Use of Carboxylated Nitrile Rubber and Natural RubberBlends as Retreading Compound for OTR Tires

Kaushik Pal,1 Tanya Das,2 Samir K. Pal,1 Chapal K. Das21 Department of Mining Engineering, Indian Institute of Technology, Kharagpur 721302, West Bengal, India

2 Materials Science Centre, Indian Institute of Technology, Kharagpur 721302, West Bengal, India

Ore transportation is one of the important unit opera-tions in a mineral industry. In this study, three raw rub-ber compounds are prepared in three different blendratios, and four types of raw rubber samples of pureNR with silica reinforced has been collected from thedifferent tire retreading industries. Blend propertieslargely depend on the blend ratio and on the blendingtechnique. The improvement in the physical propertiessuch as cure characteristics, mechanical characteriza-tion, cross-link density, FTIR, thermal characterization,SEM studies, and dynamic mechanical analysis hasbeen studied in those samples. It has been found thatretread rubber made with 80 phr XNBR and 20 phr NRhas given the better results when compared with theother samples against all the characterization done. Itis also seen that rubber made by the researchers arevery good in tough, rigid and these are extremely ableto withstand for using as a retread rubber for 35Tdump trucks tire when compared with the retread rub-ber made by the tire retreading industries for differentmines in India. POLYM. ENG. SCI., 48:2410–2417, 2008.ª 2008 Society of Plastics Engineers

INTRODUCTION

Tires used in mining vehicles are very costly and need

regular maintenance, because it is impossible to accept its

replacement expense within very short term. The rugged

working conditions in mining industries reduce the life

span of tires on account of cuts, contamination, abrasion,

wear, speed fluctuations, etc. There are several types of

damage occurred in the dump-truck tire such as tread

detachment, sidewall cuts, impact ruptures, bead damage,

etc. For transportation of minerals from one place to

another, the wear and abrasion must be filled by changing

of tire compounds.

Tire industries consume more than 60% of the rubber

product and the prime factors of considerations are safety

and tread life. Thus, 30% of the mechanical work avail-

able from the fuel is dissipated in the tires. A reduction

of 15% in tire rolling resistance may improve fuel con-

sumption by 4.5% [1]. For this problem, Coal India Lim-

ited, India, is spending lots of money every year towards

the tire retreading expenses for increasing the tire life as

well as to reduce the new tire replacing cost, which is

very much expensive one.

Carboxyl groups have also been introduced into rub-

bers in order that reactions characteristic of the carboxylic

functional group might be employed to crosslink the poly-

mer chains or attach them to other molecules or surfaces

[2]. Also, the group is added to significantly improve the

abrasion resistance of NBR while retaining excellent oil

and solvent resistance. XNBR compounds provide high

tensile strength, tough, abrasion resistant, and good physi-

cal properties at high temperatures. Also, XNBR generally

exhibits poor hysteresis properties and reduced cold tem-

perature flexibility, but in regard to chemical resistance

XNBR is considerably superior.

Also, natural rubber (NR) is known to exhibit numerous

outstanding properties, and reinforcing fillers are necessarily

added into NR in most cases in order to gain the appropriate

properties for specific applications. A wide variety of partic-

ulate fillers are used in the rubber industry for various pur-

poses, of which the most important are reinforcement,

reduction in material costs, and improvements in processing

[3]. Reinforcement is primarily the enhancement of strength

and strength-related properties, abrasion resistance, hard-

ness, and modulus [4, 5]. In most applications, carbon black

(CB) and silica have been used as the main reinforcing fill-

ers that increase the usefulness of rubbers by tire retreading

industries. In general, a CB-reinforced rubber has a higher

modulus than a silica-reinforced one. However, silica pro-

vides a unique combination of tear strength, abrasion resist-

ance, aging resistance, and adhesion properties [6]. In tire

treads, silica yields a lower rolling resistance at equal wear

resistance and wet grip than CB [7]. However, NR exhibits

a limited ozone resistance and a high dependence of

dynamic properties on temperature because of damping

derived from high glass transition temperature (Tg) [8].

Correspondence to: K. Pal; e-mail: pl_kshk@yahoo.co.in

Contract grant sponsor: Coal India Limited, Kolkata.

DOI 10.1002/pen.21196

Published online in Wiley InterScience (www.interscience.wiley.com).

VVC 2008 Society of Plastics Engineers

POLYMER ENGINEERING AND SCIENCE—-2008

A literature search shows a lack of studies about

XNBR with NR blends alone. With this work, we pretend

to partially fill this gap. Blending of elastomers has been

often used to obtain an optimum number of desirable

combinations, physical properties, processability, and cost.

NR shows very interesting physical properties because of

its ability to crystallize under stretching. These com-

pounds are capable of forming a chemical link between

these dissimilar rubbers to produce a technologically com-

patible blend. The blend vulcanizates thus produced ex-

hibit enhanced physical properties by judicious selection

of the NR:XNBR ratio [9]. The effort toward improving

the efficiency of such transportation system is essential

for reduce running costs and cutting down the end cost

figures by using the XNBR and NR rubber blends.

So, in this study the main goal is to prepare the better

abrasion resistant retread tire than the retreading compa-

nies and maximize the tire life. For this, XNBR and NR

blends with various compositions have been examined for

testing the wear resistance properties.

EXPERIMENTAL

Materials Used in Rubber Preparation

The carboxylated nitrile rubber (XNBR) used was

Nipol N-34 grade, of Nippon Zeon Co., Japan. Its specific

gravity is 0.98, Mooney viscosity at 1008C is 45. Bound

acrylonitrile content is 27%. Natural rubber (NR) of

RMA-1X grade was supplied by the Rubber Board, Kot-

tayam, Kerala. Zinc oxide, stearic acid, N-cyclohexyl-2-benzothiazyl sulfonamide (CBS), and antioxidant (HQ)

was supplied by Bayer (India). Standard rubber grade pro-

cess oil (Elasto 710), carbon black was purchased from

the local market.

Preparation of Raw Rubber

The compounding formulation for the carboxylated

nitrile rubber and natural rubber blends with its various

ingredients were mixed in a two roll mill at a friction

ratio of 1:2 following standard mixing sequence.

Cure Characteristics of Rubber Compound

The cure characteristics of the rubber compound were

studied with the help of a Monsanto Oscillating Disc Rhe-

ometer (ODR-100s), which complies with ASTM D2084

at 1508C. From the graphs, the optimum cure time, scorch

time, and rate of cure [tmax 2 tmin (dN�m)] could be

determined.

Mechanical Characterization (Tensile and Tear)

Vulcanized slabs were prepared by compression mold-

ing, and the dumbbell shaped specimens were punched

out from a molded sheet by using ASTM Die C. The tests

were done by means of a universal tensile testing machine

(Hounsfield H10KS) under ambient condition (25 6 28C),following the ASTM D 412-99 and ASTM D 624-99. The

moduli at 100%, 200% elongation, tensile strength, tear

strength, and elongation at break (%) were measured at

room temperature. The initial length of the specimens was

25 mm and the speed of the jaw separation was 500 mm/

min.

Five samples were tested for each set of conditions, at

the same elongation rate. The values of the tensile

strength, modulus at 100% elongation, 200% elongation,

and elongation at break were averaged. The relative error

was below 5%. The Shore A hardness was measured.

Determination of Crosslink Density

The crosslink density was determined by immersing a

small amount (known mass) of sample in 100 ml toluene

to attain equilibrium swelling. After this, the sample was

taken out from the toluene and the solvent was blotted

from the surface of the sample and weighed immediately.

TABLE 1. Different composition of the rubber.

Ingredients

Sample code (wt. in phr)

MC-1 MC-2 MC-3

Carboxylated nitrile rubber (XNBR) 80 50 20

Natural rubber (NR) 20 50 80

Carbon black 40 40 40

Stearic acid 2 2 2

Process oil-Elasto 710 2 2 2

Antioxidant (HQ) 1 1 1

Sulfur 1 1 1

Accelerator (CBS) 0.7 0.7 0.7

Activator (ZnO) 5 5 5

TABLE 2. Different composition of the collected rubber from the industries.

Basic ingredients

Sample code

PC-1 (%) OC-1 (%) PC-2 (%) OC-2 (%)

NR 60 50 60 60

Carbon black 30 40 30 30

ZnO 2 2 1.5 1.5

Other chemicals 6.5 (Silica 3–4%) 6.5 (Silica 2–3%) 7.5 (Silica 2–2.5%) 7.5 (Silica 2–3%)

Curatives 1.5 1.5 1.5 1

DOI 10.1002/pen POLYMER ENGINEERING AND SCIENCE—-2008 2411

This sample was then dried out at 808C to constant

weight. Then the chemical crosslink density was calcu-

lated by the Flory-Rehner equation [10].

