Sulfonated EPDM processing

Sulfonated EPDMs are formulated to form a number of rubbery products including adhesives for footwear, garden hoses, and in the formation of calendered sheets. Perfluori-nated ionomers marketed as Nation (DuPont) are used for membrane applications including chemical-processing separations, spent-acid regeneration, electrochemical fuel cells, ion-selective separations, electrodialysis, and in the production of chlorine. It is also employed as a solid -state catalyst in chemical synthesis and processing. lonomers are also used in blends with other polymers. 

The sulfonation of EPDM as shown in Reaction 41b has recently been announced to be under commercial development by Uniroyal (78). Sulfonated EPDM can be classified as an ionic thermoplastic elastomer, whereby ionic interactions between chains act as thermally reversible cross-links. Above certain temperatures these ionic interactions break down, and plastic flow can occur. Upon cooling, these ionic cross-links reform to give the desired property characteristics. To enhance the processability of sulfonated EPDM an ionic plasticizer "ionolyzer" (i.e., zinc stearate) is added to about 20 phr (parts per 100 rubber). Care must be taken to ensure complete neutralization, because it was observed that residual acid can result in covalent cross-linking during fabrication. 

EPDM-Derived Ionomers. Another type of ionomer containing sulfonate, as opposed to carboxyl anions, has been obtained by sulfonating ethylene—propjlene—diene (EPDM) mbbers (59,60). Due to the strength of the cross-link, these polymers are not inherently melt-processible, but the addition of other metal salts such as zinc stearate introduces thermoplastic behavior (61,62). These interesting polymers are classified as thermoplastic elastomers (see ELASTOLffiRS,SYNTHETIC-THERMOPLASTICELASTOLffiRS). 

Metal sulfonate-containing ethylene-propylene-diolefin ter-polymers (EPDM) were plasticized with stearic acid and derivatives for the reduction of the melt viscosities of these ionomers through interaction with the very strong ionic associations. Substantial improvements in melt flow were achieved with stearic acid and the zinc, lead, and ammonium stearates, while other metal stearates were ineffective. Zinc stearate and lead stearate not only markedly improved melt flow but, remarkably, also enhanced the mechanical properties of the plasticized systems. These unique additives were fully compatible with the EPDM ionomers and provided thermoelastic systems with excellent physical properties and ready processability. 

It is possible to add agents to metal sulfonate-containing EPDM to reduce melt viscosity and to improve melt processability. Canter and Buckley (3) were the first to preferentially plasticize metal sulfonate-... 

Another interest of irradiation in the field of the conductivity of polymer blends was shown by Faez etal. These authors incorporated EPDM to lANl in order to improve mechanical properties of the material. PANl was doped not with irradiation, but with dodecylbenzene sulfonic acid by reactive processing in an internal blender. To cross-link the EPDM, a phenolic resin and e-beam irradation (75 and 150 kGy) were compared. Contrary to the cross-linking by phenolic resin, the cross-linking by e-beam irradiation did not interfere with the presence of the acid necessary for doping PANl. Consequently, better mechanical properties were obtained. Moreover, irradiation-induced additional conductivity led to a slightly more conductive material. 

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