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141Progress in Rubber, Plastics and Recycling Technology, Vol. 25, No. 3, 2009

Improved Polymer–Filler Interaction with an Ecofriendly Processing Aid

∗Corresponding author. Tel./fax: +91 2952 232019. E-mail address: [email protected]

©Smithers Rapra Technology, 2009

Improved Polymer–Filler Interaction with an Ecofriendly Processing Aid. Part 1

S. Dasgupta1, S.L. Agrawal1, S. Bandyopadhyay1∗, R. Mukhopadhyay1, R.K. Malkani2, and S.C. Ameta2

1Hari Shankar Singhania Elastomer and Tyre Research Institute (HASETRI), PO Tyre Factory, Dist. Rajsamand, Rajasthan 313 342, India2Department of Polymer Science and Department of Chemistry, Mohanlal Sukhadia University, Udaipur 313 001, Rajasthan, India

Received: 12 April 2008, Accepted: 16 October 2008

ABSTRACT

Internationally there is a trend towards the use of ecofriendly materials in view

of the environmental benefi t and the improvement in properties. In the present

work, the chemical and analytical properties of an eco processing aid and a

soluble-zinc-soap-based processing aid (Zincolet PN60) were assessed. The two

processing aids were also analysed in a styrene butadiene rubber/natural rubber/

butadiene rubber blend based on tyre tread compounds. Compounds mixed with

the eco processing aid exhibited better mixing properties, better polymer–fi ller

interaction, marginally better fi ller dispersion and fl ow behaviour, and better

heat build-up and fatigue-to-failure properties.

INTRODUCTION

Rubber compounds show complex behaviour in the mixing process owing to their complicated microcomposite structure. In the case of carbon black compounds, the behaviour becomes more complex because of the colloidal properties of carbon black particles, i.e. their higher surface activity and higher structure formation. In addition, the interaction between carbon black and the rubber cannot be neglected. Processing additives are used to improve the interaction between rubber and fi ller and the dispersion of the fi ller.

142 Progress in Rubber, Plastics and Recycling Technology, Vol. 25, No. 3, 2009

S. Dasgupta, S.L. Agrawal, S. Bandyopadhyay, R. Mukhopadhyay, R.K. Malkani, and S.C. Ameta

Processing additives are defi ned as materials used in rubber compounds at relatively low dosage, improving the processing characteristics of the rubber compounds without signifi cantly affecting their physical properties(1,2). The ASTM(3) defi nes process oil as ‘Hydrocarbon oil derived from petroleum or other sources, used as an extender or process aid’. Processing additives can be subdivided(2,4) into different groups:

• hydrocarbons: mineral oils, waxes, and petroleum resins, to improve fi ller incorporation, fi ller dispersion, compound fl ow, etc.;

• fatty acid derivatives: fatty acids, fatty acid esters, fatty alcohols, metal soap, fatty acid amides, to improve fi ller incorporation, fi ller dispersion, homogenisation, compound fl ow, and compound release properties, for better reinforcement, etc.;

• synthetic resins: phenolic resins, to improve tack;

• low molecular weight polymers: liquid rubbers and norbornene, to improve fi ller incorporation, fi ller dispersion, and compound fl ow hardness.

• organothio compounds: as peptising and reclaiming agents.

Plasticisers are organic substances added to polymers to improve their processability. They increase the softness, elongation, and low-temperature fl exibility and decrease the concentration of intermolecular forces and the glass transition temperature (Tg) of polymers. They are classifi ed into primary, secondary, and extenders(5).

Coconut and cottonseed oils are used as resinous plasticisers(6). Rubber seed oil and epoxidised rubber seed oil have been used as a secondary plasticiser and heat stabiliser in polyvinyl chloride(5).

Various authors have conducted studies on ecofriendly processing aids and process oils(7–12). An investigation of the infl uence of a processing additive on carbon black incorporation and its dispersion behaviour from the temperature dependence of the dynamic viscoelastic properties of rubber compounds has also been reported(13).

The use of rubber-soluble zinc soap is a well-known practice in rubber compounding to improve the processing properties, particularly the dispersion of the fi llers. However, no systematic study has been made of the carbon black dispersion and other processing characteristics. In the present paper, a study was made of the use of a soluble-zinc-soap-based processing aid (Zincolet



PN60) and a non-conventional processing aid (an eco processing aid) in typical SBR-based and NR/BR-blend-based tyre tread formulations. Dispersion of black and processing behaviour were studied by well-known methods such as measurement of the electrical conductivity (on an electroscanner), optical methods using both a dispersion grader and a microscope, and also by a rubber process analyser (RPA2000).

