slide 1: ________________________________________
Author for correspondence E-mail: samiralnesrawyyahoo.com Mo.: 009647801889584
Int. J. Chem. Sci.: 144 2016 2439-2449
ISSN 0972-768X
www.sadgurupublications.com
EFFECT OF RECLAIM RUBBER LOADING ON THE
MECHANICAL PROPERTIES OF SBR COMPOSITES
AHMED M. AJAM SAMEER HASSAN AL-NESRAWY
and
MOHAMMED AL-MAAMORI
a
College of Education for Pure Science University of Babylon HILLA IRAQ
a
College of Materials Engineering University of Babylon HILLA IRAQ
ABSTRACT
This article explores the possibility of using mix of reclaim rubber as reinforcement in styrene-
butadiene rubber SBR. Mix of reclaim rubber used in this research to enhancement some of the
mechanical properties of SBR as additives or fillers. Six different compound was prepared from SBR
100 pphr and loading level from Reclaim rubber 0 50 100 150 200 250 pphr in series while the
hardness tensile strength tear résistance elongation elastic modulus and specific gravity have been
studied in this research. We found that some of these properties are increasing with the increment of mix
of reclaim rubber loading such as tensile strength elongation tear resistance specific gravity from other
hand hardness elastic modulus were decreased with increment reclaim rubber loading .
Key words: Composite materials Mechanical properties Waste of rubber R. R.
INTRODUCTION
The blending of two or more types of rubber is a useful technique for preparing
materials with superior properties which are absent in the component rubbers
1-4
. The
mechanical behavior of a polymer is strongly dependent on its morphology which in turn is
influenced by the thermo-mechanical history during processing. Molecular orientation
affects the crystallization behavior in two different aspects: Thermodynamics and
hydrodynamic. The thermodynamic effect involves the reduction of entropy in extended
chains and this will increase the opportunity of crystal formation by increasing the melting
point while kinetically the extended chain is closer to a crystal state than a random chain.
The hydrodynamic effect is a phase transformation which is responsible for the resultant
morphology
5
. The present authors
6
have dealt with the various reclaiming processes of
vulcanized rubber in the presence of different chemicals. Mechanochemical reclaiming of
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ground vulcanized rubber was reclaimed by diaryl disulfide and process oil at 110
o
C for
10 min in an open cracker cum two roll mixing mill
7
. The mechanical reclaiming of
ground rubber tire GRT by tetramethylthiuram disulfide TMTD as reclaiming agent the
extent of reclaiming and the performance evaluation of NR/RR blend were studied by the
authors
89
.
Styrene-Butadiene Rubber SBR: Is synthetic copolymer chemically SBR is a
copolymer of styrene and butadiene typically containing about 23 styrene and 77
polybutadiene with a glass temperature T
g
is about -55
o
C see Fig. 1
1011
.
CH CH
2
CH
2
CH CH CH
2
CH
3
CH
3
H
2
C
CH
3
CH
3
CH
2
CH
3
CH
3
Butadiene Styrene
Fig. 1: Compositional formula of SBR Rubber
Reclaim rubber is a rubber-compounding ingredient. Scrap rubber unlike scrap steel
undergoes a special process before it can be reused and the obtained rubber at the end of this
process is known as reclaimed rubber
12
. Reclaim is in fact a mixture of rubber carbon black
oil zinc oxide stearic acid and other compounding ingredients used in the original
compounds. It is lowers the green strength and tensile strength of the compounds in which it
is used. Reclaim can be used in many tire applications such as internal casings components
and inner liner compounds sidewalls chafers and rubber used in bead components
13
.
Vulcanizing Agents: Sulfur is the most well-known vulcanizing agent. It is easily
available in powder and prilled form packed in polyethylene bags. Sulfur vastly improves
the properties of raw rubber which is sticky and soluble in solvents. With the addition of
sulfur rubber is converted into a nontacky tough and elastic product
14
.
This article study some of the mechanical properties such as tensile set and specific
gravity and hardness specific gravity tests were carried out by Densitron according to
Archimedes principle it was weighed in air and in water. The specific gravity is calculated
by the following equation:
Specific gravity
in water Weight air in Weight
air in Weight
−
× Specific gravity of water …1
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So we can calculate the tensile strength T.S. by the equation
T.S. F/A …2
where F is the observed force required to break the specimen and
A is the cross sectional area.
