STYRENE-BUTADIENE RUBBER (SBR)-NANOCARBON FILLED MASTERBATCHES AND USES THEREOF

Abstract

The present invention relates to the use of nanocarbon (carbon nanotubes and/or carbon nanofibers) in the preparation of reinforced (filled) styrene-butadiene rubber (SBR). Furthermore, the present invention relates to a method of preparing reinforced SBR master batches having nanocarbon as reinforcing agent wherein the nanocarbon is uniformly predispersed within the SBR, as well reinforced rubber compositions containing said reinforced SBR which have nanocarbon and carbon black as reinforcing agents, and to uses thereof.

Claims

1. A nanocarbon-reinforced styrene-butadiene rubber (SBR) masterbatch composition comprising less than 5 pphr (parts by weight per hundred parts by weight of SBR) of nanocarbon, wherein the nanocarbon has not been subjected to an acid treatment before incorporation into the SBR, wherein the composition is a liquid composition obtained by combining a liquid dispersion of the nanocarbon and liquid SBR in the form of a latex, and wherein the combined nanocarbon dispersion and SBR latex mixture is masticated.

2. A nanocarbon-reinforced styrene-butadiene rubber (SBR) masterbatch composition comprising from 0.5 to 4.5 pphr (parts by weight per hundred parts by weight of SBR) of nanocarbon, wherein the nanocarbon has not been subjected to an acid treatment before incorporation into the SBR, wherein the composition is a liquid composition obtained by combining a liquid dispersion of the nanocarbon and SBR in the form of a latex, and wherein the combined nanocarbon dispersion and SBR latex mixture is masticated.

3. The composition according to claim 1 wherein the nanocarbon is present as carbon nanotubes (CNT), and as CNTs having a length of less than 50 μm and/or an outer diameter of less than 20 nm.

4. The composition according to claim 1 wherein the SBR is E-SBR.

5. The composition according to claim 1 wherein the nanocarbon comprises from 0.5 to 4.0, pphr nanocarbon per 100 parts by weight of SBR.

6. The composition according to claim 1 wherein the SBR is in the form of a latex having a solid content of from 40% to 50%.

7. The composition according to claim 1 wherein the SBR is in the form of a latex having a total solid content of 45%, and a pH of 8.0, specific gravity of 1.0 and a boiling point of 100° C.

8. The composition according to claim 1 wherein the composition is masticated either before or after the addition of the aqueous nanocarbon dispersion to the SBR latex.

9. The SBR composition according to claim 1 wherein the mastication is mechanical mastication in the presence of one or more masticating agents, and optionally one or more chemical plasticizers, one or more nonionic dispersing agents, one or more homogenizing agents and mixtures and combinations thereof.

10. The SBR composition according to claim 8 wherein the mastication agent is one or more peptizing agents each independently present at a level of from 0.1 to 0.3 pphr.

11. A method of making a liquid nanocarbon-reinforced SBR masterbatch composition comprising: (i) providing a dispersion of nanocarbon in an aqueous medium, wherein the aqueous medium optionally comprises one or more surfactants; (ii) combining the dispersion of nanocarbon to a styrene butadiene rubber latex, (SBR latex); (iii) mixing on a 2-roll mill or in an internal mixer to provide a nanocarbon-reinforced SBR masterbatch; (iv) addition of one or more optional masticating agents and mastication in SBR latex-containing stage (ii) or (iii); wherein the nanocarbon is not subjected to an acid treatment before incorporation into the composition, and wherein the nanocarbon-reinforced SBR masterbatch composition comprises less than 5 pphr of nanocarbon relative amount in parts by weight per hundred parts by weight of SBR.

12. The method according to claim 11 wherein the pH of the nanocarbon dispersion and/or of the SBR latex is/are adjusted so that the difference between the pH values of the two components is less than 2 pH units.

13. The method according to claim 12 wherein the pH of the adjusted SBR latex is between pH 8.0 and pH 10.0.

14. The method according to claim 12 wherein the nanocarbon is carbon nanotubes (CNT) and wherein the SBR is E-SBR.

15. The method according to claim 11 wherein the concentration of the nanocarbon in the nanocarbon dispersion is from 1% to 5% by weight of the aqueous dispersion.

16. The method according to claim 11 wherein total level of surfactant present is from 5% to 20% by weight of the added aqueous component.

17. The method according to claim 11 wherein the composition is a dry composition obtained by coagulating the masticated liquid nanocarbon filled SBR latex composition and drying the coagulate.

18. The method according to claim 17 wherein the coagulants are independently selected from aqueous solutions of: calcium chloride; calcium nitrate; sulphuric acid; and mixtures thereof.

19. The method according to claim 17 wherein the coagulants are independently selected from aqueous solutions of: calcium chloride at 20% aqueous concentration; calcium nitrate at from 15% to 25% aqueous concentration; dilute sulphuric acid at from 40% to 70% concentration; and mixtures thereof.

20. A nanocarbon-reinforced styrene-butadiene rubber (SBR) composition comprising a mixture of rubber components, nanocarbon, and carbon black wherein the rubber components comprise nanocarbon-reinforced SBR, and one or more additional nonreinforced (virgin) rubber components, wherein the relative amount in parts by weight per hundred parts by weight of nanocarbon-reinforced SBR to non-reinforced (virgin) rubber is in the range of from 4:5 to 5:4 and wherein the relative amounts in parts by weight per hundred parts by weight of nanocarbon to carbon black is in the range of: 1:100 to 1:9, wherein the relative amount of nanocarbon to total rubber is in the range of: 0.5:100 to 4.5:100, wherein the nanocarbon component is pre-dispersed within the nanocarbon-reinforced SBR component, wherein the nanocarbon has not been subjected to an acid treatment before incorporation into the reinforced SBR component of the composition, and wherein the composition optionally includes: one or more curing agents; one or more activators; one or more delayed-accelerators; one or more antioxidants; one or more processing oils; one or more waxes; one or more scorch inhibiting agents; one or more processing aids; one or more tackifying resins; one or more reinforcing resins; one or more peptizers, and mixtures thereof.

21. The nanocarbon-reinforced SBR composition according to claim 20 wherein the relative amounts in parts by weight per hundred parts by weight of nanocarbon to carbon black is in the range of from: 1:50 to 1:7.

22. The nanocarbon-reinforced SBR composition according to claim 20 wherein the relative amounts in parts by weight per hundred parts by weight nanocarbon to total rubber is in the range of from: 1:100 to 1:25.

