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Tribology International 43 (2010) 1542–1550

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Tribology International

0301-67

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Influence of fillers on NR/SBR/XNBR blends. Morphology and wear

Kaushik Pal a,b,c,�, Samir K. Pal b, Chapal K. Das c, Jin Kuk Kim a

a Polymer Science and Engineering, School of Nano and Advanced Materials, Gyeongsang National University, Jinju 660-701, Koreab Department of Mining Engineering, IIT Kharagpur-721302, Indiac Materials Science Centre, IIT Kharagpur-721302, India

a r t i c l e i n f o

Article history:

Received 7 July 2009

Received in revised form

23 February 2010

Accepted 23 February 2010Available online 4 March 2010

Keywords:

Elastomer

Composites

Wear

Rock

9X/$ - see front matter & 2010 Elsevier Ltd. A

016/j.triboint.2010.02.015

esponding author at: Polymer Science and

vanced Materials, Gyeongsang National Univ

2 55 751 5299; fax: +82 55 753 6311.

ail address: pl_kshk@yahoo.co.in (K. Pal).

a b s t r a c t

The blends of carboxylated acrylonitrile butadiene rubber (XNBR), styrene-butadiene rubber with high

styrene content (SBR) and natural rubber (NR) were prepared with different types of carbon black. The

effect of filler on morphological and wear characteristics was studied. Intermediate super abrasion

furnace (ISAF) carbon black showed improve result on curing study and mechanical properties by

reacting at the interface between XNBR, SBR and NR matrix. Blends containing ISAF carbon black

showed high abrasion resistant properties against Du-Pont abrader, DIN abrader and different mining

rock surfaces and also was found to be the toughest rubber against all types of rock.

& 2010 Elsevier Ltd. All rights reserved.

1. Introduction

Polymer blends are being used extensively in numerousapplications; this statement is also true with rubber blends,especially in tyre manufacture. Apart from blends of commonrubbers, specialty rubber is also being utilized, depending onservice demands and components of the tyre [1,2]. Many reportscovering a wide range of rubber blends have been published.Natural rubber (NR) is known to exhibit numerous outstandingproperties such as good oil resistance, low gas permeability,improved wet grip and rolling resistance, coupled with highstrength; having properties resembling those of synthetic rubbers.Natural rubber coming from latex is mostly polymerized isoprenewith a small percentage of impurities in it. This will limit therange of properties available to it. Also, there are limitations onthe proportions of cis and trans double bonds resulting frommethods of polymerizing natural latex. This also limits the rangeof properties available to natural rubber, although addition ofsulfur and vulcanization are used to improve the properties.Synthetic rubber is any type of artificially made polymer materialwhich acts as an elastomer. Synthetic rubber serves as asubstitute for natural rubber in many cases, especially whenimproved material properties are needed. However, syntheticrubber can be made from the polymerization of a variety

ll rights reserved.

Engineering, School of Nano

ersity, Jinju 660-701, Korea.

of monomers including isoprene (2-methyl-1,3-butadiene),1,3-butadiene, chloroprene (2-chloro-1,3-butadiene), and isobu-tylene (methylpropene) with a small percentage of isoprene forcross-linking. Furthermore, these and other monomers can bemixed in various desirable proportions to be copolymerized for awide range of physical, mechanical, and chemical properties. Themonomers can be produced pure and addition of impurities oradditives can be controlled by design to give optimal properties. Awide variety of particulate fillers are used in the rubber industryfor various purposes, of which the most important are reinforce-ment, reduction in material costs and improvements in processing[3]. Reinforcement is primarily the enhancement of strength andstrength-related properties, abrasion resistance, hardness andmodulus [4,5]. The idea of blending synthetic rubbers withnatural rubber is certainly not a new one, but it is only nowthat this can be shown to be possible with consistently positiveresults, by the use of new techniques developed over the last fiveyears. These compounds are capable of forming a chemical linkbetween these dissimilar rubbers to produce a technologicallycompatible blend. The blend vulcanizates thus produced exhibitenhanced physical properties by judicious selection of theNR:SBR:XNBR ratio [6]. The use of carbon black is synonymouswith the history of tyres. Although it has lost some ground toother reinforcing fillers such as silica, by virtue of its unrivalledperformance, it is still the most popular and widely usedreinforcing filler. However, the primary properties of carbon blacksare normally controlled by particle size, surface area, structure,surface activity and they are in most cases interrelated [7].

There are several types of damage occurred in the dump-trucktyre such as tread detachment, sidewall cuts, impact ruptures,

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Table 1Compound formulations.

Compounds Sample codes

K. Pal et al. / Tribology International 43 (2010) 1542–1550 1543

bead damage, etc. [8,9]. Tyres used in mining vehicles are verycostly and need regular maintenance, as it is impossible to acceptits replacement expense within very short term. The ruggedworking conditions in mining industries reduce the life span oftyres on account of cuts, contamination, abrasion, wear, speedfluctuations, etc. The simplest form of wear, which is particularlyimportant in the friction of rigid materials, is abrasive wear andthis had also been observed previously [10–13] as the weargoverned by the abrasion of the surface layer of materials by thesharp edges of hard projections from the rough surface of theabradant. An increase in the abrasion resistance of rubberproducts can be achieved by studying the mechanism of wear ofrubber under different operating conditions. The mechanism ofwear provides a link between the abrasion resistance of rubberand its mechanical properties, which will predict the life of aproduct in service, and also to develop the method of testingabrasion.