EXPERIMENTAL

Materials

The materials used in the study are given in Table 1.

Physicochemical Characterisation

The processing aids were characterised for specifi c gravity (ASTM D1817), ash content (ASTM D4574), drop melt point (ASTM D127), and iodine number (ASTM D1959). The sulfur content was determined by means of an elemental analyser (NCS 2500, Thermoquest, Italy). A Fourier transform infrared (FTIR) spectroscopic study of the processing aids was performed on a 2000 FTIR system (Perkin Elmer, USA) to check the functional groups. A carbon chain distribution study was conducted by autosystem gas chromatography (GC) (Perkin Elmer, USA). For the GC study, samples were dissolved in cyclohexane. A degradation study was performed by using a thermogravimetric analyser (TGA Pyris 1, Perkin Elmer, USA). For the TGA study, samples were scanned from 50 to 850 °C at 40 °C/min. Samples were scanned in a nitrogen atmosphere up to 600 °C, followed by an oxygen atmosphere.

Material Characterisation for an SBR-based Tyre Tread Compound

Compound Mixing

Mixing of the rubber compound was carried out using a two-wing rotor laboratory Banbury mixer of 1.5 L capacity (Stewart Bolling, USA) in two stages (master batch and fi nal batch). The compound formulations are given in Table 2.

Master batch mixing was done by setting the temperature control unit (TCU) at 90 °C and the rotor speed at 60 r/min. The polymer was masticated for 30 s. Then the processing aid, black, oil, zinc oxide, and stearic acid were added. After the power integrator (PI) indicated achievement of 0.32 kW h, the master batch was dumped. The dump temperature of the master batches was found



Table 1. Material and suppliersMaterial SupplierNatural rubber, RMA #4 MARDEC International, Kualalumpur,

MalaysiaPolybutadiene Rubber, BR01 Indian Petrochemical Corporation Ltd.,

Vadodara, IndiaStyrene Butadiene Rubber, SBR 1502 BST Elastomers, Bangkok, ThailandPenta chloro thio phenol (PCTP) based Peptiser, PEPTIZOL - 7

Acmechem Limited, Ankeleshwar, India

Eco Processing Aid Indian MarketSoluble Zinc soap based processing aid, Zincolet PN60

E. Eyres Rubber Chemicals Pvt. Ltd., Mumbai, India

Homogeniser for polymer blend, Pukhomix 400 (A blend of aliphatic and aromatic hydrocarbon resins)

E. Eyres Rubber Chemicals Pvt. Ltd., Mumbai, India

High abrasion furnace black (HAF, N330)

Cabot India Ltd., Mumbai, India

Ppt. Silica, MFIL200G Madhu Silica Pvt. Ltd., Bhavnagar, India

Aromatic oil, RPO 701 Sah Petroleum Limited, Daman, IndiaRed Seal zinc oxide Zinc – O – India, Ltd., Alwar,

Rajasthan, IndiaStearic acid Godrej Industries Ltd., Mumbai, IndiaAntiozonant, 6PPD, 1, 3 dimethyl butyl para phenylene diamine, PILFLEX 13

NOCIL, Thane, India

Antioxidant, TMQ, polymerized 1, 2 dihydro 2, 2, 4 trimethyl quinoline, PILNOX TDQ

NOCIL, Thane, India

Paraffi nic Wax Gujarat Paraffi ns Pvt. Ltd., Ahmedabad, India

Rubber makers sulfur (soluble sulfur) Jain Chemicals, Kanpur, IndiaAccelerator, TBBS, tertiary butyl benzo thiazyl sulfenamide, Rubenamid T

Flexsys America LP, USA

Accelerator, CBS, cyclohexyl benzo thiazyl sulfenamide, Pilcure CZ

NOCIL, Thane, India

Scorch Inhibitor, CTP, N-Cyclo hexyl thio pthalimide, (Pre-vulcanising inhibitor) PVI 100, ACCITARD RE

ICI, Rishra, India



to be within the 140–150 °C range. The master batches were sheeted out in a laboratory two-roll mill (Santosh Industries, New Delhi, India). Further mixing of the master batches was carried out after a maturing period of 8 h.

For fi nal batch mixing, the TCU was kept at 60 °C and the rotor speed at 30 r/min. The earlier prepared master batch was mixed with sulfur and accelerator. The batch was dumped at a PI reading of 0.12 kW h. The dump temperature of the batches was found to be within the 95–105 °C range. The fi nal batches were also sheeted out on a laboratory two-roll mill.

