Attenuated total reflection infrared spectroscopy was used to analyze ultrahigh molecular weight polyethylene wear test specimens. Three different specimens were analyzed. One specimen was gamma irradiated to a dose of 5.0 MRad, another to a dose of 2.5 MRad, and the final specimen was unirradiated. There was no conclusive evidence of chemical changes (i.e., unsaturation or oxidation) in the surface regions of any of the polyethylene samples. Therefore, it was concluded that the gamma irradiation sterilization procedure shoud not alter the boundary lubricating properties of the polyethylene

Jones, W. R.

Lauer, J. L.

English

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3 1176 00138 7761 
NASA-TM-79228 19790021158 
NASA Technical Memorandum 79228 
INFRARED ANALYS IS OF POLYETHYLENE WEAR 
SPECIMENS US ING ATTENUATED TOTAL 
REFLECTION SPECTROSCOPY 
William R. Jones 
Lewis Research Center 
Cleveland, Ohio 
and 
James L. Lauer 
Rensselaer Polytechnic Institute 
Troy, New York 
July 1979 
11111/1111111 1111 11111 11111111111111111111111 
NF00516 
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LAnGLEY RESE/,RC!-l CENTER 
L1BR,'\RY, NASA 
Hr,r,~PTOrl, VIRGINIA 
https://ntrs.nasa.gov/search.jsp?R=19790021158 2020-03-11T19:15:48+00:00Z
SUMMARY 
Attenuated total reflection infrared spectroscopy (ATR) was used to 
analyze ultrahigh molecular weight polyethylene wear test specimens. Three 
different specimens were analyzed. One specimen had been gamma irradiated 
to a dose of 5.0 MRad, another to a dose of 2. 5 MRad, and the final specimen 
was unirradiated. There was no conclusive evidence of chemical changes 
(i. e., unsaturation or oxidation) detected by ATR in the surface regions of any 
of the polyethylene samples. Therefore, it was concluded that the gamma ir-
radiation sterilization procedure should not alter the boundary lubricating 
properties of the polyethylene with regard to adsorption of lubricant surface 
active species. 
INTRODUCTION 
Ultrahigh molecular weight polyethylene (illlMWPE) is commonly used 
in total joint prostheses. This polymer possesses high wear resistance, 
chemical inertness, and is compatible with the body (ref. 1). However, the 
conventional sterilization technique of steam autoclaving cannot be used with 
polyethylene components because the deformation temperatures of the polymer 
are exceeded. Therefore, polyethylene components are normally sterilized 
with gamma irradiation (2.5 MRad dose) (ref. 2). 
The effect of gamma irradiation (0 to 5 MRad) on the friction and wear 
properties of UHMWPE under dry conditions has been reported (ref. 3). In 
that study, sterilization doses of 2.5 and 5.0 megarads greatly altered the 
average molecular weight and molecular weight distribution of illiMWPE, but 
friction and wear properties of the polymer were not significantly changed. 
Shen and Dumbleton (ref. 4) have reported on the friction and wear behavior 
or polyethylene irradiated at higher levels (20 to 1000 MRad). In general, 
both friction and wear increased with increasing dose. Infrared analysis of 
their specimens indicated the presence of h'ans- unsaturation by the appearance 
of an absorption peak at a wave number of 966 em-I. Infrared analysis has 
also been used to detect polymer surface oxidation. Atkinson, et al. (ref. 5) 
reported the presence of carbonyl bonds in streamer wear debris from pin-
o~-disk tests. Distinct infrared absorption peaks were observed at 1724 cm- 1 
in thin sheets of hot pressed wear debris but not present in slivers of bulk 
UHMWPE hot pressed in the same way. 
The presence of either unsaturation or carbonyl bonds would indicate 
that the polymer has been chemically degraded. This type of degradation may 
alter the boundary lubricating characteristics of the polymer (ref. 6 and 7) . 
2 
Internal reflection spectroscopy (ref. 8) is the technique of recording 
optical spectra by placing a material in contact with a transparent medium of 
greater refractive index and measuring the reflectance from the interface. If 
the material in contact with the transparent medium is absorbing, the reflectance 
for total internal reflection will be attenuated to some value between zero and 
unity in regions of the spectrum where absorption of radiant energy can take 
place. Therefore, the emerging beam will resemble the spectrum of the ab-
sorbing material as if it were measured by ordinary transmission techniques. 
