POLYMERTESTING

Polymer Testing 27 (2008) 277–283

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Material Properties

Characterisation of eco-friendly processing aidsfor rubber compound: Part II

S. Dasguptaa,�, S.L. Agrawala, S. Bandyopadhyaya, S. Chakrabortya,R. Mukhopadhyaya, R.K. Malkanib, S.C. Ametab

aHari Shankar Singhania Elastomer and Tyre Research Institute (HASETRI), P.O. Tyre Factory, Rajsamand 313342, Rajasthan, IndiabDepartment of Polymer Science and Chemistry, Mohanlal Sukhadia University, Udaipur 313001, Rajasthan, India

Received 18 September 2007; accepted 8 November 2007

Abstract

According to the KEMI report, products with polycyclic aromatic compounds, PCA, levels exceeding 3% by weight

must be labelled. The report pointed out that worn tyre tread material was being spread on the roadsides, introducing high

amounts of PCA into the environment. PCA is having toxic effects on aquatic organisms. Polyaromatic-hydrocarbon-rich

extender oils are to be banned by December 2009, which gives rise to challenges for the oil and rubber industries. In the

present work, 10 types of naturally occurring oils and six types of petroleum-based oils were characterised in natural-

rubber-based truck tyre tread cap compound. Compounds made with some of the naturally occurring oils showed better

mechanical and dynamic mechanical properties.

r 2007 Elsevier Ltd. All rights reserved.

Keywords: Eco-friendly oils; Vegetable oils; Polycyclic aromatics; Cross-link density; Dynamic mechanical properties; Physical properties

1. Introduction

Plasticisers are organic substances added topolymers to improve their flexibility and processa-bility. They increase the softness, elongation andlow-temperature flexibility, and decrease the con-centration of intermolecular forces and the glasstransition temperature, Tg, of polymers. They areclassified into primary, secondary and extenders [1].

Distillate aromatic extracts (DAE) with a highcontent of polycyclic aromatic hydrocarbons arewidely used as aromatic process oils for themanufacturing of oil-extended natural or synthetic

front matter r 2007 Elsevier Ltd. All rights reserved

lymertesting.2007.11.004

ng author. Tel./fax: +91 2952 232019.

ss: saikat@ktp.jkmail.com (S. Dasgupta).

rubber, and also in finished tyres [2–4]. However,various studies report a potential carcinogenicity ofthese oils after tumours have been observed in miceafter skin painting tests [2–4]. The Europeanlegislation (EU Substance Directive 67/548/EEC)classifies these DAE as ‘carcinogenic’ and allocatesthe risk phrase ‘R45’ (may cause cancer) and thelabel ‘T’ (skull and cross-bones) to these mineral oilproducts [2–4]. The KEMI study, published in 1994in Sweden, highlighted the environmental problemsarising from the use of these potentially carcino-genic products in tyre treads [2–4].

Non-carcinogenic alternatives have been devel-oped to replace DAE in rubber and tyre formula-tions. These new products, also known as MES andTDAE process oils, can be made via the solvent

.

ARTICLE IN PRESSS. Dasgupta et al. / Polymer Testing 27 (2008) 277–283278

extraction or hydro-treating process in various oilrefineries [2–4].

Vegetable and fish oils have long been used asbinders in traditional paints and varnishes. Linseed oilhas been the most important oil in the coatingindustry. Castor oil provides an excellent combinationof fast drying, flexibility, good colour and good colourretention properties. Soybean oil has excellent colourand colour retention characteristics. Coconut andcottonseed oils are used as resinous plasticisers [5].

