Vegetable oil extended high styrene emulsion styrene butadiene rubber for tire tread of high-quality motorcycle

doi:10.21203/rs.3.rs-4857530/v1

Worldwide the quality of motorcycle has undergone revolutionary change over last decade. Technological upgradation, customer demand and road infrastructure has contributed to this revolution. These necessitate higher performance of motorcycle tires as tires being interface between powerful engines and the road. Among the various parameters of motorcycle tire tread performance, dry and wet traction, rolling resistance and mileage, are important as they conform the safety requirement, fuel economy and durability. In general, Oil-extended Styrene Butadiene Rubber (OE-SBR) with high styrene provides better traction and abrasion with little deterioration in rolling resistance properties. In this study, vegetable origin oil extended high styrene (40%) SBR’s were characterized in motorcycle tire tread recipe. The use of vegetable oil results in almost zero polycyclic aromatic (PCA) content and therefore, these OE-SBR’s are environmentally friendly, renewable, and sustainable. SBR grades prepared with vegetable oils were showing less mixing energy (around 10%), better flow behavior (low activation energy by around 5%), lower filler-filler interaction (lower Payne effect by more than 25%) and lower tanδ@60°C (around 5%) as compared to petroleum oil.

High quality motorcycle

Eco-friendly materials

Oil extended styrene butadiene rubber

Angle abrasion tester

Rolling resistance

Traction

etc

Vegetable oils are good alternative to petroleum-based oils as they are renewable, easily available and are having bio-degradability and less toxicity. Most of the vegetable origin oils are rich for oleic and linoleic acid. Coconut oil is the most saturated vegetable oil and do not contain linolenic acid. Palm oil has both saturated and unsaturated carbon chains due to presence of palmitic acid and oleic acid. Ratio of unsaturated to saturated acid content is very high for castor oil and it is very low for coconut oil. Palm oil has this ratio slightly higher with respect to coconut oil. Groundnut, Soybean and Mustard oil has the moderate ratio. [1–6]. Vegetable oils may be modified by various techniques like blending, fractionation, hydrogenation, chemical catalyzed transesterification, enzyme catalyzed transesterification, etc. to achieve desired performance [7]. Solubility parameter is important factor to decide proper miscibility between rubber matrix and oil. Hansen solubility parameter was used to select suitable vegetable oil as process aid [8–13].

Dasgupta et al. [14–17] have characterized many vegetable oils in rubber compound and observed that few vegetable oils were showing better processing and tire performance properties like mileage, etc. Moringa and Niger oils have shown comparable properties with respect to Naphthenic oil in natural rubber-silica based compound and have also shown better filler dispersion and rolling resistance [18]. Few researchers found that Palm, Soybean and Sunflower oils can be used as processing aid and activator in Natural Rubber (NR) based recipe [19]. Mohamed et. al. [20] found Sunflower and Soybean oil as an alternate process aid for greener tire tread compound development. Double bonds present in Soybean oil can react with active site of rubber molecular chains during the vulcanization, which makes it reactive plasticizer [21].

Diene modified Soybean oil has improved wet traction in SBR-carbon black filled recipe [22]. Tire tread compound durability was improved with use of modified Soybean oil with use of sulfur which reduced the amount of double bonds [23]. Polymerized Soybean oil provided better thermal stability with respect to petroleum oils in NR/SBR based compound [24]. Natural rubber-based compounds prepared with epoxidized Palm, Sunflower and Soybean oils have also shown better polymer-filler interactions and carbon black dispersions [25]. Epoxidized palm oil and polymerized soybean oil evaluated against mineral oils in carbon-filled NR/SBR based compound [26]. Various general-purpose rubber-based compounds prepared with epoxidized Palm oil have shown comparable rheological and mechanical properties and better abrasion resistance with respect to DAE oil due to improved filler dispersion and polymer filler interaction [27–28].

SBR latex is usually extended with aromatic oil (due to good compatibility) which contains approx. 10 to 15 wt % Polyaromatic hydrocarbons (PAHs)/ Polycyclic aromatics (PCAs) content. However, aromatic oil is toxic and carcinogenic due to high PCA content [29]. Petroleum oils release aromatic hydrocarbons during automobile tire production, use and recycling and can cause adverse effects on human health and environment [30]. Abrasion resistance (AR) and rolling resistance (RR) have been improved by using SBR extended with non-carcinogenic low aromatic oils [31]. So, eco-oils with negligible quantity of aromatic compounds may provide good AR and RR properties in tires.

It was investigated that sequence of materials addition during rubber extension with oil has affected the vulcanizate properties [32]. Bio oil extended SSBR has shown better abrasion resistance due to high plasticization capacity and better filler dispersion [33]. Various researchers have used vegetable oils for extension of solution and emulsion SBR’s [34–40].

In the present research study, researchers have prepared emulsion SBR’s with extension of various petroleum and vegetable origin oils. These rubber samples were characterized in gum compound and motorcycle tire tread recipe.

