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Title:
STABILIZED THIOSULFATES AND THEIR USE IN RUBBER COMPOSITIONS
Document Type and Number:
WIPO Patent Application WO/2020/081283
Kind Code:
A1
Abstract:
Stabilized thiosulfate blends are disclosed that include a compound having at least one thiosulfate functional group; and silica particles. The inventive blends may have a pH from about 4.5 to about 9, as measured according to ASTM D1293-18.

Inventors:
FORCINTI LEANDRO (US)
FIELDS DONALD L (US)
CHAPELET JUDICAEL JACQUES (US)
NIKNEZHAD SEPIDEH (US)
Application Number:
PCT/US2019/055095
Publication Date:
April 23, 2020
Filing Date:
October 08, 2019
Export Citation:
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Assignee:
FLEXSYS AMERICA LP (US)
International Classes:
C08K3/36; B60C1/00; C07C381/02; C08K5/41; C08L7/00; C08L21/00
Domestic Patent References:
WO2010085324A12010-07-29
Foreign References:
EP2708529A12014-03-19
EP0829508A11998-03-18
US20030015271A12003-01-23
US4704334A1987-11-03
US4417012A1983-11-22
US20050032945A12005-02-10
US4417102A1983-11-22
US201862753949P2018-11-01
Other References:
KANGSHIN INDUSTRIAL CO.,LTD.: "Nipsil & Nipgel series", 4 November 2015 (2015-11-04), XP055658520, Retrieved from the Internet [retrieved on 20200116]
Attorney, Agent or Firm:
CARRIER, Michael K. (US)
Download PDF:
Claims:
CLAIMS

1. A stabilized thiosulfate blend comprising:

a compound having at least one thiosulfate functional group; and silica particles,

wherein the blend has a pH from about 4.5 to about 9, as measured according to ASTM D1293-18.

2. The stabilized thiosulfate blend of claim 1 , wherein the blend has a pH from 5.0 to 8.5, as measured according to ASTM D1293-18.

3. The stabilized thiosulfate blend of claim 1 , wherein the silica comprises one or more of silicon dioxide, aluminum silicate, calcium silicate, and precipitated silica.

4. The stabilized thiosulfate blend of claim 1 , wherein the silica particles have an average primary particle size from about 5nm to about 1500nm.

5. The stabilized thiosulfate blend of claim 1 , wherein the silica particles have an average primary particle size from 25nm to about 1000nm

6. The stabilized thiosulfate blend of claim 1 , wherein the silica particles have a pH from about 3.0 to about 8.0, as measured according to ASTM D1293-18.

7. The stabilized thiosulfate blend of claim 1 , wherein the silica particles have a pH from 4.0 to 7.5, as measured according to ASTM D1293- 18.

8. The stabilized thiosulfate blend of claim 1 , wherein the silica particles are present in an amount from about to about 0.1 wt.% to about 20 wt. %, based on the total weight of the stabilized thiosulfate blend.

9. The stabilized thiosulfate blend of claim 1 , wherein the silica particles are present in an amount from 0.5 wt.% to 18 wt. %, based on the total weight of the stabilized thiosulfate blend.

10. The stabilized thiosulfate blend of claim 1 , wherein the silica particles are present in an amount from about to about 1 wt.% to about 15 wt. %, based on the total weight of the stabilized thiosulfate blend.

11. The stabilized thiosulfate blend of claim 1 , wherein the compound having at least one thiosulfate functional group comprises one or more of: sodium S,S'-(azanediylbis(ethane-2,1 -diyl)) bis(sulfurothioate); sodium S,S'- ([1 ,1 '-biphenyl]-4,4'-diylbis(methylene)) bis(sulfurothioate); sodium S,S'- ((ethane-1 ,2-diylbis(oxy))bis(ethane-2,1 -diyl)) bis(sulfurothioate); or disodium S,S'-hexane-1 ,6-diyldisulfurothioate.

12. The stabilized thiosulfate blend of claim 1 , wherein the compound having at least one thiosulfate functional group comprises one or more of: S,S',S"-((1 ,3,5-triazinane-1 ,3,5-triyl)tris(propane-3,1 -diyl)) tris(sulfurothioate), S,S',S"-((1 ,3,5-triazinane-1 ,3,5-triyl)tris(ethane-2,1 -diyl)) tris(sulfurothioate), S,S',S"-((1 ,3,5-triazinane-1 ,3,5-triyl)tris(methane-1 ,1 -diyl)) tris(sulfurothioate), S,S',S"-((1 ,3,5-triazinane-1 ,3,5-triyl)tris(butane-4,1 -diyl)) tris(sulfurothioate), or S,S',S"-((1 ,3,5-triazinane-1 ,3,5-triyl)tris(pentane-5,1 -diyl)) tris(sulfurothioate).

