Effects of gamma and electron beam irradiation on the properties of ...

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Radiation Physics <strong>and</strong> Chemistry 79 (2010) 297–300
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Radiation Physics <strong>and</strong> Chemistry
journal homepage: www.elsevier.com/locate/radphyschem
<strong>Effects</strong> <strong>of</strong> <strong>gamma</strong> <strong>and</strong> <strong>electron</strong> <strong>beam</strong> <strong>irradiation</strong> on the properties <strong>of</strong>
calendered cord fabrics
Ays-e Aytac- a , Veli Deniz a, , Murat S-en b , El-Sayed Hegazy c , Olgun Güven b
a Kocaeli University, Department <strong>of</strong> Chemical Engineering, 41040 Kocaeli, Turkey
b Hacettepe University, Department <strong>of</strong> Chemistry, Beytepe, 06532 Ankara, Turkey
c The National Centre for Radiation Research <strong>and</strong> Technology (NCRRT), Cairo, Egypt
article info
Keywords:
Gamma <strong>irradiation</strong>
E-<strong>beam</strong> <strong>irradiation</strong>
Tyre cord
Pre-vulcanization
abstract
The effects <strong>of</strong> <strong>gamma</strong> <strong>and</strong> e-<strong>beam</strong> <strong>irradiation</strong> on mechanical <strong>and</strong> structural properties <strong>of</strong> nylon 66 (Ny
66), nylon 6 (Ny 6) <strong>and</strong> poly(ethylene terephthalate) (PET) fabrics used in tyres were investigated. The
untreated (greige), treated cords <strong>and</strong> calendered fabrics were irradiated at different doses. It is found
that the effects <strong>of</strong> high energy <strong>irradiation</strong> on greige, treated cords <strong>and</strong> calendered fabrics are similar. No
protective effect <strong>of</strong> compounds used in calendering was observed against radiation-induced oxidative
degradation. The deterioration effect <strong>of</strong> <strong>gamma</strong> <strong>irradiation</strong> on mechanical properties is much higher
than that <strong>of</strong> e-<strong>beam</strong> <strong>irradiation</strong> for all types <strong>of</strong> samples. Limiting viscosity numbers <strong>of</strong> both <strong>gamma</strong> <strong>and</strong>
e-<strong>beam</strong> irradiated nylon 6 <strong>and</strong> nylon 66 cords were found to decrease with increasing dose. It is
concluded that PET calendered fabric has higher resistance to ionizing radiation. Ny 6 <strong>and</strong> Ny 66
calendered fabrics are more sensitive even at low doses. Therefore, the effects <strong>of</strong> high energy <strong>irradiation</strong>
on tyre cords have to be taken into consideration during tyre design reinforced with particularly Ny
fabrics if pre-vulcanization with high energy radiation is to be applied.
& 2009 Elsevier Ltd. All rights reserved.
1. Introduction
Corresponding author. Tel.: +90 2623033531; fax: +90 2623033003
E-mail address: vdeniz@kocaeli.edu.tr (V. Deniz).
The curing process is the final step in tyre manufacturing,
whereby a green tyre is built from plies made <strong>of</strong> rubber
compounds <strong>and</strong> reinforcing fabrics. Curing <strong>and</strong> shaping <strong>of</strong> tyres
are accomplished by internal <strong>and</strong> external heat treatment. In
curing process, green tyre is placed into curing machine while a
bladder permanently remains inside <strong>of</strong> the green tyre <strong>and</strong> the
desired shape <strong>of</strong> the tyre is formed during curing under press
(Han et al., 1999). Curing process has a major effect on tyre
uniformity. During bladder expansion the materials should be
distributed evenly for more uniform thickness, better balance <strong>and</strong>
uniformity. One <strong>of</strong> the solutions for tyre uniformity problem is
radiation processing <strong>of</strong> rubber plies for pre-vulcanization.
