Vulcanized Parel elastomer

However, triphenylphosphine is a reagent which can be utilized advantageously. It reduces polysulfides to disulfidesbut does not break the polymer chains in Parel elastomer. To determine the types of cross-links which are produced in representative cure systems, two samples of vulcanized Parel elastomer were prepared. One was cured with sulfur alone, and the other with the formulation shown in Table 1. The samples were then treated with triphenylphosphine in benzene. The results of continuous stress relaxation measurements run on the products at 150°C. are shown in Figure 1. The stabilizers were extracted by the benzene used in the triphenylphosphine treatment so subsequent tests in air could not be compared with previous test results. Therefore, all of these stress relaxation measurements were made in nitrogen. 

Figure 1. Effect of polysulfides on the stress relaxation of vulcanized Parel elastomer...

TYPICAL PHYSICAL PROPERTIES OF VULCANIZED PAREL ELASTOMER... 

When properly compounded, vulcanized Parel elastomer is quite stable in hot air. Nickel dibutyldithiocarbamate (NBC) has been found to be a very effective stabilizer for this rubber. 

Effect of stabilizer on vulcanized Parel elastomer aged at 150°C... 

Parel elastomer, natural rubber, and neoprene, compounded with standard recommended formulas for each, were heat aged in a 125 C. forced draft oven. Figure 3 is a plot of the change in tensile strength and hardness of the vulcanized Parel and neoprene elastomers. Neoprene maintained its properties for 3 days, but after a week at 125 C., it was quite hard and brittle. Results with natural rubber are not included in the figure because it failed so quickly at 125 C. It was seriously deteriorated in about 3 days at 100 C. 

Figures 5 and 6 compare the compression set of vulcanized Parel, natural rubber, and neoprene elastomers at 100 and 150 C., respectively. At 100 C., the compression set of Parel elastomer is within experimental error of that of natural rubber neoprene is clearly superior. When the compression set test was run for a long time at 150 C. (Figure 7), Parel elastomer was the best of these three rubbers. Natural rubber had 100% compression set...

Figure 7 shows stress relaxation results with Parel elastomer and neoprene at 125 C, their rates of chain scission are similar. In this test, neoprene maintained a larger fraction of its initial modulus than the vulcanized Parel elastomer. However, Figure 8 shows stress relaxation results with these two rubbers at 150 C. Under these conditions, the greater oxidative stability of the Parel elastomer is more significant than its somewhat greater loss of modulus in the first few hours of test. 

Some of the key properties of PAREL elastomer vulcanizates are summarized in Table I. They have excellent low teiqierature properties excellent dynamic properties, which are much like those of natural rubber good ozone resistance and good heataging resistance. This interesting combination of properties is leading to substantial specialty markets in such applications as automotive engine mounts. Vulcanization and stabilization studies on PAREL elastomer, as well as additional specific properties of PAREL elastomer, are reported in this book by Boss. 

Sulfur cure systems are well known to be complex in their reactions and in the types of cross-links they produce. There is general agreement that if sulfur alone is used to vulcanize a rubber, most of the cross-links will have more than two sulfur atoms in themW. These polysulfides are less stable than monosulfides or disulfides. This phenomenon has been examined in some vulcanized elastomers by using chemical probes, which modify or break only certain kinds of cross-links CDW(. Parel elastomer is more difficult to study in this fashion than styrene-butadiene rubber (SBR) or natural rubber because many of these chemical reagents also react with the C-0 bonds of the polyether. 

Parel elastomer, a copolymer of propylene oxide and allyl glycidyl ether, has a combination of properties that make it very useful in many rubber applications. It can be vulcanized with a conventional mixture of sulfur and accelerators. The cured elastomer has a low glass transition temperature (approximately -55 to -60 C.), and the excellent dynamic properties of natural rubber. It can be made very stable to high temperature oxidative degradation, and is better than neoprene in this respect, when NBC is added as a stabilizer. 

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