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r 4

STUDIES OF MOLECULAR PROPERTIES OF POLYMERIC M1Aerospace Environmental Effects on Three Linear

Wynford L. Harries (Principal InvestigatorHeidi R. Ries, Cynthia A. Bradbury,

Stephanie L. Gray, and William D. Collini

Department of PhysicsSchool of Sciences and Health Professions

Old Dominion UniversityNorfolk, Virginia 23508-0369

and

Sheila Ann T. Long and Edward R. Long, Jr.

National Aeronautics and Space AdministrationLangley Research Center

Hampton, Virginia 23665-5225

;NASA-TH-87532) STUDIES OF NCLECULAR N86-15391PROPERTIES OF ECLYHERIC MATERIALS: TBRU tAEROSPACE ENVIRCRIENTAI EfFECIS GN THREE N86-15353LINEAR POLYMERS Final Techoical Report, 1 UnclasNot. 1984 - 31 Gct. 1585 (NASA) 42 p G3/27 03170

Final Technical ReportFor the period November 1, 1984, through October 31, 1985

Prepared underNASA Cooperative Agreement NCCl-90

December 1985

r•

^ AtPt , ^'^

9 • ♦•

-ii-

STUDIES OF MOLECULAR PROPERTIES OF POLYMERIC MATERIALSAerospace Environmental Effects on Three Linear Polymers

Wynford L. Harries, Heid R. Ries, Cynthia A. Bradbury, •Stephanie L. Gray t , and William D. Collins

Department of Physics

Old Dominion UniversityNorfolk, Virginia 23508-0369

and

Sheila Ann T. Long and Edward R. Long, Jr.National Aeronautics and Space Administration

Langley Research CenterHampton, Virginia 23665-5225

ABSTRACT

The development of crystal handling techniques for reflection

infrared spectroscopy and methods for the fabrication and testing

of tensile specimens are discussed.

Data from mechanical, AC and DC electrical, and electron

paramagnetic resonance studies conducted to determine the effects

nnof 0.1-MeV and 1.0-MeV electron radiation on Mylalo, Kapto-A—, Ulteat°',

and metal-doped Ultem are presented. Total doses ranging from 1 X 108i

cads to 1 X 10 10 cads and dose rates from 5 X 107 rads/hr to 1 X 109

1

rads/hr were employed. i;+

The results of a study on the effects of aircraft

service-environment fluids on Ultem are also reported. The weights

and mechanical properties of Ultem were evaluated before and after

exposure to water, JP4, Skydroilt, an antifreeze, and a paint

stripper.

lPresently attending the School of Engineering and Applied Science,University of Virginia, Charlottesville, Virginia.

2Presently attending the School of Engineering, Virginia

Polytechnic Institute and State University, Blacksburg, Virginia.

Cti

-iii-

Acknowledgement

The authors wish to thank W. S. Slemp and R. M. Stewart, both ofthe NASA Langley Research Center, for providing the 1.0-MeV electronbeam. The authors also wish to acknowledge Dr. C. K. Chang ofChristopher Newport College and Dr. J. W. Wilson of the NASA LangleyResearch Center for calculating the dose in these materials resulting

from the electron beam.

-iv- I

• f

TABLE OF CONTENTS

Page

LIST OF TABLES iv

LIST OF FIGURES v

I. INTRODUCTION AND PURPOSE 1

II. DEVELOPMENT OF EXPERIMENTAL APPAFATUS AND TECHNIQUES 2

A. DC Resistivity Measuremerzs 2

B. Multiple Internal Reflection Infrared Spectroscopy 2

C. Mechanical Testing Techniques 4

III. SPACE ENVIRONMENTAL EFFECTS 5

A. Mylar 5

B. Kapton 6

C. Ultem 7

D. Metal-Doped Ultem 9

IV. AERONAUTICAL ENVIRONMENTAL EFFECTS 9

V. PAPERS 11

REFERENCES 11

APPENDIX A 34

LIST OF TABLES

Table Page

1. Mechanical data for 10-mil Mylar with 1.0-MeV electron 5radiation

i

-v-

LIST OF FIGURES

Figure Page

1. Experimental arrangement for direct current 12

resistivity measurements.