The wear of rubber is a complex phenomenon and dependenton a combination of processes such as Mechanical, Mechano-Chemical and Thermo-Chemical, etc. Schallamach [14] and later,Grosch [15] reviewed abrasion of rubber and tyre wear.Schallamach [14] also suggested about different types of abrasionpatterns. Champ et al. [16] and Thomas [17] suggested thatabrasion takes place through a cyclic process of cumulativegrowth of cracks and tearing. As regards physical ideas on thenature of abrasion, Kragelskii et al. [18] and Schallamach [19]were the first to examine the simple case of the failure of rubberby the action of a hard projection moving over its surface. It hasbeen observed [19] that during intense abrasion in sliding contact,a high temperature is developed, and consequently the abrasionresistance of the rubber depends, to a large extent, on itsresistance to high temperature and heat. The earlier literaturereview discussed different types of damage in the tyre and theircause [20–40].

The effort towards improving the efficiency of such transpor-tation system is essential for reduce running costs and cuttingdown the end cost figures by using the XNBR, SBR and NR rubberblends. In this study, the cure characteristics, dynamic, morpho-logical and mechanical properties of carbon black filled blends ofNR, styrene-butadiene rubber with high styrene content (SBR)and carboxylated acrylonitrile butadiene rubber (XNBR) wereinvestigated. These rubber compounds were examined in aspecially fabricated experimental set-up for evaluating their wearresistance properties when abraded against various rock types.The parameters such as influence of composition of rubbervulcanizates on wear characteristics and the mechanism of wearof these compounds against different rocks were reported. Aliterature search shows a lack of studies about wear of XNBR, SBRwith NR blends alone. With this work, we attempt to partially fillthis gap.

A B C D E F G H I

Weight in phr

NR 70 70 70 70 70 70 70 70 70

HSR 10 10 10 15 15 15 20 20 20

XNBR 20 20 20 15 15 15 10 10 10

Carbon blacks

1. SAF (N110) 20 – – 20 – – 20 – –

2. SRF (N774) 20 – – 20 – – 20 – –

3. ISAF (N234) – 40 – – 40 – – 40 –

4. ISAF (N231) – – 40 – – 40 – – 40

Stearic acid 2 2 2 2 2 2 2 2 2

Sulfur 2 2 2 2 2 2 2 2 2

IPPD 1 1 1 1 1 1 1 1 1

CBS 0.7 0.7 0.7 0.7 0.7 0.7 0.7 0.7 0.7

Zinc oxide 5 5 5 5 5 5 5 5 5

Wax 1 1 1 1 1 1 1 1 1

Process oil 2 2 2 2 2 2 2 2 2

2. Experimental

2.1. Materials used in rubber preparation

The acrylonitrile butadiene rubber used was Nipol N-34 grade,of Nippon Zeon Co. Ltd., Japan. Its specific gravity is 0.98, Mooneyviscosity at 100 1C is 45. Bound acrylonitrile content was 27%. Thestyrene-butadiene rubber with high styrene content (SBR) usedwas Krylene HS 260, No.-5 of 1948 grade of Bayer AG. Its styrenecontent is 63.571.0, specific gravity is 0.94 and Mooney viscosityat 100 1C is 5075. Natural rubber (NR-RMA1X) was suppliedby the Rubber Board, Kottayam, Kerala. Zinc oxide, stearic acid,N-cyclohexyl-2-benzothiazyl sulfenamide (CBS) and anti oxidant(HQ) was supplied by Bayer (India) Ltd. Carbon black was

supplied by Birla Carbon. Standard rubber grade process oil(Elasto 710) was purchased from the local market.

2.2. Preparation of raw rubber

The compounding formulation for the XNBR, SBR and NRblends with its various ingredients were mixed in a two roll millat a friction ratio of 1:2 following standard mixing sequence.Compounding formulations based on changing of the carboxy-lated acrylonitrile butadiene rubber (XNBR), styrene-butadienerubber with high styrene content (SBR), and natural rubber (NR)contents were shown in Table 1. Also, three types of carbon blacksand one semi reinforcing furnace were used, such as, SAF (N110),ISAF (N231 and N234) and SRF (N774). For vulcanization theamounts of additives such as sulfur, CBS were based on 100 phr ofrubber and the samples have the code name ‘A’, ‘B’, ‘C’, ‘D’, ‘E’, ‘F’,‘G’, ‘H’ and ‘I’, respectively. The physical properties of the differenttypes of carbon black used in this study have already beenpublished in our earlier literature [41]. The main differencebetween the carbon black was their particle size, tensile strengthand relative roadwear abrasion (1.25 for SAF, for 1.15 ISAF and0.60 for SRF). The reinforcing filler (carbon black) was added alongwith the process oil followed by curatives.

