WO2023059316A1

WO2023059316A1 - Reduced graphene oxide imno functionalized elastomer composition

Info

Publication number: WO2023059316A1
Application number: PCT/US2021/053615
Authority: WO
Inventors: Jeremy John MEHLEM; Frederic Vautard
Original assignee: Compagnie Generale Des Etablissements Michelin
Priority date: 2021-10-05
Filing date: 2021-10-05
Publication date: 2023-04-13
Also published as: CN118103219A

Abstract

The subject matter of the present invention relates to rubber mix having improved wear resistance comprised of IMNO functionalized elastomer and a reduced graphene oxide filler. The resulting rubber has comparable wear resistance and better rigidity versus energy dissipation compromise as compared to rubber mixes having non-functionalized elastomer and RGO reinforcement.

Description

REDUCED GRAPHENE OXIDE IMNO FUNCTIONALIZED

ELASTOMER COMPOSITION

FIELD OF THE INVENTION

[0001] The subject matter of the present invention relates to improved rubber compositions and particularly to reduced graphene oxide (RGO) IMNO functionalized elastomer compositions with improved properties.

BACKGROUND OF THE INVENTION

[0002] It’s long been shown that fillers improve the properties of rubber elastomers, improving wear resistance, increasing rigidity, increasing thermal conductivity and tear resistance. Formulations of rubber compositions are created by combing different proportions of elastomers, fillers and other components to create rubber compositions having specific properties and performance characteristics. These properties and characteristics can be varied by changing the composition ratios resulting in improved properties or performances in some or many aspects and a decrease in properties or performance in another aspect resulting in a compromise as the composition is changed as the formulator optimizes the composition for a particular purpose (wear resistance for the tread of a tire, or low hysteresis for a sidewall rubber of a tire. These compromises are sometimes broken and all-around performance characteristics are achieved when the components of new compositions are found to work synergistically to unexpectedly improve all or many of the properties or characteristics of the rubber.

[0003] Different fillers lend positive and negative traits to elastomer formulations and new filler-elastomer discoveries represent breakthroughs in standard performance characteristics of elastomers resulting in a break from the standard compromises. Among the innovative fillers Reduced Graphene Oxides (RGOs) have shown very interesting properties regarding the rigidity/energy dissipation compromise, surpassing conventional fillers like carbon black and silica. Indeed, high levels of rigidity were obtained at low concentration (4-5 wt.% SBR2300 to obtain a rigidity equivalent to a mix made with 32 wt.% of N234) and low levels of energy dissipation were obtained.

[0004] While many properties of RGO elastomers are encouraging, wear studies indicate that the resistance to wear of RGO elastomers to be poor. This represents disappointing results discouraging the use of RGO in tread-rubber formulation. A need exists for improvement to wear resistance. A RGO formulation that improves the elastomer’s rigidity vs. energy dissipation compromise and reduce the rolling resistance of the tire would be particularly useful.

SUMMARY OF THE INVENTION

[0005] Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.

[0006] In one exemplary embodiment, an IMNO functionalized elastomer is mixed with a reduced graphene oxide filler to produce a rubber composition.

[0007] These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate properties of embodiments of the invention and, together with the description, serve to explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] 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:

[0009] FIG. 1 shows an SEM picture of a 5 wt.% RGO/SBR2300 mix showing nonreinforced rubber between RGO aggregates.

[0010] FIG. 2 shows RPA curves of N002-PDE/SBR2300 mixes with and without IMNO.

[0011] FIG. 3 shows MSV curve of N002-PDE/SBR2300 mixes with and without IMNO, density of interactions v = 0.6 molecules/nm2.

[0012] FIG. 4 shows MSV curve of N002-PDE/SBR2300 mixes with and without IMNO, density of interactions v = 1.3 molecules/nm2.

[0013] FIG. 5 shows MSV curve of N002-PDE/SBR2300 mixes with and without IMNO, density of interactions v = 3.9 molecules/nm2.

[0014] FIG. 6 shows DMA curve, low density of IMNO grafting; G* (MPa) vs. strain sweep at 23 °C. [0015] FIG. 7 shows DMA curve, low density of IMNO grafting; Tan delta vs. strain sweep at 23 °C.

[0016] FIG. 8 shows DMA curve, low density of IMNO grafting; G* (MPa) vs. temperature sweep at stress = 0.7 MPa between 0°C and 100°C.

