Two of the major environmental hazards in the Geosynchronous Earth Orbit (GEO) are energetic charged particles and ultraviolet radiation. The charged particles, electrons and protons, range in energy from 0.1 to 4 MeV and each have a flux of 10 to the 8th sq cm/sec. Over a 30 year lifetime, materials in the GEO will have an absorbed dose from this radiation of 10 to the 10th rads. The ultraviolet radiation comes uninhibited from the sun with an irradiance of 1.4 kw/sq m. Radiation is known to initiate chain sission and crosslinking in polymeric materials, both of which affect their structural properties. The 30-year dose level from the combined radiation in the GEO exceeds the threshold for measurable damage in most polymer systems studied. Of further concern is possible synergistic effects from the simultaneous irradiation with charged particles and ultraviolet radiation. Most studies on radiation effects on polymeric materials use either electrons or ultraviolet radiation alone, or in a sequential combination

Kiefer, Richard L.

Orwoll, Robert A.

English

A study is presented of the effect of radiation on polymers. It helps to estimate the impact of the space environment on composite structures. Two commercially available polymer films were used; a polyetherimide, and a polysulfone. Both films were irradiated in vacuum with 85 KeV electron. Properties of the films before and after irradiation were monitored by tensile elongation measurements, ultraviolet/visible spectroscopy, glass transition temperature measurements, gel permeation chromatography, and infrared spectroscopy. The results of these characterizations are presented and briefly discussed

