Peroxide-cured EPDM system

In sulfur-cured EPDM systems, the primary amino- and mercaptofunctional silanes can participate in the cure mechanism to a far greater extent than the vinylsilane as shown by the higher modulus values. In the peroxide-cured EPDM system, all silanes promote significant improvements in modulus but in different degrees depending on their relative reactivity. The methacryloxy functional silane... 

Ha [29] has shown that in PP-HDPE (of high-den-sity PE) dynamically cured EPDM, the cured EPDM act as a compatibilizer to the HDPE-PP system. Blending was done in two ways. EPDM was cured first and then blended with PP and HDPE. In the second case, EPDM was cured in the presence of PP and HDPE using dicu-myl peroxide (DCP) as the vulcanizing agent. In EPDM-rich composition, mechanical properties were increased by increasing the concentration of DCP, whereas in PP-rich composition, the reverse was the case. 

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]. 

NR/modified EPDM, in which EPDM was modified by pendant sulfur, exhibited improved endurance to repeated stress over that of covulcanized EPDM-NR mbber blends (68). The effects of ethylene and diene contents in EPDM, blend ratio, dicumyl peroxide curing system on the physical properties, interfacial adhesion force, and dynamic crack growth were examined (69). As the ethylene and diene contents in EPDM increased, the physical properties, such as dynamic cut growth, adhesion to other component were also increased. The mechanical properties of the blends are compared to those of the pure components in Table 15.3 (56). The ultimate tensile strength of noncompatibilized blends is lower than that of pure NR, as expected since these blends are incompatible. 

Formula CH2CH3CC00(CH2CH20)nC0CHCH3CH2 Uses Crosslinking agent for radiation and peroxide cure systems incl. adhesives (anaerobic), concrete polymers and sealants, cosmetics, dental polymers, elastomers, plastics, plastisols, sealants vulcanizer for peroxide curing of BR, CR, EPDM, NBR, IR, SBR... 

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 ... 

Commercial vinylsilanes usually have the vinyl group directly attached to the silicon atom. Common hydrolyzable groups are methoxy, ethoxy, or 2-methox-yethoxy. The vinyl functionality is used in polymers that are cross-linked by a free-radical process (peroxide cure), but it is, however, not sufficiently reactive for all systems, and methacryloxy functionality is sometimes preferred as shown in Table 4.2 [35]. Vinylsilanes because of their overall cost/performance advantages have become the industry standard for EPR and EPDM and wire and cable applications. 

EPDM is a terpolymer of ethylene, propylene, and a small amount of an unsaturated diene as a third monomer to provide a cure site. Unlike the elastomers previously discussed, the unsaturation in EPDM is not in the main chain, but it is pendent to the chain. Peroxide-based cure systems afford better aging resistance and low compression set. A comparison of a sulfur-based cure to two different peroxides in EPDM is shown in Table 21 (4). Initial properties for these three compounds are reasonably close. However, after air aging, the advantages of peroxide curing are apparent. Most dramatic is the improved compression set... 

The Saret 633/peroxide-cure system also promotes good adhesion to other untreated metals, including aluminium, zinc, brass, and stainless steel. This is illustrated in Figure 8.9 for EPDM containing 10 phr Saret 633. In each case, shear adhesion increased with the addition of Saret 633, compared with peroxide alone. 

APPLICATION OF BISMALEEVflDE BV EPDM PEROXIDE CURING SYSTEM... 

Mechanical and Physical Properties of EPDM and EPDM-SBR Blends Cured with Peroxide and Sulfur Co-Agent Cure System... 

Ultrasonic devulcanization also alters revulcanization kinetics of rubbers. It was shown (Isayev et al., 1996b) that the revulcanization process of devulcanized SBR was essentially different from those of the virgin SBR. The induction period is shorter or absent for revulcanization of the devulcanized SBR. This is also true for other unfilled and carbon black-filled mbbers such as GRT, SBR, NR, EPDM, and BR cured by sulfur containing curative systems, but not for silicone rubber cured by peroxide. It was suggested that a decrease or disappearance of the induction period in case of the sulfur-cured rubbers is due to an interaction between the rubber molecules chemically modified in the course of devulcanization and unmodified rubber molecules resulting in crosslinking. It was shown that approximately 85% of the accelerator remained in the ultrasonically devulcanized SBR rubber (Levin et al., 1997a). 

As shown in Figure 8.7, strong rubber-to-metal bonding can be obtained with Saret 633 as an internal adhesion promoter for a variety of rubbers such as silicone rubber, EVA, EPDM, NR and Hypalon. All of the compounds contained 5 phr of Saret 633 and were cured with peroxide. In each case, shear adhesion was significantly increased with the Saret 633 cure system over the peroxide control. 

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