Description:FIELD OF INVENTION
The present disclosure relates to novel bio-based coupling agents. More, particularly it relates to cardanol based coupling agents, method of preparing such coupling agents, and rubber compositions comprising such coupling agents.

BACKGROUND
The silica/rubber composites are widely utilized in the green tire industry. Rubber compounds reinforced by silica have enhanced wet skid resistance and lower rolling resistance. However, the surface of silica has a large number of hydroxyl groups. Due to the presence of these hydroxyl groups, the silica particles easily form agglomerates. Therefore, it is difficult to disperse silica well in rubber matrix. This leads to weak performance of the tire.
To improve dispersion of silica in the rubber matrix, the silica surface needs to be modified. This can be done using a coupling agent which has functional groups capable of linking both the rubber and silica. Silane Coupling Agents (‘SCAs’) are known to improve dispersion of silica and form a chemical interaction between silica and rubber. Bis-(triethoxysilylpropyl)tetrasulfide (‘TESPT’), a bifunctional coupling agent, is widely used in the industry.
Although, TESPT enhances the mechanical strength and dynamic properties of silica/rubber composites it also suffers from certain drawbacks. The ethoxy group contained in TESPT reacts with the hydroxyl group on the surface of the silica. This results in the generation of a large number of Volatile Organic Compounds (‘VOCs’) during the rubber mixing and curing process. In the large-scale tire industry, around 5–6 mL/kg VOCs (VOC/rubber composites) can be generated from coupling agents during the rubber processing procedures, about 130,000 m3 per year. VOCs not only increase porosity of the rubber composites but also pollute the environment and endanger human health and life. Many countries have regulations governing VOC emissions. Therefore, reducing VOCs emissions and reducing the porosity of vulcanizates are major technical challenges facing the rubber industry.
SUMMARY
A cardanol based coupling agent is disclosed. The cardanol based coupling agent is obtained by reacting 3-pentadecyl phenol ethoxylate with sulfur to obtain a sulfurized 3-pentadecyl phenol ethoxylate and reacting the sulfurized 3-pentadecyl phenol ethoxylate with a diisocyanate compound.
A process for preparing a cardanol based coupling agent is also disclosed. The process comprises reacting 3-pentadecyl phenol ethoxylate with sulfur to obtain a sulfurized 3-pentadecyl phenol ethoxylate and reacting the sulfurized 3-pentadecyl phenol ethoxylate with a diisocyanate compound.

BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 depicts Fourier Transform Infrared (‘FTIR’) spectra of the cardanol based coupling agent in accordance with an embodiment of the present disclosure.
FIG. 2 depicts the sear number of Control and Trial 1-3 compositions.
FIG. 3 depicts the abrasion, grip, and rolling resistance of the Vulcanized Control and Vulcanized Trial 1-3 compositions.
FIG. 4 depicts the Scanning Electron Microscope (‘SEM’) images of the Vulcanized Control and Vulcanized Trial 1 compositions.

DETAILED DESCRIPTION
Reference will now be made in detail to embodiments of the present disclosure. The terminology used in the description presented herein is not intended to be interpreted in any limited or restrictive manner, simply because it is being utilized in conjunction with a detailed description of certain specific embodiments of the invention. Furthermore, embodiments of the invention may include several features, no single one of which is solely responsible for its desirable attributes, or which is essential to practicing the inventions herein described.
It will be understood by those skilled in the art that the foregoing general description and the following detailed description are explanatory of the invention and are not intended to be restrictive thereof.
The terms “a,” “an,”, and “the” are used to refer to “one or more” (i.e., to at least one) of the grammatical object of the article.
Reference throughout this specification to “an aspect”, “another aspect” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention.
The terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion and are not intended to be construed as “consists of only”, such that a process or method that comprises a list of steps does not include only those steps but may include other steps not expressly listed or inherent to such process or method.
Likewise, the terms “having” and “including”, and their grammatical variants are intended to be non-limiting, such that recitations of said items in a list are not to the exclusion of other items that can be substituted or added to the listed items.
Also, any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of "1 to 10" is intended to include any and all subranges between and including the recited minimum value of 1 and the recited maximum value of 10, that is, all subranges beginning with a minimum value equal to or greater than 1 and ending with a maximum value equal to or less than 10, and all subranges in between.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the disclosure, the preferred methods, and materials are now described.
The term “cardanol” refers to the phenolic lipid synthesized from anacardic acid, and represented by the following Formula:

wherein n=0, 2, 4, or 6.