23. The nanocarbon-reinforced SBR composition according to claim 20 wherein the SBR component containing the nanocarbon contains from 0.5 to 4.5 pphr nanocarbon.

24. The nanocarbon-reinforced SBR composition according to claim 20 wherein the additional rubber component is one or more natural sourced rubber components, one or more synthetic rubber components, or a mixture or combination thereof.

25. The nanocarbon-reinforced SBR composition according to claim 20 wherein the additional rubber component is one or more synthetic rubbers, and optionally non-reinforced (virgin) E-SBR.

26. The reinforced SBR composition according to claim 20 wherein carbon black is present at a level of from 10 to 50 pphr by weight versus 100 parts of the rubber present.

27. The SBR composition according to claim 20 containing a vulcanizing agent a level of from 1 pphr to 4 pphr.

28. The SBR composition according to claim 20 containing one or more vulcanizing delaying accelerators at individual levels of from 1.5 pphr to 8 pphr.

29. The SBR composition according to claim 20 containing one or more vulcanizing activating agents each at a level of from 0.5 pphr to 4 pphr.

30. The SBR composition according to claim 20 containing one or more antioxidants each at a level of from 0.5 pphr to 5 pphr.

31. The SBR composition according to claim 20 containing one or more mineral oils each at a level of from 2 pphr to 6 pphr.

32. The reinforced SBR composition according to claim 20 for use in the manufacture of one or more articles independently selected from: car or light truck tires; truck tire tread compounds; automotive floor mats; brake and clutch pads; footwear such as soles and heels for footwear; domestic and commercial products including floor mats, conveyor belts, garden and industrial hosing, insulation and jacketing for electrical cables; use in foodstuffs including food packaging.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0135] FIG. 1: illustrates a sample micrograph of the 3 pphr CNT reinforced SBR matrix of Example 1, captured using Field Emission Scanning Electron Microscope (FESEM) model LEO 1525, and shown at 100× magnification. SEM micrograph of a sample from a SBR masterbatch reinforced with 3 pphr of CNT at 100× magnification.

[0136] FIG. 2: illustrates a sample micrograph of the 3 pphr CNT reinforced SBR matrix of Example 1, captured using FESEM model LEO 1525, shown at 200× magnification, and with the diameter of the CNT measured.

[0137] FIG. 3: is a histogram showing the relative effects of mechanical peptizer on Mooney viscosity, Vc of four unvulcanised compositions: Mix 1—gum SBR, Mix 2—SBR+3 pphr carbon black (ISAF), Mix 3—SBR+3 pphr CNT, Mix 4—SBR+3 pphr CNT (MB pre-masticated with mechanical peptizer).

[0138] FIG. 4: is a histogram showing the effect of mechanical peptizer on hardness of four vulcanised compositions: Mix 1—gum SBR, Mix 2—SBR+3 pphr carbon black (ISAF), Mix 3-SBR+3 pphr CNT, Mix 4—SBR+3 pphr CNT (MB pre-masticated with mechanical peptizer).

[0139] FIG. 5: is a histogram showing the effect of mechanical peptizer on M100 and M300 of the four vulcanised compositions as indicated in FIG. 4.

[0140] FIG. 6: is a histogram showing the effect of mechanical peptizer on tensile strength of the four vulcanised compositions as indicated in FIG. 4.

[0141] FIG. 7: is a histogram showing the effect of CNT on Mooney viscosity of SBR-carbon black-filled rubber compound in four test vulcanised rubber compounds (black-filled SBR vulcanizates) and a reference compound: Mixes 5 and 6 are rubber compounds containing mixed SBR components, CNT-reinforced SBR and non-reinforced (virgin) SBR, as well as carbon black and other chemical components; Control formulation of non-reinforced (virgin) SBR (100) with as well as carbon black and other chemical components; Mix 7 a differently-reinforced (virgin) SBR (100) compound with carbon black and other chemical components; the composition of the text reference compound is as defined herein at Example 4.

[0142] FIG. 8: is a histogram showing the effect of CNT on hardness of SBR-carbon black-filled rubber compound in the test and reference vulcanised rubber compounds as detailed in FIG. 7.

[0143] FIG. 9: is a histogram showing the effect of CNT on M100 and M300 of SBR-carbon black-filled rubber compound in the test vulcanised rubber compounds as detailed in FIG. 7.

[0144] FIG. 10: is a histogram showing the effect of CNT on tensile strength of SBR-carbon black-filled rubber compound in the test and reference vulcanised rubber compounds as detailed in FIG. 7.

[0145] FIG. 11: is a histogram showing the effect of CNT on elongation at break (EB) of SBR-carbon black-filled rubber compound in the four test vulcanised rubber compounds as indicated in FIG. 7.

[0146] FIG. 12: is a histogram showing the effect of CNT on the resilience of SBR-carbon black-filled rubber compound in the four test and reference vulcanised rubber compounds as indicated in FIG. 7.

EXPERIMENTAL METHODS

[0147] The various physical properties of the compositions exemplified can be measured according to any of the standard methodologies as are known in the art. For example, onset of vulcanisation can be detected via an increase in viscosity as measured with a Mooney viscometer (Vc).

[0148] These measurements can be made according to various internationally accepted standard methods ASTM 01616-07(2012) (http://www.astm.org/Standards/01646.htm). Oensity (specific gravity), elasticity (M100, M300) and tensile strength as measurable according to ASTM 0412-06ae2 (http://www.astm.org/Standards/0412.htm), or http://info.admet.com/specifications/bid/34241/ASTM-0412-Tensile-Strength-Properties-of Rubber-and-Elastomers. Elongation at break (EB) as measurable by the method described in http://www.scribd.com/doc/42956316/Rubber-Testing or in http://harboro.eo.uk/measurement of rubber properties.html where alternative methods for measurement of tensile strength, are also provided. Hardness (International Rubber Hardness Degree, IRHO), as measured according to ASTM 01415-06(2012) (http://www.astm.org/Standards/D1415.htm).

