Effect of Antidegradants on the Vulcanization of Synthetic Rubbers
Abstract Generated abstract
This study examines how common amine antidegradants affect the vulcanization behavior and physicomechanical properties of synthetic rubbers used in tires and technical rubber goods. Experimental compounds based on SKI-3, SKS-30 ARKM-15, and nairite were prepared with varied accelerator and vulcanizing systems, including Altax, DPG, thiuram, sulfur, metal oxides, and additions of Neozone D, product 4010, and DFFD. The results show that antidegradants can broaden the vulcanization plateau, alter cure rate, and change strength and heat resistance, with effects depending strongly on the rubber and accelerator system. Product 4010 generally activated vulcanization more than Neozone D but could reduce heat resistance, while added antidegradants were most effective when they were not already present in the base rubber.
Full Text
EFFECT OF ANTIDEGRADANTS ON THE VULCANIZATION OF SYNTHETIC RUBBERS
V. D. Bogoslovskii, S. M. Terezova
(Presented by the Scientific-Methodological Seminar of the Organic Departments of the Faculty of Chemical Technology)
Modern rubber compounds based on synthetic rubbers, as a rule, include antidegradants in their composition. The antidegradants included in rubbers and synthetic rubbers usually belong to the class of aromatic or heterocyclic amines and their derivatives. Components of a rubber compound that act as bases (inorganic or organic) may be regarded as vulcanization activators [1]. In turn, many vulcanization accelerators, including thiurams, thiazoles, and sulfenamides, are substances that retard the aging of rubber vulcanizates.
The purpose of the study was to establish the dependence of vulcanization, and consequently of the physicomechanical characteristics of vulcanizates of SKI-3, SKS-30 ARKM-15, and nairite, on the composition of the accelerator–vulcanizing group of rubbers containing various antidegradants, taking into account the presence of antidegradants in the rubbers themselves. In other words, the aim of the work was to study the combined action of certain accelerators and antidegradants on the vulcanization of synthetic rubbers widely used in the production of tires and rubber technical goods.
Stereoregular polyisoprene rubber SKI-3 contained a mixture of antidegradants: 0.5% Neozon D (phenyl-β-naphthylamine) and 0.5% DFPD (diphenyl-p-phenylenediamine), calculated on the rubber. Its standard compound composition was: SKI-3 — 100 parts by weight, stearin — 1.0 part by weight, DPG — 3.0 parts by weight, Altax — 0.6 part by weight, zinc oxide — 5.0 parts by weight, sulfur — 1.0 part by weight; both the standard and experimental compounds were vulcanized in a press at \(133 \pm 1^\circ\mathrm{C}\).
Oil-extended divinyl–styrene rubber of emulsion polymerization with a rosin emulsifier was charged with 1.3–2.0% Neozon D. The standard compound composition was: SKS-30 ARMK-15 — 100 parts by weight, stearin — 2.0 parts by weight, zinc oxide — 5.0 parts by weight, Altax — 1.5 parts by weight, DPG — 0.3 part by weight, DG carbon black — 100–50 parts by weight, sulfur — 2.0 parts by weight; both the standard and experimental rubbers were vulcanized in a press at \(143 \pm 1^\circ\mathrm{C}\).
Chloroprene rubber nairite, as antidegradants, contains a combination of 1.6% Neozon D and 2.7% Thiuram E (tetraethylthiuram disulfide) [2]. Its standard compound composition was: nairite — 100 parts by weight, magnesium oxide — 7.0 parts by weight, zinc oxide — 5.0 parts by weight; both the standard and experimental compounds were vulcanized in a press at \(143 \pm 1^\circ\mathrm{C}\).
The study was carried out in two stages. In the first stage, the effect of antidegradants on the vulcanization of rubbers in standard compounds was investigated. In the second stage, the combined action of accelerators and antidegradants was studied with changes in the composition and dosages of the accelerator–vulcanizing groups in the formulations of the standard compounds.