In an aspect of the present disclosure, a cardanol based coupling agent is disclosed. The disclosed cardanol based coupling agent is obtained by reacting 3-pentadecyl phenol ethoxylate with sulfur to obtain a sulfurized 3-pentadecyl phenol ethoxylate and reacting the sulfurized 3-pentadecyl phenol ethoxylate with a diisocyanate compound.
In accordance with various embodiments, the reaction of 3-pentadecyl phenol ethoxylate with sulfur is carried out at a temperature in the range of 100-180 ºC. In an embodiment, the reaction is carried out at 150 ºC.
In accordance with various embodiments, the reaction of the sulfurized 3-pentadecyl phenol ethoxylate with the diisocyanate compound is carried out at a temperature in the range of 110-170 ºC.
Any suitable form of sulfur may be used. In accordance with an embodiment, sulfur is a powdered sulfur. In various embodiments, the powdered sulfur has a density in the range of 1.9-2.1 g/cm3. In an embodiment, the density is 2 g/cm3. In some embodiments, the powdered sulfur has purity in the range of 90-99.9%. In some embodiments, the purity is in the range of 95-98%.
The diisocyanate compound may be any suitable diisocyanate compound. Examples of the diisocyanate compound include but are not limited to toluene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, and isophorone diisocyanate.
In some embodiments, 80-90 wt.% of 3-pentadecyl phenol ethoxylate is reacted with 8-15 wt.% of sulfur to obtain the sulfurized 3-pentadecyl phenol ethoxylate. In accordance with some embodiments, 84-88 wt.% of 3-pentadecyl phenol ethoxylate is reacted with 8-12 wt.% of sulfur to obtain the sulfurized 3-pentadecyl phenol ethoxylate.
In various embodiments, 90-98 wt.% of the sulfurized 3-pentadecyl phenol ethoxylate is reacted with 4-8% of the diisocyanate compound to obtain the disclosed coupling agent. In some embodiments, 92-96 wt.% of the sulfurized 3-pentadecyl phenol ethoxylate is reacted with 5-7% of the diisocyanate compound to obtain the disclosed coupling agent.
In accordance with an embodiment, 3-pentadecyl phenol ethoxylate is obtained by reacting 30-90 wt.% of cardanol oil and 25-70 wt.% of ethylene oxide at a temperature in the range of 100-160 oC.
The cardanol oil and ethylene oxide may be reacted in the presence of a suitable base. Examples of the suitable base include but are not limited to sodium hydroxide, potassium hydroxide, sodium methoxide, sodium hydride, and/or tetrabutyl ammonium hydroxide.
In accordance with an embodiment, the coupling agent has a sulfur content in the range of 8-15%. In some embodiments, the sulfur content is in the range of 8-12%.
In various embodiments, the coupling agent has a volatile content in the range of = 3.0.
In various embodiments, the coupling agent has a specific gravity in the range of 1.0-1.1 g/cc.
In some embodiments, the coupling agent has a pH in the range of 6-8 in 50% water. In an embodiment, the pH is 7.
The coupling agent may be represented by one or more of Formula 1-5:

