Peroxide vulcanization elastomers

Methyl Niclate . [R.T. Vanderbilt] Nidrel dimediyiditidocarbainate antioxidant for epchloiohydrin and peroxide vulcanized elastomers. 

Ethylene—Propylene Rubber. Ethylene and propjiene copolymerize to produce a wide range of elastomeric and thermoplastic products. Often a third monomer such dicyclopentadiene, hexadiene, or ethylene norbomene is incorporated at 2—12% into the polymer backbone and leads to the designation ethylene—propylene—diene monomer (EPDM) mbber (see Elastomers, synthetic-ethylene-propylene-diene rubber). The third monomer introduces sites of unsaturation that allow vulcanization by conventional sulfur cures. At high levels of third monomer it is possible to achieve cure rates that are equivalent to conventional mbbers such as SBR and PBD. Ethylene—propylene mbber (EPR) requires peroxide vulcanization. 

There are a number of advantages, listed below, associated with the peroxide vulcanization of elastomers ... 

The blends of EPDM terpolymers and isotactic PP with curing agents, such as peroxide, phenol resins, and sulfur, are termed as thermoplastic vulcanized elastomer (TPV) since the rubber domains are vulcanized. Polyolefin copolymers, such as random copolymer of propylene with ethylene, copolymers of other olefins, elastomeric PP, and elastomeric PE, are developed with recent advances of... 

Urethane elastomers suitable for peroxide vulcanization typically are prepared from a hydroxyl-group-terminated oligomeric adipate polyester and 4,4 -methylenediphenylisocyanate (MDI). A typical structural representation is as follows ... 

Peroxide Vulcanization of Unsaturated Hydrocarbon Elastomers. The initiation step in peroxide-induced vulcanization is the decomposition of the peroxide to give free radicals. If the elastomer is derived from butadiene or isoprene, the next step is either the abstraction of a hydrogen atom from an allyUc position on the polymer molecule or the addition of the peroxide-derived radical to a double bond of the polymer molecule. In either case, polymeric free radicals are the result (Scheme 17). 

Peroxide Vulcanization of Urethane Elastomers. Urethane elastomers suitable for peroxide vulcanization are typically prepared from an hydroxyl-group-terminated oligo-... 

The new co-agents revealed high tendency to agglomeration in elastomer matrix what had a beneficial effect on vulcanizates mechanical properties. ApplicatitMi of unsaturated acids and metal oxides as the new co-agents in peroxide vulcanization of HNBR caused mostly a decrease of vulcanization time, considerable improvement of vulcanizates mechanical properties, as well as the increase of cross-link efficiency. Thus, they may be used successfully in rubber technology. 

In contrast to nitrile rubber, fully hydrogenated NBR is not attacked by ozone. Even under extreme conditions (e.g., 2 ppm ozone, 40 °C, 50% rel. humidity, 60% strain, 168 h) no cracks appear. Even under cyclic load these rubbers exhibit excellent ozone crack resistance. Elastomer parts based on HNBR are highly ozone-resistant without the addition of antiozonants. Partially-hydrogenated grades behave differently, depending on the vulcanization system. Ozone resistance quickly decreases with increasing double bond content. However, peroxide vulcanized rubbers behave more favorably than sulfur vulcanized rubbers [697]. 

For organic peroxide vulcanization, a variety of organic peroxides have been shown to be effective [7]. Such peroxides would include di-t-butyl peroxide dicumyl peroxide t-butyl cumyl peroxide l,l-di(t-butylperoxy)-3,3,5-trimeihyl cyclohexane 2,5-dimethyl-2,5-di(r-butylperoxy)hexane 2,5-dimethyl-2,5-di(r-butylper-oxy)hexyne-3 a,a-bis(t-butylperoxy)diisopropylbenzene t-butyl perbenzoate and t-butylperoxy isopropylcarbonate. In contrast to NBR elastomers where 1-3 phr of peroxide is effective, HNBRs generally require peroxide levels of 5-8 phr for effective vulcanization. As discussed earher, this is due to the very low levels of unsaturation present in the HNBR polymers. The specific peroxide chosen will depend on the process safety desired and the vulcanization temperature to be used. Generally, the most common organic peroxides used in HNBR elastomers are Dicumyl peroxide, such as Varox Dicup 40C from R.T. Vanderbilt, on an inert carrier for vulcanization below 177°C and a,a-bis(t-butylperoxy)diisopropylbenzene, such as Varox VC40KE from Vanderbilt, on an inert carrier for vulcanization above 150°C. 

Dluzneski, P.R., Peroxide Vulcanization of Elastomers. Rubber Chemistry and Technology, 2001. 74(3) 451. 

Rubber Chemistry and Technology lA, No.3, July/Aug. 2001, p.451-92 PEROXIDE VULCANIZATION OF ELASTOMERS... 

Double-Bond Cure Sites. The effectiveness of this kind of reactive site is obvious. It allows vulcanization with conventional organic accelerators and sulfur-based curing systems, besides vulcanization by peroxides. Fast and controllable vulcanizations are expected so double-bond cure sites represent a chance to avoid post-curing. Furthermore, blending with other diene elastomers, such as nitrile mbber [9003-18-3] is gready faciUtated. 

Extrusion. Extmsion techniques are used in the preparation of tubing, hose, O-ring cord, preforms and shaped gaskets. Typical extmsion conditions are 70 to 85°C for the barrel temperature and 95 to 110°C for the head temperature. The extmded forms are normally cured in a steam autoclave at 150 to 165°C. Some special grades of peroxide curable fluorocarbon elastomers can be hot air vulcanized. 

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