2. Schematic of multiple internal reflection accessory 13

for surface IR measurements.

3. Infrared spectra for Mylar: (a) transmission and 14

(b) reflection.

4. EPR spectra of Mylar before and 30 min. after exposure 15

to 1.0-MeV electron radiation.

5. EPR radical density in Mylar before and 30 min. after 16

exposure to 1-MeV electron radiation.

6. Decay of EPR signal from Mylar after exposure to 1.0-MeV 17 i

electron radiation, dose rate - 5 X 10 reds/hr.

7. Decay of EPR organic radical density in Mylar after 18

expome to 1.0-MeV electron radiation, total dose =5 X l0 rads and dose rate - 5 X 10 reds/hr.

8. Dissipation factor curves and glass transition temperatures 19for Mylar before and after ex osure to 1.0-MeV electron

radiation, dose rate - 5 X 10 reds/hr.

9. Glass transition temperature for Mylar vs. exposure toi

20 '.,.1.0-MeV electron radiation, dose rate - 5 X 10 7 rads/hr. '':

10. Dissipation factor curves and glass transition temperatures 21

for research -grade Kapton before and after exposure to1.0-MeV electron radiation, dose rate - 5 X 10 7 rads/hr.

11. EPR radical densities in Mylar, Ultem, and Kapton, before 22and 30 min. after exposure to 1.0-Mev electron radiation,dose rate - 5 X 10 7 rads/hr.

12. Decay of EPR signal from Kapton after e^Cposure to 1.0-MeV 23electron radiation, total dose - 5 X 10 rads and doserate - 5 X 10 cads/hr.

13. Electrical conductivities of Mylar, Ultem, and Kapton, 24before and 30 min. after exposure to 1.0-MeV electronradiation, dose rate - 5 X 10 rads/hr.

L

kI

-vi-

14. Decay of EPR radical density in Kapton after exposure

to 1.0-MeV electron raiation, total dose 5 X10 rads

and dose rate = 5 X 10 rads/hr.

15. Electrical conductivity of Kapton as a function of timeafter exposure to 1.0-MeV electron radiation, total dose5 X 10 rads and dose rate = 5 X 10 rads/hr.

16. Decay of EPR signal from Ultem after exposure to 1.0-MeV

electron radiation, total dose = 5 X 10 rads and doserate = 5 X 10 rads/hr.

17. Decay of EPR signal from Ultem, dose rate = 1 X 10 9 rads/hr. 28

18. Decay of EPR radical density in Ultem, dose rate = 1 X 10929rads/hr.

19. Decay of EPR phenoxyl radical density in Ultem, dose rate 301 X 109 rads/hr.

20. EPR radical density in Ultem, 3 minutes after exposure 31for various total doses, dose rate - 10 9 rads/hr.

21. EPR radical densities in Ultem, 3 minutes after exposure 32for two different dose rates.

22. EPR organic radical densities in metal-doped Ultem 33aftep exposure to 100-keV ele§trop radiation, total dose= 10 rads and dose rate = 10 rads/hr.

25

26

27

-T .4717 / _ 1 _^_^. JYi

T+71 i

N86-15392

STUDIES OF MOLECULAR PROPERTIES OF POLYMERIC MATERIALS

Aerospace Environmental Effects on Three Linear Polymers

I. INTRODUCTION AND PURPOSE

The purpose of this work is to study aerospace environmental

effects on polymeric materials. The polymers under study are being

considered for use ae structural materials for spacecraft and advanced

aircraft. It is necessiiry to understand the durability of these

polymers to the environment in which they are to be used.

In the geosynchronous space environment, materials are constantly

being bombarded by electron radiation. The interaction between the

material and the radiation causes changes in the molecular structure.

These changes may alter the functional properties of the material.

