Optimizing tire compound reversion resistance without sacrificing performance characteristics.Reversion reversion: see atavism. is the thermal degradation of sulfidic crosslinks leading to a reduction of crosslink density, a change in the distribution of crosslinks types and an introduction of mainchain modifications. It leads to a decline in compound physical properties such as modulus See modulo. , tensile tensile, adj having a degree of elasticity; having the ability to be extended or stretched. and elongation elongation, in astronomy, the angular distance between two points in the sky as measured from a third point. The elongation of a planet is usually measured as the angular distance from the sun to the planet as measured from the earth. and in performance characteristics such as tear, fatigue and hysteresis hysteresis (hĭs'tərē`sĭs), phenomenon in which the response of a physical system to an external influence depends not only on the present magnitude of that influence but also on the previous history of the system. . These changes in compound properties are generally translated into reduced tire performance characteristics and/or shorter service life. Reversion of sulfur cured rubber compounds occurs when vulcanizates are overcured during manufacturing or exposed to anaerobic anaerobic /an·aer·o·bic/ (an?ah-ro´bik) 1. lacking molecular oxygen. 2. growing, living, or occurring in the absence of molecular oxygen; pertaining to an anaerobe. thermal aging conditions during service life. Over the years (ref. 1), the tire industry has moved toward the use of higher accelerator levels and lower sulfur levels (or the use of sulfur donors) to more "efficiently" use the available sulfur by generating crosslinks with fewer sulfur atoms and thus provide greater thermal stability. As indicated in table 1, in which we compare a semi-efficient (SEV SEV Severity SEV Schienenersatzverkehr (German: Rail-Substitution-Traffic; by Bus During Engineering Works) SEV State Equalized Value SeV Sendai Virus SEV Schweizerischen Elektrotechnischen Vereins (Switzerland) ) cure system to a traditional conventional (CV) system, a variety of compromises are created which must be taken into consideration when developing new formulations. Table 1 - comparison of SEV and CV cure systems Properties SEV CV Tensile strength = +/= Modulus = = Elongation - + Flex life - + Tear strength - + Hysteresis - + Thermal stability + - Oxidative stability + - Heat build-up + - + signifies improvements Over the last few years (refs. 2-4), Flexsys has introduced two new rubber chemicals, 1,3 bis Second version. It means twice in Old Latin, or encore in French. Ter means three. For example, V.27bis and V.27ter are the second and third versions of the V.27 standard. (citraconimidomethlyl benzene benzene (bĕn`zēn, bĕnzēn`), colorless, flammable, toxic liquid with a pleasant aromatic odor. It boils at 80.1°C; and solidifies at 5.5°C;. Benzene is a hydrocarbon, with formula C6H6. ) (BCI-MX) and hexamethylene-1,6-bisthiosulfate disodium salt dihydrate (HTS HTS Heights HTS Harmonized Tariff System HTS High Throughput Screening (biomolecular assay screening) HTS High-Throughput Screening (Pharmaceutical Industry) HTS Harmonized Tariff Schedule ) which provide two different ways to improve the thermal aging resistance of sulfur-based vulcanizates as compared to existing technology. Each functions by uniquely different mechanisms of action and each provides different levels of performance improvements. In this article, a comparison of HTS and BCI-MX to CV and SEV cure systems will illustrate the potential benefits of these approaches to address reversion in tire compounds. Results and discussion Semi-efficient cure As already indicated when accelerated sulfur vulcanized rubber India rubber, vulcanized. - Knight. See also: Vulcanize compounds are exposed to overcure or high temperature conditions either during the manufacturing process or product service life, a thermal degradation of the crosslink structure will occur such that both the extent of crosslinking and the nature of the crosslinks will be drastically changed. As would be expected, these changes in the vulcanizate structure will translate into reduction in physical properties and performance characteristics. An example of these effects is outlined in table 2, where even a SEV system, which is designed to provide improved thermal stability, exhibits significant changes in properties. Table 2 - effects of reversion on physical properties and performance characteristics of a SEV cure Rheometer reversion @ 150 [degrees] C % reversion in 60 min. 9 Modulus reversion Modulus 300%, MPa at t90 @ 150 [degrees] C 15.5 60' @ 150 [degrees] C 13.5 Fatigue resistance, kC to failure (strain energy [not equal to] 3.5 x [10.sup.3] [kJm.sub.