ª. BÜLBÜL: IMPROVING THE CROSSLINK DENSITY AND THE MECHANICAL PROPERTIES AFTER VULCANIZATION ...
71–78
IMPROVING THE CROSSLINK DENSITY AND THE
MECHANICAL PROPERTIES AFTER VULCANIZATION FOR AN
IRON OXIDE LAYER (SCALE) AND SBR/RUBBER
MASTERBATCH
IZBOLJ[ANJE GOSTOTE PRE^NEGA ZAMRE@ENJA IN
MEHANSKIH LASTNOSTI Z VULKANIZACIJO IZDELANEGA
KOMPOZITA IZ STIREN-BUTADIENSKE GUME IN [KAJE
ªaban Bülbül
Necmettin Erbakan University, Faculty of Seydiþehir Ahmet Cengiz Engineering, 42370 Konya, Turkey
Prejem rokopisa – received: 2019-06-14; sprejem za objavo – accepted for publication: 2019-08-18
doi:10.17222/mit.2019.129
In this study iron oxide layers (IOLs) formed on the surfaces of ingots during a rolling process were supplemented into
stiren-butadiene rubber (SBR) based on a referenced rubber-back composition of 5–10–15–20 %, and accordingly five different
samples were prepared. After vulcanization, the hardness, density, abrasion loss, tensile strength, percentage elongation, tearing
strength and crosslink densities were measured. In addition to that, the effects of the crosslink density on the mechanical
properties are discussed. The properties of the generated new compounds are comparatively discussed, both with respect to
themselves and with those of the referenced rubber. It was observed that the iron oxide layer significantly reduces the cost of
compound, and increases the wearing resistance with the increasing of the crosslink density, and provides an advantage for the
properties of hardness, tensile strength, tearing strength and percentage elongation. In order to explain the changes in the
mechanical properties, the fracture surfaces were characterized by Scanning Electron Microscopy (SEM) and Energy-Dispersive
Spectroscopy (EDS). When the SEM images are examined, it is seen that the filler dispersion in the rubber matrix is adversely
affected by its increasing amount. The improved materials are discussed in terms of their usability in outsole applications.
Keywords: compound, mechanical properties, iron oxide layer, crosslink
V prispevku avtor predstavlja {tudijo priprave kompozitov na osnovi stiren-butadienske gume (SBR), kateri je bil kot oja~itvena
faza dodan `elezov oksid (IOL), ki nastaja kot {kaja na povr{ini ingotov med postopkom vro~ega valjanja. Pripravili so pet
razli~nih me{anic s (5, 10, 15 in 20) %, IOL. Po vulkanizaciji so dolo~ili trdoto, odpornost proti abrazijski obrabi, gostoto,
natezno trdnost, raztezek, stri`no trdnost in gostoto pre~nega zamre`enja. Dodatno so analizirali vpliv gostote pre~nega
zamre`enja na mehanske lastnosti. Lastnosti novih kompozitov so primerjali med seboj in z referen~no osnovo (~isto SBR, brez
dodatka polnila). Ugotovili so, da IOL pomembno zmanj{a ceno kompozita, izbolj{a odpornost proti obrabi s pove~anjem
gostote pre~nega zamre`enja, kakor tudi druge lastnosti, kot so: trdota, natezna in stri`na trdnost ter raztezek. Da bi razlo`ili
spremembe mehanskih lastnosti izdelanih kompozitov, so okarakterizirali prelomne povr{ine z vrsti~nim elektronskim
mikroskopom (SEM) in energijsko disperzijsko spektroskopijo (EDS). Na osnovi SEM posnetkov avtorji ugotavljajo, da
porazdelitev polnila oz. njegova disperzija v matrici gume, u~inkuje sorazmerno z nara{~ajo~im dele`em polnila. Avtorji v
zaklju~ku {e ugotavljajo, kak{na je uporabnost teh kompozitov v ~evljarstvu za izdelavo podplatov.
