11 - Molding industrial products from tire ground rubber

Abstract

The state of the art of molding of ground tire rubber (GTR) is discussed in this chapter. Starting from the evolution of the scientific debate in this sector, all the main findings on GTR molding within the last 20 years are discussed. Most of studies refer to GTR composites where a thermoplastic or thermosetting resin is used as matrix and GTR as filler. Primarily, GTR particles are mixed with polypropylene or polyethylene, recovered from waste as well to increase the green side of the final products. In alternative, GTR rubber compounds are molded with a percentage of devulcanized GTR, and also additive manufacturing is discussed. A special mention is given to direct molding, namely compression molding of GTR in the absence of virgin material or additives. This technique allows primary recycling of tire rubber and it has been assessed at laboratory and industrial scale. Some achieved results are discussed together with new findings, as well as the effect of the type of rubber depending on the part of the tire used to obtain it (the tread and the side walls) on the molded product performance. The effect of the recycling technology used (by water jet, shredder, or mill) is also discussed. The results show that part properties may be tailored if all the material aspects are taken into account, from grain size distribution to purity. Nevertheless, minimal performance is always achieved even in the case of bad GTR selection.