The technique for obtaining spectra in this manner is called attenuated total 
reflection spectroscopy (ATR). Because the beam penetrates the absorbing 
material for a distance on the order of a wavelength of infrared light, ATR 
provides essentially a surface absorption spectrum. 
The objective of this investigation was to analyze the surfaces and the 
bulk of ultrahigh molecular weight polyethylene wear test specimens using 
attenuated total reflection infrared spectroscopy. 
TEST SPECIMENS 
The test specimens were O. 476-centimeter radius hemispherically tipped 
riders approximately 2 centimeters in length. They were made of ultrahigh 
molecular weight polyethylene (RCH1000). The specimens were from a pre-
vious wear test program (ref. 3) and the details of their history appear in 
table I. 
APPARATUS 
An infrared grating spectrophotometer (Perkin- Elmer Model 221) was 
used for all measurements. An internal reflection attachment (fig. 1) (Harrick 
Instruments Corp.) was used in the sample space of the spectrophotometer. 
The radiation from the source is reflected by mirror M1 to enter the internal 
reflection plate (a 5 by 12 by 2 mm plate of pure germanium) and is returned 
in such a way that mirrors M2 and M3 bring it onto the spectrometer entrance 
slit with the same convergence it would have had in the absence of the attach-
ment. 
The angles of internal reflection within the plate are all greater than 
the critical angle (germanium- polyethylene), and the arrangement of the unit 
is such that five reflection will occur on either surface on the way into the re-
flection plate and five more on the way out, for a total of ten reflections. 
1I0\\"l'H'1', because of size limitations of the rider wear specimens, only a 
single l"d1eetion could be used for the wear surface and three for the reference 
or bulk matedal. 
3 
PROCEDURE 
One 100 pm thick slice was cut from the end of the rider containing the wear 
scar. Three 100 pm slices were cut from the opposite end (discarding the ex-
treme end, except for one sample). A precision biological microtome was used 
for the cutting operation. The slices were cleaned with water and detergent, 
rinsed with distilled water, then with alcohol, and finally with pentane and then 
dried. 
The slices were placed on a well-cleaned germanium plate with the outer sur-
faces facing the plate (where applicable). Three full- diameter slices were placed 
on one side of the plate together, like pancakes on a griddle. However, slices 
containing the wear scars were placed alone on the plate. For this reason, the 
absorption bands of the references were always stronger than those of the wear 
scar surfaces. 
The entire spectrometer was covered by a plastic enclosure and the assembly 
continuously flushed with air dried and cleaned of carbon dioxide by passing 
through a large column of Linde Molecular Sieve No. 5A. 
RESULTS 
The infrared spectrum for the unworn end of the 5 MRad irradiated specimen 
appears in figure 2(a). The surface facing the germanium plate was the flat, un-
worn end of the rider specimen. The procedure for removal of moisture and 
carbon dioxide was effective as evidenced by the lack of fine structure in the 
-1 -1 1400 to 1800 cm region. The most intense bands are at 2851 and 2919 cm 
(C-H stretching), 1460 cm- 1 (C-H deformation), and at 827 and 741 cm- 1 
(CH 2 rocking). These are bands that would be expected for a polyethylene 
surface (ref. 9). 
There is a slight indication of a band at 1743 cm- 1 , which would indicate 
the presence of carbonyl, but it is very weak. The spectrum of the wear scar 
surface for the 5 MRad specimen is shown in figure 2 (b) . This spectrum is 
identical to the one for the unworn surface (fig. 2(a» with two exceptions. There 
is no indication of a band at 1743 cm- 1 and a weak broad band is present from 
3100 to 3300 cm- 1. This weak band probably is due to a small amount of moisture 
adsorbed on the surface. 
The infrared spectra of the wear scar surface and the polymer interior for 
the 2.5 MRad specimen appear in figures 3(a) and (b), respectively. Again, 
these spectra appear identical. Both have the broad weak band centered at 
3100 cm- 1 nnd the other bands associated with polyethylene. 
Figure -l contains the corresponding spectra for the unirradiated polymer. 
The spectrum for the wear scar surface appears in figure 4(a) and the spectrum 
4 
for the polymer interior in figure 4 (b). Both spectra are essentiall,v the :3anll' 
and very similar to the spectra for the two irradiated specimens. 
