r AGING AND DURABILITY OF HIGH TEMPERATURE ELECTRICAL INSULATION GRANT NO. F496209510396 1 SEPT 1995-31 AUGUST 1999 FINAL REPORT PROJECT MANAGER PRINCIPAL INVESTIGATOR DR. CHARLES Y-C LEE CLARENCE J WOLF AfOSR WASHINGTON UNIVERSITY DTIC QUALITY INSPECTED 3 20000428 045 L
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r
AGING AND DURABILITY OF HIGH TEMPERATURE ELECTRICAL INSULATION
GRANT NO. F496209510396
1 SEPT 1995-31 AUGUST 1999
FINAL REPORT
PROJECT MANAGER PRINCIPAL INVESTIGATOR DR. CHARLES Y-C LEE CLARENCE J WOLF AfOSR WASHINGTON UNIVERSITY
DTIC QUALITY INSPECTED 3 20000428 045 L
REPORT DOCUMENTATION PAGE
Public reporting burden for this collection of information is estimated to average 1 hour per response, in< gathering and maintaining the data needed, and completing and reviewing the collection of information, collection of information, including suggestions for reducing this burden, to Washington Headquarters Se Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget, F
AFRL-SR-BL-TR-00- sources, it of this Sefferson
1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED
FINAL 01 SEP 95 - 31 AUG 99 4. TITLE AND SUBTITLE AGING AND DURABILITY OF HIGH TEMPERATURE ELECTRICAL
INSULATION
6. AUTHOR(S)
Clarence J Wolf
7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)
Washington University St Louis MO
9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)
AFOSR/NL 801 N Randolph St., Rm 732 Arlington VA 22203-1977
5. FUNDING NUMBERS
F49620-95-1-0396
8. PERFORMING ORGANIZATION REPORT NUMBER
F49620-95-1-0396
10. SPONSORING/MONITORING AGENCY REPORT NUMBER
11. SUPPLEMENTARY NOTES
12a. DISTRIBUTION AVAILABILITY STATEMENT
Approved for public release; Distribution unlimited 12b. DISTRIBUTION CODE
13. ABSTRACT (Maximum 200 words) The objectives of this program are to investigate the long-term aging processes which occur in typical high temperature polymeric systems. The primary system of interest is irradiated ethylene tetrafluorethylene (ETFE) coated over silver plated copper. The two specific goals of this research are: (1) To determine thermal oxidative degradation of a high temperaure polymer such as ETFE in the presence of metal surfaces, and (2) To determine the effect of the polymer on the overall stability and morphology of the metal surface. The kinetics of the ETFE degradation process as a function of radiation dose (used to cross-link the polymer, thereby enhancing its mechanical properties), temperature and catalytic metal surface were studies by several different thermal oxidative methods. Kinetic parameters, temperature coefficients (i.e., activation energies), and degradation rates as a function of temperature, radiation dose, and catalytic surfaces were investigated. Analytical procedures were used to determine the most accurate and reproducible method for kinetic analysis. The diffusion and subsequent surface reactions of copper through a thin silver plate (silver plated copper conductor) were studied by scanning Auger electron and optical spectroscopies. The kinetics of the copper diffusion are evaluated in order to correlate changes in the polymer degradation reactions with the change in surface chemistry and morphology of the metal. The initial silver surface slowly changes to an oxidized copper surface of the general stochiometry Cu 27 o as the copper diffuses through the silver layer. The diffusion is more rapid and the copper surface layer is thicker when the conductor is covered with polymer. In this case the ratio of copper to oxygen at the surface is approximatley 3:1. The solubility of 14. SUBJECT TERMS
17. SECURITY CLASSIFICATION OF REPORT
UNCLASS
18. SECURITY CLASSIFICATION OF THIS PAGE
UNCLASS
19. SECURITY CLASSIFICATION OF ABSTRACT
UNCLASS
15. NUMBER OF PAGES
54 16. PRICE CODE
20. LIMITATION OF ABSTRACT
Standard Form 298 (Rev. 2-89) (EG) Prescribed by ANSI Std. 239.18 Designed using Perform Pro, WHS/DIOR, Oct 94
r Aging and Durability of High Temperature Electrical Insulation
Grant No". F496209510396 (lSept 1995-31 Aug 1999)
Project Manager Dr. Charles Y-C Lee
AFOSR
Clarence J. Wolf Washington University
St. Louis, Mo
Executive Summary
The objectives of this program arc to investigate the long-term aging processes
which occur in typical high temperature polymeric systems. The primary system of
interest is irradiated ethylene tetrafluorethylene (ETFE) coated over silver plated copper.
