Materials Sciences and Applications, 2011, 2, 486-496
doi:10.4236/msa.2011.25066 Published Online May 2011 (http://www.SciRP.org/journal/msa)
Copyright © 2011 SciRes. MSA
Processing and Material Characteristics of a
Reclaimed Ground Rubber Tire Reinforced
Styrene Butadiene Rubber
Debapriya De1*, Debasish De2
1Chemistry Department, MCKV Institute of Engineering, Liluah, India; 2Chemistry Department, Meghnad Saha Institute of Tech-
nology, Kolkata, India.
Email: debapriyad2001@yahoo.com
Received January 21st, 2011; revised May 6th, 2011; accepted May 12th, 2011.
ABSTRACT
Mechanochemically partially devulcanized ground rubber tire (GRT) was revulcanized in composition with virgin sty-
rene butadiene rubber (SBR). Reclaiming of GRT was carried out by tetra methyl thiuram disulfid e (TMTD) in presence
of spindle oil. The cure characteristics and tensile properties of SBR compounds were investigated. Results indicate that
the minimum torque and Mooney viscosity of the SBR compounds increase with increasing reclaim rubber (RR) loading
whereas the scorch time remain unaltered but optimum cure time exhibit a decreasing trend. Increasing RR loading
also gives SBR compounds better resistance towards swelling but the 100% modulus, 200% modulus tensile strength,
and the elongation at break increases. Thermogravimetric analysis of SBR/RR vulcanizates was carried out in order to
get thermal stability of the vulcanizates. Scanning electron microscopy (SEM) studies further indicate the coherency
and homogeneity in the SBR/RR vulcanizates.
Keywords: Rubber Recycling, SBR, TMTD, Reclaimed Rubber, Thermogravimetric Analysis, Crosslink Density
1. Introduction
Dwindling source and rising price of crude oil have be-
come a serious concern for availability of feed stock to
the synthetic rubber industry. Huge quantities of rubbers
are used in tire industry and the world’s rubber markets
are dominated by two rubbers – one being natural rubber
(NR) and the other being styrene butadiene rubber (SBR).
Among different rubbers, tire industry consumed largest
quantity of SBR which is mainly used in car tire tread.
But after a long run when these tires are not serviceable
only a few grams or kilograms of rubber are abraded out
from the tire. The entire amount of rubber from the
worn-out tires is discarded, which again require very long
time for environmental degradation due to cross- link
structure of rubbers. Various approaches such as land
filling [1], incineration [2], pyrolysis [3,4], civil engi-
neering [5,6] applications etc. have been adopted for reuse
of waste discarded rubber products. But in almost all the
applications no value is added from the product side.
Tire recycling or reclaiming are one of the preferable
routes, according to the so-called waste management
hierarchy, under environmental aspect. The recycling of
tires not only saves our valuable resource of petroleum
from which the synthetic rubbers are originated, but also
protects our precious environment. Thus reclaiming of
tires in alternative applications is actually the use of base
polymer in new formulations with simultaneous cost
saving in raw material and preserving both natural re-
source and environment. Incorporation and dispersion of
reclaim rubber in fresh rubber play important roles to-
wards the product quality, production economy and
market competition. Compatibility of reclaim rubber with
virgin rubber is an essential requirement for optimum
mechanical properties of the vulcanizates. Therefore it is
necessary to evaluate the performances of such fresh
rubber/reclaim rubber blends.
