Effect of dicumyl peroxide crosslinking on the UV stability of ethylene-propylene-diene (EPDM) elastomers containing 5-ethylene-2-norbornene (ENB)

Abstract

Ethylene-propylene-diene (EPDM) elastomers, containing various concentrations of the third monomer, 5-ethylene-2-norbornene (ENB), were crosslinked using dicumyl peroxide. The influence of the amount of peroxide on the UV stability was investigated. The crosslinked EPDM samples were UV aged using a weather-O-meter (WOM) and by oxygen absorption experiments. It was found that crosslinking of ENB-containing EPDM with dicumyl peroxide dramatically influenced the UV ageing. For WOM ageing, linear relationships were found between relative carbonyl absorbance and third monomer content as well as between relative carbonyl absorbance and peroxide concentration, at a fixed ageing time. The values of the relative carbonyl absorbance as a function of the WOM ageing time showed a trend comparable to that observed in the oxygen absorption experiments. We showed previously [Snijders EA, Boersma A, van Baarle B, Noordermeer J. Effect of third monomer type and content on the UV stability of EPDM. Polym Degrad Stab, in press] the linear trends for the relative carbonyl absorbance and the oxygen absorption rate as a function of the third monomer content for uncompounded, non-crosslinked EPDM elastomers. The microhardness of the various crosslinked EPDMs as a function of the WOM ageing time showed a maximum, although the samples were crosslinked before UV ageing. The decrease in microhardness, after the maximum, did not depend on the peroxide concentration. However, it was linearly dependent on the third monomer content. The crosslink density as a function of the WOM ageing time was determined using equilibrium swelling experiments of the samples in decalin. These results showed a trend comparable to that for microhardness. It was also shown that the relationship between the soluble part of the sample and the microhardness throughout the WOM ageing was linear. This shows indeed that upon UV ageing crosslinking and chain-scission reactions compete.