The two specific goals of this research arc:
• To determine thermal oxidative degradation of a high temperature polymer such as
LTFE in the presence of metal surfaces, and
• To determine the effect of the polymer on the overall stability and morphology of the
metal surface.
The kinetics of the ETFE degradation process as a function of radiation dose (used to
croN-hnk the polymer, thereby enhancing its mechanical properties), temperature and
eat.ilvtie metal surface were studied by several different thermal oxidative methods.
Kinetic parameters, temperature coefficients (i.e. activation energies), and degradation
rates as a function of temperature, radiation dose, and catalytic surfaces were
investigated. Analytical procedures were used to determine the most accurate and
reproducible method for kinetic analysis.
r The diffusion and subsequent surface reactions of copper through a thin silver
plate (silver plated copper conductor) were studied by scanning Auger electron and
optical spectroscopies. The kinetics of the copper diffusion are evaluated in order to
correlate changes in the polymer degradation reactions with the change in surface
chemistry and morphology of the metal. The initial silver surface slowly changes to an
oxidized copper surface of the general stochiometry Cu270 as the copper diffuses through
the silver layer. The diffusion is more rapid and the copper surface layer is thicker when
the conductor is covered with polymer. In this case the ratio of copper to oxygen at the
surface is approximately 3:1.
The solubility of organic fluids, carbon disulfide and toluene into another model
syMcm. polyphenylene sulfide, was investigated. The effect of temperature, morphology
ar.J pre-sorption annealing on the transport process was studied.
r Appendix I: Support Personnel
Graduate Students Jonathan Elders Dept of Chemical Engineering Washington University St. Louis, MO 63130
Chris Long Dept of Chemical Engineering Washington University St. Louis, MO 63130
Other Researchers
1. DanWaddill Professor Dept of Physics and Materials Science University of Missouri - Rolla Rolla, MO
2. Sean McKinney Department of Material Sciences University of Missouri - Rolla Rolla, MO
3. Bernie Sunier Department of Material Sciences Washington University 'o'
4. Angela Aiduck (Graduated) Department of Material Sciences Washington University St. Louis, MO 63130
5. Enrique Farfun (Graduated) Department of Chemical Engineering Washington University St.Loufs.MO 63130
5. Cynthia Chew Department of Chemical Engineering Washington University St. Louis, MO 63130
6. Scott Hager (Graduated) Department of Chemical Engineering Washington University St. Louis, MO 63130
Appendix II: Publications
1. C.J. Wolf, HJ. Brandon, V.L. Young, K.U. Jerina and A.P. Srivastave, "Chemical, Physical and Mechanical Analysis of Explanted Breast Implants," Immunology ofSilicones, M. Potter and N.R. Rose Eds., Springer Verlag, New York, 1996, p 25.
2. Wolf CJ, Brandon JH, Jerina KL, Young VL. "Long-Term Aging of Implanted Silicone/Silica Composite Breast Implants." Proceeding, Eleventh International Conference on Composite Materials, Gold Coast, Queensland, Australia: ed. M.L. Murray, p 467 (1998).
3. "Thermo-Oxidative Degradation of Ethylene-Tetrofluorethylene," J.P. Elders and CJ. Wolf, 3rd National Graduate Research Polymer conference, 21-24 June 199S, University of Akron Polymer chemistry Division (ACS), pp 9-15.
4. H.J. Brandon, CJ. Wolf, V.L. Young and K.L. Jerina. "Effect of Surgical Implantation on the Local Shell Properties of SILASTIC®II Silicone Gel Breast Implants," J. Biomatl. Sei. (Polym. Ed.) in press.