13. An elastomeric formulation, comprising at least one elastomer and the stabilized thiosulfate blend of claim 1.

14. The elastomeric formulation of claim 13, wherein the stabilized thiosulfate blend is present in an amount from about 0.01 parts by weight to about 30 parts by weight, with respect to 100 parts by weight of the at least one elastomer.

15. The elastomeric formulation of claim 13, wherein the stabilized thiosulfate blend is present in an amount from about 0.1 parts by weight to about 20 parts by weight, with respect to 100 parts by weight of the at least one elastomer.

Description:
STABILIZED THIOSULFATES AND THEIR

USE IN RUBBER COMPOSITIONS

FIELD OF THE INVENTION

[0001] The present invention relates to stabilized thiosulfates and their use in rubber compositions.

[0002] Modern elastomeric formulations such as those used in tires must meet a number of conflicting demands, to simultaneously achieve such properties as abrasion resistance, crack growth resistance, reduced rolling resistance or hysteresis, and wet and dry traction. Often, one property can be improved only at the expense of another. For example, reducing rolling resistance, that is, lowering hysteresis, typically results in decreased crack growth resistance, while increasing crack growth resistance can increase hysteresis or worsen the commercial processing of the uncured rubber vulcanizate.

[0003] Compounds having thiosulfate groups of the formula -S- S03-M linked by an organic bridging group are used in sulfur vulcanizates as network stabilizers and rubber to metal bonding promoters, see for example U.S. Pat. Nos. 4,704,334 and 4,417,012, EU0070143, and EU0109955). Another potential use of these compounds is to reduce or replace the use of materials of concern that are used as bonding agents, such as cobalt fatty acid salts.

[0004] When commercially processing rubber, the initial onset of vulcanization needs to be controlled in order to enable a processing safety time, as can be measured by T5 scorch (ASTM D 1646). The network stabilizers of the above references can affect this vulcanization process by causing a reduction in this scorch safety time. One way the scorch time has been improved for these network stabilizers is the reduction of particle size below 15 micrometers (US Pat. Publication. No. 2005/0032945). While this improves the scorch safety, a percent drop in T5 scorch is still reported. In addition, this approach has no improvement in other critical properties such as powder flow.

[0005] It is thus desirable to develop a composite material that stabilizes the thiosulfate salt, that improves one or more of scorch safety, flow properties, and network stability performance in rubber compositions.

SUMMARY OF THE INVENTION

[0006] The present invention relates to stabilized thiosulfates. In one aspect, the stabilized thiosulfates of the invention comprise a blend of a compound having at least one thiosulfate functionality and silica.

[0007] Further aspects and areas of applicability will become apparent from the description and the claims provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the spirit and scope of the present invention.

DETAILED DESCRIPTION

[0008] As used herein, the following terms or phrases are defined as follows:

[0009] The term“elastomer” means a polymer which, after vulcanization or crosslinking and at room temperature, can be stretched under low stress to, for example, at least about twice its original length and, upon immediate release of the stress, will return with force to approximately its original length, including without limitation rubber.

[0010] The term "butadiene-containing elastomer" refers generally to an elastomer comprising butadiene polymer units, that is, to a polymer that may be called a polybutadiene. The butadiene-containing elastomer may also include polymer units of isoprene, styrene and/or other polymer units.

[0011] The term "isoprene elastomer" refers generally to an elastomer comprising isoprene polymer units, that is, to a polymer that may be called a polyisoprene. Isoprene elastomers are preferably obtained from natural rubber, although they may be produced as a synthetic natural rubber. Preferred isoprene elastomers include those that have relatively high molecular weights. The isoprene elastomer may be substantially free of butadiene and styrene polymer units, and in one aspect may consist essentially of isoprene polymer units.

[0012] The term "non-isoprene elastomer" refers to an elastomer that is substantially free of isoprene elastomer polymer units. Examples of non-isoprene elastomers include a homopolymer butadiene elastomer, certain butadiene-containing elastomers, and a copolymer of butadiene and styrene.

[0013] “Styrene-butadiene rubber” as used herein means an elastomer having significant amounts of both styrene and butadiene polymer units.