Processing Properties

Mooney viscosity and Mooney scorch. Mooney viscosity, ML (1 + 4) at 100 °C, and Mooney scorch, MS at 135 °C using the large rotor, were determined in a Mooney viscometer (MV 2000E, Alpha Technologies, USA) in accordance with ASTM D1646.

Flow behaviour through RPA 2000. Newton’s power law index for checking the fl ow behaviour of master batches and fi nal batches was measured using the frequency sweep confi guration in a rubber process analyser (RPA2000, Alpha Technologies, USA).

Reduction in viscosity with increasing shear rate (constant strain and increasing frequency) is due to the pseudoplastic nature of a rubber compound. At low frequency, the initial uniform decrease in complex viscosity can be attributed to alignment of chain segments of rubber molecules and fi llers in the direction of the applied stress. At intermediate frequency, the rate of reduction in the complex viscosity (η*) is reduced owing to stress-induced crystallisation (in the case of NR). At high frequency, the sharp fall in complex viscosity is due to alignment of these crystallites in the direction of shear(14). If viscosity is a function of the shear rate, a decrease in viscosity with increasing shear rate is called shear thinning, and an increase in viscosity is called shear thickening. Shear-thinning fl uids are also called pseudoplastic fl uids(15,16).

Table 2. SBR based tyre tread compound formulation (phr)Ingredients Mix Id.

SBR_Control SBR_PN60 SBR_Eco Process AidZincolet PN60 0.0 2.0 0.0Eco Process Aid 0.0 0.0 2.0Rest ingredients are as (phr): SBR1502: 100.0, N330: 50.0, Aromatic oil: 8.0, Zinc oxide: 3.0, Stearic acid: 1.0, Soluble sulfur: 1.75 and TBB: 1.0



As per Newton’s power law, shear stress is proportional to (shear rate)n, which implies that shear stress/shear rate(17) is proportional to (shear rate)n-1 and that complex viscosity (η*) is proportional to (shear rate)n-1, as Newton’s basic equation suggests that dynamic viscosity is the ratio of shear stress to shear rate.

The slope of the log η* and log shear rate plot is equal to n − 1, which implies that

Power law index (n) = slope+1 (1)

Filler Dispersion Study

The dispersion of carbon black was measured by the following methods:

• By measuring the fraction recovery of G′ (G′at plateau/G′initial) at a specifi ed test confi guration in the RPA2000. Above a threshold loading, carbon black forms an aggregate–aggregate network when mixed into a rubber compound. Applied strain breaks down this network. After a suffi cient relaxation time, the network reforms again. The nature of this network affects a compound’s processability in the uncured state and its mechanical properties in the cured state(18). Dispersion of fi ller was determined using the RPA 2000 according to the experiments done by Coran and Donnet(19). The higher the fraction recovery of G′, the better is the quality of fi ller dispersion.

• By Dispersegrader 1000 (Optigrade, AB, Sweden). Rating X: 1 = poor dispersion, 10 = excellent dispersion [mode R CB (x, y) used].

• By measuring the electrical conductivity on a Tangent electroscanner (E10, Tangent Ltd, Ireland). A lower conductivity value indicates better dispersion of the fi ller(20):

Conductivity =

admittance (in mS) 0.00078specimen thickness (in mm) (2)

• By optical microscope. The test was performed using a cured specimen. The dispersion rating was determined by comparison with reference photographic standard pictures given in ISO 11345, method A, at 30× magnifi cation. A higher rating value indicates better dispersion.

Polymer–Filler and Filler–Filler Interaction Study

The addition of fi llers to rubber compounds has a strong impact on the static and dynamic behaviour of rubber. Besides the strain-independent contribution of the hydrodynamic effect, the fi ller–rubber interaction, and the crosslinking of



the matrix, the complex modulus (G*) also shows a strong dependency at low strains, i.e. the modulus decreases with increasing strain. This stress softening at small deformations, also known as the Payne effect, plays an important role in understanding reinforcement mechanisms in fi lled rubber samples, and can be attributed to the breakdown of the fi ller–fi ller networks, an indication of interactions between fi ller particles(21).

The fi ller networking or agglomeration of fi ller particles, which is controlled mainly by fi ller–fi ller interactions in a rubber compound, was quantifi ed from the strain dependence of the elastic modulus G′. The fi ller network was gradually destroyed as the strain increased (at strains well below 100%). This resulted in a decrease in elastic modulus G′ with strain amplitude. The ratio of the elastic modulus G′ at low and high strain levels related to the fi ller–fi ller interactions(22–25).