Fourier Transformed Infrared Spectroscopy

Fourier transform infrared spectroscopy was performed

using a NEXUS 870 FT-IR (Thermo Nicolet) instrument

in dry air at room temperature. Spectra were taken in the

range 4000–0 cm21 in transmission mode.

Thermal Characterization (DTA-TGA)

TGA studies were carried out Shimadzu-DT-40 instru-

ment in presence of air at a rate of 108C/min from 25 to

6008C temperature. Degradation temperature of the com-

posites was calculated by TGA plot.

Scanning Electron Microscopy

The tensile fracture surface of the samples were stud-

ied in a scanning electron microscope (JSM-5800 of

JEOL; Acceleration voltage, 20 kV; type of coating, gold)

at 500 and 1000 times zooming.

Dynamic Mechanical Analysis

Dynamic mechanical analysis was performed in tension

mode of a TA instrument DMA 2980 dynamic mechanical

analyzer at a frequency of 1 Hz with a heating rate of

108C/min. The temperature dependence of storage modulus

(E0), loss modulus (E00), and loss tangent (tan d) was meas-

ured from 258C to 1508C with a heating rate 108C/min.

RESULTS AND DISCUSSIONS

Compound Formulation

Compounding formulations based on changing of the

carbo-oxylated nitrile rubber (XNBR) and NR contents

are shown in Table 1. For vulcanization, the amounts of

additives such as sulfur, CB, process oil, CBS were based

on 100 g of rubber.

Two types of raw (unvulcanized) rubbers, such as pre-

mium quality, mainly used in iron ore and uranium mines

for good mileage as well as better service, and general

quality, mainly used in coal mines, have been collected

from tire retreading industries, India. The industry is the

main supplier of retread tire to Uranium Corporation of

India Limited (UCIL), Airport authority, Eastern Coal-

fields Limited (ECL), Steel Authority of India Limited

(SAIL), Tata Iron and Steel Company Limited (TISCO),

and also some Pvt. Company.

Another two types of raw (unvulcanized) rubbers

namely premium quality and general quality have been

FIG. 1. Rheometric plot of the vulcanizates.

TABLE 3. Rheometric parameters of the vulcanizates.

Cure characteristics MC-1 MC-2 MC-3 PC-1 OC-1 PC-2 OC-2

Minimum

torque (dN m) 20 17 12 5 7 17 14

Maximum

torque (dN m) 80 36 53 53 59 84 77

Scorch time

(min) 1 3 3 4 2 4 2

Optimum cure

time (min) 31 8 10 13 10 15 11

Cure rate

index (min21) 3.33 20.00 14.29 11.11 11.11 9.09 11.11

TABLE 4. Mechanical properties of the rubber samples.

Sample

code

Tensile

strength (MPa)

Tear

strength (N/mm)

Elongation

at break (%)

100% modulus

(MPa)

200% modulus

(MPa)

Hardness

(Shore A)

Crosslink density

(moles/g) 3105

MC-1 8.269 42.00 119.2 3.359 6.254 75 10.19

MC-2 3.906 21.70 171.6 1.552 2.640 70 7.081

MC-3 1.388 58.30 76.80 1.482 2.223 64 7.989

PC-1 20.23 26.15 896.0 1.939 3.534 65 7.422

PC-2 4.105 13.33 201.9 1.936 3.320 75 —

OC-1 10.05 57.26 540.0 3.197 7.135 69 6.470

OC-2 9.379 30.37 424.5 2.766 5.349 70 —

2412 POLYMER ENGINEERING AND SCIENCE—-2008 DOI 10.1002/pen

collected from another reputed tire retreading industries in

India. They supply the retread tire to different mines

under Coal India Limited (CIL), Mahanadi Coalfields

Limited (MCL), and Northern Coalfields Limited (NCL).

All the four raw rubber samples have been collected

from those tire retreading companies are depicted in Ta-

ble 2, but the right proportions of the composition is not

found from the companies because of their trade secret.

FIG. 2. (a–g): FTIR plots for rubber samples.

DOI 10.1002/pen POLYMER ENGINEERING AND SCIENCE—-2008 2413

Cure Characteristics of the Rubber Vulcanizates

The torque versus strain curve for all the rubber vul-

canizates are shown in Fig. 1. The optimum cure time for

MC-2 and MC-3 rubber is lesser than PC-1, PC-2, OC-1,

and OC-2 due to the mixing of XNBR with NR and is

shown in Table 3. The optimum cure time of the 80 phr

XNBR and 20 phr NR is much higher than all other rub-

ber vulcanizates. The rate of cure (tmax 2 tmin) always

increased with increasing concentration of NR. This

increase in cure rate may be due to the fact that an

increasing concentration of NR caused the vulcanization

reaction to increase and create more active cross-link sites

in the rubber compound.