Electron beams with energies of 0.1-MeV and 1.0-MeV are used to

E

irradiate the polymeric specimens. After the irradiation, mechanical

tests, electron paramagnetic resonance spectroscopy, AC and DC

electrical measurements, and internal reflection infrared spectroscopy

are employed in order to relate the changes in the molecular properties

to the changes in the functional properties.

In the aircraft service environment, the structural components will

be exposed to many fluids that may cause a degradation of the polymeric

component of the fiber/polymer composite. A study of the degradation

effects of aircraft fluids on a polyetherimic'e has been conducted.

After exposure, tensile, weight, and dimensicnal property measurements

-2-

are performed and comparisons are made to the baseline data.

In this report, the results achieved to date under the ongoing NASA

Cooperative Agreement NCCl-90 are presented.

II. DEVELOPMENT OF EXPERIMENTAL APPARATUS AND TECHNIQUES

A. DC Resistivity Measurements

Equipment and techniques for making DC resistivity measurements on

thin polymer samples were developed, as reported in detail in the

Progress Report l for the period November 1, 1984, through May 1, 1985.

The DC resistivity measurements are made in accordance with ASTM D 257.

Palladium/chromium, 2.75-inch diameter electrodes are sputtered onto the

specimens, with a guard ring provided on the low voltage side. A

Keithley 247 High Voltage Supply delivers the 500V voltage required, and

a Keithley 619 Electrometer/Multimeter controlled by a Hewlett Packard

9816 computer is used for the current measurements (Figure 1).

B. Multiple Internal Reflection Infrared Spectroscopy

Multiple internal reflection infrared spectroscopy (MIRIR) is a

technique to analyze materials too thick to produce suitable

transmission spectra. It utilizes a MIR accessory and a regular IR

instrument. This accessory includes a mirror assembly that directs the

radiant energy through a crystal (Figure 2). The crystal produces

multiple internal reflections, the number being dependent upon the angle

of entry of the electromagnetic wave. Even in the case of total

reflection, electromagnetic fields exist on t1

•3-

crystal. If a sample is placed against the crystal face, it can

{ . •

interact with this field, absorbing energy at characteristic

frequencies. A reflection spectrum that is almost identical to a

transmission spectrum of the same sample is obtained (figure 3).

The crystal used is a KRS5 (thallium bromoiodide, ionic

coordination lattice) 45 0 trapezoid. To be compatible with the

materials currently being studied, its index of refraction must be

higher. The crystal does, however, mar readily with handling. To

increase its usable life, a holder was developed to eliminate the

movement of the mount pieces against the crystal when mounting a

specimen. This reduces the scratching of the crystal surface. A

proposed NASA Tech Brief that fully describes this holder is being

prepared.

A key parameter in the reproducibility of the spectra is the

contact between the sample and the crystal. Contact is accomplished by

pressure supplied by three screws. To insure that this pressure is the

same each time, a torque screwdriver with one inch-pound resolution was

used.

Studies were conducted to compare reflection versus transmission

spectra. They are being analyzed using a ratio of peak intensities.

This technique eliminates the effect of any changes in peak intensity

due to the sample handling procedure and, therefore, enhances the

sensitivity with which changes occurring due to radiation damage are

detected.

-4-

C. Mechanical Testing Techniques

Mzthods for the fabrication of tensile specimens from neat-resin

sheet stock with thicknesses from 10 to 20 mils were evaluated. The

method for evaluation was visual inspection followed by tensile testing

and comparison of the data to those previously determined from 3-mil

specimens. Two methods were investigated: slicing and shearing.

Slicing was not found to be practical for the hand-powered method

previously used for the 3-mil sheet stock. Power methods, such as

motor-driven and ultrasonics, were considered, but have not been

evaluated. The shearing method was found to be acceptable, unless the

shearing blade, are nicked. The consequence of nicked blades was

jagged-edged specimens that failed prematurily.

A fixture for machining compression shear specimens from pultruded

constant-cross-section stock was designed and fabricated. This fixture

was designed to be used with a small table •aw. A fixture was also

fabricated for holding shear specimens while they were tested for shear

properties in the compression mode. The support fixture was evaluated

using shear specimens fabricated from pultruded stock. This also

yielded preliminary information about the shear properties of

pultruded composites. The date from the study will be a part of a

larger evaluation of the mechanical properties of rultruded

graphite/epoxy and KevlaA/epoxy materials to be conducted in the near

future.