More recently, the interaction parameter (σ/η) has been proposed for the measurement of interaction between polymer and fi ller26. Here, σ is the slope of the stress–strain curve in the linear region and at typical extension ratios varying from 1 to 3. The moduli in this deformation relate to polymer–fi ller interaction(27). The non-dimensional term η is the ratio of the dynamic modulus G′ at 1% and 25% strain. This is related to fi ller–fi ller interaction.

The conditions for the fl ow behaviour, fi ller dispersion, and fi ller–fi ller and polymer–fi ller interaction studies on the RPA 2000 are given in Table 3.

The Payne effect for both the master batches and fi nal batches was calculated as the difference between the elastic modulus G′ at low strain (1%) and high strain (25%).

Rheometric Properties

The rheometric properties at 160 °C for 30 min were determined in a rubber process analyser (RPA2000) in accordance with ASTM D5289.

Physical Properties

The green rubber compounds were cured in accordance with ASTM D3182 in an electrically heated hydraulic curing press using compression moulding. The conditions followed to cure the compounds were 145 °C for 50 min.

The tensile and tear properties were measured using a Zwick UTM 1445 instrument in accordance with ASTM D412 and ASTM D624. The hardness was measured with a Shore A durometer (Prolifi c Engineers, New Delhi,



India) (ASTM D2240) and with a dead load IRHD tester (HW Wallance and Company Ltd, UK) (ASTM D1415).

Material Characterisation for an NR/BR-blend-based Tyre Tread Compound

Compound Mixing

Mixing of the rubber compound was carried out using the mixer mentioned above in three stages (master batch, repass and fi nal batch). The formulations are given in Table 4.

Table 4. NR/BR blend based tyre tread compound formulation (phr)Ingredients Mix Id.

SBR_Control NB_PN60 NB_Eco Process AidZincolet PN60 0.0 2.0 0.0Eco Process Aid 0.0 0.0 2.0Rest Ingredients are as (phr): RMA # 4: 70.0, BR01: 30.0, PCTP: 0.10, N330: 54.0, Silica: 8.0, Aromatic Oil: 10.0, Pukhomix 400: 2.0, Zinc Oxide: 4.5, Stearic acid: 2.0, TMQ: 1.5, 6PPD: 1.5, Paraffi n Wax: 1.0, Soluble sulfur: 2.0, CBS: 1.0, PVI 100: 0.1

Table 3. Test confi guration in RPA 2000 Parameter Temperature (°C) Strain (%) Frequency (Hz)Flow behavior studyFrequency sweep 120 15 0.1, 0.2, 0.5, 1.0, 2.0,

5.0, 10.0, 20.0, 30.0Filler dispersion studyConditioning of the compound for 1.0 min

50 1 1.667

10 s static delay 50 0 0High strain 50 50 1.66710 s static delay 50 0 0Low strain repeated until stable

50 1 1.667

Repeated last two steps until G’ reaches plateau60 s delay 50 0 0After 10 s G’ was measured

50 1 1.667

Filler-fi ller and polymer-fi ller interaction studyStrain sweep 110 0.5, 1, 5, 10, 15,

20, 25, 30, 35, 40, 45, 50

0.2



Master batch mixing was conducted by setting the temperature control unit (TCU) at 90 °C and the rotor speed at 60 r/min. The polymer and the peptiser were masticated and blended for 45 s. Then, the processing aid, black, silica, oil, zinc oxide, stearic acid, Pukhomix 400 resin, and antidegradants (TMQ, 6PPD, and paraffi nic wax) were added. After the power integrator (PI) indicated the achievement of 0.32 kW h, the master batch was dumped. The dump temperature of the master batches was found to be within the 140–150 °C range. The master batches were sheeted out in a laboratory two-roll mill. Further mixing of the master batches was carried out after a maturing period of 8 h.

For repass batch mixing, the TCU was kept at 80 °C and the rotor speed at 30 r/min. The earlier prepared master batch was mixed, and the batch was dumped at a PI reading of 0.20 kW h. The dump temperature of the batches was found to be within the 135–145 °C range. The repass batches were also sheeted out on a laboratory two-roll mill.

For fi nal batch mixing, the TCU was kept at 60 °C and the rotor speed at 30 r/min. The earlier prepared repass batch was mixed with sulfur, accelerator, and prescorch inhibitor. The batch was dumped at a PI reading of 0.12 kW h. The dump temperature of the batches was found to be within the 95–105 °C range. The fi nal batches were also sheeted out on a laboratory two-roll mill.


