Description:FIELD OF THE INVENTION
The present disclosure relates to a graphite silica composite. The present disclosure also relates to a method for the preparation of graphite silica composite.
BACKGROUND
Rubber is a natural polymer that that finds use in a wide variety of applications. Natural rubber is soft and lacks sufficient strength for applications such as tires. To improve its properties, such as strength, stiffness etc., filles are added to natural rubber. Currently, highly dispersible grade silica products along with petroleum-based carbon black are being used as reinforcing filler in tire and rubber applications. Both these fillers have spherical morphology with a very wide range of particle properties such as BET surface area, CTAB surface area, Sears number value, DOA absorption value, particle size distribution etc. There is a need to reduce carbon content in rubber compounding for tyre industry.
SUMMARY
A graphite silica composite is provided. The graphite silica composite comprising graphite, poly(diallyldimethylammonium) chloride, and silica wherein the ratio of graphite: poly(diallyldimethylammonium) chloride: silica is in a range of 0.5:1:100 to 10:1:100.
A process of preparing a graphite silica composite is also provided. The process comprises preparing an aqueous dispersion of graphite-poly(diallyldimethylammonium) chloride; mixing the aqueous dispersion of graphite-poly(diallyldimethylammonium) chloride and graphite powder to obtain an aqueous dispersion of graphite-poly(diallyldimethylammonium) chloride; mixing the aqueous dispersion of graphite-poly(diallyldimethylammonium) chloride, and an aqueous precipitated silica slurry at high shear mix, to obtain a slurry of graphite silica composite; and drying the slurry of graphite silica composite.

DETAILED DESCRIPTION
For the purpose of promoting an understanding of the principles of the disclosure, reference will now be made to embodiments and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby intended, such alterations and further modifications in the disclosed composition and method, and such further applications of the principles of the disclosure therein being contemplated as would normally occur to one skilled in the art to which the disclosure relates.
It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the disclosure and are not intended to be restrictive thereof.
Reference throughout this specification to “one embodiment”, “an embodiment” 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 disclosure. Thus, appearances of the phrase “in one embodiment”, “in an embodiment” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.
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.
The present disclosure relates to a graphite silica composite comprising of graphite, Poly(diallyldimethylammonium) chloride, and silica wherein the ratio of graphite: Poly(diallyldimethylammonium) chloride : silica is in a range of 0.5:1:100 to 10:1:100.
In an aspect, the BET surface area of the graphite silica composite is in a range of 170-210 m2/g. The Sears number of the graphite silica composite is in a range of 14 to 28 ml/5gram.
In an embodiment, the sears number of the graphite silica composite is at least 2 to 3 units lower than the silica. In an embodiment, the zeta potential value of the graphite silica composite is at least 10 to 15 mV more than the silica.
The present disclosure also provides a process of preparing a graphite silica composite. The process comprises of
- preparing an aqueous dispersion of Poly(diallyldimethylammonium) chloride;
- mixing the aqueous dispersion of Graphite-Poly(diallyldimethylammonium) chloride and graphite powder to obtain an aqueous dispersion of Graphite-Poly(diallyldimethylammonium) chloride (PDDAC);
- mixing the aqueous dispersion of Graphite-Poly(diallyldimethylammonium) chloride (PDDAC) and an aqueous precipitated silica slurry at high shear mix, to obtain a slurry of graphite silica composite; and
- drying the slurry of graphite silica composite.
In accordance with an aspect, the amount of Graphite-Poly(diallyldimethylammonium) chloride is in a range of 1.5 to 11% with respect of solid content in the silica slurry. Alternatively, the ratio of Graphite-Poly(diallyldimethylammonium) chloride: silica is in a range of 1.5:100 to 11:100 In an embodiment, the aqueous dispersion of Graphite-Poly(diallyldimethylammonium) chloride is prepared by dissolving 1% of Poly(diallyldimethylammonium) chloride (PDDAC) (with respect to silica solid content in silica slurry) in water.
In accordance with an aspect, the amount of graphite powder (with respect to silica solid content) is in a range of 0.5 to 10% with respect of solid content in the silica slurry. Alternatively, the ratio of graphite powder: silica is in a range of 0.5:100 to 10:100. In an embodiment, the 5% graphite powder (with respect to silica solid content) is used.
The graphite powder may be obtained from either synthetic sources or natural sources. The graphite powder has a BET surface area in a range of 5 to 50 m2/g, and a zeta potential in a range of -15 to -25(mV).
The silica has a BET surface area in a range of 150 to 220 m2/g, a sears number in a range of 15-35 ml/5g, and a zeta potential in a range of -20 to -40 (mV).
In accordance with an aspect the aqueous precipitated silica slurry and the homogeneous aqueous graphite-PDDAC dispersion is mixed in high shear mix at 500 to 2500 rpm at room temperature for a period of 10 minutes to 30 minutes. In an embodiment, the aqueous precipitated silica slurry and the homogeneous aqueous graphite-PDDAC dispersion is mixed in high shear mix at 1500 rpm for 15 minutes.
The pH of the slurry is maintained at 3-6.5. The pH of the slurry is maintained between 3 to 6.5 by addition of sulphuric acid or ammonia.
To obtain the powder of graphite silica composite, the slurry of graphite silica composite is dried such that the moisture is reduced to 2-7%. Any known method for drying may be used to obtain the powder of graphite silica composite. In an embodiment the slurry of graphite silica composite is dried by spay drying.
Examples.
A) Preparation of graphite-silica composite
Step-1: Preparation of aqueous dispersion of Graphite-Poly(diallyldimethylammonium) chloride (PDDAC): The aqueous dispersion of Graphite-Poly(diallyldimethylammonium) chloride (PDDAC) is prepared by dissolving 1% of Poly(diallyldimethylammonium) chloride (PDDAC) (with respect to silica solid content in silica slurry) to 100ml of distilled water. Then 5% graphite powder (with respect to silica solid content) is added to the above PDDAC solution and mixed uniformly.
Step-2: Preparation of graphite-silica composite: To the aqueous precipitated silica slurry with a total silica content of 10-20%, the homogeneous aqueous graphite-PDDAC dispersion (disclosed in step 1 above) is added and mixed in high shear mix at 1500 rpm at room temperature for 15 minutes.
The pH of the slurry was maintained at 5.5-6.5 by addition of sulphuric acid or ammonia. The resultant slurry was then spray dried to a moisture content in a range of 2-7% to obtain the graphite-silica composite powder.
Post-synthesis, a detailed characterization of synthesized graphite silica composite was carried out. The properties were tabulated in the table 3 below.
The details of the chemicals used, including their properties are tabulated below.
Table 1: Properties of graphite:
Supplier IMERYS Graphite & Carbon
Product code TIMREX KS10 (TIMCAL graphite)
CAS number 7782-42-5
Properties Unit Value
Formula - Carbon
Form - Fine black powder
Ash % 0.06
Moisture % 0.1%
Crystallite height nm 80
Interlayer distance nm 0.3357
BET surface area m2/g 16
Particle size distribution (Hydro method) µm D10=2.5, D50=6.2, D90=12.5
Zeta potential mV -17.9 (±5.76)