In a review paper the author [7] have discussed the
various reclaiming processes of vulcanized rubber in
presence of different chemicals. The mechanical rec-
laiming of GRT by TMTD as reclaiming agent was stu-
died by the author [8]. Here the extent of reclaiming was
monitored by measurement of sol content, inherent vis-
cosity of sol rubber, crosslink density and Mooney vis-
Processing and Material Characteristics of a Reclaimed Ground Rubber Tire Reinforced Styrene Butadiene Rubber
Copyright © 2011 SciRes. MSA
487
cosity of reclaim rubber as function of milling time and
concentration of reclaiming agent. The optimization of
the reclaiming agent concentration and time of reclaim-
ing was also reported. The performance evaluations of
such type of reclaim rubber/virgin natural rubber blend
was also studied [9] by the author. In this paper mecha-
nochemically partially devulcanized GRT was blended
with fresh NR in 20% - 60% level. The reclaim rubber,
prepared in this investigation, when blended with fresh
NR has been found to reduce the tensile strength by
about 7% for 20% reclaim containing vulcanizate and
46% for 60% reclaim containing vulcanizate. It is ob-
served that the aging performances of the reclaim rubber
containing vulcanizates are better than the control for-
mulation, which does not contain any reclaim rubber.
TGA shows that the thermal stability of the vulcanizate
increases with increasing reclaim rubber content. Noor-
dermeer et al. [10] reclaimed waste latex rubber by di-
phenyl disulfide, 2-aminopheny disulfide and 2, 2'-diben-
zamidodiphenyl disulfide as a function of concentration
of reclaiming agent, time and temperature. The compara-
tive study of the reclaiming efficiency of the three rec-
laiming agents was carried out. From the study it was
evident that 2, 2'-dibenzamidodiphenyl disulfide is able
to break the crosslink bonds at around 20˚C. Sombat-
sompop and Kumnuantrip [11,12] incorporated reclaim
rubber from tire tread into two grades of NR and investi-
gated various properties of the blend. They found that
Mooney number, shear viscosity and cure rate increased
with RR content but optimum cure time is independent of
it. Sreeja and Kutty [13] studied the cure characteristics
and mechanical properties of NR/RR blends, using the
EV system. They reported that scorch time and tensile
properties of the blend reduced with RR loading. The
curing characteristics and mechanical properties of
SBR/RR blend system was reported by the author [14].
Here reclaiming of waste rubber was carried by a simple
process with an eco-friendly renewable resource material
[15,16]. The main constituent of this material is diallyl
disulfide. Other constituents are disulfides, mono sulfides,
poly sulfides and thiol compounds. Nevatia et al. [17]
mixed RR with recycled poly ethylene and evaluated
physical properties, dynamic mechanical properties and
rheological behaviors of the blend. They reported that
50/50, RR/PE vulcanizate showed optimum processibili-
ty, ultimate elongation and set properties. Here sul-
fur-accelerator cured system gave superior product prop-
erties than peroxide cured system.
This paper describes a new elastomer products based
on virgin SBR and reclaimed GRT. Initial step involves
the mechanochemical reclaiming of GRT by TMTD and
subsequent incorporation of reclaimed GRT into virgin
SBR in different proportion. The (re)vulcanization of
different SBR/RR blends was found to give a new low
cost product with adequate properties. The term (re)vul-
canization was used because there are two simultaneous
processes such as vulcanization of the virgin rubber and
(re)vulcanization of partially devulcanized GRT and
even the co-vulcanization of them. Curing characteristics
and mechanical properties before and after aging of
SBR/RR blend system have been studied. Thermal beha-
vior of RR, SBR and different SBR/RR vulcanizates was
also studied. Finally the dispersion of reclaim rubber into
SBR was evaluated by scanning electron microscopy
(SEM).
2. Experimental
2.1. Materials
GRT, purchased from local market was used in this in-
vestigation. The GRT was an unclassified ground rubber
from the tread and side walls of passenger and truck tires.
The particles of GRT were of various sizes ranging from
a few millimeters to 100 microns. Styrene butadiene rub-
ber (SBR 1502, Synthetics & Chemicals Ltd. India), te-
tramethylthiuram disulfide (TMTD) (Alpha Chemika,
Maharashtra, India), zinc oxide (S. D. Fine Chem. India),
stearic acid (Loba Chemi. India), sulfur (S. D. Fine Chem.
