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DOI 10.1515/polyeng-2013-0330 J Polym Eng 2014; 34(6): 543554

Fazliye Karabork*, Erol Pehlivan and Ahmet Akdemir

Characterization of styrene butadiene rubberand microwave devulcanized ground tire rubber

composites

Abstract: Ground tire rubber (GTR) was devulcanized by

microwaves at the same heating rate (constant power) and

different times of exposure. The devulcanized rubber (DV-

R) and untreated GTR were characterized physically and

thermally. Composite materials were prepared from differ-

ent proportions of the GTR, which was used as a filler, and

the DV-R, which was used as part of the styrene butadiene

rubber (SBR) matrix, and by varying the exposure time of

the microwave power. These composites were comparedwith a control sample that was prepared from virgin SBR.

The sol content (soluble part) and Fourier transform infra-

red spectroscopy (FTIR) analyses of the devulcanized

samples were examined to define the efficiency of devul-

canization. The cure characteristics and tensile properties

of the SBR composites were researched. In this study, it

was found that using DV-R as part of the rubber matrix

produced much better properties than using GTR as a

filler, thereby showing the significant benefits of micro-

wave devulcanization. At the DV-R content of 50 phr,

the elongation at break of the DV-R 5 min/SBR compos-

ites increased to 445.06% from 217.25% for the GTR/SBR

composites, i.e., the elongation at break was enhanced by

105% by the devulcanization of GTR. Scanning electron

microscopy (SEM) photographs displayed a better inter-

face coherence between the DV-R 5 min and SBR matrix

than the GTR/SBR composites.

Keywords: cure properties; ground tire rubber; mechani-

cal properties; microwave devulcanization; SBR.

*Corresponding author: Fazliye Karabork, Department of

Mechanical Engineering, Aksaray University, 68100, Aksaray,

Turkey, e-mail: [email protected]

Erol Pehlivan: Department of Chemical Engineering, Selcuk

University, 42003, Konya, Turkey

Ahmet Akdemir: Department of Mechanical Engineering, Selcuk

University, 42003, Konya, Turkey

1 Introduction

In the last few decades, the rubber industry has faced a

major problem in finding a suitable way for dealing with

the huge amount of rubber products, especially tires, at

the end of their life. Millions of tons of used tires and

similar products at the end of their limited service life

are dumped in natural environments. The environmen-

tal problems created by waste rubber and discarded tires

have become a serious issue. Many attempts have been

made to recycle waste rubber for both environmental and

economic reasons [1, 2]. Every year, approximately 3.3

million tons of used tires (at the end of their useful life)

are generated in Europe (etrma.org) and approximately

180,000 tons in Turkey (lasder.org.tr). The recycling

of discarded tires has some very important outcomes

including environmental protection, energy savings and

provision of raw materials. Therefore, the development

of an efficient way to utilize rubber waste is an emergent

economic and environmental task faced by the rubberindustry worldwide [2, 3].

Rubber recycling is a difficult task because of the vul-

canization reaction, which takes place in three-dimen-

sional structures. After undergoing reactions, vulcanized

rubber turns into an infusible and insoluble form and

cannot be converted into other forms [4, 5]. The crosslinks

in the main skeleton of the polymer, which form during

the vulcanization process, turn the thermoplastic struc-

tures into thermosets that are impossible to reshape by

heating. Therefore, physical and chemical treatments for

waste tires are necessary to destroy the three-dimensional

structure [6, 7].

A lot of study has revealed that ground tire rubber

(GTR) recycling should target the production of thermo-

plastic elastomers, and its reuse in the rubber industry

[8]. Rubber recycling currently is receiving special atten-

tion, because other disposal methods, such as burning

for energy generation, are dangerous for the environ-

ment [3]. Some new physical and chemical devulcani-

zation techniques for recycling are being developed to

recycle used tires. However, all of these devulcanization

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544 F. Karabork et al.: Characterization of SBR and microwave devulcanized GTR composites

methods are unable to produce a product that is similar

to virgin rubber. Rubber recycling technologies such as

mechanical [9, 10], mechanochemical [1115], ultrasonic

[16], chemical [1719], microwave [3, 2022] and biologi-

cal methods [23] have been developed with the targets

of higher product quality and percent yield. Devulcani-

zation provided the advantage of rendering the rubber

suitable for reformulating and recycling into usable

products [24].