[0149] According to an alternative embodiment there is additionally provided a method of making a nanocarbon-reinforced SBR masterbatch composition wherein the method comprises the following steps: [0150] (i) providing a dispersion of nanocarbon in a aqueous medium, wherein the aqueous medium optionally comprises one or more surfactants; [0151] (ii) providing a styrene butadiene rubber latex, (SBR latex); [0152] (iii) combining the styrene butadiene rubber latex, (SBR latex) with the aqueous dispersion of nanocarbon to provide a liquid composition; [0153] (iv) mixing on a 2-roll mill or in an internal mixer to provide a nanocarbon-reinforced SBR masterbatch; [0154] (v) addition of one or more optional masticating agents and mastication in SBR-latex-containing stage (ii) or (iii);
wherein the nanocarbon is not subjected to an acid treatment before incorporation into the composition, and wherein the nanocarbon-reinforced SBR masterbatch composition comprises less than 5 pphr of nanocarbon, relative amount in parts by weight per hundred parts by weight of SBR.

[0155] The present invention is illustrated by the following examples, which are not intended to limit the invention. Whilst specific embodiment of one or more aspects of the present invention have been described in the Examples hereinafter, it will be appreciated that departures from the described embodiments, which incorporate yet further features or aspects as detailed hereinbefore will fall within the scope of the present invention. For example, use of alternative nanocarbon or carbon black reinforcing agents, and/or alternative virgin SBR may be used.

EXAMPLES

[0156] The nanocarbon used in the examples consisted of carbon nanotubes having a length of <50 μm and an outer diameter of <20 nm; it had a C-purity of >85% and non-detectable free amorphous carbon. In the examples according to the invention the CNTs were employed as supplied, i.e. without acid pre-treatment. In that state the CNTs were present as agglomerated bundles of CNTs with average dimensions of 0.05 to 1.5 mm.

[0157] All percentages stated in the examples are by weight unless stated otherwise. As is common in the field of rubber technology, “pphr” stands for parts per hundred parts of rubber, and where specified relates to reinforced SBR rubber (in a nanocarbon-reinforced SBR masterbatch composition), or to total rubber component level, reinforced SBR, virgin SBR and/or natural rubber (in a reinforced rubber composition or rubber compound).

[0158] Where appropriate commercial sources for the materials utilized are provided. For standard chemicals such as for example the vulcanizing agent, sulfur any suitable commercially available source may be used.

Example 1

1.1 Preparation of Nanocarbon Slurry and Nanocarbon Dispersion

[0159] A 3% nanocarbon dispersion was prepared from 15 g of nanocarbon, 75 g of surfactant and 410 g of distilled water as shown in Table 1.

TABLE-US-00001 TABLE 1 Preparation of 3% CNT dispersion Pphr (vs aqueous Total weight Ingredients dispersion) (g) Nancarbon, CNT 3 15 (C-100*) 20% Surfactant, 15 75 K laurate** Distilled water 82 410 Total 500 *CNTs having a length of <50 μm and outer diameter of <20 nm, a C-purity of >85% and nondetectable, Graphistrength ® C100 CNTs from Arkema lnc. King of Prussia, PA19406 USA. **SC-215871 from Santa Cruz Biotechnology lnc. California 95060, USA

[0160] The nanocarbon, surfactant and water were placed in a suitable container, such as for example a glass beaker, and the resultant mixture was stirred by means of mechanical stirrer at 80 rpm for about 10 minutes to obtain an aqueous nanocarbon-containing slurry. The slurry was transferred to a ball mill for grinding to break down any agglomerates of nanocarbon. Ball milling was carried out for 24 hours and a nanocarbon dispersion was obtained. The dispersion was then transferred into a plastic container and the pH of the dispersion was adjusted to that of the SBR latex to which it was to be added. In this case the pH of the CNT dispersion was adjusted to between pH 8.0 and pH 10.0 by the addition of potassium hydroxide (KOH).

1.2. Preparation of Nanocarbon-Containing SBR Rubber Master Batches

[0161] The nanocarbon dispersion, from Example 1.1, was added to an SBR latex in a suitable container, such as for example a glass beaker. The SBR latex was used at 45% concentration without further dilution. In further experiments the Applicant has found that the SBR latex may be diluted to 30% if thickening occurs during mixing. The mixing of the SBR with the nanocarbon dispersion was then done in the presence of about 5 pphr of surfactant, where the surfactant was provided as a 5% to 20% solution as shown in Table 2.

TABLE-US-00002 TABLE 2 Preparation of 3 pphr CNT-SBR masterbatch from 3% CNT (C-100) dispersion Total Pphr Wet weight wet weight Ingredients (vs SBR) (g) (g) 3% nanocarbon, 3 100 300 CNT, C-100 10% Surfactant, 5 50 150 K laurate 40.5% SBR 100 222.2 666.6 latex* Total 372.2 1116.6 *cold polymerized emulsion SBR (E-SBR) having 40.5% styrene polymer, Nipol LX110, obtained from Zeon Corporation, Division of Synthetic Latex, Shin Marunouchi Center Bldg., 1-6-2 Marunouchi, Chiyoda-ku, Tokyo 100-8246, Japan.

[0162] The nanocarbon dispersion and the surfactant used were the same as detailed in Example 1 were discharged into a suitable container containing the SBR latex. The mixture was subjected to mechanical stirring for 60 minutes at stirring speed of from 80 to 100 rpm at a temperature of from 23 to 30° C.

[0163] The SBR latex filled with CNT was then coagulated using 500 ml of calcium chloride at a concentration level of 20% w/w for each 500 ml of the CNT-filled SBR latex. For the avoidance of doubt alternative suitable coagulants such as sulfuric acid (40-70% concentration), calcium nitrate (15-25% w/w concentration), and/or calcium chloride (15-20% w/w concentration); and/or mixtures thereof can be used. The coagulum formed was washed with water and squeezed to remove excess surfactants and water. The coagulum was further soaked in water overnight.

[0164] The following day, the coagulum was cut into small granules and washed with water. These granules were then dried in an electrically heated oven at from 50-80° C. until they were fully dried to provide a nanocarbon-reinforced SBR rubber masterbatch in accordance with an aspect of the present invention.

1.3. Preparation of Rubber Compound and Evaluation of Physical Properties of CNT-SBR Vulcanizate

[0165] Four test compositions were prepared and their physical properties prior to vulcanization and post-vulcanization were measured.

[0166] Rubber compounds according to one aspect of the invention, were prepared by mixing a CNT-reinforced SBR component, from the masterbatch products of Example 1.2, with a vulcanization agent (sulfur), a vulcanizing delayed accelerator (TBBS), and vulcanization activating agents (zinc oxide and stearic acid) by using a 2-roll mill, alternatively the compounds have also been prepared using a laboratory internal mixer. The full formulations are shown in Table 3. The cure characteristics of the compounded rubbers were determined by using a curemeter at 150° C. Various test-pieces were prepared by compression molding, and vulcanized to provide rubber compositions at an optimum state of cure at 150° C.

