Application of sepiolite to prevent bleeding and blooming for EPDM rubber composition

To prevent bleeding and blooming of additives in ethylene-propylene-non-conjugated diene terpolymer (EPDM) rubber composition, sepiolite was added as adsorbate to the rubber composition. The mixed composition was molded using a vulcanizing press at 170°C for 10 min to prepare EPDM rubber sheets. The resulting sheets were kept in air at room temperature for 30 d, and subjected to visual observation. The sheets were also analyzed using attenuated total reflection (ATR) infrared spectroscopy and ATR infrared microscopy. There was neither bleeding nor blooming on the surface of rubber composition with sepiolite, because sepiolite adsorbed additives such as not only paraffin process oil and stearic acid, but also zinc stearate formed by the reaction of zinc oxide with stearic acid during curing. In particular, sepiolite has prevented zinc stearate from oozing from the inside to the surface of the sheet because it adsorbed zinc stearate. On the other hand, the absence of sepiolite resulted in bleeding of paraffin process oil and blooming of stearic acid and zinc stearate. Without sepiolite the zinc stearate has oozed out through paraffin process oil from the inside to the surface of the sheet.