The microwave devulcanization technique is based

on the application of a controlled amount of microwave

energy to the material at a certain energy level that is

sufficient to cleave carbon-sulfur (302 kJ/mol) and sul-

fur-sulfur bonds (273 kJ/mol), but insufficient to cleave

carbon-carbon bonds, which have a higher bond energy

(349 kJ/mol). In this method, tire waste can be reclaimed

without depolymerization as a material that is capable of

being recompounded and revulcanized and has physi-cal properties essentially equivalent to the original vul-

canizate [6, 25]. The use of microwaves for heating has

the advantage of volumetric heating, which is faster and

supports a more homogeneous heating than other con-

ventional methods based on different heat transfer mech-

anisms, such as convection and conduction. However, one

critical requirement of the microwave process is the pres-

ence of polar groups or components in the polymer. The

presence of carbon black in nonpolar rubbers makes the

rubbers receptive to microwave energy. This fact makes

it possible to use the microwave heating to devulcanize

waste tire rubber [7, 26].

The goals of this research were to obtain devulcanized

rubber (DV-R) from waste tires and then to combine it with

a styrene butadiene rubber (SBR) matrix to produce a new

composite material. The curing characteristics, mechani-

cal properties and morphology of these materials were

investigated and compared with the characteristics of

untreated GTR/SBR composites.

2 Materials and methods

2.1 Materials and characterization

The GTR used in this study was supplied by Un-sal Rubber

Co. Ltd (Adana, Turkey). The GTR, which was prepared by

grinding under ambient conditions, was an unclassified

ground rubber from the treads and sidewalls of car, truck

and bus tires. The original rubber, SBR 1502, was obtained

from Petkim (Izmir, Turkey). Toluene was purchased

from Merck (Germany). Sulfur, cyclohexyl benzothiazyl

sulfenamide (CBS), stearic acid and zinc oxide (ZnO) for

vulcanization studies were procured from local sources.

The particle size distribution of the GTR was charac-

terized using 35, 60, 120 and 230 mesh sieves. The thermal

characterization was performed by thermogravimetric

analysis (TGA) to determine the composition and thermal

degradation properties of the samples. The analysis was

performed with a Perkin Elmer thermogravimetric ana-

lyzer under nitrogen from ambient temperature to 800C

with a heating step of 10C/min.

2.2 Microwave treatment of GTR andcharacterization of DV-R

The GTR was treated in an adapted microwave apparatus

consisting of a domestic-type microwave oven (Samsung

MW71E) and a stirring apparatus. The power of the mag-netron was set to 800 W, and 100 g of the GTR was put in

a 1000 ml beaker and stirred at a speed of 6 rpm. The pro-

cessing variable was the exposure time, which was varied

from 1 to 5 min. The samples were identified as DV-R fol-

lowed by a number corresponding to the exposure time in

min. The temperature of the samples was measured after

each treatment.

The sol content of the GTR and DV-R material was

measured with a Soxhlet apparatus using toluene as

solvent. The extraction was completed in 24 h, and it was

made with 2 g of both GTR and DV-R. After the extraction,

the sample was dried for 24 h at 70C, and its weight was

recorded. The percent sol content was calculated from the

following equation [27]:

i iSolcontent % [(W -W)/W ] 100%=

where Wiis the weight of the sample before extraction and

W is the weight of the dry rubber sample after extraction.

The chemical groups of GTR, before and after

the sample was devulcanized, were analyzed with a

Perkin Elmer Spektrum 400 [Fourier transform infrared

spectroscopy (FTIR)] from 4000 to 450 cm-1with a 4 cm-1

resolution and then the efficiency of devulcanization was

determined.

2.3 Preparation of DVR and SBR composites

Virgin SBR, other additives and various proportions of

the DV-R samples were mixed for 15 min on an open two-

roll mixing mill at room temperature. The formulations

of the composites are presented in Table 1. Formulation

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F. Karabork et al.: Characterization of SBR and microwave devulcanized GTR composites 545

1 does not contain DV-R and is a control sample. For-

mulations 2, 3 and 4 were prepared at 10, 30 and 50 phr

DV-R. For comparison, untreated GTR was mixed with

SBR in the same series. In the formulation of GTR/SBR

composites, GTR was used as a filler. As DV-R was con-

sidered to be an elastomeric component, it was used

as a component of raw rubber and not a filler. Because

DV-R contains rubber and carbon black, the amounts of

SBR and carbon black were adjusted in the formulations

of the composites. The amounts of the other additives

(ZnO, stearic acid and sulfur) in the formulations were

based on 100 g of rubber without taking the DV-R into

account, because it was assumed that the additives in

the DV-R originated from the parent compound and wereinactive [28].