Formula 1

Formula 2

Formula 3

Formula 4

Formula 5
wherein n is 1-14; and R1 is independently alkylene, substituted alkylene, arylene, substituted arylene or cyclic ketone.
In some embodiments, n is 5-12. In some embodiments, R1 is independently pentamethylene, hexamethylene, isophorone, or toluene.
In another aspect of the present disclosure, a process for preparing a cardanol based coupling agent is disclosed. The process comprises reacting 3-pentadecyl phenol ethoxylate with sulfur to obtain a sulfurized 3-pentadecyl phenol ethoxylate; and reacting the sulfurized 3-pentadecyl phenol ethoxylate with a diisocyanate compound.
In accordance with various embodiments, the reaction of 3-pentadecyl phenol ethoxylate with sulfur is carried out at a temperature in the range of 100-180 ºC. In an embodiment, the reaction is carried out at 150 ºC.
In accordance with various embodiments, the reaction of the sulfurized 3-pentadecyl phenol ethoxylate with the diisocyanate compound is carried out at a temperature in the range of 110-170 ºC.
Any suitable form of sulfur may be used. In accordance with an embodiment, sulfur is a powdered sulfur. In some embodiments, the powdered sulfur has a density in the range of 1.9-2.1 g/cm3. In an embodiment, the density is 2 g/cm3. In some embodiments, the powdered sulfur has purity in the range of 90-99.9%. In an embodiment, the purity is 95-98%.
The diisocyanate compound may be any suitable diisocyanate compound. In accordance with some embodiments, the diisocyanate compound is selected from toluene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, and isophorone diisocyanate.
In some embodiments, 80-90 wt.% of 3-pentadecyl phenol ethoxylate is reacted with 8-15 wt.% of sulfur to obtain the sulfurized 3-pentadecyl phenol ethoxylate. In accordance with some embodiments, 84-88 wt.% of 3-pentadecyl phenol ethoxylate is reacted with 8-12 wt.% of sulfur to obtain the sulfurized 3-pentadecyl phenol ethoxylate.
In various embodiments, 90-98 wt.% of the sulfurized 3-pentadecyl phenol ethoxylate is reacted with 4-8% of the diisocyanate compound to obtain the disclosed coupling agent. In some embodiments, 92-96 wt.% of the sulfurized 3-pentadecyl phenol ethoxylate is reacted with 5-7% of the diisocyanate compound to obtain the disclosed coupling agent.
In accordance with some embodiments, 3-pentadecyl phenol ethoxylate is obtained by reacting 30-90 wt.% of cardanol oil and 25-70 wt.% of ethylene oxide at a temperature in the range of 100-160oC.
In an embodiment, cardanol oil and ethylene oxide are reacted in the presence of one or more of a suitable base. Examples of the suitable base include but are not limited to sodium hydroxide, potassium hydroxide, sodium methoxide, sodium hydride, and/or tetrabutyl ammonium hydroxide.
In an embodiment, the process comprises neutralizing the cardanol based coupling agent by adding an acid or a base. Any suitable acid or base may be used. In some embodiments, acid is acetic acid, hydrochloric acid, and/or sulphuric acid. In some embodiments, base is sodium hydroxide and/or ammonia.
The coupling agent obtained from the disclosed process is represented by one or more of Formula 1-5:

Formula 1

Formula 2

Formula 3

Formula 4

Formula 5

wherein n is 1-14; and
R1 is independently alkylene, substituted alkylene, arylene, substituted arylene or cyclic ketone.
In some embodiments, n is 5-12. In some embodiments, R1 is independently pentamethylene, hexamethylene, isophorone, or toluene.
In various embodiments, the obtained coupling agent has a sulfur content in the range of 8-15%. In some embodiments, the sulfur content is in the range of 8-12%.
In some embodiments, the obtained coupling agent has a volatile content in the range of = 3.0.
In some embodiments, the obtained coupling agent has a specific gravity in the range of 1.0-1.1 g/cc.
In some embodiments, the obtained coupling agent has a pH in the range of 6-8 in 50% water. In an embodiment, the obtained coupling agent has pH is 7.
The present disclosure also relates to a rubber composition comprising the above disclosed cardanol modified coupling agent.
In accordance with various embodiments, the rubber composition comprises 2-5 parts per hundred rubber (‘phr’) of the disclosed coupling agent and 2.4-4 phr of an elastomer.
In various embodiments, the elastomer comprises a natural and/or synthetic rubber. In an embodiment, the elastomer is a diene elastomer selected from the group consisting of polybutadienes, polyisoprenes, natural rubber, butadiene-styrene copolymers, butadiene-isoprene copolymers, butadiene-acrylonitrile copolymers, isoprene-styrene copolymers, butadiene-styrene-isoprene copolymers, and a mixture thereof.
The rubber composition may include one or more suitable additives. Examples of such additives include, but are not limited to one or more of processing aid, antioxidant, antiozonant, filler, and accelerator.
Examples of the processing aid include but are not limited to a plasticizer, a tackifier, an extender, a chemical conditioner, and a homogenizing agent.
The filler may be one or more of a reinforcing filler. Examples of the reinforcing filler include but are not limited to carbon black and silica. In an embodiment, the reinforcing filler is carbon black. In some embodiments, carbon black is added in an amount in the range of 6-10 phr. In various embodiments, the reinforcing filler is silica. In some embodiments, silica is added in an amount in the range of 30-100 phr.
The accelerator is added to the rubber composition to control the time and/or temperature required for vulcanization and to improve the properties of the rubber composition. Examples of the suitable accelerator include but are not limited to sulfenamide, guanidine and thiuram. The accelerator may be added in an amount ranging between 2-10 phr.
In an embodiment, one or more of a curing agent is added to cause the vulcanization of the rubber composition. Any known curing agent may be employed. In accordance with an embodiment, the curing agent is a sulfur-based curing agent. In accordance with a related embodiment, the curing agent is added in an amount ranging between 1-4 phr.
The invention will now be described with respect to the following examples which do not limit the disclosed invention in any way and only exemplify the claimed invention. It will be apparent to those skilled in the art that various modifications and variations can be made to the coupling agent and the process of the present disclosure without departing from the scope of the disclosure. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein.

