Open Journal of Polymer Chemistry, 2013, 3, 99-103
Published Online November 2013 (http://www.scirp.org/journal/ojpchem)
Open Access OJPChem
Study the Effect of Recycled Tire Rubber on the
Mechanical and Rheological Properties of TPV
(HDPE/Recycled Tire Rubber)
Ziyad T. Al-Malki1, Einas A. Al-Nasir1, Moayad N. Khalaf2*, Raed K. Zidan2
1Department of Chemical and Technology of Polymer, Polymer Research Centre, University of Basrah, Basrah, Iraq
2Department of Chemistry, College of Science, University of Basrah, Basrah, Iraq
Received August 10, 2013; revised September 10, 2013; accepted September 18, 2013
Copyright © 2013 Ziyad T. Al-Malki et al. This is an open access article distributed under the Creative Commons Attribution Li-
cense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Thermoplastic elastomeric blends were prepared from blending of (10%, 20%, 30%, 40% and 50 wt%) high density
polyethylene(HDPE) and (10%, 20%, 30%, 40% and 50 wt%) ground rubber tire (TPV-R). The blends prepared contain
(HDPE)/polybutadiene (TPV-V). The two blends were successfully prepared through a dynamic vulcanization process,
involving dicumyl peroxide (3%) as vulcanizing agent. The data of the mechanical (tensile strength at yield, %elonga-
tion and young modulus) and rheological properties (shear stress, shear rate, viscosity, flow behavior index and activa-
tion energy of melt flow) of the TPV-V and TPV-R showed that there were comparable results between the two blends.
Keywords: Thermoplastic Vulcanized Rubber; Rubber Recycling; Mechanical Properties
In recent decades, improved properties of polymer mix-
tures such as thermal stability impact resistance, flame
retardant, ductility and stiffness etc. had paved the de-
velopment of blending of polymer mixtures. The total
market volume for polymer blends is currently estimated
to be more than 1.1 million metric tons a year . It in-
cludes a significant number of large volume products
such as PPE/HIPS blends (Norly (R)), PC/PBT blends
(Xenoxy), and PA/PPE blends (Noryl GTX) [2,3] etc.
which are being generated to equip the multipurpose
needs of plastics industry. One of the growing challenges
to the environment pollution was the rubber polymer be-
cause not only in industrialized countries but also in less
developed nations, rubber products are everywhere to be
found, though few people recognize rubber in all of its
applications. Since 1920, demand for rubber manufac-
turing has been largely dependent on the automobile in-
dustry, the biggest consumer of rubber products. Rub-
ber is used in radio and T.V sets and in telephones. Elec-
tric wires are made safe by rubber insulation. Rubber
forms a part of many mechanical devices in the kitchen.
It helps to exclude draughts and to insulate against noise.
Sofas and chairs may be upholstered with foam rubber
cushions, and beds may have natural rubber pillows and
mattresses. Clothing and footwear may contain rubber:
e.g. elasticized threads in undergarments or shoe soles.
Most sports equipment, virtually all balls, and many me-
chanical toys contain rubber in some or all of their parts.
Still other applications have been developed due to spe-
cial properties of certain types of synthetic rubber, and
now there are more than 100,000 types of articles in
which rubber is used as a raw material . Recycling of
polymeric wastes is an environmental problem of great
concern especially the tire rubber . The scrap of tire
rubber discarded each year was very large volume, which
was caused by the fast development of the automobile
industry . More than 17 million tons of rubber is used
in the production of automobile tires. This is responsible
for a vast amount of wastes. The different chemical com-
positions and the crosslinked structures of rubber in tires
are the prime reason, that it was highly resistance to bio-
degradation, photochemical decomposition, chemical re-
agents and high temperatures. Therefore the serious
threat to natural environment was the increasing numbers
of used tires , which start to be perceived as a poten-
tial source of valuable raw materials. The most limited
option was the processibility of the rubber. The blending
Z. T. AL-MALKI ET AL.
of thermoplastic polymer like polyethylene has the abil-
ity to flow under certain conditions (supported usually by
the action of heat and/or pressure), so that it can be
shaped into products at acceptable cost . This can be
achieved using thermoplastics, thermosetting resins and
rubber compounds as potential matrices. In this paper the
effect of ground tire rubber (GTR) on the mechanical and
rheological properties of thermoplastic vulcanized rubber
(TPV-R) was compared with version rubber. The data
show that TPV-V containing version rubber had better
mechanical properties and less viscosity value than the
TPV containing GTR.