2.1 Materials

Materials used for study are given in Tables 1 and 2.

Table 1

Material and suppliers
Material	Supplier
Styrene butadiene rubber latex (40% styrene content)	Reliance Ind. Ltd., India
Sulfuric acid	Labort Fine Chem Pvt. Ltd., India
Styrenated phenol (SP) antioxidant	National Chemical, India
Polybutadiene rubber, Neodymium catalyst (Synteca 44)	Synthos S. A., Poland
N330 carbon black	PCBL, India
Zinc oxide	Silox India Pvt. Ltd., India
Stearic acid	Godrej, India
Antiozonant MC wax	Gujarat Paraffins, India
Antioxidant TQ	NOCIL, India
Antioxidant 6PPD	NOCIL, India
Soluble sulfur	Jain Chemicals, India
Accelerator CBS	NOCIL, India
Accelerator TBBS	Yaso Industries, India

Table 2

Various oil and their suppliers
Sl. No.	Source of oils	Name of oils	Supplier
1	Petroleum	Panoil C 160A, Distillate Aromatic Extract (DAE) oil	Panama Petrochem Ltd., India
2		Panoil 2500, Treated Distillate Aromatic Extract (TDAE) oil	Panama Petrochem Ltd., India
3		Elasto Supreme H, Residual Aromatic Extract (RAE) oil	Hindustan Petroleum Corporation Ltd., India
4		RPO, Naphthenic oil	Apar Industries Ltd., India
1	Vegetable	NO_2 (RQ, DECAS oil)	Jayant Agro-Organics Ltd., India
2		NO_6 (RBD Palmolein oil)	Satguru Oils Pvt. Ltd., India
3		NO_7 (Ground nut oil)	Local market
4		NO_8 (Soybean oil)
5		NO_9 (Mustard oil)
6		NO_10 (Coconut oil)

2.2 Physico-chemical characterization of various oils

The detailed characterizations like Flash point, Pour point, Kinematic viscosity, Refractive index, Metal content by ICP-OES, Surface groups by FTIR and Structural groups by NMR for various petroleum and vegetable origin oils were reported in an earlier publication by the same authors [41].

2.3 SBR latex preparation and its characterization

SBR latex was prepared using emulsion polymerization of styrene and butadiene monomer in 3:4 weight ratio. Free radical polymerization technique was used, and reaction temperature was maintained between 0° to 20°C. Organic peroxide was used as initiator, rosin/fatty acid used as emulsifier, mercaptan as chain modifier to control molecular weight, water was used as emulsifying media and hydroxylamine was used as short stop to achieve desired level of conversion.

SBR latex was characterized for Solid content by acid coagulation and drying step. Then, further characterizations like Mooney viscosity using MV2000E from Alpha Technologies (ASTM D1646), Bound styrene content through refractive index checked by Abbemat 300 Refractometer from Anton Paar (ASTM D5775), Degradation study using Thermo Gravimetry Analyzer, TGA-Q50 from TA Instrument (ASTM D6370), Glass transition temperature using Differential Scanning Calorimetry, DSC-Q20 from TA Instrument (ASTM E794), Gel permeation chromatography study for molecular weight and its distribution using GPC1260 Infinity from Agilent Technologies, etc. were done.

2.4 SBR extension with oils at laboratory scale

SBR latex was extended with various oils (shown in Table 2).

For this purpose, oil emulsion was prepared using oil and fatty soap in 1:1 ratio, heated with continuous stirring (250–350 rpm, 60°-90°C). Measured amount of this oil emulsion was mixed with SBR latex with continuous stirring at high speed (700–1200 rpm). Oil content in rubber was maintained as 37.5 phr for all the samples. The latex was then coagulated with sulfuric acid and salt mixture. The coagulated crumbs were washed and dried as per standard procedure.

2.5 Physico-chemical characterization of OE-SBR’s

Total extractables (ASTM D5774) was measured using acetone and Bound styrene content was measured using Abbemat 300 Refractometer from Anton Paar (ASTM D5775).

OE-SBR’s were characterized for Density using Bulk Density Tester model RD3000 from M/s MonTech, Germany (ASTM D297), Mooney viscosity using MV2000E (ASTM D1646), Moisture content using Halogen Moisture Analyzer, Degradation study using Thermo Gravimetry Analyzer, TGA-Q50 and Glass transition temperature (Tg) using Differential Scanning Calorimetry, DSC-Q20.

2.6 Compound mixing and characterization

2.6.1 ASTM gum compound

Mixing was carried out using a two-wing rotor laboratory Miniature internal mixer, MIM (350 cc) from Thermo Fisher Scientific. The formulation used for compound evaluation shown in Table 3. Single stage mixing was done setting the Temperature Control Unit (TCU) at 60°C and rotor speed at 60 rpm for 9 min. The mixed batches were sheeted out in a laboratory two-roll mill using standard procedure.