DISCUSSION 
As briefly described in the introduction, the ATR spectrum is of the nature 
of a surface absorption spectrum. The intensity of the bands is a function of the 
"effective optical path" and is strongly dependent on the angle of incidence on the 
plate and sample. Multiple reflections build up the band intensities. However, 
as previously mentioned, only one reflection could be used for the wear surface 
and three for the bulk polymer because of size limitations. Accordingly, the 
intensities of the spectral bands are necessarily weak. 
Taking this into account, there does not appear to be any significant polymer 
surface degradation (oxidation or unsaturation) resulting from either the irradia-
tion procedure or the friction and wear process. It would follow that the surface 
adsorption characteristics of the irradiated polyethylene should not be grossly 
different from those for the virgin polymer. 
Since the boundary lubricating characteristics are highly dependent on the 
adsorption of polar molecules onto the polymer surface, one would not expect 
gross differences in these characteristics either. Obviously, other factors, 
such as changes in polymer physical properties, may affect the boundary char-
acteristics. However, the physical changes induced by the gamma irradiation 
did not alter the unlubricated friction and wear properties (ref. 3). 
SUMMARY OF RE~ULTS 
Attenuated total reflection infrared ::lpectroscopy was used to analyze 
ultrahigh molecular weight polyethylene wear test specimens. The following 
results were obtained~ 
1. Neither gamma sterilization irradiation (to 5.0 MRad) nor the friction 
and wear proces::l itself produced any substantial amount of polymer surface 
degradation. 
2. The only spectral band detected on most of the polymer surfaces and 
-1 
not related to the polyethylene itself was a broad weak band centered at :noo cm . 
This was probably the result of a small amount of adsorbed moisture. 
:1, Therefore, it was concluded that the sterilization process should not 
alter the boundary lubricating properties of the polyethylene with regard to 
:lctsol'ption of lubl'icant surface active species. 
5 
REFERENCES 
1. Semlitsch, M;: Metals and Plastics for Artificial Hip Joints, Investigations 
of Surfaces in the Scanning Electron Microscope, Sulzer Tech. Rev. 
Research Number, 1971, pp. 3-16. 
2. Ungethum, M.: Requirements of Operational Tests and Test Results in Total 
Hip and Knee Arthroplasty. Advances in Artificial Hip and Knee Joint 
Technology, VoL 2, M. Schaldach and D. Hohmann, eds., Springer-
Verlag (Berlin), 1976, pp. 493-518. 
3. Jones, W. R., Jr.; Hady, W. F.; and Crugnola A.: Effect of Sterilization 
Irradiation on Friction and Wear of Ultrahigh-Molecular- Weight Polyethylene, 
NASA TP-1462, 1979. 
4. Shen, C.; and Dumbleton, J. H.: The Friction and Wear Behavior of Ir-
radiated Very High Molecular Weight Polyethylene. Wear, vol. 30, 1974, 
pp. 349-364. 
5. Atkinson, J. R.; Brown, K. J.; and Dowson, D.: The Wear of High Molecular 
Weight Polyethylene. Part I. The Wear of Isotropic Polyethylene Against 
Dry Stainless Steel in Uni- Directional Motion. J. Lubr. Technol., vol. 100, 
no. 2, Apr. 1978, pp. 208-218. 
6. West, G. H.; and Senior, J. M.: Frictional Properties of Polyethylene. 
Wear, vol. 19, 1972, pp. 37-52. 
7. Fort, Tomlinson, Jr.: Adsorption and Boundary Friction on Polymer Surfaces. 
J. Phys. Chern., vol. 66, no. 6, June 1962, pp. 1136-1143. 
8. Varadi, P. F.: Infrared Spectroscopy in Vacuum and Surface Studies. 
Hesearch/Development, vol. 24, no. 4, Apr. 197:1, pp. 46-52. 
9. Avram, M. and Mateescu, Gh. D. (Ludmila Birladeanu, transl.), Infrared 
Spectrocopy, Wiley-Interscience, 1972. 
TABLE I. - HISTORY OF WEAR TEST SPECIMENS (REF. :1) 
Specimen* Load, Sliding speed, Sliding dist, Wear Average Average 
N m/s m scar friction wear 
diameter, coeffi- rate, 
mm cient :11 m N-m 
C') 
Unirradiated 9.8 0.076 182 000 3.38 0.40 0.75xIO- 15 
2.5 MRad 9.8 .063 185 000 :1.38 .45 .76xl0- 15 
5.0 MRad 9.8 .076 93 500 2.86 .42 .78xl0- 15 
* All specimens were run unlubricated in dry air against 316 L stainless steel disks. 