Rubber seed oil and epoxidised rubber seed oilwere used as secondary plasticiser cum heat stabiliserin polyvinyl chloride [1]. Rubber trees (Hevea

brasiliensis) are widely used as the source of naturalrubber and the seed has been found to be rich in oil.Fresh seed contains about 65% kernel and 35%shell. Though there is variation in the oil content ofthe seed from different clones, the average oil yield isabout 42% of the weight of the dried kernel. Rubber

Table 1

Material and suppliers

Material

Natural rubber, RMA no. 4

Pentachlorothiophenol (PCTP)-based peptiser, PEPTIZOL-7

High-abrasion furnace black (HAF, N330)

Red seal zinc oxide

Stearic acid

Antiozonant 6PPD, PILFLEX 13

Antioxidant TMQ, PILNOX TDQ

Rubber makers sulphur (soluble sulphur)

Accelerator, N-oxydiethylene benzothiazyl sulphenamide (NOBS), PIL

Scorch inhibitor, N-cyclohexylthiopthalimide, (CTP) (pre-vulcanising i

ACCITARD RE

Sl. No. Source of oils Name of oils

1 Aromatic oil, RPO 701

2 Paraffinic oil

3 Petroleum Naphthenic oil

4 Low PCA oil

5 Poweroil TDAE_A

6 Poweroil TDAE_B

1 NO_1 (Rubber seed) (Patent filed

2 NO_2 (Neem) (Patent filed by HA

3 Natural NO_3 (Dolma, Madhuca Indica)

4 NO_4 (Soybean)

5 NO_5 (Alsi)

6 NO_6 (Kurunj, Pongamia glabra

7 NO_7 (Sesamum)

8 NO_8 (Mustard)

9 NO_9 (Ground nut)

10 NO_10 (Arandi, Castor)

seed oil is a light yellow, semidrying oil whichcontains about 18–22% saturated and 78–82%unsaturated higher fatty acids [1].

The effect of vulcanised vegetable oil (VVO),obtained by heating fatty oils with sulphur andaccelerator, on ozone resistance, ageing and flowproperties of rubber compound has been investi-gated [6]. The preparation and characterisation offactice by vulcanisation of purified oil extractedfrom ‘Pongamia glabra’ was reported [7].

In this research work, extensive study has beencarried out with a number of eco-processing oils,which have shown encouraging compound properties.

2. Experimental

2.1. Materials

The materials studied are given in Table 1.

Supplier

MARDEC International, Kualalumpur,

Malaysia

Acmechem Limited, Ankeleshwar, India

Cabot India Ltd., Mumbai, India

Zinc-O-India, Ltd., Alwar, Rajasthan,

India

Godrej Industries Ltd., Mumbai, India

NOCIL, Thane, India

NOCIL, Thane, India

Jain Chemicals, Kanpur, India

CURE MOR NOCIL, Thane, India

nhibitor) PVI 100, ICI, Rishra, India

Supplier

Sah Petroleum Limited, Daman, India

Sah Petroleum Limited, Daman, India

Apar Industries Ltd., Thane, India

Apar Industries Ltd., Thane, India

Apar Industries Ltd., Thane, India

Apar Industries Ltd., Thane, India

by HASETRI) Rubber Board, Kottayam, Cochin, India

SETRI) Local market

)

ARTICLE IN PRESSS. Dasgupta et al. / Polymer Testing 27 (2008) 277–283 279

2.2. Physico-chemical characterisation

The detailed characterisation of the natural andpetroleum-based process aids through differentchemical and analytical techniques was carried outand was reported in an earlier communication bythe same authors [8].

2.3. Compound mixing and characterisation

Mixing of rubber compound was carried outusing a two-wing rotor laboratory Banbury mixer of1.5 l capacity (Stewart Bolling, USA) in two stages(master batch and final batch) and the formulationsare given in Table 2.

Master batch mixing was done setting thetemperature control unit (TCU) at 90 1C and rotorspeed at 60 rpm. First, the natural rubber wasmasticated along with the peptiser (pentachlor-othiophenol (PCTP)) for 45 s. Then, the black,process oil, zinc oxide, stearic acid and the anti-degradants (6PPD and TMQ) were added. After thepower integrator (PI) indicated achievement of0.32 kWh, the master batch was dumped. The dumptemperature of the master batches was found to bewithin 140–150 1C. The master batches were sheetedout in a laboratory two-roll mill. Further mixing ofthe master batches were carried out after a maturingperiod of 8 h.