[0167] Table 3 illustrates the four compounds tested, Mixes 1 and 2 being based on virgin (nonreinforced/un-filled) SBR, and mixes 3 and 4 being based on CNT-reinforced SBR from the masterbatch of Example 1.2. Each test mix contains an SBR component, carbon black and further chemical components. For the avoidance of doubt the remaining chemical components in the formulations are included at the same relative levels across all four mixes, as expressed versus 100 pphr virgin SBR (in Mixes 1 and 2) and CNT-reinforced SBR (in Mixes 3 and 4). The CNT-reinforced SBR component of Mix 4 was mechanically masticated in the presence of zinc soaps of unsaturated fatty acids as processing agents and provided as Struktol WB16 at a level of 5 pphr, available from Struktol and as discussed hereinbefore. Up to 1 Opphr Struktol WB16 can be used.

[0168] Table 3, part A) illustrates the properties of the un-vulcanized rubber compositions, and Table 3, part B) illustrates the properties of the vulcanized rubber compositions.

TABLE-US-00003 TABLE 3 Test Compositions Mixes 1 to 4 of rubber formulations Mix no Ingredients 1 2 3 4 Virgin SBR (1502)* 100 100 — — CNT-reinforced SBR (from — — 103 103 masterbatch of Ex. 1.2) Vulcanizing activting agent, 3 3 2 3 Zinc oxide Vulcanizing activting agent, 2 2 1 2 Stearic acid Antioxidant, 6PPD 1 1 1 1 Carbon Black, ISAF black — 3 — — (N220) from Yucheng Jinhe Industrial Co. Vulcanizing delayed 1.4 1.4 1.4 1.4 accelerator, TBBS Vulcanization agent, 1.5 1.5 1.5 1.5 Sulfur A) Properties of un-vulcanized rubber compounds V.sub.c(M.sub.L 1 + 4, 100° C.) 37.7 41.8 146.8 69.7 Cure characteristics MDR 2000 (arc 0.5°) at 150° C. Scorch time, t2 16.78 12.77 4.80 4.04 Optimum cure, t95 39.95 34.68 16.76 13.01 Cure time 40 35 17 13 B) Properties of vulcanized rubber Hardness (IRHD) 41 42 60 68.2 Modulus M100 (MPa) 0.76 0.84 2.11 1.7 Modulus M300 (MPa) 1.38 1.67 — 5.95 Tensile strength (MPa) 1.72 3.21 6.28 8.3 Elongation strength (EB) (%) 373 462 256 387 Rolling Resilience (%) 68.5 68.3 75 68.2 *cold polymerized emulsion SBR (E-SBR) having 23.5% styrene polymer and specific gravity of 0.94, SBR Nipol 1502 obtained from Zeon Corporation, Division of Synthetic Latex, Shin Marunouchi Center Bldg., 1-6-2 Marunouchi, Chiyoda-ku, Tokyo 100-8246, Japan.

Example 2. Evaluation of CNT Dispersion in the Rubber Matrix

2.1 Field Emission Scanning Electron Microscope (FESEM)

[0169] A test sample from the CNT-reinforced SBR masterbatch of Example 1.2 was placed in a container filled with liquid nitrogen for 10 minutes. Then the hard and frozen sample was crushed and one piece of the cross section surface of the sample was placed on the SEM sample stub and attached thereto with carbon tape. The sample was then sputter coated with gold particles, and was then inserted into the SEM chamber for measurement. The sample micrograph was captured using Field Emission Scanning Electron Microscope (FESEM) model LEO 1525. The results are shown in FIGS. 1 and 2 at 100×, and 200× levels of magnification respectively. In FIGS. 1 and 2 the CNT is illustrated by the lighter areas and the SBR is illustrated as the darker areas. The appearance of the lighter (CNT) areas throughout the sample show how well dispersed the CNT is within the SBR rubber matrix. In FIG. 2 the measured diameter of dispersed CNT particles Pa1 and Pa2, having diameters of and 27.98 nm and 32.12 nm respectively are illustrated.

2.2 Electrical Resistivity

[0170] The electrical resistivity test was also conducted as a means of assessing the CNT dispersion in the rubber matrix for a test sample from the CNT-reinforced SBR masterbatch of Example 1.2 when compared to a virgin (non-reinforced) SBR control sample. The SBR control sample is Sample 1 from Example 1.3. The electrical resistivity test was done in accordance with the standard method of BS 903: Pt. C1: 1991 & Pt. C2: 1982. The results are shown in Table 4.

TABLE-US-00004 TABLE 4 Results of Electrical Resistivity Test Parameters Virgin SBR CNT-reinforced SBR Applied voltage, (V) 35 7 Surface resistivity (ohms)  1.4 × 10.sup.15 7.05 × 10.sup.13 Volume resistivity, (ohms .Math. cm) 1.46 × 10.sup.14 4.29 × 10.sup.13

[0171] It is well known that rubber is an excellent electrical insulator, and as such the very high electrical resistivity of the virgin SBR sample, as indicated by the high surface resistivity as well as its high volume resistivity, is as anticipated. In contrast, the CNT-reinforced SBR test sample demonstrated lower electrical resistivity than the virgin SBR. This confirms that presence of CNT in the SBR matrix provides an enhanced electrical path. The surface conductivity of CNT-reinforced SBR is about 700× more conductive than virgin SBR, and the bulk of CNT-reinforced SBR is about 43× more conductive than virgin SBR. The enhancement in the electrical conductivity is attributed to CNT dispersed within the SBR matrix. Both the SEM micrographs and electrical resistivity tests complement each other implying that good dispersion of CNT in the SBR matrix has been achieved.

Example 3. Results on Mooney Viscosity, Cure Characteristics and Physical Properties

3.1 Effect of CNT on Mooney Viscosity

[0172] FIG. 3 is a histogram showing the effect of mechanical peptizer on Mooney viscosity, V.sub.c of four different SBR masterbatches: Mix 1—gum (virgin) SBR; Mix 2—SBR+3 pphr carbon black (ISAF); Mix 3—SBR+3 pphr CNT; Mix 4—SBR+3 pphr CNT (MB pre-masticated in the presence of WB 16).

