Study on Dielectric, Mechanical and Thermal Properties of Polypropylene (PP) Composites with Ground Tyre Rubber (GTR)

Mass production of tyres and their subsequent storage after use is a serious environmental problem whose solution has been attempted in various ways. One of these is the mixture of old, used tyres (GTR) with various thermoplastic and thermostable polymers. These blends are made by modifying the pre-treatment to which the GTR is subjected, the degree of devulcanization, the mixing or pressing conditions, etc. Later, the mixtures are analyzed structurally and mechanically, looking for possible industrial applications. The present work aims to obtain materials suitable for the electrical industry from the mixture of polypropylene (PP) with old used tyres (GTR), starting from the requirement of minimum recycling costs, i.e. by using vulcanized GTR without any prior treatment, but acting on the particle sizes with a simple and inexpensive screening. A large number of composites have been analyzed, and these have been submitted to dielectric, mechanical, thermal and microstructural examination. Composites were obtained using the three GTR particle sizes (p<200 μm, 200500 μm), and the seven concentrations of GTR in the composite (0%, 5%, 10%, 20%, 40%, 50% and 70%), meaning a total of 21 new composites. In addition, in order to have the dielectric tests as exhaustive as possible and show the behaviour of the composite under widely changing conditions, a wide range of temperatures (30 °C to 120 °C) and frequencies (1·10 ^-2 Hz and 3·10 ⁶ Hz) were used. All these data have allowed an accurate characterization of the properties of the new composites, and according to these results, possible electrical applications have been explored, with the requirement that they must comply with Official Regulations.