Vulcanization of SKS-30 ARM-15 in the Presence of 9-Ethyl-3,6-diaminocarbazole Stearate
Abstract Generated abstract
This study examines the use of 9-ethyl-3,6-diaminocarbazole stearate as an additive in the sulfur vulcanization of SKS-30 ARM-15 oil-extended butadiene-styrene rubber with Altax as accelerator. The compound was synthesized from 9-ethylcarbazole through nitration, reduction to the diamine hydrochloride, and salt formation with stearic acid, then tested in tread-type rubber formulations vulcanized at 143°C. Physicomechanical testing showed that formulations containing the carbazole stearate and Altax were not susceptible to premature vulcanization, vulcanized more rapidly in some ratios, and produced vulcanizates with higher strength, improved elasticity, broader vulcanization behavior, and better heat resistance than the control. The results suggest that the additive can function both as a vulcanization accelerator component and as an antioxidant in SKS-30 ARM-15 compounds.
Full Text
VULCANIZATION OF SKS-30 ARM-15 IN THE PRESENCE OF 9-ETHYL-3,6-DIAMINOCARBAZOLE STEARATE
V. D. Bogoslovskii, N. I. Yukhnovets
(Presented by the scientific-methodological seminar of the organic departments of the Faculty of Chemical Technology)
Oil-extended copolymeric butadiene-styrene synthetic rubbers, which include SKS-30 ARM-15, when mixed with the other ingredients of a rubber compound, do not require preliminary mastication. Being general-purpose rubbers, oil-extended butadiene-styrene rubbers have found wide application in the manufacture of rubber articles by press vulcanization (tires, technical rubber goods, molded rubber footwear).
The task of increasing the productivity of vulcanization equipment in the vulcanization of molded articles requires the creation of rapidly vulcanizing rubbers with a definite set of physicomechanical properties and no tendency toward premature vulcanization. In the general case, acceleration of vulcanization is achieved by the rational selection and dosage of a combination of vulcanization accelerators and the vulcanizing agent. For butadiene-styrene and some other types of synthetic rubber, delayed-action accelerators of the sulfenamide type are recommended.
Amines activate vulcanization accelerators of the thiazole group. In the presence of accelerators activated by bases, fatty acids can exert an additional activating effect. The activating effect of bases is partially compensated by the action of fatty acids. Therefore, by using fatty acids and base-activated accelerators of the mercapto-derivative type, it is possible to increase the period during which rubbers retain plastic flow at the vulcanization temperature, while simultaneously improving the physicomechanical properties of the vulcanizates [1].
The aim of the work was to test the possible activating action of 9-ethyl-3,6-diaminocarbazole stearate on the vulcanization of a standard tread-type compound for tires. The compound was prepared on SKS-30 ARM-15 rubber. The vulcanization accelerator was altax (benzothiazole disulfide).
The synthesis of 9-ethyl-3,6-diaminocarbazole stearate included several stages. The first stage was the preparation of 9-ethyl-3,6-dinitrocarbazole by nitration of 9-ethylcarbazole with fuming nitric acid in nitrobenzene medium.
In the second stage, the dinitrocarbazole obtained was reduced with tin and hydrochloric acid in acetic acid medium. The resulting 9-ethyl-3,6-diaminocarbazole is an unstable, readily oxidized com-
Table 1
Physicomechanical properties of experimental rubbers and vulcanizates based on SKS-30 ARM-15; vulcanization temperature 143°C
| Indicators | Formulation 1, 10 min | Formulation 1, 20 min | Formulation 1, 30 min | Formulation 1, 45 min | Formulation 1, 90 min | Formulation 2, 10 min | Formulation 2, 20 min | Formulation 2, 30 min | Formulation 2, 45 min | Formulation 2, 90 min | Formulation 3, 10 min | Formulation 3, 20 min | Formulation 3, 30 min | Formulation 3, 45 min | Formulation 3, 90 min |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Plasticity of the initial compound | — | — | 0.40 | — | — | — | — | 0.32 | — | — | — | — | 0.37 | — | — |
