative
Research and Development Agreement (CRADA), sponsored by the Department of Energy Defense
Programs and 10 industrial partners, was established to advance the electron beam curing of PMC
technology. Over the last several years a significant amount of effort within the CRADA has been
devoted to the development and optimization of resin systems and PMCs that match the performance
of thermal cured composites. This highly successful materials development effort has resulted in
a board family of high performance, electron beam curable cationic epoxy resin systems possessing
a wide range of excellent processing and property profiles. Hundreds of resin systems, both
toughened and untoughened, offering unlimited formulation and processing flexibility have been
developed and evaluated in the CRADA program.
*Cooperative Research and Development Agreement (CRADA) No. Y 1293-0233.
**Managed by Lockheed Martin Energy Research Corporation for the U.S. Department of Energy
under contract DE-AC05-96OR22464.
***Managed by Lockheed Martin Energy Systems for the U.S. Departrnent of Energy under contract
DE-AC05- 84OR21400.
1 Paper 4
https://ntrs.nasa.gov/search.jsp?R=19970024959 2020-06-18T00:18:10+00:00Z
Our research has determined that conventional epoxy resins can be cured by exposure to electron
beam radiation as provided by a high energy/power electron beam accelerator to provide materials
with high glass transition temperatures and mechanical properties comparable to thermally cured
epoxies (1-3). A cationic photoinitiator at a concentration of 1-3 parts per hundred of the epoxy
resin is required for this process. These cationic photoinitiators are triaryl sulfonium and
diaryliodonium salts of weakly nucleophilic anions. Diaryliodoniurn salts of the
hexafluoroantimonate anion have been found to be the most effective commercially available
photoinitiators. The cationic photoinitiator decomposes when subjected to irradiation from
ultraviolet light or high energy electrons to produce a Bronsted acid (proton) which catalyzes the ring
opening polymerization of the epoxy group. The weakly nucleophilic anion from the initiator is not
strongly attracted to the cation that is generated, nor does it interfere with the growing polymer chain
(4). Properties of the electron beam cured cationic epoxies include: glass transition temperatures
(Tg's) ranging from 100-400°C (212-752°F), high flexural moduli [up to 4.0 GPa, (580 ksi)], low
moisture absorption (<2%), good toughness obtained by the addition of toughening agents [0.41-0.92
MPam'/q (373-837 psi in i/,); and low-moderate cost of the epoxy resin-photoinitiator compositions.
Several toughened and untoughened compositions were selected for evaluation as composite
matrices. PMCs made from these easily processed resins have exhibited: low shrinkage after
electron beam cure, low void content (0.6-1.8%) and good mechanical properties with IM7 carbon
fiber [0 ° flexurai strengths, 1.71-2.01 GPa (248-292 ksi); 0 ° flexural moduli, 150-196 GPa (21.8-
28.4 msi; and 0 ° interlaminar shear strengths 77-89 MPa (11.2-12.9 ksi)]. Many composite parts
manufactured via hand lay-up, tow/tape placement, filament winding, resin transfer molding (RTM),
and vacuum assisted resin transfer molding (VARTM) have been produced using these materials,
demonstrating their fabrication versatility.
Electron beam processing is potentially more economical than conventional thermal cure processing.
Complex part shapes can be made with inexpensive tooling and part throughput is extremely high.
Since electron beam curing is at near ambient temperatures, inexpensive, lightweight, and disposable
fabrication tools or mold materials such as thermoplastics, foam plastics, plasters, waxes, and wood
can be used instead of metals. Electron beam processing also allows the simultaneous curing of
several different cationic epoxy resin compositions. Thus, a single composite structure fabricated
from electron curable cationic epoxies with different thermal and mechanical properties can be cured
in a single cycle. As electron beam curing can be conducted at room temperature or lower, stresses
are reduced. This factor can be critical in the design of structures such as cryogenic tanks that must
perform at low temperatures. Electron beam curable epoxy resins are friendly to the environment
and greatly reduce the amount of waste generated in composite fabrication processes. No hardener
such as an amine is required - only a few parts per hundred of a relatively nontoxic photoinitiator.
Formulated and prepregged resin have essentially unlimited pot life and shelf life at room
temperature provided that the resins are not exposed to ultraviolet or sunlight.
One particular epoxy resin-photoinitiator composition (designated Electron Beam Resin 8H)
exhibited a very high glass transition temperature after electron beam curing; Tg, 396°C (745°F)
from the peak of the DMA tan delta curve. This resin was extensively evaluated as a matrix resin
for PMCs using Hercules IM7-GP-12K carbon fiber. Unidirectional prepreg of 8H with this fiber
was manufactured by YLA, Inc. of Benicia, California. All test panels (16 plies unidirectional x 30.5
Paper 4 2
cm x 30.5cm) werepreparedusingconventionalay-uptechniques.Intermediatedebulkswere
conductedundervacuumbagpressureeveryfour pliesat roomtemperaturefor 15minutes. The
final debulk and bleed cycle was performed under vacuum bag pressure at 70°C (158°F) for one
hour. The panels were electron beam cured at the Whiteshell Laboratories of Atomic Energy of
Canada Limited (AECL) using the AECL I 10/1 Electron Linear Accelerator. Curing was performed
under vacuum bag pressure while the panels were at room temperature at a dose per pass of 50 kGy
for a total dose of 250 kGy.
