High-value recycling of waste tire rubber powder by wet mixing method

Abstract

Producing waste rubber into powder and adding it to rubber products as filler is one of the most direct and valuable methods to recover waste rubber. However, weak interface adhesion between waste rubber powder and rubber matrix severely damages the properties of rubber composites. To solve this problem, we propose a method of filling waterjet-produced rubber powder (WPRP) in natural rubber (NR) matrix via a wet mixing process. The characterizations of WPRP, the wet mixing mechanism participated by WPRP, and the properties of the wet-mixing rubber composites are carefully investigated. The surface of WPRP is irregular and contains some hydroxyl groups generated by the cavitation effect of waterjet, which endows the WPRP surface with certain hydrophilicity. The hydrophilic groups enable the stable suspension and uniform distribution of WPRP in latex. The active and irregular surface accelerates the flocculation during high-speed shear mixing, promotes the entanglement of NR molecular chains with WPRP, and forms a network between WPRP and NR matrix, which improves the dispersion of carbon black. When adding 5 parts per hundred rubber (phr) of WPRP, the tensile strength and elongation at break of the rubber composites are 27.8 MPa and 614.1%, respectively, which are even better than those of pure NR. When adding 10 phr of WPRP, the tensile strength and elongation at break of the rubber composite maintain 97.6% and 96.2% of that without WPRPs, respectively. Additionally, the addition of WPRP can reduce the rolling resistance of the rubber composites. This method will allow more waste rubbers to be incorporated into high-value rubber products, thereby relieving environmental pressure and realizing the recycling of rubber materials.