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Unsaturated rubbers, accelerated-sulfur

The crosslinking of unsaturated rubbers by sulfur is a very complex process. It requires a zinc oxide/stearic acid activator, cure accelerators such as MBTS (ben-zothiazyl disulfide), MBS, TMTD (tetramethylthiuram disulfide), and so on, and sulfur, which usually exists as Sg. Scheme 3.1 shows a simplified mechanism for rubber crosslinking by sulfur [17]. [Pg.132]

Most EPDM applications require crosslinking except when used as an impact modifier for PP, polystyrene (PS) and polyamides or as an oil additive, e.g., as viscosity index improver or dispersant. Most commonly, accelerated sulfur vulcanisation is used for the crosslinking of EPDM. As a result of the low amount of unsaturation in EPDM (< 1 mole/ kg versus NR -15 mole/kg), sulfur vulcanisation of EPDM is rather slow and a relatively large amount of accelerators is needed. Because of the low polarity of EPDM the solubility of polar accelerators is limited, often resulting in low effectivity and/or blooming. Typically, up to 5 different accelerators are used in EPDM formulations. As for other rubbers environmental issues, such as nitrosamine formation and may be in the future the presence of zinc, are prompting the development of new accelerator systems. [Pg.208]

The mechanism of the accelerated sulfur vulcanisation of EPDM is probably similar to that of the highly unsaturated polydiene rubbers. The vulcanisation of EPDM has been studied with emphasis on the cure behaviour and mechanical and elastic properties of the crosslinked EPDM. Hardly any spectroscopic studies on the crosslinking chemistry of EPDM have been published, not only because of the problems discussed in Section 6.1.3 but also because of the low amount of unsaturation of EPDM relative to the sensitivity of the analytical techniques. For instance, high-temperature magic-angle spinning solid-state 13C NMR spectroscopy of crosslinked EPDM just allows the identification of the rubber type, but spectroscopic evidence for the presence of crosslinks is not found [72]. [Pg.216]

Curatives. The function of curatives is to cross-link the polymer chains into a network the most common ones are the sulfur type for unsaturated rubber and peroxides for saturated polymers. Chemicals called accelerators may be added to control the cure rate in the sulfur system these materials generally are complex organic chemicals containing sulfur and nitrogen... [Pg.695]

Accelerated-Sulfur Vulcanization of Various Unsaturated Rubbers... [Pg.363]

Accelerated-Sulfur Vulcanization of Various Unsaturated Rubbers. Over the years, much of the research on accelerated-sulfur vulcanization was done by using natural... [Pg.241]

Since EPR rubber molecules do not contain unsaturation, they can be vulcanized only by organic peroxide curing systems. If a third monomer is added during the polymerization, i.e., a diene monomer (wherein only one of the two double bonds takes part in the polymerization), unsaturation can be introduced into the molecule, and it can then be vulcanized by accelerated sulfur curing systems. A chemical structure for ethylene-propylene-diene-monomer (EPDM) rubbers can be expressed as follows ... [Pg.267]

Typically, the activator stearic acid reacts with the activator zinc oxide during the curing process to solubilize the divalent zinc ion. This in turn reacts with the organic rubber accelerator to enable the eight-membered ring of the sulfur molecule to break up and rapidly establish sulfur crosslinks between the unsaturated rubber... [Pg.257]

Here PNO2 partial pressure of nitrogen dioxide in pascals (1 Pa = 0.000145 psi), and the activation energy is 3870 kJ/mol. Other saturated polymers are less susceptible to attack by NO2 than most unsaturated polymers such as synthetic rubbers (polyiso-prene, polybutadiene, and butyl rubber). The presence of oxygen also tends to accelerate degradation by NO2. The reaction of sulfur dioxide with saturated polymers is complex, but appears to be activated by ultraviolet radiation. [Pg.265]

The filler/silane intermediate can now react with the allyl position of unsaturated sites on the polymer chain. The vulcanization of rubber is known to proceed via reaction of an accelerator, such as a sulfenamide, with sulfur, zinc oxide, and stearic acid, to generate a sulfurating agent (Bateman et al., 1963). [Pg.441]

Vulcanizing additive Thermoset elastomers must be vulcanized or crosslinked to obtain strong, dimensionally stable resilient materials. To accomplish this purpose, a formidable array of chemicals is employed. Classically, sulfur vulcanizes unsaturated elastomers such as SBR and natural rubber however, because the rate of vulcanization is too slow for industrial applications, chemicals like benzothiazyl disulfide (MBTS) are added. The latter is typical of a class called accelerators. [Pg.545]


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