In a thermal cure cycle there is a considerable decrease in resin viscosity as temperature increases,
followed by an abrupt increase in viscosity with the onset of gelation. This factor combined with
autoclave pressures may allow poorly laid-up laminates to be well consolidated. Since electron
beam curing occurs at near ambient temperature, there is no viscosity decrease before gelation and
curing. Thus, lay-up technique is critical in obtaining, good laminate properties. To date the best
series of panels had a void volume of 1.77% by acid digestion, with the following room temperature
mechanical properties: 0° flexural strength, 1.99 GPa (288 ksi); 0° flexural modulus, 196 GPa (28.4
msi); 0 ° compressive strength, 1.57 GPa (228 ksi); 0 ° compressive modulus, 149 GPa (21.6 msi);
and 0 ° interlaminar shear strength, 77 MPa (11.2 ksi). Long term aging studies were conducted on
early specimens of these laminates at NASA Lewis Research Center (LeRC). Weight loss in air after
1000 hours at 232°C (450°F) was only 4.25% but 18.4% after 1000 hours at 288°C (550°F).
Mechanical properties were not significantly changed after 1000 hours at 232°C, but noticeably
deteriorated on aging at 288°C.
Future efforts in the area of electron beam cured PMC's for high temperature applications will focus
on improving the quality of electron beam resin 8H laminates and more extensive testing. Research
efforts will also be directed toward the development of electron beam curable polyimides as part of
a project sponsored by NASA LeRC.
References
. Janke, C. J.; Dorsey, G. F.; Havens, S. J.; and Lopata, V. J.: Electron Beam Curing of Epoxy
Resins by Cationic Polymerization. SAMPE International Symposium, vol. 41, 1996, pp. 196-
206.
2. Janke, C. J.; Dorsey, G. F.; Havens, S. J.; and Lopata, V. J.: Toughened Epoxy Resins Cured
by Electron Radiation. SAMPE International Technical Conference, vol. 28, 1996, pp. 877-889.
° Lopata, V. J.; Chung, M.; Janke, C. J.; and Havens, S. J.: Electron Curing of Epoxy Resins:
Initiator and Concentration Effects on Curing Dose and Rheological Properties. SAMPE
International Technical Conference, vol. 28, 1996, pp. 901-910.
4. Crivello, J. V.; Lam, J. H. W.; and Volante, C. N.: Photoinitiated Cationic Polymerization
Using Diaryliodonium Salts. Journal of Radiation Curing, vol. 4, July 1977, pp. 1-16.
3 Paper 4
Acknowledgements
THE EI_EAM CRADA TEAM
• AECL Technologies, Inc.
• Applied Poleramic, Inc.
• The Boeing Company
• Ciba-Geigy Corporation
• E-BEAM Services, Inc.
• Lockheed Martin Aero and Naval
Systems
• Lockheed Martin Energy Systems,
Inc.
• Lockheed Martin Tactical Aircraft
Systems
Nicolet Imaging Systems
Northrop Grumman Corporation
Sandia Corporation
UCB Chemicals Corporation
• Department of Energy
Defense Programs
• YLA, Inc. - Sean Johnson,
Susan Robataille and Steve
Smith
Paper 4 4
Presentation Outline
• Introduction
• Electron Beam Curable Cationic Epoxy Resins
& Composites- Advantages and Highlights
• High Temperature Composite Properties
- Weight Loss
Flexural Properties
- Interlaminar Shear Properties
• Conclusions
• Future Research Areas
Introduction
• Electron Beam Curing is a Very
Fast, Nonthermal, Nonautoclave
curing method that uses High-
Energy, High-Power Radiation
to cure polymer matrix
composites.
