EPDM peroxide-curing effects

Influences of the different methacrylates and 1,2-polybutadiene as coagents on the mechanical and rheological properties of the peroxide-cured PP/EPDM TPVs were reported by Rishi and Noordermeer [39, 40]. They interpreted the results in terms of solubility parameter and cure kinetics. The effects of coagents on both processing and properties of the compound depend on the nature of the polymer, type of peroxide, and other compounding ingredients. Among the methacrylate... 

The effect of co-agents in the peroxide-curing of EPDM is very similar to the effect of third monomers. It was concluded that the pendent unsaturation of the third monomer acts as a co-agent, i.e., the amount of third monomer governs the amount of chemical crosslinks formed by macroradical addition reactions via the unsaturated moiety of the third monomer, whereas the amount of peroxide governs the amount of crosslinks formed by macroradical combination reactions. 

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. 

The basic feature involves blending polypropylene (10%-50%) with EPDM (50%-90%), plus less than the usual amounts of peroxide. The effect the dynamic semicure, the rubber, plastic, and curing agent are worked on an open roll mill, a Banbury mixer, or an extruder mixer.During this time, between 60% and 93% of the material becomes insoluble in cyclohexane at 73 F. (Note the plastic portion probably was already insoluble under these conditions the reaction is partly gelling the elastomer.)... 

Mill roll surface preparation is extremely important Polyepichlorohydrin type ECO and GECO compounds tend to stick to mill roll surfaces when certain residues from previously processed compounds, based on different polymer types, remain on the rolls and if the mill roll is too cold. One of the worst residues seems to come from an EPDM compound cured with a peroxide. The mill rolls must be consistently thoroughly cleaned to avoid problems with sticking. Millathane Glob has been an effective, safe method of cleaning the rolls. 

Excellent elastomeric NBR-nylon compositions have also been prepared by dynamic vulcanization during the melt-mixing of intimate blends of NBR with various nylons. In this case, the effect of curatives was complicated by the fact that some nitrile rubbers tend to self-cure at temperatures of mixing. Sulfur, phenolic, maleimide, or peroxide curatives can be used. The thermoplastic elastomeric compositions prepared by the dynamic vulcanization of nylon-NBR blends are highly resistant to hot oil. As in the case of the EPDM-polyolefin blends, increases in the amount of rubber in the composition reduce stiffness but increase resistance to permanent set. 

The failure of rubber parts used in domestic water applications has been reported flem several US states. The complaints involved swelling and cracking and are related to nitrile and ethylene-propylene copolymer type compoimds. The failure of the rabber parts coincides with the implementation and use of chloramines as a method of water purification. This investigation was designed to determine if EPDM composition variables influenced resistance to chloramines. Also evaluated were peroxide vs sulphur cure systems, the effect of antioxidants and whether practical compoimds can be developed for water systems. 5 refs. 

The role of accelerators in the curing and mechanical properties of EPDM/SBR blends is investigated. In this study, blend properties were optimised by selecting accelerators with a shorter scorch time and a faster cure rate in the EPDM phase than in the SBR phase. The accelerators investigated included a sulphenamide-based accelerator and a system composed of a combination of a thiuram and thiazole-based accelerator. By use of techniques described in this work, sulphur vulcanisates with compound properties comparable to those cured with a cure system composed of peroxide and sulphur coagent were obtained. The effects of the accelerators in final compound properties are discussed, with reference to mechanical properties, ozone resistance, heat ageing, and compression set. 13 refs. 

Sartomer s Saret zinc diacrylate and zinc dimethacrylate coagents were evaluated in the peroxide vulcanisation of EPDM automotive belt and hose compounds. Cure characteristics and effects on mechanical properties, heat and water resistance and adhesion of EPDM to metal and synthetic fibre reinforcements and to other mbbers were investigated. The results of this study and other experiments with Saret coagents in rabber formulations are discussed. 6 refs. 

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