Materials Science s a nd Applications, 2011, 2, 1682-1687
doi:10.4236/msa.2011.211224 Published Online November 2011 (http://www.SciRP.org/journal/msa)
8 MeV Electron Induced Changes in Structural
and Thermal Properties of Lexan Polycarbonate
K. Hareesh, Ganesh Sanjeev*
Microtron Centre, Department of Studies in Physics, Mangalore University, Mangalagangotri, India.
Received September 20th, 2011; revised October 29th, 2011; accepted November 8th, 2011.
ABSTRACT
Lexan polycarbonate films were irradiated by 8 MeV electron beam at different fluences and characterized using X-ray
Diffractogram (XRD), UV-Visible spectroscopy, Fourier Transform Infrared (FTIR) spectroscopy, Differential Scan-
ning Calorimetry (DSC) and Thermogravimetric Analysis (TGA). The structural parameters such as degree of crystal-
linity and crystallite size were found to decrease after irradiation due to chain-scission. The UV-Visible spectroscopic
study show the formation of chromophore groups upon irradiation and was reduced at larger wavelength. FTIR Study
shows the carbonate linkage was found to be the radiation-sensitive linkage and benzene ring does not undergo any
changes after irradiation. The DSC studies showed a decrease in glass transition temperature and heat of fusion after
irradiation due to chain-scission which indicates polymer was moving towards more disordered state. Thermal decom-
position temperature of Lexan polycarbonate increases upon irradiation.
Keywords: Lexan Polycarbonate, Irradiation, Structural, Thermal Properties
1. Introduction
In the recent few years, studies related to irradiation ef-
fects on polymers have emerged as an important area of
basic as well as applied research [1]. The irradiation of
polymers can modify their structure and properties due to
chain-scission and cross-linking. Therefore, some of the
irradiation-based polymer processing methods have
emerged such as radiation assisted diffusion, growth of
polymer nano-composites, polymer blends, polymer
grafting etc. [2,3]. Systematic investigations on effects of
a wide range of radiations on various polymers are thus
important for providing useful information for radiation
processing of polymers. The radiation induced changes
in the properties are very specific to type of polymer,
radiation and its environment [4]. Amongst the range of
low to high energy radiations, electron beam are of spe-
cial interest. The polymers, which are difficult to process
by chemical methods, can be easily modified using elec-
tron irradiation [5,6]. This leads to significant changes in
structural [7-11] and thermal [12] properties due to ra-
diochemical alterations such as unsaturation, evolution of
gases [13], formation of carbon clusters, change in free
volume [6], creation of defects and amorphization [6,14]
etc. As a result, electron beam irradiation of polymers
has shown great potential for the fields such as microe-
lectronics, biomedical, device technology, nano-materials
and materials science [15-17].
Lexan polycarbonate (Lexan) is the most promising
polymer utilized in all fields of science and technology,
especially in optical, medical [18] and electronic applica-
tions due to its low cost, easy processability and low
weight. Literature survey indicates that the effects of
radiation on Lexan are being extensively studied. Expo-
sure to gamma [13,18,19] and RF plasma [20] shows
significant optical, chemical and surface modifications.
However, to modify the polymer, energy loss of ion
beam is very important and specific to its nature, energy
and environment. The effects of such parameters of elec-
tron beam on structural and thermal properties of Lexan
have not been paid much attention. Therefore, in this
paper, the effects of 8 MeV electron on structural and
thermal properties of Lexan have been studied in detail.
2. Experimental
Lexan films of thickness 200 μm were irradiated at dif-
ferent fluences sealed in polyethylene bags. The irra-
diation was carried out at Microtron Centre, Mangalore
University, India using 8 MeV electron beam. The details
of the Microtron accelerator were reported elsewhere
[21]. The electron fluence delivered to the samples was