[0014] The abbreviation "phr" means the number of parts by weight per 100 parts by weight of rubber. For example, in the case of a rubber blend, it would be based on 100 parts by weight of total rubber.

[0015] The pH values provided herein are those measured according to ASTM D1293-18, taken at 20 weight% and at room temperature; that is, 20 wt% stabilized thiosulfate is dispersed in water and the pH of the water is then measured per the referenced ASTM test method, as further described in the experimental section below.

[0016] The term "rubber blend" refers to two or more elastomers or rubbers in the neat form used to prepare a blend or a mixture of two or more different neat elastomers, such as a blend of two or more natural (e.g., isoprene) and/or synthetic (e.g., butadiene and/or styrene) rubber materials.

[0017] The term "rubber composition" refers to a composition containing at least one elastomer and/or rubber blend(s) and which optionally further include other ingredients such as fillers, softeners, activators, vulcanizing agents, and/or accelerators.

[0018] The t5 values provided herein, were measured using an Monsanto Mooney Viscometer Model MV2000E at 121 C. T5 is a measure of scorch, an indication of premature vulcanization, in which a higher t5 value indicates higher resistance to scorch, or higher scorch safety. As used herein, the t5 values are relative and obtained from rubber samples subjected to the same test conditions. Those skilled in the art will understand that the precise test conditions used in a given instance are less important than are the relative values achieved under the same testing conditions.

[0019] The "ts1 " values provided herein, were measured using a Flexsys Moving Die Rheometer MDR 2000E at 150 C cure temperature and are an alternative indication of the onset of cure vulcanization. Again, those skilled in the art will understand that the precise test conditions used in a given instance are less important than are the relative values achieved under the same testing conditions.

[0020] The term "viscosity" of a rubber composition herein, unless otherwise indicated, shall refer to Mooney Viscosity, defining the standard measure of the viscosity of the rubber. A Mooney viscometer is used to measure the Mooney viscosity. Units of measurement are in Mooney units.

[0021] In one aspect, the invention relates to stabilized thiosulfates that are a blend of a compound having at least one thiosulfate functionality, and silica, wherein the stabilized thiosulfate has a pH from about 4.5 to about 9. Alternatively, the pH of the blend may be from 5.0 to 8.5, or from 5.5 to 8, in each case as measured according to ASTM D1293-18 as described above. The pH of the stabilized thiosulfates of the invention may thus be at least about 4.5, or at least 5.5, or at least 6, up to about 7.5, or up to 8.0, or up to 8.5, or up to 9, in each case as measured according to ASTM D1293-18.

[0022] The stabilized thiosulfates useful according to the invention include any compound having at least one thiosulfate functionality. Examples include those disclosed and claimed in U.S. Pat. Nos. 4,704,334 and

4,417,102, the disclosures of which are incorporated herein by reference. Thus, thiosulfates useful according to the invention include sodium salts of hexamethylene dithiosulfate dihydrate. [0023] In one aspect, the compounds having at least one thiosulfate functional group thus correspond to those having at least one of the following thiosulfate functional groups:

-S-SO2R2, wherein R2 may represent either (a) a radical -OM where M is a monovalent metal, the equivalent of a multivalent metal, a monovalent ion derived by the addition of a proton to a nitrogenous base or the equivalent of a multivalent ion derived by the addition of two or more protons to a nitrogenous base, or (b) an organic radical selected from aliphatic, cycloaliphatic, aromatic and heterocyclic radicals, and radicals which are combinations of any two or more such radicals.

[0024] The thiosulfate group may be linked by an organic group (X) or attached to an organic polymer chain by the following structure:

R1-X-S-SO2R2 wherein X may correspond to one of the following:

-(CH2)n-, wherein n > 2, or from 5-16

-(CH2)X-0-(CH 2 )X-, wherein x is from 2 - 20, or from 3-8

-(CH2)X-0-CH2-0-(CH2)X-, wherein is from 2 - 20, or from 3 - 8 -(CH2-CH2-0)n-CH2-CH2-, wherein n > 2, or from 5-16

-(CH2)n -CO-0-(CH2)n-, wherein n > 2, or from 5-16

-(CH2)n -C0-0-Y-0-C0-(CH2)n-, wherein n > 2, or from 5-16

-(CH 2 )X- S0 2 -(CH 2 )X-, wherein x is from 2 - 20, or from 3-8

-(CH2)X-NH-(CH2)X-, wherein x is from 2 - 20, or from 3-8

-(CH+)X-NH2+ -(CH 2 )X-, wherein x is from 2 - 20, or from 3-8

-CH P CH -

2 \=/ 2

Or

wherein Y may be (CH2)f and f is greater than 2, or from 3-15.