The maximum sol content and suitable temperature

(Table 2) were obtained in the samples that were exposed

for 4 and 5 min but not the samples that were exposed

for 1, 2 and 3 min. Therefore, DV-R/SBR composites were

prepared by exposing the samples in the microwave for 4

and 5 min.

Table 1 Formulations of the devulcanized rubber (DV-R)/styrene

butadiene rubber (SBR) composites.

Ingredients (phra)

SBR . . .

Devulcanized rubber

Carbon black (N) . . . .

Process oil . . . .

ZnO

Stearic acid

CBS . . . .

Sulfur . . . .

aParts per hundred rubber.

CBS, cyclohexyl benzothiazyl sulfenamide.

2.4 Characterization of DV-R/SBRcomposites

2.4.1 Cure characteristics

The cure characteristics of the rubber composites were

investigated by using a rheometer, Beijing RADE MR-C3,

at 170C. From the rheographs, the minimum torque (ML),

scorch time (ts2

), maximum torque (MH) and optimum

curing time (t90

) were obtained. The ML is a measure of

the rubbers resistance to flow during processing, and the

MHrelates to the compounds final stiffness. The number

of min to reach 90% of the MHor t

90briefly expresses the

cure time required to almost complete the vulcanization

process. These samples were identified as R followed by

two numbers corresponding to the exposure time in min

and the DV-R content (1/10).

2.4.2 Measurement of mechanical properties

The mechanical properties of the DV-R/SBR and GTR/SBR

composites were measured with a Shimadzu AG-IC tensile

testing machine according to ASTM D 412 under laboratory

conditions (232C). The testing speed was 500 mm/min.

Dumbbell-shaped specimens were punched from the com-

pression-molded sheets, and the hardness (Shore A) of the

new composites was measured with a Bareiss Shore meter

according to ASTM D 2240. At least three samples for each

composition were tested, and the average value is reported.

2.4.3 Determination of crosslink density

The chemical characteristics of the DV-R/SBR and GTR/

SBR composites were investigated by determining their

crosslink densities. The test specimens, which weighed

approximately 0.2 g each, were immersed in a solvent con-

taining 100 ml of toluene at room temperature (23C) for

72 h. The excess solvent on the surfaces of the specimens

was removed by drying with filter paper. The weightsof the swollen specimens were measured, and then the

specimens were dried to a constant weight. The crosslink

densities of the composites were determined by the Flory-

Rehner equation with the Kraus correction [28, 29]:

2

1/3

ln( 1- ) ( )1-

2 - /2

r r r

c

r r

v v X v

Vs v v

+ +

=

where c is the crosslink density of composite (mol/m3),

Vsis the molar volume of the solvent (1.06910-4m3/mol),

Table 2 Sample temperatures after microwave treatment and sol

contents.

Sample Max temperature (C) Sol content (%)

Na .

DV-R .

DV-R .

DV-R .

DV-R .

DV-R .

aUntreated ground tire rubber (GTR).

DV-R, devulcanized rubber.

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vr is the volume fractions of filled rubber in the swollen

specimen and X is the rubber-solvent interaction para-

meter (0.3795 in this study [30]).

2.5 Morphology

The morphology of the GTR surface and the fracture sur-

faces of the DV-R/SBR and GTR/SBR composites were

evaluated with a ZEISS EVO LS 10 scanning electron

microscope (SEM). The sample surfaces were sputter-

coated with gold powder using a Sputter Coater Auto 108.

3 Results and discussion

3.1 Physical and thermal characterizationof GTR

Figure 1 shows the particle size distribution of the GTR

used in these experiments. Particle size analysis showed

that the majority of the ground rubber particles were in

the 35120 mesh (0.50.125 mm) range. The particles in the

size range higher than 120 mesh (smaller than 0.125 mm)

were found in small quantities. It is well known that parti-

cles of GTR that are suitable for utilization in new formula-

tions and for devulcanization processes should be smaller

than 0.6 mm and have high surface areas [3134].

An SEM photograph of representative GTR is shown in

Figure 2. It was observed that the GTR particles had irregu-

lar shapes and their surfaces were rough.

The partial composition of the GTR was determined by

TGA and results are given in Figure 3. The thermogram in

Figure 3 shows that the first weight loss (13%) below 350C

corresponded to a loss of water and highly volatile materi-

als, such as low molecular weight plasticizers, oils, waxes

70

60

50

40

Weight(%)

30

20

10

0

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microwave exposure and were almost linear with the time

of exposure.