Table 3

ASTM gum compound recipe
Ingredients	phr
Oil extended styrene butadiene rubber (40% styrene)	137.5 (100 rubber)
Zinc oxide	3
Stearic acid	1
Soluble sulfur	1.75
Accelerator TBBS	1.38

2.6.2 Motorcycle tire tread compound

Master and final batch mixing was carried out using MIM. The formulation used for compound evaluation shown in Table 4. Master batch mixing was done setting the Temperature Control Unit (TCU) at 90°C and rotor speed at 60 rpm for 5 min. Final batch mixing was done setting the TCU at 60°C and rotor speed at 30 rpm for 3 min. The master and final batches were sheeted out in a laboratory two-roll mill using standard procedure. Density of the final batch compounds was checked using Compressed Volume Densimeter from Montec (ASTM D297).

Table 4

Motorcycle tire tread compound recipe
Ingredients	phr
Oil extended styrene butadiene rubber (40% styrene)	89.375 (65 rubber)
Polybutadiene rubber, Neodymium catalyst	35
N330 carbon black	70
Respective process oil	3
Zinc oxide	4
Stearic acid	2
Antiozonant MC wax	1
Antioxidant TQ	1
Antioxidant 6PPD	1
Soluble sulfur	1.7
Accelerator CBS	1.2

2.7 Characterizations of uncured rubber compound

2.7.1 ASTM gum compound

Cure characteristics (ASTM D5289) by MDR2000 from M/s Alpha Technologies, USA at 160°C for 45 min.

2.7.2 Motorcycle tire tread compound

Bound rubber content was done by chemical method for master batch rubber compounds. Final compounds were characterized for processing parameters like Mooney viscosity (ASTM D1646), Power law index and Activation energy for flow (ASTM D6204). Cure characteristics measured by MDR200 at 160°C for 30 min. Frequency sweep and temperature sweep tests were performed using RPA2000 from M/s Alpha Technologies, USA. RPA test conditions shown in Table 5.

Table 5

RPA test conditions for various tests
Parameter	Temperature (°C)	Strain (%)	Frequency (Hz)
Flow behavior study (Power law index)
Frequency sweep (compounded rubber)	100	14	0.05, 0.1, 0.2, 0.4, 0.9, 1.8, 3.7, 7.6, 15.6, 30, 31, 32
Activation energy study (Arrhenius equation)
Temperature sweep (Shear rate, 5.03 sec^− 1) for compounded rubber	70, 80, 90, 100, 110, 120, 130	100	0.8
After cure (@160°C for tC90) properties by RPA
Dynamic properties	40 and 70	5	10
Filler-filler interaction study (Payne effect) by strain sweep	70	0.5, 1, 2, 3, 4, 5, 6, 8, 10, 15, 20, 25, 30, 40, 50	10

2.7.2.1 Bound rubber content test

It was measured for master batch (without curatives) rubber compound to check polymer-filler interaction [42–44]. Test method is shown in Fig. 1. The bound rubber content (%) was calculated using the below mentioned formula :

Bound rubber content (%) = {(W_d – W_f)/ W_o} X 100 - - - (1)

Where, W_d = Final weight of the dried sample in gm

W_f = Weight of the filler in the sample in gm

W_o = Weight of the rubber in the sample in gm

2.7.2.2 Mooney viscosity

Mooney viscosity of rubber compounds checked as ML(1 + 4)@100°C using Mooney Viscometer MV2000E from M/s Alpha Technologies, USA.

2.7.2.3 Frequency sweep test

Rubber compound has shown its flow behavior by measuring power law index in frequency sweep test [14] as per Newton’s power law.

2.7.2.4 Temperature sweep test

Activation energy of the rubber compound can be measured using temperature sweep test in RPA. Complex viscosity (η*) was measured at interval of 10°C between 70°C and 130°C. Activation energy can be calculated using the Arrhenius-Eyring formula [14].

2.8 Characterizations of cured rubber compound

Uncured rubber compounds were vulcanized for various tests using compression molding press model LP3000 from M/s MonTech, Germany. Tensile slabs were molded at 160°C for tC90 + 2 min and other specimen were molded at 160°C for tC90 + 5 min as per ASTM D3182. Cured specimen were tested for parameters like Stress-strain (ASTM D412) by UTM Z005 from M/s Zwick, Germany, Hardness (ASTM D2240) by Shore A Durometer from M/s Gibitre, Italy, Abrasion loss (ASTM D5963) using DIN Abrasion tester from M/s Zwick, Germany with 10 N load on specimen and Akron angle abrasion tester GT7012-A from M/s Gotech Testing Machines Inc., Taiwan with 20° slip angle for 4000 cycles, Heat Build Up (HBU) by Goodrich Flexometer EKT-2002GF from M/s Ektrontec, Taiwan (ASTM D623) following chamber temperature as 50°C, test time 30 min and 7 Kg load, Rebound @ 30° and 70°C (ISO4662-2) using Rebound Resilience tester 2108RR-T from M/s Ektrontec, Taiwan, Tg using DSC-Q20 and Volume resistivity (ASTM D257) using High Resistance Meter (model 6517B) and Resistivity test fixture (model 8009) from M/s Keithley (A Tektronix company), US. Dynamic properties and Payne effect (ASTM D6601) were performed using RPA (test conditions shown in Table 5). Dynamic mechanical properties of cured rubber specimen were measured using DMA1000 + from M/s Metravib, France (ASTM D5992).