India), spindle oil (MCI, India), carbon black (N330,
Philips Carbon Ltd. India) and toluene (S. D. Fine Chem.
India) were used as received.
2.2. Experimental Procedure
The optimization of reaction conditions and the concen-
tration of TMTD used for reclaiming of GRT were re-
ported in the author’s previous work [8]. Hundred grams
of ground rubber was thoroughly mixed with 2.75 g
TMTD and 10 mL spindle oil. The mixture was then
reclaimed mechanically in an open two-roll mixing mill
at a friction ratio of 1.2 for 40 minutes near ambient
temperature. It has been found that with progress of mil-
ling the materials become soft, sticky and band formation
occurs on the roll. The extent of reclaiming was moni-
tored by measurement of sol content (30.3%), inherent
viscosity of sol rubber (0.3944), crosslink density (6.587
× 104 mol/cm3), molecular weight between crosslink
bonds (33.093 × 103), swelling ratio (4.099) and Mooney
viscosity [ML (1 + 4) 100˚C] (70.6) of reclaim rubber
[8].
2.3. Preparation of SBR/RR Vulcanizates
Mixing of fresh SBR, various proportions of reclaim
rubber and compounding ingredients was carried out for
15 minutes at room temperature on an open two-roll
mixing mill. Compound formulations are presented in
Table 1. The amount of additives such as ZnO, stearic
Processing and Material Characteristics of a Reclaimed Ground Rubber Tire Reinforced Styrene Butadiene Rubber
Copyright © 2011 SciRes. MSA
488
Table 1. Mix formulation and curing characteristics of SBR/RR Compounds.
Ingredients (phr) 1 2 3 4 5 6 7 8 9 10
Styrene Butadiene rubber (SBR) 100 80 70 60 50 40 100 80 80 80
Reclaim rubber (RR) - 20 30 40 50 60 - 20 20 20
Zinc oxide 5 5 5 5 5 5 5 5 5 5
Stearic acid 2 2 2 2 2 2 2 2 2 2
TMTD 2.16 1.61 1.335 1.06 0.785 0.51 2.16 1.61 1.61 1.61
Sulfur 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5
carbon Black (N330) - - - - - - 40 20 30 40
Spindle oil - - - - - - 4 2 3 4
Curing Characteristics
Optimum cure time (t90, min) 7.5 5.5 5.25 4.75 4.5 4.25 10 5.25 6.0 4.5
Scorch time (ts2, min) 1.5 0.5 1.0 1.0 1.0 1.0 0.5 0.5 0.5 0.5
Extent of cure, (dNm) 49 54.2 55.5 55.6 56 58 68.5 58 63 68
Cure rate index, (min1) 16.7 20 23.5 26.7 28.6 30.8 10.5 21 18.2 25
Mechanical Properties
100 % Modulus, MPa 1.255 1.59 1.62 2.10 2.13 2.28 3.5 2.146 3.267 4.196
200 % Modulus, MPa 1.698 2.25 2.31 3.08 3.19 3.32 5.477 3.264 4.985 6.465
Tensile Strength, MPa 2.335 2.781 2.974 3.835 4.573 5.017 12.014 7.515 9.946 12.577
% Elongation at break 432 377 382 390 427 445 537 587 521 509
Hardness, (Shore A) 50 60 65 64 62 60 65 60 63 65
Crosslinking value, (1/Q) 0.238 0.292 0.324 0.358 0.376 0.406 0.300 0.300 0.325 0.337
Mooney Viscosity [ML (1 + 4) 100˚C]40.7 51.0 65.7 70.6 71.8 75.0 - - - -
acid and sulfur were used based on 100 g of rubber ir-
respective of the amount of reclaim rubber, because it
was reported that the additives in reclaim rubber origi-
nated from parent compound are inactive [18]. The
amount of TMTD was maintained at 9 m mol in all the
vulcanizates based on the amount of TMTD used during
reclaiming of GRT. This is due to the fact that in sulfur,
TMTD vulcanization system the optimum concentration
of TMTD is chosen as 9 m mol i.e. 2.16 g per hundred
gm of fresh rubber (i.e. RR and SBR). Formulation 1
contains no reclaim rubber and formulation 2 - 6 contains
different proportion of reclaim rubber from 20 - 60 wt%.