[0173] As shown by the results presented in Table 3, and as illustrated in FIG. 3, virgin SBR (Mix 1) has very low Mooney viscosity. Whilst the addition of 3 pphr carbon black (ISAF) (Mix 2) did provide a marginal increase in the viscosity, in contrast the addition of 3 pphr of CNT (Mix 3) increased the viscosity substantially. Without wishing to be bound to any particular theory it is proposed herein that this substantial increase in the viscosity is associated with enhanced interaction levels between the SBR and the nanocarbon reinforcing agent.

[0174] As high Mooney viscosities, such as that observed for Mix 3, can lead to processing difficulties, such as poor dispersion of compounding ingredients, high heat generation during mixing and poor flow, the Applicant developed an improved method for preparing CNT-reinforced SBR masterbatches which involved the addition of a processing agent, the mechanical peptizer WB16.

[0175] As also illustrated in FIG. 3, without the incorporation of mechanical peptizer, Mix 4, a CNT-reinforced SBR masterbatch gave very high Mooney viscosity. The results illustrated in FIG. 3, for this improved CNT-reinforced SBR masterbatch (Mix 4) confirm that pre-mastication with mechanical peptizer facilitated flow and provided a resultant masterbatch having reduced Mooney viscosity. Without wishing to be bound to any particular theory it is proposed herein that inclusion of the mechanical peptizer in Mix 4 facilitated flow due to provision of internal lubrication within the rubber chains, and thereby reduced viscosity of the rubber compound produced, via the presence of the fatty acid soaps.

3.2 Cure Characteristics

[0176] As illustrated in Table 3 and as discussed hereinbefore, the addition of nanocarbon in general, and CNT in particular to SBR results in reductions in both the scorch and cure times respectively. Care has to be taken during processing since the scorch time has reduced. However, the biggest advantage is the substantial reduction of cure time by more than 50% that would bring advantages during production since it is more economical to cure at shorter time than at longer time.

[0177] The results on mechanical properties are discussed hereinafter.

[0178] Ultimate tensile strength, or simply tensile strength, is the maximum force the rubber can withstand without fracturing when stretched, and provides an indication of how strong a rubber composition is.

[0179] Indentation hardness (IRHD) is a measurement of how resistant the material is to applied force.

[0180] Elongation at break (EB), with respect to tensile strength testing, is a measurement of how much a sample will stretch prior to break and is usually expressed as a percentage i.e. the maximum elongation.

3.3 Effect of CNT on Hardness

[0181] The four compositions illustrated in Table 3, Mixes 1 to 4 were vulcanised and their physical properties were compared. FIG. 4 is a histogram which illustrates the effect of mechanical peptizer on hardness. Mix 1: virgin SBR gave 41 IRHD units of hardness which is a typical value for non-reinforced vulcanized SBR rubber. Surprisingly the addition of 3 pphr (ISAF) carbon black, in Mix 2, did not produce desirable levels of SBR reinforcement, but rather provided similar levels to the virgin Mix 1, 42 vis 41 IHRD units of hardness.

[0182] On the basis of the experimental data provided herein far higher loadings of carbon black reinforcing agent would be required to increase the hardness to desirable levels, when compared to the amount of nanocarbon in the reinforced SBR compounds exemplified herein.

[0183] Advantageously, and as illustrated in the results obtained for Mixes 3 and 4, SBR reinforcement with nanocarbon, and specifically CNT at 3 pphr (relative to SBR parts per 100) in accordance with the methods herein, produces desirable levels of reinforcement as indicated by the high hardness values of 60 IRHD units and above. Of particular note is the increased hardness of Mix 4 where pre-mastication in the presence of a processing agent, and in particular a mechanical peptizer (Strucktol WB 16) would appear to have increased further the hardness by 8 points. Without wishing to be bound to any particular theory it is proposed herein that this improved hardness results from improved nanocarbon/CNT dispersion within the reinforced-SBR component, which may also be related to internal lubrication within the SBR-rubber chains associated with the fatty acid soaps.

3.4 Effect of CNT on M100 & M300 I Tensile Strain

[0184] The four compositions illustrated in Table 3, Mixes 1 to 4 were vulcanised and their physical properties were compared. FIG. 5 is a histogram which illustrates the effect of mechanical peptizer on their ability to withstand tensile strain as measured by modulus, M100 and M300 for each of Mixes 1 to 4. Mix 1: virgin SBR gave typical values for non-reinforced vulcanized SBR rubber, of around 0.76 and 1.38 for M100 and M300 respectively. Once again the addition of 3 pphr of (ISAF) carbon black, in Mix 2, did not produce desirable modulus results, but once more provided levels similar to those shown by the virgin Mix 1, 0.84/1.67 for M100/M300 for Mix 2 vs 0.76 and 1.38 for Mix 1.

[0185] The results for Mixes 3 and 4 which include 3 pphr CNT as reinforcing agent in the SBR show improvements versus both Mix 1 and Mix 2. In particular, Mix 4 has >4× improved M300 and >2× improved M100 performance.

[0186] Thus it has been demonstrated that the addition of 3 pphr of CNT, as a dispersed reinforcing agent in the SBR matrix, has increased the tensile stress at 100% strain denoted as M100 by more than a factor of 2, and tensile stress at 300% strain denoted as M300 by more than a factor of 4 respectively. This provides a clear picture of the positive impact of effective dispersion of CNT as a reinforcing agent in the SBR matrix.

3.5 Effect of CNT on Tensile Strength

[0187] The four compositions illustrated in Table 3, Mixes 1 to 4 were vulcanised and their physical properties were compared. FIG. 6 is a histogram which illustrates the effect of mechanical peptizer on tensile strength (MPa). Mix 1: virgin vulcanised SBR is very weak having a tensile strength of only 1.7 Mpa. Whilst the addition of 3 pphr (ISAF) carbon black, in Mix 2, did produce a marginal increase in tensile strength, to 3.2 Mpa, in the context of rubber processing this is still low and is not suitable for many practical applications.

[0188] In contrast the results obtained for the nanocarbon-reinforced SBR compositions of Mixes 3 and 4 clearly demonstrate that addition of 3 pphr of CNT increased the tensile strength significantly, to 6.3 Mpa and 8.3 Mpa respectively. Such tensile strengths are especially desirable in certain applications such as industrial rubber products including hoses, belts and seals/gaskets for example.

