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RUBBER COMPOSITION HAVING GRAPHENE AND LIQUID RUBBER

20240084097 ยท 2024-03-14

    Inventors

    Cpc classification

    International classification

    Abstract

    An improved rubber composition and method to create the improved rubber composition is achieved by milling reduced graphene oxide (RGO) in liquid rubber to induce a reduction of bulk density of the reduced graphene oxide while maintaining dispersibility in rubber without using a solvent-based process resulting in an industrially scalable process and an improved rubber composition.

    Claims

    1. A reduced graphene oxide reinforced rubber composition comprising: a milled material comprising: a reduced graphene oxide milled with; a liquid rubber; an uncured rubber elastomer; an anti-degradant package; and a curing package.

    2. The composition of claim 1 wherein the liquid rubber has a molecular weight in the range of 1,500 g.Math.mol.sup.1 to 54,000 g.Math.mol.sup.1.

    3. The composition of claim 2 wherein the liquid rubber has a molecular weight in the range of 1,500 g.Math.mol.sup.1 to 34,000 g.Math.mol.sup.1.

    4. The composition of claim 3 wherein the liquid rubber has a molecular weight in the range of 1,500 g.Math.mol.sup.1 to 28,000 g.Math.mol.sup.1.

    5. The composition of claim 4 wherein the liquid rubber has a molecular weight in the range of 1,500 g.Math.mol.sup.1 to 10,000 g.Math.mol.sup.1.

    6. The composition of claim 5 wherein the liquid rubber has a molecular weight in the range of 1,500 g.Math.mol.sup.1 to 2,000 g.Math.mol.sup.1.

    7. The composition of any one of the above claims wherein the reduced graphene oxide and liquid rubber is milled in the absence of oxygen to form the milled material.

    8. The composition of claim 7 wherein the milling of the reduced graphene oxide and liquid rubber occurs in nitrogen.

    9. The composition of claim 8 wherein the milling of the reduced graphene oxide and liquid rubber occurs in a ball mill.

    10. The composition of claim 9 wherein the milling of the reduced graphene oxide and liquid rubber uses stainless steel media.

    11. The composition of claim 10 wherein the milling of the reduced graphene oxide and liquid rubber uses stainless steel media having a diameter in the range of 3 mm to 5 mm.

    12. The composition of any of the above claims wherein the uncured rubber elastomer comprises styrene butadiene.

    13. The composition of any of the above claims wherein the anti-degradant package comprises 6PPD.

    14. The composition of any of the above claims wherein the curing package includes sulfur and an accelerator such as CBS.

    15. The composition of any of the above claims wherein the composition is placed into a mold and heated to form a cured rubber product.

    Description

    BRIEF DESCRIPTION OF THE DRAWINGS

    [0014] A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which:

    [0015] FIG. 1 shows a schematic of reactive ball-milling process involving graphite.

    [0016] FIG. 2 shows the true secant modulus curves corresponding to N002 PDR milled with and without liquid rubber.

    [0017] FIG. 3 shows G* of the dynamic mechanical analysis (DMA) of a strain sweep at 23 C.-return, corresponding to N002 PDR milled with and without liquid rubber.

    [0018] FIG. 4 shows the Tan delta of the dynamic mechanical analysis (DMA) of a strain sweep at 23 C.-return, corresponding to N002 PDR milled with and without liquid rubber.

    [0019] The use of identical or similar reference numerals in different figures denotes identical or similar features.

    DETAILED DESCRIPTION OF THE INVENTION

    [0020] The present invention provides a method for creating a composite rubber composition comprising Reduced Graphene Oxide (RGO) by use of liquid rubber as a novel milling co-agent. For purposes of describing the invention, reference now will be made in detail to embodiments and/or methods of the invention, one or more examples of which are illustrated in or with the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features or steps illustrated or described as part of one embodiment, can be used with another embodiment or steps to yield a still further embodiments or methods. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.

    [0021] In at least one embodiment an RGO liquid rubber composition is created by combining RGO with liquid rubber in a suitable mill, for example a planetary ball mill, along with suitable milling media, for example stainless steel spheres 3-10 mm in diameter. In this embodiment the ambient air is purged and replaced with a less reactive covering gas, such as nitrogen. The RGO and liquid rubber is mechanically milled until the RGO particles reach the desired size. The RGO-liquid rubber mixture may then be added as an ingredient to a rubber formulation. In other embodiments the mill may be a twin-screw extruder or a Haake style mixer.