Klju~ne besede: spojina, mehanske lastnosti, plast `elezovega oksida, pre~no zamre`enje
1 INTRODUCTION
Rubber can be examined in two groups as natural
rubber derived from the essence (latex) of the rubber tree
(hevea brasiliensis), and synthetic rubber produced from
petroleum. The areas of usage of rubber materials are
increasing day by day. Especially in the automotive
sector, it is widely used in medical applications, toys,
shoe soles, oil and water pumps, energy transfer,
buildings and highways.
1
Although there are applications
where the desired performance properties can be
obtained by using a single rubber type; in the majority of
applications, more than one rubber is blended so as to
benefit from the properties of all the included rubbers, at
certain levels, and sometimes superior properties are
obtained. The blending of rubbers is applied in some
cases to lower the cost.
The strengths of rubbers are low when used as a
reinforcing filler. They are often mixed with reinforcing
fillers to prepare rubber with higher strength. This makes
it important for both the careful selection of the filler
used, and to carry out further works to improve the
properties of the fillers. The most commonly used fillers
in the production of rubber materials are fillers of carbon
blacks and silicates. Moreover, it is also possible to use
non-reinforcing fillers such as calcium carbonate, talk,
barite, etc. for reducing the costs; there are also studies
in which many herbal and mineral origin wastes are
utilized as a filler.
2–4
The varying price of carbon black,
arising from the instability in oil prices, produced from
unrenewable resources such as petroleum and natural
Materiali in tehnologije / Materials and technology 54 (2020) 1, 71–78 71
UDK 620.1:67.017:621.792.053 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 54(1)71(2020)
*Corresponding author's e-mail:
sabanbulbul42@hotmail.com (ªaban Bülbül)

gas, has recently enforced the industry to search for
alternative filler materials.
5
When the relevant studies in the literature are
reviewed, it is seen that many filler materials such as rice
husk, clay, wood ash, regenerated (recycled) rubber, blast
furnace flue dust, mica powder, wollastonite etc. are used
as an alternative to carbon black.
6–8
In addition, it is
known that these fillers and additives added to the rubber
have a significant effect on the crosslink density after
vulcanization. When the studies discussing the effects of
fillers on the crosslink density are reviewed, a great num-
ber of alternative fillers are seen to be used. P. Pitchapa
et al. added pineapple leaf fibers, together with carbon
black, into a natural rubber (NR) matrix, and investigated
the effects of crosslink density within the matrix
included hybrid filler, on the mechanical properties, by
changing the sulfur ratio by2%t o4% .T h e yobserved
an increase in the tearing and tensile strengths of the
material, with the increase in the amount of crosslink in
the in which single filler had been used. But they stated
that this increase was more evident in the case of hybrid
filler use. Similarly, the percentage elongation of the
improved material with the increase in the amount of
crosslink.
9
It was emphasized in a limited number of
studies done regarding the effect of crosslink density on
the mechanical properties that filler and additive ma-
terials also affect the density of the crosslink.
10–12
Wong
et observed an increase in the crosslink density when a
certain amount of graphene oxide was added into a BR
compound with a SBR matrix. They emphasized that the
tensile strengths and percentage elongation of the with
SBR matrix increased, depending on the increase in the
crosslink density. As a consequence, it has been proven
that graphene oxide can be used as an agent that can
increase the crosslink efficiency when used as an
additional filler in addition to the other fillers.
13
The crosslink density for rubber is one of the most
influential parameters on the physical, mechanical and
dynamic properties. The hardness of the material in-
creases with the increasing crosslink density, which also
leads to an increase in the hardness. The elastic pro-
perties, and accordingly the permanent deformation gets
better, with a high crosslink density. However, as well as
crosslink density, the type of crosslink is also effective
on mechanical properties, such as tensile strength,
percentage elongation, tearing strength, and on aging
strength.
14
The effect of crosslink density on the material
properties is an issue that needs to be evaluated from
various aspects. Today, the utilization of wastes, not
possible to be recycled with other methods, as a filler for
appropriate matrices, especially for polymeric materials,
for a sustainable economy and environment draws a
great deal of interest. In this way, it may be possible to
reduce the dependence on non-renewable raw materials.
Besides, it is seen that many wastes have the potential to
improve the properties of the polymeric matrix into
which they have been added, in the event that an
appropriate interface can be obtained. B. Karaaðaç,
15
in
his study, used pistachio husk as an alternative filler
material in a NR/SBR-based conveyor belt compound.