[0025] Specific examples of compounds having at least one thiosulfate functional group thus include the following sodium salt compounds, and corresponding salts of other metals such as nickel:

Na03S2(CH2)5S203Na; Na03S2(CH2)6S203Na;

Na03S2(CH2)10S2O3Na; Na03S2(CH2)40(CH2)4S203Na;

Na03S2(CH2)40CH20(CH2)4S203Na;

Na03S2(CH2)20CH20(CH2)2S203Na; and Na03S2(C6H6)S203Na.

[0026] Further examples include:

sodium S,S'-(azanediylbis(ethane-2,1 -diyl)) bis(sulfurothioate),

sodium S,S'-([1 ,1 '-biphenyl]-4,4'-diylbis(methylene)) bis(sulfurothioate),

sodium S,S'-((ethane-1 ,2-diylbis(oxy))bis(ethane-2,1 -diyl)) bis(sulfurothioate), and

disodium S,S'-hexane-1 ,6-diyldisulfurothioate.

[0027] Other examples of compounds having at least one thiosulfate functional group include those disclosed and claimed in U.S. Pat. Appln. No. 62/753,949 filed November 1 , 2018, the disclosure of which is incorporated herein by reference in its entirety. These compounds correspond to those represented by formula I:

wherein Ri comprises a hydrogen atom or an alkyl group having 1 -2 carbon atoms; wherein Fte comprises an alkylene group, an arylene group, or a heterocyclic group; and wherein M comprises a monovalent metallic cation such as sodium, lithium, or potassium; or a multivalent metallic cation such as zinc, nickel, iron, titanium, or cobalt; or an ammonium or alkyl ammonium cation derived by addition of proton(s) to a nitrogenous base.

[0028] In this aspect, specific examples thus include S,S',S"-((1 ,3,5- triazinane-1 ,3,5-triyl)tris(propane-3,1 -diyl)) tris(sulfurothioate), S,S',S"-((1 ,3,5- triazinane-1 ,3,5-triyl)tris(ethane-2,1 -diyl)) tris(sulfurothioate), S,S',S"-((1 ,3,5- triazinane-1 ,3,5-triyl)tris(methane-1 ,1 -diyl)) tris(sulfurothioate), S,S',S"-((1 ,3,5- triazinane-1 ,3,5-triyl)tris(butane-4, 1 -diyl)) tris(sulfurothioate), and S,S',S"- ((1 ,3,5-triazinane-1 ,3,5-triyl)tris(pentane-5,1 -diyl)) tris(sulfurothioate).

[0029] Silica particles useful according to the invention include those having a relatively high surface area particle of neutral to acidic nature, with a pH for example less than about 8, or less than 7.8, or less than about 7.5, or less than about 7.0, in each case as measured by ASTM D1293-18.

[0030] The pH of the silica particles useful according to the invention affect the pH of the resulting stabilized thiosulfate blends, such that the amount of silica used may be determined at least in part by the effect of the silica on the pH of the resulting stabilized thiosulfates. The effect on the pH of the resulting stabilized thiosulfate is thus a function both of the amount of silica used, as well as the pH of the silica. In alternative embodiments, the pH of the silicas useful according to the invention may be, for example, from about 8 to about 3.0, or from 7.5 to 4, or from 7.0 to 5.0, in each case as measured by ASTM D1293-18.

[0031] The silica particles useful according to the invention include those having a relatively high surface area, for example silica particles having BET surface areas, for example, from about 25 to about 750 m 2 /g, or from 40 to 500 m 2 /g, or from 50 to 400 m 2 /g, in each case as measured, for example, according to ASTM D1993-18. In one aspect, a surface area from about 100 to about 250 m 2 /g allows for a stable relatively low pH material to be developed without the formation of free thiols.

[0032] In acidic conditions and under heat, we have found that thiosulfates degrade into free thiols and as such an extremely low pH material is not desirable; however, by powder mixing, for example about 0.5 wt/wt percent or more, a high surface area silica and up to about 20 wt/wt% one can get a lower pH, that is, significantly less than the pH of the compound having at least one thiosulfate functionality, and still have a stable product with little formation of free thiols and equal activity as measured by rubber reversion in rubber formulations. We have found that a rubber composition containing more than about 10% by wt/wt free high surface area silica may negatively impact the activity of the composite material whereas one with less than 1 wt/wt% of silica tends to have minimal effect on the pH of the stabilized thiosulfates.

