BACKGROUND

[0001] This application claims priority to U.S. Serial No. 63/290,292, filed December 16, 2021, which is incorporated herein by reference. Graphene is an allotrope of one of the several physical forms of carbon, other examples being graphite, fullerenes, and diamond, an allotrope being one of various forms an element may assume. At the atomic level, it is in the form of a sheet with a thickness nominally under about 1.0 nanometer and up to about 1 micron in diameter. Sheets of such dimensions when added to other materials to form composites facilitate increases in thermal and electrical conductivity and in the case of elastomer nanocomposites, improvements in hysteresis, compounding ingredient dispersion, aging resistance, and reductions in permeability.

[0002] At the molecular level, graphene has a hexagonal lattice structure of isolated, single-layer plates of graphene, which can be directly seen with transmission electron microscopy (TEM) as sheets of graphene suspended between bars of a metallic grid. Some of these images showed a rippling of the flat sheet, with amplitude of about one to three nanometers. Graphene has a theoretical specific surface area (SSA) of 2500 to 2700 m ² /g. This is much larger than for carbon black (typically less than 900 m ² /g) or for carbon nanotubes. With sheet thickness of less than about 1.0 nanometer, diameters of more than about 1 micron, graphene is thus much greater than that observed with other rubber nanocomposites such as those containing clays. There are essentially three forms of graphene, i) graphene oxide (GO), ii) reduced graphene oxide, and iii) pure graphene (Figure 1). Pure graphene, or as sometimes referred to as pristine graphene, when exfoliated into monolayer sheets will be of an inert condition, i.e., no chemical functionality such as carboxylic acid, ketone, aldehyde, or hydroxyl groups on the graphene plate surface or plate edges observed in other graphene oxide derivatives (Figure 1).

[0003] Graphene in polymer or rubber nanocomposites has been reported to have many unique properties such as antioxidant properties, reductions in permeability, thermal conductivity, electrical conductivity, and reduction in permeability. Abrasion resistance of rubber nanocomposites is also noted, suggesting better tire wear. In addition, improvement in hysteresis as measured by the loss modulus divided by the storage modulus or tangent delta has also been reported. In this instance such improvements can be reductions in whole tire rolling resistance with no loss in traction qualities.

[0004] In further viewing literature reports of rubber nanocomposites applications, the modern radial tire was in many respects made possible through the introduction and use of halobutyl rubber innerliners. Use of polymers, such as bromobutyl, in the innerliner compound enabled improvements in air retention performance, significant improvements in liner-to-tire casing adhesion and improvements in tire durability. This second generation technology represented a major advance over the use of first-generation liner technologies using regular butyl rubber found in tubes and liners of bias tires and early radial tire constructions. Since the introduction of halobutyl rubber there has been no significant advance in the composition of innerliner formulas used in the industry. Some of this might be due to the tolerances in properties that innerliner compounds must meet. For example, small increases in liner compound 300% modulus could lead to reduction in fatigue resistance and cracks with consequent loss in tire durability.

[0005] A nanocomposite is a polymer containing nano-sized dispersed particles such as graphene. In this section of the work rubber nanocomposites are based on isobutylene elastomers and graphene, under the commercial name, Prophene™, which has particles which have large aspect ratios, i.e., where the graphene plate thickness is in the order of up to about 1.0 micron but the plate width can be between about 0.3 nm (3 A ⁰ ) and about 1.0 nm. The graphene will be exfoliated in butyl rubber, i.e., separated into individual sheets, sets of sheets, or several sheets together, but not in an aggregated state or intercalated condition with sheets stacked upon one another.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The present teachings are described hereinafter with reference to the accompanying figures.

[0007] FIG. 1 shows different chemical structures of graphene:

[0008] FIG. 2 shows a graph of reduction in permeability;

[0009] FIG. 3 shows the tortuous path phenomenon;

[0010] FIG. 4 shows a graph of permeation coefficient;

[0011] FIG. 5 shows a graph of air permeability;

[0012] FIG. 6 shows a graph of improved tear strength and adhesion; [0013] FIG. 7 shows a graph of improved abrasion resistance;

[0014] FIG. 8 shows a graph of improved fatigue resistance;

[0015] FIG. 9 shows a graph of aged tensile strength;

[0016] FIG. 10 shows a graph of improved adhesion;

[0017] FIG. 11 shows a cutaway view of radial and bias tire constructions;

[0018] FIG. 12 shows a graph of tire leaving contact area;

[0019] FIG. 13 shows a cutaway view of the tread and a high resolution photograph of tread;

[0020] FIG. 14 shows examples of treadwear patterns; and

[0021] FIG. 15 shows different types of tire wear.