The vulcanized characteristics, mechanical, thermal,
morphological and abrasion characteristics of containing
pistachio husk were investigated. Increasing the rate of
addition of the pistachio husk into the rubber compound
led the vulcanized degree to decrease, and the tensile
strength to reduce. However, the abrasion resistance
could be improved significantly with the inclusion of
pistachio husk. It has been reported that the low price,
environmentally friendly and high abrasion resistant
could be produced if some losses in the tensile properties
could be tolerated. Another study in which non-recycl-
able materials were used as fillers was conducted by R.
L. Timings.
16
New compound compositions were formed
by adding paper, fabric pieces and wood dust in specific
ratios into the rubber compound. It was reported that
wood dust reduces the cost and the pieces of paper and
cloth improved the electrical insulation. Finally, M. N.
Ichazo et al.
17
proved that permanent deformation and
aging properties of natural rubber strongly depend on the
particle sizes of the fillers added, and concluded that
these properties were almost unaffected by the addition
of wood dust with small particle size (less than 250–300
μm). On the other hand, the addition of wood dust to
rubber compound increased the tensile strength, and the
reinforced with 300–425 μm wood dust yielded better
results than the reference. Therefore, it has been con-
cluded that wood dust from tropical trees such as "Puy"
and "Algarrobo" can be used as a semi-strengthening
filler.
The aim of this study was to investigate whether the
oxide layer, which is produced as waste in rolling plants
and not possible to be recycled with other methods, can
be used as a filler, and whether the resulting compound
compositions can be used for outsole applications. In this
way it will be possible to prevent the environmental
damage that may be caused by the disposal of the waste
oxide layer directly into the nature, and shed light on
new studies on the recyclability of wastes with a similar
structure.
2 EXPERIMENTAL PART
2.1. Materials
The SBR 1502 / Rubber masterbatch used in this
study was supplied from Defne Kauçuk Import and
Export Co. Ltd., (Turkey), and rubber powders and
calcite (CaCO
3
) from Petkim Inc (Turkey). The oxide
layer was supplied from a rolling plant, namely,
Yolbulan Demir San. and Co. Ltd., (Turkey). Other
additives used in the study were purchased from Bayer
Kimya Co. Ltd., (Turkey). The densities of all fillers are
given in Table 1.
The solvents used in the swelling test (acetone and
chloroform) were supplied from Bereket Kimya Co.
Ltd., Turkey.
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72 Materiali in tehnologije / Materials and technology 54 (2020) 1, 71–78

Table 1: Densities of compound components
Components Density (g/cm
3
)
SBR 1502 0.94
Rubber Masterbatch 1.18
Rubber Powder 1.17
Calcite (CaCO
3
) 2.71
Scale (Iron Oxide Layer) 3.40
2.1.1. Rubber back (Masterbatch)
It was extracted from non-vulcanized, regarded as
non-standard by plants producing technical rubber
compound, prepared by mixing filler, process oil and
vulcanizing agents together with two or more rubbers.
Rubber masterbatch used in this study contains 70 %
natural rubber, 20 % SBR and 10 % cis-butadiene rubber
(CBR). Its specific weight is about 1.18 g/cm
3
and the
tensile strength after being vulcanized is about
17–22 MPa, while the hardness is about 65 Shore A.
2.1.2. Oxide layer
The oxide layer is a metal oxide layer formed as a
result of reacting of iron annealed up to 700 °C, with
oxidizing gases (such as sulfur and oxygen), while being
rolled. The oxide layer contains 69.94 % Fe and 30.06 %
O
2
when it is in the pure state. Rolling equipment
oriented oil inclusions can occur during the rolling
process. The oil content usually varies between 0.1 and
2.0 %, but sometimes this rate extends up to 10 %. The
chemical analysis of the oxide layer used in the study is
given in Table 2.
Table 2: Chemical analysis of the oxide layer used in the study
Content Fe2O3 TiO2 SiO2 CaCO3 MgCO3 Al2O3
Percentage
by weight
94.52 0.23 1.74 0.96 1.05 0.40
It was seen that approximately3%oftheoxide layer
formed on the ingots were broken away from the surface.