[0033] Thus, the amount of silica particles present in the stabilized thiosulfate blends may vary widely, from about 0.1 wt.% to about 20 wt.%, or from 0.5 to 18 wt.%, or from 1 wt.% to 15 wt%, in each case based on the total weight of the stabilized thiosulfate blend. Thus, the amount of silica particles present in the stabilized thiosulfate blends may be at least about 0.1 wt.%, or at least 0.2 wt%, or at least 0.5 wt.%, or at least 1.0 wt%, or at least 2 wt.%, or at least 5 wt.%, up to about 15 wt.%, or up to 16 wt.%, or up to 18 wt.%, or up to 20 wt.%, or up to 25 wt%, or up to 30 wt%, in each case based on the total weight of the stabilized thiosulfate blend.

[0034] Another unexpected benefit of using the stabilized

thiosulfates of the invention is improved rubber formulation scorch safety as measured by Mooney scorch and the onset of cure ts1 . A further advantage of the use of the silica particles of the invention is improved flowability and compressibility of the rubber compositions obtained. [0035] Primary particle sizes of the silica particles useful according to the invention can vary widely, and are related to the surface area, the chemical composition of the particles, and the way in which they are made.

For example, the primary particle sizes may vary widely from about 5 nm to about 1 ,500 nm, or from 10nm to 1 ,200 nm, or from 25 nm to 1 ,000 nm, or from 50nm to 750 nm. Thus, the primary particle sizes of the silica particles may be at least 5nm, or at least 10nm, or at least 25nm, or at least 50nm, up to about 750nm, or up to about 1 ,000 nm or up to 1 ,200 nm, or up to 1 ,500 nm.

[0036] The silica particles useful according to the invention include precipitated aluminum silicates, for example having a primary particle size from about 100 nm to about 1000 nm; calcium silicates, for example from about 100nm to about 1000 nm; and precipitated silica, for example from about 5nm to about 100nm.

[0037] A wide range of elastomers and rubber compositions may take advantage of the stabilized thiosulfates of the invention. Thus, natural rubber (NR), styrene-butadiene rubber (SBR), or a blend of NR and SBR or NR and SBR, with one or more other rubbers, can be used according to the invention, it being understood that for purposes of this invention the term "rubber" includes any elastomer containing a hydrocarbon unit which is a polymer with some unsaturated chemical bonds. Typically, SBR, a blend of SBR with natural rubber (NR), a blend of SBR with polybutadiene rubber or butadiene rubber (BR), or a blend of SBR with NR and BR is used. The types rubbers used will affect the amounts of stabilized thiosulfate that are needed.

[0038] The stabilized thiosulfates of the invention were added to rubber formulations containing at least one diene-based rubber and potentially more than one with at least one reinforcing particulate such as N300 series carbon black or in another embodiment precipitated silica with a bi-functional silane. These rubber formulations were additionally compounded with antiozonants and antioxidants such as 6-PPD and accelerators such as sulfenamide type accelerators with sulfur either composed of rubber maker sulfur or insoluble sulfur such as Crystex HD OT 20. These rubber formulations were made in at least one mix pass with potentially more mix passes added to get the correct rubber green viscosity. These rubber formulations were made in an internal mixer and sheeted out to the appropriate thickness using a mill. These compounded rubber formulations containing the stabilized thiosulfates (the composite bunte salt) were then tested for cure using a moving die rheometer. Additionally, these formulations were evaluated for the onset of cure by using a Mooney viscometer to measure the onset of cure. It was shown that formulations containing the stabilized thiosulfates could give a 10% improvement in the onset of cure as defined by ts1 in the MDRs and/or t5 in the Mooney viscometer. These improvements were shown to exist without trade-offs in the thiosulfate reversion resistance nor negative impact in the T25 or T90 of the rheometer curve suggesting some pre-vulcanization inhibition that is provided with the stabilized thiosulfates that is not expected.

[0039] Not wishing to be bound by any theory, the reduction in scorch safety of rubber compositions containing thiosulfates may be driven by their high pH, that is, their basic nature. We have found that, when you acidify them, for example below about 4.5, you may degrade the stabilized thiosulfates (bunte salt) through hydrolysis and thus create free mercaptans, reducing their efficacy. According to the invention, a stabilized thiosulfate is achieved having a pH that is lowered by the silica particles, for example to from about 4.5 to about 9, or from 5 to 8.5, or as disclosed elsewhere herein, without being so low as to cause degradation.

