Recycling Waste Tires into Ground Tire Rubber (GTR)/Rubber Compounds: A Review

Abstract

Recycling and recovery of waste tires is a serious environmental problem since vulcanized rubbers require several years to degrade naturally and remain for long periods of time in the environment. This is associated to a complex three dimensional (3D) crosslinked structure and the presence of a high number of different additives inside a tire formulation. Most end-of-life tires are discarded as waste in landfills taking space or incinerated for energy recovery, especially for highly degraded rubber wastes. All these options are no longer acceptable for the environment and circular economy. However, a great deal of progress has been made on the sustainability of waste tires via recycling as this material has high potential being a source of valuable raw materials. Extensive researches were performed on using these end-of-life tires as fillers in civil engineering applications (concrete and asphalt), as well as blending with polymeric matrices (thermoplastics, thermosets or virgin rubber). Several grinding technologies, such as ambient, wet or cryogenic processes, are widely used for downsizing waste tires and converting them into ground tire rubber (GTR) with a larger specific surface area. Here, a focus is made on the use of GTR as a partial replacement in virgin rubber compounds. The paper also presents a review of the possible physical and chemical surface treatments to improve the GTR adhesion and interaction with different matrices, including rubber regeneration processes such as thermomechanical, microwave, ultrasonic and thermochemical producing regenerated tire rubber (RTR). This review also includes a detailed discussion on the effect of GTR/RTR particle size, concentration and crosslinking level on the curing, rheological, mechanical, aging, thermal, dynamic mechanical and swelling properties of rubber compounds. Finally, a conclusion on the current situation is provided with openings for future works.

Structural Changes and Their Implications in Foamed Flexible Polyurethane Composites Filled with Rapeseed Oil-Treated Ground Tire Rubber

“…The influence of oil-assisted thermo-mechanical treatment of ground tire rubber in a twin-screw extruder and the impact of oil type (fresh or waste rapeseed oil) and content (20 or 40 parts per hundred rubber) on the processing, structure, and performance of composites based on a foamed flexible polyurethane matrix was investigated. The application of oil as a modifier of GTR may enable its swelling and, according to the literature data, it may improve the heat transfer in rubber during thermo-mechanical treatment [32]. Moreover, the oil may act as a processing aid, and by the decrease, the screws' torque reduces the amount of mechanical energy required for GTR processing [33].…”

Crumb Rubber as a Secondary Raw Material from Waste Rubber: A Short Review of End-Of-Life Mechanical Processing Methods

“…This thermoplastic elastomeric material can be used for the preparation of conveyor belts, drive belts, flooring and walkways, floor tiles, rugs, mounting flanges, shock absorber covers, sound barriers, safety guards, carpet backing, car bumpers, wheel arch gaskets, car door and window seals, sealing rings, gaskets, irrigation systems, pipe or hose materials, flowerpots, building blocks, roofing materials, geomembranes, and so on. The development of composites with a polymer matrix and crumb rubber is well described in a recent review [72]. Uses of ground tire rubber in insulation materials containing polymeric matrix are reviewed in [73].…”

Composite Material Recycling Technology – State-of-the-Art and Sustainable Development for the 2020s.

“…Rubber. While rubber is not the main focus, it deserves a short mention here -vulcanized rubbers are also thermoset materials and play a role in sustainable development of the composite and automotive industries, i.e., in tires [46,47]. Based on the current environmental situation and social acceptance, discarded tires should no longer be viewed as a useless waste material, but rather as a durable and inexpensive raw material to produce different and innovative parts.…”

“…Based on the current environmental situation and social acceptance, discarded tires should no longer be viewed as a useless waste material, but rather as a durable and inexpensive raw material to produce different and innovative parts. The incorporation of even a small fraction of waste tires into polymer matrices (thermosets, thermoplastics, rubbers) can lead to a substantial consumption of discarded tires as a partial replacement of virgin raw materials with advantages such cost reduction and sustainable compound production [46]. Waste tires (GTR and RTR, Regenerated Tire Rubber) can be used as a source of valuable raw materials in different polymeric matrices for the manufacture of low-cost products and a cleaner environment [46].…”

“…The incorporation of even a small fraction of waste tires into polymer matrices (thermosets, thermoplastics, rubbers) can lead to a substantial consumption of discarded tires as a partial replacement of virgin raw materials with advantages such cost reduction and sustainable compound production [46]. Waste tires (GTR and RTR, Regenerated Tire Rubber) can be used as a source of valuable raw materials in different polymeric matrices for the manufacture of low-cost products and a cleaner environment [46]. Rubber-Concrete technology: addition of rubber particles increases the durability of the material but reduces its mechanical strength -by correctly balancing the fine and coarse rubber fractions promising physical-mechanical performance can be obtained [48].…”