This broken oxide layers were collected and ground into
the grain size of 20 μm, with the help of a Super Mixer
brand SM 132 model grinder working at high speed
(11,000 min
–1
).
2.2. Methods
2.2.1. Preparation of rubber compound
Rubber master batch, SBR and filler materials were
mixed in a laboratory-type banbury device (Farrell
brand) at 60 min
–1
and 80 °C for 10 min. The compound
was mixed in a two-roll mill at a speed of 40 min
–1
at
80 °C for 5 min., after being conditioned for 24-hour
incubation. The oxide layers in the amounts of 5 %,
10 %, 15 % and 20 % by weight were added and mixing
process continued for 5 min. more. Finally, softeners,
activators, accelerators and sulfur were added into the
compound and mixed for 2 min. and the process was
finished after transforming the compound into sheet. The
formulations of the compounds are given in Table 3.
Table 3: Composition of rubber compounds
Compounds
Sample Codes
G IOL1 IOL2 IOL3 IOL4
Weight in phr.
SBR 1502 90 90 90 90 90
Masterbatch 10 10 10 10 10
Rubber powder 50 50 50 50 50
Calcite (CaCO
3
) 1 01 01 01 01 0
Sulfur 33333
MBT
a
0.5 0.5 0.5 0.5 0.5
CZ
b
11111
DPG
c
11111
Stearic acid 44444
Zinc oxide 44444
Scale (Iron oxide layer) 0 5 10 15 20
a
2-Mercaptobenzothiazole,
b
N-Cyclohexyl-2-benzothiazole sulfo-
namide,
c
Diphenyl guanidine
2.2.2. Vucalization of rubber compounds
The rubber compounds transformation into flat sheet
were cut in small pieces, placed in a (180 × 180 × 6) mm
mold that could be compressed by press (Hidrosan)
device for 150 °C at 6 min. under 16 MPa pressure and
the compounds were vulcanized under the same con-
ditions. All these compounds used in experimental
studies were prepared under same parameters.
2.2.3. Characterization
The samples were conditioned for 24 h at 25±2 °C in
an environment containing 50 % relative humidity before
the test was performed. The tensile test was carried out
in accordance with ISO 37 standard at a speed of
10 mm/s through a Tinius brand H25KS model tensile
testing device. The hardness of the material was
measured in Shore A, in accordance with ISO 868,
through a AffriCommerciale brand AFFRI 3001 model
durometer. The tearing test was performed through the
same tearing device, in accordance with ISO 34
standard. The density measurements were made pursuant
to ISO 2781, in accordance with Archimedes principle,
and pure water was used as the reference liquid. In the
wearing tests, performed pursuant to ISO 4649 standard;
the volume loss was measured, occured after a test
sample under a 10 N perpendicular force, placed on a
drum rotating at 84 min
–1
, covered a distance of 40 m.
The crosslink densities of the rubbers were calculated
using equilibrium volume swelling equation known as
the Flory-Rehner equation.
18
This method is based on the
principle of swelling rubbers in a suitable solvent. It is
known that the elastic recovery forces are inversely
proportional to the length of the polymer chains between
the cross-linking points. Therefore, the crosslink density
was considered lower in samples that exhibited high
swelling in the solvent. The test samples were kept
waiting in a chlorofrom medium for 72 h, and cross-link
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Materiali in tehnologije / Materials and technology 54 (2020) 1, 71–78 73

density, interrelated to swelling ratio in the solvent, was
calculated using Flory-Rehner equation (Equation (1)):
[]
V
VVV
VV
V
e
s
=
−−++
−
⎡ ⎣ ⎢ ⎤ ⎦ ⎥ ln( )
/
1
2
222
2
2
13
2
 (1)
In above equation,
V
e
: Crosslink density (mol/cm
3
)
V
2
: Volume fraction of swollen sample
V
s
: Molar volume of solvent (cm
3
/mol)
 : Polymer – solvent interaction parameter
The morphologies of the fracture surfaces of the
samples after the wearing test were reviewed using a
Zeiss Ultra/Plus scanning electron microscope (SEM).