[0017] FIG. 9 shows DMA curve, low density of IMNO grafting; Tan delta vs. temperature sweep at stress = 0.7 MPa.

[0018] FIG. 10 shows DMA curve for medium and high density of IMNO grafting; G* (MPa) vs. strain sweep at 23 °C.

[0019] FIG. 11 shows DMA curve for medium and high density of IMNO grafting; Tan delta vs. strain sweep at 23 °C.

[0020] FIG. 12 shows DMA, medium and high density of IMNO grafting, G* (MPa) vs. temperature sweep at stress = 0.7 MPa between -80°C and 100°C.

[0021] FIG. 13 shows DMA, medium and high density of IMNO grafting, Tan delta vs. temperature sweep at stress = 0.7 MPa between -80°C and 100°C.

[0022] FIG. 14 shows DMA, medium and high density of IMNO grafting, Tan delta vs. temperature sweep at stress = 0.7 MPa between 0°C and 100°C.

[0023] FIG. 15 shows the abrasion resistance as measured by a proprietary abrasion test, high density of IMNO interaction.

DETAILED DESCRIPTION OF THE INVENTION

[0024] The present invention provides a reduced graphene oxide containing rubber composition having an improved rigidity versus energy dissipation compromise while improving wear resistance. This rubber formulation may find particular use for articles including tires and particularly for the tread rubber of tires.

[0025] 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 embodiment or method. 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. [0026] In the examples that follow, various material properties are described. These properties were obtained using tests as ordinarily used to quantify such properties and are described as follows:

[0027] “Mn” is the number average molecular weight. This is the total weight of all polymer molecules contained in a sample divided by the total number of polymer molecules of the sample. It is an arithmetic average - all chains are equally important when calculating this parameter.

[0028] “Mw” is the weight average molecular weight. This is based on the fact that a bigger molecule contains more of the total weight of the polymer sample than smaller molecules. This parameter is highly susceptible to chains of high molecular weight.

[0029] “IP” is the polydispersity of an elastomer. This measures the amplitude of the Molecular Weights Distribution curve (MWD) and represents the ratio between the average molecular weight (Mw) and the average molecular weight in number (Mn).

[0030] A true secant modulus of elongation (MPa) was measured at 10% (MAIO), 100% (MA100) and 300% (MA300) at temperature of 23°C based on ASTM Standard D412 on dumb bell test pieces.

[0031] The elongation property was measured as strain at break (%) and the corresponding stress at break (MPa), which is measured at 23 °C in accordance with ASTM Standard D412 on ASTM C test pieces.

[0032] The shear modulus G* at 10% strain and the maximum tan delta dynamic properties for the rubber compositions were measured at 23 °C on a Metravib Model VA400 ViscoAnalyzer Test System in accordance with ASTM D5992-96. The response of a sample of vulcanized material (double shear geometry with each of the two 10 mm diameter cylindrical samples being 2 mm thick) was recorded as it was being subjected to an alternating single sinusoidal shearing stress at a frequency of 10 Hz under a controlled temperature of 23° C. Scanning was effected at an amplitude of deformation of 0.05 to 50% (outward cycle) and then of 50% to 0.05% (return cycle). The shear modulus G* at 10% strain and the maximum value of the tangent of the loss angle tan delta were determined during the return cycle.

[0033] To test fatigue of the elastomer samples, fatigue to fracture or “FTF” testing in accordance with ASTM D4482 - 11(2017) Standard Test Method for Rubber Property was carried out. The extension cycling fatigue temperature was set at 25 °C.

[0034] The “Hot Dz test” is used to test tear strength of the elastomer samples, testing in accordance with ASTM D624 - 00(2012) “Standard Test Method for Tear Strength of Conventional Vulcanized Rubber and Thermoplastic Elastomers” was conducted at 100°C.

The Dz index is equivalent to the rupture force times the elongation at break divided by 100.

[0035] To determine the wear performance of rubber, a proprietary abrasion resistance test was conducted where a rubber specimen of known mass was loaded against a simulated road surface to a pressure of 1 bar, then moved under pressure for a distance of 4 m. The mass of the sample was then measured again to determine the amount of rubber lost.