    [0022] The rubber composition may then be further processed, a desired anti-degradant package and a curing package may be added to the rubber mixture. The uncured rubber mixture may be calendared into sheets or extruded as a product having a desired cross-sectional shape. These products may be combined with other reinforcements to form a composite structure. Finally the green rubber is placed into a mold where heat and pressure is applied to cure the rubber, forming a cured rubber product.

    Example

    [0023] Milling with Liquid Rubber

    [0024] The Reduced Graphene Oxide (RGO) used in this study was N002 PDR from the Global Graphene Group (Dayton, OH, USA).

    [0025] The physical properties of the different liquid rubbers are displayed in Table 1. The compositions of the rubber mixes made with the milled N002 PDR are displayed in Table 2.

    TABLE-US-00001 TABLE 1 Physical properties of the liquid rubbers used in the study. LBR L-SBR-841 LIR-30 LIR-50 LIR-403 Rubber Polybutadiene Styrene polysoprene polysoprene polysoprene type butadiene copolymer (random) Molecular 1500-2000 10 000 28 000 54 000 34 000 weight (g .Math. mol.sup.1) Viscosity 80 (at 25 C.) 100 (at 60 C.) 70 (at 38 C.) 500 (at 38 C.) 200 (at 38 C.) (Pa .Math. s) Pendant No No No No Maleic functional anhydride group

    TABLE-US-00002 TABLE 2 Mix compositions in grams. Mix 1 Mix 3 Mix 4 Mix 5 Mix 6 PDR Mix 2 L-SBR- LIR- LIR- LIR- control LBR 841 30 50 403 SBR2300 46.06 46.06 46.06 46.06 46.06 46.06 Liquid 2.52 2.52 2.52 2.52 2.52 Rubber ZnO 0.97 0.97 0.97 0.97 0.97 0.97 SAD 0.58 0.58 0.58 0.58 058 0.58 6PPD 0.97 0.97 0.97 0.97 0.97 0.97 N002 PDR 2.19 2.19 2.19 2.19 2.19 2.19 S 0.71 0.71 0.71 0.71 0.71 0.71 CBS 0.71 0.71 0.71 0.71 0.71 0.71

    [0026] For the grinding process, a planetary ball-mill MSK-SFM-1 from the MTI Corporation was used with four 250 mL stainless-steel vacuum jars (FIG. 3). Stainless steel spherical milling media with diameter from 3 to 5 mm was used. Specifically, two 3-mm balls, three 4-mm balls and two 5-mm sized balls were placed in each jar. Long milling times (8 hours, 4 hours in each rotation direction) were used.

    [0027] Since the generated radicals at the surface of the broken RGO platelets could react with ambient oxygen, the jars were flushed with nitrogen for an hour before milling. At the end of the grinding process, the product was added to the rubber as is. No extra step of purification to remove the non-reacted liquid rubber from the surface of the graphene-like particles was performed.

    [0028] For the control sample without any liquid rubber, the N002 PDR was compacted during ball-milling. N002 PDR is a very fluffy powder. A jar of 250 mL contained 1.26 g of N002 PDR with a tap density of approximately 0.005 kg. L.sup.1. After milling, the volume of the powder was reduced to approximately 15 mL with a resulting tap density of 0.090 kg. L.sup.1.

    [0029] Rubber Mixing and Milling

    [0030] The following processes were followed for mixing and milling of the rubber composite. A Haake mixer was used set for a rotation speed of 90 rpm and a temperature of 110 C. The rubber was mixed for 1 min. The rotation speed was reduced to 30 rpm and the milled material was added and mixed for 1 min. The rotation speed was then increased to 90 rpm and mixing continued 1 min. SAD (Steric Acid), ZnO (Zinc Oxide), and 6PPD (n-(1,3-dimethylbtityI)-n-phenyl-p-phenylenediamine) were then added and mixed for another 1 min. The mixer piston was then dropped and mixing continued 1 minute.

    [0031] After internal mixing, the mixture was milled on a 2-roll mill at 40 C. The mixture was milled for 12 passes after full incorporation of S (Sulfur) and CBS (n-cyclohexyl-2-benzothiazole sulfonamide).