In order to study the effect of carbon black, various pro-
portion of carbon black was added in SBR/RR (80/20)
blend system. Formulation 7 contains only SBR with 40
phr carbon black and formulation 8 - 10 contain different
Processing and Material Characteristics of a Reclaimed Ground Rubber Tire Reinforced Styrene Butadiene Rubber
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489
proportion of carbon black (20, 30 and 40 phr) in
SBR/RR blend. It has been observed that with increase in
the proportion of carbon black its incorporation and dis-
persion become gradually difficult. With higher propor-
tion of carbon black loading the compounds become stiff
and the temperature rises due to high shearing action
required for better dispersion.
The cure characteristics of SBR/RR compounds were
determined with the help of a Monsanto Oscillating Disc
Rheometer, R-100 at 160˚C. It has been found that all
cure curves were level off in the region of 60 minutes,
where torque-time gradient of each sample was constant
or did not change significantly.
The compounded rubber stock were then cured in a
compression molding machine at 160˚C and at applied
pressure of 34.5 MPa for the respective optimum cure
time (t = t90) obtained from rheographs. After curing, the
vulcanized sheet was taken out of the mold and imme-
diately cooled under tap to restrict from further curing.
2.4. Measurement of Mechanical Properties
The mechanical properties such as modulus, tensile
strength and elongation at break was measured by a
Hounsfield, model H10 KS tensile testing machine as per
ASTM D 412-51T at room temperature (25 ± 2˚C) at a
uniform speed of separation 500 mm/min. Hardness
(Shore A) of the vulcanizates were measured by a Hiro-
sima Hardness tester as per ASTM D 1415-56T. The
values reported were based on the average of five mea-
surement of each sample. The aging characteristics of the
vulcanizates was evaluated by accelerated aging test in
an air aging oven at 100 ± 2˚C after 24, 48 and 72 h ag-
ing.
Mooney viscosities of rubber compounds were deter-
mined by a Monsanto Mooney viscometer 2000 at ML (1
+ 4) 100˚C as per ASTM D 1646.
2.5. Swelling Value of the Vulcanizates
The swelling value (Q) was determined with about 0.5 g
of cured samples (accurately weighed). The sample was
immersed in 250 mL toluene for 72 h to attain equilibrium
swelling. After equilibrium swelling the sample was taken
out and the solvent was blotted from the surface of the
sample and weighed immediately. It was then dried under
vacuum at 100˚C upto constant weight. The crosslinking
value of the vulacanizates was calculated from the fol-
lowing equation [19].
0
1
100
SD
F
WW
QW
W



(1)
where ,,
SDO
WWW and
F
W are swollen weight, dried
weight, weight of the original sample and formula weight
respectively. Formula weight (
F
W) is the total weight of
rubber plus compounding ingredients based on 100 parts
of rubber.
2.6. Determination of Crosslink Density
The crosslink densities of SBR/RR vulcanizates were
determined by the Flory-Rehner equation [20] by using
swelling value measurement.

1
232
ln 12r
rr rsswellrV
VV VVV
f


 



(2)
where r
V is the volume fraction of rubber in the swollen gel,
S
V is the molar volume of the toluene (106.2 cm3·mol1
in this study),
is the rubber-solvent interaction para-
meter (0.378 in this study),
s
well
is cross-link density of
the rubber (mol·cm3) and
f
is functionality of the
crosslinks (being 4 for sulphur curing system).