High density polyethylene (HDPE) SCPILEX 6003 was
supplied by state company for petrochemical industry
(SCPI) in Basra (MFI = 6.0 gm/10 min, density = 0.963
gm/cm3. Polybutadiene was obtained from Malaysian
company with (Mooney viscosity ML (1 + 4) at 100˚C
45 ± 5). Dicumyl peroxide was supplied by Fluka com-
pany and use as it is. Ground tire rubber was obtained
from scrap tires, which are first shredded into larger
pieces (avarege size 20 _ 20 mm) and then ground to less
than 1 mm. Spikes, cords and textiles are subsequently
3.1. Rheological Measurements
Rheological properties were carried out by using a capil-
lary rheometer device (Instron model 3211), according to
ASTM D-3835. The diameter of the capillary is 0.76 mm,
the length to diameter (L/D) ratio of 80.9, with an angle
of entry of 90˚. Load weighing which dropped on the
polymer melts by plunger transverse from the top to the
bottom of the barrel was constant (2000 kg). The con-
stant plunger speeds ranged from 0.06 to 20.0 cm·min−1
and the extrusion temperature was 180˚C.
3.2. Mechanical Measurements
The tensile testing measurements were performed with
an Instron 1193 tensile machine at room temperature us-
ing dumbbell-shaped specimens (at least five specimens
for each sample) as per ASTM D 638-5. The crosshead
speed was 50 mm·min−1.
3.3. Preparation of the Thermoplastic
Vulcanized (TPV-GTR) and (TPV-P)
Mixer-600 attached to Haake Rhechard Torque Rheome-
ter supplied by Haake Company was used for the prepa-
ration of the TPV. The total weight of the (HDPE/Rub-
ber) was 60 gm. GTR or Polybutadiene in the percent
(0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% and
90 wt%) was feed to Mixer-600 at temperature = 140˚C
and RPM = 32. After 2 min. of mixing the high density
polyethylene was added and continue mixing for 5 min.
Then the dicumyl peroxide (3%) was added and the ve-
locity of mixing was changed to RPM = 64 and the mix-
ing time continue for 10 min.
4. Result and Discussion
4.1. Mechanical Properties
The mixture of the HDPE and rubber (GTR and BP)
blends have good mechanical properties [9,10]. Figures
1 and 2 show the tensile strength and Young’s modulus
of the TPV-P and TPV-R blends. It can be seen with in-
creasing the rubber content the tensile strength of both
TPV-R and TPV-P was decreased, this can be attributed
to the rubber content. The elastomer phase remains as
dispersed particles in the TPV-R and TPV-P blends and
the HDPE was bearing the tensile force applied on the
blends which is in agreement with previous work .
While the higher value of tensile strength and Young’s
Figure 1. Effect of % polyethylene on the tensile strength at
yield of TPV-V and TPV-R.
Figure 2. Effect of % rubber on the young modulus of
TPV-V and TPV-R.
Open Access OJPChem
Z. T. AL-MALKI ET AL. 101
modulus of TPV-R and TPV-P blends were due to the
smaller size and uniform dispersion of the dispersed
phase. Agglomeration and particle-particle interaction of
the rubber powder were observed decrease in tensile
strength and Young’s modulus of TPV-P and TPV-R
blends. The reduction of tensile strength and Young’s
modulus value of TPV-R and TPV-P may be due to de-
creasing of the blend rigidity. This is a common observa-
tion since many researchers [12,13] also reported similar
findings. However, at a similar rubber content, tensile
strength and Young’s modulus of TPV-R blends are
slightly higher than TPV-P blends. In TPV-P blends, the
molecular entanglements in the rubber chains alone are
insufficient to prevent rapid flow and fracture in response
to the applied stress. This results in the lower tensile
strength and Young’s modulus of the HDPE/PB blend.
For HDPE/GTR blends, the presence of the crosslinking
rubber powder and others curatives in GTR has allowed
the rubber particles to reach higher strains and at the
same time confers mechanical strength to the particles
Figure 3 shows the variation of elongation at break,
Eb (%elongation at break) for TPV-R and TPV-Pblends,
respectively. It can be seen that for both blends, Eb in-
creases with increasing rubber content due to the elastic-
ity of rubber. However, at a similar rubber content, Eb
for TPV-P the blend is higher than TPV-R blend. Again
this observation is due to the presence of crosslinking
rubber particles and other ingredients in GTR which limit
the flow and mobility of the TPV-R blend .
4.2. Rheological Properties
Rheological behavior of polymeric melts is an important
aspect to understand the flow behavior of the materials
during processing. Capillary rheometry is the most com-
mon technique used to determine deformation of poly-
meric melt under shear flow . The polymer standard
flow curve (shear stress vis. Shear rate) was divided to
Figure 3. Effect of % rubber on the %elongation at break
of TPV-V and TPV-R.
four regions as shown in Figure 4. The addition of vul-
canizing agent improves the (HDPE/Rubber) properties
of the blend substantially . Figure 5 show the flow
curves (shear stress vis. shear rate) for TPV-R and
TPV-V, From the figure it was seen that the curves was
smooth and linear and there was no discontinuity in the
flow curves in the four region of the standard flow curve
as seen in Figure 5 with the value of shear stress for the
TPV-R higher than the TPV-V. The higher value for the
TPV-R because the GTR chain was already crosslinked
and the TPV-R (HDPE/GTR crosslinking) will be ran-
domly oriented and entangled chains, for that this will
restricted the chains to become oriented and disentangled
more that the TPV-V(HDPE/BP) .
