Devulcanization of ground tire rubber: thermo-oxidation followed by microwave exposure in the presence of devulcanizing agent

Abstract

The disposal of recycled tires is a problem that has gained considerable importance since it has involved the environmental as well as various disciplines and points of view. Currently, the burning and outdoor storage of disposed tires are forbidden practices because of their polluting effect, damage to health and the fact that they contribute to the spread of diseases due to vectors such as insects. Therefore, it is important to research alternative methods that provide added value. In this work, waste ground tire rubber was treated by applying a combination of oxidation with potassium permanganate/hydrogen peroxide, followed by microwave exposure in the presence of a devulcanizing agent. Devulcanized tire rubber was analyzed by Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, cross-link density and sol fraction. Styrene butadiene rubber composites were prepared using devulcanized tire rubber and sulfur cure system. The blends were mixed in a two roll mill laboratory. The vulcanized specimens were obtained by compression molding. Curing properties, tensile and tear strength, elongation at break, hardness (Shore A units), abrasion resistance (mm3), and compression set of these rubber composites were evaluated and the morphology of the fractured surfaces from tensile specimens were analyzed with scanning electron microscopy. The results showed that microwave exposure with devulcanizing agent reduced the cross-link density and increased the soluble fraction of rubber tire. Improved flow through viscosity reduction (low torque) and higher mechanical strength were obtained by compounding styrene butadiene rubber with ground rubber tire (thermo-oxidized followed by microwave exposure with devulcanizing agent), whose market values were similar to those obtained for virgin styrene butadiene rubber/silica composite.