-3]) t90 @ 150 [degrees] C 130 60' @ 150 [degrees] C 90 Heat build-up, [Delta] T at 100 [degrees] C t90 @ 150 [degrees] C 27 60' @ 150 [degrees] C 37 Blow-out time, min. at 100 [degrees] C t90 @ 150 [degrees] C 14 60' @ 150 [degrees] C 10 Crosslink density, [(2 Mc, chem).sup.-1] x [10.sup.5] gmmole/RH t90 @ 150 [degrees] C 5.11 60' @ 150 [degrees] C 4.80 Formulation: SMR (Specialized Mobile Radio) The communications services used by police, ambulances, taxicabs, trucks and other delivery vehicles. Throughout the U.S., approximately 3,000 independent operators are licensed by the FCC to offer this service, which provides always-on CV, 100; N-330, 50; zinc oxide zinc oxide, chemical compound, ZnO, that is nearly insoluble in water but soluble in acids or alkalies. It occurs as white hexagonal crystals or a white powder commonly known as zinc white. , 5; stearic acid stearic acid /ste·a·ric ac·id/ (ste-ar´ik) a saturated 18-carbon fatty acid occurring in most fats and oils, particularly of tropical plants and land animals; used pharmaceutically as a tablet and capsule lubricant and as an emulsifying , 2 aromatic aromatic /ar·o·mat·ic/ (ar?o-mat´ik) 1. having a spicy odor. 2. in chemistry, denoting a compound containing a ring system stabilized by a closed circle of conjugated double bonds or nonbonding electron pairs, e.g. oil, 3; Santofiox 6PPD (1) (Parallel Presence Detect) The method used by earlier SIMM memory modules to communicate their capacity to the computer. A binary number coming from a parallel set of pins was read by the system, with each pin representing one bit. Contrast with SPD. , 2; Santocure CBS (Cell Broadcast Service) See cell broadcast. , 1.4; sulfur, 1.4. BCI-MX It has been proven in our laboratories (ref. 5) that BCI-MX, due to its unique chemical structure, reacts with the dienes/trienes formed along the polymer backbone as a result of reversion via the classical Diels-Alder reaction The Diels-Alder reaction is an organic chemical reaction (specifically, a cycloaddition) between a conjugated diene and a substituted alkene, commonly termed the dienophile, to form a substituted cyclohexene system. mechanism to form new thermally stable, long and flexible carbon-carbon crosslinks which compensate for the loss of sulfidic crosslinks occurring during reversion (figure 1). [Figure 1 ILLUSTRATION OMITTED] This compensation reaction thus provides for the maintenance of crosslink density and therefore physical properties as thermal degradation is occurring and creates new flexible and thermally stable crosslinks which are less susceptible to further changes. Apart from this compensation effect, the decrease in the concentration of conjugated conjugated adj. Conjugate. estrogens, conjugated Warning - Hazardous drug! C.E.S. dienes/trienes unit will favorably fa·vor·a·ble adj. 1. Advantageous; helpful: favorable winds. 2. Encouraging; propitious: a favorable diagnosis. 3. influence a number of vulcanizates properties such as resilience resilience (r  ·zilˑ·yens),n , strength, fatigue to failure, thermal and oxidative ox·i·da·tive adj. Of, relating to, or characterized by oxidation. oxidative, adj having the ability or property to oxidize. oxidative pertaining to or emanating from oxidation. aging, etc. One of the novel aspects of BCI-MX is that it is one of the few rubber chemicals which can be added to a formulation without affecting processing characteristics because it does not directly participate in the vulcanization vulcanization (vŭl'kənəzā`shən), treatment of rubber to give it certain qualities, e.g., strength, elasticity, and resistance to solvents, and to render it impervious to moderate heat and cold. reaction but only begins to function as soon as the system shows signs of reversion. The thermal stable crosslinks formed by BCI-MX during reversion provide significant improvements in the maintenance of physical properties and in the enhancement of performance characteristics such as lower heat build-up build·up also build-up n. 1. The act or process of amassing or increasing: a military buildup; a buildup of tension during the strike. 