Radiation processing has been widely accepted for use in many
areas <strong>of</strong> the global industry. Sterilization, polymer cross-linking
(tapes, tubes, cables), tyre component curing, the conservation <strong>of</strong>
art objects, the <strong>irradiation</strong> <strong>of</strong> selected food items are wellestablished
technologies. One <strong>of</strong> the successful industrial applications
<strong>of</strong> radiation processing has been the pre-vulcanization <strong>of</strong>
tyres imparting shape stability prior to final vulcanization. It is
important to keep the dimensional consistency <strong>of</strong> each component
in due course <strong>of</strong> tyre building <strong>and</strong> final vulcanization. The
carcass, however, tends to deform <strong>and</strong> flow during assembly <strong>and</strong>
vulcanization due to an extensive transformation under high
pressure, <strong>and</strong> results in the reduction in thickness <strong>and</strong> uneven
distribution <strong>of</strong> compounds in the tyre. The conventional tyre
technology overcomes this problem by using more thick <strong>and</strong>
expensive compound layers. The results <strong>of</strong> pre-vulcanization are
the improved green strength <strong>of</strong> the rubber compounds, especially
<strong>of</strong> the inner liner <strong>and</strong> stabilization <strong>of</strong> carcass plies <strong>and</strong> higher
quality tyre with more uniform thickness <strong>and</strong> better balance
(Drobny, 2005; Makuuchi, 2007). Dose requirements for prevulcanization
are in the range <strong>of</strong> 30–50 kGy (Sarma, 2005;
Makuuchi, 2007). Electron <strong>beam</strong> <strong>irradiation</strong> in tyre industry for
pre-vulcanization is already being applied commercially worldwide,
for example, 23 major Japanese tyre companies are using
<strong>electron</strong> accelerators for the production <strong>of</strong> radial tyres (Makuuchi,
2007; Minbiole, 2008). Since <strong>electron</strong> <strong>beam</strong> <strong>irradiation</strong> can be
applied to different components <strong>of</strong> radial tyre, such as inner liner
<strong>and</strong> carcass which is a composite <strong>of</strong> reinforcing materials <strong>and</strong>
rubber compounds (Makuuchi, 2007), the influence <strong>of</strong> high energy
<strong>irradiation</strong> on the reinforcing materials, i.e. on the textile cord
needs to be investigated.
In our previous work, the effect <strong>of</strong> <strong>gamma</strong> <strong>irradiation</strong> <strong>of</strong>
untreated <strong>and</strong> treated high tenacity Ny 66 <strong>and</strong> PET tyre cords was
investigated (Aytac- et al., 2007). It has been found that <strong>gamma</strong>
<strong>irradiation</strong> <strong>of</strong> tyre textile cords in air has slightly affected some
0969-806X/$ - see front matter & 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.radphyschem.2009.08.022

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mechanical properties <strong>of</strong> Ny 66 at relatively high doses, but has
not affected the mechanical properties <strong>of</strong> PET cords up to 200 kGy.
Some properties such as hot shrinkage, was improved to some
extent with dose.
In this study, the investigation <strong>of</strong> the effects <strong>of</strong> <strong>gamma</strong> <strong>and</strong>
e-<strong>beam</strong> <strong>irradiation</strong> on mechanical <strong>and</strong> structural properties <strong>of</strong> Ny
66, Ny 6 <strong>and</strong> PET fabrics was aimed. The untreated (greige),
treated cords <strong>and</strong> calendered fabrics (also called as carcass plies)
were irradiated at different doses with e-<strong>beam</strong> <strong>and</strong> <strong>gamma</strong> rays.
The effects <strong>of</strong> types <strong>of</strong> <strong>irradiation</strong> <strong>and</strong> cord types on the
mechanical properties <strong>of</strong> the cords are discussed.
2. Experimental
Breaking Strength (N)
160
150
140
130
120
110
100
Ny 6
e-BEAM
GAMMA
0
20 40 60 80
Dose (kGy)
2.1. Material
The Ny 66 <strong>and</strong> PET greige yarns <strong>and</strong> treated fabrics were
supplied from Kordsa Global (Turkey). The treated Ny 6 cord fabric
was supplied from SRF Limited (India). Resorcinol–formaldehyde–
latex (RFL) solution was used as dipping solutions where latex was
styrene/butadiene/vinyl pyridine terpolymer. All types <strong>of</strong> fabrics,
i.e. Ny 6 (940 dtex), Ny 66 (1400 dtex) <strong>and</strong> PET (1670 dtex) were
calendered by Turk Pirelli Lastikleri A.S. in Izmit, Turkey. Natural
rubber based compounds were used for calendering process.
Thickness <strong>of</strong> the calendered fabrics was about 1.0–1.2 mm for all
types.
2.2. Method
Breaking Strength (N)
240
220
200
180
160
Ny 66
e-BEAM
GAMMA
0 20 40 60 80
Dose (kGy)
2.2.1. Irradiation source
Tyre cords <strong>and</strong> calendered fabrics were irradiated with <strong>gamma</strong>
rays at ambient temperature by using a Gamma cell 220 type
g-irradiator at a fixed dose rate <strong>of</strong> 0.13 kGy/h. They were also
irradiated by high-energy <strong>electron</strong> <strong>beam</strong> with an accelerator <strong>of</strong>
1.5 MeV–25 mA with 25 Gy/pass. All <strong>irradiation</strong>s were carried out
in air.