Table 1
Dosages of the vulcanizing group and antidegradants in experimental compounds based on SKI-3, % by rubber weight
| Ingredients | C-1 | C-2 | C-3 | C-4 | C-5 | C-6 | C-7 | C-8 | C-9 | C-10 | C-11 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| DPG | 3.0 | 3.0 | 3.0 | — | — | — | — | — | — | — | — |
| Altax | 0.6 | 0.6 | 0.6 | 3.0 | 3.0 | 3.0 | 2.5 | 2.5 | 2.5 | 3.0 | 2.5 |
| Thiuram | — | — | — | — | — | — | 0.3 | 0.3 | 0.3 | — | 0.3 |
| Sulfur | 1.0 | 1.0 | 1.0 | 1.5 | 1.5 | 1.5 | 1.0 | 1.0 | 1.0 | 1.5 | 1.0 |
| Neozone D | — | 3.0 | — | 3.0 | — | — | — | 3.0 | — | — | — |
| 4010 | — | — | 3.0 | — | 3.0 | — | — | — | 3.0 | — | — |
| DFFD | — | — | — | — | — | — | — | — | — | 3.0 | 3.0 |
Table 2
Dosages of the vulcanizing group and antidegradants in experimental compounds based on SKD-30 ARKM-15, % by rubber weight
| Ingredients | A-1 | A-2 | A-3 | A-4 | A-5 | A-6 | A-7 | A-8 | A-9 | A-10 | A-11 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Altax | 1.5 | 1.5 | 1.5 | 2.0 | 2.0 | 2.0 | 1.5 | 1.5 | 1.5 | 2.0 | 1.5 |
| DPG | 0.3 | 0.3 | 0.3 | — | — | — | — | — | — | — | — |
| Sulfur | 2.0 | 2.0 | 2.0 | 2.0 | 2.0 | 2.0 | 2.0 | 2.0 | 2.0 | 2.0 | 2.0 |
| Thiuram | — | — | — | — | — | — | 0.3 | 0.3 | 0.3 | — | 0.3 |
| Neozone D | — | 3.0 | — | — | 3.0 | — | — | 3.0 | — | — | — |
| 4010 | — | — | 3.0 | — | — | 3.0 | — | — | 3.0 | — | — |
| DFFD | — | — | — | — | — | — | — | — | — | 3.0 | 3.0 |
The composition of the experimental rubber compounds based on the rubbers selected for the study is given in Tables 1, 2, and 3. Tables 1, 2, and 3 give the dosages of sulfur, organic accelerators, and antidegradants. Formulations S-1, A-1, and N-1 are standard; S-2, A-2, and N-2 are standard formulations containing an additional amount (3.0 phr) of Neozone D; S-3, A-3, and N-3 are standard formulations with the addition of 3.0 phr of product 4010 (phenylcyclohexyl-p-phenylenediamine), and N-14 is a standard compound based on nairite with the addition of 3.0 phr of DFFD.
Table 3
Dosages of the accelerating-vulcanizing group and antidegradants in experimental rubber compounds based on nairite, % by weight of rubber
| Ingredients | N-1 | N-2 | N-3 | N-4 | N-5 | N-6 | N-7 | N-8 | N-9 | N-10 | N-11 | N-12 | N-13 | N-14 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Thiuram | — | — | — | 3.0 | 3.0 | 3.0 | — | — | — | 1.5 | 1.5 | 3.0 | — | — |
| Altax | — | — | — | — | — | — | 3.0 | 3.0 | 3.0 | 1.5 | 1.5 | — | 3.0 | — |
| Neozone D | — | 3.0 | — | 3.0 | — | — | — | 3.0 | — | 1.5 | — | — | — | — |
| 4010 | — | — | 3.0 | — | 3.0 | — | — | — | 3.0 | 1.5 | — | — | — | — |
| DFFD | — | — | — | — | — | — | — | — | — | — | — | 3.0 | 3.0 | 3.0 |
The remaining experimental compounds, apart from the antidegradant, had in their composition a modified accelerating-vulcanizing group.
The physicomechanical characteristics of the compounds and vulcanizates of the experimental rubbers are given in Tables 4, 5, and 6.
Analysis of the physicomechanical characteristics makes it possible to conclude that the introduction of the antidegradants Neozone D and 4010 into standard compounds based on SKI-3 (accelerator—a combination of Altax with DPG), SKS-30 ARKM-15 (accelerator—a combination of Altax with DPG), and nairite, which is vulcanized with metal oxides without sulfur or organic accelerators, broadens the vulcanization plateau and increases the strength of the vulcanizates.
Product 4010 activates vulcanization more strongly than Neozone D, somewhat increases the tendency of rubber compounds toward premature vulcanization, and lowers the heat resistance of vulcanizates under thermal aging. Product 4010 is usually recommended for introduction into rubber compounds as an antiozonant and antifatigue agent, Neozone D for increasing heat resistance, and DFFD for protection against the action of salts of metals of variable valence and repeated deformations [3].
