GRAPHENE AS AN ADDITIVE AS A NUCLEATING AGENT

Abstract

A method for improving processing speed, dimensional stability, and physical properties in extruded elastomers is herein disclosed, including the steps of mixing natural rubber with pristine graphene, the pristine graphene acting as a nucleating agent for strain induced crystallization of the natural rubber, and the pristine graphene inducing additional shear during mixing.

Claims

1. A method for improving processing speed, dimensional stability, and physical properties in extruded elastomers, the method comprising the steps of: mixing natural rubber with pristine graphene; the pristine graphene acting as a nucleating agent for strain induced crystallization of the natural rubber; and the pristine graphene inducing additional shear during mixing.

2. The method of claim 1 further comprising the steps of: exfoliating the pristine graphene; and, dispersing the pristine graphene in the natural rubber.

3. The method of claim 1, wherein Mooney viscosity, tensile strength, elongation at break, and 300% modulus of the mixture of natural rubber and pristine graphene is substantially the same as that of natural rubber alone.

4. The method of claim 1, wherein the pristine graphene has a thickness of less than about 3.2 nm, a particle size of between about 50 nm and about 10 μm, and contains greater than about 95% carbon.

5. The method of claim 1, wherein the pristine graphene is present in an amount of between about 0.1 PHR and about 50.0 PHR.

6. The method of claim 5, wherein the pristine graphene has a surface area from about 100 m.sup.2/gram to about 250 m.sup.2/gram.

7. The method of claim 6, wherein the pristine graphene has an oxygen content of less than about 1%.

8. The method of claim 7, wherein the thickness of the pristine graphene is less than about 1 nm and the aspect ratio of the pristine graphene is about 1000.

9. The method of claim 5, wherein the pristine graphene is present in an amount of between about 0.5 PHR and about 8.0 PHR.

10. The method of claim 9, wherein the pristine graphene is present in an amount of between about 1.0 PHR and about 2.0 PHR, wherein the mixture of natural rubber and pristine graphene has no clay fillers.

11. The method of claim 1, wherein the pristine graphene has substantially no carboxylic acids, alcohols, ketones, aldehydes, or other oxygenated or nitrogen functional groups.

12. A composition made according to claim 1.

13. The composition of claim 12, wherein the pristine graphene has a thickness of less than about 3.2 nm, a particle size of between about 50 nm and about 10 μm, and contains greater than about 95% carbon.

14. The composition of claim 12, wherein the pristine graphene is present in an amount of between about 0.1 PHR and about 50.0 PHR.

15. The composition of claim 14, wherein the pristine graphene has a surface area from about 100 m.sup.2/gram to about 250 m.sup.2/gram.

16. The composition of claim 15, wherein the pristine graphene has an oxygen content of less than about 1%.

17. The composition of claim 16, wherein the thickness of the pristine graphene is less than about 1 nm and the aspect ratio of the pristine graphene is about 1000.

18. The composition of claim 14, wherein the pristine graphene is present in an amount of between about 0.5 PHR and about 8.0 PHR.

19. The composition of claim 18, wherein the pristine graphene is present in an amount of between about 1.0 PHR and about 2.0 PHR, wherein the mixture of natural rubber and pristine graphene has no clay fillers.

20. The composition of claim 12, wherein the pristine graphene has substantially no carboxylic acids, alcohols, ketones, aldehydes, or other oxygenated or nitrogen functional groups.

Description

III. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The present teachings are described hereinafter with reference to the accompanying drawings.

[0016] FIG. 1 shows the chemical structure of pristine graphene;

[0017] FIG. 2 shows the potential states of graphene;

[0018] FIG. 3 shows a graph of tear strength;

[0019] FIG. 4 shows a graph of abrasion resistance;

[0020] FIG. 5 shows the surface topography of truck tire treads; and

[0021] FIG. 6 shows a graph of increase in modulus.

IV. DETAILED DESCRIPTION

Example 1

[0022] Three grades of pristine graphene are described as carriers for both enzymes in bio-systems and as catalysts (Table 1). Though not limited to this, there are three commercial grades of graphene under the commercial name of Prophene*, provided by Akron Polymer Solutions, considered in the present teaching. [0023] Grade PS50 with particle, sheet, or plate sizes of 50 nm to 5 microns; [0024] Grade PS100 with sheet or plate sizes 100 nm to 5 microns and increasing conductivity; and [0025] Grade PS150 with sheet or plate sizes of 150 nm to 10 microns.

[0026] Properties in rubber nanocomposites include electrical conductivity, thermal conductivity, improved nanocomposite compound hysteresis, tear strength, abrasion resistance, and reduction in permeability or gas flow.

