Modifying the performance of sulfenamide accelerators with thiurams. (Process Machinery).Over the last few years, BFGoodrich, now Noveon, has been developing two new thiuram accelerators for use in the tire industry (refs. 1-5). Cure-rite IBT (1) (Instructor Based Training) Training courses conducted by human teachers. (2) (Internet Based Training) Training courses provided via the Internet. and Cure-rite IBM (International Business Machines Corporation, Armonk, NY, www.ibm.com) The world's largest computer company. IBM's product lines include the S/390 mainframes (zSeries), AS/400 midrange business systems (iSeries), RS/6000 workstations and servers (pSeries), Intel-based servers (xSeries) (see table 1 for a list of abbreviations) are now commercially available. Chemically, they are N,N,N',N'-tetraisobutylthiuram disulfide di·sul·fide n. A chemical compound containing two sulfur atoms combined with other elements or radicals. Also called bisulfide. and N,N,N',N'-tetraiso-butylthiuram monosulfide, and the structures are shown in figure 1. Both are Toxic Substance Control Act (TSCA TSCA Toxic Substances Control Act of 1976 (15 USC) TSCA Traditional Small Craft Association (Mystic, CT, USA) TSCA Tibetan Spaniel Club of America TSCA Traditional Siamese Cat Association ) listed, while at this time only IBT is European European emanating from or pertaining to Europe. European bat lyssavirus see lyssavirus. European beech tree fagussylvaticus. European blastomycosis see cryptococcosis. Inventory of Existing Commercial Chemical Substances (EINECS EINECS European Inventory of Existing Commercial Chemical Substances ) listed. [FIGURE 1 OMITTED] Initially, these two compounds were designed to reduce the amount of nitrosamines nitrosamines highly hepatotoxic compounds formed in the rumen by the combination of amines and nitrite. They do not appear to occur naturally in large quantities. Nitrosamine poisoning has also been caused by feeding nitrite-treated fishmeal and Solanum incanum. (NA) that would be generated from them during 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. relative to the most commonly used thiurams, TMTD TMTD tetramethylthiuram disulfide. and TMTM TMTM The Muppets Take Manhattan (movie) TMTM The More, the Merrier . Table 2 shows the approximate amounts of respective NAs that are generated from the various commercially available accelerators. While TMTD and TMTM produce approximately 100 ppb ppb abbr. parts per billion as measured in the rubber, IBT and IBM produce in the 1-2 ppb level, nearly a 100-fold reduction. On the other hand, TBzTD is claimed to produce no NAs. However, to achieve a zero level of NA, the cost of the thiuram increases. So, while TMTD is the least expensive thiuram, TBzTD is the most expensive. IBT and IBM compromise those two economic extremes. When one substitutes one thiuram for another, it is important to do this on a molar molar /mo·lar/ (mo´lar) 1. pertaining to a mole of a substance. 2. a measure of the concentration of a solute, expressed as the number of moles of solute per liter of solution. Symbol M, , or mol/L. equivalency equivalency the combining power of an electrolyte. See also equivalent. basis, rather than on a weight basis, in order to keep the accelerator accelerator: see particle accelerator. (1) A key combination such as Alt-G or Ctrl-Shift H that is used to activate a task. (2) An incubator that expects to develop the company considerably faster than normal. See incubator. activity the same. Replacing TMTD with a higher molecular weight thiuram like TBzTD requires using a greater part level of that thiuram in the same recipe. Therefore, the added cost to the recipe increases by both the cost/purchased pound and by the increased loading in the recipe. Again, both IBT and IBM meet a compromise between the two extremes of TMTD (or TMTM) and TBzTD. Experimental The SBR/BR masterbatch, weight 214.0, used in this study contains: * OE-SBR, Ameripol 1712, 55; * SBR SBR - Spectral Band Replication , Ameripol 1500, 25; * Taktene 1203 (95% cis- cis- a prefix denoting on this side, the same side, or the near side. cis- pref. Having a pair of identical atoms or groups on the same side of a plane that passes through two carbon atoms linked by a double bond: 1,4-polybutadiene, solution polymerized), 35; * 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. , 3; * 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; * N234 carbon black, 70; * Sundex 8125, 20; * antioxidant antioxidant, substance that prevents or slows the breakdown of another substance by oxygen. Synthetic and natural antioxidants are used to slow the deterioration of gasoline and rubber, and such antioxidants as vitamin C (ascorbic acid), butylated hydroxytoluene , Agerite Resin D, 2; * antiozonant, Antozite 67F, 2. Cure rates and Mooney scorches in this masterbatch were, unless otherwise indicated, determined at 160[degrees]C and 138[degrees]C, respectively. The natural rubber masterbatch, weight 159.0, used in this study contains; * SIR natural rubber, 100; * N234 carbon black, 45; * Sundex 790 oil, 6.0; * zinc oxide, 5.0; * stearic acid, 2.0; * Agerite Resin D, 1.0. Cure rates and Mooney scorches in this masterbatch were, unless otherwise indicated, determined at 150[degrees]C and 130[degrees]C, respectively. These ingredients were combined in a BR internal mixer mixer, either of two electronic devices in which two or more signals are combined. In the type of mixer used in radio receivers, radar receivers, and similar systems, a signal is translated upward or downward in frequency. , and a masterbatch was obtained by combining a number of batches on a mill. The curatives were added on the mill. ASTM ASTM abbr. American Society for Testing and Materials procedures D 1600, D 1625 and D 2100 were used for determining the cure and vulcanizate properties. Discussion Figure 2 shows graphically the relative cure rates (320[degrees]C) and Mooney scorch times (302[degrees]C) of the various commercial thiurams when they are used alone to cure SBR/BR. TMTD exhibits the greatest cure rate and the shortest scorch safety among the thiurams examined. TETD loses a little in cure rate while its scorch safety improves. IBT, IBM and TBzTD possess nearly identical cure rates but slower than the first two examples. The scorch safeties of IBT and TBzTD are also nearly identical to each other and longer than TMTD. IBM is an exception in scorch in that it possesses the longest scorch delay of all the thiurams. One can easily conclude that IBT appears to be a drop-in replacement for TBzTD, while IBM can provide increased scorch safety if that is needed. [FIGURE 2 OMITTED] Thiurams are not used as the primary accelerator in the tire industry. Typically, when thiurams are used, they are used to modify the cure, e.g., cure rate or scorch time, or vulcanizate, e.g., type of sulfur sulfur or sulphur (sŭl`fər), nonmetallic chemical element; symbol S; at. no. 16; at. wt. 32.06; m.p. 112.8°C; (rhombic), 119.0°C; (monoclinic), about 120°C; (amorphous); b.p. 444.674°C;; sp. gr. at 20°C;, 2. crosslinks, characteristics of rubber compounds in which the primary accelerator may be a benzothiazole type like TBBS TBBS The Bread Board System TBBS The Big Blue Sky (website) or CBS (Cell Broadcast Service) See cell broadcast. . In those instances, the standard part level of the benzothiazole is reduced to accommodate for the addition of the thiuram. Table 3 shows the cure rates and Mooney scorch times achieved when the various thiurams are used with TBBS and CBS in SBR/BR and NR. The amounts of thiuram used are adjusted from one to another to accommodate for the changes in molecular weight, as discussed above. The benzothiazole without thiuram is also shown. The cure rates and scorch times for each series of cures are graphically displayed in figures 3-6 for easy comparison. Figure 3 shows the comparison of cure rates and scorch times when thiurams are used with TBBS in an SBR/BR recipe. One can see that all the thiurams increase the cure rate substantially, but not necessarily in the same order as when the thiurams are used alone (figure 2). That is, TMTD does not improve the cure rate the most and, in fact, is the least effective. TMTM and IBM, the monosulfides, improve the cure rate to the same extent as TMTD, while TETD appears to be the most effective. IBT and IBM show a near identical and intermediate improvement in the cure rates. [FIGURE 3 OMITTED] When TMTD is added to a TBBS recipe, the scotch scotch 1 tr.v. scotched, scotch·ing, scotch·es 1. To put an abrupt end to: The prime minister scotched the rumors of her illness with a public appearance. 2. safety is substantially decreased, as expected. TMTM and the higher molecular weight compounds recover the original scorch safety of the TBBS. However, the scorch safety of IBM stands out as exceptional and exceeds that of the other recipes. Again, IBT and TBzTD possess very similar scorch times. Figure 4 represents the data for the thiurams used with CBS in SBR/BR. Again, as expected, all the thiurams improve the cure rates, with IBT improving the rates the most, and IBM the least. TMTD does not impart the greatest increase. As with TBBS, TMTD contributes to a scorch time decrease, while all the other thiurams pretty much maintain the scorch safety of the CBS alone. The one exception is IBM, which improves the scorch time beyond that of CBS, unlike that of the other thiurams. [FIGURE 4 OMITTED] Figures 5 and 6 represent the data for the same thiurams when used with TBBS and CBS, respectively, in natural rubber. Natural rubber is very susceptible to acceleration and all the thiurams impart excellent improvements in the cure rates over that of the TBBS or CBS. In fact, the pattern of cure rate improvements seems to be nearly identical in both TBBS and CBS. As in SBR/BR, TMTD substantially decreases the scorch safety, while the other thiurams are not nearly as detrimental det·ri·men·tal adj. Causing damage or harm; injurious. det  ri·men . But, as
seen earlier, IBM improves the scorch safety over that of the
sulfenamides themselves.[FIGURES 5-6 OMITTED] Natural rubber vulcanizates are very susceptible to reversion reversion: see atavism. . Reversion is the loss in already developed crosslink density when the vulcanizate is subjected to higher curing or end use temperatures or to normal curing temperatures for longer periods of time, e.g., overcure. This can particularly occur when thick section rubber articles are cured, as the parts in contact with the mold mold, name for certain multicellular organisms of the various classes of the kingdom Fungi, characteristically having bodies composed of a cottony mycelium. The colors of molds are caused by the spores, which are borne on the mycelium. are exposed to high temperatures for a long period of time so that the inner portions of the article can cure sufficiently. This has recently become a fruitful fruit·ful adj. 1. a. Producing fruit. b. Conducive to productivity; causing to bear in abundance: fruitful soil. 2. area of research in rubber vulcanization resulting in the development of rubber additives that help prevent reversion. Reversion can be seen both in rheometer rhe·om·e·ter n. An instrument for measuring the flow of viscous liquids, such as blood. cure curves as a loss in torque after maximum cure and in the physical properties of a vulcanizate by a loss in tensile tensile, adj having a degree of elasticity; having the ability to be extended or stretched. on over curing compared to optimum cure. Figure 7 graphically displays the percent reversion in a NR formulation formulation /for·mu·la·tion/ (for?mu-la´shun) the act or product of formulating. American Law Institute Formulation as taken from rheometer curves after 60 minutes for recipes cured with TBBS or CBS alone and in combination with various thiurams. When TMTD, TMTM and TETD are used with the primary accelerator, reversion is aggravated ag·gra·vate tr.v. ag·gra·vat·ed, ag·gra·vat·ing, ag·gra·vates 1. To make worse or more troublesome. 2. To rouse to exasperation or anger; provoke. See Synonyms at annoy. relative to a recipe with no thiuram. The percent reversion that occurs is less than with IBT, IBM or TBzTD in the recipe. [FIGURE 7 OMITTED] The effects on physical properties of the vulcanizates obtained in a more detailed examination of the reversion characteristics of the thiurams when used with TBBS are shown in figures 8 and 9. Two different levels of thiuram (those shown in table 3 and twice those levels) and three temperatures (150, 170, 180[degrees]C) for curing were examined. The properties after a one hour cure were compared to those after a t95 optimum cure and are reflected as percent retention of those physical properties at respective temperatures. One can see from figure 8 that both IBM and IBT excel at Verb 1. excel at - be good at; "She shines at math" shine at excel, surpass, stand out - distinguish oneself; "She excelled in math" tensile retention relative to the other thiurams, although the loss rate on going to higher cure temperatures is about the same for all the thiurams. Figure 9 depicts the 300% modulus See modulo. data and again shows the superior characteristics of IBM and IBT, although TBzTD matches the modulus loss at higher temperatures. Figure 10 demonstrates that using twice the level of any thiuram does not make a marked improvement in the moduli In theoretical physics, moduli are scalar fields whose different values are equally good (each one such scalar field is called a modulus). The reason is that the potential energy for moduli is constant, which can be guaranteed, for example, by supersymmetry (with after overcure. [FIGURES 8-10 OMITTED] Better reversion resistance should be reflected in improved 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. times. Blowout times, peak temperatures and tear resistance are shown in table 4. These recipes were not adjusted for optimal characteristics but are the same as have been used throughout this study. The blowout time and peak temperatures are graphically represented in figure 11. For both SBR/BR and NR, the blowout times were improved with the use of IBT, IBM and TBzTD. In NR, the peak temperatures at blowout were lower for the same three thiurams. [FIGURE 11 OMITTED] Reversion, and therefore the properties that are affected by reversion, would be largely determined by the crosslink density and ranks in the vulcanizate. Crosslink characteristics were determined by the MRPRA using published techniques (ref. 6) on unfilled gum rubber vulcanizates cured with the thiurams alone and also when used with TBBS (table 5). These data are plotted in figures 12-14. One can see that the total crosslink density decreases in changing from TMTD to TBzTD and decreases further with IBM and IBT. The percent of monosulfidic crosslinks formed within each of the thiurams is highest for IBM and IBT, followed by TBzTD, while the other three thiurams are lowest. Interestingly enough, the disulfidics are about the lowest percent in IBM and IBT. One may conclude that the nature of the crosslinks formed by IBM and IBT may differ enough from the other thiurams to impart better reversion resistance. [FIGURES 12-14 OMITTED] A similar study was performed on TBBS/thiuram cured vulcanizates, which would better represent the tree crosslink types in samples used for reversion studies. These data are represented in figures 13-14. One sees that total crosslink density increases when any thiuram is used with TBBS compared to TBBS alone. Interestingly enough, both IBM and TMTM generate the same total density, while TBzTD, TETD and IBT are nearly identical. The major difference is that the combined mono- and disulfidic crosslinks are at the highest concentration for TBzTD, IBT and IBM. Figure 13 confirms that TBzTD, IBT and IBM vulcanizates possess a higher combined percentage of the shorter crosslinks. It is well recognized that shorter crosslinks are less prone to reversion, and this might explain the better reversion resistance with those three thiurams. Individual mono- and disulfidic concentrations could not be determined for most of the samples due to physical degradation DEGRADATION, punishment, ecclesiastical law. A censure by which a clergy man is deprived of his holy orders, which he had as a priest or deacon. of the samples during the swelling/de-swelling procedures. With IBT, those two concentrations were nearly equal. Conclusions Cure-rite IBT appears to be a reasonable substitute for TMTD, providing improved scorch safety, cure rates and reversion resistance when used with primary accelerators like the benzothiazoles. It can be a replacement for TBzTD, providing lower cost while exhibiting similar curing properties. Cure-rite IBM is unique when used with the benzothiazole accelerators in that it extends scorch time and cure rate beyond that of the benzothiazole itself, thus acting like a retarder retarder, n a chemical added to a substance to slow a chemical reaction, prolong the set of the material, and provide more working time. and accelerator at the same time. In addition, it improves reversion resistance. This behavior is unlike any other thiurams, including TMTM, and appears unique among commercial vulcanization chemicals. Crosslink analysis of thiuram and thiuram/TBBS natural rubber vulcanizates suggests that sufficient differences exist to explain the differences in reversion properties.
Table 1--abbreviations used
CBS N-cyclohexyl-2-benzothiazole sulfenamide
IBM N,N,N', N', -tetraisobutylthiuram monosulfide
IBT N,N,N', N', -tetraisobutylthiuam disulfide
NAs Nitrosamines
NR Natural rubber
OE-SBR Oil extended styrene butadiene rubber
SBR/BR Styrene butadiene rubber/butadiene rubber
TBBS N-t-butyl-2-benzothiazole sulfenamide
TBTD N,N,N', N', -tetra-n-butylthiuram disulfide
TBzTD N,N,N', N', -tetrabenzylthiuram disulfide
TETD N,N,N', N', -tetraethylthiuram disulfide
TMTD N,N,N', N', -tetra methylthiuram disulfide
TMTM N,N,N', N', -tetra methylthiuram monosulfide
Table 2--comparison of miscellaneous
properties of thiurams
Thiuram Cost ($) (a) NA (ppb) MW Ratio (c)
TMTD 2.05 ~100 240 1.0
TETD 2.88 ~20-40 296 1.2
TBTD 5.15 ~10 408 1.7
IBT 4.95 ~1-2 408 1.7
TBzTD 12.44 0 544 2.3
TMTM 3.25 ~80-100 208 0.9
IBM 8.00(b) ~1-2 376 1.6
(a)-obtained from Chemical Marketing Reporter
(b)-estimated
(c)-parts needed compared to TMTD = 1 part
Table 3--cure rates/scorch times of thiurams with
BBTS/CBTS in SBR/BR and NR
SBR/BR
TMTD TMTM TETD TBTD IBT
Thiuram 0.00 0.15 0.13 0.18 0.26 0.26
BBTS 1.30 1.00 1.00 1.00 1.00 1.00
Cure rate 15.2 18.0 18.5 25.4 21.2 21.6
Scorch (min.) 14.0 12.3 14.2 14.6 14.6 14.5
CTBS 1.40 1.05 1.05 1.05 1.05 1.05
Cure rate 16.9 21.7 21.5 24.8 23.4 32.8
Scorch (min.) 13.0 11.5 13.1 12.3 13.2 12.5
NR
Thiuram 0.00 0.13 0.11 0.16 0.22 0.22
BBTS 1.00 0.80 0.80 0.80 0.80 0.80
Cure rate 12.0 28.4 28.1 34.8 29.2 35.5
Scorch (min.) 17.2 13.8 16.2 15.2 16.7 16.5
CBTS 1.11 0.90 0.90 0.90 0.90 0.90
Cure rate 23.4 33.8 34.1 39.7 33.2 40.5
Scorch (min.) 15.6 12.8 15.0 14.1 15.8 15.4
SBR/BR
IBM TBzTD
Thiuram 0.24 0.34
BBTS 1.00 1.00
Cure rate 18.8 22.6
Scorch (min.) 15.5 14.3
CTBS 1.05 1.05
Cure rate 19.9 25.6
Scorch (min.) 14.2 13.1
NR
Thiuram 0.20 0.29
BBTS 0.80 0.80
Cure rate 29.3 35.6
Scorch (min.) 18.7 16.1
CBTS 0.90 0.90
Cure rate 37.0 42.7
Scorch (min.) 16.3 14.7
Table 4--comparison of TBBS/thiuram cured vulcanizates in
blowout/tear tests
No TMTD TMTM TETD
SBR/BR thiuram
Flexometer (100[degrees]C, 489N)
Blowout time, min. 6.0 5.1 5.1 4.9
Peak temp., [degrees]C 167.0 166.0 165.0 162.0
Static compression, % 41.6 41.7 41.0 41.0
Tensometer (speed 51 cm/min.,
load 175 N/mm)
Tear resistance, N/mm 36.1 36.4 36.6 36.4
Durometer A 70 70 70 71
NR
Flexometer (100[degrees]C, 489N)
Blowout time, min. 7.6 7.6 7.6 10.5
Peak temp., [degrees]C 162 160 160 160
Static compression, % 44.1 40.6 42.2 40.0
Tensometer (speed 51 cm/min.,
load 175 N/mm)
Tear resistance, N/mm 103.8 104.0 109.0 106.6
Durometer A 65 69 70 69
IBT IBM TBzTD
SBR/BR
Flexometer (100[degrees]C, 489N)
Blowout time, min. 6.3 6.5 6.6
Peak temp., [degrees]C 165.0 168.0 167.0
Static compression, % 40.3 39.6 40.6
Tensometer (speed 51 cm/min.,
load 175 N/mm)
Tear resistance, N/mm 36.2 36.6 36.4
Durometer A 68 71 71
NR
Flexometer (100[degrees]C, 489N)
Blowout time, min. 10.9 8.5 10.3
Peak temp., [degrees]C 159 159 159
Static compression, % 38.9 39.0 39.3
Tensometer (speed 51 cm/min.,
load 175 N/mm)
Tear resistance, N/mm 104.3 107.8 101.2
Durometer A 70 68 69
Table 5--recipes (a) used in crosslink analysis
Masterbatch (b) 108.0 108.0 108.0 108.0 108.0 108.0 108.0
Sulfur 2.00 2.00 2.00 2.00 2.00 2.00 2.00
TBBS
TMTM 0.50
TMTD 0.45
TETD 0.60
TBzTD 1.15
IBM 0.80
IBT 0.85
Masterbatch (b) 108.0 108.0 108.0 108.0 108.0 108.0 108.0
Sulfur 2.00 2.00 2.00 2.00 2.00 2.00 2.00
TBBS 1.00 0.80 0.80 0.80 0.80 0.80 0.80
TMTM 0.13
TMTD 0.11
TETD 0.16
TBzTD 0.29
IBM 0.20
IBT 0.22
(a) recipes cured at 150[degrees]C for 195
(b) Natural rubber, 100; zinc oxde, 5; stearic acid, 2; resin D,1
References (1.) R. W. Layer and D. W. Chasar, Rubber Chem. Technol., 67, 299 (1994). (2.) A.G. Ferradino, "Economical low nitrosamine ni·tros·a·mine n. Any of a class of organic compounds present in various foods and other products and found to be carcinogenic and mutagenic in laboratory animals. ultra accelerators," a poster presented at the 145th meeting of ACS (Asynchronous Communications Server) See network access server. Rubber Division, Chicago, April 20-21, 1994. (3.) D. W. Chasar, Rubber World, 214 (5), 25 (1996). (4.) D.W. Chasar, Rubber Chem. Technol., 70, 634 (1997). (5.) D. W. Chasar, "Tetraisobutylthiuram monosulfides: Some further applications of this unique retarder/kicker," presented at the 152nd meeting of ACS Rubber Division, Cleveland, October 21-24, 1997. (6.) D.S D.S Drainage Structure (flood protection) . Campbell, A.V. Chapman, I.R. Goodchild and W.S. Fulton, J. Nat. Rubb. Res., 7, 168 (1992). |
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