NASA Technical Reports Server

J/.._III_ L_I/ _/ s
/
SEMIANNUAL STATUS REPORT
NASA Research Grant NAG-I-678
SPACE ENVlRONM_ALEFFECTS ON POLYMERIC MATERIALS
March I, 1986 to January i, 1987
(_AsA-CR- 180336) SPACE EE¥IEC _BER'I&L
E}FEC_S CN pOI._EBJ.C _A'IESIAI.£ 5_siannual
status Ee_o_t, 1 Ear- 1986- 1 Jan. 1987
_college of _illiam a_d MarY) 15 P Avail:
li,;IS EC AO21EF A01 CSCL 11B 63/27
S87-27034
unclas
0063_34
Principal investigators:
Grantee Institution:
RICHARD L. KIEFER AND ROBERT A. ORWOLL
THE COLLEGE OF WILLIAM AND MARY
WILLIAMSBURG, VIRGINIA 23185
https://ntrs.nasa.gov/search.jsp?R=19870017601 2020-03-20T09:26:56+00:00Z
SPACE ENVIRONMENT EFFECTS ON POLYMERIC MATERIALS
Space structures in geosynchronous orbit will be subjected to radiation
doses of about I0 I0 rads over a 30 year lifetime. In addition, daily ther-
mal cycling will occur. These structures will likely be constructed of
polymer matrix composite materials because of their light weight, high
strength, and low-thermal expansion. Radiation is known to initiate chain
scission and crosslinking in polymeric materials, both of which affect their
structural properties. Thus, a study of the_effe ct of radiation on polymers
is important in estimating the impact of the space environment on composite
structures.
In this study, two commercially available polymer films were used; a
polyetherimide, and a polysulfone. The polyetherimide was produce d by the
General Electric Company with the trade name Ultem. The polysulfone was
produced by the Union Carbide Corporation as PI700. The two polymers were
chosen for study because they had been well characterized, they were commer-
cially available in good quality films, and they are both linear systems.
Both films were irradiated in vacuum with 85 KeV electrons. Properties of
the films before and after irradiation were monitored by tensile elongation
measurements, ultraviolet/visible spectroscopy, glass transition temperature
measurements, gel permeation chromatography, and infrared spectroscopy.
The polyetherimide, Ultem, becomes colored when it is irradiated, a charac-
teristic common to many polymer films. However, when Ultem is exposed to
air after irradiation, the color fades. In order to quantify this color
change, ultraviolet/visible (UV/VIS) spectra of irradiated Ultem films were
recorded at various times after the irradiation beginning at 5 minutes and
extending to at least 4 hours, as shown in figure i. The spectra were
recorded on a Perkin-Elmer Model 330 spectrophotometer. Irradiations were
performed with total doses of I00, 320, 640, 2000, and 4000 Mrads. Dose
rates ranged from 4.2 to 170 Mrads/hr. The percent transmittance was deter-
mined at a specific wavelength (490 nm) for each spectrum so that a plot of
%T vs time after exposure could be made as shown in figure 2. It can be
-2-
seen that the %Tat 490 nm increased with time after exposure up to a maxi°
mumvalue which was always less than that of the unirradiated film. The %T
at each time was then subtracted from this maximumor equilibrium value.
The log of the remainder is plotted as a function of time after exposure in
figure 3. This plot shows the decay of the color and thus the decay of the
specie causing the color. Figure 3 shows two distinct groups of points,
those from films irradiated at high doses (2000 and 4000 Mrads) and those
irradiated at lower doses (320 and 640 Mrads). The color of the films
irradiated at high doses decayed with a 90 minute half-life while that of
the films irradiated at the lower doses decayedwith a 40 minute half-life.
It has been shown by ESRspectroscopy that for a 1600 Mrad irradiation ofi
Ultem, the radicals decay with a 90 minute half-life. Thus, there is good
evidence that the decay of the color centers is due to radical decay. It
has also been shown that the critical gel dose for Ultem is about ii00
Mrads. 2 Therefore, it appears that above the critical gel dose, the radi-
cals decay more slowly due to a decrease in mobility or to a change in decay
mechanism. The UV/VIS data as a function of total dose is summarized in
figure 4.
Because the Ultem contains radicals which decay with a measurable half-life
when exposed to air, tensile elongation studies were run as a function of
time after irradiation to see if the radical decay affected the mechanical
properties of the polymer. Total doses and dose rates were the same as
those used for the UV/VIS studies. In these studies, the irradiated films
were removed from the vacuum chamber and immediately immersed in liquid
nitrogen. Films were then removedand exposed to air for a period of time
before the tensile elongation test was made. Time periods of 0, 15, 30, 60,
and 120 minutes were used. Within experimental limits, no effect of time in
air on the tensile elongation was noted at any total dose studied. In
addition, two samples were irradiated at 320 Mrads and allowed to remain in
vacuumfor 4 days before making the tensile elongation measurements. Again,
no effect with time was noted. The data are summarizedin figures 5, 6, and
7. The infrared spectrum was also measuredas a function of exposure time
in air, and again, no effect was noted.
-3-
The Ultem irradiations show that for optical properties, post-irradiation
effects are important, particularly for the first several hours. Post-
irradiation handling appears to have no effect on the tensile elongation and
the infrared spectrum.
To compare the behavior of Ultem with that of another polymer, polysulfone
(PI700) was irradiated and treated in an identical manner as the Ultem. No
effect was found in either the tensile elongation or the UV/VIS spectrum as
a function of exposure time in air. Figure 8 showsthe UV/VIS spectrum for
polysulfone as a function of exposure time in air. This can be compared
with figure i.
Since polysulfone showedno post-irradiation effects, it appeared to be an
ideal polymer to use for a study of dose rate and temperature effects on the
tensile elongation. In the dose rate study, the total dose was held con-
stant at 350 Mrads and the temperature was constant at 25°C while the dose
rate was varied between 1.8 and 260 Mrads/hr. The results as shown in
figure 9 indicate that over the range of dose rates studied, there is no
effect on the tensile elongation.
For the temperature study, the total dose and dose rate were constant at 350
Mrads and 87.5 Mrads/hr respectively, while the temperature was varied
between 25 and 175°C. The results are shownin figure i0. Above ll0°C, the
tensile elongation drops to zero. This probably occurs because the critical
gel dose decreases at the higher temperatures so that by 125°C it is below
350 Mrads. Brown and O_Donnell have shown that for gammairradiation of
polysulfone (PI700), the critical gel dose decreased from 400 Mrads at 35°C
to i00 Mrads at 125°C.3 This is qualitatively in line with our data. There
appears to be a slight increase in tensile elongation as the temperature
increases from 25° to ll0°C. It has been shown for this polysulfone that
the ratio of chain scission to crosslinking, G(S)/G(X), increases with
3increasing temperature. This would cause an increase in tensile elongation
with increasing temperature up to the point where the critical gel dose is
exceeded.
-4-
The data indicate that for polysulfone (PI700), temperature affects the
tensile elongation and thus the structural properties, while dose rate over
the range studied has no effect.
References
i. E.R. Long and S.A.T. Long, NASA TP-2429, May 1985.
2. R. Basheer and M. Dole, Radiat. Phy_s. Chem., 25, 389 (1985).
3. J.R. Brown and J.H. O'Donnell, _. A_p_l. Po__l. Sci., 23, 2763 (1979).
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Space environmental effects on polymeric materials

