Vulcanization peroxides

The saturated rubbers such as butyl or EPDM cannot be cross linked by sulphur and accelerators. Organic peroxides are necessary for the vulcanization of these rubbers. When the peroxides decompose, free radicals are formed on the polymer chains and these chains can then combine to form cross links of the type where only carbon-carbon bonds are formed, unlike in sulphur vulcanization. These carbon-carbon bonds are quite stable ones. Such bonds are also formed by vulcanization using gamma or x-ray radiation of compounded rubbers. Some rubbers can be vulcanized by the use of certain bisfunctional compounds which form bridge type cross 

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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. 

Po[yamine disulphides do not inhibit peroxide vulcanization of polyethylene, are stable in air up to 300-350°C, exhibit good compatibility and show no sweating out from the polyethylene mass. Table 8 gives the comparison between the efficiency of polyamine disulphides as thermostabilizers of cured polyethylene. 

Uses. In baking dough, prodn of hydrogen peroxide, vulcanization of rubbers, medicines, pharmacology, dentifrices, fanning, chewing gums. etc. (Ref 6)... 

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

Of the polymers that can be cross-linked, the cross-link efficiency varies considerably. In general the relative efficiency of peroxides vulcanization of polymers [50,51] follows as ... 

Peroxides vulcanization of EPDM is growing in popularity because of enhanced aging resistance. A comparison of sulfur- and peroxide-cure system is shown in Table 14.31 [53]. 

Influence of the ZnCFO contents (3,0 5,0 7,0 phr) on crosslink kinetics of the modelling unfilled rubber mixes from NBR-26 of sulfur, thiuram and peroxide vulcanization of recipe, phr NBR-26 - 100,0 sulfur - 1,5 2-mercaptobenzthiazole - 0,8 stearic acid - 1,5 tetramethylthiuramdisulfide - 3,0 peroximon F-40 - 3,0, is possible to estimate on the data of fig. 7. As it is shown, the increase of ZnCFO concentration results in increase of the maximum torque and, accordingly, crosslink degree of elastomeric compositions, decrease of optimum cure time, that, in turn, causes increase of cure rate, confirmed by counted constants of speed in the main period (k2). The analysis of vulcanizates physical-mechanical properties testifies, that with the increase of ZnCFO contents increase the tensile strength, hardness, resilience elongation at break and residual deformation at compression on 20 %. That is, ZnCFO is effective component of given vulcanization systems, as at equal-mass replacement of known zinc oxide (5,0 phr) the cure rate, the concentration of crosslink bonds are increased and general properties complex of rubber mixes and their vulcanizates is improved. 

It is possible to explain the decrease of ZnCFO efficiency as component of various vulcanization systems for rubbers of general and special assignment in the earlier submitted line (fig. 10) also by character of formed morphology of compositions. So, at use of ZnCFO as the activator of sulfur vulcanization the structure of rubbers with the minimal value of parameter r is formed, and at transition from sulfur to peroxide vulcanization of elastomeric compositions the particles size of heterophase is increased (fig. 11 b). 

Das et al. [89] observed that both sulfur and peroxide vulcanizations of NBR filled with organoclay lead to intercalated-exfoliated structures of the layered silicate. They also reported that the use of excess stearic acid could lead to exfoliation of the clay layers in NBR when cured with sulfur. 

The vulcanizing agenl, which supplies the bridge between the polymer chains, is furnished predominantly by the sulfur molecule m commercial formulations. Peroxide vulcanizers that produce carhon-to-carbon crosslinks are also important. 

The networks obtained through vulcanization by peroxides display high thermal stability. Nevertheless, the peroxide vulcanization process allows less control of the vulcanization than the sulfur process. Consequently it... 

Important processing methods peroxide vulcanization, molding, mixing, extrusion... 

Di-Cup. [Hercules Hercules Europe] Dicumyl peroxides vulcanizing agent, polymerization catalyst for robbo and plastics. 

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

PeroximoBK [Akrochem] Peroxides vulcanizing and crosslinking agents for rubber ind try. 

Thermacure . [Cook Composites ft Polymers] Dicumyl peroxide vulcanizing agent (X polymerizing catalyst in rubber or plastte. 

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