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 composite, 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, which is 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 VOC 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 carbonyl 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 carbonyl 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 compositions.
FIG. 3 depicts the abrasion, grip, and rolling resistance of vulcanized Control and 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 one 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 carbonyl 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 carbonyl 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 various 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%.
In various embodiments, the carbonyl compound is an anhydride or an acid.
In accordance with an embodiment, the carbonyl compound is an anhydride. In some embodiments, the anhydride is maleic anhydride.
In accordance with an embodiment, the carbonyl compound is an acid. In various embodiments, the acid is cinnamic acid, glutaconic acid, or itaconic acid.
In accordance with some embodiments, 80-90 wt.% of 3-pentadecyl phenol ethoxylate is reacted with 5-15 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 accordance with various embodiments, 90-98 wt.% of the sulfurized 3-pentadecyl phenol ethoxylate is reacted with 4-8 wt.% of the carbonyl compound to obtain the disclosed coupling agent. In accordance with some embodiments, 92-96 wt.% of the sulfurized 3-pentadecyl phenol ethoxylate is reacted with 5-7% of the carbonyl 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 100-160 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 some embodiments, 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 6.0-8.0 in 50% water. In an embodiment, the pH is 6.9.
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 –

In some embodiments n is 5-12.
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 carbonyl 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 carbonyl 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 some embodiments, the purity is in the range of 95-98%.
In various embodiments, the carbonyl compound is an anhydride or an acid.
In accordance with some embodiments, the carbonyl compound is an anhydride. In an embodiment, the anhydride is maleic anhydride.
In accordance with some embodiments, the carbonyl compound is an acid. In various embodiments, the acid is cinnamic acid, glutaconic acid, or itaconic acid.
In various embodiments, the process comprises reacting 80-90 wt.% of 3-pentadecyl phenol ethoxylate with 5-15 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 carbonyl compound. In some embodiments, the process comprises reacting 84-88 wt.% of 3-pentadecyl phenol ethoxylate with 8-12 wt.% of sulfur to obtain the sulfurized 3-pentadecyl phenol ethoxylate and reacting 92-96 wt.% of the sulfurized 3-pentadecyl phenol ethoxylate is reacted with 5-7% of the carbonyl compound to obtain the disclosed coupling agent.
In various 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 100-160 oC.
In an embodiment, cardanol oil and ethylene oxide are reacted in the presence of one or more 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. Examples of the suitable acid include but are not limited to acetic acid, hydrochloric acid, and/or sulphuric acid. Examples of the suitable base include but are not limited to 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 –

In some embodiments, n is 5-12.
In some 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 various embodiments, the obtained cardanol based coupling agent has a volatile content in the range of = 3.0.
In various embodiments, the obtained cardanol based coupling agent has a specific gravity in the range of 1.0-1.1 g/cc.
In some embodiments, the obtained cardanol based coupling agent has a pH in the range of 6.0-8.0 in 50% water. In an embodiment, the pH is 6.9.
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 a 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 additives. Examples of such additives include but are not limited to one or more of a processing aid, an antioxidant, an antiozonant, a filler and an 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 filler. Carbon black may be added in an amount in the range between 6-10 phr. In an embodiment, the reinforcing filler is silica. Silica may be added in an amount in the range between 30-100 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 2-10 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 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, the process, and the compositions 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 3000 millilitre reactor flask equipped with a reflux condenser, temperature controller, heating mantle, and magnetic stirrer, 0.84 kg of 3-pentadecyl phenol ethoxylate and 0.10 kg of sulfur powder were charged and heated to 150 °C for 3 hours to obtain a reaction mass. To the obtained reaction mass, 0.06 kg of maleic anhydride was added slowly. Post-complete addition of the maleic anhydride, the reaction was allowed to continue at 150 °C for 1 hour to obtain a second reaction mass. The second reaction mass was neutralized with ammonia to obtain 1 kg of the cardanol modified coupling agent. Table 1 provides characteristics of the cardanol modified coupling agent obtained above.
Table 1: Characteristics of the Cardanol Modified Coupling Agent

S. No. Parameter Method Characteristic
1. Appearance - Brown liquid
2. Purity (%) HPLC 85%
3. pH in 50% water pH meter 6.9
4. Volatile Matter, 105oC (%) Moisture balance 0.25