5. Brandon, HJ, Peters, W., Young, V.L, Jerina, K.L., Wolf, C.J., and M.W. Schorr, "Analysis of Two Dow Corning Breast Implants Removed After 28 Years of Implantation," Aesthetic Surgery, Jan/Feb, 1999.
6. Brandon, HJ, Young, V.L, Jerina, K.L. and Wolf, CJ, "Effect of Implantation Surgery on the Average Strength Properties of Silicone Gel Breast Implants," Aesthetic Surgery, May/June, 1999.
7. Brandon. HJ. Jerina, K.L., Wolf, CJ, and Young, V.L, "Ultimate Strength Properties of Control and Explanted SILASTICeO and SILASTIC*! Silicone Gel-Filled Breast Implant Shells," Aesthetic Surgery Journal, Sept/Oct., 1999.
t
N Brandon. HJ, Jerina, K.L., Wolf, CJ, and Young. V.L, "Ultimate Strength Properties of Control and Explanted SILASTIC^II Silicone Gel Breast Implant Shells" Aesthetic Surgery Journal, Mar./Apr. 2000.
9. Brandon, HJ, Young, V.L, Jerina, K.L. and Wolf, CJ, "SEM Characterization of Surgical Instrument Damage to Breast Implants," Submitted to Plastic and Reconstructive Surgery.
Book Reviews for ACS (Appear in JACS)
1. Resins for Coatings: Chemistry, Properties and Applications. D. Stöye and W. Frectay (Hanser-Gardner: Cincinnati, 1996).
2. Hydrocarbon Resins, R. Mildenberg, G. Collin and M. Zander (Wiley-VXH; New York 1997).
Publication supported by AFOSF
1. Environmental Stress Deformation of Poly (ether ether ketone), A.P. Srivastour, N. Depke, and C.J. Wolf, J. of Appl. Polym. Sei. 66 725-731 (1997).
2. Thermo-Oxidative Degradation of Irradiated Ethylene Tetrafluorethylenes, in Oxidative Behavior of Materials in Thermal Analytical Techniques, Eds. A.T. Riga and G.H. Patterson STP 1326 ASTM, 1997 pp. 116-127.
3. Sorption Toluene into Low Temperature Annotated Polyphenylene Sulfide, Mo. J. Undergrad Chem. Res. 7 45-55 (1998/1999).
4. C. J. Wolf and C. Chew. "Sorption of Toluene in Polyphenylene Sulfide (PPS)," J. Polym. Sei. (Phys. Ed.) (submitted).
5. C.J. Wolf. "Sorption of Carbon Disulfide in Polyphenylene Sulfide (PPS)," J. Polym. Sei. (Phys. Ed.) (submitted.)
Asing and Durability of High Temperature Electrical Insulation Grant No". F496209510396
(lSept 1995-31 Aug 1999)
Final Report
Clarence J. Wolf Washington University
St. Louis, Mo
1.0 Summary
The primary objectives of this program are to determine the long-term aging
processes which occur in typical high temperature polymeric systems. Of particular
interest is a determination of the factors which control the long-term durability of
electrical insulation systems. In a separate, but related series of experiments, we have
shown that the primary mode of failure of fluorinated thermoplastic co-polymers used as
elect! ical insulation is stress cracking. Furthermore, we have observed that the cracks
c;i:i be directly correlated with the thermal degradation of the insulation. Other polymers
exhibit a different critical mode of failure, for example the polyimide, pp' diphenylene
o\uie pvromellitimide (commercially sold by DuPont as Kapton") cracks when stressed
in the presence of water, i.e. stress hydrolysis. (1) The particular system of interest in
this s:ud> is irradiated ethylenc tetrafluoroethylene (ETFE) over silver plated copper.
The two specific goals of this research are:
• To determine thermal oxidative degradation mechanism of high temperature polymer
such as ETFE in the presence of metal surfaces, and
• To determine the effect of the polymer on the overall stability and morphology of the
metal surface.
The kinetics of the ETFE degradation process as a function of radiation dose (cross-
linked polymer), temperature and catalytic metal surface were studied by several different
methods. Kinetic parameters, temperature coefficients (i.e. activation energies), and
degradation rates as a function of temperature, radiation dose, and catalytic surfaces were
investigated. A combination of physical analytical methods, including'ATR-FTIR, TGA,
DSC, and GC/MS were used to study the polymer.