The fracture surfaces of the samples were coated with
5-nm-thick pure gold to increase its conductivity.
19
The
operating voltage of the microscope during the review of
microstructure images was selected as 30 kV. The
Energy-Dispersive Spectroscopy (EDS) analysis method
was used to distinguish the components in the sample.
3 RESULTS AND DISCUSSION
3.1. Crosslink density
The crosslink densities of SBR/Rubber masterbatch
are given in Figure 1, interrelatedly to the amount of
oxide layer contained. It was observed that the crosslink
density increased systematically with the increasing IOL.
The highest crosslink density was measured in the IOL4
compound (62.4947 × 10
6
mol/cm
3
). The crosslink den-
sity of the G compound, taken as a reference and not in-
cluded oxide layer was measured 42.1338×10
6
mol/cm
3.
Accordingly, it was seen that the crosslink density of the
reference compound increased by about 48 %, with the
addition of the oxide layer by 20 %. This increase is
thought to be caused by two reasons. The first of these is
the increase in the heat capacity of the compound, with
the metal oxide added to the matrix, and the post-cure
event that takes place due to more slowly decreasing of
heat during the rest period.
The second one is the activities of metal oxides for
moving their accelerator radicals to rubber main chains.
Although the main activator used to exhibit this activity
is zinc oxide, it is well known that all metal oxides
perform similar tasks to zinc oxide.
20,21
However, it is ob-
vious that far more detailed chemical analyzes are
required to clarify the activating effect of the oxide layer.
3.2. Physical-mechanical properties
The mechanical properties of SBR/Rubber master-
batch depend on many factors, such as chemical struc-
ture of rubber matrix, type and rate of fillers, amount and
type of crosslinkers, degree of crosslinking, decompo-
sition of crosslinkers and conditions of vulcanization. In
this study the mechanical properties, in the presence of
IOL, were evaluated by interrelating with the crosslink
density.
The tension-deformation graph, for all, is given in
Figure 2a. As well as tensile strength values are approxi-
mate to the referenced vulcanizate; an explicit increase
was observed in the percantage elongation values. The
high percentage elongation behavior for similar tension
levels points out decreasing tension modulus levels in
containing IOL. However, the crosslink density values,
increasing in paralel with the amount of IOL, would
require an increase in the tension modulus in the absence
of another physical effect, which suggests that the
increase in the percantage elongation values, in the pre-
sence of IOL, is due to the physical interactions between
the chains rather than the crosslink structure of the
material. It is also emphasized in the literature that with
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74 Materiali in tehnologije / Materials and technology 54 (2020) 1, 71–78
Figure 2: IOL amount dependent variation of mechanical properties
of compounds: a) tensile strength and percantage elongation, b) tear-
ing strength Figure 1: Crosslink density of compounds

a high crosslink density there is a greater elongation in
the presence of the additional physical interactions (such
as van der Waals forces).
22
It is seen in Figure 2 that the highest tensile strength
was obtained for IOL4 coded vulcanizate, suplemented
with IOL by 20 % (7.47 MPa). The minimum tensile
strength for rubber soles (outsole), according to relevant
standards, is 5.8 MPa,
23,24
which can suggest that
outsoles is a potential application area for economical
and environmentally friendly rubber materials that can
be produced by the addition of an oxide layer. When the
test results of the percentage elongation values of com-
pound G and IOL supplemented compounts were
reviewed, it was seen that while the percentage elon-
gation of compound G was 233 %, that of IOL supple-
mented varied between 359 and 390. It can be said that
as well as the increase in the unit elongation amount
caused a decrease in the tension module of, with
increasing IOL addition, it also improved the elasticity
property of the material.
25
The potential physical interactions in fillers, added to
the rubber compound, is high if the diffusion is suffi-
cient, which strengthens the rubber-filler interface. It is
known that the tensile strength, percantage elongation,
and tearing strength properties of the material obtained
from this compound are improved with the contribution
of a high crosslink density.
26–28
In this study, it is thought
that the mechanical properties are improved with the
development of rubber-filler interface in increasing oxide
layer ratios. Figure 2b shows that while the tearing
strength of the G-coded referenced compound was
6.68 kN/m, that of the IOL4-coded compound, prepared
with oxide layer addition by 20 %, ratio up 7.89 kN/m.