2.2.2. Tensile tests
Tensile tests were performed by using Instron tester 4502, with
cross head speed <strong>of</strong> 300 mm/min <strong>and</strong> gauge length <strong>of</strong> 254 mm
according to ASTM D885. An average <strong>of</strong> 5 test results has been
reported.
2.2.3. Viscosimetric studies
The viscosities <strong>of</strong> solutions <strong>of</strong> unirradiated <strong>and</strong> irradiated
samples were measured by an Ubbelohde type viscometer at
30 1C, formic acid for nylons <strong>and</strong> o-chlorophenol for polyester
cords being the solvents used throughout the experiments.
3. Results <strong>and</strong> discussion
The breaking strength <strong>and</strong> the elongation at break values are
widely used for the measurement <strong>of</strong> mechanical properties <strong>of</strong> tyre
cords. In this study, the effects <strong>of</strong> <strong>gamma</strong> <strong>and</strong> e-<strong>beam</strong> <strong>irradiation</strong>
on these mechanical properties <strong>of</strong> Ny 6, Ny 66 <strong>and</strong> PET fabrics
were evaluated. The breaking strength–dose curves for the
calendered fabrics made <strong>of</strong> Ny 6, Ny 66 <strong>and</strong> PET are shown in
Fig. 1(a) (b) <strong>and</strong> (c), respectively. As it can be seen in Fig. 1(a) <strong>and</strong>
(b), the tensile strength decreased with increasing dose for Ny 6
<strong>and</strong> Ny 66 cords, whereas slightly decreased for PET cords,
Fig. 1(c). Both types <strong>of</strong> Ny fabrics, i.e. Ny 6 <strong>and</strong> Ny 66 were much
affected adversely from ionizing <strong>irradiation</strong>. In other words, PET
fabrics have higher resistance to ionizing radiation than the nylon
fabrics. The ultimate effect <strong>of</strong> <strong>irradiation</strong> strongly depends on the
Breaking Strength (N)
240
220
200
180
160
e-BEAM
GAMMA
PET
0 20 40 60 80
Dose (kGy)
Fig. 1. Breaking strength–dose curves for calendered cords; (a) Ny 6, (b) Ny 66, (c)
PET.
Table 1
Effect <strong>of</strong> <strong>irradiation</strong> on the elongation at break values for calendared cords at
50 kGy.
Cord <strong>and</strong> <strong>irradiation</strong> type Elongation at break (%)
Un-irradiated Irradiated (50 kGy) Decrease (%)
Ny 66 Gamma 21.6 20.2 6.4
E-<strong>beam</strong> 20.8 3.7
Ny 6 Gamma 24.9 23.0 7.6
E-<strong>beam</strong> 24.4 2.0
PET Gamma 14.0 13.9 0.7
E-<strong>beam</strong> 13.9 0.7
chemical structure <strong>of</strong> polymers. It is well known that PET shows
good resistance to radiation due to the presence <strong>of</strong> the aromatic
rings on the main chain (Dole, 1973). The deterioration effect <strong>of</strong>

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<strong>gamma</strong> <strong>irradiation</strong> on mechanical properties is higher than that <strong>of</strong>
e-<strong>beam</strong> <strong>irradiation</strong> for all types <strong>of</strong> samples for a given dose. This is
a well-known fact due to dose rate difference between <strong>gamma</strong>
rays <strong>and</strong> e-<strong>beam</strong>. It has been found that the effects <strong>of</strong> high energy
<strong>irradiation</strong> on untreated, treated cords <strong>and</strong> calendered fabrics are
almost similar conforming to our previous findings for untreated
<strong>and</strong> treated Ny 66 cords. This was also confirmed by FTIR spectra
(Aytac- et al., 2007). No protective effect <strong>of</strong> the compounds used in
the coating <strong>of</strong> the cord in calendering against oxidative
degradation was observed. This demonstrates that there has
been still remaining oxygen interlayer phase <strong>and</strong>/or oxygen can
easily diffuse into rubber compound during calendering.
When we compare the effects <strong>of</strong> <strong>irradiation</strong>s on the calendered
fabrics, the breaking strength values were found to decrease down
to 90–80% <strong>of</strong> their original values with increasing dose up to
50 kGy for nylon 66 <strong>and</strong> nylon 6 fabrics, whereas almost
unchanged for PET fabric up to 75 kGy. The elongations at break
values for calendered fabrics irradiated at 50 kGy were given in
Table 1. Generally, elongation at break values slightly decreased
for nylons but unchanged for PET cords. The highest decrease in
0.12
Ny 6
Limiting viscosity number (dL/g)
0.10
0.08
0.06
0.04
0.02
e-BEAM
GAMMA
0.00
0
15 30 45 60 75 90
Dose (kGy)
1.4
Ny 66
Limiting viscosity number (dL/g)
1.2
1
0.8
0.6
0.4
0.2
0
e-BEAM
GAMMA
0 20 40 60 80
Dose (kGy)
Limiting viscosity number (dL/g)
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
e-BEAM
GAMMA
PET
0
0
20 40 60 80
Dose (kGy)
Fig. 2. Limiting viscosity number–dose curves (a) Ny 6 (b) Ny 66, (c) PET tyre cords.

