Accelerated liquefaction of vulcanized natural rubber by thermo-oxidative degradation

Abstract

Liquefaction of vulcanized natural rubber presents a high value-added way out to the challenge of ever-increasing waste rubber. In this work, accelerated liquefaction of vulcanized natural rubber (NR) into liquid rubber through thermo-oxidative degradation was carried out at 210 ℃ in 15 min. The structural evolution of degraded NR was characterized by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), elemental analysis (EA) and X-ray photoelectron spectroscopy (XPS). The results showed that vulcanized NR underwent a rapid process of oxygen absorption at the initial stage of degradation, which led to fast liquefaction. It was also illustrated by more oxygen-containing functional groups (–S=O and –C=O) increased with time in the liquid rubber. The Mn of the sol part sharply decreased to 1.259 $$\times$$ 104 g mol−1 in 15 min. The volatile gases generated in the degradation process were characterized by thermogravimetric analysis coupled with Fourier transform infrared spectroscopy and mass spectrometry. These results indicated that the liquid rubber was obtained by efficient oxidative scission of the cross-linked sulfur bonds and the main chains. A liquefaction mechanism of vulcanized NR was proposed, which was also confirmed by density functional theory (DFT) calculations. This study provides a promising efficient approach to liquefy waste NR into a raw material for the recycling circle of rubber.