•5-

III. SPACE ENVIRONMENTAL EFFECTS

The effects of electron radiation on various properties of Mylate,

lCaptotP, Ultes1, and metal-doped Ultem were studied. The Mylar, Kapton,

and Ultem data will be included in a presentation that is currently

being proposed for the 1956 Regular Meeting of the Division of High

Polymer Physics of the American Physical Society.

A. Mylar

Castings of 10-mil Mylar, a polyethylene terephthalate)

manufactured by Dupont, were exposed to 1.0-MeV electrons for total

doses of 1 X 109 rads and 5 X 10 9 reds. The dose rate was 5 X 107

rads/h*.

In each case, mechanical measurements were made. Decreases in the

ultimate stress, modulus, and total elongation-to-failure were observed

(Table I).

TABLE I. MECHANICAL DATA FOR 10 —MIL MYLARWITH 1.0—MEV ELECTRON RADIATION(Dose Rate - 5 X 107 rads/hr)

Dose, Ultimate stress, Modulus, Elongation,rods psi psi •

0 27135 458578 1821 X 10 9 14624 226295 715 X 10 9 7139 234561 2.2

s .

e

-6-

The DC resistivity was observed to decrease from 2.1 X 10 17 ohm-cm

to 1.5 X 1017 ohm-cm for a total dose of S X 109 reds. The measurements

at 1 X 109 rads were inconclusive.

EPR measurements indicated over two orders of magnitude increase in

the organic radical density after the irradiation (Figures 4 and 5).

There is little difference between the results for 1 X 10 9 rads and

5 X 109 rads. However, this is probably due to an unexpected shutdown

of the electron accelerator that resulted in a 72-hour interruption in

the 5 X 109 rad exposure, during which time radical decay took place.

Post-irradiation decay in air at room temperature of the radical density

occurred (Figures 6 and 7).

Measurements of the glass transition temperature (Tg) were

made using an AC electrical technique. In this technique, the

dissipation factor is measured as a function of the temperature. By

convention, the Tg is the temperature at the intersection of the tangent

lines to the dissipation factor curve in the first region of major

increase in the dissipation factor. The Tg was observed to decrease

with increased radiation dose (Figures 8 and 9). The dissipation factor

also changed with dose.

B. Kapton

Films of 3-mil research-grade Kapton, a polyimide manufactured by

Dupont, were exposed to 1.0-MeV electrons at a dose rate of

5 X 10 7 rads/hr for a total dose of 9.5 X 10 9 rads. The glass

transition temperature decreased upon irradiation from 388 oC to 366 oC

(Figure 10). No significant changes in the magnitudes of the

dissipation factor, the capacitance, or th_ impedance were observed at

10 kHz from room temperature up to 500 oC. •

Films of 3-mil standard-stock Kapton were exposed to 1.0-MeV

electrons at a dose rate of 5 X 10 7 rads/hr for a total dose of

5 X 109 rads. After the irradiation the radical density increased by

more than an order of magnitude (Figure 11). The EPR signal was

observed to decay upon exposure to air at room temperature (Figure 12).

The DC conductivity was observed to increase by nearly five orders of

magnitude (Figure 13). Both the EPR radical density and the DC

conductivity increases were observed to decay in time with two distinct

decay rates (Figures 14 and 15). These decay studies were conducted in

air at room temperature. A theory that relates the DC and the EPR

results for decay is currently being developed.

C. Ultem

Exposures of 3-mil and 20-mil Ultem, a polyetherimide manufactured 1

by General Electric, were made using 1.0-Mev electrons at a dose rate of r

5 X 107 rads/hr. No significant changes in the Tg, the dissipation

a. ti

afactor, the capacitance, or the impedance were observed using 3-mil

Ultem for a total dose of 5 X 10 9 rads.