2. and higher blow-out resistance as demonstrated in table 3. Table 3 - effect of BCI-MX (1.0 phr) on physical properties and performance characteristic in a CV cure Rheometer reversion @ 150 [degrees] C % reversion in 60 min. 6 Modulus reversion Modulus 300%, MPa at t90 @ 150 [degrees] C 15.2 60' @ 150 [degrees] C 14.6 Fatigue resistance, kC to failure (strain energy [not equal to] 3.5 x [10.sup.3] [kJm.sub.-3]) t90 @ 150 [degrees] C 160 60' @ 150 [degrees] C 150 Heat build-up, [Delta] T at 100 [degrees] C t90 @ 150 [degrees] C 30 60' @ 150 [degrees] C 26 Blow-out time, min. at 100 [degrees] C t90 @ 150 [degrees] C 12 60' @ 150 [degrees] C 42 Crosslink density, [(2 Mc, chem).sup.-1] x [10.sup.5] gmmole/RH t90 @ 150 [degrees] C 5.20 60' @ 150 [degrees] C 5.12 Formulation: SMR CV, 100; N-330, 50; zinc oxide, 5; stearic acid, 2; aromatic oil, 3; Santoflex 6PPD, 2; Santocure CBS, 0.6; sulfur, 2.5; and Perkalink 900, 1.0 Comparing the properties of a typical SEV cure (table 2) and a conventional cure with BCI-MX (table 3), it is clear that incorporation of BCI-MX in a CV cure retains the features of a CV cure together with improvements in thermal stability and hysteresis provided by BCI-MX. The level of BCI-MX needs to be optimized based on the expected degree of reversion (as determined by the accelerator/sulfur ratio and rheometer rhe·om·e·ter n. An instrument for measuring the flow of viscous liquids, such as blood. curve). Table 4 provides recommended starting point Noun 1. starting point - earliest limiting point terminus a quo commencement, get-go, offset, outset, showtime, starting time, beginning, start, kickoff, first - the time at which something is supposed to begin; "they got an early start"; "she knew from the levels for various types of systems including polymer types. Table 4 - compounding guidelines for BCI-MX Polymer system Vulcanization system BCI-MX 100% NR, IR or EV to SEV 0.25 to 0.40 phr blend with > 50% SEV to conventional 0.50 to 0.75 phr NR, IR high sulfur 0.50 to 0.75 phr SBR/BR blends SEV to conventional 0.25 to 0.40 phr Other unsaturated SEV to conventional 0.25 to 0.5 phr polymers e.g. NBR HTS The unique chemical structure of HTS allows it to participate in the vulcanization scheme to form hybrid crosslinks which incorporate a flexible hexamethylene group between the sulfur connection on the polymer backbone as illustrated in figure 2. [Figure 2 ILLUSTRATION OMITTED] By controlling the sulfur chain length at the points of attachment to the polymer backbone, thermal stability of the crosslink is improved. Incorporating a relatively long, flexible and thermally stable alkyl group alkyl group (ăl`kĭl), in chemistry, group of carbon and hydrogen atoms derived from an alkane molecule by removing one hydrogen atom (see radical). within the crosslink structure provides enhanced flexibility under dynamic operating conditions. Addition of HTS to an existing vulcanization system will provide directional In one direction. Contrast with omnidirectional. improvement in reversion resistance and enhanced compound properties, however maximum performance is best achieved by optimizing the sulfur/accelerator/HTS ratios. An example of the benefits provided by HTS is outlined in table 5.
Table 5 - improved reversion resistance with HTS
Control Control + Optimized D-
D-HTS HTS system
Sulfur 2.5 2.5 1.5
Santocure TBBS 0.6 0.4 1.1
HTS 20 1.5
Rheometer reversion @
181 [degrees] C % reversion
in 60 min. 35 23 15
Modulus reversion
Modulus 300%, MPa
t90 @ 144 [degrees] C 14.5 15.2 17.4
10x90 @ 144 [degrees] C 11.3 14.8 19.5
t90' @ 181 [degrees] C 10.1 13.3 14.8
Fatigue resistance, KC to
failure (100% extension)
unaged 189 251 136
aged (48 hrs @
100 [degrees] C) 37 51 34
Heat build up, [Delta]T
100 [degrees] C
t90 + 5' @ 144 [degrees] C 20 24 16
Blow out time, min.
