Ethylene-propylene curing systems

Propellants cast into rockets are commonly case-bonded to the motors to achieve maximum volumetric loading density. The interior of the motor is thoroughly cleaned, coated using an insulating material, and then lined with a composition to which the propellant binder adheres under the environmental stresses of the system. The insulation material is generally a mbber-type composition, filled with siUca, titanium dioxide, or potassium titanate. SiUca-filled nitrate mbber and vulcanizable ethylene—propylene mbber have been used. The liner generally consists of the same base polymer as is used in the propellant. It is usually appHed in a thin layer, and may be partially or fully cured before the propellant is poured into the rocket. 

Elastomers, plastics, fabrics, wood and metals can be joined with themselves and with each other using nitrile rubber/epoxy resin blends cured with amines and/or acidic agents. Ethylene-propylene vulcanizates can also be joined using blends of carboxylated nitrile rubber, epoxy resin and a reactive metal filler (copper, nickel, cobalt). However, one of the largest areas of use of nitrile rubber modified epoxy systems is in the printed circuit board area [12]. 

Mechanical Properties and Cure Rate Index of the Mixes—Role of Dry Bonding System on the Reinforcement of Ethylene-Propylene-Diene Monomer (EPDM) Rubber with Melamine Fiber ... 

FIGURE 12.16 Plots of tan S versus temperature of maleated ethylene-propylene-diene monomer (EPDM) rubber-melamine fiber composites cured by using mixed cross-bnking system. (From Rajeev, R.S., Bhowmick, A.K., De, S.K., and Bandyopadhyay, S., J. Appl. Polym. Sci., 89, 1211, 2003. With permission.)... 

Cure Systems in Ethylene-Propylene Diene Monomer (EPDM)... 

These post-polymerization reactions are very expensive so HNBRs usually command a premium price. HNBR is usually cured with peroxides, similar to ethylene-propylene elastomers, because it has no unsaturation for a conventional sulfur cure system. 

Ethylene-propylene elastomers are one of the main choices of automotive chemists and material engineers for sealing applications, as well as isolation systems, weather stripping, electrical components, etc. Heat aging resistance up to 130°C can be expected with certain sulfur cures and up to 160°C with peroxide-cured compounds [3], They also respond well to high tiller and plasticizer loads. Typical properties are shown in Table 8.7 [4],... 

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). 

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 ... 

A.S.Z. Naseri, A. JalaU-Arani, A comparison between the effects of gamma radiation and sulfur cure system on the microstructiire and crosslink network of (styrene butadiene rubber/ethylene propylene diene monomer) blends in presence of nanoclay. Radiation Physics and Chemistry, ISSN 0969-806X 115 (October 2015) 68-74. http //dx.doi. org/10.1016/jjadphyschem.2015.05.037. 

SBR and BR. Ethylene-propylene rubber (EPR) is typically vulcanized using a peroxide-based cure system. 

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... 

This technique has found the following applications in addition to those discussed in Sections 10.1 (resin cure studies on phenol urethane compositions) [65], 12.2 (photopolymer studies [66-68]), and 13.3 (phase transitions in PE) [66], Chapter 15 (viscoelastic and rheological properties), and Section 16.4 (heat deflection temperatures) epoxy resin-amine system [67], cured acrylate-terminated unsaturated copolymers [68], PE and PP foam [69], ethylene-propylene-diene terpolymers [70], natural rubbers [71, 72], polyester-based clear coat resins [73], polyvinyl esters and unsaturated polyester resins [74], polyimide-clay nanocomposites [75], polyether sulfone-styrene-acrylonitrile, PS-polymethyl methacrylate (PMMA) blends and PS-polytetrafluoroethylene PMMA copolymers [76], cyanate ester resin-carbon fibre composites [77], polycyanate epoxy resins [78], and styrenic copolymers [79]. 

NR is normally blended with ethylene-propylene-diene rubber (EPDM) to improve the ageing resistance of the former without losing its good mechanical properties. However, due to the difference in unsaturation level between these components, a mutual incompatibility can exist, which decreases the mechanical performance. In addition to the poor interfacial adhesion caused by the thermodynamic incompatibility, these blends usually present cure rate incompatibility because of the differences between the reactivity of the elastomers with the curing agents and/or differences in solubilities of the curatives in each phase. In the case of NR/EPDM blends, the curing system can be consumed by the vulcanization of the NR phase, which is more rapidly vulcanizable because of the higher unsaturation level. ... 

Uncured ethylene-propylene copolymers are soluble in hydrocarbons and have rather poor physical properties useful technological properties are developed only on vulcanization. As mentioned above, the saturated copolymers are vulcanized by heating with peroxides whilst the terpolymers are vulcanized by conventional sulphur systems. The peroxide-cured rubbers have somewhat better heat aging characteristics and resistance to compression set but sulphur-cured rubbers are more convenient to process and allow greater compounding freedom. 

The curing system developed for butyl rubbers has been extended to ethylene-propylene terpolymer (EPDM). Mechanisms of curing by p-dinitrosobenzene have been discussed. The cured cements are promising as outdoor sealants in terms of oxidative stability. 

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. 

G Ivan, E Bugaru, P Bujenita. Resin curing of EPDM rubber. Activation System Influence on Crosslinking Density. Paper presented at PRI International Conference Various Aspects of Ethylene-Propylene Based Polymers , Leuven, 1991. 

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