A slight increase in the DC conductivity was found for both

thicknesses of Ultem for a total dose of 5 X 10 9 rads (Figure 13). No

significant change in the DC conductivity was observed for the 3-mil

Ultem for a total dose of 1 X 109 rads. Possible explanations for the

vastly different responses of the DC conductivity to irradiation for

Ultem and Kapton are being considered.

-4.

i

-8-^

3

The EPR radical density increased by over three orders of magnitude i

for each thickness of Ultem (Figure 11). This induced radical density

increase in Ultem was observed to decay much more rapidly ( Figure 16)

than that in Kapton.

Films of 3-mil Ultem were exposed to 100-keV electrons at a

dose rate of 1 X 109 reds/hr for a total dose of 5 X 10 9 reds. No

Lisignificant change in the Tg was observed.

As discussed in detail in Appendix A of the Progress

Report l , EPR radical decay studies at room temperature in vacuum of

3-mil Ultem exposed to 100-keV electrons for a total dose of 2.5 X 108

rads were conducted (Figures 17 and 18). The total EPR radical signal

was stored on a computer; and the portion of the signal attributable to

the phenoxyl radical was separated from the total, using the known

characteristics of the phenoxyl radical. The phenoxyl decay curve thus

obtained is shown ( Figure 19).

The EPR radical density in 3-mil Ultem was determined as a

function of total dose over the range from 1 X 108 to 1 X 10 10 rads

(Figure 20). The dose rate was 1 X 10 9 reds /hr using 100-keV electrons.

E I A preliminary dose rate study was conducted using 3-mil Ultem film

irradiated with 100-keV electrons for a total dose of 1 X 10 8 reds

(Figure 21). Little difference was observed between the EPR radical

density produced using 1 X 108 reds/hr and that produced using 1 X 109

reds/hr.

E

ia •.

-9-

D. Metal-Doped Ultem

The effects of 100-keV electron irradiation on Ultem doped with

cerium trifluoride were also considered. This material is currently

under development by the Virginia Commonwealth University. No organic

radical signal was distinguishable from the metal signal background

before the irradiation. The EPR organic radical density after the

irradiation with a total dose of 1 X 10 9 reds is shown (Figure 22). The

infrared and UV-Vis spectra before and after radiation were also taken.

These data are currently being analyzed.

IV. AERONAUTICAL ENVIRONMENTAL EFFECTS

A series of three-month-soak exposures and tests to evaluate the

effects of aircraft fluids on the tensile, weight, and dimensional

properties of 3-mil specimens of Ultem were performed. The fluids were

water, JP4 (a jet fuel), and Skydro^ (a hydraulic fluid manufactured by

Monsanto). The data from this experiment indicated that the hydraulic

fluid had the most significant effect, in that it caused extensive

embrittlement of the Ultem. The JP4 also caused embrittlement, but not

to the same extent. Each of these no fluids caused a weight gain of

approximately three percent and an approximate two percent increase in

thickness. As expected, there was little or no weight gain caused by

the water. On the other hand, there was an embrittlement which,

although small compared to that caused by the other two fluids, was

completely unexpected.

-10-

Two additional fluids, as well as the preceding three, were

included in a second fluid-effects study: ethylene glycol (an

antifreeze) and methylene chloride (a paint stripper). Thicker, 20-mil,

film specimens of Ultem, as well as specimens of the original 3-mil

thickness, were used for this study. In addition to these specimens for

measuring changes in weight, thickness, and mechanical properties,

ultra-thin, 0.25-mil, specimens of Ultem were used to record the effects

of these fluids on the infrared spectra of Ultem. The mechanical and

physical data showed repeatability for the fluids studied previously and

similar effects for the two additional fluids. The infrared data have

not yet been analyzed.

The data from this fluid-effects study will be analyzed and

prepared for a proposed report.

a

V. PAPERS

Stephanie L. Gray: "Electron-Radiation Induced Molecular Changes

in a Polyetherimide Film." Virginia Junior Academy of Science, Spring

1985. l

William D. Collins: "A Study of the Effects of Fluid Environments

on the Physical and Mechanical Properties of ULTEM Resin." Virginia

Junior Academy of Science, Spring 1985.