[0040] Thus, in one aspect, the amount of stabilized thiosulfates used in the rubber formulations of the invention may be, for example, from about 0.01 phr to about 30 phr, or from 0.1 to 20 phr, or from 0.5 to 10 phr. In other aspects, the amount of stabilized thiosulfate blends useful in the rubber formulations of the invention will be at least 0.1 phr, or at least 0.7 phr, or at least 1 phr, up to 10phr, or up to 15 phr, or up to 25 phr. [0041] According to the invention, the stabilized thiosulfates of the invention may be mixed with rubber formulations, for example in internal mixers, extruded into green components, and used as the road contacting surface of pneumatic tires, including those used in high severity services for heavy tires. Heavy tires are those, for example, having tread depths of 18/32” or deeper. High severity services are service conditions which involve a predominance of breaking, acceleration and turning versus steady state rolling. In another embodiment, these formulations are used as the road contacting surface of pneumatic tires used in light tires where a balance of wear and hysteresis are needed. Light tires are defined as tires with tread depths, for example, from about 1/32” to about18/32”. In both cases, formulating with these new types of stabilized thiosulfates may result in compounds that will give an improvement in network stability whilst improving their green state processing.

[0042] The rubber blend compositions according to the invention may include at least one isoprene elastomer and at least one butadiene-containing elastomer. The isoprene elastomer may be a natural rubber. The butadiene- containing polymer may be a synthetic rubber such as butadiene rubber (BR), styrene-butadiene rubber (SBR) or mixtures or co-polymers of BR and SBR. The butadiene-containing polymer may be a copolymer containing isoprene units. One suitable butadiene-containing rubber is a styrene-isoprene- butadiene rubber (SIBR).

[0043] Examples of suitable synthetic elastomer polymers that may be incorporated in the rubber blends include the homopolymerization products of butadiene and its homologues and derivatives, for example, methylbutadiene, dimethylbutadiene and pentadiene as well as copolymers such as those formed from butadiene or its homologues or derivatives with other

unsaturated monomers. Among the latter are acetylenes, for example, vinyl acetylene; olefins, for example, isobutylene, which copolymerizes with isoprene to form butyl rubber; vinyl compounds, for example, acrylic acid, acrylonitrile (which polymerize with butadiene to form NBR), methacrylic acid and styrene, the latter compound polymerizing with butadiene to form SBR, as well as vinyl esters and various unsaturated aldehydes, ketones and ethers, e.g., acrolein, methyl isopropenyl ketone and vinylethyl ether. The rubber blend composition may also include at least one neat rubbers selected from the group consisting of: neoprene (polychloroprene), polybutadiene (including cis-1 ,4-polybutadiene), polyisoprene (including cis-1 ,4-polyisoprene), butyl rubber, halobutyl rubber such as chlorobutyl rubber or bromobutyl rubber, styrene/isoprene/butadiene rubber, copolymers of 1 ,3-butadiene or isoprene with monomers such as styrene, acrylonitrile and methyl methacrylate, as well as ethylene/propylene terpolymers, also known as ethylene/propylene/diene monomer (EPDM), and in particular, ethylene/propylene/dicyclopentadiene terpolymers. Additional examples of rubbers which may be used in the rubber blend include alkoxy-silyl end functionalized solution polymerized polymers (SBR, PBR, IBR and SIBR), silicon-coupled and tin-coupled star-branched polymers. The preferred rubber blends include a natural rubber elastomer and a synthetic rubber elastomer including at least one compounds selected from the group consisting of: polyisoprene, polybutadiene and SBR.

[0044] Unless otherwise indicated, the rubber blend is present at 100 parts per hundred rubber (phr), as all other material are added based on 100 parts of rubber material. Batches can be conveniently scaled for different sizes of mixtures using this measurement system.

[0045] The following examples, while provided to illustrate with specificity and detail the many aspects and advantages of the present invention, are not be interpreted as in any way limiting its scope. Variations, modifications and adaptations which do depart from the spirit of the present invention will be readily appreciated by one of ordinary skill in the art.

ANALYTICAL METHODS

[0046] Ph measurements of stabilized thiosulfate as used herein were carried out according to ASTM standard D1293-18. The Mettler Toledo

Seven Easy pH probe was first standardized with three buffers conformant to test method A of the above ASTM standard. 20 m/m% of the stabilized or non-stabilized thiosulfate, or the silica particles as the case may be, was added to Dl water whilst stirring. Stirring was continued during the period of pH measurement. The pH electrode had an integral temperature sensor. Measurement was taken until two successive portions differed by no more than 0.03 pH units and showed drifts of less than 0.03 pH units.

