Rubber wastes recycling for developing advanced polymer composites: A warm handshake with sustainability

Recycling and management of rubber wastes experiences an early-stage maturity in the quest for sustainable and circular materials. Up to now, solutions proposed for sustainable development of rubber wastes are limited, so that properties and performance features of recycled products are inadequate for practical applications. Herein, an experimental protocol is introduced for manufacturing semi-sustainable polymer composites based on ground tire rubber (GTR) and ethylene-vinyl acetate copolymer (EVA), varying carbon black (CB) content (5–50 phr), CB type, i.e., low-surface area CB (L-CB) and high-surface area CB (H-CB), and EVA/GTR composition (50/50 and 75/25 w/w). Processing (printability potential and fluidity/flexibility), properties (thermal, and mechanical), and performance (fire safety and electrical conductivity) features of the resulting composites are analyzed and interpreted. Highly-loaded 50/50 GTR/EVA systems reveal promising properties and performance. The flexibility of product is promising for additive manufacturing. Tensile strength is independent from CB type and blend composition, while elongation at break change pursuing a percolation threshold for CB ≤ 10 phr and CB > 10 phr depending on CB type. Thermal stability is considerable for 50/50/50 (w/w)/phr GTR/EVA/CB system with high amount of GTR. A long-standing flame retardancy is observed for 50/50/50 GTR/EVA/L-CB and 50/50/25 GTR/EVA/H-CB (w/w)/phr composites. A frequency-independent direct current (DC) branch is appeared by increasing temperature at low-frequency region, characteristic of rubber-like dielectric materials. The DC part is intensified even at low temperatures (<10 °C) when CB content increased, so that percolation thresholds are 5 phr and 10 phr for H-CB and L-CB loaded blends, respectively. This work opens new gates of hope towards development of fully sustainable polymer composites from recycled rubber wastes.