E. R. Long, Jr., S. A. T. Long, H. R. Ries, and W. L. Harries:

"Radio-Frequency Electrical Properties of Some Neat and Metal-Doped

Polyimides." Abstract submitted to the 1986 IEEE International

Symposium on Electrical Insulation.

REFERENCES

1W. L. Harries, H. R. Ries, S. L. Gray, and W. L. Collins: "Studies

of Molecular Properties of Polymeric Materials." Progress Report for

the period November 1, 1984, through May 1, 1985, prepared for the

National Aeronautics and Space Administration, Langley Research Center

under NASA NCC1-90.

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APPENDIX A

12---35-

N86-15393

RADIO-FREQUENCY ELECTRICAL PROPERTIES OFSOME NEAT AND METAL-DOPED POLYIMIDES

Edward E. Long, Jr. and Sheila Ann T. Long

National Aeronautics and Space AdministrationLangley Research Center

Hampton, Virginia 23665-5225

and

Heidi R. Ries and Wyrford L. HarriesDepartment of Physics

Old Dominion UniversityNorfolk, Virginia 23508-0369

ABSTRACT

As the size and complexity of aerospace systems increase, the uses ofpolymers are also expected to increase. Polyimides constitute one promising

generic class of polymeric materials. They retain good mechanical and physicalproperties at higher temperatures and absorb less moisture than do theepoxies, which are the polymers most frequently used in present aerospacesystems. The properties of these polyimide materials are, therefore, ofconsiderable interest to the aerospace community. Of particular importance arethe electrical properties because these properties relate to both electrical

and structural applications.This paper presents data on the radio-frequency electrical properties of

two thermoset polyimides, pyromellitic dianhy aride - oxydianiline (PMDA-ODA)and benzophenone tetracarboxylic acid dianhydri^.z oxydianilic•e (BTDA-ODA),and one thermoplastic, a polyetherimide. Two commercial grades of the PMDA-ODAwere investigated and neat and metal-doped forms of the BTDA-ODA were studied.

Capacitance, inductance, and impedance properties are reported for afrequency range from 10 kilohertz to 10 megahertz. In addition, the effects oftemperature on some of these properties are reported for 10 and 100 kilohertz.

The research-grade of the PMDA-ODA displayed approximately 20 percenthigher capacitance and 20 percent lower inductance and impedance than did thestock-grade at room jemperature. The thermal variation of the dissipations ofthese two grades indicated that the second -order glass-transition temperaturewas 388 °C for the research - grade and 400 °C for the stock-grade. The roomtemperature electrical properties for the BTDA -ODA were similar to those forthe PMDA- •ODA. The second-order thermal transition for the BTDA-ODA occurred at319 °C. The polyetherimide displayed a much lower value for capacitance, amuch higher value for inductance, and a similar value for impedance, comparedwith the PMDA-ODA. The second - order thermal transition for the polyetherimide

°occurred at 213 C.

-36-

The volume resistivity was approximately 10 17 ohm-cm for all four neatpolymers. This is a typical value for the volume resistivity of dielectrics;It represents a potential problem for charge buildup in a charged-particleenvironment, such as that which exists for geosynchronous orbit applications.Metal doping is one method proposed for preventing charge buildup. The effectsof metal doping on the values of the radio-frequency electrical parameterswere studied for the BTDA-ODA doped with three different metals. Silver andtin were studied for one concentration each, and palladium was studied for twoconcentrLtions. Only palladium significantly reduced the resistivity, and thenonly for the high -concentration formulation Qs 2 mole ratio of metal complexto polymer). The dissipation for the high -concentration palladium-dopedBTDA-ODA was an order of magnitude larger than that for the neat BTDA-ODA,from 10 to 100 kilohertz. The other dopants did not alter the dissipation. Thecapacitance values for the silver-doped and the low-concentrationpalladium -doped BTDA-ODA were lower than that for the neat BTDA-ODA at allfrequencies. None of the dopants affected the impedance and inductanceproperties.

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