Table 2: Properties of Poly(diallyldimethylammonium chloride):
Supplier Sigma Aldrich
Product code 522376-1L
CAS number 26062-79-3
Properties Unit Value
Formula (C8H16ClN)n
Form Liquid
Boiling point °C 100
Melting point °C = -2.8
Density 1.04
Table 3: Particle property of Bare silica (without graphite) and Graphite-silica composite
Properties Reference Test Method Units Observed Value
Bare silica Graphite-silica
Composite
Nitrogen surface area (BET) ISO 9277 m2/g 200 182
CTAB surface area ISO 5794-1G m2/g 193 177
DOA Absorption value (Powder) ASTM D6854 mL/100g 320 323
Sears Number Internal ml /5g 17.2 14.4
Moisture Internal % 4.35 5.37
pH ISO-787-9 - 6.74 6.45
Conductivity ISO 787-14 µS/cm 110 233
Zeta potential Internal mV -37.4 -18.6

B) Rubber compounding studies
Rubber compounding study was performed at a third party named Indian Rubber Manufacturers Research Association (IRMRA), located in Thane, Maharashtra, India. The SSBR was purchased from Zeon Corp. (Japan) for use in this study. Carbon black (N234) was used at 5phr in Formulation-1 composition only and in formulation-2, no carbon black was used with graphite silica composite for rubber compounding. A detailed formulation is shown in the below table.
Table 4: Formulation
Ingredients Formulation 1
Bare silica + carbon black Formulation 2
Graphite-silica composite
Solution SBR (clear) 75 75
PBD 25 25
Formulation 1 65 0
Formulation 2 0 65
Carbon black N234 5 0
TDAE Oil (IPOL Artec 8000) 8 8
SILANE COUPLING AGENT-Si 69 6.6 6.0
Stearic Acid 2 2
MC wax 2 2
ZnO 2.5 2.5
6PPD 2 2
TMQ 0.5 0.5
Process Aid (Struktol 40MS) 2 2
Insoluble Sulphur 2 2
TBBS 1.7 1.7
DPG 2 2