Polymeric materials that may be exposed on spacecraft to the hostile environment beyond Earth's atmosphere were subjected to atomic oxygen, electron bombardment, and ultraviolet radiation in terrestrial experiments. Evidence is presented for the utility of an inexpensive asher for determining the relative susceptibility of organic polymers to atomic oxygen. Kapton, Ultem, P1700 polysulfone, and m-CBB/BIS-A (a specially formulated polymer prepared at NASA Langley) all eroded at high rates, just as was observed in shuttle experiments. Films of Ultem, P1700 polysulfone, and m-CBB/BIS-A were irradiated with 85 keV electrons. The UV/VIS absorbance of Ultem was found to decay with time after irradiation, indicating free radical decay. The tensile properties of Ultem began to change only after it had been exposed to 100 Mrads. The effects of dose rate, temperature, and simultaneous vs. sequential electron and UV irradiation were also studied

Polymer-matrix composites have considerable potential for use in the construction of orbiting structures such as the space station and space antennas because of their light weight, high strength, and low thermal expansion. However, they can suffer surface erosion by interaction with atomic oxygen in low-Earth orbit and degradation and/or embrittlement by electrons and ultraviolet radiation especially in geosynchronous orbit. Thus, a study of the effect of these environmental hazards on polymeric materials is an important step in the assessment of such materials for future use in space