8 MeV Electron Induced Changes in Structural and Thermal Properties of Lexan Polycarbonate1683
measured using current integrator calibrated against ap-
propriate radiation dosimeters. XRD diffractogram were
recorded in the 2θ range (4˚ - 60˚) with a scanning speed
and step size of 1˚/min and 0.01˚ respectively using a
Advance X-ray diffractometer (Bruker AXS D8) with
CuKα radiation of wavelength λ = 1.5406 Å. UV-Visible
spectra of the pristine and electron irradiated Lexan sam-
ples were analysed using, UV-Visible spectrophotometer
(UV-1800, Shimadzu, JAPAN) in the wavelength range
190 - 1100 nm with reference to air. FTIR spectra of all
samples were recorded using spectrophotometer (NIC-
OLET 5700, FTIR, USA) in the wave number range 400
- 4000 cm–1 having a resolution of 4 cm–1. The ther-
mograms i.e. plot of heat flow as a function of tempera-
ture for pristine and electron irradiated Lexan samples
weighing 1.3 - 2.3 mg were obtained using DSC (Q20
TA Instruments, USA) in the temperature range of 27˚C -
200˚C at a constant predetermined heating rate of 10˚C
/min under nitrogen atmosphere. The most reliable tech-
nique for obtaining thermal degradation parameters for
polymer is the Thermogravimetric analysis. The appara-
tus consists of a microbalance within a furnace, allowing
the weight of the sample to be continuously monitored
while the temperature is controlled. So, the weight (%) of
the sample is recorded as a function of temperature. In
this work, the thermograms of the decomposing poly-
mers were recorded using SDT (Q600 TA Instruments,
USA) heated at a rate of 10˚C/min under Nitrogen at-
mosphere.
3. Results and Discussions
The schematic representation of the mechanism of elec-
tron irradiation induced reaction of Lexan is as shown in
Figure 1.
3.1. X-Ray Diffraction Study
XRD technique has been utilized to detect changes in
crystalline and amorphous regions along with the degree
of crystallinity. It is used to measure crystallite size, per-
centage of crystallinity, microstrain and dislocation den-
sity of materials through interaction of X-ray beams with
samples. The XRD spectra of pristine and electron irra-
diated Lexan films is as shown in Figure 2. The diffract-
tion pattern clearly indicates that the Lexan is semicrys-
talline in nature with main peak at 17.56˚. For irradiated
samples also identical peaks were obtained but they
slightly shift towards higher angel indicating decrease in
lattice spacing. As compared to pristine sample, the dif-
fraction pattern of irradiated films show the broadening
of main peak indicating the decrease in crystallite size
[22,23]. The crystallite size (D) was calculated using
following equation [24],

cos
K
Db


 (1)
where K is shape factor and is 0.9,  is wavelength of
X-ray beam and is 1.5406 Å, b is full width at half
maximum,  is diffraction angle or Bragg angle. The
calculated values of crystallite size are listed in Table 1.
The percentage of crystallinity (X) can be calculated
using equation [25],
Figure 1. Schematic representation of chemical reaction
induced in Lexan after electron irradiation.
Figure 2. XRD pattern for pristine and electron irradiated
Lexan.
Table 1. Crystallite size (D) and percentage of crystallinity
(X) of pristine and elec tron irradiated Lexan.
Fluence (electrons/cm2) 2  (degree) D (Å) X (%)
0 17.56 15.98 43
3.02 × 1014 17.68 14.15 33
6.79 × 1014 17.95 13.79 27

8 MeV Electron Induced Changes in Structural and Thermal Properties of Lexan Polycarbonate 1684
100
c
ca
A
XAA 
 (2)
where Ac and Aa are the area of crystalline and amor-
phous halos respectively. The percentage of crystallinity
for all the samples is listed in Table 1. It has been ob-
served from Table 1 that both crystallite size and per-
centage of crystallinity were decreases after irradiation
due to breakage of polymeric bonds and emission of
some volatile gases, which may form the disordered state
in the polymeric film. The decrease in crystallinity can
be further confirmed from DSC studies.
3.2. UV-Visible Spectroscopic Study
The optical absorption spectra of pristine and electron
irradiated Lexan samples are shown in Figure 3. After
electron irradiation, the polymer surface showed a visible
colour change from transparent to yellow and the inten-
sity of the colour increases with increase in electron flu-
ence. This is also confirmed with UV-Visible absorbance
spectra where the absorption edge shifts progressively
towards longer wavelength. This may be attributed to the
formation of chromophore groups (conjugated double
bonds) as a consequence of the beam induced bond
breaking and reconstruction. If there are enough chro-
mophore groups in the conjugation within the sample,
absorption edge is expected to move towards the visible
region [25,26]. But in the present study, the absorption
edge was in the UV region indicating less formation of
chromophore groups.
The absorbance difference (A-A0) versus electron
fluence was plotted in Figure 4 at wavelengths 290 nm,
300 nm, 310 nm and 320 nm. The linear dependence of
absorbance with the electron fluence was observed. The
solid lines in Figure 4 fit the experimental data using the
relation [25],
Figure 3. Absorbance spectra for pristine and electron
irradiated Lexan.
Figure 4. Plot of absorba nc e difference (A-A0) vers us electr o n
fluence for Lexan samples.
0
A
kn A