In addition, the gradual decrease in scorch time and

cure time for MC-2 and MC-3 might be decreased

because these compounds have experienced greater ther-

mal history during mixing as a result of their higher com-

pound viscosities. For all samples, the scorch time of the

NR is increased.

It is known that the shear heating during mixing

increases when silica loading is increased due to the

increase of compound viscosity [11]. This explanation is

supported by the value of minimum torque determined

from rheometer cure curves.

Mechanical Properties of the Rubber Samples

Tensile strength, modulus, elongation at break, tear

strength, shore hardness, and cross-link density are all

shown in Table 4. The tensile strength of MC-1 is much

higher than MC-2 and MC-3 due to the addition of more

NR with XNBR. But tensile strength of PC-1 and OC-1 is

higher to all other rubber vulcanizates because of the

addition of additives such as silica. Some researchers [11]

found that tensile retention tends to be enhanced when

the silica content is increased. The tear strength of the

MC-1 is moderate than MC-2 and MC-3. Also the tear

strength of PC-1 and OC-1 is higher than OC-2 and PC-2,

respectively.

From the data, it was found that MC-2, MC-3, PC-2,

and OC-2 have lower tensile strength and percentage of

elongation at break compared to MC-1, PC-1, and OC-1.

This can be explained because PC-2 and OC-2 rubber

contains certain amount silica, whereas MC-2 and MC-3

contain lesser amount of XNBR, which causes main chain

degradation and lowers the percentage of elongation and

hence tensile strength. Another factor, which may be re-

sponsible to decrease the tensile strength, is the presence

of greater amount of cross-linked gel in those rubbers

compared with other vulcanizates, which are not dispersed

in the continuous matrix of the rubber.

The module of all the XNBR vulcanizates increased

with an increasing concentration of XNBR. This was for

one or two possible reasons: the restriction of molecular

chain mobility and an increase in the cross-link density.

The latter can be confirmed by the cross-link density data

that is given in Table 4. Addition of large amounts of NR

decreases the cross-link density in vulcanization steps.

Shore hardness of the MC-1 is much higher than all other

vulcanizates. It is clearly visible that addition of more

percentage of NR with XNBR decreases the hardness of

the vulcanized rubber.

FTIR Spectral Analysis

The IR Spectra of the different samples are shown

below in their respective graphs. Figure 2a shows the IR

Spectra of 80 phr XNBR and 20 phr NR (MC-1). Here, a

distinct peak at 3700 cm21 which may be due to the

asymmetric stretching peak of C��H bond of XNBR is

observed. The peak at 2900 cm21 is due to the symmetric

stretching of the C��H bond. The peak at frequency range

of 2500 cm21 may be due to the C��N triple bond.

Similarly from the Fig. 2b, a distinct peak at frequency

2900 cm21 for C��H bond is seen. The peak at 1800

cm21 may be due to the C��H bond of NR. Other peaks

are similar as earlier because of the presence of the

XNBR. The peaks at 1597 cm21 is due to the stretching

frequency of the C¼¼C of the XNBR group.

Figure 2c shows a similar bond frequencies when com-

pared with the above graph because the composition is

same with varying ratios. So, a slightly shift in the band

frequencies is observed from the FTIR plots.

In Fig. 2d, the peak at 2920 cm21 is due to the C��H

bond of NR. The peak at 1600 cm21 is due to the C¼¼C

bond of NR.

The rest figure also shows similar bond frequencies. In

case of Fig. 2d–g, we can see a new peak at 1028 cm21,

which may be due to the incorporation of the silica group

in the matrix.

These observations suggest that silica reacts with the

carbon–carbon double bonds and slower the reversion

reaction rate and hence increases the mechanical proper-

ties of the vulcanizates.

Another important observation was that unlike Padella.

et al. [12] there was no peak in the range of 1730 cm21

FIG. 3. TGA plots of rubber vulcanizates.

2414 POLYMER ENGINEERING AND SCIENCE—-2008 DOI 10.1002/pen

([C¼¼O stretching peak), which indicated that the oxida-

tion of main polymeric chain did not occur at the time of

rubber milling with the help of cracker cum mixing mill

at high temperature.