In a standard compound based on nairite, DFFD slows vulcanization, increases the tendency of the rubber compound toward premature vulcanization, and reduces
Table 4
Physico-mechanical characteristics of compounds and vulcanizates of experimental rubbers based on SKI-3. Vulcanization temperature 133°C
| Indicators / compound code | C-1 | C-2 | C-3 | C-4 | C-5 | C-6 | C-7 | C-8 | C-9 | C-10 | C-11 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Plasticity of the compound | 0,63 | 0,60 | 0,60 | 0,65 | 0,64 | 0,61 | 0,60 | 0,60 | 0,61 | 0,60 | 0,61 |
| Plasticity of the compound after conditioning in water for 30 min | 0,63 | 0,60 | 0,35 | 0,65 | 0,64 | 0,61 | 0,60 | 0,60 | 0,61 | 0,65 | 0,61 |
| Optimal vulcanization time, min | 20 | 30 | 30 | 50 | 40 | 60 | 40 | 30 | 60 | 60 | 60 |
| Tensile strength, kg/cm² | 294 | 289 | 292 | 121 | 210 | 38 | 323 | 306 | 177 | 230 | 120 |
| Relative elongation, % | 920 | 870 | 880 | 1020 | 880 | 1100 | 730 | 800 | 830 | 860 | 9,5 |
| Shore elasticity | 38 | 36 | 36 | 42 | 44 | 34 | 36 | 38 | 38 | 38 | 40 |
| Aging coefficient (72 h at 100°C), by strength | 0,81 | 0,95 | 0,48 | 1,3 | 1,1 | 1,2 | 0,60 | 0,80 | 0,80 | 1,1 | 0,98 |
| Aging coefficient (72 h at 100°C), by relative elongation | 0,85 | 0,84 | 0,52 | 0,85 | 0,78 | 1,2 | 0,48 | 0,80 | 0,78 | 0,91 | 0,86 |
Table 5
Physicomechanical characteristics of mixtures and vulcanizates based on SKS-30 ARKM-15 experimental resin at a vulcanization temperature of 143°C
| Indicator / Mixture code | A-1 | A-2 | A-3 | A-4 | A-5 | A-6 | A-7 | A-8 | A-9 | A-10 | A-11 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Plasticity of mixture | 0,36 | 0,38 | 0,38 | 0,42 | 0,42 | 0,42 | 0,42 | 0,42 | 0,42 | 0,42 | 0,42 |
| Plasticity after boiling in water for 30 min | 0,36 | 0,38 | 0,20 | 0,41 | 0,42 | 0,41 | 0,42 | 0,42 | 0,42 | 0,42 | 0,42 |
| Optimal vulcanization time, min | 70 | 50 | 40 | 90 | 80 | 60 | 60 | 60 | 60 | 70 | 60 |
| Tensile strength, kg/cm² | 256 | 223 | 235 | 234 | 171 | 232 | 158 | 130 | 141 | 255 | 126 |
| Relative elongation, % | 750 | 810 | 710 | 670 | 630 | 700 | 200 | 200 | 300 | 640 | 250 |
| Elasticity by Shob | 27 | 29 | 30 | 33 | 30 | 30 | 30 | 30 | 30 | 32 | 30 |
| Aging coefficient (72 h at 100°C), by strength | 0,64 | 0,59 | 0,48 | 0,98 | 1,1 | 0,90 | 0,60 | 0,80 | 0,78 | 0,99 | 0,99 |
| Aging coefficient (72 h at 100°C), by relative elongation | 0,72 | 1,0 | 0,52 | 1,0 | 1,1 | 0,90 | 0,60 | 0,80 | 0,80 | 1,0 | 0,99 |
Table 6
Physico-mechanical characteristics of mixes and vulcanizates prepared on Nairit. Vulcanization temperature 143°C
| Indicator / Mix code | H-1 | H-2 | H-3 | H-4 | H-5 | H-6 | H-7 | H-8 | H-9 | H-10 | H-11 | H-12 | H-13 | H-14 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Plasticity of the mix | 0,73 | 0,73 | 0,75 | 0,73 | 0,72 | 0,74 | 0,74 | 0,73 | 0,73 | 0,73 | 0,73 | 0,66 | 0,66 | 0,66 |
| Plasticity after heating in water for 30 min | 0,73 | 0,73 | 0,68 | 0,73 | 0,32 | 0,72 | 0,65 | 0,72 | 0,48 | 0,50 | 0,73 | 0,61 | 0,60 | 0,45 |
| Optimum vulcanization time, min | 50 | 60 | 50 | 60 | 60 | 50 | 60 | 50 | 60 | 60 | 40 | 80 | 90 | 90 |
| Tensile strength, kg/cm² | 243 | 239 | 266 | 172 | 218 | 204 | 208 | 123 | 198 | 184 | 193 | 180 | 175 | 205 |
| Relative elongation, % | 950 | 935 | 975 | 940 | 860 | 950 | 940 | 990 | 950 | 880 | 990 | 900 | 880 | 950 |
| Shore elasticity | 54 | 55 | 58 | 55 | 57 | 47 | 41 | 43 | 45 | 46 | 42 | 44 | 48 | 49 |
| Aging coefficient (72 h at 100°C) by strength | 0,70 | 0,94 | 0,58 | 0,85 | 0,66 | 0,89 | 0,45 | 0,96 | 0,40 | 0,84 | 0,90 | 1,0 | 0,99 | 0,85 |