* All quantities in PHR (Parts Per Hundred Rubber)
B2. Rubber compounding (Mixing Sequence)
The mixing was carried out in a 1.6 ltr. (Bainite make, Model MB Series 1.6 L IM RES-O-LAB) mixer with fill factor 74%. Mixing starting temperature is 50-55°C and dumping temperature is 155±2°C, RAM pressure is 20kg. For initial 6 minutes polymer along with Silica, Coupling agent, Carbon black, Processing Oil, Stearic acid, and Wax is masticated at speed 40-60RPM. In second stage, 6PPD, TDQ and ZnO are added and further masticated for 3 to 4 minute till dumping temperature 155±2°C. During this process speed is varied between 50-70RPM to achieve the dumping temperature. The mixing sequence is given in the table 5below.
Table 5: Mixing sequence
Mixing Stage Time Temperature Activity
I 0 min 50-55°C Polymer + silica + coupling agent + carbon black + stearic acid + 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
Note: For graphite-silica composite rubber compounding (Formulation-2), no conventional carbon black is used during rubber compounding.
The final moulded and compounded batch was prepared in an open two-roll mill, Lab mill (12 X 16”) at room temperature, with friction ratio of 1:1.25. While adding accelerator and curatives nip gap is kept approx. 1mm and masticated for 4 to 6 minutes. For all compounds, final sheet was taken out from approximately 3.8mm nip gap. All compounds were conditioned for 24hrs at room temperature and then submitted for characterization. The compounded rubber processing studies are given below.
Table 6: Properties of un-vulcanized rubber compounds:
Properties UOM Formulation-1
Bare Silica with carbon black Formulation-2
Graphite-silica composite Observations
Scorch Time ts2 @ 160oC mins 1.00 1.00 Similar scorch safety at 160°C
Mooney Viscosity Mooney Units (MU) 88
92 Comparable Mooney viscosity
Mooney Scorch Time, T5 @ 125oC mins 4 4 Similar scorch safety at 125°C
?G’, Payne Effect KPa 525 479 Lower value indicates reduced filler-filler interactions & better filler dispersion in rubber matrix

For testing properties on vulcanized rubber compounds, rubber slab and other samples were cured at 160°C as per curing time given in the table below.
Table 7: Curing times
Sample Formulation-1
Bare Silica with carbon black Formulation-2
Graphite-Silica composite
Observations
Curing Time (mins) 24.8 24.5
Lower is better for production cycle

All the molded samples are free from visible defects. Molded samples were preconditioned at room temperature before further testing.
Table 8: Modulus at various strains before and after aging (80°C for 7 days in air oven)
Properties Before Aging
Or
After Aging UOM Formulation-1
Bare Silica with
carbon black Formulation-2
Graphite-silica composite
Modulus @ 50% Before Kg/cm2 22 24
Modulus @ 100% 43 48
Modulus @ 200% 121 115
Modulus @ 50% After 26 30
Modulus @ 100% 50 59
As can be observed from the table above, comparable to better modulus properties at 50 to 200% strain were obtained both before as well as after aging for the graphite-silica composite.
Table 9: Tensile Strength, Elongation, Tear Strength and Hardness at various strains before & after aging (80oC for 7 days in air oven)

Properties Before/After Aging? UOM Formulation-1
Bare Silica with carbon black Formulation-2
Graphite-Silica
Composite
Tensile Strength Before Kg/cm2 123 128
Elongation % 202 216
Tear Strength Kg/cm 47 47
Hardness Shore A 71 68
Tensile Strength After Kg/cm2 134 125
Elongation % 199 193
Tear Strength Kg/cm 41 58
Hardness Shore A 76 72
As can be seen from the table above, comparable to better physical properties such as tensile strength, elongation and tear strength was observed both before as well as after aging for the graphite-silica composite.
Table 10: Abrasion Resistance Index, Cut Initiation & Cut Growth and specific gravity
Properties UOM Formulation-1
Bare Silica with carbon black Formulation-2
Graphite-Silica
composite
Abrasion Resistance Index -- 177 173
De-Mattia Cut Initiation cycles 600 400
De-Mattia Cut Growth (Upto 12mm) cycles 3000 3500
Specific Gravity -- 1.18 1.17

