Structural and mechanical studies on modified reused tyres composites

Reused tyres powder was used as reinforcement in HDPE-reused tyre composites. In order to improve the compatibility between both components, several pre-treatments performed over the rubber tyres were applied: sulphuric acid etching, use of a silane coupling agent and chlorination with trichloroisocyanuric acid (TCI). Mechanical properties of the resulting materials (e.g. tensile strength, Young’s Modulus, toughness and elongation at break) were studied and compared. Chemical modifications on the surface of reused tyres were monitored by FTIR and physical modifications and behaviour to fracture were followed by means of SEM. The influence of rubber pre-treatment was assessed by comparing the results of treated and untreated composites with those for neat HDPE. Reused tyre rubber, added to the HDPE in small quantities, acts as a filler, improving the stiffness and providing a more brittle behaviour. Pre-treatment with TCI gave poor results in terms of mechanical properties obtaining lower values than neat HDPE in some cases and always worst properties than sulphuric or silane coupling agent. Treatments with H2SO4 and silane coupling agent improve the ability of rubber to interact with the HDPE, increasing the material’s stiffness and its tensile strength. Sulphuric acid modificates chemical and physically the particles’ surface improving mainly mechanical adhesion, whereas silane acts as a compatibilizer developing chemical matrix-reinforcement interactions.