EFFECTS OF CROSSLINK BOND TYPE OF IIR-BASED WASTE RUBBER POWDER ON THE EPDM-ASSISTED DEVULCANIZATION REACTION

Zhiyuan Xing; Ling Zhang; Yuncan Zhang; Dongxu Li

doi:10.5254/rct.21.79956

Article Contents

ABSTRACT
INTRODUCTION
EXPERIMENTAL
RESULTS AND DISCUSSION
CONCLUSIONS
ACKNOWLEDGEMENT
REFERENCES

Editorial Type:

Article Category: Research Article

Online Publication Date: 05 Mar 2021

EFFECTS OF CROSSLINK BOND TYPE OF IIR-BASED WASTE RUBBER POWDER ON THE EPDM-ASSISTED DEVULCANIZATION REACTION

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Page Range: 575 – 590

DOI: 10.5254/rct.21.79956

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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 (M_η) 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.

Fig. 1. —

Structure of alkylphenol polysulfide 480 (n, 10–20; m, 20–50).

Fig. 2. —

Screw configuration of the co-rotating twin-screw extruder (TE-35).

Fig. 3. —

Effects of the vulcanizing agent of the WRP and screw rotation speed on the Mooney viscosity of the devulcanized blends (DWRP/EPDM) at 180 °C and 2.0 MPa ethanol vapor pressure.

Fig. 4. —

Effects of the vulcanizing agent of WRP and the screw rotation speed on the gel content of the devulcanized blends (DWRP/EPDM) at 180 °C and 2.0 MPa ethanol vapor pressure.

Fig. 5. —

Effects of the vulcanizing agent of WRP and the screw rotation speed on the [μ] of the sol of the devulcanized blends (DWRP/EPDM) at 180 °C and 2.0 MPa ethanol vapor pressure.

Fig. 6. —

Effects of the vulcanizing agent of WRP and the screw rotation speed on the (a) tensile strength of the direct-revulcanized materials, (b) elongation at break of the direct-revulcanized materials, (c) tensile strength of the mixed-revulcanized materials, and (d) elongation at break of the mixed-revulcanized materials.

Fig. 7. —

¹H-NMR spectra of the sol of the devulcanized blends (DWRP¹/EPDM) at different screw rotation speeds (180 °C and 2.0 MPa ethanol vapor pressure): 1–200, 2–300, 3–400, 4–500, and 5–600 r min⁻¹ and C (the relative contents [%] of ¹H NMR peaks) = (A_{characteristic peak}/A_{reference peak}) × 100%.

Fig. 8. —

¹H-NMR spectra of the sol of the devulcanized blends (DWRP²/EPDM) at different screw rotation speeds (180 °C and 2.0 MPa ethanol vapor pressure): 1–200, 2–300, 3–400, 4–500, and 5–600 r min⁻¹ and C (the relative contents [%] of ¹H NMR peaks) = (A_{characteristic peak}/A_{reference peak}) × 100%.

Fig. 9. —

¹H-NMR spectra of the sol of the devulcanized blends (DWRP³/EPDM) at different screw rotation speeds (180 °C and 2.0 MPa ethanol vapor pressure): 1–200, 2–300, 3–400, 4–500, and 5–600 r min⁻¹ and C (the relative contents [%] of ¹H NMR peaks) = (A_{characteristic peak}/A_{reference peak}) × 100%.

Fig. 10. —

SEM images of the fractured surfaces of the mixed-revulcanized materials of IIR/(DWRP¹/EPDM), IIR/(DWRP²/EPDM), and BIIR/(DWRP³/EPDM): (a) 400 r min⁻¹ for PF201-vulcanized WRP¹, (b) 500 r min⁻¹ for PF201-vulcanized WRP¹, (c) 600 r min⁻¹ for PF201-vulcanized WRP¹, (d) 200 r min⁻¹ for sulphur-vulcanized WRP², (e) 300 r min⁻¹ for sulphur-vulcanized WRP², (f) 400 r min⁻¹ for sulphur-vulcanized WRP², (g) 400 r min⁻¹ for zinc oxide-vulcanized WRP³, (h) 500 r min⁻¹ for zinc oxide-vulcanized WRP³, and (i) 600 r min⁻¹ for zinc oxide-vulcanized WRP³.