ABSTRACT

Isobutylene–isoprene rubber (IIR)–based waste rubber powder (WRP) present in WRP/ethylene–propylene–diene monomer (EPDM) blends was devulcanized through a stress-induced reaction by increasing the screw rotation speed in the presence of subcritical ethanol. The effects of crosslink bond type (which was cured using phenolic resin, sulphur, or zinc oxide) of WRP and the screw rotation speed on devulcanization were investigated. The results showed that the Mooney viscosity and gel content of the devulcanized blends (DWRP/EPDM) decreased with an increase in the screw rotation speed, and the optimal screw rotation speed maximized the molecular weight (Mη) of sols and enhanced the mechanical properties of the revulcanized material. The optimal screw rotation speed for the phenolic resin-cured WRP1 and zinc oxide-cured WRP3 was 500 r min−1 and that for sulphur-cured WRP2 was 300 r min−1. At the optimal screw rotation speed, crosslink bonds severely fractured, and the main chain structure remained relatively intact. The 1H-NMR spectra of the sol in the devulcanized blends (DWRP/EPDM) confirmed that the content of the alpha and double-bond protons of sols are the highest at the optimal screw rotation speed, and many promoting agent (480) molecules penetrate and participate in devulcanization. Scanning electron microscopy images indicated that the size of the unfused gel particles in the mixed-revulcanized materials of IIR/(DWRP1/EPDM), IIR/(DWRP2/EPDM), and BIIR/(DWRP3/EPDM) was the smallest at the optimal screw rotation speed.

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