DETAILED DESCRIPTION

[0022] The specific grade of graphene described herein is considered pristine, unlike all other commercial grades of graphene available.

[0023] Aircraft tires for the purpose of the present teaching can be classified in one of two ways: by application and by construction. Of the four fundamental types of tires by application, there are military, commercial, business, business jets and private/recreational, and rotary. Regarding construction, tires will either have a bias construction or radial construction.

[0024] Regardless of the tire construction or the type of aircraft tire, i.e., tire for either commercial, private or military use, four fundamental parameters govern tire performance capability, i) hysteresis and heat build-up during taxi, take-off and landing, ii) High centrifugal forces due to high speeds of rotation and take-off and landing, iii) tensile strength and compressive forces due to loads and impacts, and iv) abrasion and tread wear. Fundamental tire compound properties influencing these performance parameters are compound impermeability of the innerliner, all compounds tear strength and compound component to component adhesion, all compounds tensile strength, and compound abrasion resistance. Compound compositions will change with tire manufacturer. However Table I shows the primary rubber polymer used in each general component in the aircraft tire.

Table I Compound Rubber Polymer By Component Carbon

Compound Polymers Black Tread NR N220 Cushion NR N33O Shoulder Wedge NR N550 Sidewall NR, BR N33O

Belts, Breakers NR N326

Fabric Ply NR N326

Fabric Ply NR N326

Gum Strips NR N326 Sidewall NR, BR N33O Bead Filler NR N550 Barrier /

Squeegee NR N326, N660 Innerliner HIIR, BR N660

[0025] In the present teaching, it is demonstrated that addition of graphene will allow improvements in the performance of many of these compounds with no trade off in other properties.

[0026] Compounding is the operation of bringing together all the ingredients required to mix a batch of rubber compound. Each component has a different mix of ingredients according to the properties required for that component. Mixing is the process of applying mechanical work to the ingredients in order to blend them into a homogeneous substance. Internal mixers are often equipped with two counter-rotating rotors in a large housing that shear the rubber charge along with the additives. The mixing is done in two or three stages to incorporate the ingredients in the desired order. The shearing action generates considerable heat, so both rotors and housing are water-cooled to maintain a temperature low enough to assure that vulcanization does not begin. [0027] Graphene in this instance, described by the trade name Prophene™, is added to the rubber and mixed as noted above. Prophene™ will be added to a rubber formulation such as one based on butyl or halobutyl at levels from about 0.1 PHR to about 50.0 PHR, from about 0.5 PHR to about 10.0 PHR, and from about 0.1 PHR to about 4.0 PHR. Prophene™ is described in Table II.

Table II Properties of Pristine Prophene™

[0028] Compound permeability would follow a decrease, initially very large but though continuing to decrease, tapering as graphene levels increase. To those knowledgeable in such phenomenon, it is known to follow the Neilson model (see Neilson, J Macromol. Sci Chem Al 5 P929 1967). Gas-permeability decreases with increasing graphene loading of only about 0.4 vol% in rubber composites. This percolation threshold is about 40 times lower than that for claybased composites. According to the Nielsen model on gas permeability, the thickness of an individual graphene-based sheet dispersed in the graphene styrene -butadiene rubber (SBR) composite with 2.0 vol.% of GO was predicted to be 1.47 nm (Figure 2).

[0029] Graphene, when added to a butyl or halobutyl rubber compound formulation, can be in various forms as follows:

1. As a powder;

2. In pastilles or pellets using wax as a carrier, aiding dust suppression;

3. In pre- weigh sealed low met temperature polyethylene bags; and

4. Melt or solution blended with a compatible polymer such as butyl rubber or halobutyl rubber and then compounded as part of the total rubber hydrocarbon content.