For final batch mixing, the TCU was kept at60 1C and rotor speed at 30 rpm. The earlierprepared master batch was mixed with sulphur,accelerator and scorch inhibitor. The batch wasdumped at a PI reading of 0.12 kWh. The dumptemperature of the batches was found to be within95–105 1C. The final batches were also sheeted outon a laboratory two-roll mill.

Table 2

Bias tyre tread cap compound formulation

Ingredients phr

RMA no. 4 100.0

PCTP 0.10

N330 48.0

Process oil 8.0

Zinc oxide 5.0

Stearic acid 2.5

6PPD 1.5

TMQ 1.0

Soluble sulphur 2.20

NOBS 0.50

PVI 100 0.15

2.4. Processing properties

The detailed characterisation of the processingproperties of the compounds with natural andpetroleum-based process aids was carried out andwas reported in an earlier communication by thesame authors [8].

2.5. Cross-link density

For cured rubber vulcanisates, the volume frac-tion, Vr, of the test specimen in the swollen state isthe preferred way of expressing the amount of therubber component present at equilibrium swelling[9]. When a cross-linked polymer is placed in asuitable solvent, the polymer absorbs the solventand undergoes swelling to an extent determinedmainly by the cross-link density, the nature of thepolymer and the solvent [10].

Volume fraction was also performed to get anindication of apparent cross-link density. A weighedsample of cured rubber vulcanisate was immersed intoluene for 48 h at room temperature. Excesssolvent was then blotted from the sample and theswollen weight was measured. The swollen samplewas dried in an oven at 100 1C to constant weight.The dried weight of the sample was measured aftercooling the sample in a desiccator.

The volume fraction, Vr [9–11], of the rubbervulcanisate was calculated using the following formula:

V r ¼ðD� FTÞ=rr

ðD� FTÞ=rr þ Ao=rs, (A)

where D is the weight of the de-swollen sample, F isthe weight fraction of the insoluble non-rubberingredients, T is the original dry weight of thesample, Ao is the weight of solvent absorbed, rr isthe density of the rubber (0.92 for NR) and rs is thedensity of the solvent (0.863 for toluene).

The cross-link density X [12–14] of the rubbervulcanisate was calculated using the Flory–Rehnerrelationship:

X ¼ �lnð1� V rÞ þ V r þ wðV rÞ

2

2� rr � V s � ðV rÞ1=3

, (B)

where X is the cross-link density (gmol/gRH), Vr isthe volume fraction in the swollen gel, w is therubber–solvent interaction parameter (0.42 for filledNR, obtained from published [14] data), rr is thedensity of the rubber (0.92 for NR) and Vs is themolar volume of toluene (106.9 cm3/mol).

ARTICLE IN PRESS

Table 3

Cross-link density

Name of the oil Swell

index

Volume

fraction

Cross-link density

(gmol/gRH)

Aromatic oil 2.88 0.234 7.90E�05

Paraffinic oil 2.94 0.230 7.59E�05

Naphthenic oil 2.91 0.236 8.06E�05

Low-PCA oil 2.85 0.238 8.22E�05

Poweroil TDAE_A 2.95 0.228 7.44E�05

Poweroil TDAE_B 3.03 0.222 6.99E�05

NO_1 2.98 0.230 7.59E�05

NO_2 3.01 0.226 7.29E�05

NO_3 2.99 0.224 7.14E�05

NO_4 3.11 0.217 6.64E�05

NO_5 3.06 0.221 6.92E�05

NO_6 2.98 0.224 7.14E�05

NO_7 3.01 0.225 7.21E�05

NO_8 3.06 0.221 6.92E�05

NO_9 3.03 0.223 7.07E�05

NO_10 2.96 0.231 7.67E�05

S. Dasgupta et al. / Polymer Testing 27 (2008) 277–283280

2.6. Physical properties

The green rubber compounds were cured ingeneral accordance with ISO 2393 in an electricallyheated hydraulic curing press using compressionmoulding. The moulding conditions were as follows:141 1C for 45min for the stress–strain, dynamicmechanical analysis (DMA) and fatigue to failuretest (FTFT) and 141 1C for 1 h for the determinationof heat build up, abrasion loss and reboundresilience.