The volume fraction of a rubber network in the swollen
phase is calculated from equilibrium swelling data as:
2
2
12
12
r
W
d
VWW
dd






(3)
where 1
W is the weight fraction of solvent, 1
d is the
density of the solvent, 2
W is the weight fraction of the
polymer in the swollen specimen and 2
d is the density of
the polymer.
2.7. Thermo Gravimetric Analysis (TGA)
The thermo gravimetric analysis (TGA) of SBR/RR vul-
canizate was carried out by using a TGA 50, Shimadzu,
Japan, thermo-gravimetric analyzer in nitrogen (flow rate
50 mL/min) within the temperature range of 20 to 800˚C.
All these analysis were carried out at heating rate of
10˚C/min.
2.8. Scanning Electron Microscopy
The tensile fracture surface of the samples were studied
in scanning electron microscope (SEM) (JEOL, JSM
5800) at 0˚ tilt angle after coating the surface with sput-
tered gold.
3. Results and Discussion
3.1. Curing Characteristics
Curing characteristics of different SBR/RR blend system
and SBR/RR (80/20) blend system with various propor-
tions of carbon black loading are given in Table 1. The
optimum cure time decreases but scorch time remain
unaltered with increase in reclaim rubber content in all
Processing and Material Characteristics of a Reclaimed Ground Rubber Tire Reinforced Styrene Butadiene Rubber
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490
the cases. From Table 1 it has been found that with in-
crease in the proportion of reclaim rubber extent of cure
increases due to the presence of crosslinked gel in the
reclaim rubber. It is also evident that with increase in
carbon black loading the optimum cure time and scorch
time remain unaffected but extent of cure increases with
increasing carbon black loading.
3.2. Tensile Properties of Rubber Compound
The stress-strain behavior of SBR/RR vulcanizates with
various proportion of reclaim rubber are shown in Figure
1. The moduli at 100% and 200% elongation increases
with increasing reclaim rubber content in all the SBR/RR
vulcanizates. The stress strain was decreased with in-
creasing reclaim rubber content. From the Figure it is
shown that the stress-strain of SBR/RR vulcanizates was
decreased after 50% elongation compare to that of the
fresh SBR vulcanizate. Tensile properties, Mooney vis-
cosity and crosslinking value of the SBR/RR vulcani-
zates are presented in Table 1. From the values in Table
1 it is seen that moduli at 100% and 200% elongation,
tensile strength, elongation at break and hardness in-
creases with increasing reclaim rubber content. The rea-
son for higher 100% and 200% moduli may be due to
higher crosslink density (Figure 2) of the vulcanizates,
arising out of the gel present in reclaim rubber or may be
due to the presence of active functional sites in reclaim
rubber which may participate in crosslinking during the
process of vulcanization. As crosslink density of the vul-
canizates increases with increasing reclaim rubber con-
tent, chain mobility decreases and more load is required
for 100% and 200% elongation. The increasing value of
tensile strength with reclaim rubber content is probably
due to the presence of carbon black left in the reclaim
rubber [12]. It is known [7,21,22] that the partial devul-
canization of ground rubber tire (GRT) facilitates the
interface adhesion between the surface chains of reclaim
rubber (RR) particles and surrounding rubber matrix due
to their co-crosslinking in the interphase layer. The in-
crease in the value of elongation at break with reclaim
rubber content can indicate a better compatibility in in-
terphase layer of the rubber matrix and reclaimed rubber
particles [23,24]. The growth of the values of hardness
observed at increasing RR content in SBR/RR (re)vulca-
nizates obviously evidences of more intensive post vul-
canization process in the blends due to presence of addi-
tional sulfur released at the devulcanization of GRT [15].
Effect of carbon black loading was studied in SBR/RR
(80/20) blend system. It is seen that with increase in car-
bon black loading 100% and 200% moduli, tensile
strength increases. This can be explained by correspond-
ing increase in crosslinking value data. The higher cross-
linking value of the vulcanizates is conclusive evidence
0100 200 300 400 500
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
Stress (MPa)
Strain (%)
SBR 100
SBR/RR = 40/60
SBR/RR = 50/50
SBR/RR = 60/40
SBR/RR = 70/30
SBR/RR = 80/20
Figure 1. Stress – Strain be havior of SBR/RR ble nd system.
Figure 2. Crosslink density of SBR/RR blend system as a
function of reclaim rubber cont ent and carbon black loading.
for the presence of a network with a greater number of
filler polymer interactions, constraining molecular mo-
bility in the polymer. The tensile strength of 40 phr car-
bon black loaded SBR/RR (80/20) vulcanizate is higher
compared to that of the control formulation 7 i.e. vulca-
nizate containing no reclaim rubber. Elongation at break
decreases with increasing carbon black loading. Hardness
increases because with increasing carbon black loading
vulcanizates become stiff and hard. The increase in the
value of Mooney viscosity with carbon black loading
further indicates that the processing of the rubber com-
pound become difficult if higher amount of carbon black
is incorporated into the rubber matrix.
3.3. Effect of Thermal Aging
The aging characteristics of SBR/RR vulcanizates should
Processing and Material Characteristics of a Reclaimed Ground Rubber Tire Reinforced Styrene Butadiene Rubber
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491
be given proper attention because reclaim rubber itself is
a degraded mass. Thus accelerated aging test were per-
formed for SBR/RR vulcanizates. Percent retention of
100% and 200% modulus are shown in Figures 3 and 4.
In all the cases it was observed that percent retention of
100% and 200% modulus increases with increasing rec-
laim rubber content and with progress of aging. This may
be due to residual crosslinking during progress of aging
which is further enhanced due to the presence of reclaim
rubber, containing active functional sites. Percent reten-
tion of tensile strength is shown in Figure 5. From the
figure it is evident that percent retention of tensile
strength decreases with progress of aging but increases
with increasing reclaim rubber content at a particular
time of aging. This may be due to increasing crosslink
density of the vulcanizates with progress of aging. The
percent retention of elongation at break for the various
SBR/RR systems at different RR content after aging is
shown in Figure 6. But percent retention of elongation at
break values at higher reclaim content such as 50 and 60
wt% reduces considerably; this is a result of both thermo-
oxidative degradation and post vulcanization of SBR/RR
(re)vulcanizates studied. Percent retention of hardness is
shown in Figure 7. With progress of aging as the vulca-
nizates become stiff therefore hardness increases.
Effect of carbon black loading on % retention of prop-
erties after 72 h aged SBR/RR (80/20) blend system was
shown in Figure 8. The percent retention value of both
100% and 200% modulus continuously increases with
increasing carbon black loading. But the percent reten-
tion values of tensile strength and elongation at break
shows a different behavior. Both the properties shows
maximum percent retention values for 20 phr carbon
black loading compared to that of the control formulation.
0 1020304050607080
100
105
110
115
120
125
% Retention of 100 % modulus
Time of aging (h)
RR (0)
RR (20)
RR (30)
RR (40)
RR (50)
RR (60)
Figure 3. Effect of reclaim rubber content on % retention of
100% Modulus.
0 1020304050607080
100
105
110
115
120
125
130
% Retention of 200 % modulus
Time of aging (h)
RR (0)
RR (20)
RR (30)
RR (40)
RR (50)
RR (60)
Figure 4. Effect of reclaim rubber content on % retention of
200% Modulus.
0 1020304050607080
70
75
80
85
90
95
100
% Retention of tensile strength
Time of aging (h)
RR (0)
RR (20)
RR (30)
RR (40)
RR (50)
RR (60)
Figure 5. Effect of reclaim rubber content on % retention of
Tensile Strength.
However, for 30 and 40 phr carbon black loading the
percent retention values considerably decreases due to
aging. Although the percent retention of tensile strength
for 30 and 40 phr carbon black loading is not less than
that of the control formulation. It is seen from Figure 8
that percent retention of hardness was almost constant
with increasing carbon black loading. These results show
the effectiveness of 20 phr carbon black in the SBR/RR
(80/20) blend system. Thus the aging performances of
formulation containing reclaim rubber are superior than
that of the control formulation which does not contain
any reclaim rubber. This phenomenon indicates the anti-
aging characteristics of reclaim rubber.
3.4. Thermogravimetric Analysis
Thermal degradation of different SBR/RR vulcanizates
Processing and Material Characteristics of a Reclaimed Ground Rubber Tire Reinforced Styrene Butadiene Rubber
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492
0 1020304050607080
65
70
75
80
85
90
95
100
% Retention of elongation at break
Time of aging (h)
RR (0)
RR (20)
RR (30)
RR (40)
RR (50)
RR (60)
Figure 6. Effect of reclaim rubber content on % retention of
Elongation at Break.
0 1020304050607080
100
105
110
115
120
% Retention of hardness
Time of aging (h)
RR (0)
RR (20)
RR (30)
RR (40)
RR (50)
RR (60)
Figure 7. Effect of reclaim rubber content on % retention of
Hardness.
in inert atmosphere was analyzed and corresponding re-
sults are given in Figure 9. The thermogravimetric ana-
lysis were performed in nitrogen atmosphere, which
shows only thermal degradation behavior compare to the
combine effect of thermal as well as termooxidative de-
gradation in presence of oxygen or air. The tempera- ture
interval of degradation stages evaluated from DTG
curves, temperature of the stages maximum rate of deg-
radation, sample weight loss at the temperatures and char
residue values are listed in Table 2. All SBR/RR blend
system shows two characteristic degradation peak in DTG
curve between 320˚C - 530˚C (Figure 9). But for all the
vulcanizates initial weight loss occurs between 50 - 300˚C.
Pure SBR shows 3.6% wt loss up to 300˚C whereas with
increase in reclaim rubber content it goes up to 10% for
SBR/RR blend system. This initial weight loss under N2
0 10203040
60
70
80
90
100
110
120
130
140
150
% Retention of Properties
Carbon Black Content (Phr)
100% Mod
200% Mod
Tensile Strength
Elongation at Break
Hardness
Figure 8. Effect of carbon black loading on % Retention of
properties after 72 h aged SBR/RR (80/20) blend system.
atmosphere between 50˚C - 300˚C is due to the volatili-
zation of processing oil or any other low boiling point
component present in pure and blend system. As reclaim
rubber contain large amount of processing additives
compare to virgin rubber, so with increasing reclaim
rubber content initial weight loss increases from 3.6% to
10%.
As RR contain some NR for that reason SBR/RR
blend shows two distinct peak in DTG curve which was
also observed for NR/SBR blend system [25]. Pure SBR
shows 10.57% wt loss in 1st degradation step. With in-
crease in reclaim rubber content % wt loss in 1st degrada-
tion step gradually increases and maximum 24.13% was
observed at 40phr SBR containing SBR/RR blend system.
1st degradation was faster with increase in RR content in
SBR/RR blend system. Low temperature degradation
was much pronounced with increase in RR content in
SBR/RR blend system. If we compare our TGA results
with pure RR system, it was observed that reclaim rubber
shows three steps degradation. Out of three steps, 2nd
degradation step occurs in between 334.4˚C - 507.5˚C.
Actually 2nd degradation step of pure reclaim rubber par-
tially merge with the 1st degradation step of SBR/RR
blend system. As a result of which % wt loss increases in
1st degradation step of SBR/RR blend system with in-
crease in reclaim rubber content.
But in case of second degradation the complete oppo-
site train was observed. Pure SBR shows around 80%
weight loss in second degradation step. This is the cha-
racteristic degradation peak for pure SBR in thermo-gra-
vimetric analysis. The % wt. loss of blend vulcanizates is
decreased in 2nd degradation step with increase in reclaim
rubber content. This may be due to the low SBR content
in SBR/RR blend system. The same reason was also ap-
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493
Figure 9. Thermogravimetric analysis of SBR/RR Vulcanizates.
Table 2. Degradation temperature and % weight loss of SBR/RR vulcanizates.
Blend Initial wt. Loss
1st degradation 2nd degradation
% residue
Start Peak End % wt lossStart Peak End % wt loss
SBR (100) 3.66 343.53 395.44417.12 10.57 417.12 476.85 512.75 79.83 5.384
SBR/RR (80/20) 6.76 346.38 395.44418.90 11.83 418.90 476.85 514.18 69.49 11.195
SBR/RR (70/30) 7.77 340.69 395.44423.17 15.16 423.17 479.69 512.64 62.35 14.045
SBR/RR (60/40) 8.77 340.69 388.33421.75 16.98 421.75 476.85 512.64 56.62 16.945
SBR/RR (50/50) 10.00 340.69 398.29431.70 22.08 431.70 476.85 523.07 47.42 19.784
SBR/RR (40/60) 9.63 328.96 394.02428.86 24.13 428.86 478.27 531.59 43.01 22.607
RR
Initial wt.
Loss
1st degradation 2nd degradation 3rd degradation
9.81
Start Peak End% wt Loss Start Peak End % wt LossStartPeakEnd % wt Loss
15.00 160 274 33613.28 336 400 507 49.99 507 566 671 25.79
Processing and Material Characteristics of a Reclaimed Ground Rubber Tire Reinforced Styrene Butadiene Rubber
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494
plicable for 2nd degradation step in blend system which
shows less % wt loss with increase in RR content. This is
due to the fact that the 3rd degradation step of pure rec-
laim rubber affects the 2nd degradation step of SBR/RR
blend system. The lower % wt loss in the second step is
due to both the higher carbon black content and to the
greater % wt loss of the first step.
3.5. SEM Study
Scanning electron micrograph of the tensile fractured
surface of fresh SBR and different SBR/RR vulcanizates
are displayed in Figure 10. The micrograph of fresh SBR
vulcanizate showed homogeneous surface morphology.
Whereas in the reclaim rubber containing vulcanizates
several number of crack paths in different directions was
observed which is making the vulcanizate susceptible
under mechanical stress. Here in case of reclaim rubber
containing vulcanizate, the fracture mode showed the
failure mode that was less rubbery in nature, due to high-
er cross link density of the vulcanizate.
4. Conclusions
Mechanochemical reclaiming of GRT was carried out by
multifunctional reclaiming agent, TMTD. The reclaimed
rubber prepared in this investigation, when mixed with
fresh SBR has been found to increase the tensile strength
by about 19% for 20% reclaim containing vulcanizate
and 115% for 60% reclaim containing vulcanizates. It is
observed that the aging characteristics of the reclaim
rubber containing vulcanizates are superior compared to
that of the control formulation, which does not contain
any reclaim rubber. TGA shows that the thermal stability
of the vulcanizate increases with increasing reclaim rub-
ber proportion. SEM studies indicate that reclaim rubber
containing vulcanizates are vulnerable under mechanical
stress. Another advantage of this reclaiming agent is the
(a) (b)
(c) (d)
Figure 10. Tensile fractured surface of (a) SBR (100) (b) SBR/RR (80/20) (c) SBR/RR (50/50) and (d) SBR/RR (40/60) blend
system.
Processing and Material Characteristics of a Reclaimed Ground Rubber Tire Reinforced Styrene Butadiene Rubber
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495
reduced smell during the reclamation process and of the
final reclaims, one of the most important short comings
of other disulfides used for this purpose.
5. Acknowledgements
The authors, Debapriya De thankfully acknowledge the
financial support by the Department of Science and
Technology (DST), New Delhi, India for carrying out the
present research work.
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