Blends of Dissimilar Rubbers—Cure-Rate Incompatibility

Abstract

Abstract The mechanical properties of a vulcanizate of a blend which comprises both a high-diene rubber such as NR and an ozone-resisting concentration (at least 30 to 40 wt.% of the polymers) of EPDM can be greatly improved if the EPDM is chemically modified by the action of maleic anhydride. The effect of the EPDM modification of the vulcanizate properties is to give increased tensile strength, improved fatigue resistance, and reduced hysteresis and set. The excellent ozone resistance which results from the presence of about 30 to 40% unmodified EPDM is also obtained when the modified EPDM is used. Good results are obtained when only 1 to 2% (as a wt.% of EPDM) of maleic anhydride is used in the modification of the EPDM. Good results are obtained when only part of the EPDM is modified by the action of maleic anhydride. However, best results are obtained when all of the EPDM is treated with maleic anhydride. The ozone-resisting effect provided by the incorporation of a para-phenylenediamine antidegradant into a 60/40 NR/EPDM blend vulcanizate is overwhelmed and made obscure by the very large beneficial effect due to the presence of the EPDM. However, the use of an antidegradant such as 6PPD is still necessary because of its ability to impart a great improvement in fatigue life.