Thermal Analysis

High temperature TGA (30–7008C) curves for the sam-

ple are shown in Fig. 3. The temperature for the onset of

degradation (T1), the temperature at which 10% degrada-

tion occurred (T10), the temperature at which 50% degra-

dation occurred (T50), and the temperature at which 90%

degradation occurred (T90) were calculated from the TGA

plots and are given in Table 5.

It was observed that the onset degradation temperature

was higher for higher concentration of XNBR rubber than

NR one. The onset degradation temperature thereby prob-

ably decreased in the case of other rubber samples due to

a decrease in cross-link density. Cross linking increased

the rigidity of the system, which in turn increased the

thermal stability. The rate of degradation was almost the

same up to 90% degradation for all the samples.

DMA Analysis

The storage modulus versus temperature curves are

shown in Fig. 4. The storage modulus of the MC-1 was

higher than MC-2 and MC-3, and it increased due to the

increasing concentration of the XNBR rubber, the cross-

link density was found to increase along with its storage

modulus. Storage modulus at 30, 50, 75, 100, and 1258Chas been calculated and all the data are depicted in Table

6. The storage modulus decreases with the increase in the

temperature.

For OC-2, storage modulus is much higher than MC-1

due to the incorporation of silica, but cross-link density is

much lower than MC-1.

However, the increase in the storage modulus at small

strains with increasing silica content is mainly caused by

the increase in strong filler–filler interaction [13, 14].

Others, such as PC-1, PC-2, and OC-1 show the moderate

storage modulus with the change in temperature.

Figure 5 shows the tan d versus temperature of the

rubber samples. The a-relaxations peak of the MC-1 and

MC-2 was shifted to lower temperature side within the

temperature but MC-3, PC-1, PC-2, OC-1, and OC-2 are

shifted to higher temperature side. It seems that NR con-

tain certain chain degradation (evidence from decrease in

cross-link density, Table 4), which restricted the molecu-

lar chain mobility, and hence, the a-relaxations peak tem-

perature shifted toward the higher side.

Also, it has been reported that rolling resistance of

tires is related to tan d value at temperatures of 50–808C[15]. A low tan d value is needed for achieving the low

rolling resistance and saving energy.

FIG. 5. Tan d of the rubber samples as a function of temperature.

TABLE 5. TGA parameters of the samples (8C).

Sample code T1 T10 T50 T90

MC-1 387 396 463 547

MC-2 264 342 449 548

MC-3 258 344 452 547

PC-1 253 314 422 546

OC-1 263 334 412 541

PC-2 261 332 423 535

OC-2 225 346 441 546

FIG. 4. Storage modulus of the rubber samples as a function of temper-

ature.

TABLE 6. Storage modulus of the samples at different temperatures.

Sample Code

Storage Modulus (MPa)

308C 508C 758C 1008C 1258C

MC-1 17.66 14.01 9.10 5.34 4.20

MC-2 7.61 6.54 4.68 3.06 2.40

MC-3 6.29 5.64 4.62 3.42 2.94

PC-1 12.03 10.84 7.91 5.76 4.88

OC-1 7.25 6.89 5.69 4.62 4.20

PC-2 10.36 9.70 7.85 6.23 5.39

OC-2 17.84 16.10 11.91 8.92 7.43

DOI 10.1002/pen POLYMER ENGINEERING AND SCIENCE—-2008 2415

In this experiment, tan d of the vulcanizates having

various filler ratios was determined at 1508C. The result

shows that tan d of the vulcanizates tends to reduce for

MC-1 and MC-2, and subsequently goes up when silica

loading is higher for PC-1, PC-2, OC-1, and OC-2. It

seems that rubber contain certain amount of main chain

degradation (evidence from decrease in cross-link density,

Table 4), which restricted the molecular chain mobility,

FIG. 6. SEM photographs of the (a) MC-1, (b) MC-2, (c) MC-3, (d) PC-1, (e) OC-1, (f) PC-2, and (g) OC-

2 rubber samples.

2416 POLYMER ENGINEERING AND SCIENCE—-2008 DOI 10.1002/pen

and hence, the a-relaxation peak temperature shifted to-

ward higher side [16]. The result obviously suggests the

lowest rolling resistance in the vulcanizates containing

80 phr XNBR and 20 phr NR.

SEM Study

The tensile fracture samples were scanned after gold

coating and are represented in Fig. 6(a–g). The smooth

fracture surfaces observed for all rubber samples. The

micrographs of the 80 phr XNBR and 20 phr NR rubber

(MC-1) shows the smooth filler dispersion and unidirec-

tional tear path oriented along the direction of flow,

which is smooth rubbery in nature, leading to high tensile

strength and high elongation at break than MC-2 and

MC-3. Figure 6b and c is characterized by a smooth, rub-

bery failure (which is a smooth failure in the case of rub-

ber samples without the formation of necking) where the

additives are clearly seen; the appearance is associated

with a low tensile strength. On increasing the silica with

NR (Fig. 6d–g), the fracture mode was completely

changed and it appears that the number of tear paths in

different directions was being constructed by the addi-

tives, giving the samples high tensile and modulus than

all the rubber samples. Figure 6a, d, and e is again char-

acterized by a unidirectional crack path without any fold-

ing making the vulcanizate high tensile and high elonga-

tion at break.

CONCLUSIONS

Preparation of abrasion resistant tires treads rubber

with the help of an open two-roll-mixing mill represent a

novel method for making valuated rubber products. The

XNBR with addition of NR obtained from this process

has very good mechanical properties when compared with

some collected rubbers from different tire retreading

industries.

It is found that the XNBR has potential as an effective

modifier for natural rubber because its incorporation into

rubber enhances the plastication of NR during mastication

in the mill. Vulcanizate properties of NR such as modu-

lus, resistance to abrasion, and compression set are

improved on incorporation of XNBR at a blend ratio of

80 phr XNBR with NR. Data obtained from different rub-

ber characterization in this study show that both modulus

and crosslink density of rubber samples influence their re-

sistance to abrasion, but the former parameter has an

overriding effect.

80 phr of XNBR and 20 phr of NR blends has the

good curing properties and thermal properties than of all

prepared and collected rubber samples. It is also found

that 80 phr of XNBR and 20 phr of NR blends rubber as

retreading tire compound has the ability to withstand with

the mines harsh condition, and also given more tire life

than those of the samples collected from the tire retread-

ing industries.

ACKNOWLEDGMENTS

The authors thank the tire retreading companies for

their immense support and supply of raw retreading com-

pounds. The authors also thank the members of the pro-

ject and key laboratory of Materials Science Centre and

Central Research Facility at IIT, Kharagpur.

REFERENCES

1. K. Pal and S.K. Pal, National Seminar on ‘‘Tires in Mining& Allied Sectors: Status and Outlook,’’ ISM, Dhanbad, India

(2003).

2. H. Brown, Rubber Chem. Technol., 30(5), 1347 (1957).

3. W.H. Waddell and L.R. Evans, Rubber Chem. Technol.,69(3), 377 (1996).

4. S.-S. Choi, C. Nah, S.G. Lee, and C.W. Joo, Polym. Int.,52(1), 23 (2002).

5. G. Heinrich, M. Kluppel, and T.A. Vilgis, Curr. Opin. SolidState Mater. Sci., 6(3), 195 (2002).

6. A.S. Hashim, B. Azahari, Y. Ikeda, and S. Kohjiya, RubberChem. Technol., 71(2), 289 (1998).

7. J.W.T. Brinke, S.C. Debnath, L.A.E.M. Reuvekamp, and

J.W.M. Noorermeer, Compos. Sci. Technol., 63(8), 1165

(2003).

8. M. Arroyo, M.A. Lopez-Manchadoa, J.L. Valentina, and J.

Carretero, Compos. Sci. Technol., 67(7/8), 1330 (2007).

9. N. Naskar, S.C. Debnath, and D.K. Basu, J. Appl. Polym.Sci., 80(10), 1725 (2001).

10. S.P. Manik and S. Banerjee, Die Angew. Makromol. Chem.,6(71), 171 (1979).

11. N. Rattanasoma, T. Saowapark, and C. Deeprasertkul,

Polym. Test., 26(3) 369 (2007).

12. F. Padella, F. Cavalieri, G. D’Uva, A. La Barbera, and F.

Cataldo, Polym. Recycl., 6(11) (2001).

13. J.-B. Donnet, Rubber Chem. Technol., 71(3), 323 (1998).

14. S. Pattanawanidchai, M. Sc. Thesis (Polymer Science and

Technology), Mahidol University, Thailand, Bangkok

(2004).

15. M.-J. Wang, Rubber Chem. Technol., 71(3), 520 (1998).

16. R.J. Roe in Encyclopedia of Polymer Science and Engineer-

ing, Vol. 7, 536.

DOI 10.1002/pen POLYMER ENGINEERING AND SCIENCE—-2008 2417