2.3. Cure characteristics of rubber compound

The cure characteristics of the rubber compound were studiedwith the help of a Monsanto Oscillating Disc Rheometer (ODR–100 s) at 150 1C as per ASTM D-2084-07. From the graphs theoptimum cure time and rate of cure (min�1) could be determined.Also, in rubber manufacture, the time during which a rubbercompound can be worked at a given temperature before curingbegins known as scorch time (TS5, min) also could be obtained.

2.4. Determination of crosslink density

The crosslink density was determined by immersing a smallamount (known mass) of sample in 100 ml toluene to attainequilibrium swelling. After this the sample was taken out fromthe toluene and the solvent was blotted from the surface of thesample and weighed immediately. This sample was then dried outat 80 1C to constant weight. Then the chemical crosslink densitywas calculated by the Flory–Rehner equation [42].

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K. Pal et al. / Tribology International 43 (2010) 1542–15501544

2.5. Fourier transformed infrared spectroscopy

Fourier Transform Infrared Spectroscopy was performed usinga NEXUS 870 FT-IR (Thermo Nicolet) instrument in dry air at roomtemperature. Spectra were taken in the range of 4000–500 cm�1

in transmission mode.

2.6. Mechanical characterization (tensile and tear)

Vulcanized slabs were prepared by compression molding, andthe dumb-bell shaped specimens were punched out from amolded sheet by using ASTM Die C. The tests were done by meansof a universal tensile testing machine (Hounsfield H10KS) underambient condition (2572 1C), following the ASTM D 412-06 andASTM D 624-00(2007). The tensile strength, tear strength, moduliat 100% and 300% elongation and elongation at break (%) weremeasured at room temperature. The initial length of the speci-mens was 25 mm and the speed of the jaw separation was500 mm/min.

Five samples were tested for each set of conditions, at the sameelongation rate. The values of the tensile strength, modulus at100% elongation, 300% elongation and elongation at break wereaveraged. The relative error was below 5%. The hardness wasmeasured by Shore A hardness tester followed by ASTM D2240-05.

2.7. Differential scanning calorimetry (DSC)

DSC measurements were carried out using a Perkin-ElmerPYRIS Diamond DSC instrument. The samples (r10 mg), sealedunder aluminum pans were scanned in the temperature range of�80 1C to 100 1C. The heating rate was 10 1C min�1 under thenitrogen atmosphere with a flow rate of 40 ml min�1.

2.8. Thermal characterization (DTA-TGA)

TGA studies were carried out Shimadzu-DT-40 instrument inpresence of air at a rate of 10 1C/min from 50 to 600 1Ctemperature. Degradation temperature of the composites wascalculated by TGA plot.

2.9. Scanning electron microscopy (SEM)

The tensile fracture surface of the samples were studied in ascanning electron microscope (JSM-5800 of JEOL Co.; Accelerationvoltage: 20 kV; type of coating: gold) at 1000 times zooming,Scanning electron microscopy has been used to study themorphology of the samples prepared.

Fig. 1. Schematic diagram of

2.10. Heat build up study

Heat build up study was carried out using Goodrich Flexometerfor the selective compounds having higher tensile strength.

The test pieces were prepared in cylindrical shape having diameter17.870.15 mm and height of 2570.25 mm by compression moldingat 150 1C. The test pieces were kept at initial temperature of 50 1C andstoke of 4.4570.03 mm. The temperature and the load were keptconstant throughout the study. The temperature attained by thesamples after the time periods of 10 and 20 min has been recorded.

2.11. Din abrasion test

DIN abrasion test was done by the DIN abrasion tester fordetermining the abrasion resistance of compounds of vulcanizedrubber recommended by the Indian Standards Institution videIS:3400 (Part 3)—1987. For this test, a cylindrical elastomersample was mounted in a rotating holder and abraded acrossthe surface of a rotating abrasive drum for a distance of 40 m. Theholder carries a load of either 5 or 10 N, depending on thehardness of the sample. The abrasion resistance was calculated bymeasuring the weight loss after the sample was tested andcomparing it to the original sample. The results were reported as avolume loss, typically in cubic millimeters (mm3).

2.12. The experimental set-up

The indigenous experimental set up was specially fabricated inour lab and the full arrangement of the experimental set up,preparation of rubber specimen and rock sample were alreadydiscussed in our earlier literature [41] during wear testing of therubber sample of XNBR-NR blend and the machine schematicdiagram was shown in Fig. 1. At first, rubber disc was fixed tightlyto the shaft of the step cone pulley by the set-screw. The smoothlycut rock sample was then clamped in the rock holder. The lengthof projected portion of the rock sample outside the rock holderwas adjusted so as to obtain a reading of 2.5 mm on the dial gaugeattached to top surface of the cantilever beam which ensure itshorizontality.

Total weight of 450, 900 and 1350 g was placed on the hanger ofthe cantilever beam, so as to produce normal load of 4.41, 8.82 and13.23 N at the rock–rubber contact and the test run was conductedfor 500 revolutions with sandstone sample placed in the rock holder.The temperature, normal load and frictional force were recorded onthe computer during the wheel rotation. The above procedure wasrepeated on rubber discs of different XNBR-SBR-NR combinationwith carbon black variation using other types of rocks as abrader.The mass loss of the rubber samples after 500 revolutions (M500)

the experimental setup.