5 Paper 4
ADVANTAGES OF PMC ELECTRON BEAM CURING
OVER THERMAL CURING
• Shorter cure times
• Amenable to high production rates
• Lower overall energy requirements
• Reduced thermal stresses in cured part
• Effective with thick PMC parts
• Lower tooling costs
• Reduced environmental, safety, and health concerns
• Improved material handling
• Reduced overall manufacturing costs (25% - 65% Cost Savings vs Thermal
cameo
Paper 4
The CRADA Has Developed Hundreds Of EB
Curable Cationic Epoxy Resin Systems
(Toughened and Untoughened)
_aoxtes
• Bisphenol A Liquid Epoxy Resins
• Bisphenol F Epoxy Liquids
• Epoxy Novola¢ Resins
• Multifunctional Epoxy Resins
• Cycloaliphatic Epoxy Liquids
• Hydrocarbon Epoxies
• Toughened Epoxies
• Flexible Epoxies
• Fusion Solid Epoxies
• Multi-Epoxy Resins (Blends)
• Diluted Liquid Epoxy Resins
• Multifunetional Epoxy Diluents
Cationic Initiators (wl Various Anions)
• Diaryliodonium Salts
• Triarylsulfonium Salts
• Iron Complexes
• Diaryldisulfones
• Triazine Compounds
• Engineering Thermoplastics
• Hydroxy-Containing Thermoplastics
• Reactive Flexibilizers
• Elastomers
• Rubbers
• Undissolved Thermoset Particles
• Undissolved Thermoplastic Particles
• Polyarylates
6
Advantages of Electron Beam
Curable Cationic Epoxies
• Most Commercially Available (Non-Amine Containing)
Epoxies EB Cure
• Unlimited Variety Of Epoxy Resin Systems Can Be
Formulated
• No Hardeners Required (less environmental/health
concerns)
• Indefinite Shelf Life (must be kept away from UV)
• No Oxygen Inhibition Problems During Cure
• Resin System Costs Are Comparable To Thermally
Curable Epoxy Variants
Advantages of Electron Beam Curable
Cationic Epoxies (Resin Properties Only)
Minimal Volatile Emissions During Cure; (< 0.1%)
Wide Range Of T_ (tan delta); 130 to >3950C; (Tg - Tcure) ranged from 100 to >
3700C
Very_ Low Water Absorption After 48 hr. H20 boil; some < 1% most < 2%: vs.
thermal cured epoxies 3-6%
J._y__arJ_dl_; 2 - 3% vs. thermal cured epoxies 4-6% vs. EB cured acrylates 8-
20*
i_eslns Are Tou_henable; RT Ktes ranged from 0.41-0.97 MPa tn°'s vs. 0.90 for
Fiberite 977-3; -1000C Kits surpass RT valu_
Low Total Mass Loss; 0.05-1.00% for resins after vacuum oven aging
@125°C/5days vs. goal of <1% for composites
7 Paper 4
Highlights of EB Curable Cationic
Epoxy Containing Composites
• Many Cat. Epoxies Have Been Successfully Prepr___ged
- Numerous prepregs have been made via solution dip, direct hot melt coating, and
film calendering methods
• Many Cat. Epoxies Have Been Processed Using Several Fabrication Methods
- Many PMC parts have been manufactured via hand lay-up, tow placement, filament
winding, RTM, and VARTM processes
• Void Contents Are Comparable To Autoclave Cured PMCs
- Many PMCs fabricated using hand lay-up and filament winding processes have less
than 1% void contents
• Improved Mechanical Properties Compared To Autoclave Cured PMCs
- PMCs exhibit some mechanical properties exceeding those of Fiberite's, autoclave
cured, 977-2 and 977-3 toughened epoxy PMCs
• Cryogenic & Thermal Cyclin_ Of PMCs Showed Excellent Retention Of Properties
- Mechanical properties of PMCs after cryogenic & thermal cycling were unaffected
and in some cases increased in value
Property_ Com narison Of Electron Beam Cured Vemus Thermal Cured IM71Resin IXI Unidirectional Laminates
/Data Normalized to 62% fiber volume)
Fiber_ 977:2
Resin (Fibente
Systems Marketing
iterature Data
Autoclave
Cure Cured (6 hrs.
Conditions @ 350°F @ 8=_
psi)
VoidVolume, i NotReported%
Tg,*C(Tan
l_lta)
(:3*Rex. Str.,
MPa(ksi)
0 ° Flex, Mod..
GPa (msi)
(3*Comp.Str.,
MPa(ksi)
(3*Comp.,
Mod.,GPa
(msi)
(3*ILSS,MPa
(ksi)
Hot/WetO°
ILSS*,MPa
Iksi_
" 1wk.in H20 @ 1600F,tested@ 2200F
200
1641 (238)
147 (21.3)
1580 (230)
152 (22)
110 (16)
- Fiberite 977-3
(Fiberite
Marketing
Literature Data
Autoclave
Cured (3 hrs. "
@ 355"F @ 85
psi)
Not Reported
190/240
1765 (256)
150 (21.7)
1680 (244)
154 (22.3)
127(18.5)
89 (12.9)
r EB ' EB Resin 3 EB Resin 1
EB Resin Resin 2 41EB Resin 5
8. i !
250 kGy
1.77
396
1986 (288)
196 (28.5)
1565 (227)
149 (21.6)
77 (11.2)
61 (8.8)
150 kGy
O.72
392
2006 (291)
163 (23.6)
79 (11.5)
150 kGy
1.24
232
1793 (260)
163 (23.7)
79 (11.5)
150 kGy
0.64
212
1765 (256)
154 (22.3)
89 (12.9)
150 kGy
1.18
212
1710 (248)
150 (21.8)
77 (11.2)
Paper 4 8
1E+11
Resin 8H
Electron Beam; Dose: 150 kGy
0.14
m¢L
"O
O
1E+10
1E+09
1E÷08
S °
E"
,,,..j--'-
Tan(delta)
0 100 200 300 400
Temperature, C
0.12
0.10
0.08"_
0.06
I,.-
0.04
0.02
0.00
500
WEIGHT LOSS OF ELECTRON BEAM RESIN 8HIIM7
LAMINATES IN AIR
25
= 20u)
0
..I
J_
.__ 15
G)
= 10
Q
L_
a. 5
0
_..__288°C (550°F)
--o- 232oc (450OF)
0 200 400 600 800 1000
Time (hours)
9
I
1200
Paper 4
FLEXURAL STRENGTH OF ELECTRON BEAM RESIN 8HllM7
UNIDIRECTIONAL LAMINATES VERSUS AGING TIME IN AIR-
TESTED AT 25°C
250
°
A
=m
.¢
C
L
u_
m
¢=
¢_
>¢
e
M.
200
150
100
50
0
__o_ Aged at288°C (550°F! .... _T
Bars indicate one standard deviation
I I t I I I
0 200 400 600 800 1000 1200
Time (hours)
FLEXURAL STRENGTH OF ELECTRON BEAM RESIN 8H/IM7
UNIDIRECTIONAL LAM|NATES VERSUS AGING TIME IN AIR
AT 232°C (450°F)
250
Paper 4
r-
r"
IL_
m
L-
X
n
200
150
100
50
0
._,,-- Tested at 25°C
--o- Tested at 232°C (450°F)
____----_..
Bars indicate one standard deviation
I I I I I
200 400 600 800 1000
Time (hours)
0
I0
I
1200
FLEXURAL MODULUS OF ELECTRON BEAM RESIN 8HIIM7
UNIDIRECTIONALLAMINATES VERSUS AGING TIME IN AIR -
TESTED AT 25°C
25
A
m
m
u
"O
O
I
z._
X
i,¢.
20
15
10
5
0 I t t I I I
200 400 600 800 1000 1200
Time (hours)
0
FLEXURAL MODULUS OF ELECTRON BEAM RESIN 8HIIM7
UNIDIRECTIONAL LAMINATES VERSUS AGING TIME IN AIR
AT 232°C (450°F)
25
20
"5 15
"0
0
•_ 10
t_
X
,T 5
0
-,,- Tested at 25°C
-o- Tested at 232°C
Bars indicate one standard deviation
I I I I I
200 400 600 800 1000
Time (hours)
]1
0
I
1200
Paper 4
p.
O_
¢9._¢
lb. v
C
m
E
m
INTERLAMINAR SHEAR STRENGTH OF ELECTRON BEAM
RESIN 8H/IM7 UNIDIRECTIONAL LAMINATES VERSUS AGING
TIME IN AIR - TESTED AT 25°C
15
10
5
0
Bars indicate one standard deviation
-o- Aged at 288°C (550°F)
I I I I I I
0 200 400 600 800 1000 1200
Time (hours)
INTERLAMINAR SHEAR STRENGTH OF ELECTRON BEAM
RESIN 8HIIM7 UNIDIRECTIONAL LAMINATES VERSUS AGING
TIME IN AIR AT 232°C (450°F)
15
.Q
10
C
"_ 5
e-
m
0
Bars indicate one standard deviation
o
_._ Tested at 25°C
-o- Tested at 232°C (450OF)
I I I I I I
0 200 400 600 800
Time (hours)
1000 1200
Paper 4 12
SUMMARY AND CONCLUSIONS
• Electron Beam Resin 8H exhibited a glass transition temperature of 396°C (745°F)
after electron beam cure at room temperature
• Electron Beam Resin 8H/IM7 laminates exhibit good mechanical properties at 25°C
• Weight loss for the laminates is 4.25 and 18.4% after 1000 hours in air at 232°C
(450°F) and 288°C (550°F), respectively
• Mechanical properties of Electron Beam Resin 8H are not affected by aging at 232°C,
but are degraded by aging at 288°C
FOCUS OF FUTURE HIGH TEMPERATURE ELECTRON BEAM
RESIN RESEARCH
• Optimize Electron Beam Resin 8H/IM7 fabrication to maximize mechanical properties
• Rerun aging tests on optimized laminates
• Explore feasibility of electron beam curable polyimides by screening of model
compounds
13 Paper 4



Electron Beam Cured Epoxy Resin Composites for High Temperature Applications

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server