| Aging coefficient (72 h at 100°C) by relative elongation | 0,85 | 1,0 | 0,76 | 0,78 | 0,70 | 0,87 | 0,45 | 0,98 | 0,49 | 0,90 | 0,95 | 1,0 | 0,99 | 0,85 |
strength of the vulcanizate, but increases its heat resistance. Neozone D and DFFD increase the heat resistance of vulcanizates.
Experimental rubber compounds based on SKI-3 in the presence of a single accelerator—Altax—vulcanize slowly. The introduction into the compounds of the antidegradants Neozone D, 4010, and DFFD activates vulcanization in the presence of Altax. Product 4010 and DFFD are more active vulcanization activators than Neozone D. In the presence of a single accelerator—Altax—or of a combination of the accelerators Altax and thiuram (tetramethylthiuram disulfide), compounds based on SKI-3 vulcanize with an induction period.
Compounds based on SKI-3 vulcanized in the presence of the accelerator combination Altax and thiuram, without additional introduction of antidegradants or with Neozone D, give strong, fast-vulcanizing vulcanizates. The introduction of 4010 and DFFD into rubber compounds based on SKI-3 vulcanized in the presence of the accelerator combination Altax and thiuram reduces the strength of the vulcanizates. The compounds are not prone to premature vulcanization.
Additional introduction of antidegradants or their combinations into experimental compounds with various accelerators based on SKI-3, SKS-30 ARKM-15, and nairit, with the exception of the introduction of 4010 into standard compounds and compounds based on nairit, increases the heat resistance of the vulcanizates.
Neozone D introduced into an experimental compound based on SKS-30 ARKM-15 with the accelerator Altax reduces the physicomechanical properties of the vulcanizates, except for heat resistance. Product 4010 and DFFD provide good strength properties and heat resistance of the vulcanizates. Evidently, this is due to the synergism of the action on vulcanization of Neozone D contained in the rubber and of 4010 or DFFD introduced into the compound. The introduction of DFFD strongly delays the onset of vulcanization.
The combination of the accelerators Altax with thiuram tested in compounds based on SKS-30 ARKM-15 proved unsuccessful. The physicomechanical properties of the vulcanizates, both in the presence of antidegradants and in their absence, were low. Neozone D and DFFD increased the heat resistance of the vulcanizates. Product 4010 somewhat reduced heat resistance in comparison with the compound without an antidegradant.
Experimental compounds based on nairit containing antidegradants, in the presence of thiuram or Altax, have lower physicomechanical properties than standard compounds and a broad vulcanization plateau. With the exception of heat resistance, the properties in the presence of Neozone D and DFFD are lower than with 4010. The presence of a large amount of antidegradants in the rubber, including Neozone D, has an effect. In combination with thiuram, 4010 provides higher heat resistance of nairit vulcanizates.
In rubber compounds based on nairit, the tested antidegradants slow vulcanization at the beginning of the process and broaden the vulcanization plateau.
The effectiveness of introducing antidegradants into rubber compounds is the greater, the less antidegradant is contained in the rubber. The introduction into a rubber compound of antidegradants already contained in the rubber is less advisable than the introduction of antidegradants absent from the rubber.
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§. Order 2838.