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Table 2Cure characteristics of the blends.

Properties A B C D E F G H I

Min. torque (dN.m) 12.87 14.06 13.09 8.67 9.04 9.66 8.03 8.97 8.54

Max. torque (dN.m) 23.35 26.36 25.32 20.32 21.84 20.75 18.53 18.99 18.78

TS2, induct time (min) 6.27 5.85 6.03 5.77 5.65 5.32 4.97 4.76 4.32

TS5, scorch time (min) 10.95 10.4 10.5 8.98 9.22 9.01 7.69 7.31 6.97

TC90, opt. cure time (min) 20.67 24.25 22.48 18.57 19.53 19.07 17.32 17.95 17.69

Cure rate index (min�1) 6.94 5.43 5.89 6.8 7.2 7 7.8 7.1 7.4

Crosslink density (mol/g)�10�5 4.30 4.65 8.90 4.01 3.84 5.21 3.45 4.78 4.99

K. Pal et al. / Tribology International 43 (2010) 1542–1550 1545

was measured at room temperature and dynamic coefficient offriction (m) and abrasion loss (V) were computed.

Fig. 2. FTIR study of different types of blend.

3. Results and discussions

3.1. Cure characteristics of the rubber compounds

The optimum cure time for ‘B’, ‘E’ and ‘H’ rubber sample ishigher than other rubber vulcanizates due to the mixing of ISAFN234 carbon black with XNBR, SBR and NR is shown in Table 2.The rate of cure (tmax�tmin) always increases with increasingconcentration of SBR. This increase in cure rate may be due to thefact that an increasing concentration of SBR causes thevulcanization reaction to increase and create more active crosslink sites in the rubber compound.

The torque difference (MH�ML) which shows the extent of crosslinking [43], is found to have lesser variation from one compoundto other. The lesser torque difference is found for the compoundcontaining 10 phr of XNBR. The obtained cross-link density valuesget corresponded with the variation in torque differences.

Faster cure rate index is observed in Table 2 for the compoundscontaining SAF N110 and ISAF N234 type carbon black may be dueto the rise in temperature at the time of mixing. Whereas,moderate cure rate is found for the compounds that contain ISAFN231 type carbon black. The decrease in cure rate may be due tothe greater thermal history formed during mixing, as a result oftheir higher compound viscosities. The possible formation of a Zncomplex in which sulfur and ammonium modifier participate mayfacilitate for the increase in rate of cure [44].

3.2. FT-IR spectral analysis

The IR spectra of the different samples are shown in Fig. 2. Thepeak at 3430–2900 cm�1 may be due to the O–H bond createdfrom the presence of stearic acid.

Similarly, a distinct peak at frequency 2920 cm�1 for C–H bondfor CH3 group in NR is seen. The peak visible at 2260–2240 cm�1 isdue to the symmetric stretching of the CRN bond. The peak at1650 cm�1 is due to the CQC bond of isoprene and butadiene. Thepeak at frequency range of 1022 cm�1 is may be due to the styrene.

Another important observation is that unlike Padella et al. [45]there is no peak in the range of 1730 cm�1 (4CQO stretchingpeak), which indicated that the oxidation of main polymeric chaindid not occur at the time of rubber milling with the help of crackercum mixing mill at high temperature.

3.3. Mechanical properties of the rubber samples

Tensile strength, modulus, elongation at break, tear strengthfor all the compounds are shown in Table 3. The tensile strengthof G, H and I is higher with the addition of 20 phr SBR and 10 phrXNBR. The tear strength for all the samples is moderate, but it

varies with varying the matrix ratio with the effect of ISAF N 234type of carbon black. So the system with carbon black ISAF N231gives better reinforcing effect as well as tear strength but themodulus of all the NR vulcanizates increased with using of ISAFN234 type of carbon black. This is for one or two possible reasons:The restriction of molecular chain mobility, and an increase in thecross-link density. Elongations at break values are higher for theblends enriched with SBR. The hardness value of the vulcanizatesindicates the same trend as the modulus values.

The mechanical property of rubber vulcanizates markedlydepended on the number of conjugate double bonds and it isfound for the sample ‘G’, ‘H’ and ‘I’. These observations suggestthat more SBR and XNBR react with the carbon-carbon doublebonds of ISAF N231 and slower the reversion reaction rate andhence increases the mechanical properties of the vulcanizates[46,47]. In Table 4, it has been observed that mechanicalproperties are almost double for samples ‘H’ and ‘I’ than othersamples. Also, it is noteworthy that sample ‘H’ and ‘I’ shows theminimum abrasion loss which is confirmed by the DIN abrasiontest and rock–rubber abrasion test.

While for other blend types, mainly where XNBR percentageincreased and SBR percentage decreased (Samples A to F), thetensile and tear strength is decreased, may be due to the effect ofcarbon black which suppresses the XNBR and SBR effect in thesystem and the filler is uniformly dispersed in the natural rubbermatrix that can be attributed to the aggregation of XNBR and SBR[48]. The aggregation leads to the formation of weak point in theNR matrix, accordingly reduces the elastomeric strength [49,50].