| Plasticity after 60-min boiling in water | — | — | 0.46 | — | — | — | — | 0.31 | — | — | — | — | 0.34 | — | — |
| Tensile strength, kg/cm² | 8 | 40 | 125 | 195 | 261 | 25 | 60 | 130 | 220 | 262 | 32 | 104 | 196 | 250 | 278 |
| Relative elongation, % | 1100 | 1300 | 1200 | 1000 | 810 | 960 | 1110 | 1100 | 870 | 650 | 1070 | 1050 | 1000 | 860 | 670 |
| Permanent elongation, % | 140 | 120 | 110 | 60 | 38 | 120 | 110 | 62 | 50 | 30 | 110 | 68 | 52 | 40 | 24 |
| Shore hardness | 16 | 26 | 34 | 36 | 45 | 32 | 35 | 38 | 42 | 47 | 28 | 37 | 43 | 45 | 50 |
| Elasticity by Shob | 28 | 27 | 27 | 28 | 28 | 29 | 27 | 27 | 28 | 29 | 27 | 27 | 28 | 29 | 28 |
| Aging coefficient (144 h at 70°C) for a 60-min vulcanizate: by strength | 230:270=0.85 | 230:270=0.85 | 230:270=0.85 | 230:270=0.85 | 230:270=0.85 | 270:260=1.04 | 270:260=1.04 | 270:260=1.04 | 270:260=1.04 | 270:260=1.04 | 256:285=0.94 | 256:285=0.94 | 256:285=0.94 | 256:285=0.94 | 256:285=0.94 |
| Aging coefficient (144 h at 70°C) for a 60-min vulcanizate: by relative elongation | 680:900=0.73 | 680:900=0.73 | 680:900=0.73 | 680:900=0.73 | 680:900=0.73 | 600:780=0.77 | 600:780=0.77 | 600:780=0.77 | 600:780=0.77 | 600:780=0.77 | 550:800=0.69 | 550:800=0.69 | 550:800=0.69 | 550:800=0.69 | 550:800=0.69 |
Therefore, hydrochloric acid was taken in excess and a more stable hydrochloride salt of the diamine was obtained.
At the last stage, 9-ethyl-3,6-diaminocarbazole stearate was obtained. The diamine hydrochloride was neutralized with the calculated amount of alkali, and the rapidly filtered 9-ethyl-3,6-diaminocarbazole was transferred into a hot solution of stearic acid in benzene.
The reaction mass was filtered, and upon cooling a salt precipitated from the filtrate in the form of a white crystalline substance with a melting point of 70–76°C. The yield of the salt was 94% of theory.
Experimental rubber compounds were prepared according to the following formulations (in % per 100 parts by weight of rubber):
| Formulation 1 | Formulation 2 | Formulation 3 | |
|---|---|---|---|
| SKS-30 ARM-15 | 100 | 100 | 100 |
| Stearic acid | 2.0 | 2.0 | 2.0 |
| Zinc oxide | 5.0 | 5.0 | 5.0 |
| Furnace carbon black | 50 | 50 | 50 |
| Sulfur | 2.0 | 2.0 | 2.0 |
| Altax | 2.0 | 1.0 | 1.5 |
| 9-Ethyl-3,6-diaminocarbazole stearate | — | 2.4 | 1.2 |
Formulation 1 is the standard tread compound for SKS-30 ARM-15 rubber. The accelerator dosages in the compounds are equimolecular. The dosage ratio is 0.5 : 0.5 molar for compound 2 and 0.75 : 0.25 for compound 3.
The experimental compounds were vulcanized in a press at 143±1°C. The physico-mechanical indices of the experimental rubbers and vulcanizates were determined by standard methods [2].
The experimental rubber compounds are not prone to premature vulcanization. Vulcanizates of rubbers vulcanized in the presence of 9-ethyl-3,6-diaminocarbazole stearate were distinguished by high strength, better elasticity, and a broader vulcanization plateau. The remaining indices were analogous to those for the control compound with a single accelerator—Altax.
Rubber compounds containing the accelerator combination vulcanized more rapidly at the beginning of the vulcanization process. The time to reach the vulcanization optimum, by the product of elasticity, was 45 min for control compound 1 and experimental compound 2, and 30 min for experimental compound 3. The experimental compounds are distinguished by better heat resistance.
From an analysis of the results of physico-mechanical tests of the experimental rubbers and vulcanizates it follows that 9-ethyl-3,6-diaminocarbazole stearate in combination with Altax serves as an active antioxidant and vulcanization accelerator for rubbers based on SKS-30 ARM-15. The rubbers are not prone to premature vulcanization and give vulcanizates with improved physico-mechanical characteristics. The vulcanization time can be reduced.
REFERENCES
- V. Gofman, Vulcanization and Vulcanizing Agents. Khimiya, L., 1968.
- Rubber. Test Methods. Standartiz, Moscow, 1960.