I, 
\ 
\ 
L Spectrometer 
entrance 
slit 
M2 --- r.. Mirrors 
I " 
I ' 
I ' 
I ' M3 Ml 
light 
h'---I-------- beam 
~ Internal 
/'- reflection 
Polymer-.;;;-'::'-- / plate 
specimens ',-..... 
..... " 
..... 
..... , 
" 
source 
Figure I. - Optical diagram of internal reflection attachment to infrared spectrometer. 
4 
6 
8 
0 
.... 
u 
:z 
< 
a:> 
a:: 
0 
VI 
a:> 
< 
2 
4 
6 
8 
0 
~ 
2919 2854 
3000 2500 
~1460 
(a) From unworn surface . 
{OOO 
cm-1 
(b) From Y«>rn surface. 
1500 
~ 828~ 
1000 
Figure? - Infrared ct>sorption spectra from gamma irradiated polyethylene wear test specimen 
(5.0 mrad). 
2 
--
~ 
2917VV2850 
4 
6 
8 ~ 
0 744 
.... 
u 
z IiII From worn surface. <: 
a:J 
c.: 
0 
V> 
a:J ~ <: 
2 
zrn0fV2853 --
4 
6 ~ 8 0 744 
1000 
(bl From polymer interior. 
Figure 3. - Infrared adsorption spectra from gamma irradiated polyethylene wear test specimen (2.5 mradl. 
~ ~ 7 
2919 ?853 ~ 4 6 8 0 
.... 
(a} From worn surface . 
u 
z 
<: 
<Xl 
a:: 
0 
VI ~464 <Xl <: 
7 ~ 
4 
6 ~ 8 745 0 
7500 2000 1500 1000 
cm-1 
(b} From polymer interior. 
Figure 4. -Infrared absorption spectra from unirradiated polyethylene wear test specimen. 
1 Hf'IH!I' Nil I 2 Governmenl Acce·",on No. 3. Recip,ent's Catalog No. 
NA~A TM-7922H 
4 l,tl<' On,1 Subtitle INFRARED ANALYSIS OF POLYETHYLENE WEAR 5. Report Date 
SPECIMENS USING ATTENUATED TOTAL REFLECTION 
SPECTROSCOPY 6. Performing Organization Co~e 
7. Authoris) B. Performing Organization Report No. 
William R. Jones, Lewis Research Center; and James L. Lauer, E-130 
Rensselaer Polytechnic Institute, Troy, New York 12181 10. Work Unit No. 
9 Perl or ming Organization Name ond Address 
National Aeronautics and Space Administration 11. Contract or Grant No. 
Lewis Research Center 
Cleveland, Ohio 44135 13. Type 01 Report and Period Covered 
12 Sponsoring Agency Name and Address Technical Memorandum 
National Aeronautics and Space Administration 
14. Sponsoring Agency Code 
WaShington, D. C. 20546 
15. Supplementary Notes 
tE Abs~rac~ 
Attenuated total reflection infrared spectroscopy was used to analyze ultrahigh molecular weight 
polyethylene wear test specimens. Three different specimens were analyzed. One specimen 
had been gamma irradiated to a dose of 5.0 MRad, another to a dose of 2.5 MRad, and the final 
specimen was unirradiated. There was no conclusive evidence of chemical changes (i. e. , 
unsaturation or oxidation) in the surface regions of any of the polyethylene samples. Therefore, 
it was concluded that the gamma irradiation sterilization procedure should not alter the boundary 
lubricating properties of the polyethylene. 
17 Ke~ Words (Suggested by Author(s)) lB. Distribution Statement 
Infrared spectroscopy Unclassified - unlimited 
mtra high molecular weight polyethylene STAR Category 27 
19. Security Classil. (01 this report I 
/20. Security Classi!. (of this page) _121. No. 01 Pages 22. Price' 
Unclassified UnclasSified 
• For sale by the National Technical Information Service, Springfield, Virginia 22161 
End of Document 


Infrared analysis of polyethylene wear specimens using attenuated total reflection spectroscopy

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