Youngs modulus was reported as the slope of the initial linear region of the stress–
strain. Actual experimental values were reported as stress–strain curves. The stress σ and
strain ε are described by the following expression
15
σ Force or load F/Cross sectional area A …3
Strain ε L-L
o
/L
o
…4
Thus Youngs modulus in a tensile test is given by
E Δσ/ Δε …5
Therefore the ultimate elongation is mathematically calculated by the relation
E L-L
o
/L
o
100 …6
where L
o
Initial thickness and
L Final thickness.
with respect to the tear strength or the tear resistance in rubber it may be described
as the resistance for growing a neck or cut when the tension is applied on the specimen and
it depends upon the width and thickness of the test piece and the test results as the load
necessary to tear specimen of standard width and thickness.
Tear strength Ft
1
/t
2
…7
where F Maximum force
t
1
Thickness of standard piece and
t
2
The measured thickness of the specimen tested.
Hardness may be defined as resistance to indentation under specific conditions. This
test is conducted on rubbers in accordance with ASTM D2240-75 ASTM D1415-68 and
ASTM D531-78.
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EXPERIMENTAL
Materials
The SBR used is SBR–1502 with 23.5 styrene content made by the emulsion
process Supplied by the Petkim Turkey. The Properties of SBR are listed in Table 1. The
properties of reclaim rubber are listed in Table 2.
Table 1: Properties SBR 1502
Properties
Density g/cm
3
0.95
Bound styrene 23.5 ± max
Volatile matter 0.75 max
Ash 1.5 max
Soap 0.5 max
Organic acid 4.7-7.2
Zinc oxide 97 and stearic acid 99.4 were supplied by Durham U.K. MBS N-
oxydiethylenebenzothiazole 2-sulfonamide 98.2 is supplied by ITT India. Paraphenic
oil was supplied by the South Patrol Company. Sulfur was supplied by the Durham U.K.
Table 2: Properties of reclaimed rubber products
Type of reclaim
Hardness
shore A
Resilience
Tensile strength
Mpa
Elongation at
break
Mechanical waste NR/SBR 1:1 61 22 6.6 270
Mechanical waste NBR 63 5 6.8 220
Mechanical waste CR 64 12 4.6 230
Truck tires 80-100 NR 58 35 4.4 200
Passenger car tires 80–100 SBR 60 22 7.4 200
Equipments
Laboratory mill: Baby mill was used the two roll mills having provisions for
passing cold water. These rolls are cylindrical in shape and of 150 mm diameter and 300 mm
length. The roll speed is 20 r.p.m. The hydraulic press is equipped with thermocouple and
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maximum temperature is equal to 300°C and vulcanization process done at 20 min.
Ingredients of SBR composite are listed in Table 3.
Table 3: Ingredients of SBR composite
Compounding ingredients Ratio pphr
SBR Styrene-butadiene rubber 100
R. R. Reclaim rubber 0 50 100 150 200 250
Zinc oxide 3.5
Stearic acid 1.25
TMTD 1.75
Sulfur 1.75
Equipment for the measurement of tensile strength tear resistance elongation and
modulus of elasticity
Tests are carried out on samples which were prepared mill laboratory according to
ASTM D412. Monsanto T10 tensometer was used. The test sample which is movable at
speed of 200 mm/min for all except tear resistance at 50 mm/min.
Equipment for hardness
The International Hardness test is used in measurement of the penetration of rigid
ball according to Brinall method into the rubber specimen. The measured penetration is
converted to the international rubber hardness degrees. The scale of degrees is so chosen that
zero represents a material having elastic modulus equal to zero and 100 represents a material
of infinite elastic modulus. The scale covers all the normal range of hardness. Test was
carried out according to ASTM D1415 specifications.
Equipment for specific gravity measurement
Mansanto-Densitron equipment was used to measure the specific gravity. The
operating of equipment according to Archimedes principle the sample prepared was weighed
in air then in water the resulting data were given to the compile which was linked to the
equipment.
Moulds preparation
The necessary moulds were manufactured for test samples to study their mechanical
properties according to British standard BS.