Considering that the tearing strength limit for outsole
materials, which are deemed as potential usage area, is 6
kN/m according to ISO 5676 standard, it is logical to
think that the oxide-layer-reinforced material can be used
safely for this purpose. The oxide layer chemically con-
tains a small amount of SiO
2
(Silica), CaCO
3
(Calcite),
Al
2
O
3
and highly stable Fe
2
O
3
(Table 2). In the literature
there are studies reporting that the physical and mecha-
nical properties can be improved with the addition of a
major part of these components.
29–31
The target density in the elastomeric materials varies
depending on the environment and conditions in which
the material will be used. The desired maximum density
value of the soles, according to ISO 4649 standard, is
1.5 g/cm
3
. Figure 3a shows that samples’ densities are
below the upper limit value specified in the standard. As
the supplement ratio of IOL filler increased, the densities
of the material expectedly increased as well. The reason
for this increase is that the density of the oxide layer,
added to SBR/Rubber masterbatch compound, is higher
than that of other fillers and the rubber matrix used in the
study (Table 1). Other parameters discussed for the
SBR/Rubber masterbatch compound after the addition of
oxide layer are the hardness and the abrasion loss. The
change of both parameters according to the amount of
IOL is given in Figure 3b.
As can be seen from the figure, as the amount of IOL
added to the SBR/Rubber masterbatch compound in-
creases, the hardness of the compound also increases
after the vulcanization. In the hardness measurements
made in accordance with the ISO 868 standard; as well
as the hardness of G-coded compound was measured to
be 65 Shore A; the hardness values in parallel with IOL
amount, were seen to increase between 6.1 % and 10.7 %
as compared to reference. Regarding the samples with
IOL filler; the lowest hardness value was measured as 69
Shore A at IOL1, the highest hardness value was
measured as 72 Shore A at IOL4. It is known that metal
oxides and carbide oxides are far harder than polymeric
materials in general. Fe
2
O
3
constitutes an important
fraction of the IOL filler used in the study. Another
reason for the increase in the hardness is thought to be an
increase in the crosslink densities of the material.
A standard rubber stated that in ISO 4649 is required
to determine the abrasion resistance index (ARI) of the
vulcanisates for comparison. According to the standard,
the maximum acceptable abrasion loss is 250 mm
3
.
Figure 3b shows the abrasion loss of the vulcanisates
were relatively similar. It is seen that the maximum
abrasion loss occurred in the reference G sample. The
minimum abrasion loss was measured in the IOL4
sample containing the oxide layer in the ratio of 20 %
(214 mm
3
). The high abrasion resistance of the metal
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Materiali in tehnologije / Materials and technology 54 (2020) 1, 71–78 75
Figure 3: Change of physical properties of compounds depending on
increasing IOL ratio: a) density, b) hardness and abrasion loss

oxides contained in the oxide layer improved the total
abrasion resistance of the rubber material in proportion
to the fraction in which it is contained. This finding
shows parallelism with the results of the studies in the
literature.
32–34
It was seen that all the containing oxide
layer could ensure the abrasion resistance standard
required for the outsole.
3.3. Morphological analysis
The SEM images of the fracture surfaces of all after
fracture tensile tests are given in Figure 4.W h e nt h e
fracture surfaces were examined, it was seen that with
the increase of the amount of oxide layer, the oxide layer
on the fracture surface became clearer, the grain sizes
changed and the filler diffusion on the interface was
expectedly disrupted. It was observed that the distance
between the filler agglomerates decreased, even they
formed an aggregate imagine by gathering. The fracture
largely occurred throughout the oxide layer agglome-
rates, which is such as to verify the parallel relationship
between the increase in the oxide layer amount, and
fracture. Another factor for the improvement of the frac-
ture resistance is considered to be the increasing cross-
link density at increasing oxide-layer rates. In the
G-coded compound (Figure 4a); instead of deep pit
zones formed during the exit of the fracture filler, the
fracture zones of the rubber, offering a wavy imagine
draw the attention, which suggests that a different facture
mechanism is being followed.
