Dynamic pyrolysis behaviors, products, and mechanisms of waste rubber and polyurethane bicycle tires.

ABSTRACT

Given their non-biodegradable, space-consuming, and environmentally more benign nature, waste bicycle tires may be pyrolyzed for cleaner energies relative to the waste truck, car, and motorcycle tires. This study combined thermogravimetry (TG), TG-Fourier transform infrared spectroscopy (TG-FTIR), and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) analyses to dynamically characterize the pyrolysis behavior, gaseous products, and reaction mechanisms of both waste rubber (RT) and polyurethane tires (PUT) of bicycles. The main devolatilization process included the decompositions of the natural, styrene-butadiene, and butadiene rubbers for RT and of urethane groups in the hard segments, polyols in the soft segments, and regenerated isocyanates for PUT. The main TG-FTIR-detected functional groups included C-H, C=C, C=O, and C-O for both waste tires, and also, N-H and C-O-C for the PUT pyrolysis. The main Py-GC/MS-detected pyrolysis products in the decreasing order were isoprene and D-limonene for RT and 4, 4'-diaminodiphenylmethane and 2-hexene for PUT. The kinetic, thermodynamic, and comprehensive pyrolysis index data verified the easier decomposition of PUT than RT. The pyrolysis mechanism models for three sub-stages of the main devolatilization process were best described by two-dimensional diffusion and two second-order models for RT, and the three consecutive reaction-order (three-halves order, first-order, and second-order) models for PUT.