Study the Effect of Recycled Tire Rubber on the Mechanical and Rheological Properties of TPV (HDPE/Recycled Tire Rubber)

doi:10.4236/ojpchem.2013.34017

Paper Menu >>

Journal Menu >>

Open Journal of Polymer Chemistry, 2013, 3, 99-103

Published Online November 2013 (http://www.scirp.org/journal/ojpchem)

http://dx.doi.org/10.4236/ojpchem.2013.34017

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

Email: *[email protected]

Received August 10, 2013; revised September 10, 2013; accepted September 18, 2013

cense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

ABSTRACT

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

1. Introduction

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 [1]. 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 [4]. Recycling of

polymeric wastes is an environmental problem of great

concern especially the tire rubber [4]. The scrap of tire

rubber discarded each year was very large volume, which

was caused by the fast development of the automobile

industry [5]. 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 [6], 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

*Corresponding author.

Z. T. AL-MALKI ET AL.

100

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 [7]. 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.

2. Experimental

2.1. Material

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

removed.

3. Instrument

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 [11].

While the higher value of tensile strength and Young’s

0 2040608010

Ty(MPa)

Rubber

TPV ‐R

TPV‐V

Figure 1. Effect of % polyethylene on the tensile strength at

yield of TPV-V and TPV-R.

100

200

300

400

500

600

0 20406080100

YoungModulus(MPa)

%Rubber

‐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

[11].

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 [11].

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 [14]. The polymer standard

flow curve (shear stress vis. Shear rate) was divided to

100

200

300

400

500

600

0 20406080100

%ElongationatBreake

%RUbber

‐

TPV‐R

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 [15]. 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) [16].

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 [15]. 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 [16].

aRT





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 [17]. The variation of Ea (Table 1) could

be attributed to the change in the morphology under

shear deformation [18]. 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

[16].

Table 1. Variation of the activation energy (kJ/mol) at dif-

ferent shear rates 5.4, 18, 54, 180, 540 and 1800 s−1.

Shear Rate

5.4 s−118 s−154 s−1 180 s−1 540 s−11800 s−1

Type

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

Z. T. AL-MALKI ET AL.

Open Access OJPChem

102

100

150

200

250

300

350

400

450

500

02004006008001000 1200 1400 1600 1800 2000

shear rate(1/sec)

shear strees(kpa)

ζ1ζ2

Figure 4. Standard flow curve for the polymer (τ1 = first critical shear stress and T2 = second critical shear stress).

180

280

380

480

580

680

05001000 1500 2000

ShearStress(KP a)

ShearRate(s

‐1

)

TPV‐V

TPV‐R

Figure 5. Variation of shear stress with shear rate for

TPV-V and TPV-R (70Rubber/30HDPE) at 180˚C.

-0.6

-0.1

0.4

0.9

1.4

1.9

05001000 1500 2000

LogViscosity(KPa.s)

ShearRate(s‐1)

TPV‐

‐R

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:





 (1)

-1n





 (2)

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. [19] and

Oomenn et al. [20], 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.

5. Conclusion

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-

dicating that the free volume of the system decreases, so

the K-value increases.

REFERENCES

[1] A. Fainleib and O. Grigoryeva, “Recent Developments in

Polymer Recycling,” Chapter 6, Academic Press, Wal-

tham, 2011.

[2] L. A. Utracki and B. D. Favis, “Polymer Alloys and

Blends,” In: P. N. Cheremisinoff, Ed., Handbook of Poly-

mer Science and Technology, Marcel Dekker Inc, New

York, 1989, pp. 121-201.

[3] L. M. Robeson, “Polymer Blends: A Comprehensive Re-

view,” Hanser Gardner, Munich, 2007.

http://dx.doi.org/10.3139/9783446436503

[4] A. Fainleib and O. Grigoryeva, “Recent Developments in

Polymer Recycling,” Chapter 2, Academic Press, Wal-

tham, 2011.

[5] H. S. Liu, J. L. Mead and R. G. Stacer, “Environmental

Effects of Recycled Rubber in Land-Fill Applications,”

Rubber Chemistry & Technology, Vol. 73, No. 3, 2000,

pp. 551-564. http://dx.doi.org/10.5254/1.3547605

[6] M. Magioli, A. S. Sirqueira and B. G. Soares, “The Effect

of Dynamic Vulcanization on the Mechanical, Dynamic

Mechanical and Fatigue Properties of TPV Based on

Polypropylene and Ground Tire Rubber,” Polymer Test-

ing, Vol. 29, No. 7, 2010, pp. 840-848.

http://dx.doi.org/10.1016/j.polymertesting.2010.07.008

[7] M. Sienkiewicz, J. Kucinska-Lipka, H. Janik and A. Balas,

“Progress in Used Tyres Management in the European

Union: A Review,” Waste Management, Vol. 32, No. 10,

2012, pp. 1742-1751.

http://dx.doi.org/10.1016/j.wasman.2012.05.010

[8] D. Mangaraj, “Role of Compatibilization in Recycling

Rubber Waste by Blending with Plastics,” Rubber Chem-

istry & Technology, Vol. 78, No. 3, 2005, p. 536.