[0047] Moving die rheometers (Monsanto MDR 2000E) were used to determine the cure characteristics of the rubber formulations with the stabilized thiosulfates, or the unstabilized thiosulfate salts used as controls. The instruments conformed to ASTM standard D5289-17 and are defined as rotorless cure meters. A rubber test piece is contained in a die cavity which may be closed or almost closed and maintained at an elevated temperature. The cavity is formed by two dies one of which is oscillated through a small rotory amplitude. This action produces a sinusoidal shear torque which depends on the stiffness of the rubber compound. The stiffness of the rubber test piece increases as vulcanization proceeds. The test is completed when the recorded torque rises to either an equilibrium or maximum value or when a predetermined time has elapsed. A curve representing the torque at peak strain in one direction of the oscillation cycle is continuously recorded as a function of time. Critical parameters to report include MH which is the highest value measured by a torque transducer at the peak strain amplitude of the oscillating cycle (S’) during a specified period of time when no plateau or maximum torque is obtained. ML which is the minimum S’ torque in dN * m. T25 is equal to the time to satisfy this equation (ML+25 * (MH-ML)/100). T90 is equal to the time to satisfy this equation (ML + 90 * (MH-ML)/100). The scorch time is defined as ts1 which is in minutes time to an increase of 1 unit of S’ torque from ML value with an oscillation amplitude of +/- 0.5.

[0048] A Mooney viscometer with a large rotor was used to determine the viscosity and pre-vulcanization characteristics of the rubber formulations containing the stabilized thiosulfates. Monsanto’s Mooney MV 2000E conforming to ASTM D1646-17 was used. Part C test method where the viscosity of vulcanizable rubber compounds is recorded during heating at a specified temperature (i.e., 121 C) was ran. The minimum viscosity and times for the viscosity increase by specified amounts are used as arbitrary measures of the start and rate of vulcanization. The difference between this method and the aforementioned method above is that this method cannot be used to study complete vulcanization because the continuous rotation of the disk will result in slippage when the specimen reaches a stiff consistency. However, given the historical significance of using this test to measure the incipient cure (scorch) time it is important to evaluate the improvement in scorch safety using this method in combination with the rotor-less cure meters. The test specimens consisted of two test pieces of the rubber formulation having a combined volume of 25 +/- 3 cm 3 . A barrier film

consistent with ASTM standard D1646 is used. The properly calibrated instrument is adjusted to a temperature of 121 C. The torque indicator is adjusted to zero read while the viscometer is running unloaded with the rotor in place. The disk is then stopped. After the hot rotor is removed one of the test pieces is punctured then the rotor is but back in place and the second test piece is placed on the center of the rotor. The dies are closed immediately and the timer turned on. A 1 minute lag between when the dies are closed is allowed to elapse then the rotors are turned on. The viscosity is recorded and the following information is gathered: (1 ) Minimum viscosity. (2) The time 5 units of viscosity increase occurs (ts). (3) The time 35 units in viscosity increase occurs (t3s). Here ts is defined as the time to scorch whereas t35 is defined as the time to cure

[0049] Powder flow rheology was measured using a Freeman Technology FT4 Powder Rheometer conformant to ASTM D7891 -15. A shear vessel was used with the appropriate spindle-mounted attachment. The shear cell vessel was assembled compliant to the ASTM standard The mass of the empty shear vessel was tared. The shear vessel was then filled with sufficient powder such that following the compression stage, the specimen is not compressed below the split level of the leveling assembly. Calculation of flow function was based on the ASTM standard. EXAMPLES

Example 1

[0050] A hexamethylene thiosulfate salt (structure

Na03SS(CH2)6SS03Na * 2 H2O) was mixed with silica that has a specific surface area as measured by BET of 130 m A 2/g (Ultrasil VN2 Evonik).