[0030] Graphene has an aspect ratio of near 1000, assuming the graphene plate thickness is about 1 nm. The plate length/diameter can be up to about 1 micron. The graphene can thus function as a barrier. The graphene exfoliates into sheets when added to the rubber compound, which improves the barrier properties when perpendicular alignment to the sheet direction is achieved. The graphene plates provide a barrier to oxygen and nitrogen migration, and moisture or water vapor molecules migrating through the liner compound of the tire or other product requiring such properties. Such gas molecule transport phenomenon is described as a “Tortuous Path” (Figure 3). With continuing reference to Figure 3, with the addition of graphene as a filler, there is no tradeoff or loss in conventional processing and mechanical properties. Graphene has a very high aspect ratio. Small amounts have a large impact on reducing permeability. The nominal aspect ratio of graphene of up to 1000 compares with the typical aspect ratio of 20 for kaolin clay fillers. The clay fillers have to be added at about 40 PHR and also need a surfactant for compatibility. Due to the relatively large size of the graphene plates versus inorganic fillers, graphene can be added at about 1 PHR to about 2 PHR.

Measurement of Properties of Rubber Compositions

[0031] Mooney viscosity (ML1+4) at 100°C was measured in accordance with ASTM D1646. Vulcanization kinetics and associated properties was measured by following the procedure in ASTM D5289. Tensile strength and associated data generated through measurement of tensile strength was determined following ASTM D412. Shore-A Hardness was measured following the method in ASTM D2240. Tear strength and adhesion were measured following ASTM D624. Oxygen permeability was measured using an Ametek Mocon OX-TRAN 2/22 permeability tester and following ASTM D3985. Air permeability determined according to the method in ASTM D1434.

Example 1 Aircraft Tire Innerliner

[0032] To meet low temperature cracking resistance requirements aircraft tire innerliners have up to 20 PHR of polyisoprene or natural rubber. This results in a significant increase in permeability, air pressure loss in service, and increased tire inflation pressure maintenance requirements. Addition of graphene at very low levels will allow substantial improvement in inflation pressure retention (IPR) as shown in Figures 4 and 5. This terminology of inflation pressure maintenance and impact of natural rubber is described in the text, Tire Engineering, and introduction, CRC Press, Chapter 4.

Table III

Example 2

Aircraft Tire Natural Rubber Based Tread Compound

[0033] A model aircraft tire tread compound based on natural rubber tread is utilized. As shown in Table IV below, graphene is added at 0.5, 1.0, 2.0, 4.0, and 10.0 PHR. The compounds are mixed via laboratory two-stage mix process using BR scale Banbury. The addition of graphene to the aircraft tire tread does not shift the viscosity, as well as no change in compound processing or vulcanization kinetics.

[0034] Figures 6 and 7 show much improved aircraft tire tread compound abrasion resistance and tear strength with small additions of graphene.

Table IV

Aircraft Tire Tread Compound Formulation

Compound Grade 1 2 3 4 5 6

Natural Rubber TSR20, RSS2 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 N121, Alter:

Carbon Black (N121) N234 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

Table V Processing data

1 2 3 4 5 6

Mooney

Viscosity ML1+4

Mooney Peak 95.14 87.93 94.32 96.08 86.60 89.26

ML1+4 100°C 61.63 61.66 62.20 62.20 61.06 61.69

Aged Mooney

Viscosity 7 days

Mooney Peak 111.60 95.40 99.90 98.80 100.40 94.80

ML1+4 100°C 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 Arc degrees 0.5 0.5 0.5 0.5 0.5 0.5

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 tsl 3.04 3.03 3.04 3.04 3.08 2.97

Torque at tlO 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 tlO 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 VI

Compound Properties

Compound Grade 1 2 3 4 5 6

ERTNB1 ERTNB1 ERTNB 1 ERTNB 1 ERTNB1 ERTNB1 0-76-1 0-76-2 0-76-3 0-76-4 0-76-5 0-76-6

TSR2

Natural 0,

Rubber RSS2 100.00 100.00 100.00 100.00 100.00 100.00

Peptizer (Renecit

H) 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

Tensile Strength:

ASTM D412 Die C

Tensile

Strength MPa 26.00 27.00 26.00 26.60 26.70 25.00

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

1" strip Tensile Strength Tensile

Strength MPa 10.94 12.44 11.35 12.29 13.59 15.40

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

200% modulus MPa 5.70 5.76 5.58 5.98 5.90 7.60

300% modulus MPa 10.95 10.85 11.19 11.12 13.00 Shore

Hardness A 59 58 60 59 60 63

Tear

Strength KN/m 112.85 153.4 129.67 109.91 94.07 84.37

Strebler

(hot) Ibf/in 516.4 439.6 314.4 142.0 80.3 37.7

Example 3

Aircraft Tire Sidewall

[0035] A model aircraft tire sidewall formulation was prepared with varying levels of Graphene.