5. Specific Gravity @ 25 °C (g/cc) Specific gravity bottle 1.04

6. Sulfur content (%) Carbon Hydrogen Nitrogen Sulfur (‘CHNS’) Analyser 11

Fig. 1 depicts the FTIR spectra of the obtained cardanol-modified coupling agent. The spectra indicate a peak in the region of 1702 cm-1 which indicates the formation of COOC linkage in the obtained cardanol modified coupling agent. A peak at 695 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, 105 oC (%) 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 Si69.
Samples 1-4 were analysed for sear number. Fig. 2 depicts the sear number of samples 1-4. The results are provided in Table 3.
Table 3: Sear Number of Samples 1-4
Sample Sears Number, ml/5g
Sample 1 25.4
Sample 2 22.8
Sample 3 20.4
Sample 4 20
Example 3: Preparation of rubber compositions.

The rubber compositions listed in Table 4 were prepared:

Table 4: Ingredients for the Rubber Compositions

Ingredients Composition
Control Trial 1
Solution Styrene Butadiene Rubber (‘SBR’) (clear) 75 75
Polybutadiene Rubber (‘PBD’) 25 25
Silica 65 65
Carbon N234 5 5
ARTEC 8000 IPOL GP Petroleum 8 8
Standard TESPT 6.5 0.0
30:70 mixture of cardanol coupling agent obtained in Example 1: TESPT 0.0 6.5
Stearic acid 2 2
Microcrystalline
(‘MC’) wax 2 2
Zinc oxide (‘ZnO’) 2.5 2.5
N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (‘6PPD’) 2 2
Trimethyl-quinoline (‘TMQ’) 0.5 0.5
Sulphur 2 2
N-cyclohexylbenzothiazole-2-sulphenamide
(‘CBS’) 2 2
Tetrabenzylthiuram disulfide (‘TBzTD’) 1.7 1.7
Diphenylguanidine (‘DPG’) 2 2
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 74%. The mixing started at a temperature of around 50-55 °C. The dumping temperature was maintained at 155±2°C. The Ram pressure was 20 kg.
In stage I, for the initial 6 minutes SBR and PBD along with silica, coupling agent, carbon black, ARTEC 8000 IPOL GP Petroleum, stearic acid, and MC wax is masticated at a speed of 40-60 RPM to prepare a master composition. In stage II, 6PPD, TDQ, and ZnO are added to the master composition and further masticated in stage III for 3 to 4 minutes till the dumping temperature of 155±2°C. During this process speed is varied between 50-70 rpm to achieve the dumping temperature. The mixing sequence is given in the Table 5 below.

Table 5: Mixing Sequence

Mixing Stage Time Temperature Activity
I 0 min 50-55 °C Polymer + silica + coupling agent + carbon black + stearic acid + MC wax
II 7 min 80-105 °C 6PPD + TDQ + ZnO
III 10 min - Master batch dumping between 9th to 10th minute at 155±2°C

The mixing of the compositions was continued in an open two-roll mill, lab mill (12 X 16”) at room temperature, with friction ratio of 1:1.25. Thereafter CBS and sulphur were added, while keeping the nip gap is kept approx. 1mm. The obtained compositions were masticated for 4-6 minutes. For the Control and Trial 1 compositions, a final sheet was taken out from approximately 3.8 mm nip gap. Control and Trial 1 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 characterized for processing properties such as Mooney viscosity, Mooney scorch time, cure time and Payne effect. The properties are listed in Table 6.

Table 6: Processing Properties
Properties Unit Composition
Control Trial 1
Scorch Time ts2 @ 160 oC mins 1.1 1.0
Cure time ts90 mins 17.4 16.8
Mooney Viscosity Mooney Units (MU) 80 91
Mooney Scorch Time, T5 @ 125 oC mins 4 4
?G’, Payne Effect KPa 617 599

Example 5: Preparation of vulcanized rubber compositions
The rubber compositions of Example 3 were cured at 160 °C for the time given in Table 7 below to prepare vulcanized Control composition and vulcanized Trial 1 composition.

Table 7: Curing Time
Composition Curing Time
Control 19
Trial 1 18

Example 6: Properties of 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 80 °C for 7 days in an air oven. The results are provided in Table 8.