Soxhlet extraction evaluates only the fraction of

soluble matter present in the sample, which is a good

parameter to use to evaluate the efficiency of the devul-

canization process [3, 7]. The initial sol content of theGTR was 2.30% and it rose to 25.36% and 34.77% after

microwave devulcanization for 4 and 5 min, respectively.

The higher sol content showed that the devulcaniza-

tion process was more efficient. It can be observed that

the time of treatment in the microwave has a significant

influence on the sol content. This was expected because

when the starting material was treated for longer periods

of time, it reached higher temperatures and generated

materials with higher sol contents. The sol content of the

devulcanized GTR in this study was compared with the sol

content obtained with different devulcanization methods

in other references in Table 3.To obtain information about the structure and func-

tional groups after microwave devulcanization, FTIR

spectra are presented in Figure 4, where the FTIR spectra of

the DV-R (after microwave exposure times of 4 and 5 min)

and GTR were compared. During the microwave devulcani-

zation of GTR, the amount of energy released is utilized for

Table 3 Comparison of the sol content of the devulcanized ground tire rubber (GTR) from this study and other devulcanization methods.

Devulcanization

method

Literature Material Sol content (%)

Mechanochemical De et al., [] Ground tire rubber and

devulcanization agent (TMTD)

.

Thermochemical Grigoryeva et al., [] Ground tire rubber and

devulcanization agent

.

(Phthalic anhydride)

Mechanical Li et al., [] Ground tire rubber .

Microwave This study Ground tire rubber .

4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 450

3296.89

2915.732847.65

1538.70

1423.06 1028.00

820.872338.16

2125.60 1633.40

1372.92 959.692950.08

3302.02

2913.82

2846.89

1427.77

1036.06

818.85

1528.89

1372.92

961.30

871.26 712.082315.61

3297.49

2845.90

2315.771427.84

1046.16

2141.70

2901.77

1369.70

810.16

787.65

2019.763790.51

A

B

C

Wave number (cm-1)

Figure 4 Fourier transform infrared spectroscopy (FTIR) spectra of: (A) ground tire rubber (GTR); (B) DV-R4; and (C) DV-R5.

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breaking S-S bonds instead of C-C bonds, because the S-S

bond energy is lower than the energies of various organic

bonds. However, a few C-C and C-S bonds may break along

with the S-S bonds at higher temperatures and after longer

durations of heating. The devulcanization was carried out

for a maximum of 5 min at 37010C (maximum tempera-

ture) and the rubber crosslinks can break easily without

main chain scission. The peaks of the C-H stretching vibra-

tion (30002800 cm-1) and the -CH2deformation (1447 cm-1

and 1372 cm-1) did not show significant differences between

GTR and DV-R [23, 36]. The peak at 1538 cm-1was assigned

to the C-S bond, which represents untreated GTR. After

the devulcanization process, the peak value of the C-S

bond decreased (especially for the DV-R5 sample), which

showed the devulcanization of the GTR during the micro-

wave devulcanization.

3.3 Characterization of DV-R/SBRcomposites

3.3.1 Cure characteristics

The cure characteristics of the DV-R/SBR and GTR/SBR

composites are given in Table 4. The DV-R content and

microwave exposure time affected the curing behavior.

The effects of the DV-R content on the MLand the M

H

are shown in Figure 5A and B. The MLincreased slightly

with the addition of DV-R in all cases (4 and 5 min), but

it increased remarkably with the addition of untreatedGTR. This indicates firstly that there was some interaction

between the DV-R and the virgin rubber and secondly that

the processing of composites containing GTR was more

difficult than for composites containing DV-R. The reason

for the increase in the MLcould be the agglomeration of

waste rubber particles in the SBR matrix [1].

The MH, a measure of crosslink density, decreased

slightly with the addition of DV-R and the microwave

exposure time, but it increased with the addition of

untreated GTR. The MH increased remarkably with the

addition of 30 phr of GTR, and further additions of GTR

resulted in a decrease in the torque. This relationship

indicated that the elastic modulus was lower in the com-

posites containing DV-R. The decrease in the value of the

MHmay be due to the presence of short rubber chains and

crosslink precursors in the DV-R [14].