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Table 4: The dimensions of the samples and forms
Standard Samples and dimensions Test
ASTM
D 3182
ASTM
D 13192
Tensile
Modulus
Elongation
ASTM
D 624-54
Tear
Resistance
ASTM
D 1415
Hardness
Specific
Gravity
Mould for preparing samples for tensile tear elongation and modulus tests
For preparing samples for the above tests the sheet sample from each recipe with a
dimension of 1501502.5 mm was prepared by using mould which consists of three parts
the middle one in a dimension of 395 mm158 mm2.5 mm contains six sections with
1501502.5 mm dimension fixed on base of 39516010 mm and covered with a cover of
the same dimension as that of the base for regulation of thickness.
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Mould for testing hardness and specific gravity
For preparing samples for hardness impact and water absorption the mould in the
laboratories of Tyre Company was used the mould consists of three parts the middle part in
a dimension of 2001806.5 mm which contains nine circular equivolume open with
65 mm diameter and 5 mm thickness while one of other two parts is bottom base and the
other is a cover for the purpose of samples thickness regulation. They have a dimension of
15015010 mm.
Samples preparation
Hand-made wooden molds has been used with measurements and dimensions
according to the American Society for testing and Materials ASTM. Table 4 shows the
dimensions of the samples and forms.
RESULTS AND DISCUSSION
Tensile elongation modulusm and tear resistance
Figs. 2-5 show that the increasing of loading ratio of reclaim rubber causes increasing
in tensile strength elongation and tear resistance because of increasing cross-link between
rubber and filler and this result due to sulfur presence in reclaim rubber which leads to
increased cross-link density between the rubber chains as well as the existence of the
proportion of carbon black and thus the cross-link density increase gradually and this go along
with
1516
while the elastic modulus inversely proportional to the increase in elongation in the
rubber chains lead to reduced elastic modulus of material and give a spongy elastic property.
Tensile Mpa
Reclaim rubber loading pphr
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
0 50 100 150 200 250 300
Fig. 2: Effect of adding reclaim rubber on tensile strength
slide 8: A. M. Ajam et al.: Effect of Reclaim Rubber Loading on…. 2446
Elastic modulus M a P
Reclaim rubber loading pphr
0.09
0.08
0.07
0.06
0.05
0 50 100 150 200 250 300
Fig. 3: Effect of adding reclaim rubber on elastic modulus
Elongation
Reclaim rubber loading pphr
700
600
500
400
300
200
100
0 50 100 150 200 250 300
Fig. 4: Effect of adding reclaim rubber on elongation
Tear resistance Mpa
Reclaim rubber loading pphr
1.6
1.4
1.2
1
0.8
0.6
0.4
0 50 100 150 200 250 300
Fig. 5: Effect of addingreclaim rubber on tear resistance
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Hardness
Fig. 6 show that the increasing of loading ratio of reclaim rubber causes decreasing
in hardness and this result due to reclaim rubber contain proportion of processing oil which
in turn leads to sliding and divergence of rubber chains that lead to decreasing ability to
resist penetration surface and this go along with
17
.
Hardness shore A
Reclaim rubber loading pphr
60
55
50
45
40
0 50 100 150 200 250 300
Fig. 6: Effect of adding reclaim rubber on hardness
Specific gravity
Fig. 7 show that the increasing of loading ratio of reclaim rubber causes increasing
in specific gravity because of increasing cross-link between rubber and filler and thus
material is more stacked lead to decrease formed pores within the sample and converge the
molecules of material from each other.
Specific gravity g/cm
3
Reclaim rubber loading pphr
1.07
1.05
1.03
1.01
0.99
0.97
0.95
0 50 100 150 200 250 300
Fig. 7: Effect of adding reclaim rubber on specific gravity
slide 10: A. M. Ajam et al.: Effect of Reclaim Rubber Loading on…. 2448
Therefore it works reducing of weight for unit size due to sulfur presence in reclaim
rubber which leads to increased cross-link density between the rubber chains as well as the
existence of the proportion of carbon black and thus the cross-link density increase gradually
and this go along with
15
.
CONCLUSION
i The increasing of additives ratios of reclaim rubber due to increase the tensile
strength elongation and tear resistance.
ii The increasing of additives ratio of reclaim rubber causes decreasing in elastic
modulus.
iii The increasing of additives ratios of reclaim rubber causes decreasing in
hardness.
iv The increasing of additives ratios of reclaim rubber due to increase the specific
gravity.
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Accepted : 23.09.2016