On the use of ground tire rubber as thermoplastic polymer modifiers

ROSALES, CAREN; PETTARIN, VALERIA

Waste Rubber Recycling Routes

Central West Publishing

Año: 2021; p. 1 - 27

The huge quantity of waste rubber is mainly derived from the continue development of the automotive market. In fact, approximately 80 % of waste rubber comes from end of life tires [1]. Land filling was the first way of dispose waste tires. However, it causes serious environmental troubles. The impermeability and hollowed shape of tires allow them to serve as water holders, providing sites for mosquito larva to grow, these being vectors of deadly diseases. Furthermore, discarded tires could produce fires that are difficult to extinguish [2]. The global concern about the continue accumulation of discarded tires and the developing ecological awareness demand new ways and regulations to solve this problem. The developed regulations promote the research of the scientific community to explore alternative solutions to reuse this waste material [1, 3].However, the reuse or recycling of tires is not a simple task. Tires are a complex and sophisticated assemblage of components: high mechanical standard requirements like flexibility, forces and adhesion make the design of this engineering structure to be constructed from several materials. For example, automobile tires are made of more than ten elements, and tires used for trucks have near twenty different elements. Even tough, vulcanized rubbers constitute the major relative component of tires [2]. Vulcanization is an irreversible process wherein rubber crosslinking happens through the formation of sulfur bonds [4]. As a result, a cross-linked structure is obtained due to transverse bonds that connect different rubber chains. This vulcanized structure makes rubber an elastic thermoset material that cannot be reprocessed by melting as thermoplastic polymers due to its insoluble and infusible characteristics [2]. It is therefore of crucial relevance to find methods for tires recycling that combine both low cost and technological feasibility. One proposed way is to devulcanize the rubber and reuse it. Although such processes work out well, they are expensive and consequently they are not frequently applied in industrial scale [5]. Another industrial recycling method of tires is their down-sizing or down-cycling. It consists on disassembling tires and grinding rubber into particles achieving a powder know as ground tire rubber (GTR) [1, 3]. Even though this is a technologically complex process that involves specific equipment [2], it is already well established in industry. GTR is actually used in surfaces of athletic tracks or games, or in combination with other materials such as asphalts [6?8], concrete [9?11] and mortars [12]. On the other side, a commonly used practice in industry to improve mechanical behavior and toughness of a polymer is to incorporate rubber particles into it. Then, an attractive option seems to be to add GTR to a polymeric material, so competitive products can be shaped. The polymer matrix could be thermoplastic, thermoset or even rubber[5]. Compound of waste tire rubber with polymers allows to lower the cost of the final products while contributing to the world?s 3R (reduce, reuse and recycle) concept: reducing the volume of used virgin polymer, reusing end-of-life rubbers, and recycling the waste rubber [2]. The incorporation of GTR to thermoplastic polymers is especially attractive due to different reasons. The incorporation of only 10% of GTR in thermoplastics, would mean a large use of recycled GTR. In addition, the thermoplastic material can act as a matrix for dispersed GTR, or as a binder in a blend where GTR is the main component [5]. It is well known that the mechanical performance of composite materials depends on several factors such as quantity and behavior of each component, size, shape, geometrical arrangement and interfacial adhesion of present phases, as well as on the way they are obtained and prepared [13, 14]. In this sense, one of the main problems when compounding GTR and polymers is their incompatibility, and then, it is necessary to promote interfacial adhesion between GTR and polymer matrix. Moreover, GTR obtained by standard industrial grinding process presents high particle size (between 400 and 600 μm approximately), being this a drawback since it is well known that the addition of such large particles in a thermoplastic matrix results in composite materials with brittle behavior [3]. Different strategies to compatibilize GTR with polymers and to diminish GTR?s particle size have been reported [3]. Sometimes, the search of compatibility involves an increase in costs that damages the initial premise of obtaining a material at an acceptable cost. Through this chapter, results obtained from the incorporation of GTR in thermoplastic polymers are reviewed. Strategies applied to improve performance of the obtained composites are also explained, and their results summarized.