Figure 6A and B show the ts2

and optimum cure time

(t90

) as functions of DV-R content. The ts2

of the compos-

ites decreased slightly with an increase in both the GTR

and DV-R concentrations. Furthermore, the ts2

of the

DV-R/SBR composites are lower than those of the GTR/

SBR composites. It is clear that there are more unsatu-

rated rubber bonds in the DV-R than in the GTR. The

shorter ts2

for the composites indicate that the crosslink-

ing reactions start earlier in the vulcanization process.

Ishiaku et al. [37] showed that a reaction between the SBRmatrix and the DV-R can catalyze crosslinking. Diffusion

of the accelerator from the DV-R into the virgin rubber

can reduce the ts2

[27, 38]. De et al. [14] reported that the

revulcanized rubber has active crosslinking sites, which

lower the ts2

.

The t90

is the vulcanization time required to obtain

a product with optimum physical characteristics. The t90

of the composite decreased with an increase in the con-

centration of both the GTR and DV-R in the composite

skeleton. Both ts2

and t90

decreased considerably with the

addition of DV-R5 to the matrix, which demonstrates the

presence of active functional sites in these composites.

3.3.2 Mechanical properties of composites

The DV-R content and the exposure time were found to

have a strong, distinct effect on the mechanical properties

of the DV-R/SBR and GTR/SBR composites. The mechani-

cal properties of the SBR composites with different

Table 4 Cure characteristics of the devulcanized rubber (DV-R)/styrene butadiene rubber (SBR) and ground tire rubber (GTR)/SBR

composites.

Sample RKa R R R R R R R R R

DV-R (phr)

Control

min

min

Untreated GTR

ML(dNm) . . . . . . . . . .

MH(dNm) . . . . . . . . . .

ts

(min) . . . . . . . . . .

t

(min) . . . . . . . . . .

aControl sample.

MH, maximum torque; M

L, minimum torque; t

90, optimum curing time; t

s2, scorch time.

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concentrations of GTR and DV-R are shown in Table 5.

These composites tend to become weak and brittle with

increasing concentrations of GTR and DV-R. The results inTable 5 show that the mechanical properties of the DV-R/

SBR were far superior to the properties of SBR filled with

GTR at the same loading.

The effects of the GTR and DV-R contents on the

tensile strength and the elongation at break are shown in

Figure 7A and B. With the addition of 10 phr of DV-R andGTR to the composite, the values of the tensile strength

and elongation at break increased. These increases may

be because the smaller DV-R and GTR particles act as

20 35

30

25

20

15

10

0

5

ControlA B

Control 10 30 50

Devulcanized rubber content (phr)

Control 10 30 50


DV-R4 DV-R5 GTR Control DV-R4 DV-R5 GTR

18

16

14

12

MinT

orque,

ML(dNm)

MaxT

orque,

MH

(dNm)

10

8

6

4

2

0

Figure 5 Effects of devulcanized rubber content on: (A) minimum torque (ML); and (B) maximum torque (M

H).

3.5

3.0

2.5

2.0

1.5

1.0

0

0.5

ControlA B

Control 10 30 50


Control 10 30 50


DV-R4 DV-R5 GTR Control DV-R4 DV-R5 GTR1.8

1.6

1.4

1.2

Skorchtime,

ts2

(min)

Optimum

curetime,

t90

(min)

1.0

0.8

0.6

0.4

0.2

0

Figure 6 Effects of devulcanized rubber content on: (A) scorch time (ts2); and (B) optimum cure time (t

90).

Table 5 Mechanical properties of devulcanized rubber (DV-R)/styrene butadiene rubber (SBR) and ground tire rubber (GTR)/SBR

composites.

PropertiesSample

Elongationat break (%)

Tensile strength(N/mm)

% Modulus(N/mm)

% Modulus(N/mm)

% Modulus(N/mm)

Hardness(Shore-A)

Crosslinkdensity (mol/m)

RK . . . . .

R . . . . .

R . . . . .

R . . . . .

R . . . . .

R . . . . .

R . . . . .

R . . . . .

R . . . .

R . . . .

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ControlA B

Control 10 30 50


Control 10 30 50


DV-R4 DV-R5 GTR Control DV-R4 DV-R5 GTR10 700

600

500

400

300

200

100

0

9

8

76

5

4

32

1

0

Tensilestrenght(N/mm

2)

Elong

ationatbreak(%)

Figure 7 Effects of devulcanized rubber content on: (A) tensile strength; and (B) elongation at break.