 (3)
where Aλ(  ) is the absorbance at a wavelength λ and at a
fluence  ; kλ is absorption coefficient of the chromopho-
res produced (cm–2); n is the number of chromophores
which absorb at a particular λ created per incident pri-
mary ion and per unit area, and σ is the cross-sectional
area of a cylinder within which n chromophores are cre-
ated. Thus nσ represent the efficiency of the chromo-
phore groups formation induced by ion beam and there
fore, the slope kλnσ of the plot (A-A0) versus electron
fluence (  ) represents the efficiency multiplied by kλ. The
value of kλnσ for electron bombardment for λ = 290, 300,
310 and 320 nm are found to be 2.10 × 10–15 cm2, 1.18 ×
10–15 cm2, 1.05 × 10–15 cm2 and 0.91 × 10–15 cm2 respec-
tively. It is observed that the value kλnσ decreases with
increase in wavelength. The (A - A0) value at wavelength
290 nm is significantly more when compared to 300nm.
This indicates that the absorption profile of the chromo-
phore groups where different absorption at different
wavelengths are due to difference in the absorption coef-
ficients of the chromophore groups, for example, the
absorption coefficient (k

) at 290 nm is maximum when
compared to the absorption coefficient (k

) of other
wavelengths.
3.3. FT-IR Spectral Analysis
The Vibration modes of chemical bonds are character-
ized by the absorption bands [27]. Figure 5 shows the
FT-IR spectra for the pristine and electron irradiated
Lexan films at different fluences. There is almost no
change in the spectra of samples irradiated at the fluence
3.02  1014 electrons/cm2. On irradiation to the fluence of
6.79  1014 electrons/cm2, the intensity of the peak cor-
responding to 3500 cm–1 changed by a small value. Apart