2.8.1 Reinforcement index

Reinforcement index was calculated using below formula [45–47] :

RI = M300/M100 - - - (2)

where M300 is modulus of rubber compound at 300% elongation in MPa

M100 is modulus of rubber compound at 100% elongation in MPa

2.8.2 Crosslink density

Specimen were kept in toluene for 48 hrs and Swell index was measured using ASTM D3616. It was calculated as the ratio of swollen weight to original specimen weight. Volume fraction was measured by drying the swollen specimen in oven at 100°C for 2 hrs. It was calculated using following formula [48–49] :

V_r = [(D – FT)/ρ_r]/[(D – FT)/ρ_r + A_o/ρ_s] - - - (3)

where D is the weight of the de-swollen specimen

F is the weight fraction of the insoluble non-rubber ingredients

T is the original dry weight of the specimen

A_o is the weight of solvent absorbed; it can be calculated as (S-T)

ρ_r is the density of the respective raw rubber

ρ_s is the density of the solvent (0.867 for toluene)

The cross-link density X, of the rubber specimen was calculated using the Flory – Rehner relationship as given below [50–54] :

X = (-) [ln (1-V_r) + V_r + χ(V_r)²] / [2 * ρ_r * V_s * (V_r)^1/3] - - - (4)

where X is the cross-link density (mol/ cm³)

χ is the rubber-solvent interaction parameter (0.31 for SBR-toluene)

V_s is the molar volume of solvent (106.3 for toluene)

2.8.3 Strain sweep test

In strain sweep test, Payne effect was measured as difference between elastic modulus (G′) at low and high strain. Payne effect (after curing in RPA cavity) through strain sweep (ASTM D6204).

2.8.4 Dynamic mechanical properties by DMA

Rectangular specimens (2 mm thickness, 10 mm width) were tested at 10 Hz frequency, 1% dynamic and 2% static strain. Loss factor (tanδ) were measured at 0°, 30° and 60°C temperature, respectively.

3.1 Physico-chemical characterization

3.1.1 SBR latex characterization

Test results for physico-chemical properties of SBR latex is given in Table 6. All the properties of high styrene (40%) SBR latex sample were found within the specified range. This latex was used for oil extension and further study.

Table 6

Physico-chemical properties of styrene butadiene rubber latex
Parameters	Value
Solid content (%)	21.0
Mooney Viscosity (MU)	127.7
Refractive index	1.5488
Bound styrene content (%)	39.4
Degradation temperature by TGA (°C)	405.4
Glass transition temperature by DSC (°C)	-31.8
Mn by GPC (gm mole^-1)	2.0 lacs
Mw by GPC (gm mole^-1)	7.7 lacs
Polydispersity index by GPC	3.8

3.1.2 OE-SBR’s characterization

Physico-chemical properties of rubber samples shown in Table 7a and 7b. Acetone extraction for SBR’s prepared with vegetable oils were found to be comparable with petroleum oil-based rubbers which indicates proper oil present in these rubbers, and this may be due to good compatibility of these oils with SBR. Bound styrene content was calculated through refractive index value, and which was found comparable within the specified range for these extracted SBR rubber samples. This indicates comparable composition of monomer for all SBR samples.

Table 7

a: Physico-chemical properties of oil extended styrene butadiene rubber
Sample id/ Parameters →	Total extractables (%)	Bound styrene content (%)	Density (gm cc^-1)	Mooney viscosity (MU)	Moisture content (%)
S40_DAE	33.7	40.5	0.979	62.3	0.13
S40_TDAE	32.3	40.4	0.962	61.7	0.14
S40_RAE	33.2	39.7	0.971	63.6	0.17
S40_Naphthenic	33.6	39.5	0.946	52.6	0.12
S40_NO_2	32.8	40.3	0.963	40.2	0.19
S40_NO_6	34.2	40.9	0.961	50.0	0.15
S40_NO_7	33.3	41.0	0.955	52.5	0.17
S40_NO_8	34.3	40.1	0.957	52.0	0.12
S40_NO_9	32.2	39.4	0.956	54.3	0.18
S40_NO_10	31.8	40.4	0.958	56.0	0.14