SEMI-ANNUAL PROGRESS REPORT 
NASA Research Grant NAG-1-678 
SPACE ENVIRONMENTAL EFFECTS ON POLYMERIC MATERIALS 
June 1 to November 30, 1987 
Principal Investigators: RICHARD L. KIEFER 
ROBERT A. ORWOLL 
Grantee Institution: THE COLLEGE OF WILLIAM AND MARY 
WILLIAMSBURG, VIRGINIA 23185 
[NASA-CR-182018) SPACE E I V I B O N H E I T A L  1188-1 so a2 
EFPECTS OM POLYMERIC HATEBIALS Semiannual 
Proqress Report,  1 Jun. - 30 Nov. 1987 
(College of Yilliam and Hary) 6 p C S C L  11s Unclas 
G 3 / 2 7  0120339 
https://ntrs.nasa.gov/search.jsp?R=19880005700 2020-03-20T07:42:30+00:00Z
8 
1 
SPACE ENVIRONMENTAL EFFECTS ON POLYMERIC MATERIALS 
Richard L. Kiefer and Robert A. Orwoll 
Department of Chemistry 
College of William and Mary 
Williamsburg, Virginia 23185 
INTRODUCTION 
Polymer-matrix composites have considerable potential for use in the 
construction of orbiting structures such as the Space Station and space 
antennas because of their light weight, high strength, and low thermal 
expansion. However, they can suffer surface erosion by interaction with 
atomic oxygen in low-earth orbit and degradation and/or embrittlement by 
electrons and ultraviolet radiation especially in geosynchronous orbit. 
Thus, a study of the effect of these environmental hazards on polymeric 
materials is an important step in the assessment o f  such materials for 
future use in space. 
ATOMIC OXYGEN 
Atomic oxygen, which is the major atmospheric component in the low-earth 
orbit, is chemically very reactive. It can be generated in the laboratory 
by subjecting molecular oxygen at low pressure to radio-frequency radiation. 
In our study, atomic oxygen was generated in a chamber 4 inches in diameter 
and 6 inches long kept at a pressure of 200 millitorr. So that the products 
of the reaction of polymeric materials and atomic oxygen could be 
identified, three U-tubes were placed in the line between the chamber and 
the vacuum pump. The first tube was immersed in a dry ice/acetone bath, 
while the other two were immersed in liquid nitrogen. After a sample was 
exposed to atomic oxygen, the contents of each tube was analyzed separately 
by warming the tube to room temperature and transferring the contents to a 
2 
gas cell. The products were identified by infrared spectroscopy. In all 
cases, the first tube contained water ( H 2 0 ) ,  the second tube contained 
carbon dioxide ( C 0 2 ) ,  and the third tube had no measurable product. 
Polyimides also formed nitrogen dioxide (NO ) and polysulfone formed sulfur 
dioxide (SO2). In both cases, the extra product was found in the second 
tube. No other products could be identified, implying that the interaction 
of atomic oxygen with polymeric materials results in the formation of simple 
oxides of each element present. 
2 
Additional studies on atomic oxygen focused on the rate of interaction with 
various polymers and in developing polymeric systems which are more 
resistant to interaction with atomic oxygen. Table 1 shows the mass loss 
for various materials after exposure to atomic oxygen. It is clear that 
fluorinated materials are resistant to attack by atomic oxygen. It has also 
been shown that silicon-containing materials are similarly resistant. To 
test the effectiveness of silicon-containing compounds in polymeric systems, 
polydimethylsiloxane (PDMS) was incorporated into two polymers; a 
polysulfone (P1700), and a polyetherimide (Ultem) . Films of both systems 
were cast and samples of each were exposed to atomic oxygen. The results 
are shown in Table 2 .  Since the incorporation of PDMS in the polymer film 
was effective in reducing the attack by atomic oxygen, other silicon- 
containing compounds are currently being assessed. 
It was shown on several Space Shuttle flights that the interaction of atomic 
oxygen with polymeric materials results in surface erosion. We have 
employed diffuse reflectance infrared spectroscopy to study surface 
interactions. A graphite-Ultem composite was studied by comparing the 
diffuse reflectance infrared spectrum before and after exposure to atomic 
oxygen. The data show that certain chemical groups on the polymer interact 
more rapidly than others. Specifically, the carbonyl group seems to react 
most rapidly, followed by the imide and methyl groups. The benzene ring 
appears to react more slowly than the other groups. The structure of Ultem 
is shown in Figure 1. 
ELECTRONS AND ULTRAVIOLET RADIATION 
Irradiation by energetic electrons and ultraviolet radiation is the greatest 
environmental hazard to polymeric materials in the geosynchronous orbit. To 
assess the resistance of materials to these radiations, a unique apparatus 
was built at the NASA Langley Research Center. It consists of a chamber 9 
inches in diameter and 9 inches high into which a sample can be mounted. 
The chamber can be evacuated to a pressure of torr. An electron gun 
and a mass spectrometer are also incorporated in the vacuum system, and an 
ultraviolet lamp is positioned so that the sample can be irradiated with 
electrons and ultraviolet radiation simultaneously or separately. The mass 
spectrometer can monitor the volatile products from the interactions of the 
radiations with the polymeric material. While some background problems have 
plagued the instrument, we have obtained some results for polysulfone. When 
this polymer is irradiated with either electrons or ultraviolet radiation, 
the mass spectrum shows peaks at mass 48 and at mass 6 4 .  These masses 
correspond to the chemical structures SO and SO Other workers have shown 
that SO The structure of 
polysulfone (P1700) is shown in Figure 2. This study will be extended to 
include measurements with infrared spectroscopy. 
2' 
is a product of irradiation of polysulfone.3 2 
REFERENCES 
1. W. S .  Slemp, B. Santos-Mason, G. F. Sykes, Jr., and W. G. Witte, Jr., 
"Effects of STS-8 Atomic Oxygen Exposure on Composites, Polymeric Films and 
Coatings," AIAA 23rd AerOSDaCe Sciences Meetine;, AIM-85-0421, January 1985. 
2. Lubert J. Leger, "Effects of the Low Earth Orbital Environment on 
Spacecraft Materials," Proceedings of the Third European SvmDosium on 
SDacecraft Material in SDace Environment, ESASP-232, October 1985. 
3. J. R. Brown and J. H. O'Donnell, "The Radiation Stability of an Aromatic 
Polysulfone," Journal of Polymer Science, Part B ,  8 ,  121, 1970. 
A 
4 
TABLE 1. 
Mass Loss o f  Ma te r ia l s  A f t e r  Exposure t o  Atomic Oxygen 
Exposure Time 
Mater i  a1 (min.) 
Graphi te F i  ber (HMS 34-1) 360 
FEP Tef lon  37 5 
Polysul  fone (P1700) 37 5 
Polyether imide (Ultem) 300 
Mass Loss 
(ms) % Loss 
121 80.0 
2.6 2.4 
46.7 56.9 
9 .o 25 .O 
TABLE 2. 
Polymeric Mater ia ls  Containing Polydimethyls i loxane (PDMS) 
Exposed t o  Atomic Oxygen 
Polysul  fone (P1700) 
%PDMS Exposure Time Mass Loss 
(by weight )  (min.) (ms) % Loss 
0 180 5.8 8.8 
0 -43 180 3.2 6.5 
0.89 180 2.2 5.6 
Polyether imide (Ultem) 
0 360 24.2 29 .O 
1.35 360 12.5 13.1 
4.31 360 12.7 12.8 
. 
F i g u r e  1. Chemical s t r u c t u r e  of polyether imide (Ultem). 
F i g u r e  2 .  Chemical s t r u c t u r e  of polysulfone (P1700). 


Space environmental effects on polymeric materials

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