Table 10 clearly indicates that better De-Mattia Cut Growth is observed for the graphite-silica composite with comparable abrasion resistance index.
Table 11:. Dynamic Mechanical Analysis
Properties UOM Formulation-1
Bare Silica with carbon black Formulation-2
Graphite-Silica
composite Observations
Tan d @ 0oC -- 0.225 0.243 Higher value indicates better wet grip
Tan d @ 60oC -- 0.096 0.088 Lower value indicates lower rolling resistance improving fuel efficiency therefore better fuel mileage

Table 11, clearly indicates that the use of graphite-silica composite, improved wet grip/traction as well as rolling resistance properties.
Thus, the disclosed graphite silica composite, has optimum properties and provides substantially better dispersibility in rubber compounds due to synergistic effect of graphite functionalized on silica surface which enhances the magic triangle properties and exhibits better tyre performance comparing to conventional silica-carbon black filler system.
INDUSTRIAL APPLICABILITY
The disclosed graphite-silica grade will be a single reinforcing filler system which will be able to replace the conventional petroleum carbon black from the conventional carbon black-silica filler system being used in tyre tread formulation. This disclosed composite has the desired particle properties like low Sears number with desired range of other key particle properties like BET surface area, CTAB surface area, pore volume, particle size distribution etc. The synergistic effect of graphite-silica composite with customized and controlled particle properties will have better reinforcing property in elastomer composition leading to enhance the end product performance.
Moreover, the process is very simple and does not require any complicated steps, such as heating etc. , Claims:1. A graphite silica composite comprising graphite, poly(diallyldimethylammonium) chloride, and silica wherein the ratio of graphite: poly(diallyldimethylammonium) chloride: silica is in a range of 0.5:1:100 to 10:1:100.
2. The graphite silica composite as claimed in claim 1, wherein the BET surface area of the graphite silica composite is in the range of 170-210 m2/g.
3. The graphite silica composite as claimed in claim 1, wherein the sears number of graphite silica composite is at least 2 to 3 units lower than the silica.
4. The graphite silica composite as claimed in claim 1, wherein the zeta potential value of graphite silica composite is at least 10 to 15 units more than the silica.
5. A process of preparing a graphite silica composite comprising:
- preparing an aqueous dispersion of graphite-poly(diallyldimethylammonium) chloride;
- mixing the aqueous dispersion of graphite-poly(diallyldimethylammonium) chloride and graphite powder to obtain an aqueous dispersion of graphite-poly(diallyldimethylammonium) chloride;
- mixing the aqueous dispersion of graphite-poly(diallyldimethylammonium) chloride, and an aqueous precipitated silica slurry at high shear mix, to obtain a slurry of graphite silica composite; and
- drying the slurry of graphite silica composite.
6. The process as claimed in claim 5, wherein the amount of graphite-poly(diallyldimethylammonium) chloride is in a range of 1.5 to 11% with respect of solid content in the silica slurry.
7. The process as claimed in claim 5, wherein the amount of graphite powder is in a range of 0.5 to 10% with respect of solid content in the silica slurry.
8. The process as claimed in claim 5, wherein the graphite powder has a BET surface area in a range of 5 to 50 m2/g, and a zeta potential in a range of -15 to -25(mV).
9. The process as claimed in claim 5, wherein the silica has a BET surface area in a range of 150 to 220 m2/g, a sears number in a range of 15-35 ml/5g, and a zeta potential in a range of -20 to -40 (mV).
10. The process as claimed in claim 5, wherein the aqueous precipitated silica slurry and the homogeneous aqueous graphite- graphite-poly(diallyldimethylammonium) chloride dispersion are mixed in high shear mix at 500 to 2500 rpm at room temperature for a period of 10 minutes to 30 minutes.
11. The process as claimed in claim 5, wherein the pH of the slurry is maintained at 3-6.5.
12. The process as claimed in claim 5, wherein the slurry of graphite silica composite is dried such that the moisture is reduced to 2- 7%.
13. A graphite silica composite obtained from the process as claimed in claims 5 to 12.
14. A reinforced rubber comprising the graphite silica composite as claimed in claims 1-4, wherein the amount of graphite silica composite is in a range of 20 parts per 100 rubber to 90 parts per 100 rubber.