The effect of the polymer on the metal surfaces and the subsequent surface
reactions of copper through a thin silver plate (silver plated copper) were studied by
scanning Auger and scanning electron microscopy (SEM). The initial silver surface
slowly changes to an oxidized copper surface of the general stochiometry Cu, 70 as the
copper diffuses through the silver layer. The new surface layer has a catalytic effect upon
the decomposition of the overlaying polymer.
The diffusion and solubility of two penetrants, carbon disulfide and toluene, into
poi\ phenvlenesulfide (PPS) were investigated. PPS composite is a tough material
prj-ciulv used in the nose of commercial aircraft. The effects of temperature,
nv.'rrhologv. and annealing on the transport process were investigated. The data suggest
th.;: the voids/channels (free volume) formed during solvent induced crystallized are
.sm.tiiei liian 92.-V but larger than 49 .V and may be the rate determining factor in the
trailspe:; process.
2.0 Introduction
The use of polymers and polymeric materials in critical components of both
military and commercial aerospace systems is expanding rapidly. These materials have
outstanding physical and chemical properties and their full potential has not been utilized.
One of the major limitations of these materials is a lack of knowledge about their long-
term properties (durability) in a hostile environment. Thus, the determinations of their
lifetime, or aging characteristics, is an area of immediate concern. The prediction of the
aeine process is particularly difficult for new materials designed for the harsh complex
aerospace environment. The high level of sophistication of modern aircraft requires a
deep understanding of the effects of the environment on the operating system. One of the
major areas of concern is the electrical system of the aerospace vehicle. Recent tragedies
sue cost that electrical insulation particularly with regard to cracking and flaking, may be
the Achilles heel of fly-by-wire aircraft.
The high level of sophistication in modern aircraft electronic systems requires
!.>:r_' term protection from a harsh operating environment. Modern aircraft require miles
oi electrical wiring to connect the various aircraft components. For example, smaller Air
Force aircraft, such as the F-15 Eagle or F-16 Falcon, require more than 100,000 feet
130.00'.» in) of electrical wiring. Due to the tight demands on space, weight, energy and
maintenance cost in aircraft of this high degree of sophistication, the insulation must be
lightweight, have excellent dielectric properties, and must maintain thermal stability at
high temperatures for a long period of time.
In addition to the high temperature requirements, the wire system must remain
flexible at all operating conditions. As a general class of compounds, thermoplastic
resins exhibit many desirable properties, and one such resin system, irradiated
ethylenetetrafluoroethylene is presently being extensively used in aerospace wiring
systems. This is an extremely complex system, consisting of a semi-crystalline
thermoplastic resin which is irradiated with high-energy elections to enhance its
mechanical properties; in addition it contains several additives to minimize oxidation and
maximize flame resistance. This complex system is placed in direct contact with an
active metal, the conductor (silver coated copper), and maintained at elevated
temperature for long periods of time. Aerospace wiring systems have a design goal of
10.000 hours at 200°C! The aging of a wire system is a complex phenomenon in which
an organic polymer is in direct contact with a metal surface, the conductor. Many
electronic systems which utilize circuit boards encounter a similar problem, i.e. organic
polymer in contact with an active metal surface for an extended time period at elevated
temperature.
The ETFE system is of particular interest for two reasons:
1) it comprises the basic part of the new, so-called "hybrid," insulation of use on
main modern Air Force and Navy aircraft, and
2) it is a semi-crystalline thermoplastic resin system which is cross-linked by
electron irradiation.
Therefore, we have material which has great practical use, a "high temperature," semi-
cry.stalline, cross-linked thermoplastic in direct contact with a silver/copper metal surface.