[0027] The specific types or grades of graphene described here render their application suitable in bio- and catalysis systems because: [0028] 1. No, to very limited, functionality on the graphene plate surface: functionality being presence of reactive groups such as carboxylic acids, aldehyde groups, ketones, quinones, alcohols, and other oxygenated entities, and surface defects such as electronic vacancies in the graphene 6-membered aromatic rings; [0029] 2. Potential plate edge minor functionality lending the plates suited to partial immobilization of entities such as catalysts and enzymes (FIG. 1); [0030] 3. Very large aspect ratio of graphene, with plates up to ten to fifteen microns; and [0031] 4. Ease of exfoliation in many suspension and solution systems.

Example 2

[0032] In rubber nanocomposite systems the graphene plates are believed to be exfoliated, or as a minimum an intercalated state is obtained, i.e., where the graphene is very well dispersed but there are still stacks of pristine graphene plates 2 to 6 layers deep (FIG. 2). The high level of dispersion results in increased shear during composite blending, due to the very large aspect ratio of the graphene plates. The quality, uniformity, and homogeneity of the dispersion is thus improved.

TABLE-US-00001 TABLE 1 Properties of Proposed Graphenes for Carriers Grade PS 50 PS 100 PS 150 Form Light Light Light powder powder powder Color Dark grey/ Dark grey/ Dark grey/ Black Black Black Odor None None None Resistivity ohm <50 <100 <150 (Powder) cm Particle size nm 50 nm-5μm 100 nm-5 μm 150 nm-10 μm Particle max 1.7 nm 2.5 nm 2.8 nm thickness Layer count < 10 <15 <16 Density g/cm.sup.3 2.200 2.200 2.200 Specific m.sup.2/g 250.0 180.0 100.0 surface area

[0033] The high level of shear thus results in a highly dispersed mixer and high level of mixture homogeneity. This allows for better mechanical properties as observed in rubber nanocomposites.

[0034] Such systems also show increased electrical conductivity due to an apparent low percolation point not observed with conventional systems, such as those containing carbon black. Such conductivity might lend itself to uses in built-in antennae for articles such as RFID sensors in tires or other applications.

Example 3

[0035] Graphene was added to the model natural rubber compound illustrated in Table II at levels of 0.5, 1.0, 2.0, 4.0, and 10.0 PHR to give a total of six compounds including the control at -0-PHR. Some observations from the data were as follows: [0036] 1. Increase in graphene had no impact on Mooney viscosity (ML1+4), peak Mooney viscosity, or aged Mooney viscosity (7 days at 100° C.). Peak Mooney viscosity has been related to formation of bound rubber which in turn could be due to functional groups on the polymer or filler. The absence of any shifts in viscosity is consistent with the pristine nature of the graphene in this study. [0037] 2. There was no shift in vulcanization state of cure, ΔT, maximum torque or MH, or MDR rheometer t90. [0038] 3. Vulcanization kinetics determined simply from the cure rate index (equation 1) similarly did not shift.

Cure Rate Index=(t90−t10)/100  (1)

[0039] The cure rate index gives a simple means of estimating how a compounding ingredient may influence vulcanization kinetics and, in this instance, no shift was observed. This in turn is consistent with observations of the pristine nature of the graphene samples and no effect of reaction kinetics.

[0040] Tensile strength, elongation at break, and 300% modulus were not affected by graphene content. However, tear strength showed a rapid increase at 0.5 PHR and then dropped off as graphene level increased. The result is consistent with the gaussian distribution of tear strength data observed for halobutyl compounds.

TABLE-US-00002 TABLE II Graphene in Truck Tire Compounds Compound Grade 1 2 3 4 5 6 Natural Rubber TSR20 100.00 100.00 100.00 100.00 100.00 100.00 Peptizer (Renecit 11) 0.10 0.10 0.10 0.10 0.10 0.10 Carbon Black N121 50.00 50.00 50.00 50.00 50.00 50.00 Graphene 0.00 0.50 1.00 2.00 4.00 10.00 Escorez 1102 2.00 2.00 2.00 2.00 2.00 2.00 TDAE (aromatic oil) 3.00 3.00 3.00 3.00 3.00 3.00 6PPD 2.50 2.50 2.50 2.50 2.50 2.50 TMQ 1.50 1.50 1.50 1.50 1.50 1.50 Paraffin wax 1.00 1.00 1.00 1.00 1.00 1.00 Microcrystalline wax 1.00 1.00 1.00 1.00 1.00 1.00 Zinc Oxide 4.00 4.00 4.00 4.00 4.00 4.00 Stearic acid 2.00 2.00 2.00 2.00 2.00 2.00 TBBS 1.00 1.00 1.00 1.00 1.00 1.00 Sulfur 1.00 1.00 1.00 1.00 1.00 1.00 PVI 0.20 0.20 0.20 0.20 0.20 0.20 Mooney ML1 + 4, Viscosity 100° C. Mooney Peak 95.14 87.93 94.32 96.08 86.60 89.26 ML1 + 4 61.63 61.66 62.20 62.20 61.06 61.69 Aged Mooney Viscosity Mooney Peak 7 days, 100° C. 111.60 95.40 99.90 98.80 100.40 94.80 ML1 + 4 61.70 61.50 62.00 62.10 61.30 62.00 MDR Rheometer Temperature 160° C. 160° C. 160° C. 160° C. 160° C. 160° C. MH 9.67 9.56 9.89 9.77 9.67 10.05 ML 1.85 1.75 1.9 1.81 1.78 1.86 Delta Torque 7.82 7.81 7.99 7.96 7.89 8.19 Torque at t10 2.63 2.53 2.70 2.61 2.57 2.68 Torque at t50 5.76 5.66 5.90 5.79 5.73 5.96 Torque at t90 8.89 8.78 9.09 8.97 8.88 9.23 t10 2.55 2.45 2.65 2.52 2.45 2.66 t50 4.47 4.53 4.51 4.50 4.48 4.51 t90 6.73 6.76 6.81 6.67 6.88 6.91 CRI 23.92 23.20 24.04 24.10 22.57 23.53

TABLE-US-00003 TABLE V (Continued) Graphene in Truck Tire Compounds Compound Grade 1 2 3 4 5 6 Natural Rubber 100.00 100.00 100.00 100.00 100.00 100.00 Peptizer (Renecit 11) 0.10 0.10 0.10 0.10 0.10 0.10 Carbon Black 50.00 50.00 50.00 50.00 50.00 50.00 Graphene 0.00 0.50 1.00 2.00 4.00 10.00 Tensile Strength: ASTM D412 Die C Tensile MPa 26.00 27.00 26.00 26.60 26.70 25.00 Strength Elongation % 568 565 577 593 583 519  50% modulus MPa 1.18 1.15 1.20 1.23 1.35 1.60 100% modulus MPa 2.10 2.00 2.10 2.20 2.50 3.10 200% modulus MPa 5.90 5.90 5.90 5.80 6.50 7.40 300% modulus MPa 11.30 11.40 11.50 11.00 11.90 13.00 Tensile Strength: ASTM D412 Die C AGED 7 days 100 C. Tensile MPa 26.04 23.93 — 24.81 — 23.53 Strength Elongation % 494 478 — 486 — 453 100% modulus MPa 3.25 2.89 — 3.21 — 4.43 200% modulus MPa 8.73 7.53 — 8.13 — 9.43 300% modulus MPa 15.08 13.58 — 14.43 — 15.54 Energy at J/m3 59.92 50.99 — 55.63 — 52.05 Break Tensile 100 89 — 93 — 94 Strength Elongation 87 85 — 82 — 87 300% Modulus 133 119 — 131 — 120 1″ strip Tensile Strength Tensile MPa 10.94 12.44 11.35 12.29 13.59 15.40 Strength Elongation % 296 329 312 322 346 343  50% modulus MPa 1.09 1.12 1.15 1.19 1.23 1.60 100% modulus MPa 1.92 2.01 2.02 2.18 2.25 3.20

Example 4

[0041] Potential Mechanisms for Graphene Functionality in Natural Rubber Compounds

[0042] Five compounds were selected with graphene increasing from 0.0 PHR to 4.00 PHR and Din abrasion measured (FIG. 4). Volume loss measured after the test showed a significant reduction (improvement) beginning at 0.5 PHR through to 2.0 PHR, after which there was an inflection upwards in volume losses. Low levels of graphene can thus have a significant impact on performance.

[0043] A potential explanation could be compound homogeneity, with the graphene plates inducing additional shear during compound mixing, achieving better dispersion, and in turn improved abrasion resistance. Scanning the topography of test specimens, the greater red shaded area indicates greater surface roughness and greater susceptibility to abrasion losses (FIG. 5).

[0044] In order to further elucidate a possible mechanism for this phenomenon, tensile strength properties were further studied. Tensile strength measured using 2.5 cm wide strips of compound had been reported as a simple means of identifying if a compounding additive served as nucleating agent for strain induced crystallization in natural rubber. This has been observed here. As graphene level increased and as strains exceeded 50%, modulus increased.

[0045] Thus, graphene will improve the properties of a natural rubber compound via four mechanisms: [0046] 1. As a nucleating agent for strain induced crystallization of natural rubber chains; [0047] 2. Improvement of tear strength both via rubber strain crystallization and deflection of tear propagation; [0048] 3. Antioxidant properties; and [0049] 4. Improved compound homogeneity and component dispersion.

[0050] Though all four mechanisms would participate, improvement due to strain crystallization would dominate.

[0051] Non-limiting aspects have been described, hereinabove. It will be apparent to those skilled in the art that the above methods and apparatuses may incorporate changes and modifications without departing from the general scope of the present subject matter. It is intended to include all such modifications and alterations in so far as they come within the scope of the appended claims or the equivalents thereof.

[0052] Having thus described the present teachings, it is now claimed: