抄録
The mechanism of the chemical deterioration of black-filled ethylene propylene diene terpolymer (EPDM) in sodium hypochlorite (NaOCl) solution of pH 10 was studied at various temperatures from 277 to 323 K. At pH 10, free available chlorine (FAC) mainly exists as dissociated form, i.e., hypochlorite ion (OCl-). When EPDM specimens were immersed in the NaOCl solution of 500 ppm for 7 days, decreases in pH and FAC concentration of the NaOCl solution occurred owing to the oxidative action of OCl-. These changes became marked at 323 K, and the NaOCl solution became suspended by carbon black. X-ray photoelectron spectroscopy (XPS) analysis showed that C-Cl and C-O groups were formed on EPDM surface only at 313 and 323 K. It was also found that no significant diffusion of Cl and O into EPDM was observed at 277 to 303 K, but both their diffusion and the swelling of EPDM surface by water increased markedly at 323 K. These results suggested that the oxidative cleavage of EPDM by OCl- was accelerated at 323 K, resulting in a decrease in the crosslink density of the surface. The diffusion of Cl and O into EPDM was probably due to the conversion of OCl- to HOCl caused by a drop in pH at EPDM surface.