Tel Tack. The samples for tack index study were prepared using a compression moulding technique in a hydraulic curing press (Hind Hydraulics, New Delhi, India) at 100 °C for 3 min with a moulding pressure of 10 MPa. Samples for the tack study were prepared after milling the compound to 1.0 mm thickness, and pieces measuring 15 cm × 15 cm were cut. On one side of the milled rubber compound, rubberised fabric was applied to provide suffi cient reinforcement for Tel Tack testing. Both sides of the sample were then covered with cellophane paper. This was done to protect the surface of the green rubber compound from any contamination, and also to prevent sticking to the mould. The moulded samples were then cut into 5 cm × 1 cm pieces. The cellophane paper on the compound side (not the fabric-reinforced side) was removed just before testing. The tack index was determined using a Monsanto Tel Tack Tester (Monsanto, USA). The test was performed using two strips (5 cm × 1 cm) adhering in crosswise direction to produce a contact surface area of 1 cm2. A preload of approximately 227 g was applied for 30 s of contact time to the sample. The maximum separation force and the separation time were measured. The tack index was calculated using the following formula(28):



Tack index =

separation force (separation time)1/3

contact force (contact time)1/3 (3)

The test was performed at least 16 h after sample preparation. It was performed in unaged condition (just after removal of the cellophane paper) and in aged condition (8 h after removal of the cellophane paper), and the percentage retention of tack index was calculated as follows:

Tack retention =aged tack index

unaged tack index100

(4)

Mixing Behaviour. The mixing behaviour of the processing aids was checked in a Brabender plasticorder (PL2000-3, Brabender OHG, Duisburg, Germany). Master batch mixing was done by setting the temperature control unit (TCU) at 75 °C and the rotor speed at 30 r/min. The masticated polymer was added and blended for 45 s. Then, the processing aid, black, silica, oil, zinc oxide, stearic acid, Pukhomix 400 resin, and antidegradants (TMQ, 6PPD, and paraffi nic wax) were added and mixed for a total of 5 min. The total mixing energy was measured.

Extrusion Rate and Die Swell Index. When a polymer is forced through an orifi ce, it expands in cross-section (die swell, the Barus effect(17)) and correspondingly shrinks in length (extrusion shrinkage). Die swell is usually defi ned as the ratio of the cross-sectional area of the extrudate to the cross-sectional area of the capillary. As per Cotton(17), for a given compound the extrusion shrinkage at constant shear stress was independent of die geometry and temperature of extrusion and was related to the molecular orientation imposed on the polymer during extrusion, this orientation being dependent on the shear stress developed in the die. In elastomeric materials(17) the relaxation of internal stresses starts immediately after exit from the die and continues as the material cools down. The three-dimensional entanglement networks give the polymer an additional ability to remember its previous shape for a short time after extrusion. Thus, extrusion shrinkage is mainly determined by molecular orientation.

Extrusion rate and die swell index were measured using a round die with a diameter of 5 mm in a Brabender plasticorder (PL2000-3) following ASTM D5099. For determination of the extrusion rate and the die swell index, the rotor speed was kept at 45 r/min, the barrel temperature at 70 °C, and the head and die temperatures at 110 °C(29). For extrusion rate determination, the weight of the extrudate (in g/min) was taken. The die swell index was calculated as the ratio of extrudate diameter to die diameter (5 mm).



Rheometric Properties

The rheometric properties at 141 °C for 60 min were determined on a rubber process analyser (RPA2000) in accordance with ASTM D5289.

Physical Properties

The green rubber compounds were cured in accordance with ASTM D3182 in an electrically heated hydraulic curing press using compression moulding. The moulding conditions followed to cure the compounds were 141 °C for 45 min for the stress–strain and fatigue-to-failure test (FTFT) and 141 °C for 1 h for the determination of heat build-up and abrasion loss.

The tensile and tear properties were measured using a Zwick UTM 1445 instrument in accordance with ASTM D412 and ASTM D624. The hardness was measured with a Shore A durometer (Prolifi c Engineers, New Delhi, India) (ASTM D2240) and with a dead load IRHD tester (HW Wallance and Company Ltd, UK) (ASTM D1415). Ageing of the tensile specimens was performed at 105 °C for 3 days using an ageing oven (Prolifi c, India) following ASTM D865. The fatigue-to-failure properties (FTFT) at 100% extension ratio were measured in a Monsanto FTFT machine (ASTM D4482). The fatigue life was calculated using the Japanese Industrial Standard (JIS) average method. The abrasion loss at 10 N load was measured in a Zwick DIN abrader (ASTM D5963). Heat build-up (ASTM D623) was measured at 100 °C temperature, 0.175″ stroke height, and 30 min time using a Goodrich fl exometer tester (BF Goodrich, USA).