The tensile properties were measured using aZwick UTM 1445 in accordance with ISO 37 andISO 34. The hardness was measured with a Shore ADurometer, M/s Prolific Engineers, New Delhi,India (ISO 7619), and with a dead load IRHDtester, M/s H.W. Wallance and Company Ltd., UK(ISO 48). The fatigue to failure properties (FTFT)at 100% extension ratio were measured in aMonsanto FTFT machine (ISO 6943). The fatiguelife was calculated using the Japanese IndustrialStandard (JIS) average method. The abrasion lossat 10N load was measured in a Zwick DIN Abrader(ISO 4649). In dynamic mechanical property test-ing, the values of tan d, complex, elastic and viscousmodulus at 30, 70 and 100 1C, at 5% strain level andat 11Hz frequency were measured using a MetravibDynamic Mechanical Analyser, VA4000 (ISO4664). Rebound resilience at room temperatureand 70 1 was measured using a Zwick ReboundResilience Tester (ISO 4662). Heat build up (ISO4666-3) was measured at 100 1C temperature,0.175 in. stroke height and 30min time using aGoodrich Flexometer tester from M/s BF Good-rich, USA.

3. Results and discussion

3.1. Physico-chemical characterisation

The acid value, saponification value, iodinenumber, flash/fire point, pour point, aniline point,specific gravity, saybolt viscosity, VGC, azo dye,sulphur content, ash content, metal content, clay gelanalysis, aromatic content and FTIR surface groupstudy were reported in an earlier communication bythe same authors [8].

3.2. Processing properties

The Mooney viscosity, stress relaxation, Mooneyscorch, power law index, extrusion rate, die swell

index, activation energy, filler dispersion study,polymer–filler and filler–filler interaction study andrheometric study were reported in an earliercommunication by the same authors [8].

3.3. Cross-link density

Swell index, volume fraction and cross-linkdensity values are given in Table 3.

All the compounds made with petroleum oilsexcept that made with poweroil TDAE_B showedhigher cross-link density, whereas all the com-pounds made with natural oils except that madewith NO_10 showed lower cross-link density. Thismay be due to the presence of higher sulphurcontent in all the petroleum oils and natural oilNO_10.

3.4. Physical properties

The results for unaged tensile properties, hard-ness (IRHD and Shore A), heat build up, abrasion,specific gravity and flex to fatigue properties arereported in Table 4.

Compounds having paraffinic, naphthenic andlow-PCA oils showed higher static modulus, where-as the compound containing NO_4 oil showedlower static modulus. Compounds having NO_1,NO_5 and NO_6 oils showed higher hardness.Tensile strength and elongation at break were foundto be comparable for all the compounds. Com-pounds containing naphthenic, paraffinic, low-PCA

ARTICLE IN PRESS

Table 4

Physical properties

Name of the oil Modulus at

100%

(MPa)

Modulus at

200%

(MPa)

Modulus at

300%

(MPa)

Tensile

strength

(Mpa)

Elongation

at break (%)

Hardness

(IRHD)

Hardness

(Sh-A)