[0189] In particular the results for Mix 4, which was pre-masticated in the presence of a mechanical peptizer demonstrated the largest improvement in tensile strength. The tensile strength of SBR-filled CNT is about a factor of 5 higher than virgin SBR (comparing Mix 4 versus Mix 1).

[0190] The results illustrated in Table 3, FIGS. 3 to 6 and as discussed at 3.3, 3.4 and 3.5 herein show the enhancement of the physical properties of vulcanised rubbers in hardness, M100, M300 and tensile strength for nanocarbon (CNT) reinforced SBR compositions as defined herein, specifically for such compositions incorporating of 3 pphr of CNT.

Example 4: Physical Properties of CNT-SBR Black-Filled Vulcanizate

[0191] The physical properties of five further test compound formulations were investigated to determine the impact of pre-mastication with mechanical peptizer on nanocarbon-reinforced SBR masterbatches and on compositions prepared therefrom. For the avoidance of doubt the pre-mastication step in the presence of mechanical peptizer for Mixes 5 and 6 in the following experiments was carried out in accordance with the procedure discussed at Example 3.1 hereinbefore. These five further test compound formulations are shown in Table 5.

[0192] Mixes 5 and 6 are rubber compounds containing mixed SBR components, CNR-reinforced SBR (53) and non-reinforced (virgin) SBR (50), as well as carbon black (50 and 30 respectively) and other chemical components. The control formulation is non-reinforced (virgin) SBR (100) with carbon black (52) and other chemical components. Mix 7 is a further non-reinforced (virgin) SBR (100) compound with carbon black (30) and other chemical components. Mix 8 is a reference rubber compound suitable for use in tractor tyre treads and as disclosed in Tractor Tire Tread, Struktol Compounding Guide for the Rubber Industry (Revised December 1992, p 60, Struktol, Schill & Seilacher (GmbH & Co), Edision Published in December 1992 and incorporated herein by reference.

[0193] For the avoidance of doubt the remaining chemical components in the formulations are included at the same relative levels across the Control and mixed 5, 6, and 7, as expressed versus 100 pphr virgin SBR (in Control and Mix 7) and combined SBR level (103) (in Mixes 5 and 6).

[0194] Table 5, part A) illustrates the properties of the un-vulcanized rubber compositions, and Table 5, part B) illustrates the properties of the vulcanized rubber compositions

TABLE-US-00005 TABLE 5 Test Formulations - Mixes 5 to 7, Control and Reference formulation Mix no Ingredients Control 5 6 7 Ref. SBR 1712 — — — — 137.5 Virgin SBR (1502) 100 50 50 100 — CNT-reinforced SBR, from — 53 53 — — Experiment 1.2 Masterbatch Vulcanizing activating 3 3 3 3 3 agent, Zinc oxide Vulcanizing activating 2 2 2 2 1 agent, Stearic acid Antioxidant, Santoflex 1 1 1 1 1.5 13 (6PPD) Carbon Black, ISAF black 52 50 30 30 60 (N220) Antioxidant, poly(2,2,4- — — — — 1 trimethyl-1,2- dihydroquinoline) (TMQ)* Mineral Oil, Shellflex 4 4 4 4 — 250 MB Vulcanizing delayed 1.4 1.4 1.4 1.4 — accelerator, TBBS Vulcanization agent, 1.5 1.5 1.5 1.5 2 Sulfur Struktol 40 MS Flakes** — — — — 5 Stuktol A 60*** — — — — 2 Vulcanizing delayed — — — — 0.2 accelerator 2- mercaptobenzothazole (MBT) Vulcanizing delayed — — — — 1.2 accereator N-cyclohexyl- 2-bensothiazole sulfenamide (CBS) A Mooney viscosity of rubber compound V.sub.c(M.sub.L 1 + 4, 100° C.) 69.4 104 76.2 63.4 67 Cure characteristics at 150° C. Scorch time, t2 (minutes) 5.08 0.07 5.55 4.3 8 Optimum cure, t95 22.85 19.3 21.7 14.6 N/A (minutes) Cure time (minutes) 23 19.5 22 15 15 B Physial properties Hardness (IRHD) 65 68 58 61 57 M100 (MPa) 1.36 2.18 2.61 1.4 — M300 (MPa) 5.3 11.1 13.4 4.91 6.3 Tensile strength (MPa) 15.3 21.2 24.5 22 19.6 Elongation at break, 528 459 478 738 600 EB (%) Rolling Resistance (%) 48.6 48.2 54.8 50.4 33 For the avoidance of doubt, unless specified otherwise, the materials used in the formulations of Table 5, are as indicated hereinbefore, in Table 3. *TMQ available from Shandong Caoxian, Shandong Province, China. **mixture of dark aromatic hydrocarbon resins available from The Struktol Company of America. ***mixture of zinc soaps of high-molecular weight fatty acids available from The Struktol Company of America.

[0195] To prepare the test nanocarbon-reinforced SBR compositions—Mixes 5 and 6, CNT-reinforced SBR, from the masterbatch of Example 1.2, was blended with virgin (non-reinforced) SBR at a ratio of about 1:1. Additional reinforcing agent, (ISAF) carbon black was also incorporated in these test nanocarbon-reinforced SBR compositions at a ratio of about 1:2 to about 2:5 relative to the total rubber content (SBR, virgin and/or CNT-reinforced SBR).

[0196] Prior to use in test compositions 5 and 6, the CNT-reinforced SBR masterbatch was subjected to pre-mastication with a processing agent/mechanical peptizer (zinc soaps of unsaturated fatty acids/Struktol WB16) for 5 minutes in a Haake laboratory internal mixer. Without wishing to be bound to any particular theory it is proposed herein that this pre-mastication process facilitates not only dispersion of the reinforcing CNT, but also the remainder of the formulation ingredients.

[0197] The conditions utilised to provide effective pre-mastication using a Haake laboratory internal mixer were: starting mixing temperature, 80° C.; rotor speed, 80 rpm.

[0198] The mastication process sequence utilised was: the SBR was added to the mixer and mixing began at 80 rpm; after about 1 minute the nanocarbon and the remaining chemical components of the formulation, with the exception of carbon black, as indicated in Table 5 for mixes 5 or 6 were added; after about 2 further minutes, the carbon black was added and a sweep was carried out; after about a further 1 minute a further sweep was carried out and after a total of 20 minutes from sequence start the pre-masticated composition was discharged from the mixer.

4.1 Effect of CNT on Mooney Viscosity of Black-Filled SBR Compound

[0199] The five compositions illustrated in Table 5, were vulcanised and their physical properties were compared. The control mix and Mix 5 were reinforced with 52 and 50 pphr of (ISAF) carbon black respectively. The addition of 3 pphr of CNT, in the form of CNT-reinforced SBR, was shown to increase the Mooney ML (1+4) 100° C. viscosity (Vc) markedly. In order to seek a reduction in the viscosity in the CNT-reinforced SBR rubber containing compound, the amount of (ISAF) carbon black was reduced to 30 pphr in Mix 6. This reduced the Mooney viscosity (Vc) of the CNT-reinforced SBR rubber containing compound in Mix 6 to a level (76.2) which was comparable to that for the control formulation level (69.4).

[0200] Mix 7 is an SBR compound, prepared from virgin SBR containing 30 pphr of (ISAF) carbon black. Comparing the results for Mix 6 and Mix 7, as presented in Table 3, the addition of 3 pphr of CNT was demonstrated to increase the viscosity of the compound as shown in FIG. 7. This result indicates that CNT has a far higher rubber-reinforcing agent interaction potential than carbon black. Without wishing to be bound to any particular theory it is proposed herein that this is as a consequence of its high surface area associated with the finer size of the CNT versus that of carbon black.

[0201] The increase in viscosity for Mix 6 has the additional advantages of enhancing the collapse resistance and retaining the extrudate profiles after extrusion process. However, there is a risk of high heat generation during processing with high viscosity rubber compounds which may lead to premature vulcanization (scorch). In order to reduce the viscosity of the compound, the amount of (ISAF) carbon black was reduced to 30 pphr as shown in Mix 6. This approach has been demonstrated to reduce the viscosity of the rubber compound to 76 Mooney units which is an acceptable level in practice.

4.2 Effect of CNT on Hardness of Black-Filled SBR Vulcanizate

[0202] The compositions illustrated in Table 5, were vulcanised and their physical properties were compared. The carbon black reinforced control compound has a hardness of 65 IRHD units, which would be anticipated for a mixture of virgin SBR: carbon black in a 2:1 ratio.

[0203] Comparing this with the hardness observed for Mix 5, the incorporation of CNT has increased the hardness by 3 points to 68 IRHD units. As shown in FIG. 8, reducing the carbon black component from 50 to 30 pphr in the CNT-reinforced SBR composition reduced the hardness to 58 IRHD units, a decrease of 10 points which is comparable to the hardness observed for the reference compound.

4.3 Effect of CNT on M100 & M300 of Black-Filled SBR Vulcanizate

[0204] The compositions illustrated in Table 5, were vulcanised and their physical properties were compared. As shown in the results listed in Table 5 and as illustrated in FIG. 9, in contrast to the trend observed in the hardness results, Mix 6 gave overall better modulus values than the Control, the Reference compound or Mixes 5 or 7.

[0205] This is surprising because in theory, the M100 and M300 values should show follow the same trend as hardness.

[0206] As also shown in Table 5, and illustrated in FIG. 9, the incorporation of 3 pphr of CNT into the rubber compositions, as CNT-reinforced SBR, increased both M100 and M300 by a factor of about 2 against mixes without CNT. Furthermore, this advantageous higher reinforcement was attained with the incorporation of a relatively small amount of CNT.

4.4 Effect of CNT on Tensile Strength of Black-Filled SBR Compound

[0207] The compositions illustrated in Table 5, were vulcanised and their physical properties were compared. As shown in the results listed in Table 5 and as illustrated in FIG. 10, the incorporation of 3 pphr of CNT, as CNT-reinforced SBR, increased the tensile strength by 38.3% (when comparing the results for Mix 5 versus those for the virgin SBR control). In FIG. 10, the the extra enhancement in the mechanical strength provided by CNT is especially clear.

[0208] Reducing the level of carbon black from 50 pphr to 30 pphr increased the tensile strength of the corresponding CNT-reinforced SBR mix (Mix 6). In line with the trend observed in earlier experiments herein, and as illustrated in FIG. 8, reducing the level of carbon black was shown to decrease the hardness and allowed the rubber to fail at higher elongation and hence at high stress level.

4.5 Effect of CNT on Elongation at Break (EB %)

[0209] The compositions illustrated in Table 5, were vulcanised and their physical properties were compared. As shown by comparison of the results listed in Table 5 and as illustrated in FIGS. 8 and 11, the incorporation of 3 pphr of CNT, as CNT-reinforced SBR, in Mixes 5 and 6 provided increases in tensile strength alongside desirable elongations.

4.6 Effect of CNT on Resilience of SBR Black-Filled Vulcanizate

[0210] The compositions illustrated in Table 5, were vulcanised and their physical properties were compared. As shown in the results listed in Table 5 and as illustrated in FIG. 12, the highest rolling resilience was observed for a rubber composition reinforced with 3 pphr of CNT, from CNT-reinforced SBR, and reinforced with a further 30 pphr of (ISAF) carbon black (Mix 6).

[0211] This demonstrates the advantageous improvement in resilience of SBR delivered by effective incorporation/dispersion of small amounts of CNT into the SBR matrix. A key advantage of such improved, higher resilience for SBR rubbers relates to their potential for use in automotive or truck tires, and in particular for providing tires which have reduced capacity for reduces heat generation and thereby providing desirable low rolling resistances. These two properties are the main requirements for the manufacturing of “green tire”.

[0212] It is proposed that the desirable, high resilience for the nanocarbon containing reinforced SBR rubber compounds are also associated with use of lower amounts of carbon black (ISAF) than have previously been possible for reinforced SBRs for utility in tires. Advantageously, the reduction in carbon black loading in Mix 6 produces lighter weight tires, which is desirable for the delivery of improvements (reductions) in oil consumption levels than heavy weight tires.

[0213] The results obtained in Experiments 1, 2, 3 and 4, and as illustrated in FIGS. 1 to 12 demonstrate that CNT SBR masterbatch filled with 30 pphr of ISAF gives better overall physical properties and higher mechanical strengths than that filled with 50 pphr ISAF, that CNT SBR masterbatch treated with mechanical peptizer gives higher mechanical strength and better physical properties than untreated CNT SBR masterbatch, and that a highly desirable combination of properties, viscosity, hardness, elongation at break, low rolling resistance and is provided by rubber compounds prepared from the nanomaterial-reinforced SBR masterbatches according to the present invention, and particularly where such masterbatches are premasticated in the presence of mechanical peptizer prior to use in the preparation of said rubber compounds.

Experiment 5: Assessment of Activated Versus Non-Activated Nanocarbon

[0214] As detailed hereinbefore, the present invention provides a method for the preparation of nanocarbon reinforced SBR masterbatches, and in particular CNT reinforced SBR masterbatches from SBR latex, and to use of such reinforced SBR in rubber compounds.

[0215] Chinese patent application CN 1663991 A used acid treatment to make CNTs hydrophilic before mixing them with a NR latex. The Applicants have demonstrated that without treating the CNT with the acid solution, the physical properties of the vulcanized natural rubber filled with untreated (virgin) CNT are better than acid treated CNT. The results of this experiment are directly applicable to the present invention because they show that acid-activation of CNT is not a pre-requisite for performance enhancement in reinforced rubber compositions per se.

5.1 Preparation of Activated CNT Dispersion and Masterbatch

[0216] Activated CNT (C-100) was prepared in accordance with the method reported in CN 1663991 A. In our experiment, the CNT used was C-100. The acid solution mixture was prepared by mixing dilute sulfuric acid (5% concentration) with dilute nitric acid (5% concentration) in the required ratio of 3:1.

[0217] In the process of CN 1663991 A, 1 g of CNTs corresponds to 10 ml of acid solution. In our experiment, 12 g of CNT (C-100) was used and mixed with 120 g of acid solution [90 g of sulfuric acid (5% concentration) and 30 g of nitric acid (5% concentration)]. The mixture was boiled at 70° C. for 30 min on an electrically heated plate. The mixture was allowed to cool before filtering the using a funnel and filter paper. The acid-treated CNT so-collected was rinsed with distilled water and the acid-treated, activated CNT was then dried in an oven at 60° C. overnight.

5.2 Preparation of 2% Acid Treated CNT (C-100) Slurry

[0218] Table 6 shows the formulation to produce 2% acid treated CNT slurry. Each ingredient was weighed accurately by using an electrical weighing balance. The coarse slurry was prepared by mixing all the ingredients shown in Table 6 in a suitable glass beaker. The mixture was stirred slowly by means of mechanical stirrer at 80 rpm for about 10 minutes before transferring into a ball mill for grinding process to breakdown any agglomeration or aggregation of CNT. The mixtures were ball milled for 24 h. At the end of the milling process, the slurry was transferred into a plastic container.

TABLE-US-00006 TABLE 6 Formulation of 2% treated C-100 slurry Dry wt Wet wt Ingredients (g) (g) Nanocarbon, C-100 (treated) 2 12 Surfactant, 10% K laurate 10 60 Water 88 528 Total 100 600

[0219] The slurry so-obtained was ready for use to prepare an acid treated CNT NR masterbatch from NR concentrated latex and the formulation of this masterbatch is shown in Table 7.

TABLE-US-00007 TABLE 7 Formulation to produce 2 pphr acid treated CNT NR MB Dry wt Wet wt Ingredients (g) (g) Nanocarbon, 2% treated 2 100 C-100 (K laurate) Surfactant, 10% K laurate 5 50 Rubber, 30% HA latex 100 333.3 Total 483.3

[0220] Each ingredient was weighed accurately by using an electrical weighing balance. The ingredients were mixed by stirring at rotational speed of 80 rpm for 30-45 minutes. The latex mix was then coagulated with acetic acid. The coagulum was then washed and soaked in tap water overnight for the leaching process. After the leaching process, the coagulum was cut into small sizes to increase its surface area to shorten the drying time. Drying was done in an electrically heated oven at 45° C. The dry weight was monitored until it was relatively constant.

5.3 Preparation of Rubber Compound Using Acid Treated CNT NR Masterbatch

[0221] Table 8 shows the compound formulations for both untreated (virgin) CNT NR masterbatch and that of acid treated CNT NR masterbatch. The mixes were prepared by mixing on a 2-roll mill at 50° C. for about 10 minutes total mixing time, with frequent cutting and folding of the rubber band during mixing process to ensure uniform mixing and good quality finalized mix. The finalized mixes were stored for 16 hours before molding the test-pieces.

[0222] Moulding of test-pieces was done by using appropriate compression molds compressed between electrically heated platens. The temperature of vulcanization was at 150° C. and cured to optimum state of cure (t95).

TABLE-US-00008 TABLE 8 Compound formulation Ingredients Pphr pphr CNT Latex MB 102 — Surface activated CNT Latex — 102 MB Vulcanizing activating agent, 3 3 ZnO Vulcanizing activating agent, 2 2 Stearic acid Antioxidant, Santoflex 13 1 1 (6PPD) Vulcanizing agent, Sulphur 1.5 1.5 Vulcanizing delayed 1.4 1.4 accelerator, TBBS Rheology and cure characteristics Mooney viscosity (MU) 20 20.6 Cure characteristics at 150° C. t.sub.2 (minutes) 6.4 5.8 t.sub.95 (minutes) 16.0 18 Physical Properties Hardness (IRHD) 48 46 M100 (MPa) 1.14 1.11 M300 (MPa) 3.10 3.07 Tensile Stress (Mpa) 26.1 19.99 Elongation at Break, EB (%) 612 614

Physical Tests

[0223] 1. Mooney viscosity (ISO/R289)—QC Tests on unvulcanized rubber compounds. [0224] 2. Cure characteristics (1803417)—QC Tests on unvulcanized rubber compounds. [0225] 3. Hardness (ISO 48)—QC Tests on vulcanized rubber compounds. [0226] 4. Tensile strength, EB and M100, M300 (18037)—QC Tests on vulcanized rubber compounds.

Results and Discussions

[0227] Table 8 shows the physical properties of both unvulcanized rubber and vulcanized rubber. There is no significant difference between the Mooney viscosity of treated and untreated CNT NR masterbatch as shown in Table 8. However, the cure time (t95) of the treated CNT NR masterbatch was slightly longer than untreated NR masterbatch. This is expected because the presence of acid retards cure.

[0228] The hardness of untreated CNT vulcanized rubber was higher by 2 points than acid treated CNT vulcanized rubber. The tensile strength and moduli M100 and M300 (stress at 100% and 300% strain) of untreated CNT vulcanized rubber were higher than that of acid treated CNT vulcanized rubber. The non-activated CNT gave overall better performance than activated CNT.