[0036] IMNO Functionalized Elastomer Synthesis

[0037] The functionalization of a dienic elastomer is well understood in the art and the functionalization of an elastomer with IMNO is described in patent applications WO 2012007441 Al, WO 2012007442, and WO 2012007684, hereby incorporated by reference. The functionalization of a dienic elastomer by IMNO is done through a cycloaddition with a nitrone functional group and leads to the grafting of a polar group (imidazolidone) that can interact with a filler surface having surface polar groups (like oxygen-containing or nitrogen-containing functional groups) shown in the chemical formulation (I) below. It was tested with the N002-PDE RGO from the Global Graphene Group (G3, Dayton, OH, USA). N002-PDE has 5-6 at. % in oxygen.

[0038] Those skilled in the art will understand that the symbol “ - ” used in formula

(I) represents an attachment of the CH of the molecule to the vinyl monomer.

[0039] Composition of the Rubber Mixes

[0040] The quantity of coupling agent Si69 in a witness mix (referred to herein as a “reference mix”) with silica RP160 corresponds to a maximal density of grafting of 1.4 molecules/nm² (two grafted coupling agent molecules per molecule of Si69 as shown in Table 1 herein). Three experimental mixes with IMNO and N002-PDE covered a range of maximal interaction densities from 0.6 molecules/nm² to 3.9 molecules/nm², including one mix at 1.3 molecules/nm² similar to the silica-based reference mix. Two different batches of N002-PDE with different specific surface areas were used (respectively 280 and 850 m²/g).

[0041] Table 1: Calculation of the maximal density of grafting/interaction for N002-

PDE/IMNO and RP160/Si69.

[0042] The three experimental samples were based on a standard test mix in SBR2300, with concentrations in N002-PDE of 4 and 5 wt.% with components as shown below in Table 1.1.

[0043] Table 1.1: Composition of IMNO and SBR2300-based mixes with N002-PDE filler (in grams).

[0044] A standard mixing process was used, but a step was added at the beginning to let the elastomer react with IMNO and 0.5 phr of TiO2 (catalyst) for 1 minute at 120°C before the adding of the filler. Mixing and milling processes were performed using a Bandbury mixer (HAAKE PolyLab OS RheoDrive from ThermoFisher) and Brabender mill. [0045] The rubber formulations were prepared by mixing the components given in Table 1.1, except for the sulfur and the accelerator (CBS), in the Banbury mixer. With the mix chamber at 110°C operating at 90 RPM the rubber is added and mixed for 1 minute. The rotation speed is decreased to 30 RPM and the filler is added and mixed for an additional 1 minute. The rotation speed is increased to 90 rpm and mixed for an additional 1 minute. Finally the anti-degradants ZnO (zinc oxide), 6PPD (N-( 1 ,3-di methyl butyl )-2V'- phenyl- 1 ,4-benzenediamine) as well as a processing aid, SAD (steric acid derivative) are added and mixed for an additional minute. The mixer piston is raised and lowered and mixed for an additional minute. The mix is dropped allowed to cool, then mixed on a 2- roll mill at 50°C. The accelerator and sulfur were added at this point and were milled for a total of 12 passes after full incorporation of the accelerator and sulfur.

[0046] A 5 wt.% RGO/SBR2300 mix was imaged under a scanning electron microscope (“SEM”) and is shown in Figure 1. Areas of a N002-PDE reduced graphene oxide particles 10 and areas of non-reinforced rubber shown in circles 20 can be observed in the SEM image.

[0047] Rheometry showed similar viscosities at the green state and a large decrease of the shear modulus in the cured state with a functionalization involving IMNO, for the three samples shown in Figure 2. Similar viscosities to the reference mix at the green state indicates good processability of the green rubber during stages of mixing, calendaring and extruding. Rheometry, shown in Figures 2, highlighted the fact that the scorch time is significantly reduced when using the IMNO rubber in comparison to SBR2300, but it should still be compatible with industrial practice. In the case of the standard mixing process, a sharp drop of the shear modulus in the cured stated is observed when switching from SBR2300 to IMNO.

[0048] Tensile properties revealed that with a potential of interaction of 0.6 molecules/nm², no reinforcement was generated (a slight decrease was even obtained) (Figure 3, 4 and 5 and Table 2). With higher potential densities of interaction, a significant increase of the MSV curve slope at high strain was observed compared to the nonfunctionalized SBR. That improvement was better with a higher density of interaction. It looks like starting with silica and Si69 as a model to determine the necessary quantity of functional groups interacting at the interface was appropriate to predict an optimal level of interfacial interactions of IMNO with RGO, even if the types of interactions may be different (polar versus covalent). [0049] Table 2: Tensile properties indicators corresponsing to Figure 4.