A B

C

100%m

odulus(N/mm

2

)

200%m

odulus(N/mm

2)

Control DV-R4 DV-R5 GTR Control DV-R4 DV-R5 GTR7.0

6.0

4.5

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0

5.0

4.0

3.0

2.0

1.0

0

300%m

odulus(N/mm

2)

6.0

4.0

5.0

3.0

2.0

1.0

0

Control 10 30 50


Control 10 30 50


Control 10 30 50


Control DV-R4 DV-R5 GTR

Figure 8 Effects of devulcanized rubber content on: (A) 100% modulus; (B) 200% modulus; and (C) 300% modulus.

reinforcing agents in the materials. This result was sup-

ported by prior work by Rooj et al. [5]. However, the values

of the tensile strength and elongation at break decreased

for 30 and 50 phr loadings of both DVR and GTR. The

deterioration of the mechanical properties of the GTR/

SBR composites is related to the weak adhesion between

the GTR particles and the SBR matrix. Because the GTR

particles are not well-dispersed in the matrix of SBR, they

are weak sites for stress-transmission and result in lower

mechanical properties for the composite. The values of

the properties for composites that contained DV-R were

much better than for the composites with GTR. Because

DV-R takes part in the crosslinking reaction, there is strong

interfacial bonding between the SBR matrix and DV-R that

leads to good tensile properties.

The tensile strength and elongation at break increased

with the time of exposure to microwave power. The higher

tensile strength and elongation at break may be due to the

decrease in the number of crosslinked sites in the DV-R5/

SBR and the strong interfacial bonds between the SBR

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A B

Ha

rdness(shoe-A)

Crosslinkdensity(mol/m

3)

70 140

120

100

80

60

40

20

0

68

66

64

62

60

58

5654

52

50Control 10 30 50


Control 10 30 50


Control DV-R4 DV-R5 GTR Control DV-R4 DV-R5 GTR

Figure 9 Effects of devulcanized rubber content on: (A) hardness; and (B) crosslink density.

Table 6 Comparison of the changes of the mechanical properties of the virgin rubber and devulcanized ground tire rubber (GTR) for the

different devulcanization methods according to control samples reported in the literature

Devulcanizationmethod

Literature Rubber blends Dev. rubber(phr or w%)

Variationof tensile

strength (%)

Variation ofelongation

at break (%)

Variationof %

modulus (%)

Mechanical Li et al., [] NR and devulcanized GTR phr +. -.

phr -. -.

phr -. -.

Mechanochemical Maridas and Gupta, [] NR and devulcanized GTR % -. -. +.

% -. -. +.

% -. -. +.

% -. -. +.

Mechanochemical De and De, [] SBR and devulcanized GTR phr +. -. +a

Thermochemical Grigoryeva et al., [] SBR and devulcanized GTR % + +.

% + -.

% + -. Mechanochemical Zhang et al., [] NR and devulcanized GTR % +. -. +.b

% -. -. +.b

% -. -. +.b

Microwave This study SBR and devulcanized GTR phr +. +. -.

phr -. -. +.

phr -. -. -.

aVariation of 200% modulus.bVariation of 100% modulus.

+ increase in the variation.

- decrease in the variation.

NR, natural rubber; SBR, styrene butadiene rubber.

matrix and DV-R, which transmit stress very well in the

composite structure.

The effects of the GTR and DV-R content on the modulus

at 100%, 200% and 300% elongations are presented in

Figure 8AC. The values of the modulus increased with

increases in the GTR content, especially at 50 phr, indicat-

ing that the GTR loading in the rubber matrix enhanced

the rigidity of the composite. The important increase in

the modulus is attributed to the higher modulus of the

GTR than the composite matrix; therefore, GTR acts like

a rigid particulate filler that cannot be deformed easily.

The addition of GTR to a soft composite matrix leads to the

development of a local stretching in the composite matrix

that exceeds the overall strain of the composite. The 300%

modulus was not obtained for the GTR/SBR composites

with 30 and 50 phr loadings. Hence, DV-R is comprised of

a gel fraction, which has a higher modulus, and a sol frac-

tion, which could be co-crosslinked with the SBR matrix,

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A

B

C

Figure 10 Scanning electron microscopy (SEM) photographs of tensile fracture surfaces: (A) ground tire rubber (GTR)/styrene butadiene

rubber (SBR) composites; (B) DV-R4/SBR composites; and (C) DV-R5/SBR composites.

and the values of the modulus of the GTR/SBR composites

were lower than the values that were obtained by loadingGTR with DV-R5.

The hardness of the composites showed an increase

with longer microwave exposure time and higher DV-R

loading (Figure 9A). The increase in the hardness of

the composites is most likely due to the increase in the

crosslink density of the composites.

Figure 9B shows the variations of the crosslink den-

sities of the composites as functions of DV-R content.

Because the crosslink density of the DV-R was reduced

by devulcanization, the crosslink density of the DV-R/

SBR composites was a little lower than that of the GTR-

filled SBR composites. The moderate increase in crosslinkdensity of the composites with the addition of DV-R was

due to the presence of active crosslinking sites in the

DV-R, which may take part in crosslinking during the vul-

canization process. It is proven that the crosslink density

of the DV-R/SBR composites is lower than that of the GTR/

SBR composites, which further confirmed that the devul-

canization was accomplished by the microwave treatment

(Figure 9B).

The changes in the mechanical properties of the

virgin rubber and devulcanized GTR for the different

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devulcanization methods are compared in Table 6. In this

table, we bring attention to the references that are related

to the devulcanization of waste tire rubber.

3.4 Morphology

SEM micrographs of tensile fractured surfaces of GTR/SBR

and DV-R/SBR composites with 30 phr and various expo-

sure times are shown in Figure 10AC. The surfaces of SBR

composites filled with the GTR exhibited a morphology of

brittle fracture, which is evidence of inferior properties,

especially elongation at break. There were some cracks,

pores and many cavities on the fracture surfaces of the

composites (Figure 10A). This morphology showed that

the adhesion of GTR to the SBR matrix was poor. The weak

adhesion results in damage or alteration of the mechani-

cal properties, which is in agreement with the other con-clusions from our experimental results. The exposure time

also affected the fracture surface morphology. The fracture

surface of the DV-R4/SBR composite was similar to the

GTR filler/SBR composite (Figure 10B) because the adhe-

sion was poor between the DV-R4/SBR composites. The

tensile fractured surface of composites with 30 phr DV-R5

is shown in Figure 10C. Desirable adhesion exists between

the DV-R filler and the SBR matrix and a crosslinking reac-

tion occurs between the DV-R and the SBR matrix.

4 Conclusions

DV-R was produced by a microwave technique and then

DV-R and untreated GTR were blended with virgin SBR in

different proportions. A considerable increase in the sol

fraction occurred during the devulcanization process.

An FTIR study confirmed the microwave devulcanization

of GTR. The sol content of the untreated GTR was 2.3%,

and the sol content reached its maximum of 34.77% for

DV-R5. The curing characteristics and mechanical proper-

ties of the DV-R/SBR composites were compared with the

properties of the GTR/SBR composites. The MLincreased

and the MHdecreased to a small extent with an increase

in the DV-R, but both characteristics showed a remarkable

increase with the addition of untreated GTR. It was a fact

that the processability of the composites did not change

meaningfully with the DV-R loadings. At 10 phr DV-R and

GTR loadings of SBR composites, the tensile strength and

elongation at break were improved in comparison to the

virgin SBR. At higher concentrations of DV-R and GTR,

these properties deteriorated. As a result of microwave

devulcanization, the DV-R/SBR composites had bettermechanical properties than the GTR-filled SBR composites

at the same loadings. However, the elongation at break of

the DV-R5/SBR composites decreased only 15.17% versus

the control sample at 50 phr loading, while the elongation

at break was 30.18% and 58.59% for DV-R4/SBR and GTR/

SBR composites, respectively. This research has shown

that the microwave treatment can be used as a convenient

technique for rubber recycling studies.

Acknowledgments: The authors acknowledge the support

of the Coordination Committee of Scientific Research Pro-

jects of Selcuk University, Turkey (Project no: 10201043).

Received December 30, 2013; accepted April 1, 2014; previously pub-

lished online May 1, 2014

References

[1] Li S, Lamminmaki J, Hanhi K.J. Appl. Polym. Sci.2005, 97,

208217.

[2] Lamminmaki J, Li S, Hanhi K.J. Mater. Sci. 2006, 41, 83018307.

[3] Zanchet A, Carli LN, Giovanela M, Crespo JS, Scuracchio CH,

Nunes RCR.J. Elast. Plas. 2009, 41, 497507.

[4] Wen L, Lin C, Lee S. Waste Manag. 2009, 29, 22482256.

[5] Rooj S, Basak GC, Maji PK, Bhowmick AK.J. Polym. Environ.

2011, 19, 382390.

[6] Adhikari B, De D, Maiti S. Prog. Polym. Sci.2000, 25, 909948.