The variation of melt viscosity as a function of shear
rate for TPV-R and TPV-V blends at 180˚C are shown in
Figure 6. The melt viscosity decreased with increasing
shear rate (Figure 6) indicating the pseudoplastic nature
of the blends. Hence, processability is improved. At
180˚C, the viscosity of TPV-R was higher than TPV-V.
The presence of the GTR which was already vulcanized
limited the TPV-R chain to be oriented leads to an in-
crease in the melt viscosity due to the greater resistance
they offer to flow . The activation energy (Ea) of the
flow process was calculated from the slope of logη ver-
sus 1/T using the Arrhenius type of equation .
where η is the melt viscosity, A is a pre-exponential fac-
tor, Ea the activation energy, T the temperature (K), and
R the universal gas constant (8.314 J K−1·mol−1). The
activation energy of flow is the minimum energy re-
quired for the molecules to just flow which is equivalent
to energy necessary to overcome the intermolecular
forces of attraction as well as the resistance due to the en-
tanglements . The variation of Ea (Table 1) could
be attributed to the change in the morphology under
shear deformation . Ea decreased with increasing
shear rate for both TPV-R and TPV-V blends, probably
due to the strong shear thinning behavior. However, the
TPV-R had higher Ea than TPV-V, indicate that the
TPV-R had less vulcanization between HDPE and GTR,
which increases chain mobility and activation energy
Table 1. Variation of the activation energy (kJ/mol) at dif-
ferent shear rates 5.4, 18, 54, 180, 540 and 1800 s−1.
5.4 s−118 s−154 s−1 180 s−1 540 s−11800 s−1
TPV Activation Energy (KJ/mol)
HDPE26.2510.974.6 1.76 0.58 0.21
TPV-V31.1112.4 5.55 2.05 0.77 0.29
TPV-R37.0315.3 5.9 2.3 0.94 0.32
Copyright © 2013 SciRes. OJPChem
Z. T. AL-MALKI ET AL.
Open Access OJPChem
02004006008001000 1200 1400 1600 1800 2000
Figure 4. Standard flow curve for the polymer (τ1 = first critical shear stress and T2 = second critical shear stress).
05001000 1500 2000
Figure 5. Variation of shear stress with shear rate for
TPV-V and TPV-R (70Rubber/30HDPE) at 180˚C.
05001000 1500 2000
Figure 6. Variation of viscosity with Shear Rate for TPV-V
and TPV-R (70Rubber/30HDPE) at 180˚C.
The flow behaviour index gives an idea about the na-
ture of flow, i.e., whether it is Newtonian or non-New-
tonian. Most polymers show pseudoplastic behavior with
flow behavior index n less than 1. The power-law equa-
tion was applied to describe the rheological behavior of
the system. The melt flow behavior can be described by
power law, which is expressed by Ostwald and de Waele
model. The equation for this model is given as follows:
where K reflects the consistency index of the polymer
melt, with higher values representative of more viscous
materials, and n is the power-law index giving a measure
of the pseudoplasticity. From (Table 2) the values of (n)
obtaining among vulcanized HDPE/GTR and HDPE/BP
blends do not differ very much from pure HDPE value ,
such behavior was reported by George et al.  and
Oomenn et al. , and they indicated that the addition
of up to 20% of rubber does not affect markedly the flow
behavior of polypropylene. And here it was found that
the addition of 30% of GTR or PB also does not affect
markedly the flow behavior of HDPE. The consistency
index (K) of the TPV-R (contain GTR) higher than the
TPV-V (contain PB). The consistency index represents the
viscosity at unit rate of shear. This indicates that the free
volume of the system decreases, so the K-value increases.
From the above results it was indicated that the GTR
(recycled tyre rubber) was comparable to the pure rubber
and it can be used in many applications, which will be
one way to control the environmental pollution by the
large quantity of used rubber. The mechanical properties
of the TPV-R which contain the GTR show comparable
data with the TPV-P which contain PB. Both blends
show the same behavior. The tensile strength, young
modulus increases and %elongation decreases with the
increase of the percent of rubber in the TPV-R or TPV-V.
Z. T. AL-MALKI ET AL. 103
Table 2. Flow behavior index (n) and consistency index (K).
Property K n
HDPE 3.016 0.198
TPV-V 4.85 0.194
TPV-R 5.039 0.168
While rheological behavior of TPV-R and TPV-V blends
was investigated. It was found that both blends show
pseudoplastic. Melt viscosity of TPV-R and TPV-V
blends was sensitive to shear rates. Activation energies
decreased with increasing shear rate for both TPV-R and
TPV-V blends, probably due to the strong shear thinning
behavior. The values of (n) obtaining among vulcanized
HDPE/GTR and HDPE/BP blends do not differ very
much from pure HDPE value. And it was found that the
addition of 30% of GTR or PB also does not affect mar-
kedly the flow behavior of HDPE which was compa-
rable with the data found in previous work with 20%
rubber. The consistency index (K) of the TPV-R (contain
GTR) is higher than the TPV-V (contain PB), which in-
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