RESULTS AND DISCUSSION

Physicochemical Characterisation

The specifi c gravity, ash content, drop melt point, iodine number, sulfur content, GC study, and TGA results for the eco processing aid and Zincolet PN60 are given in Table 5.

Ash content, drop melt point, and iodine number were found to be higher in the case of Zincolet PN60. A higher iodine number indicates the presence of higher unsaturated hydrocarbon chains in Zincolet PN60 by comparison with the eco processing aid.

FTIR and TGA graphs are shown in Figures 1 and 2.



Table 5. Analytical and chemical propertiesProperties Zincolet PN60 Eco Process AidSpecifi c gravity 1.111 0.932Ash Content, % 18.67 0.05Drop melt point, °C 90.5 42.5Iodine value, g of I2/100 g of sample 80 0.8Sulfur Content, % NIL NILGC Study:C20C22C24C28C40C44>C44

* 15.512.26.71.73.62.029.9

TGA degradation temperature, °C 420.8 457.0* Test could not be performed as sample is having zinc metal, which may deposit in the GC column

Figure 1. Fourier Transformed Infrared Spectroscopic (FTIR) study



The eco processing aid has a carbon chain distribution of long chains, as confi rmed by GC (Table 5), and ester groups, as shown by FTIR. There is a slight difference in degradation temperature for the eco processing aid and soluble-zinc-soap-based processing aid, as shown in Figure 2.

Material Characterisation for an SBR-based Tyre Tread Compound


The Mooney viscosity for the master batch and fi nal batch and the Mooney scorch for the fi nal batch as well as the power law index for the master batch and fi nal batch are given in Table 6.

A lower Mooney viscosity was observed in both the master batches and the fi nal batches for the compound with the eco processing aid. Comparable Mooney scorch results were observed for all the compounds.

Figure 2. Thermo gravimetric analysis (TGA) study



Here, a power law index (n) close to zero or lower means a plastic nature of the rubber compound, and hence better shear thinning (fl ow behaviour). All the compounds exhibited comparable fl ow behaviour for both the master batches and the fi nal batches.

The results for the dispersion study are given in Tables 7 to 10.

Table 7. Filler dispersion study by RPA2000Sample Id. Test Parameter

Master compound Final compound

G’ (MPa) initial at

1% strain, MPa

G’ (MPa) at plateau

level, MPa

Fraction recovery

of G’ (G’ at plateau /

G’ initial)

G’ (MPa) at 1% strain, MPa

G’ (MPa) at plateau level, MPa

Fraction recovery

of G’ (G’ at plateau / G’ initial)

SBR_Control 0.562 0.503 0.896 1.123 0.994 0.885SBR_PN60 0.559 0.499 0.892 1.094 0.987 0.902SBR_Eco Process Aid

0.515 0.465 0.903 1.015 0.905 0.892

Table 8. Dispersion study by Dispersegrader Sample Id. Dispersion RatingSBR_Control 2.3SBR_PN60 3.0SBR_Eco Process Aid 3.5

Table 6. Mooney viscosity, power law index and Mooney scorch Test Parameter Sample Id.

SBR_Control SBR_PN60 SBR_Eco Process AidMooney viscosity(Master batch), MU

71.9 74.1 69.2

Mooney viscosity(Final batch), MU

64.0 63.4 61.1

Power law index(Master batch)

0.27 0.27 0.27

Power law index(Final batch)

0.28 0.28 0.28

Mooney Scorch, Min 20.22 21.59 21.13



Table 9. Dispersion study by Tangent Bench-Top Laboratory Electroscanner (E10A)Sample Id. Conductivity, S/m (10-3)SBR_Control 3.34SBR_PN60 2.13SBR_Eco Process Aid 3.12

Table 10. Dispersion study by Optical microscope (Image analyzer) following ISO 11345Sample Id. Dispersion Rating SBR_Control 6SBR_PN60 8SBR_Eco Process Aid 8

Comparable fi ller dispersion for all the compounds was observed by RPA study. However, with all the other measuring techniques, the compounds mixed with a processing aid exhibited better fi ller dispersion than the compounds mixed without a processing aid.

The results for polymer–fi ller and fi ller–fi ller interactions are given in Table 11 and shown in Figure 3 for master batches and in Figure 4 for fi nal batches.