100 [degrees] C
t90 + 5' @ 144 [degrees] C 17 17 30
Formulation: SMR CV 100.0, N-330 50.0, zinc oxide 5.0, stearic acid 2.0, aromatic oil 5.0, Santoflex 6PPD 2.0 1-3 phr of HTS can be added to existing formulations to provide some improvements in reversion resistance and other physical properties, however performance can be maximized by optimizing the entire vulcanization system. Suggested starting point formulations for various types of performance improvements are listed in table 6. Table 6 - compounding guidelines for HTS Performance Overcure Hi-temp cure Lower HBU General enhancement purpose Sulfur 2.2 1.0 1.3 1.1 Accelerator 1.6 2.3 1.1 1.0 Stearic acid 2.7 0.7 2.4 1.6 HTS 1.8 1.6 3.0 2.8 Combination of BCI-MX and HTS In the foregoing discussion, it was apparent that both BCI-MX and HTS provide improvement in reversion resistance, but by different mechanism of action, and each provide different levels of performance improvements. HTS, as stated earlier, reacts during vulcanization, and BCI-MX begins to function only when the system shows the sign of reversion. The combination might provide interesting results, and with this in mind the following study was done. The compositions of the mixes are presented in table 7. Table 7 - compound composition Mixes 01 02 03 04 Santocure TTBS 0.6 0.6 0.6 0.6 Sulfur 2.4 2.4 2.4 2.4 BCI-MX - 1.0 - 1.0 HTS - - 2.0 1.0 Formulation: NR SMR 10, 100 N-375, 52; zinc oxide, 3.5; stearic acid, 2.0; aromatic oil, 4.5; Flectol TMQ TMQ Terminal-Port Queueing (Cisco) TMQ Talking Message Queue , 1.5; Santoflex 6PPD, 1.0; wax, 1.0; PVI See Present Value Index. , 0.35. Figure 3 shows the cure behavior of the mixes obtained at 150 [degrees] C. As expected, BCI-MX has little or no influence on processing characteristics. On the other hand, HTS does influence the cure, thus cure rate and scorch times are affected. This may be overcome by optimizing the whole system. The combination of BCI-MX and HTS, however, shows much better rheometer curves (mix 04, figure 3). [Figure 3 ILLUSTRATION OMITTED] It is clear from the data in table 8 that the presence of BCI-MX in a formulation provides outstanding blow out resistance and reduced heat build-up under dynamic conditions and reduced reversion upon overcure. On the other hand, HTS combines improved fatigue resistance with a good level of reversion resistance. The combination of these two materials provides a synergistic synergistic /syn·er·gis·tic/ (sin?er-jis´tik) 1. acting together. 2. enhancing the effect of another force or agent. syn·er·gis·tic adj. 1. improvement for all of the measured properties.
Table 8 - reversion resistance provided by BCI-MX
HTS and their combination
Mixes Control Control
+ Pk 900
(02)
Rheometer reversion @
150 [degrees] C
reversion in 100' 33 10
Modulus reversion 31 10
Modulus 300%, MPa
t95 @ 150 [degrees] C 15.4 15.3
45' @ 150 [degrees] C 12.4 14.5
100' @ 150 [degrees] C 11.7 14.6
Fatigue resistance, kC to
failure at 100% extension
t95 @ 150 [degrees] C 110 125
45' @ 150 [degrees] C 90 90
100' @ 150 [degrees] C 90 80
Heat build-up, [Delta]T,
[degrees] C
at 100 [degrees] C in 2 h.
t95 @ 10'@ 150 [degrees] C BO 33
55' @ 1450 [degrees] C BO 30
110' @ 150 [degrees] C BO 26
Blow-out time, min. @
100 [degrees] C
t95 + 10' @ 150 [degrees] C 14 60
55' @ 150 [degrees] C 11 > 120
110' @ 150 [degrees] C 8 > 120
Mixes Control + Control +
D-HTS Pk 900
(03) D-HTS
Rheometer reversion @ (04)
150 [degrees] C
reversion in 100' 20 5
Modulus reversion 19 5
Modulus 300%, MPa
t95 @ 150 [degrees] C 15.4 15.4
45' @ 150 [degrees] C 13.7 16.1
100' @ 150 [degrees] C 11.4 16.2
Fatigue resistance, kC to
failure at 100% extension
t95 @ 150 [degrees] C 130 110
45' @ 150 [degrees] C 110 110
100' @ 150 [degrees] C 95 105
Heat build-up, [Delta]T,
[degrees] C
at 100 [degrees] C in 2 h.
t95 + 10' @ 150 [degrees] C 52 26
55' @ 150 [degrees] C 60 27
110' @ 150 [degrees] C 66 25
Blow-out time, min. @
100 [degrees] C
t95 + 10' @ 150 [degrees] C 18 66
55' @ 150 [degrees] C 15 > 120
110' @ 150 [degrees] C 16 > 120
BO signifies blow-out Performance characteristics Outlined in table 9 is the relative level of performance which can be expected when using either HTS or BCI-MX as compared to both a conventional or semi-efficient vulcanization system.