Table 7

b: Physico-chemical properties of oil extended styrene butadiene rubber cont…
Sample id/ Parameters →	Degradation temperature (°C)	Ash content (%)	Tg by DSC (°C)
S40_DAE	394.6	0.25	-33.2
S40_TDAE	391.5	0.30	-38.4
S40_RAE	379.2	0.36	-31.5
S40_Naphthenic	386.9	0.37	-39.4
S40_NO_2	405.4	0.30	-48.8
S40_NO_6	413.9	0.28	-43.3
S40_NO_7	420.1	0.27	-47.8
S40_NO_8	416.2	0.31	-56.3
S40_NO_9	423.9	0.29	-49.5
S40_NO_10	389.2	0.24	-38.3

Mooney viscosity was found to be lower for S40_NO_2 and within the range for other samples. Moisture content was found less than 0.2% which means all rubber samples were dried properly. Degradation temperature was found in the range of 380° to 420°C in TGA test for all OE-SBR’s. S40_NO_2, S40_NO_6 to S40_NO_9 have shown lower Tg which may improve the abrasion and rolling resistance properties of the rubber compound based on these OE-SBR’s.

3.2 Compound characterization

3.2.1 Mixing behavior

Various mixing parameters including bound rubber content and density shown in Tables 8 and 9 for master and final batches, respectively. Master rubber compound mixed using S40_NO_2 and S40_NO_6 have shown slightly less mixing energy for both master and final stage as compared to compound prepared with petroleum oil based SBR. This may be due to lower Mooney viscosity of these rubber samples. Dump temperature was found comparable for all samples in both master and final stage mixing. Higher the bound rubber content value indicates more polymer-filler interaction. This is desirable to achieve better mechanical and failure properties due to higher reinforcement. Bound rubber was found to be comparable for all masterbatch compounds. Density of all final batches were found in line with the density of respective raw SBR’s.

Table 8

Motorcycle tire tread master batch mixing & characterization
Sample id/ Parameters →	Mixing Energy (kJ)	Maximum torque (N-m)	Dump temperature (°C)	Bound rubber (%)
MCT_M_DAE	203.3	186.3	145.7	19.8
MCT_M_TDAE	196.5	174.3	146.1	19.2
MCT_M_RAE	200.7	178.8	146.5	21.2
MCT_M_Naphthenic	198.5	171.2	143.3	19.6
MCT_M_NO_2	178.7	166.3	137.7	18.2
MCT_M_NO_6	178.0	156.3	140.7	20.2
MCT_M_NO_7	189.4	163.2	141.8	18.1
MCT_M_NO_8	183.3	160.7	140.9	18.2
MCT_M_NO_9	185.9	153.6	142.4	18.9
MCT_M_NO_10	184.0	162.7	140.4	19.5

Table 9

Motorcycle tire tread final batch mixing and characterization
Sample id/ Parameters →	Mixing Energy (kJ)	Maximum torque (N-m)	Dump temperature (°C)	Density (gm cc^-1)
MCT_F_DAE	59.6	116.1	114.0	1.176
MCT_F_TDAE	60.7	126.0	113.0	1.167
MCT_F_RAE	55.8	118.1	113.0	1.169
MCT_F_Naphthenic	57.4	130.2	111.0	1.152
MCT_F_NO_2	46.7	96.7	110.0	1.167
MCT_F_NO_6	50.0	103.7	111.3	1.153
MCT_F_NO_7	56.2	113.0	112.8	1.160
MCT_F_NO_8	53.7	111.4	113.4	1.162
MCT_F_NO_9	57.4	111.0	113.3	1.159
MCT_F_NO_10	53.2	115.7	112.8	1.161

3.2.2 Processing properties

3.2.2.1 ASTM gum compound

Test results for rheometric properties are shown in Table 10. Compounds prepared with S40_NO_6 and S40_NO_10 have shown rheometric properties almost comparable with naphthenic oil. Compounds prepared with S40_NO_2 and S40_NO_7 to S40_NO_9 have shown less delta torque value which may be due to presence of more olefinic content as measured by NMR in these oils.

Table 10

ASTM gum compound rheometric properties
Sample id/ Parameters →	Min TQ (dNm)	Max TQ (dNm)	tS2 (min)	tC10 (min)	tC90 (min)	Delta TQ (dNm)	Cure rate* (sec^-1)
Gum_DAE	0.79	4.68	15.62	11.07	23.28	3.89	8.2
Gum_TDAE	0.78	5.19	14.00	10.83	25.85	4.41	6.7
Gum_RAE	0.81	4.60	18.36	12.75	27.57	3.79	6.7
Gum_Naphthenic	0.67	4.35	21.36	14.68	31.63	3.68	5.9
Gum_NO_2	0.19	2.12	8.67	4.82	17.00	1.93	8.2
Gum_NO_6	0.64	4.00	21.30	13.54	30.54	3.36	5.9
Gum_NO_7	0.46	3.29	23.04	11.12	29.05	2.83	5.6
Gum_NO_8	0.24	2.36	8.43	4.88	19.65	2.12	6.8
Gum_NO_9	0.51	3.28	18.34	8.42	22.72	2.77	7.0
Gum_NO_10	0.56	4.44	18.91	12.80	29.33	3.88	6.0
* Cure rate = 100/(tC90-tC10)