Table 11. Polymer- fi ller interaction study: Payne effect (∆G’, kPa)Sample Id. Master batch Final batchSBR_Control 146 116SBR_PN60 138 112SBR_Eco Process Aid 130 107

The compound mixed with the eco processing aid exhibited a lower Payne effect. This indicates a better polymer–fi ller interaction for both the master batches and the fi nal batches.

The rheometric results are given in Table 12.

Comparable rheometric results were observed for all the compounds except the compound mixed with Zincolet PN60, for which a marginally slower cure characteristic was observed.



Physical Properties

The results for unaged tensile properties, hardness (IRHD and Shore A), and tear properties are reported in Table 13.

Comparable physical properties were observed for all the compounds.

Figure 3. Strain sweep in RPA 2000 for Payne effect study for master batches

Figure 4. Strain sweep in RPA 2000 for Payne effect study for fi nal batches



Tabl

e 12

. Rhe

omet

ric

prop

erti

es

Sam

ple

Id.

Test

Par

amet

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inim

um

torq

ue(d

N-m

)

Max

imum

to

rque

(dN

-m)

Scor

ch s

afet

y ti

me,

ts 2

(min

)Tc

40

(min

)Tc

50

(min

)O

ptim

um c

ure

tim

e, t

c 90 (

min

)

SBR

_Con

trol

2.21

18.6

75.

297.

047.

7113

.17

SBR

_PN

602.

1617

.37

5.74

7.48

8.24

14.5

0SB

R_E

co P

roce

ss A

id2.

0917

.61

5.65

7.29

7.95

13.4

1

Tabl

e 13

. Phy

sica

l pro

pert

ies

Sam

ple

Id.

Test

Par

amet

erM

odul

us a

t 10

0% (

MP

a)M

odul

us

at 3

00%

(M

Pa)

Tens

ile

Stre

ngth

(M

Pa)

Elo

ngat

ion

at B

reak

(%

)

Har

dnes

s(I

RH

D)

Har

dnes

s (S

h-A

)Te

ar

Stre

ngth

(N/m

m)

SBR

_Con

trol

2.9

14.7

19.9

382

6966

61SB

R_P

N60

2.8

13.5

19.7

404

6764

61SB

R_E

co P

roce

ss A

id2.

714

.220

.840

267

6561



Material Characterisation for an NR/BR-blend-based Tyre Tread Compound


Unaged and aged tack index results for fi nal batches are given in Table 14. Comparable unaged and aged green tack was observed for all the compounds.

Table 14. Tack index Test Parameter Sample Id.

NB_Control NB_PN60 NB_Eco Process AidUnaged tack index 1.49 1.44 1.59Aged tack index 0.75 0.81 0.72Tack Retention (%) 50 56 45

Power law index results for master, remill, and fi nal batches are given in Table 15. A lower power law index value was observed for compounds mixed with the eco processing aid in all three stages: master batches, remill batches, and fi nal batches. This indicates that compounds mixed with the eco processing aid exhibited better fl ow behaviour for the master, remill, and fi nal batches.

Table 15. Power law index Test Parameter Sample Id.

NB_Control NB_PN60 NB_Eco Process AidPower law index(Masterbatch)

0.19 0.18 0.17

Power law index(Re mill batch)

0.21 0.21 0.20

Power law index(Final batch)

0.24 0.22 0.21

The results of the dispersion study are given in Tables 16 to 18. Compounds mixed with a processing aid exhibited better fi ller dispersion in all the measured techniques by comparison with compounds mixed without a processing aid.

Table 16. Filler dispersion study by RPA2000Sample Id. Fraction recovery of G’

Master batch Re mill batch Final batchNB_Control 0.822 0.808 0.853NB_PN60 0.851 0.812 0.877NB_Eco Process Aid 0.848 0.876 0.904



Table 17. Dispersion study by Tangent Bench-Top Laboratory Electroscanner (E10A)Sample Id. Conductivity, S/m (10-3)NB_Control 1.34NB_PN60 0.92NB_Eco Process Aid 1.00

Table 18. Dispersion study by optical microscope (image analyzer) following ISO 11345Sample Id. Dispersion Rating NB_Control 9NB_PN60 9NB_Eco Process Aid 10

The results for polymer–fi ller and fi ller–fi ller interactions are given in Table 19 and shown in Figure 5 for master batches, in Figure 6 for remill batches, and in Figure 7 for fi nal batches. Compounds mixed with the eco processing aid exhibited a lower Payne effect, indicating better polymer–fi ller interaction for the master, remill, and fi nal batches.

