Thermal and Thermo-oxidative Degradation of Diene Rubbers Occurring During the Pyrolysis of Rubber Waste

Abstract

The features of thermal and thermo-oxidative degradation of industrial samples of butadiene BR-Nd, BR-Li) and isoprene (IR-3) rubbers were studied using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and mass spectrometry. The characteristic temperatures of the onset of decomposition were determined, and the kinetics of destruction and the composition of gaseous degradation products were investigated in inert (argon) and oxidative (oxygen) atmospheres.

It was found that in an inert atmosphere, isoprene rubber decomposes 40 °C earlier than its butadiene analogs, which is attributed to the presence of an electron-donating methyl group that weakens the carbon–carbon bond at the β-position. The thermal degradation of butadiene rubbers was shown to occur in two stages: the first stage (380 °C) is accompanied by an exothermic effect and is associated with cyclization reactions and the formation of vinylcyclohexene; the second stage (470 °C) proceeds with heat absorption and corresponds to the breakdown of cyclic structures, releasing butadiene and aromatic compounds.

In an oxidative environment, the degradation of all studied rubbers is accompanied by exothermic effects. It was found that the thermo-oxidative stability of IR-3 (onset oxidation temperature 241,7 °C, induction period 269,8 min at 190 °C) is significantly higher than that of butadiene rubbers, which is due to the use of a more effective aromatic amine antioxidant compared to the thiobisphenolic stabilizers used in BR.

The obtained results make it possible to predict the behavior of diene rubbers under thermal and thermo-oxidative conditions and can be used to optimize the processing and performance regimes of rubber products.