3.2.2.2 Motorcycle tire tread compound

Test results for final batch uncured compounds are shown in Tables 11 and 12. All the compounds have shown Mooney viscosity in line with respective raw OE-SBR’s Mooney viscosity. Power law index (n) close to zero or relative lower value means plastic nature of rubber compound hence better shear thinning (Flow behavior) of rubber compound. Power law index was found to be comparable for all compounds. Higher activation energy means rubber compound need high energy for compound flow, which indicates poor processing. Compounds based on S40_NO_6 to S40_NO_10 have shown lower activation energy as compared to compound prepared with petroleum oil extended SBR. This may be due to absence of aromatic content in these vegetable oils. Refractive index [55] and Nuclear Magnetic Resonance (NMR) study indicates the presence of aromatic content in oil samples. Rheometric properties for motorcycle tire tread compounds were found in line with gum compounds.

Table 11

Motorcycle tire tread final batch compound processing properties
Sample id/ Parameters →	Mooney Viscosity (MU)	Power law index	Activation Energy, Eα (kCal mol^-1 gm^-1)
MCT_F_DAE	70	0.187	2444
MCT_F_TDAE	67	0.194	2434
MCT_F_RAE	66	0.191	2550
MCT_F_Naphthenic	60	0.190	2419
MCT_F_NO_2	53	0.198	2596
MCT_F_NO_6	57	0.194	2273
MCT_F_NO_7	64	0.188	2349
MCT_F_NO_8	63	0.185	2201
MCT_F_NO_9	65	0.187	2301
MCT_F_NO_10	64	0.185	2257

Table 12

Motorcycle tire tread compound rheometric properties
Sample id/ Parameters →	Min TQ (dNm)	Max TQ (dNm)	tS2 (min)	tC10 (min)	tC90 (min)	Delta TQ (dNm)	Cure rate* (sec^-1)
MCT_F_DAE	2.70	13.31	5.08	4.27	10.81	10.61	15.3
MCT_F_TDAE	2.56	13.46	5.45	4.51	12.07	10.90	13.2
MCT_F_RAE	2.55	12.87	5.59	4.67	11.79	10.32	14.0
MCT_F_Naphthenic	2.35	12.37	5.23	4.20	11.50	10.02	13.7
MCT_F_NO_2	2.08	9.67	4.76	3.70	10.69	7.59	14.3
MCT_F_NO_6	2.31	11.37	5.09	3.89	10.41	9.06	15.3
MCT_F_NO_7	2.61	10.73	4.80	3.52	10.82	8.12	13.7
MCT_F_NO_8	2.51	10.67	4.76	3.48	10.54	8.16	14.2
MCT_F_NO_9	2.53	11.04	4.74	3.49	10.75	8.51	13.8
MCT_F_NO_10	2.56	13.19	4.67	3.70	11.18	10.63	13.4
* Cure rate = 100/(tC90-tC10)

3.2.3 Vulcanizate properties

3.2.3.1 ASTM gum vulcanizate

Test results for Stress-strain including Hardness and Reinforcement index are shown in Table 13 and Swell index, Volume fraction and Crosslink density data are shown in Table 14. Vulcanizates prepared with NO_6 and NO_10 vegetable oil-based SBR’s have shown similar (within experimental error) static modulus as compared to Naphthenic oil. Higher unsaturated to saturated acid content ratio may affect the crosslink density adversely. Due to this, vulcanizate prepared with NO_2 has shown lowest crosslink density and lowest delta torque. This results in lowest modulus and hardness of this compound. Gum compound study was done to check the effect of various oils (in absence of carbon black) on crosslink density.

Table 13

ASTM gum compound stress-strain properties
Sample id/ Parameters →	M100 (MPa)	M300 (MPa)	TS (MPa)	EB (%)	Hardness (Shore A)	RI (M300/M100)
Gum_DAE	0.6	1.7	2.7	395	31	2.8
Gum_TDAE	0.7	2.2	2.3	309	36	3.1
Gum_RAE	0.6	1.6	3.2	458	32	2.7
Gum_Naphthenic	0.6	1.6	2.5	409	29	2.7
Gum_NO_2	0.3	0.6	1.1	512	19	2.0
Gum_NO_6	0.5	1.4	2.0	444	27	2.8
Gum_NO_7	0.4	1.0	2.1	512	24	2.5
Gum_NO_8	0.3	0.6	1.6	610	20	2.0
Gum_NO_9	0.5	1.1	2.2	494	22	2.2
Gum_NO_10	0.6	1.8	2.3	366	27	3.0

