Cure Systems for EPDM

EPDM vulcanisates exhibit some unique properties such as ozone, heat, light, weathering and chemical resistance (a. 14). Because of this attractive combination of properties, EPDM has taken over a wide variety of applications. EPDM has relatively low unsaturation and therefore requires complex cure systems to achieve the desired properties. Nearly every conceivable combination of curing ingredients has been evaluated in various EPDM polymers over the years (a. 15), five systems are described in Table 13. 

In all cases, nitrosamine free or safe alternatives are looked for. Eor System 1, the following alternative was suggested  

Comparative properties of the system 1 EPDM and the NA free alternative are listed in Table 14. 

System 2 (Triple 8) S2.0 MBT 1.5 Tellurium diethyl dithiocarbamate (TDEC) 0.8 Dipentamethyl thiuram tetrasulfide (DPTT) 0.8 TMTD 0.8 Excellent physical properties and fast cure Scorchy and expensive 

System 3 S0.5 ZDBC 3.0 ZDMC 3.0 DTDM 2.0 TMTD 3.0 Excellent compression set and good heat ageing resistance Bloom and very high cost 

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General curing system for EPDM rubbers will be a thiazole (mercaptobenzothiazole or dibenzothiazole disulfide) accelerator with a thiuram and/or a dithiocarbamate. For high heat exposure condition in a process industry, sulfur donor types like tetra methyl thiuram disulfide may replace a larger part or all of the sulfur. 

TABLE 26 Typical sulfur cure systems for EPDM... 

Zheng, H., et al., A comparison between cure systems for EPDM/montmorillonite nanocomposites. Polymers and Polymer Composites, 2004. 12(3) 197-206. 

Peroxide vulcanisation of EPDM is growing in popularity because of enhanced ageing resistance. A comparison of sulfur and peroxide cure systems for EPDM is shown in Table 32 (381). 

Cure systems, for butyl rubber and EPDM, 21 802-803 Cure temperatures... 

The level of accelerator used varies from polymer to polymer. Some typical curing systems for the diene rubbers (NR, SBR, and NBR) and for two olefin rubbers (HR and EPDM—see Appendix A2 for... 

Fig. 12.5. Dependence of tensile strength (Ts) on cross-link density (vt) and cross-link structure for (a) EPDM (Royalene 301) and (b) EPM (Dutral). Tested using dumbell type 3 at 250mm/min elongation rate at 20 C. Cure systems (a) EPDM (1) tetramethylthiuram disulphide, bis (benzothiazolyl) disulphide (2) dicumyl peroxide, 1 phr sulphur (3) dicumyl peroxide, 0 3 phr sulphur (4) mercaptobenzothiazole (5) dicumyl peroxide (b) EPM (1) dicumyl peroxide, 1 phr sulphur (2) dicumyl peroxide, 0-3 phr sulphur (3) dicumyl peroxide. (From Imoto et al, 1%8.)...

Table 8 Effect of Composition of TMTD Curing System on the Charpy Notched Impact Strength (ai<) for 85/15 and 80/20 PP/EPDM Blends...

Thermoplastic elastomers based on polyolefins (TPO) are blends of PE or PP wifh EPDM elastomers wherein the elastomer is often cross-linked using thermochemical systems. TPOs more suitable for medical producfs with no chemical residuals can be made using EB processing to cross-link the elastomer portion in such an elastomer-plastic blend. The thermoplastic governs the melt transition, and thus the extrusion properties of TPOs. The radiahon response of these materials is also governed by the choice of fhe thermoplastic. An example of an EB cured blend of EPDM and polyefhylene used is for fluid transmission tubing and electrical insulation. ... 

Cure characteristics of EPDM/PP blends were investigated by Sengupta and Konar (27). They calculated the state of cure in blends containing conventional sulfur curing system under variable time-temperature conditions. They found that the activation energy for the cross-linking is almost similar for the virgin EPDM and EPDM/PP mixtures. Cross-link densities in TPVs can be analyzed by swollen-state... 

Over the years, much of the research on accelerated-sulfur vulcanization was done by using natural rubber as a model substrate. Natural rubber was the first elastomer and therefore the search for the understanding of vulcanization originated with work on natural rubber. Most of the work cited in the previous sections is related to natural rubber. However, some rather early studies have been directed to the vulcanization of butadiene 1,4-polymers (Skinner and Watson, 1969 Wolfe et al, 1329 Gregg and Katrenick, 1970). More recent is the work of Pellicioli and coworkers. Early basic work on the vulcanization of ethylene-propylene-diene-monomer rubber (EPDM) has been carried out (van den Berg et al., 1984a,b). Recently, Kuno and coworkers did basic work on EPDM networks. They found that, essentially, the vulcanizate properties depend only on the crosslink density, not on the type of curing system (Dijkhuis et al., 2009). 

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 ... 

Table 3.4 gives the properties of EPDM/PP TPVs prepared with different cure systems. As shown, there is substantial improvement in tensile properties and tension set over uncured physical blends for all the crosslinked TPVs. 

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