Table VII

[0036] Improvements were observed in fatigue resistance and aged tensile strength, both desirable properties in aircraft tire sidewalls. Similarly, adhesion improved which has an immediate impact on improvement of tire durability. [0037] With reference to FIGS. 12-15, heavy loads and high speeds contribute to strong centrifugal forces. The tire is deflected in the footprint due to load. As the rotating tire exits the runway contact area, a traction wave is generated as the tire returns to its natural shape. Stress can cause separation and the traction wave can cause groove cracking and rib under-cutting. [0038] Clause 1 - An aircraft tire tread, inner liner, and/or sidewall including natural rubber, a peptizer, carbon black, graphene, wherein the graphene has a thickness of less than about 3.2 nm, a particle size of between about 50 nm and about 10 pm, and contains greater than about 95% carbon, aliphatic hydrocarbon resin, treated distillate aromatic extract, A- ( 1, 3 -dimethylbutyl)- A’ - phenyl- 1,4-benzenediamine, 2,2,4-trimethyl-l,2-dihydroquinoline, paraffinic wax, microcrystalline wax, zinc oxide, stearic acid, N-tert-butyl-benzothiazole sulfonamide, sulfur, and pre vulcanization inhibitor.

[0039] Clause 2 - An aircraft tire tread, inner liner, and/or sidewall including natural rubber, carbon black, and graphene, wherein the graphene has a thickness of less than about 3.2 nm, a particle size of between about 50 nm and about 10 pm, and contains greater than about 95% carbon.

[0040] Clause 3 -The aircraft tire tread, inner liner, and/or sidewall of clause 2, wherein the tread contains no silica.

[0041] Clause 4 - The aircraft tire tread, inner liner, and/or sidewall of clauses 2 or 3, wherein the graphene is a graphene plate, wherein the graphene plate is between about 0.5 PHR and about 10.0 PHR.

[0042] Clause 5 - The aircraft tire tread, inner liner, and/or sidewall of clauses 2-4, wherein the graphene plate has a surface area from about 100 m ² /gram to about 250 m ² /gram.

[0043] Clause 6 - The aircraft tire tread, inner liner, and/or sidewall of clauses 2-5, wherein the graphene plate has an oxygen content of less than about 1%.

[0044] Clause 7 - The aircraft tire tread, inner liner, and/or sidewall of clauses 2-6, wherein the thickness is less than about 1 nm and the aspect ratio is about 1000.

[0045] Clause 8 - The aircraft tire tread, inner liner, and/or sidewall of clauses 2-7, wherein the graphene plate is between about 0.5 PHR and about 8.0 PHR.

[0046] Clause 9 - The aircraft tire tread, inner liner, and/or sidewall of clauses 2-8, wherein the truck tire tread further includes carbon black. [0047] Clause 10 - The aircraft tire tread, inner liner, and/or sidewall of clauses 2-9, wherein the truck tire tread further includes a peptizer, aliphatic hydrocarbon resin, treated distillate aromatic extract, an antiozonant, and an antioxidant.

[0048] Clause 11 - The aircraft tire tread, inner liner, and/or sidewall of clauses 2-10, wherein the truck tire tread further includes paraffinic wax, microcrystalline wax, zinc oxide, stearic acid, an accelerator, sulfur, and a pre vulcanization inhibitor.

[0049] Clause 12 - The aircraft tire tread, inner liner, and/or sidewall of clauses 10 or 11, wherein the antiozonant is A/-(l,3-dimethylbutyl)-A/’-phenyl-l,4-benzenediamine and the antioxidant is 2,2,4-trimethyl-l,2-dihydroquinoline.

[0050] Clause 13 - The aircraft tire tread, inner liner, and/or sidewall of clauses 11 or 12, wherein the accelerator is N-tert-butyl-benzo thiazole sulfonamide and the peptizer is 2,2’ - dibenzamido-diphenyldisulphide.

[0051] Clause 14 - The aircraft tire tread, inner liner, and/or sidewall of clauses 2-13, wherein the graphene plate is between about 1.0 PHR and about 2.0 PHR, wherein the composition has no clay fillers.

[0052] Clause 15 - The aircraft tire tread, inner liner, and/or sidewall of clauses 2-14, wherein the graphene plate is between about 3.0 PHR and about 5.0 PHR.

[0053] 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.

[0054] Having thus described the present teachings, it is now claimed: