Effect of crosslinked structure on the chemical degradation of EPDM rubber in an acidic environment

Abstract

The degradation of peroxide-cured EPDM and sulfur-cured EPDM in an acid solution (12.5 ppm H2SO4+1.8 ppm HF) was investigated, and it was found that the degradation of the two in an acid solution was different. The degradation degree of the sulfur curing system is lower than that of the peroxide curing system. During the aging process, the molecular main chain of the peroxide-cured EPDM was broken, resulting in a double bond and C=O structure. When there is a coagent TAIC in the peroxide curing system, the presence of TAIC delays the degradation time of the EPDM molecular backbone, and the hydrolysis reaction of the TAIC crosslinking point occurs preferentially, which makes the stability of EPDM improved. In addition, regardless of the presence or absence of TAIC, the peroxide-cured EPDM undergoes a crosslinking reaction in the later stage of aging, resulting in an ether-crosslinked structure, thereby improving the damaged crosslinking network. Unlike the degradation of the peroxide curing system, the breakage of the molecular backbone does not occur in the sulfur-cured EPDM, but only an internal crosslinking reaction of the curing precursor occurs, resulting in a crosslinked network dominated by polysulfide bonds, thereby increasing the crosslinking density of the EPDM during the aging process.