Loadings of 1 - 20 wt/wt% silica to hexamethylene thiosulfate salt were tried. The powder mixing was done utilizing an Inversina 2L Tumble Mixer for 15 minutes. The composite materials are indicated as Experimental A-D. To understand the impact of powder mixing hexamethylene thiosulfate salt with precipitated silica, measurements were made following ASTM D1293-18 method = at 20 m/m% concentration in deionized (Dl) water and room temperature. The results of the pH measurements of the resultant

Experimental A-D can be seen in Table 1 :

Table 1

We note that at 20 wt/wt% the material exhibited relatively poor stability and began to decompose to free mercaptans and sulfuric acid, by visual and olfactory observation. No pH readings were therefore made after the initial reading, and the samples were discarded. Interestingly, up to 10 wt/wt% we did not observe any decomposition of material and the thiosulfate was thus stabilized. To validate this observation the pH of the composite was measured as a function of time for two weeks. The results can be seen in Table 2. Table 2

[0051] Experimental A - D were then added into rubber formulations that were mixed in a 1.5 L internal mixer and compared to three controls. One the precipitated silica independently added to the rubber formulation. The other a compound prepared with the hexamethylene thiosulfate salt added without the precipitated silica. The third was a compound prepared with neither the hexamethylene thiosulfate and without the precipitated silica. The model formulation used was comprised of 100 phr of high cis-polyisoprene rubber, 50 phr of N339 carbon black, 2.0 phr of 6 PPD, 2 phr of stearic acid, and 8 phr zinc oxide. This subsequent formulation was pre-mixed with the aforementioned ingredients, then the experimental or equivalent

(hexamethylene thiosulfate) was added in a 1.5 L internal mixer and mixed until the internal batch temperature reached 165 C. The rubber was then removed and sheeted out in a mill and subsequently remixed with curatives DCBS and Insoluble Sulfur in a final pass. Table 3 shows the formulation Table 3

[0052] The unexpected result was an improvement in the delay in vulcanization necessary to process green rubber. This is typically measured using ASTM D-1646 standard test methods for rubber viscosity, stress relaxation, and pre-vulcanization characteristics (Mooney Viscometer). To confirm that the onset of cure was improved (i.e., scorch safety) but no significant impact in other cure rheometer characteristics are impacted (i.e., T25, T90, and maximum rate) moving die rheometery was performed per ASTM D5289. The results from the formulations shown in Table 2. For those physical parameters related to onset of cure (i.e., T5 and Ts1 ) the values for the experimental were compared to % change of the hexamethylene thiosulfate composite (i.e., Experimental A - D) T5 or Ts1 versus non-hexamethylene thiosulfate control (Control A), the hexamethylene thiosulfate (i.e., Duralink HTS with particle size 1 1 micrometers; Control B), and the hexamethylene thiosulfate with additional silica added freely in the rubber formulation (i.e., Control C). The calculation was as follows: T5 or Ts1 scorch % drop = -[1 - T5 (Experimental A-

D)/T5(Controls)] * 100

[0053] For other performance properties such as T25, T90, and Delta Torque those were normalized to each control through the following formula:

Compound Physical Property % = (Experimental)/(Control) * 100

Table 4.

[0054] As shown in Table 4 the scorch safety of the hexamethylene thiosulfate was improved by up to 7.1 % versus its natural control (i.e., hexamethylene thiosulfate) with as little as 1 wt/wt%. It is also desirable to have improved powder flow functionality. One way to measure powder flow is through the use of FT4 Powder Rheometer per ASTM D7891 -15. As defined in the ASTM method flow function is defined as:

FF = si/fc where s1 is the major principal stress and fc is the unconfined yield strength. The higher the flow function the more free-flowing the powder. Table 5 shows the normalized to Duralink HTS with particle size of 1 1 micrometers the flow function of the composite materials as a function of silica loading.

Table 5

[0055] As can be seen in Table 5 there is a significant improvement in the flowability of the composite material versus the Duralink HTS control.

Example 2

[0056] To evaluate the impact of other silica particle sizes on the stability of the blend of silica and hexamethylene thiosulfate, several other particle sizes were evaluated. Evonik 7000 GR with specific area of 175 m 2 /g as determine by BET and Evonik 5000 GR with a specific area of 1 15 m 2 /g were evaluated. Table 6 shows the results of Ph versus these two samples. As can be seen in Table 6 concentration above 10 wt/wt% regardless of particles size resulted in a loss of stability and began to decompose to free mercaptans and sulfuric acid. Interestingly up to 10 wt/wt% did not show any decomposition of material and stabilized the composite material. Again the hexamethylene thiosulfate without any intimate blend of silica resulted in pH above 9.0.

Table 6

[0057] The foregoing description of various embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise

embodiments disclosed. Numerous modifications or variations are possible in light of the above teachings. The embodiments discussed were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.