3.4. DSC study

To study the thermal response of the blends DifferentialScanning Calorimetry has been performed. The DSC curves for all

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Table 3Mechanical properties of the vulcanizates.

Sample code Tensile strength (MPa) Elongation at break (%) 100% modulus (MPa) 300% modulus (MPa) Tear strength (N/mm) Hardness (Shore A)

A 11.66 418 3.725 08.73 33.68 60

B 07.46 222 4.163 – 37.24 65

C 10.60 293 5.040 – 51.90 65

D 15.56 460 4.250 10.36 32.74 65

E 15.69 430 5.290 11.68 63.80 65

F 16.93 528 4.369 09.96 47.15 65

G 13.73 498 3.547 08.44 51.30 65

H 21.40 468 5.950 14.03 67.00 70

I 24.40 543 5.880 13.78 51.60 75

Table 4Heat build up of the rubber samples.

Sample code Temperature (1C)

Initial 10 min 20 min

H 50 59 63

I 50 57 60

Fig. 3. DSC studies of different types of blends.

K. Pal et al. / Tribology International 43 (2010) 1542–15501546

rubber vulcanizates are shown in Fig. 3. The criterion forcompatibility or incompatibility in polymer blends is thepresence of a single glass transition temperature Tg for thematerial, which is intermediate between the Tg of the purecomponents and the existence of two Tg

0s in the DSC thermogramsfor incompatible polymer blends. All traces show a reasonablesharp Tg transition dependent on composition; however, thegraph for blend DSC traces are not shown for brevity.

In Fig. 3 all the samples show the Tg at around �60 1C but incase of D samples the Tg shifted to the lower side. All the samplesshow only one melting peak on the DSC curves, this is attributed tothe same backbone structure of the matrix and the carbon black asreinforcing filler. Since miscible polymer blends should exhibit asingle Tg between the Tg

0s of pure components [51]. This isconsistent with the effect of blend composition on miscibility whenthe chemical structure and the molecular mass of components arefixed [52]. But in case of carbon black SAF N110 and SRF N774, themelting peak appreciably shifts to the lower side. This may be dueto the dilution of matrix as a result of the incorporation of fillers.

3.5. Thermal analysis

High temperature TGA (50–650 1C) curves for the sample areshown in Fig. 4. From this figure the temperature for onsetdegradation (T1), the temperature at which 10% degradationoccurred (T10), the temperature at which 50% degradationoccurred (T50) and the temperature at which 90% degradationoccurred (T90) are calculated.

It is observed that the onset degradation temperature is higherfor samples containing carbon black ISAF N231. The onsetdegradation temperature thereby probably decreased in the caseof other rubber samples due to a decrease in cross link density.Cross linking increased the rigidity of the system, which in turnincreased the thermal stability [53,54]. The rate of degradation isalmost the same up to 90% degradation for all the samples. Also, itis found that for sample A–F the degradation temperature isdecrease may be due to the decrease concentration of SBR.

3.6. SEM study

The tensile fracture samples are scanned after gold coating,and are represented in Fig. 5(a–i). The smooth fracture surfaces

and smooth filler dispersion and unidirectional tear path orientedalong the direction of flow, which is smooth rubbery in nature asobserved for all rubber samples [57]. The micrographs of the A, B,C, F, G, H and I rubber sample is characterized by a smooth,rubbery failure (which is a smooth failure in the case of rubbersamples without the formation of necking) where the additivesare clearly seen; the appearance is associated with a low tensilestrength. But for D and E, it clearly observed fatigue type of failurefrom the figure. It may also be concluded that rough surface hasbeen seen in the sample containing ISAF type of carbon black.

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3.7. DIN abrader test results

Fig. 6 refers to the DIN abrasion test result in terms of massloss of rubber compounds. Compounds ‘H’ and ‘I’ show higherabrasion resistance mainly due to the presence of 20 phr of SBRand 10 phr of XNBR in NR with ISAF type of carbon black. It is also

Fig. 4. TGA plots of different types of blends.

Fig. 5. SEM pictures of different types of blend, (a) A,

seen that compounds containing lesser amount of SBR shows thepoor abrasion resistance property.

3.8. Rock–rubber abrasion results

Fig. 7 shows the abrasion loss of different rubber compoundswhen abraded against various rocks at different loads. Out of alltypes of rocks the coal has been identified as the major abrader foralmost all types of rubber compounds. The rubber compound ‘H’is found to be the toughest rubber against all rock types under thepresent study. Coal being the softest rocks causes high abrasion toall types of rubber compounds under the present study.Sandstone is another rock which has abraded almost all therubber compounds extensively and may be considered as animportant rock for rock–rubber abrasion studies.

Fig. 8 refers to the DIN abrasion test result in terms of massloss of rubber compounds. Compounds ‘A’ and ‘H’ show higherabrasion resistance mainly due to the presence of 20 phr of XNBRin NR with SAF N110 and SRF N774 type of carbon black and20 phr of SBR with ISAF N234 type of carbon black. The compound‘I’ also exhibited good abrasion resistance, which also has 20 phrSBR blended with NR with ISAF N231 type of carbon black.

This may be due to the effect of XNBR which is very much wellknown highly abrasion resistant elastomers. Hence, 20 and 15 phrXNBR having better abrasion resistance values than that of 10 phr.Probably, the effect of carbon black has negligible effect on the

(b) B, (c) C, (d) D, (e) E, (f) F, (g) G, (h) H and (i) I.

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Fig. 5. (Continued)

Fig. 6. DIN abrasion results of the blends.

K. Pal et al. / Tribology International 43 (2010) 1542–15501548

abrasion resistance in the presence of higher XNBR containingcompound. Moreover, super abrasion furnace black have beenused while using 20 and 15 phr XNBR. This may probably be thepossible reason of better abrasion resistance.

3.9. Heat buildup study

The values of heat buildup for the compounds, those are havingthe tensile strength of more than 18 MPa and good abrasionresistance property gainst DIN abrader and rock–rubber abrasionstudy, are shown in Table 4. For both of the compounds, thetemperature developed is higher, due to 40 phr of carbon black.This may be due to the disproportionate breaking of the carbonblack structure and reformation of the inter-aggregate bonds ofcarbon black. The compound I showed lesser heat buildupcompared to H. The compound I contains ISAF N231, which is

low structured carbon black, whereas the compound H containsISAF N234, high structured carbon black. The low structuralarrangement of the ISAF N231 may be responsible for low heatbuildup. These high temperatures accelerate the fatigue of rubbercomponents [55]. Higher tyre temperature usually means higherenergy dissipation and thus higher fuel consumption [56]. Hence itis proved that lower percentage of XNBR leads to minimum heatbuildup. It may be concluded, that there is an important connectionbetween heat buildup and the crosslink system. Thus, the higherdegree of network stability given by low sulfur system generallycauses less heat generation. Heat generation tests before and afteraging indicate where a low degree of heat buildup can be expected,even when the degree of crosslink densities is kept similar.

3.10. Temperature generation at rock–rubber interface

Since the low thermal conductivity of rubbers can result in a veryhigh temperature at the interface, it is important to investigate theeffects of frictional heating on the sliding friction of rubbers [58].Ettles and Shen [59] have presented a paper concerning the effects ofheat generation on the level of friction at the interface.

Table 5 shows the range of temperature generated duringfriction of rocks with different rubber compounds. In general thetemperature generation has been found to be higher in case of therubber compounds containing ISAF N234 type of carbon black.The temperature generation during friction in rubber compound‘A’, ‘D’, and ‘G’ is slightly lower, which may be attributed to thepresence of SRF N774 type of carbon black. The highesttemperature is observed when rubbers are abraded against coalsurfaces whereas the lowest temperature could be noticed forsandstone. For other rocks the temperature generation is found tobe in the moderate range.

4. Conclusions

Preparation of abrasion resistant tyre tread rubber with thehelp of an open two-roll-mixing mill represents a novel method

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Fig. 7. Mass loss of rubber compounds against different rocks at different loads.

Fig. 8. Comparison of mass losses of rubber compounds in DIN abrader against

sandstone.

Table 5Temperature ranges of different rubber samples during abrasion against rocks.

Sample code Temperature range (1C) upto 500 revolutions at 4.41 N load

Sandstone Concrete Granite Shale Coal

A 22�63 24�93 23�83 21�77 20�100

B 21�62 22�99 22�87 22�72 22�106

C 22�61 22�94 22�81 22�76 21�106

D 23�68 21�92 23�83 23�79 22�104

E 22�63 22�96 22�84 23�73 23�107

F 22�66 22�93 22�93 22�85 22�101

G 21�62 22�93 22�74 23�74 24�92

H 22�66 22�93 22�85 22�79 23�105

I 21�60 22�88 22�88 22�74 23�102

K. Pal et al. / Tribology International 43 (2010) 1542–1550 1549

for making cost effective rubber products. The NR with addition ofXNBR and SBR obtained from this process has very goodmechanical properties which can be withstand the ruggedworking condition of dump truck tyre. The optimum cure timefor rubber sample mixing of ISAF N234 carbon black with XNBR,SBR and NR is higher than other rubber vulcanizates. In this blendsystem, faster cure rate index is observed for the compoundscontaining SAF N110 and ISAF N234 type carbon black may be dueto the rise in temperature at the time of mixing. Tensile strengthincreases with carbon black ISAF N231, may be due to theoutstanding reactivity of the carbon black acting as filler,increases the properties of the samples with 70 phr NR, 20 phrSBR and 10 phr XNBR. It is observed that the onset degradationtemperature is higher for samples containing carbon black SAFN110 and SRF N774. Compounds show higher abrasion resistancemainly due to the presence of 20 phr of SBR and 10 phr of XNBR inNR. The rubber compound ‘H’ is found to be the toughest rubber

against DIN abrader and all rock types in the rock rubber abrasionstudy. Coal being the softest rock causes most abrasion to all typesof rubber compounds under the present study. The heat buildupstudies showed lesser heat generation for the compound ‘I’.

Acknowledgments

The authors are deeply grateful to I-Cube Centre, GyeongsangNational University, South Korea and Coal India Limited, Kolkatafor their kind assistance. Also, special thanks to the members ofthe project and key laboratory of Materials Science Centre andCentral Research Facility at IIT, Kharagpur.

References

[1] Gunasekaran S, Natarajan RK, Kala A. FTIR spectra and mechanical strengthanalysis of some selected rubber derivatives. Spectrochim. Acta Part A2007;68:323–30.

[2] Fernandez-Berridi MJ, Gonzalez N, Mugica A, Bernicot C. Pyrolysis-FTIR andTGA techniques as tools in the characterization of blends of natural rubberand SBR. Thermochim. Acta 2006;444:65–70.

[3] Tinker AJ, Jones KP. Blends of Natural Rubber, Novel techniques for Blendingwith Speciality Polymers. London: Chapman & Hall; 1998. ISBN 0-412-81940-6.

[4] Choi S-S, Nah C, Lee SG, Joo CW. Effect of filler-filler interaction on rheologicalbehaviour of natural rubber compounds filled with both carbon black andsilica. Polym. Int. 2003;52(1):23–8.

[5] Heinrich G, Kluppel M, Vilgis TA. Reinforcement of elastomers. Curr. Opin.Solid State Mater. Sci. 2002;6(3):195–203.

[6] Naskar N, Debnath SC, Basu DK. Novel method for preparation ofcarboxylated nitrile rubber-natural rubber blends using bis(diisopropyl)thio-phosphoryl polysulfides. J. Appl. Polym. Sci. 2001;80(10):1725–36.

[7] Nasir M, Choo CH. Chemical modification of natural rubber latex withperacetic acid. Polym. J. 1989;25(4):355–9.

[8] Brinke JWT, Debnath SC, Reuvekamp LAEM, Noordermeer JWM. Mechanisticaspects of the role of coupling agents in silica–rubber composites. Compos.Sci. Technol. 2003;63(8):1165–74.

[9] Arroyo M, Lopez-Manchadoa MA, Valentina JL, Carretero J. Morphology/behaviour relationship of nanocomposites based on natural rubber/epox-idized natural rubber blends. Compos. Sci. Technol. 2007;67(7–8):1330–9.

[10] Ratner SB, Klitenik GS, Melnikova MV. Transactions of 3rd all-unionconference on friction and wear, Public Academy of Sciences, USSR, 1960.

[11] Ratner SB. Dokl. Akad. Nauk SSSR 1952;87(5):743–6.[12] Sakhnovski NL, Ivonova SA, Melnikova MV, Ratner SB. Kauch. I. Rezina

1958;17(10):10–8.[13] Ratner SB, Farberova II. Mechanical testing of plastics-wear. Sov. Plast.

1960;51(9):297.[14] Schallamach A. In: Bateman L, editor. Chemistry and Physics of Rubber-like

Substances. London: Maclaren; 1963. p. 382.[15] Grosch KA, Schallamach A. Tire friction on wet roads. Rubber Chem. Technol.

1976;49(3):862–909.[16] Champ H, Southern E, Thomas AG. Am. Chem. Soc., Div. Org. Coat. Plast. Paper

Prepr. 1974;34(1):237.[17] Thomas AG. Factors influencing the strength of rubbers. J. Polym. Sci., Polym.

Symp. 1974;48:145–57.[18] Kragelskii IV, Nepomnyashchil EF. Abrasion of Rubber. London: Publ.

Maclern and Sons Ltd.; 1967. 3–13.[19] Schallamach A, Khin I. Tekhnol. Polym. 1959;45:4.

ARTICLE IN PRESS

K. Pal et al. / Tribology International 43 (2010) 1542–15501550

[20] Nayek S, Bhowmick AK, Pal SK, Chandra AK. Wear behavior of silica filled tiretread compounds by various rock surfaces. Rubber Chem. Technol.2005;78(4):705–22.

[21] Kragelskii IV, Nepomnyashchil EF. Abrasion of Rubber. London: Publ.Maclern and Sons Ltd.; 1967. p. 3.

[22] Reznikovskii R, Warlow-Davies E. Proc. Phys. Soc. 1942;54(14):301.[23] Pal K. Speciality elastomer blends for abrasion resistant tyre tread of dump-

trucks, Ph.D. thesis, Indian Institute of Technology, Kharagpur, India, 2009.[24] Bhowmick A. Ridge formation during the abrasion of elastomers. Rubber

Chem. Technol. 1979;55(4):1055–63.[25] Southern E, Thomas A. Studies of rubber abrasion. Rubber Chem. Technol.

1979;52(5):1008–18.[26] Medalia AI, Alesi AI, Mead JL, Simonean R. Paper no. 34, Rubber Division,

A.C.S., Cincinnati, Ohio, October, 18–21, 1988; abstract in Rubber Chem.Technol. 1989;62:165.

[27] Viswanath N, Bellow DG. Development of an equation for the wear ofpolymers. Wear 1995;181–183(1):42–9.

[28] Rymuza Z. Wear in polymer micro-pairs, In: Proceedings of the thirdinternational conference on wear of materials 1981;125–32.

[29] Ratner SB. Connection between the wear resistance of plastics and othermechanical properties. Sov. Plast. 1964;7:37.

[30] Lewis RB. Predicting the wear of sliding plastic surfaces. Mech. Eng.1964;86:32–5.

[31] Rhee SK. Wear equation for polymers sliding against metal surfaces. Wear1970;16(6):431–45.

[32] Lancaster JK. Friction and wear. In: Jenkins AD, editor. Polymer Sciences,Vol. 14. Amsterdam: North-Holland Publishing Co.; 1972.

[33] Atkinson JR., Brown KJ, Dawson D. The wear of high molecular weightpolyethylene, Pt. I. Isotropic polyethylene against dry stainless steel inunidirectional motion, Trans ASME.

[34] Schallmach A. Abrasion pattern on rubber. Rubber Chem. Technol.1953;26(1):230–41.

[35] Kragelsky IV, Nepomyashic YF. Friction wear of polymers. Khimiya 1964:5–9.

[36] Ratner SB, Melnikova MV. Kauch. I. Rezina 1958;15(8).[37] Reznikovskii MM, Brodskii GI. Sov. Rubber Technol. 1961;20(7):13.[38] Savkoor AR. Some aspects of friction and wear of tyres arising from

deformations, slip and stresses at the ground contact. Wear 1961;9(1):66–78.[39] Reznikovskii MM. In: James DI, editor. Abrasion of Rubber. London:

Maclaren; 1967. p. 41.[40] Rudakov A, Kuvshinskii E. The mechanism of abrasion of vulcanized rubber.

Rubber Chem. Technol. 1964;37:291–6.[41] Pal K, Das T, Rajasekar R, Pal SK, Das CK. Wear characteristics of styrene

butadiene rubber/natural rubber blends with varying carbon blacks by DINabrader and mining rock surfaces. J. Appl. Polym. Sci. 2009;111(1):348–57.

[42] Manik SP, Banerjee S. Determination of chemical cross-links in rubbers. DieAngew. Makromolekuiare Chem. 1979;6(Nr. 71):171–8.

[43] Sezna JA, Pawlowski HA, DeConinck D. New test results from rotorlesscuremeters, Proceeding of 136th meeting of the ACS-rubber division, Fall 1989.

[44] Rajasekar R, Pal K, Heinrich G, Das A, Das CK. Development of NBR-nanoclaycomposites with epoxidized natural rubber as compatibilizer. Mater. Des.2009; doi:10.1016/j.matdes.2009.03.014.

[45] Padella F, Cavalieri F, D’Uva G, La Barbera A, Cataldo F. Recycling of scrap tiresrubber by mechanochemical devulcanization. Polym. Recycling 2001;6(1):11–6.

[46] Pal K, Rajasekar R, Das T, Kang DJ, Pal SK, Kim JK, et al. Effect of fillers onmorphological properties in NR/SBR blends for OTR tyres. Plast., Rubber andCompos. 2009;38(7):302–8.

[47] Pal K, Rajasekar R, Kang DJ, Zhang ZX, Pal SK, Kim JK, et al. Effect of fillers onnatural rubber/high styrene rubber blends with nano silica: morphology andwear. Mater. Des. 2010;31(2):677–86.

[48] Agag T, Koga T, Takeichi T. Studies on thermal and mechanical properties ofpolyimide–clay nanocomposites. Polymer 2001;42(8):3399–408.

[49] Nielsen LE. Mechanical properties of polymers and composites. New York:Marcel Dekker; 1974. p. 2.

[50] Sharifa J, Yunus WMZW, Dahlan KZHM, Ahmad MH. Preparation andproperties of radiation crosslinked natural rubber/clay nanocomposites.Polym. Test. 2005;24(2):211–7.

[51] Miyata T, Inaki K, Morikawa J, Satoto R, Hashimoto T. Effects of copolyester/polycarbonate blend composition on the thermal diffusivity of dye transferprinting. J. Appl. Polym. Sci. 2004;92(1):72–6.

[52] Paul DR, Newman S. Polymer blends, Vol. 1. New York: Academic Press;1978.

[53] Maity M, Khatua BB, Das CK. Effect of processing on the thermal stability ofthe blends based on polyurethane: part IV. Polym. Degrad. Stab.2000;72(3):499–503.

[54] Gann RG, Dipert RA, Drews MJ. ‘Flammability’. In: Kroschwitz JI, editor.Encyclopedia of polymer science and engineering. 2nd ed., Vol. 7,John Wiley & Sons, Inc., New York; 1985. p. 154.

[55] Medalia AI. Heat generation in elastomer compounds: causes and effects.Rubber Chem. Technol. 1991;64(3):481–92.

[56] Park DM, Hong WH, Kim SG, Kim HJ. Heat generation of filled rubbervulcanizates and its relationship with vulcanizate network structures. Euro.Polym. J. 2000;36(11):2429–36.

[57] Pal K, Das T, Pal SK, Das CK. Use of carboxylated nitrile rubber and naturalrubber blends as retreading compound for OTR tires. Polym. Eng. Sci.2008;48(12):2410–7.

[58] Zhang SW. State-of-the-art of polymer tribology. Tribol. Int. 1998;31(1–3):49–60.

[59] Ettles CMMC, Shen JH. The influence of frictional heating on the sliding frictionof elastomers and polymers. Rubber Chem. Technol. 1988;61(1):119–36.