Examples

Example 1: Preparation of a cardanol modified coupling agent in accordance with an embodiment of the present disclosure.

In a four-necked reactor flask equipped with a reflux condenser, a temperature controller, a heating mantle, and a magnetic stirrer, 0.86 kg of 3-pentadecyl phenol ethoxylate and 0.08 kg of sulfur powder (0.08 kg) were charged and heated to 150 °C for 3 hours to obtain a first reaction mass. To the first reaction mass, 0.06 kg of toluene diisocyanate was added slowly. Thereafter, the reaction was allowed to continue at 150°C for 1 hour to obtain a second reaction mass. This second reaction mass was neutralized with ammonia to obtain 1 kg of the cardanol modified coupling agent. Table 1 provides characteristics of the obtained cardanol modified coupling agent.
Table 1: Characteristics of the Cardanol Modified Coupling Agent

S. No. Parameter Method Characteristic
1. Appearance - Brown liquid
2. Product conversion (%) HPLC 85%
3. pH in 50% water pH meter 7.5
4. Volatile matter, 105oC (%) Moisture balance 0.45

5. Specific gravity @ 25 °C (g/cc) Specific gravity bottle 1.03

6. Sulfur content (%) Carbon Hydrogen Nitrogen and Sulfur (‘CHNS’) analyser 10.5

FIG. 1 depicts the FTIR spectra of the obtained cardanol-modified coupling agent. The spectra indicate a peak in the region of 1710 cm-1 which indicates the formation of CONH linkage in the obtained cardanol modified coupling agent. A peak at 1050 cm-1 indicates C-N bond formation, and the peak at 750 cm-1 indicates sulfurization in the cardanol-modified coupling agent.

Table 2 provides characteristics of the commercially available TESPT.

Table 2: Characteristics of TESPT
S. No. Parameter Method Characteristic
1. Appearance - Yellow liquid
2. pH in 50% water pH meter 5.14
3. Volatile matter, 105oC (%) Moisture balance 0.48

4. Specific gravity @ 25 °C (g/cc) Specific gravity bottle 1.018

5. Sulfur content (%) CHNS Analyser 25.5

Example 2: Preparation of silica samples to test the binding of silica to the coupling agent.

The following samples were prepared:
1. Sample 1: Virgin silica (Control).
2. Sample 2: 95% of silica and 5% of the sulfurized 3-pentadecyl phenol ethoxylate (SPPE).
3. Sample 3: 95% of silica and 5% of the cardanol based coupling agent of Example 1.
4. Sample 4: 95% of silica and 5% of TESPT.

Samples 1-4 were analysed for sear number. Fig. 2 depicts the sears number of samples 1-4. The results are provided in Table 3.

Table 3: Sears Number of Samples 1-4

Sample Sears Number, ml/5g
Sample 1 25.4
Sample 2 22.8
Sample 3 19.8
Sample 4 20

Example 3: Preparation of rubber compositions.