Since ETFE is a semi-crystalline thermoplastics resin, we extended our studies to
another thermoplastic polymer, i.e. polyphenylenesulfide, PPS. PPS is also considered a
high performance thermoplastic resin which has physical properties similar to
polyetheretherketone (PEEK). In fact PPS composite (E-glass fibers) is a candidate for
use on the nose of the Airbus Industries A-340 commercial jet. The melting point of PPS
is approximately 285°C and its T£ is approximately 85°C. PPS, like PEEK, can be
obtained in either the amorphous or semi-crystalline state and exhibits solvent induced
crystallization in the presence of a wide variety of solvents. We were particularly
interested in the transport properties of the organic fluids, toluene and carbon disulfide,
into PPS. Areas of particular concern were 1) solubility, 2)rates of sorption, 3)
Observed both in literature spectra and in description of Pirozhnaya and Tarutina. J. Appl. Spectroscopy 34 539-541 (19S1). Experimental unaged ETFE spectra had weaker C-H stretching bands
' Time substracted spectra peaks Explanation = 4000 - 3600 (m, broad) OH • 29S0. 2960. 2890 (m) CH stretch, seen in 290C, 21 hr samples ; 1700- 1500 (m, broad) Carbonyls (an overlay of several in 270C,
1. Clarence J. Wolf and R.S. Soloman, "Environmental Degradation of Aromatic Polyimide-insulated Electrical Wire," IEEE Trans. Elec. Insulation \9, 265 (1984).
2. J.H. Flynn and L.A. Wall, "Thermal Analysis of Polymer by Thermogravemetric Analysis," J. Res. Nad. Bur. Stand., Ser. A 70 (6) 487-523 (1966).
3. J.H. Flynne "Aspects of Degradation and Stabilization of Polymers," Chap. 12 pp. 573-603, H.H.G. Jellinck, ed. Elsevier, Amsterdam, 1978.
4. C.J. Wolf, S.C. Hager, and N.P. Depke, "Thermo-Oxidative Degradation of Irradiated Ethylene Tetrafluorethylenes," in Oxidative Behavior of Materials in Thermal Analytical Techniques," Eds. A.T. Riga and G.H. Patterson STP 1326 ASTM, 1997 pp. 116-127.
1 Clarence J. Wolf, J.A. Bornmann, and M.L. Gurpon, "The Absorption of Organic Liquids in Poly (Aryl-Ether-Ether-Ketone) [PEEK]" J. Polm. Sei. 13: Polym Phys. 29 1533-1539(1991).
7. C.J. Wolf and J.A. Bornmann, "Differential Scanning Coloremetry (DSC) to Determine Crystallinity in PEEK," Soc. Adv. Mater. Proc. Eng., 34, 1167 (1990).
35
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FIGURE 1. Fractional weight loss (1-a) remaining as a function of
time for the thermal degradation of irradiated ETFE.
FIGURE 2. Percent weight loss for the thermal-oxidative degradation (260°C) of wire as a function of time and radiation dose.
37
100 VOW
1000 2000 3000 Time (min)
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FIGURE 3. Weight loss as a function of time for the isothermal degradation of ETFE irradiated to a total dose of 4S MRads.
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CZlZr*"\ SPUTTER TIME (min.)
7. Auger sputter profile from an imaged sample of silver plated copper irradiated to a total dose of 48 MRads.
42
c
o
SPUTTER TIME fmiiO
S. Auger sputter profile of a silverplated copper sample irradiated to a total dose of 4S MUads and aged at 250*C for 1S1 hours.
43
Silver Short Term Profiles
o CD
0 *5*b
aged at o aged at
+ aged at
0 aged at
X
aged at D aged at
dashed line - aged at
solid line aged at
48 MRad wire 240C for 60 hrs
48 MRad insulatiotji 240C for 60 hrs
6 MRad wire 240C for 60 hrs
6 MRad insulation- 240C for 60 hrs
48 MRad wire 240C for 30 hrs
48 MRad insulatiotfi 240C for 30 hrs
48 MRad insulatiotji 240C for 30 hrs
48 MRad wire 240C for 30 hrs -
1000 1500 2000 2500 depth(nm)
3000 3500 400(
9. Comparison of auger sputter profiles from insulation and wire aged at different oxidizing conditions.
44
FIGURE 10. SEM photomicrograph of conductor showing silver plate dcbonding from copper substrate. Sample was aged with an ETFE overlay for 20 hours at 270'C.