Table 14

ASTM gum compound crosslink density
Sample id/ Parameters →	Swell index	Volume Fraction, Vr	Crosslink Density (mol cm^-3)
Gum_DAE	4.33	0.160	5.68*10^− 5
Gum_TDAE	3.83	0.191	8.16*10^− 5
Gum_RAE	4.38	0.161	5.82*10^− 5
Gum_Naphthenic	4.47	0.162	6.05*10^− 5
Gum_NO_2	7.16	0.100	2.36*10^− 5
Gum_NO_6	5.05	0.143	4.64*10^− 5
Gum_NO_7	5.51	0.127	3.72*10^− 5
Gum_NO_8	6.77	0.101	2.44*10^− 5
Gum_NO_9	5.63	0.126	3.68*10^− 5
Gum_NO_10	4.56	0.155	5.43*10^− 5

3.2.3.2 Motorcycle tire tread

Test results for Stress-strain including Hardness and Reinforcement index are shown in Table 15 and Swell index, Volume fraction and Crosslink density data are shown in Table 16. Modulus and hardness values for motorcycle tire tread vulcanizates were found in line with gum vulcanizates. Crosslink density for motorcycle tire tread batches were found in line with crosslink density of respective gum batches.

Table 15

Motorcycle tire tread compound stress-strain properties
Sample id/ Parameters →	M100 (MPa)	M300 (MPa)	TS (MPa)	EB (%)	Hardness (Shore A)	RI (M300/M100)
MCT_F_DAE	2.0	10.1	20.5	530	60	5.1
MCT_F_TDAE	2.0	10.2	20.7	537	60	5.1
MCT_F_RAE	2.0	10.0	20.7	536	59	5.0
MCT_F_Naphthenic	1.9	10.5	19.6	489	58	5.5
MCT_F_NO_2	1.3	6.3	18.9	707	52	4.9
MCT_F_NO_6	1.9	10.1	19.9	549	55	5.3
MCT_F_NO_7	1.6	8.4	18.6	568	53	5.3
MCT_F_NO_8	1.4	7.2	20.4	670	53	5.1
MCT_F_NO_9	1.6	8.4	21.4	640	54	5.3
MCT_F_NO_10	1.9	10.3	19.0	479	57	5.4

Table 16

Motorcycle tire tread vulcanizate crosslink density
Sample id/ Parameters →	Swell index	Volume Fraction, Vr	Crosslink Density (mol cm^-3)
MCT_F_DAE	2.43	0.234	1.29*10^− 4
MCT_F_TDAE	2.52	0.233	1.27*10^− 4
MCT_F_RAE	2.46	0.233	1.27*10^− 4
MCT_F_Naphthenic	2.53	0.230	1.24*10^− 4
MCT_F_NO_2	3.20	0.168	0.66*10^− 4
MCT_F_NO_6	2.64	0.209	1.01*10^− 4
MCT_F_NO_7	2.80	0.197	0.90*10^− 4
MCT_F_NO_8	3.03	0.174	0.71*10^− 4
MCT_F_NO_9	3.08	0.172	0.69*10^− 4
MCT_F_NO_10	2.70	0.213	1.05*10^− 4

3.2.4 Performance properties

Test results for DIN and Akron Abrasion loss, Heat build-up (HBU) and Rebound resilience @30° and 70°C are shown in Table 17. DIN abrasion was found to be comparable for all compounds. However, Akron test at high severity condition has shown different observation. Vulcanizates prepared with vegetable oil extended SBR expect S40_NO_6 and S40_NO_10 have shown high abrasion loss and high heat generation. This may be due to low crosslink density of these compounds. Rebound resilience was found comparable for all compounds. Tg results are shown in Fig. 2. Tg of all the vulcanizates were found in line with raw rubber Tg. Vegetable oil extended SBR based vulcanizates except S40_NO_10 have shown lower Tg. Despite low Tg value, vulcanizates prepared with S40_NO_2, S40_NO_7, S40_NO_8 and S40_NO_9 have shown high abrasion loss due to less crosslink density. Carbon dispersion was checked for cure specimen using volume resistivity measurement. Lower the resistivity indicates better carbon black dispersion in rubber matrix. Test results are shown in Fig. 3. Volume resistivity for compounds prepared with S40_NO_6 and S40_NO_10 was found comparable with petroleum oil. Poor carbon black dispersion for vulcanizates prepared with vegetable oil extended SBR expect S40_NO_6 and S40_NO_10 may be reason for deterioration in various properties like high abrasion loss, high heat generation and lower modulus.