Table 9 - performance characteristics of HTS and BCI-MX
Cure system SEV CV CV plus CV plus BCI-MX
HTS BCI-MX + HTS
Processing properties
Scorch safety (ts2) 100 -/= - = =
Optimum cure time (t90) 100 -/= =/= = =
Reversion resistance
Extended time 100 - + ++ +++
High temperature 100 - + ++ ++
Physical properties
Modulus 100 = =/- = =
Tensile 100 =/+ =/+ = +
Elongation 100 + =/+ = =
Performance characteristics
Heat build-up 100 - =/+ ++ ++
Blow-out resistance 100 - + +++ +++
Fatigue resistance 100 + + = +
Tear resistance 100 + + = +
Thermal stability 100 - + ++ ++
As indicated in the relative performance comparison presented above, HTS and BCI-MX provide the rubber compounder with two approaches to improve reversion resistance to a greater extent than that provided by a traditional semi-Ed system with the added advantage of enhancing other performance properties. HTS is the system of choice if good reversion resistance and improved tear or fatigue are required to enhance product performance. Specific applications include: * skim compounds - where improved reversion resistance and adhesion adhesion /ad·he·sion/ (ad-he´zhun) 1. the property of remaining in close proximity. 2. the stable joining of parts to one another, which may occur abnormally. 3. characteristics are important; * sidewall side·wall n. 1. A wall that forms the side of something. 2. A side surface of an automobile tire, between the edge of the tread and the wheel rim. Noun 1. compounds - where improved reversion resistance and maintenance of flex fatigue properties are critical. BCI-MX should be used where excellent reversion resistance must be combined with lower heat generation and outstanding blow-out resistance to ensure longer product service life. Specific applications include: * tread tread injury to the coronet of the horse's hoof by treading on it by the opposite hoof, or by another horse when they are being worked in a team. If the coronary matrix is injured there may be a subsequent crack or deformity. compounds - where lower hysteresis and comparable wear and traction Traction Definition Traction is the use of a pulling force to treat muscle and skeleton disorders. Purpose Traction is usually applied to the arms and legs, the neck, the backbone, or the pelvis. are important; * undertread compounds - where lower heat buildup build·up also build-up n. 1. The act or process of amassing or increasing: a military buildup; a buildup of tension during the strike. 2. and greater blow-out resistance arecritical; * carcass carcass, carcase 1. the body of an animal killed for meat. The head, the legs below the knees and hocks, the tail, the skin and most of the viscera are removed. The kidneys are left in and in most instances the body is split down the middle through the sternum and the vertebral compounds - for improved adhesion and durability; * apex compounds - to maintain stiffness and flexibility throughout service life. Summary HTS and BCI-MX provide two unique approaches to improve the thermal aging resistance of sulfur based vulcanizates as compared to existing compounding technology. HTS participates in the vulcanization reaction to form thermally stable and flexible hybrid crosslinks which provides improvements in both thermal aging resistance and performance characteristics such as tear and fatigue resistance. BCI-MX reacts during the reversion process to replace degraded de·grad·ed adj. 1. Reduced in rank, dignity, or esteem. 2. Having been corrupted or depraved. 3. Having been reduced in quality or value. sulfur crosslinks with thermally stable and long lasting carbon-carbon crosslinks which significantly improve dynamic mechanical properties such as heat build-up and blow-out resistance, while maintaining other performance characteristics. The use of both HTS and BCI-MX in the same formulation appears to provide a synergistic improvement in reversion resistance and performance characteristics such as blowout Blowout The rapid sale of all shares in a new securities offering. See: hot issue. blowout The nearly immediate sale of a new security issue because of great investor demand. See also hot issue. and fatigue resistance. Acknowledgements "A highly efficient cure system for BIMS BIMS Biomedical Science (educational course/major) BIMS Biobank Information Management System BIMS Butterflies In My Stomach BIMS Branson Interactive Multimedia Services (Branson, MO) " it based on a paper given at the October, 1996 meeting of the Rubber Division. "Zinc soaps for improved vulcanizates" is based on a paper given at the October, 1996 meeting of the Rubber Division. References (1.) T.D. Skinner Skin·ner , B(urrhus) F(rederick) 1904-1990. American psychologist. A leading behaviorist, Skinner influenced the fields of psychology and education with his theories of stimulus-response behavior. and A.A. Watson, Rubber Age, 99, 76, 1967. (2.) A.H. Hogt, A.G. Talma, R.F. de Block and R.N. Datta, U.S. Pat. 5,426,155, 1995. (3.) R.N. Datta and M.S. Ivany, Rubber World, 212, 24, 1995. (4.) D.G. Lloyd, European Rubber Journal, 27, 1988. (5.) A.G. Talma, R.N. Datta, A.H.M. Schotman and W.H. Hell, presented at a meeting of Rubber Division, ACS (Asynchronous Communications Server) See network access server. , Cleveland, Oct. 17-20, 1995. |
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