Recycling waste tire rubber through an innovative water-medium ionizing radiation treatment: Enhancing compatibility and mechanical performance

In this research, we solved the compatibility problems of rubber mixtures containing waste ground tire rubber (GTR) with an innovative and environmentally friendly, water-based ionizing radiation treatment, meaning that the GTR is under water. Our hypothesis was that the strong oxidizing agents that appear during the radiolysis of water can activate the surface of the GTR, resulting in reactive functional groups containing oxygen, which can help establish a better interaction between the matrix and the GTR. We treated the GTR using different absorbed doses and examined the changes in the GTR using Soxhlet-extraction and cross-link density measurements. The surface of GTR was characterized by Fourier-transform infrared spectroscopy. Then we prepared GTR-containing natural rubber-based mixtures in an internal mixer, using two different mixing techniques. The mixtures were vulcanized in a hydraulic press, and the mechanical and morphological properties were investigated. As a result of the radiation treatment, cross-link density decreased slightly, while sol content did not change significantly. The FTIR spectra indicated that oxygen-containing groups appeared on the surface of the treated GTR. In the case of one-step vulcanizates, tensile strength increased by 11% and tear strength by 40%, while elongation at break remained high. For the two-step mixtures, tensile strength improved by 25%, tear strength by 35%, while elongation at break was over 400%. An irradiation dose of 20 kGy produced the best result, which is sustainable in mass production.