[9] S. L. Zhang, Z. X. Zhang, K. Pal , Z. X. Xin, J. Suh and J.

K. Kim, “Prediction of Mechanical Properties of Waste

Polypropylene/Waste Ground Rubber Tire Powder Blends

Using Artificial Neural Networks,” Materials and Design,

Vol. 31, No. 8, 2010, pp. 3624-3629.

http://dx.doi.org/10.1016/j.matdes.2010.02.039

[10] Z. Hrdlick, A. Kuta and J. Hajek, “Preparation Thermo-

plastic Elastomer Blends Based on Waste Rubber and Low-

Density Polyethylene,” Polimery, Vol. 55, No. 11-22, 2010,

pp. 832-838.

[11] H. Ismail and Suryadiansyah, “Thermoplastic Elastomers

Based on Polypropylene/Natural Rubber and Polypropy-

lene/Recycle Rubber Blends,” Polymer Testing, Vol. 21,

No. 4, 2002, pp. 389-395.

http://dx.doi.org/10.1016/S0142-9418(01)00101-5

[12] H. Ismail and L. Mega, “The Effect of a Compatabilizer

and a Silane Coupling Agent on the Mechanical Proper-

ties of White Rice Husk and Ash Filled Polypropylene/

Natural Rubber Blend,” Polymer Plastics Technology and

Engineering, Vol. 40, No. 4, 2001, pp. 463-478.

http://dx.doi.org/10.1081/PPT-100002070

[13] H. Ismail, M. N. Nasaruddin and U. S. Ishiaku, “White

Rice Husk Ash Filled Natural Rubber Compounds: The

Effect of Multifunctional Additive and Silane Coupling

Agents,” Polymer Testing, Vol. 18, No. 4, 1999, pp. 287-

298. http://dx.doi.org/10.1016/S0142-9418(98)00030-0

[14] N. Sombatsompop and R. Dangtungee, “Effects of the

Actual Diameters and Diameter Ratios of Barrels and

Dies on the Elastic Swell and Entrance Pressure Drop of

Natural Rubber in Capillary Die Flow,” Journal of Ap-

plied Polymer Science, Vol. 86, No. 7, 2002, pp. 1762-

1772. http://dx.doi.org/10.1002/app.11212

[15] A. Y. Coran and R. P. Patel, “Thermoplastic Elastomers,”

3rd Edition, Hanser Publishers, Munich, 2004.

[16] M. Hernandez, J. Gonzalez, C. Albano, M. Ichazo and D.

Lovera, “Effects of Composition and Dynamic Vulcani-

zation on the Rheological Properties of PP/NBR Blends,”

Polymer Bulletin, Vol. 50, No. 3, 2002, pp. 205-212.

http://dx.doi.org/10.1007/s00289-003-0158-8

[17] R. Wagener and T. J. G. Reisinger, “A Rheological Me-

thod to Compare the Degree of Exfoliation of Nanocom-

posites,” Polymer, Vol. 44, No. 24, 2003, pp. 7513-7518.

http://dx.doi.org/10.1016/j.polymer.2003.01.001

[18] J. S. Borah and T. K. Chaki, “Effect of Organo-Montmo-

rillonite Addition on the Dynamic and Capillary Rheol-

ogy of LLDPE/EMA Blends,” Applied Clay Science, Vol.

59-60, 2012, pp. 42-49.

http://dx.doi.org/10.1016/j.clay.2012.02.007

[19] S. George, R. Joseph, S. Thomas and K. T. Varughese,

“Molecular Transport of Aromatic Solvents in Isotactic

Polypropylene/Acrylonitrile-Co-Butadiene Rubber Blends,”

Polymer, Vol. 36, No. 23, 1995, pp. 4405-4416.

http://dx.doi.org/10.1016/0032-3861(95)96846-Z

[20] Z. Oommen, S. Thomas, C. K. Premalatha and B. Kuria-

kose, “Melt Rheological Behaviour of Natural Rubber/

Poly(methyl methacrylate)/Natural Rubber-g-poly(methyl

methacrylate) Blends,” Polymer, Vol. 38, No. 22, 1997,

pp. 5611-5621.

http://dx.doi.org/10.1016/S0032-3861(97)00120-1