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elongation at break values was observed for <strong>gamma</strong> irradiated
nylon 6 cords.
In order to see the effects <strong>of</strong> <strong>gamma</strong> <strong>and</strong> e-<strong>beam</strong> <strong>irradiation</strong>s
on the structural properties <strong>of</strong> fabric materials, the limiting
viscosity numbers were determined. Fig. 2(a)–(c), show the effects
<strong>of</strong> <strong>gamma</strong> <strong>and</strong> e-<strong>beam</strong> <strong>irradiation</strong> on the limiting viscosity
numbers <strong>of</strong> Ny 6, Ny 66 <strong>and</strong> PET tyre cords. As shown in Fig. 2,
limiting viscosity numbers <strong>of</strong> nylon cords decreased up to 75 kGy
<strong>irradiation</strong> dose, whereas remained almost unchanged for PET
cords. The behaviour <strong>of</strong> PET under <strong>irradiation</strong> is rather different
from that <strong>of</strong> nylons, because <strong>of</strong> the presence <strong>of</strong> aromatic rings that
increase the resistance to ionizing radiation. These behaviours can
be ascribed to different mechanisms acting in the polymer during
<strong>irradiation</strong>: mainly chain scissions, responsible for the decrease <strong>of</strong>
the molecular weight, <strong>and</strong> cross-linking working in the opposite
way. They both are present at any dose <strong>and</strong> the overall trend <strong>of</strong> the
molecular weight depends on the prevailing mechanism.
Furthermore, oxidative degradation reactions must also be taken
into account due to the presence <strong>of</strong> air during <strong>irradiation</strong>
(Buttafava et al., 2005). The decrease in limiting viscosity
number <strong>of</strong> nylon cords is attributed to the radiation-induced
oxidative degradation <strong>of</strong> the main chain which causes
deterioration in the mechanical properties <strong>of</strong> the nylon cords.
4. Conclusion
The effects <strong>of</strong> <strong>gamma</strong> <strong>and</strong> e-<strong>beam</strong> <strong>irradiation</strong> on the mechanical
properties <strong>of</strong> Ny 6, Ny 66 <strong>and</strong> PET fabrics that are widely used
as reinforcing textile materials in radial tyres were investigated.
The deterioration effect <strong>of</strong> <strong>gamma</strong> <strong>irradiation</strong> on mechanical
properties is higher than that <strong>of</strong> e-<strong>beam</strong> <strong>irradiation</strong> for all types <strong>of</strong>
samples. The effects <strong>of</strong> high energy <strong>irradiation</strong> on untreated,
treated cords <strong>and</strong> calendered fabrics are almost similar. No
protective effects <strong>of</strong> both the compound used in the coating <strong>of</strong>
cords in calendering <strong>and</strong> the treatment process against oxidative
degradation are observed. The decrease in limiting viscosity
numbers <strong>of</strong> Ny cords with increasing dose is attributed to
oxidative degradation <strong>of</strong> the main chain that causes deterioration
in the mechanical properties. PET calendered fabric has higher
resistance to ionizing radiation, <strong>and</strong> Ny 6 <strong>and</strong> Ny 66 calendered
fabrics are more sensitive even at low doses. Advantages <strong>of</strong> the
use <strong>of</strong> <strong>irradiation</strong> in tyre industry, such as improving <strong>of</strong> tyre
uniformity, <strong>and</strong> the possibility <strong>of</strong> saving materials <strong>and</strong> energy
have long been acknowledged (Makuuchi, 2007). However, the
effect <strong>of</strong> high energy <strong>irradiation</strong> on cords in calendered fabrics has
to be taken into consideration design <strong>of</strong> reinforced tyres
particularly with Ny fabrics if pre-vulcanization with high energy
radiation is to be applied.
Acknowledgements
The authors are grateful to KORDSA Global Industrial Yarn <strong>and</strong>
Tyre Cord Fabric Manufacturing <strong>and</strong> Trading Inc. <strong>and</strong> Turk Pirelli
Lastikleri A.S. in Izmit (Turkey) for their valuable supports in
realization <strong>of</strong> this study.
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