The rubber compositions listed in Table 4 were prepared:

Table 4: The Rubber Compositions

Ingredients Composition
Control Trial 1 Trial 2 Trial 3
Synthetic Rubber Styrene Butadiene (‘SSBR’) 80.00 80.00 80.00 80.00
Polybutadiene Rubber (‘PBD’) 20.00 20.00 20.00 20.00
Silica 80.00 80.00 80.00 80.00
Carbon N234 8.0 8.0 8.0 8.0
ARTEC 8000 IPOL GP Petroleum 20.0 20.0 20.0 20.0
TESPT 8.0 5.6 4.0 0.0
Cardanol modified coupling agent 0.0 2.4 4.0 8.0
Zinc oxide (ZnO) 2.5 2.5 2.5 2.5
Stearic acid 1.5 1.5 1.5 1.5
Coumaron Indene Resin (‘CIR’) 6.0 6.0 6.0 6.0
Microcrystalline (‘MC’) wax 1.0 1.0 1.0 1.0
Struktol 40 MS 2.0 2.0 2.0 2.0
N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (‘6PPD’) 2.0 2.0 2.0 2.0
Trimethyl-quinoline (‘TMQ’) 0.75 0.75 0.75 0.75
Sulfur 2.0 2.0 2.0 2.0
Tetrabenzylthiuram disulfide (‘TBzTD’) 0.2 0.2 0.2 0.2
N-tert-. -butyl-2-benzothiazyl sulphenamide (‘TBBS’) 1.5 1.5 1.5 1.5
Diphenylguanidine (‘DPG’) 2.0 2.0 2.0 2.0

Note: All quantities are in phr.

The mixing of the ingredients for each of the above compositions was carried out in a 1.6-liter (Bainite make, Model MB Series 1.6 L IM RES-O-LAB) mixer with a fill factor of 63%. The mixing started at a temperature of around 55-57 °C. The dumping temperature was maintained at 158±2°C. The RAM pressure was 20 kg.

In stage 1, for the initial 30 seconds, the SSBR and PBD were masticated inside the mixer. Thereafter, in the next step, two third of silica, two third of ARTEC 8000, two third of coupling agent along with stearic acid and MC wax, were mixed for 60 seconds at a rotor speed of 65 rpm. Further in the next step, one third of silica, one third of ARTEC 8000, one third of coupling agent, along with 6PPD, TMQ, carbon black, CIR, and ZnO were added and further mixed for 90 seconds at 65 rpm rotor speed to obtain a composition. After a clean sweep, the compositions were again mixed for 90 seconds at 65 rpm. After that, in the silanization stage, the compositions were again mixed at a constant temperature between 158 and 160°C by varying the rpm of the rotor. Finally, the composition was dumped at a temperature of 158 ± 2 °C. During this stage, the rotor speed was varied between 50-70 rpm to achieve the dump temperature. The obtained compositions were analysed for Mooney viscosity and Payne effect. The values of Mooney viscosity and Payne effect were very high. Therefore, in stage 2, a repass cycle was carried out for the prepared compositions. The compositions were again mixed for 60 seconds at 55 rpm, followed by cleaning, and then again mixed for 120 seconds at 55 rpm and finally dumped at a temperature below 150°C.

Table 5: Mixing Sequence
Fill Factor: 63 TCU Temp: 55°C Ram Pressure: 20 kg
Stage 1: Master Cycle
Mixing Steps Step
time (sec) Total Time
(sec) Rotor speed
(rpm)
Step 1 Addition of rubber - 0 25
Step 2 Mastication of rubber 30 - 65
Step 3 Addition of 2/3 (silica + ARTEC 800 + coupling agent) + stearic acid + MC wax - 30 25
Step 4 Mixing 60 - 65
Step 5 Addition of 1/3 (silica + ARTEC 8000 + coupling agent) + TMQ + 6PPD + Carbon black +CIR+ ZnO - 90 25
Step 6 Mixing 60 - 65
Step 7 Sweep/clean - 150 25
Step 8 Mixing 90 65
Step 9 Sweep/clean - 240 25
Step 10 Mixing for silanization reaction 150 - Temperature between 155-160°C by varying the rpm
Stage 2: Repass Cycle
Step 11 Dump - 390 Dump at 158±2°C
Step 12 Shearing of composition 60 - 55
Step 13 Sweep/clean - 60 25
Step 14 Shearing 120 - 55
Step 15 Dump - 180 Dump below 150°C

The mixing of the compositions was continued on an open two-roll mill (12 X 16”) at room temperature, with friction ratio of 1:1.25. Thereafter, TBBS and sulfur was added, while keeping the nip gap approximately 1mm. The obtained compositions were masticated for 4-6 minutes. For the control and trial 1-3, a final sheet was taken out from approximately 3.8 mm nip gap. Control and Trial 1-3 compositions were conditioned for 24 hours at room temperature and then submitted for characterization.
Example 4: Properties of the rubber compositions
The rubber compositions of Example 3 were tested for various properties as discussed below.

1. Processing properties: The rubber compositions were characterized for processing properties such as Mooney viscosity, Mooney scorch time and Payne effect. The properties are listed in Table 6.
Table 6: Processing Properties
Properties Unit Composition
Control Trial 1 Trial 2 Trial 3
Mooney viscosity ML (1+4)@100°C MU 86 81 80 79
Mooney scorch time, T5 @ 125°C mins 4 4 4 3
?G’, Payne effect KPa 590 480 490 769

2. Rheological properties: The rubber compositions were tested for rheological properties such as scorch time, cure time, delta torque and Cure Rate Index (‘CRI’). The results are provided in Table 7.

Table 7: Rheological Properties
Properties Unit Composition
Control Trial 1 Trial 2 Trial 3
Scorch time ts2 @160°C Min 1.1 1.1 1.1 0.7
Cure time TC90 @ 160°C Min 29.0 29.7 30.4 36.7
Delta torque Lb-in 16.2 15.1 14.2 21.1
CRI =100/(TC90-ts2) min-1 3.56 3.50 3.46 2.78

Example 5: Preparation of vulcanized rubber compositions
The rubber compositions of Example 3 were cured at 160°C for the time given in Table 8 below to prepare vulcanized Control composition and vulcanized Trial 1-3 compositions.
Table 8: Curing Time
Composition Curing Time
Control 35
Trial 1 35
Trial 2 35
Trial 3 40

Example 6: Properties of the vulcanized rubber compositions
The vulcanized rubber compositions of example 5 were tested for various properties as discussed below.
1. Modulus properties: The vulcanized rubber compositions were characterized for modulus at various strains before and after aging at 100°C for 48 hours in an air oven. The results are provided in Table 9.

Table 9: Modulus at Various Strains Before and After the Aging

Modulus Before/After Aging Unit Composition
Vulcanized Control Vulcanized Trial 1 Vulcanized Trial 2 Vulcan-ized Trial 3
M @50% Before Kg/cm2 28.4 25.4 22.8 22.4
M @100% 58.2 55.8 53.0 39.0
M @200% 116.5 115.4 118.0 81.4
M @300% - - - 114.0
M @50% After 26.0 23.0 22.7 23.6
M @100% 62.5 58.8 59.7 47.4
M @200% - - - 104.4

2. Performance properties: The vulcanized rubber compositions were tested for performance properties such as tensile strength, elongation, tear strength, and hardness at various strains before and after aging at 100°C for 48 hours in air oven. The results are provided in Table 10.

Table 10: Performance Properties

Property Before/After Aging Unit Composition
Vulcanized Control Vulcanized Trial 1 Vulcanized Trial 2 Vulcanized Trial 3
Tensile strength Before Kg/cm2 129.2 140.0 143.8 126.6
Elongation % 220.0 234.0 262.0 362.0
Tear strength Kg/cm 40.0 48.7 43.0 53.3
Hardness Shore A 71.6 69.4 69.4 69.6
Tensile strength After Kg/cm2 123.8 141.0 126.3 131.6
Elongation % 155 194.0 170.0 226
Tear strength Kg/cm 34.3 44.7 38.3 45.7
Hardness Shore A 78.3 77.6 74.6 71.6

3. Abrasion Resistance Index (‘ARI’): The vulcanized rubber compositions were tested for ARI. The results are provided in Table 11.

Table 11: Abrasion Resistance Index
Property Unit Composition
Vulcanized Control Vulcanized Trial 1 Vulcanized Trial 2 Vulcanized Trial 3
ARI % 100 112 116 127

Fig.3 shows the abrasion, grip, and rolling resistance of the vulcanized Control and vulcanized Trial 1-3 compositions.

4. Demattia-cut initiation: The vulcanized Control and vulcanized Trial 1-3 compositions were tested for Demattia-cut initiation. The results are provided in Table 12.
Table 12: Demattia -Cut Initiation
Property Unit Composition
Vulcanized Control Vulcanized Trial 1 Vulcanized Trial 2 Vulcanized Trial 3
Demattia-cut initiation Number of cycles 4200 7100 6600 3500

5. Dynamic mechanical analysis: The vulcanized Control composition and vulcanized Trial 1-3 compositions were tested for dynamic mechanical analysis. The results are provided in Table 13.

Table 13: Dynamic Mechanical Analysis
Property Unit Composition
Vulcanized Control Vulcanized Trial 1 Vulcanized Trial 2 Vulcanized Trial 3
Storage modulus (E') @25oC MPa 14.2 13.6 9.30 22.30
Tan d @ 0oC -- 0.366 0.378 0.437 0.320
Tan d @ 60oC -- 0.147 0.139 0.153 0.173

Example 7: Dispersion study
The dispersion studies of the vulcanized Control composition and vulcanized Trial 1 composition were carried out according to ISO 11345 standards on the scale of 1 to 10 as indicted in Table 14 below. Normally, the Visual Dispersion Rating (‘VDR’) indicates the dispersion of the filler in the rubber compound.
Table 14: VDR
VDR Dispersion
9-10 Excellent
8 Good
7 Acceptable
5-6 Doubtful
3-4 Poor
1-2 Very poor

This test was carried out by Scanning Electron Microscope (‘SEM’), X100 magnification. For this test, samples were prepared by cutting thin section from the Control vulcanized composition and vulcanized Trial 1 composition and exposed to the SEM. The obtained SEM images was compared. Fig. 4 shows the SEM images of the vulcanized Control composition and vulcanized Trial 1 composition. The observed rating is given in Table 15 below.
Table 15: VDR
Composition VDR Dispersion
Vulcanized Control 7-8 Good
Vulcanized Trial 1 8-9 Excellent

INDUSTRIAL APPLICATION
The disclosed cardanol coupling agent is economical and industrially viable. It incorporates bio-based raw materials and is environment-friendly. It generates less or no VOCs during rubber compounding. It also enhances the dispersion of silica in rubber compositions. Further, it provides improved dynamic and static mechanical properties in comparison to the SCAs. The rubber compositions prepared using the disclosed coupling agent exhibit improvement in properties such as tensile strength, tear strength, elongation break, comparable hardness, improved abrasion resistance, and dynamic storage modulus. , Claims:1. A cardanol based coupling agent obtained by:
reacting 3-pentadecyl phenol ethoxylate with sulfur to obtain a sulfurized 3-pentadecyl phenol ethoxylate, and
reacting the sulfurized 3-pentadecyl phenol ethoxylate with a diisocyanate compound.
2. The coupling agent as claimed in claim 1, wherein the reaction of 3-pentadecyl phenol ethoxylate with sulfur is carried out at a temperature in the range of 100-180 ºC.
3. The coupling agent as claimed in any of the preceding claims, wherein the reaction of the sulfurized 3-pentadecyl phenol ethoxylate with the diisocyanate compound is carried out at a temperature in the range of 110-170 ºC.
4. The coupling agent as claimed in any of the preceding claims, wherein sulfur is a powdered sulfur.
5. The coupling agent as claimed in any of the preceding claims, wherein the diisocyanate compound is selected from the group consisting of toluene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, and isophorone diisocyanate.
6. The coupling agent as claimed in any of the preceding claims, wherein the agent is obtained by:
reacting 80-90 wt.% of 3-pentadecyl phenol ethoxylate with 8-15 wt.% of sulfur to obtain the sulfurized 3-pentadecyl phenol ethoxylate, and
reacting 90-98 wt.% of the sulfurized 3-pentadecyl phenol ethoxylate with 4-8% of the diisocyanate compound.
7. The coupling agent as claimed in any of the preceding claims, wherein 3-pentadecyl phenol ethoxylate is obtained by reacting 30-90 wt.% of cardanol oil and 25-70 wt.% of ethylene oxide at a temperature in the range of 100-160 oC.
8. The coupling agent as claimed in claim 7, wherein cardanol oil and ethylene oxide are reacted in the presence of a base selected from the group consisting of sodium hydroxide, potassium hydroxide, sodium methoxide, sodium hydride, and tetrabutyl ammonium hydroxide.
9. The coupling agent as claimed in any one of the preceding claims, having:
a) a sulfur content in the range of 8-15%;
b) a volatile matter in the range of = 3.0;
c) a specific gravity in the range of 1.0-1.1 g/cc; and
d) a pH in 50% water in the range of 6.0-8.0.
10. The coupling agent as claimed in claim 1 represented by one or more of Formula 1-5:

Formula 1

Formula 2

Formula 3

Formula 4

Formula 5

wherein n is 1-14; and
R1 is independently alkylene, substituted alkylene, arylene, substituted arylene or cyclic ketone.
11. The coupling agent as claimed in claim 10, wherein n is 5-12 and R1 is independently pentamethylene, hexamethylene, isophorone, or toluene.
12. A process for preparing a cardanol based coupling agent, said process comprising:
reacting 3-pentadecyl phenol ethoxylate with sulfur to obtain a sulfurized 3-pentadecyl phenol ethoxylate, and
reacting the sulfurized 3-pentadecyl phenol ethoxylate with a diisocyanate compound.
13. The process as claimed in claim 12, wherein the reaction of 3-pentadecyl phenol ethoxylate with sulfur is carried out at a temperature in the range of 100-180 ºC.
14. The process as claimed in claim 12, wherein the reaction of the sulfurized 3-pentadecyl phenol ethoxylate with the diisocyanate compound is carried out at a temperature in the range of 110-170 ºC.
15. The process as claimed in any of the preceding claims, wherein sulfur is a powdered sulfur.

16. The process as claimed in any of the preceding claims, wherein the diisocyanate compound is selected from the group consisting of toluene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, and isophorone diisocyanate.
17. The process as claimed in any of the preceding claims, wherein the process comprises:
reacting 80-90 wt.% of 3-pentadecyl phenol ethoxylate with 8-15 wt.% of sulfur to obtain the sulfurized 3-pentadecyl phenol ethoxylate, and
reacting 90-98 wt.% of the sulfurized 3-pentadecyl phenol ethoxylate with 4-8% of the diisocyanate compound.
18. The process as claimed in any one of the preceding claims, wherein 3-pentadecyl phenol ethoxylate is obtained by reacting 30-90 wt.% of cardanol oil and 25-70 wt.% of ethylene oxide at a temperature in the range of 100-160 oC.
19. The process as claimed in claim 18, wherein cardanol oil and ethylene oxide are reacted in the presence of a base selected from the group consisting of sodium hydroxide, potassium hydroxide, sodium methoxide, sodium hydride, and tetrabutyl ammonium hydroxide.
20. The process as claimed in any of the preceding claims, comprising neutralizing the coupling agent by adding an acid or a base.
21. The process as claimed in any of the preceding claims, wherein the coupling agent is represented by one or more of Formula 1-5:

Formula 1

Formula 2

Formula 3

Formula 4

Formula 5

wherein n is 1-14; and
R1 is independently alkylene, substituted alkylene, arylene, substituted arylene or cyclic ketone.

22. The process as claimed in claim 22, wherein n is 5-12 and R1 is independently pentamethylene, hexamethylene, isophorone, or toluene.
23. A rubber compound composition comprising the cardanol based coupling agent as claimed in claim 1 and an elastomer.
24. The rubber composition as claimed in claim 23, wherein the elastomer is selected from a group consisting of polybutadienes, polyisoprenes, natural rubber, butadiene-styrene copolymers, butadiene-isoprene copolymers, butadiene-styrene-isoprene copolymers and a mixture thereof.
25. The rubber compound composition as claimed in claim 24, further comprising one or more additives selected from the group consisting of a processing aid, an antioxidant, an antiozonant and a filler.