Table 19. Polymer-fi ller interaction study: Payne effect (∆G’, kPa)Sample Id. Master batch Re-milled batch Final batchNB_Control 340 217 150NB_PN60 309 224 146NB_Eco Process Aid 281 200 142

The mixing properties are given in Table 20. The compounds mixed with the eco processing aid exhibited a lower total mixing energy, indicating lower consumption of power in the mixing process.

Table 20. Mixing propertiesSample Id. Total Mixing Energy (kNm) NB_Control 18.30NB_PN60 17.87NB_Eco Process Aid 13.22

The extrusion properties are given in Table 21. The extrusion rate results are the average of three observations, and the die swell result is the average of ten observations Comparable extrusion rates and die swell indices were observed for all the compounds.



Figure 5. Strain sweep in RPA 2000 for Payne effect study for master batches

Figure 6. Strain sweep in RPA 2000 for Payne effect study for re mill batches

Table 21. Extrusion properties Sample Id. Test Parameter

Extrusion rate (gm/min)

Die swell index

NB_Control 78.4 1.29NB_PN60 77.3 1.22NB_Eco Process Aid 76.2 1.25



The rheometric results are given in Table 22. Comparable rheometric results were observed for all the compounds.

Physical Properties

The results for unaged and aged tensile properties, tear properties, heat build-up, abrasion, and fatigue-to-failure properties are given in Tables 23 to 24.

The compounds mixed with the eco processing aid exhibited better tear strength, heat build-up, and fatigue-to-failure properties. The remaining physical properties were found to be comparable for all the compounds.

CONCLUSIONS

The following are the advantages of using the eco processing aid, as found in this study:

• lower mixing energy, indicating better mixing properties;

• a lower Payne effect, indicating better polymer–fi ller interaction;

• a better fi ller dispersion in the rubber matrix;

• a lower power law index and a reduced compound Mooney viscosity, indicating better fl ow behaviour;

Figure 7. Strain sweep in RPA 2000 for Payne effect study for fi nal batches



Tabl

e 22

. Rhe

omet

ric

prop

erti

es

Sam

ple

Id.

Test

Par

amet

erM

inim

um

torq

ue(d

N-m

)

Max

imum

to

rque

(dN

-m)

Scor

ch s

afet

y ti

me,

ts 2

(min

)Tc

40

(min

)Tc

50

(min

)O

ptim

um c

ure

tim

e, t

c 90 (

min

)

NB

_Con

trol

2.63

16.2

510

.19

11.8

312

.92

19.7

0N

B_P

N60

2.50

16.3

410

.53

12.3

513

.17

20.1

1N

B_E

co P

roce

ss A

id2.

6115

.38

11.2

612

.67

13.3

719

.65

Tabl

e 23

. Phy

sica

l pro

pert

ies

Sam

ple

Id.

Test

Par

amet

er

Mod

ulus

at

100%

(M

Pa)

Mod

ulus

at

300%

(M

Pa)

Tens

ile

Stre

ngth

(M

Pa)

Elo

ngat

ion

at

Bre

ak (

%)

Har

dnes

s(I

RH

D)

Har

dnes

s (S

h-A

)

Tear

St

reng

th(N

/mm

)

NB

_Con

trol

2.0

(165

)9.

3(1

50)

22.3

(59)

568

(51)

62 (+4)

60 (+5)

90

NB

_PN

602.

0(1

75)

9.5

(143

)20

.7(5

8)56

7(5

4)63 (+

5)61 (+

6)79

NB

_Eco

Pro

cess

Aid

1.9

(176

)9.

1(1

53)

21.4

(62)

618

(52)

61 (+5)

59 (+6)

98

Valu

es w

ithi

n th

e pa

rent

hesi

s, (

) in

dica

tes

the

perc

enta

ge r

eten

tion

of p

hysi

cal p

rope

rtie

s af

ter

agin

g



Table 24. Physical propertiesSample Id. Test Parameter

HBU, °C Abrasion, mm3 FTFT, kCNB_Control 29.3 80 70NB_PN60 23.7 82 66NB_Eco Process Aid 18.7 75 101

• lower heat build-up;

• better fatigue-to-failure properties.

The improvement in the above properties may also improve the performance properties of the tyre. Thus, the eco processing aid can be used in the rubber industry as an ecofriendly and cost-effective processing aid.

ACKNOWLEDGEMENT

The authors would like to thank HASETRI and JK Tyre Management for kind permission to publish this work.

REFERENCES

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28. The Instruction Manual for the Tel Tack Meter. Monsanto Corporation, USA (1982).

29. ASTM D2230-96 (reapproved 2002), ‘Rubber property-extrudability of unvulcanised compounds’.

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