Table 17

Motorcycle tire tread compound performance properties
Sample id/ Parameters →	DIN Abrasion (mm³)	Akron Abrasion (mm³)	Heat Build Up (°C)		Rebound Resilience (%)
Sample id/ Parameters →	DIN Abrasion (mm³)	Akron Abrasion (mm³)	Surface	Centre	@30°C	@70°C
MCT_F_DAE	72	334	32.0	110	34.0	43.0
MCT_F_TDAE	70	291	29.3	107	35.7	46.2
MCT_F_RAE	73	288	27.1	101	34.9	45.1
MCT_F_Naphthenic	67	565	25.5	99	36.0	47.1
MCT_F_NO_2	72	716	49.1	133	35.9	47.2
MCT_F_NO_6	68	313	32.0	106	38.2	46.5
MCT_F_NO_7	74	528	42.2	116	37.6	47.2
MCT_F_NO_8	72	669	47.2	120	37.8	47.1
MCT_F_NO_9	68	648	36.3	109	38.0	47.1
MCT_F_NO_10	70	266	33.6	104	37.8	46.8

3.2.5 Dynamic properties and filler-filler network by RPA

Dynamic properties are shown in Table 18. Compounds prepared with S40_NO_6 and S40_NO_10 have shown comparable dynamic modulus @ 40° and 70°C with Naphthenic oil. This may be due to comparable maximum torque of these rubber compounds. Payne effect is shown in Fig. 4. Higher the Payne effect means more filler-filler interaction [56]. Compounds based on vegetable oil extended SBR have shown lower Payne effect as compared to petroleum oil. Lower filler-filler interaction for these compounds may be due to presence of few additional functional groups in these vegetable oils like triglyceride ester carbonyl, hydrogen bonded C-O, and acyl C-O. These groups may form bonds with surface groups present on carbon black which results in more polymer-filler interaction and less filler-filler interaction.

Table 18

Motorcycle tire tread compound dynamic properties by RPA
Sample id/ Parameters →	G′@40°C (kPa)	tanδ @40°C	G′@70°C (kPa)	tanδ @70°C
MCT_F_DAE	2754	0.34	1968	0.29
MCT_F_TDAE	2620	0.31	1873	0.27
MCT_F_RAE	2563	0.32	1828	0.27
MCT_F_Naphthenic	2410	0.29	1725	0.25
MCT_F_NO_2	2127	0.34	1378	0.33
MCT_F_NO_6	2383	0.31	1705	0.29
MCT_F_NO_7	1820	0.29	1291	0.28
MCT_F_NO_8	2113	0.31	1402	0.31
MCT_F_NO_9	2115	0.31	1441	0.30
MCT_F_NO_10	2395	0.28	1735	0.25

3.2.6 Dynamic properties by DMA

Test results are shown in Table 19. Dynamic mechanical properties (tanδ) measured at 0°, 30° and 60°C indicate about wet traction, dry traction and rolling resistance properties of tire respectively. Vulcanizates prepared with S40_NO_6 and S40_NO_10 was showing lower tanδ @60°C as compared to Vulcanizate prepared with S40_DAE. This indicates better rolling resistance for these vulcanizates. This may be due to lower filler-filler interaction in these vulcanizates.

Table 19

Motorcycle tire tread compound dynamic mechanical properties measured by DMA
Sample id/ Parameters →	tan delta @0°C	tan delta @30°C	tan delta @60°C
MCT_F_DAE	0.39	0.37	0.28
MCT_F_TDAE	0.36	0.33	0.24
MCT_F_RAE	0.40	0.35	0.27
MCT_F_Naphthenic	0.35	0.32	0.23
MCT_F_NO_2	0.36	0.33	0.24
MCT_F_NO_6	0.32	0.29	0.23
MCT_F_NO_7	0.33	0.31	0.25
MCT_F_NO_8	0.34	0.31	0.25
MCT_F_NO_9	0.36	0.31	0.25
MCT_F_NO_10	0.34	0.30	0.23

In a lab scale, oils derived from vegetables were used to extend high styrene ESBR. For the objective of oil extension, specific vegetable-origin oils with solubility parameters that were close to SBR were employed. The chemical characteristics of these rubbers were examined and found to be consistent with those of mineral oil extended SBR. Because of their light color, rubbers made from vegetable oils may be used in the production of colored goods. Because vegetable-origin oils were used in their preparation, the new SBR grades are environmentally friendly products.

Motorcycle tire tread compounds prepared with vegetable oils based SBR rubbers have shown comparable or slightly better processing properties which was confirmed by lower mixing energy, lower activation energy and better rubber-filler interaction in rubber compound. The majority of the properties of the compound made with S40_NO_6 and S40_NO_10 are comparable to those of the extended SBR-based compound naphthalene oil. Therefore, these vegetable origin oil extended SBR rubbers can be used for manufacturing of tire tread compound for high quality motorcycle.

5.0 Acknowledgement

The author would like to acknowledge Reliance Ind. Ltd. India management for giving permission for performing testing activities and for publishing this research work.

The author would also acknowledge the Jayant Agro-Organics Ltd. India, and Satguru Oils Pvt. Ltd. India for kindly supplying vegetable oils for testing purpose and Mr. Rajnikant Salvi, Mr. Pankaj Kumawat and Mr. Jayveersinh Jhala for extending various testing support.

6.0 Conflict of interest

The author declares that they have no conflict of interest.

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No competing interests reported.