[7] Scuraccio CH, Waki DA, Silva MLCP.J. Therm. Anal. Calorim.

2007, 87, 893897.

[8] Karger-Kocsis J, Meszaros L, Barany TJ. Mater. Sci.2013, 48, 138.

[9] Zhang X, Lu C, Liang M.J. Appl. Polym. 2007, 103, 40874094.

[10] Fukumori K, Matsushita M. R&D Rev. Toyota CRDL. 2003, 38,

3947.

[11] Yehia AA. Polym. Plast. Tech. Engin.2004, 43, 17351754.

[12] Yehia AA, Ismail MN, Hefny YA, Abdel-Bary EM, Mull MA.J.

Elast. Plast. 2004, 36, 109123.

[13] Jana GK, Das CK. Macro. Res.2005, 13, 3038.

[14] De D, Das A, De D, Dey B, Debnath SC, Roy BC. Euro. Polym. J.

2006, 42, 917927.

[15] Zhang X, Lu C, Liang M.J. Polym. Res. 2009, 16, 411419.

[16] Isayev AI, Yushanov SP, Chen J.J. Appl. Polym. Sci. 1996, 59,

803813.

[17] Dubey V, Pandey SK, Rao NBSN.J. Analy. Appl. Pyro.1995, 34,

111125.

[18] Dubkov KA, Semikolenov SV, Ivanov DP, Babushkin DE,

Panov GI, Parmon VN. Poly. Degr. Stab.2012, 97, 11231130.

[19] Sadaka F, Campistron I, Laguerre A, Pilard JF. Poly. Degr. Stab.

2012, 97, 816828.

Unauthenticated


7/25/2019 polyeng-2013-0330

12/12


[20] Fix SR. Elastomerics1980, 112, 3840.

[21] Sanchez BV. New Insights in Vulcanization Chemistry Using

Microwaves as Heating Source, Ph.D. Thesis: Universitat

Ramon Llull, Spain, 2008.

[22] Scagliusi SR, Arajo SG, Landini L, Lugo AB. Int. Nucl. Atl.

Conf.INAC Rio de Janeiro, 2009.

[23] Li Y, Zhao S, Wang Y.J. Polym. Environ.2012, 20, 372380.

[24] Srinivasan A, Sanmugharaj AM, Bhowmick AK. Current Topicsin Elastomer Research, Bhowmick, AK, Ed., Taylor and Francis

Group: LLC, USA, 2007.

[25] Rajan VV. Devulcanisation of NR Based Latex Products for Tyre

Applications, Ph.D. Thesis: University of Twente, Netherlands;

2005.

[26] Sun X. The Devulcanization of Unfilled and Carbon Black Filled

Isoprene Rubber Vulcanizates by High Power Ultrasound, Ph.D.

Thesis: University of Akron, USA, 2007.

[27] Jana GI, Mahaling RN, Rath T, Kozlowska A, Kozlowski M, Das

CK. Polimery2007, 52, 131136.

[28] De D, De D. Mater. Sci. Appl. 2011, 2, 486496.

[29] Flory PJ, Rehner JJ.J. Chem. Phys. 1943, 11, 521526.

[30] Mathai AE, Thomas SJ. Macromol. Sci. 1996, 35, 229253.

[31] Bilgili E, Arastoopour H, Bernstein B. Powd. Tech. 2000, 115,

265277.

[32] Naskar AK, De SK, Bhowmick AK. Rubber Chem. Technol.2000,

73, 902911.

[33] Weber T, Zanchet A, Brandalise RN, Janaina S, Crespo JS, Nunes

CRR.J. Elast. Plast.2008, 40, 147159.

[34] Fernandez-Berridi MJ, Gonzalez N, Mug CA, Bernicot C. Ther-mochim. Acta2006, 444, 6570.

[35] Grigoryeva O, Fainleib A, Starostenko O, Danilenko I,

Kozak N, Dudarenko GJ. Rubber Chem. Technol. 2004, 77,

131146.

[36] Kumar P. Investigating the Recycled Rubber Granulate-Virgin

Rubber Interface, Ph.D. Thesis: University of London, England,

2007.

[37] Ishiaku US, Chong CS, Ismail H. Polym. Polym. Compos. 1998,

6, 399406.

[38] Hong CK, Isayev AI.J. Mater. Sci. 2002, 37, 385388.

[39] Maridas B, Gupta BR. Kautsch. Gummi Kunstst.2003, 56,

232236.

Unauthenticated

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