8 MeV Electron Induced Changes in Structural and Thermal Properties of Lexan Polycarbonate1685
Figure 5. FT-IR spectra of pristine and electron irradiated
Lexan.
from this, the intensity of the peak band corresponding to
C=O stretch at 1700 cm–1 decreases slightly on irradia-
tion. This may be due to chain-scission at the carbonate
site (as shown in Figure 1) with the probable elimination
of carbon dioxide or carbon monoxide. The corrobora-
tion of chain-scission can be deduced from the decrease
in the intensity of absorption bands around 1160 cm–1
attributed to carbonate stretch. No change in the C-H
stress has been observed which indicates that the electron
irradiation have not influenced the benzene ring.
3.4. Differential Scanning Calorimetry Study
One of the important parameters of polymer namely
glass transition temperature can be determined using
DSC data. Glass transition temperature is a temperature
where the polymer goes from rigid glassy state to rub-
bery state as chain becomes more flexible. At the glass
transition temperature, the weak secondary bonds that
stick the polymer chains are broken and macromolecule
starts to move. DSC thermograms of pristine and electron
irradiated Lexan samples were measured and are shown
in Figure 6. The endothermic transformation of the unir-
radiated Lexan film occurs in a temperature range 145˚C
to 154˚C with a glass transition temperature (Tg) of
150˚C and the corresponding heat of fusion was found to
be 4.43 J/g. At the electron fluence 3.02  1014 elec-
trons/cm2, the DSC curve show a shift of Tg to 146˚C and
for 6.79  1014 electrons/cm2 Tg was observed at 143˚C,
i.e. the glass transition temperature decreases with in-
crease in electron fluence. After irradiation, the shift in
the Tg to lower temperature reveals that the electron irra-
diation leads to chain-scission and subsequently reduce-
tion in molecular weight. As a result, the polymeric sys-
tem was changing towards more disordered state [28]
which is also confirmed from XRD studies. It was found
3.02 ×10
14
electrons/cm
2
6.79 ×10
14
electrons/cm
2
Temperature (˚C)
Figure 6. DSC pattern of pristine and electron irradiated
Lexan.
that the heat of fusion for unirradiated Lexan was found
to be 4.43 J/g. After irradiation, the heat of fusion de-
creases with increase in electron fluence, i.e. for 3.02 
1014 electrons/cm2 it was found to be 4.34 J/g and for
6.79  1014 electrons/cm2 it was found to be 4.15 J/g.
This decrease in heat of fusion may be due to bond
breaking during electron irradiation.
3.5. Thermogravimetric Analysis Study
The thermal degradation is a very important process
which helps to know the influence of the polymer struc-
ture on the thermal stability and the temperature at which
the polymer can be used. Sinha et al. [12] have reported
that the thermal stability of the polycarbonate detector
decreases at high dose of gamma, and the weight loss
starts at around 420˚C and continues up to 700˚C. Figure
7 shows the thermograms of the pristine and the electron
irradiated Lexan samples showing the weight (%) as a
function of temperature. From Figure 7 it was found that
the pristine sample thermogram shows a small change in
weight loss at 250˚C and sample is thermally stable up to
440˚C. This weight loss was due to water vaporization
and was not significant. After 440˚C, the film experi-
enced a great weight loss up to 530˚C because of thermal
decomposition, and about 76% of the sample decom-
posed in to volatiles. After 530˚C, there is a small de-
crease in weight loss due to emission of volatile gases.
The thermal decomposition temperature for pristine
Lexan was found to be 495˚C. Lexan sample irradiated at
fluence 3.02  1014 electrons/cm2 was thermally stable up
to 445˚C and then there was a great loss in weight of the
sample up to 540˚C. In this region almost 75% of the
sample was decomposed in to volatiles. After 540˚C, the
weight loss of the sample was slow and corresponding
thermal decomposition temperature was found to be

8 MeV Electron Induced Changes in Structural and Thermal Properties of Lexan Polycarbonate 1686
3.02 ×10
14
electrons/cm
2
6.79 ×10
14
electrons/cm
2
Temperature (˚C)
Figure 7. TGA thermogram of pristine and electron
irradiated Lexan.
502˚C. The Lexan sample irradiated by electron of flu-
ence 6.79  1014 electrons/cm2 was stable up to 480˚C
and then sudden decrease in the weight loss was ob-
served up to 570˚C. After 570˚C, the weight loss was less
and the corresponding thermal decomposition tempera-
ture was found to be 516˚C. From this study it is clear
that, the thermal stability of Lexan increases after elec-
tron irradiation.
4. Conclusions
The conclusion drawn from the studies of 8 MeV elec-
tron irradiation effects on the structural and thermal
properties of Lexan are as follows. The XRD results
show decrease in crystallite size and percentage of crys-
tallinity upon irradiation indicating that the polymeric
system is moving towards more disordered state which is
also supported by DSC studies. Using UV-Visible stud-
ies, the chromophore group formation were obtained by
linear fit and the obtained values for the formation of
chromophore groups is decreased at longer wavelength.
The carbonate linkage is found to be the radiation-sensitive
linkage and benzene ring does not undergo any changes
after irradiation as studied from FTIR studies. TGA re-
sults reveal that thermal stability of Lexan increases after
irradiation.
5. Acknowledgements
The authors are thankful to Board of Research in Nuclear
Science, Department of Atomic Energy, Govt. of India
for financial support through a project No. 2001/34/21
-BRNS/453. Authors are thankful to research scholar and
staff of Microtron Centre for their help and support dur-
ing the course of this work. The authors are also thankful
to staff of USIC, Karnatak University and staff of STIC,
Cochin University for extending the experimental facil-
ity.
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