Investigating the combined impact of plasticizer and shear force on the efficiency of low temperature reclaiming of ground tire rubber (GTR)

Abstract

In the present work, ground tire rubber (GTR) was mechano-chemically reclaimed at ambient temperature using two-roll mills. Road bitumen and styrene-butadiene-styrene (SBS)-modified bitumen at variable content (in range: 2.5–20 phr) were applied as reactive plasticizers to enhance reclaiming of GTR. For better understanding the plasticizing effect of bitumen on the quality of obtained reclaimed rubber, mechano-chemically reclaimed GTR has been compared with GTR after thermo-mechanical reclaiming via low temperature extrusion (120 °C), which allows generation of high shear forces on GTR. Reclaiming process was evaluated by oscillating disc rheometer measurements, followed by mechanical, physical, thermal, and morphological properties analyses performed on vulcanized reclaimed rubber. The obtained results showed that application of bitumen during mechano-chemical reclaiming of GTR improves processing and prevents oxidation of reclaimed GTR through enhancement of physical and chemical interactions between GTR and bitumen. On the other hand, high shear forces acting on GTR during thermo-mechanical reclaiming caused effective scission of cross-linking bonds, while at the same time an adverse oxidative degradation of GTR occurs. Noticeably, the type of bitumen strongly affected the nature of the interfacial interactions between GTR and bitumen. Plasticization/partial reclaiming of GTR (road bitumen, SBS-modified bitumen) and encapsulation of GTR (SBS modified bitumen) were confirmed by mechanical properties, FTIR, TGA and SEM measurements.