EDS analysis was performed to determine the
fracture surface morphologies after tensile test applied to
the produced material by adding the iron oxide layer in
different ratios. The EDS analysis was realized
especially in the areas exhibiting elevations where a
regional difference was observed for the fracture surface
morphologies of the tensile test samples (Figure 5).
This was necessary in order to determine the dis-
persion of the iron oxide layer in the dispersed material.
Even though the EDS analyses reveals elemental results,
it can also give important results about the differentiation
of the dispersion as well as about the fracture surface
forms based on this differentiation. In this study, the Fe
elemental distribution was emphasized even though the
EDS analyses were carried out on alloy elements in the
chemical composition of the dopants and fillers added
into rubber compound with SBR 1502 rubber matrix.
With increasing amount of filler added into the material,
the amount of Fe on fracture surfaces was observed to
increase. Although there was no iron oxide layer within
the G compound, it was observed according to the results
of the chemical analysis that it contained Fe in the
amount of 0.7 % and was homogenously distributed. It
was thought that this was associated with the rubber
powder used in the study (tire recycling).
When all the EDS results were examined, it was
found that the amount of Fe in the microstructure
changed depending on increasing amount of iron oxide
layer, which thus made a fundamental difference and Fe
distribution played a determining role in the fracture
results.
3.4. Cost analysis
The highest price is seen to belong to the reference
compound (G) in the unit price analysis. As the ratio of
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76 Materiali in tehnologije / Materials and technology 54 (2020) 1, 71–78
Figure 4: SEM images of: a) G, b) IOL1, c) IOL2, d) IOL3 and e) IOL4 compounds

the IOL filler added to the G compound increased, a pro-
portional decrease was observed in the total compound
cost (Figure 6). The raw material cost of IOL4 com-
pound, into which oxide layer in the amount of 20 % was
added, is lower by 13.16 % than the G compound. This
decrease ranged between 2.6 and 7.91 % for the other
material.
The lack of any commercial value of oxide layer
allows the cost of raw materials to be reduced in the case
of being used as a filler in materials like rubber, which
allows mixing in the solid phase. The transportation cost
was ignored in the cost calculation. Besides, the avail-
ability of harmlessly disposal of oxide layer in this way,
released as a waste in rolling plants, attaches importance
for sustainable environmental policies. The fact that the
oxide layer can be used in the SBR/Rubber masterbatch
compound thus decreasing the cost of compound, and
improve the percentage elongation and abrasion resist-
ance, which makes the use of oxide layer attractive, and
significantly increases the value of the waste. The
SBR/Rubber masterbatch containing oxide layer was
found to have a high usage potential in outsole pro-
duction. Accordingly, it is thought that with the use of
oxide layer, especially small-scale producers can become
competitive in terms of price and quality.
4 CONCLUSIONS
In this study the effect of oxide layer support on the
physical, mechanical and morphological properties of
SBR/Rubber masterbatch matrix rubber was reviewed,
and the findings were attempted to be interrelated with
the crosslink densities of the material. The compound
compositions studied were discussed for the production
of outsoles as a potential usage area. With the addition of
oxide layer to rubber, it was seen that the density and
hardness of the material increased, the abrasion resist-
ance was improved significantly and high percentage
elongation values were obtained without any loss in the
tensile strength. All of the changes in physical and me-
chanical properties occurred in parallel with the content
of oxide layer in the compound. The improvement in the
mechanical properties was attributed to the increased
crosslink density, in the presence of oxide layer, and also
to the physical interactions of the oxide layer in the
structure of the metal oxide with rubber chains. It was
concluded that the SBR/Back Rubber prepared with the
addition of oxide layer up to 20 % satisfies the properties
specified in the production of the outsole, defined in the
ISO 4649 standard, and they can be used in the produc-
tion of competitive sole as they are economic and
environment friendly.
Acknowledgements
I would like to express my gratitude towards my
invaluable teacher Assoc. Prof. Dr. Miss Assoc. Prof. Dr.
Bagdagül KARAAGAÇ, from Kocaeli University,
Faculty of Engineering, Department of Chemical
Engineering, is thanked for helping me in this study, and
for sharing her knowledge and experiences with me.
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