[0050] Dynamic properties confirmed what was seen with the static tensile test. The sample with a low density of interaction (0.6 molecule/nm²) led to less rigidity and similar energy dissipation (Figures 6, 7, 8 and 9 and Table 3).

[0051] Table 3: Dynamic properties indicators corresponding to Figures 6, 7, 8 and 9.

[0052] With the medium density of interaction (1.3 molecule/nm²), a linearization effect was observed (Figures 10, 11, 12, 13 and 14 and Table 4). With the high density of interaction (3.9 molecule/nm²), a limited linearization effect was seen as well. The temperature sweep revealed an increase in Tg for the high density of interaction, confirming that IMNO was grafted in the SBR backbone (Figure 7).

[0053] Table 4: Dynamic properties indicators corresponding to Figure 6 and Figure 7..

[0054] The wear resistance of the mixes was measured by proprietary abrasion test shown in Figure 15. The improvement of interfacial properties generated by the high density of interaction with IMNO resulted in a significant improvement of the resistance to wear.

[0055] The RGO should have an oxygen content of 4-9 mol % or alternatively 5-8 mol% or in yet another alternative embodiment between 5-6%. In at least one embodiment, the specific surface area of the RGO should be of more than 800 m²/g and having either 4-9 mol% oxygen content, or alternatively 5-8 mol% or in yet another alternative embodiment between 5-6%.

[0056] 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. [0057] The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as “40 mm” is intended to mean “about 40 mm.” Also, the dimensions and values disclosed herein are not limited to a specified unit of measurement. For example, dimensions expressed in English units are understood to include equivalent dimensions in metric and other units (e.g., a dimension disclosed as “1 inch” is intended to mean an equivalent dimension of “2.5 cm”).

[0058] 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. As used herein, the term "method" or "process" may include one or more steps performed at least by one electronic or computer-based apparatus. 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.

[0059] As used herein, "phr" is “parts per hundred parts of rubber by weight” and is a common measurement in the art wherein components of a rubber composition are measured relative to the total weight of rubber in the composition, i.e., parts by weight of the component per 100 parts by weight of the total rubber(s) in the composition.

[0060] As used herein, elastomer and rubber are synonymous terms. [0061] 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." [0062] 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.

Claims

WHAT IS CLAIMED IS:

1. A rubber composition comprising: an IMNO functionalized elastomer; a reduced graphene oxide; and a crosslinking system.

2. The rubber composition of claim 1 wherein the IMNO functionalized elastomer is a diene elastomer being selected from the group consisting of poly butadienes, synthetic polyisoprenes, natural rubber, copolymers of butadiene, styrene-butadiene, isoprene copolymers and mixtures of these elastomers.

3. The rubber composition of claim 1 or claim 2 wherein the reduced graphene oxide has an oxygen content of 5-20 mol %.

4. The rubber composition of claim 3 wherein the reduced graphene oxide has an oxygen content of 4-9 mol %.

5. The rubber composition of claim 3 wherein the reduced graphene oxide has an oxygen content of 5-8 mol %.

6. The rubber composition of claim 3 wherein the reduced graphene oxide has an oxygen content of 5-6 mol %.

7. The rubber composition of any one of the above claims wherein the IMNO functionalized elastomer has a functional group present in the range of 1.3 to 2.9 % mol.

8. The rubber composition of any one of the above claims wherein the IMNO functionalized elastomer has a functional group present in the range of 2.7 to 2.9 % mol.

9. The rubber composition of any one of the above claims wherein the reduced graphene oxide has a specific surface area of more than 800 m²/g.

10. The rubber composition of claim 9 wherein the reduced graphene oxide has a specific surface area of equal to or more than 860 m²/g.

11. The rubber composition of any one of the above claims wherein the molecular weight (Mn) of the polymer is in the range of 105 to 130 kg/mol.

12. The rubber composition of claim 11 wherein the molecular weight (Mn) of the polymer is in the range of 107 to 128 kg/mol.

13. The rubber composition of any one of the above claims, wherein the elastomer is a styrene butadiene rubber

14. The rubber composition of claim 11 wherein the styrene butadiene rubber is obtained by solvent polymerization.

15. A tire comprising the rubber composition of any one of the above claims.