    [0032] Samples were then molded from the mixture for testing. Testing of the composition was carried out to determine the material's tensile properties. Milling without any liquid rubber resulted in the lowest MA (10) and MA (100) (FIG. 4 and Table 3), whereas milling the N002 PDR with the low molecular weight BR and the low molecular weight SBR led to the highest rigidity. The highest strain and strength at break were again obtained with the RGO milled in the lowest molecular weight liquid rubber (LBR with a molecular weight of 1500-2000 g.Math.mol-1). The ratio MA 300/MA 100 was higher when the RGO was milled in liquid rubber versus dry milling and it was the highest with the low molecular weight BR or with the liquid isoprene having the lowest molecular weight (LIR-30). The trends regarding rigidity and reinforcement are clear: the lower the molecular weight of the liquid rubber used during milling (and consequently the lower its viscosity), the higher the rigidity and reinforcement of the corresponding rubber composite.

    [0033] The size of the particles was examined with scanning electron microscopy, SEM. Similar size reduction occurred with both dry milling and milling with low molecular weight rubber, thus differences in particle size cannot explain the differences in mechanical properties.

    [0034] It is therefore hypothesized that the decrease in rigidity and reinforcement is due to the stacking of the RGO platelets during dry milting. Using low molecular weight rubber prevents the platelets front stacking very tightly and promotes a better dispersion during mixing.

    TABLE-US-00003 TABLE 3 Tensile properties indicators corresponding to FIG. 4. Tensile Tensile stress at strain at MA 10 MA 100 MA 300 break break MA 300/ (MPa) (MPa) (MPa) (MPa) (%) MA 100 No rubber 2.04 0.02 2.09 0.01 3.01 0.01 3.04 0.10 417 14 1.44 0.01 LBR 3.11 0.02 3.15 0.03 5.16 0.04 5.70 0.29 480 31 1.64 0.01 LSBR 3.16 0.04 3.21 0.01 5.03 0.02 4.09 0.53 331 52 1.56 0.01 LIR-30 2.83 0.03 2.90 0.02 4.89 0.05 4.27 0.28 351 25 1.68 0.01 LIR-50 2.17 0.07 2.23 0.01 3.57 0.01 3.16 0.29 358 31 1.60 0.01 LIR-403 2.35 0.03 2.39 0.02 3.63 0.01 2.69 0.27 295 35 1.52 0.01

    [0035] Dynamic Properties

    [0036] A strain sweep at 23 C. showed that the ranking in rigidity corresponded to the one obtained with MSV curves, FIG. 3, FIG. 4 and Table 4. Only the mixes made with N002 PDR milled in LBR or LSBR showed a slight Payne effect. Very limited energy dissipation (tan ) was observed.

    TABLE-US-00004 TABLE 4 DMA indicators corresponding to FIG. 3 and FIG. 4. G*_10% (MPa) Tan delta_10% No rubber 0.94 0.09 LBR 1.49 0.11 LSBR 1.31 0.11 LIR-50 0.97 0.10 LIR-403 1.04 0.09

    [0037] Selected combinations of aspects of the disclosed technology correspond to a plurality of different embodiments of the present invention. It should be noted that each of the exemplary embodiments presented and discussed herein should not insinuate limitations of the present subject matter. Features or steps illustrated or described as part of one embodiment may be used in combination with aspects of another embodiment to yield yet further embodiments. Additionally, certain features may be interchanged with similar devices or features not expressly mentioned which perform the same or similar function.

    [0038] As used herein, the term method or process refers to one or more steps that may be performed in other ordering than shown without departing from the scope of the presently disclosed invention. Any sequence of steps is exemplary and is not intended to limit methods described herein to any particular sequence, nor is it intended to preclude adding steps, omitting steps, repeating steps, or performing steps simultaneously. As used herein, the term method or process may include one or more steps performed at least by one electronic or computer-based apparatus having a processor for executing instructions that carry out the steps.

    [0039] The terms a, an, and the singular forms of words shall be taken to include the plural form of the same words, such that the terms mean that one or more of something is provided. The terms at least one and one or more are used interchangeably. Ranges that are described as being between a and b are inclusive of the values for a and b.

    [0040] Every document cited herein, including any cross-referenced or related patent or application is hereby incorporated herein by reference in its entirety unless expressly excluded or otherwise limited. The citation of any document is not an admission that it is prior art with respect to any invention disclosed or claimed herein or that it alone, or in any combination with any other reference or references, teaches, suggests or discloses any such invention. Further, to the extent that any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to that term in this document shall govern.