Table 8: Modulus at Various Strains Before and After the Aging
Properties Before/After Aging Unit Vulcanized Control Vulcanized Trial 1
M @ 50% Before Kg/cm2 15 14
M @ 100% 37 27
M @ 200% 91 79
M @ 50% After 26 22
M @ 100% 48 46
M @ 200% 122 119

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 80 °C for 7 days in air oven. The results are provided in Table 9.

Table 9: Performance Properties

Properties Before/After Aging Unit Composition
Vulcanized Control Vulcanized Trial 1
Tensile strength Before Kg/cm2 109 134
Elongation % 220 250
Tear strength Kg/cm 45 50
Hardness Shore A 70 69
Tensile strength After Kg/cm2 103 129
Elongation % 150 210
Tear strength Kg/cm 45 51
Hardness Shore A 74 70

3. Abrasion Resistance Index (‘ARI’): The ulcanized rubber compositions were tested for ARI. The results are provided in Table 10.

Table 10: Abrasion Resistance Index
Properties Unit Composition
Vulcanized Control Vulcanized Trial 1
ARI % 225 202

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

4. Dynamic mechanical analysis: The vulcanized rubber compositions were tested for dynamic mechanical analysis. The results are provided in Table 11.

Table 11: Dynamic Mechanical Analysis
Properties Unit Composition
Vulcanized Control Vulcanized Trial 1
Tan d @ 0 oC -- 0.275 0.300
Tan d @ 60 oC -- 0.0788 0.0774

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, 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 carbonyl 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 carbonyl 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 carbonyl compound is an anhydride or an acid.
6. The coupling agent as claimed in claim 5, wherein the anhydride is maleic anhydride.
7. The coupling agent as claimed in 5, wherein the acid is selected from the group consisting of cinnamic acid, glutaconic acid, and itaconic acid.
8. 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 5-15 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 wt % of the carbonyl compound.
9. 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.
10. The coupling agent as claimed in claim 9, wherein cardanol oil and ethylene oxide are reacted in the presence of one or more base selected from the group consisting of sodium hydroxide, potassium hydroxide, sodium methoxide, sodium hydride, and tetrabutyl ammonium hydroxide.
11. 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;
d) pH in 50% water in the range of 6.0-8.0;
e) purity in the range of 80-98%.
12. 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

13. The coupling agent as claimed in claim 12, wherein n is 1-14 and R1 is independently -

14. 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 carbonyl compound.
15. The process as claimed in claim 14, wherein the reaction of 3-pentadecyl phenol ethoxylate with sulfur is carried out at a temperature in the range of 100-180 ºC.
16. The process as claimed in claim 14, wherein the reaction of the sulfurized 3-pentadecyl phenol ethoxylate with the carbonyl compound is carried out at a temperature in the range of 100-170 ºC.
17. The process as claimed in any of the preceding claims, wherein sulfur is a powdered sulfur.
18. The process as claimed in any of the preceding claims, wherein the carbonyl compound is an anhydride or an acid.
19. The process as claimed in any of the preceding claims, wherein the anhydride is maleic anhydride.
20. The process as claimed in any of the preceding claims, wherein the acid is selected from the group consisting of cinnamic acid, glutaconic acid, and itaconic acid.
21. The process as claimed in any of the preceding claims, wherein the process comprising:
reacting 80-90 wt.% of 3-pentadecyl phenol ethoxylate with 5-15 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 wt.% of the carbonyl compound.
22. 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.
23. The process as claimed in claim 22, wherein cardanol oil and ethylene oxide are reacted in the presence of one or more of a base selected from the group consisting of sodium hydroxide, potassium hydroxide, sodium methoxide, sodium hydride, and tetrabutyl ammonium hydroxide.
24. The process as claimed in any of the preceding claims, comprising neutralizing the coupling agent by adding an acid or a base.
25. The process as claimed in 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

26. The process as claimed in claim 25, wherein n is 1-14 and R1 is independently

27. A rubber compound composition comprising the cardanol based coupling agent as claimed in claim 1 and an elastomer.
28. The rubber composition as claimed in claim 27, wherein the elastomer is selected from the group consisting of polybutadienes, polyisoprenes, natural rubber, butadiene-styrene copolymers, butadiene-isoprene copolymers, butadiene-styrene-isoprene copolymers, and a mixture thereof.
29. The rubber compound composition as claimed in claim 28 further comprising one or more additives selected from the group consisting of a processing aid, an antioxidant, an antiozonant, a filler, and an accelerator.