Experimental evaluation of mechanical and thermal properties of recycled rubber membranes reinforced with crushed polyethylene particles

Recycled rubber powder from shredded End of Life Tyres (ELTs) has been used for the development of a new membrane as sustainable construction material. However, due to the environmental exposure of this recycled rubber membrane, climate conditions may contribute to premature deterioration of the material, reducing their mechanical strength and durability over time. To improve it, crushed particles from recycled High-Density Polyethylene (HDPE) pellets can be added in the rubber matrix. Particles addition in composite materials are known for enhancing their physical and mechanical behaviour, although it is not clear how this influence works in this specific case. For these reasons, physical, mechanical and thermal behaviour of particle-reinforced rubber membranes conditioned under different environmental states have been studied. With these purposes, four different membranes with the same rubber powder gradation, but with four different percentages of crushed polyethylene particles and pre-conditioned under four different environmental conditions (dry, water-saturated, cold and ageing) have been considered. The influence of polyethylene particles on the mechanical behaviour of the membranes has been evaluated using tensile strength tests. Additionally, the heat transfer capacity of the membranes has been measured through thermal conductivity tests. Main results of the study showed that polyethylene particles reduced the bulk density of the membranes but increased the air voids content. Moreover, it was found that the crushed polyethylene particles can form channels inside the membranes that reinforce the structure of the composite material. However, probability analysis results proved that HDPE particles did not significantly contribute to improve tensile mechanical properties of the membranes evaluated under different environmental conditions. Finally, the HDPE particles addition increased the thermal conductivity of the membranes, but with low heat-transfer ability, so these membranes have potential uses with thermal facing purposes.