Aromatic oil 2.0 5.3 10.1 26.2 582 62 57

Paraffinic oil 2.2 5.9 11.1 27.1 559 64 59

Naphthenic oil 2.3 6.1 11.6 26.9 559 65 61

Low-PCA oil 2.2 6.0 11.5 28.2 577 65 61

Poweroil

TDAE_A

2.0 5.2 10.2 25.7 573 63 58

Poweroil TDAE_B 1.9 5.0 9.5 25.3 603 63 58

NO_1 2.1 5.3 10.0 26.2 591 68 62

NO_2 2.1 5.6 10.6 27.0 590 66 60

NO_3 2.0 5.3 10.1 26.9 605 63 58

NO_4 1.7 4.4 8.4 25.4 619 62 57

NO_5 2.0 5.1 9.5 25.8 615 68 61

NO_6 2.2 5.6 10.5 26.6 595 67 61

NO_7 2.0 5.2 10.0 26.5 604 64 59

NO_8 2.0 5.2 9.9 26.0 596 64 59

NO_9 2.0 5.2 9.8 25.2 597 65 60

NO_10 2.0 5.5 10.6 26.0 585 60 57

HBU (1C) Abrasion (mm3) Specific gravity FTFT (kC)

Aromatic oil 24.7 118 1.124 72

Paraffinic oil 22.3 123 1.118 108

Naphthenic oil 20.0 107 1.121 85

Low-PCA oil 22.8 105 1.122 97

Poweroil TDAE_A 26.8 133 1.124 98

Poweroil TDAE_B 36.5 141 1.122 113

NO_1 25.5 110 1.122 61

NO_2 27.9 110 1.123 78

NO_3 26.7 111 1.120 82

NO_4 38.3 130 1.119 80

NO_5 30.8 129 1.125 83

NO_6 25.6 110 1.123 81

NO_7 25.2 114 1.121 80

NO_8 31.8 117 1.121 80

NO_9 32.8 123 1.121 81

NO_10 23.4 122 1.124 71

S. Dasgupta et al. / Polymer Testing 27 (2008) 277–283 281

and NO_10 oils showed lower heat build up,whereas compounds containing NO_4, NO_5,NO_8, NO_9 and poweroil TDAE_B showed high-er heat build up. Compounds having naphthenic,low-PCA, NO_1, NO_2, NO_3 and NO_6 oilsshowed lower abrasion loss, whereas compoundscontaining poweroil TDAE_A, poweroil TDAE_B,NO_4 and NO_5 oils showed higher abrasion loss.Compounds having aromatic, NO_1 and NO_10oils showed lower fatigue to failure, whereascompounds containing poweroil TDAE_A, power-oil TDAE_B, low-PCA and paraffinic oils showedhigher fatigue to failure properties.

The results for tan d, complex, elastic and viscousmodulus at 30, 70 and 100 1C and rebound resilienceat 30 and 70 1C are reported in Tables 5–7.

Compounds having aromatic, poweroil TDAE_Band NO_10 oils showed lower rebound resilienceat 30 1C, whereas compounds containing naphthe-nic and paraffinic oils showed higher reboundresilience at 30 1C. Compounds having power-oil TDAE_B, NO_1, NO_9 and NO_10 oilsshowed lower rebound resilience at 70 1C, whereascompounds containing naphthenic, paraffinic andlow-PCA oils showed higher rebound resilience at70 1C.

ARTICLE IN PRESS

Table 5

Dynamic properties at 30 1C

Name of the oil Rebound

resilience (%)

tan d Complex

modulus (MPa)

Elastic modulus

(MPa)

Viscous modulus

(MPa)

Aromatic oil 51.4 0.215 5.92 5.79 1.24

Paraffinic oil 56.4 0.179 5.65 5.56 1.00

Naphthenic oil 57.2 0.152 5.19 5.13 0.78

Low-PCA oil 55.0 0.164 5.40 5.33 0.88

Poweroil TDAE_A 53.6 0.171 4.91 4.84 0.83

Poweroil TDAE_B 49.6 0.197 5.43 5.33 1.05

NO_1 51.8 0.174 6.15 6.06 1.06

NO_2 53.8 0.195 5.58 5.48 1.07

NO_3 55.2 0.164 5.16 5.09 0.84

NO_4 53.2 0.201 5.32 5.22 1.05

NO_5 52.6 0.228 5.92 5.78 1.32

NO_6 52.8 0.206 5.62 5.51 1.13

NO_7 54.6 0.189 5.24 5.14 0.97

NO_8 54.6 0.183 5.16 5.08 0.93

NO_9 53.4 0.201 5.54 5.43 1.09

NO_10 48.8 0.202 5.60 5.49 1.11

Table 6

Dynamic properties at 70 1C

Name of the oil Rebound

resilience (%)

tan d Complex

modulus (MPa)

Elastic modulus

(MPa)

Viscous modulus

(MPa)

Aromatic oil 57.4 0.170 4.87 4.80 0.82

Paraffinic oil 60.2 0.143 4.68 4.64 0.66

Naphthenic oil 62.6 0.128 4.37 4.34 0.56

Low-PCA oil 60.2 0.130 4.57 4.53 0.59

Poweroil TDAE_A 59.4 0.136 4.15 4.11 0.56

Poweroil TDAE_B 55.4 0.162 4.46 4.40 0.71

NO_1 55.4 0.170 4.58 4.52 0.77

NO_2 58.2 0.166 4.58 4.52 0.75

NO_3 59.2 0.133 4.36 4.32 0.58

NO_4 56.0 0.168 4.29 4.23 0.71

NO_5 55.6 0.190 4.61 4.53 0.86

NO_6 57.8 0.171 4.54 4.48 0.76

NO_7 59.2 0.162 4.26 4.20 0.68

NO_8 59.0 0.143 4.32 4.28 0.61

NO_9 55.4 0.176 4.40 4.33 0.76

NO_10 52.0 0.173 4.46 4.40 0.76

S. Dasgupta et al. / Polymer Testing 27 (2008) 277–283282

Compounds having naphthenic, low-PCA,poweroil TDAE_A and NO_3 oils showed lowertan d at 30, 70 and 100 1C, which indicates bettertraction, better rolling resistance but higher heatgeneration. Compounds having aromatic, NO_5and NO_6 oils showed higher tan d at 30 1C, whichindicates better traction properties. Compoundshaving NO_5 and NO_9 oils showed higher tan dat 70 1C, which indicates poor rolling resistance ofthe compound. Compounds having NO_5, NO_6

and NO_9 oils showed higher tan d at 100 1C, whichindicates higher heat generation.

4. Conclusions

The recent change in world scenario in shiftingtowards naturally occurring oils, and restriction onPCA-rich extender oils by December 2009 leads tosearch for non-carcinogenic process oils. The pre-sent study is focused on compound characterisation

ARTICLE IN PRESS

Table 7

Dynamic properties at 1001C

Name of the oil tan d Complex

modulus

(MPa)

Elastic

modulus

(MPa)

Viscous

modulus

(MPa)

Aromatic oil 0.151 4.24 4.19 0.63

Paraffinic oil 0.129 4.12 4.09 0.53

Naphthenic oil 0.114 3.94 3.92 0.45

Low-PCA oil 0.112 4.12 4.10 0.46

Poweroil

TDAE_A

0.113 3.74 3.72 0.42

Poweroil

TDAE_B

0.135 3.94 3.91 0.53

NO_1 0.140 3.91 3.87 0.54

NO_2 0.139 3.95 3.92 0.55

NO_3 0.114 3.81 3.78 0.43

NO_4 0.149 3.67 3.63 0.54

NO_5 0.172 4.00 3.94 0.68

NO_6 0.155 3.95 3.90 0.60

NO_7 0.140 3.68 3.65 0.51

NO_8 0.132 3.80 3.77 0.50

NO_9 0.154 3.72 3.67 0.57

NO_10 0.139 3.91 3.87 0.54

S. Dasgupta et al. / Polymer Testing 27 (2008) 277–283 283

of petroleum and naturally occurring oils in natural-rubber-based truck tyre tread cap compound. Theseoils were found to be suitable on the basis of lowPCA content. As the presently available low-PCAoils in the market in the form of MES and TDAEand naphthanic oil are comparatively costly, thesenatural oils can act as the best alternative processingaids for rubber industry, especially in developingand underdeveloped countries.

Acknowledgements

The authors would like to thank HASETRI andJK Tyre Management for kind permission topublish this work.

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