Transforming Wheel Waste into Functional Composites: Effect of Ground Tire Rubber and Hollow Glass Microspheres on Low-Density Polyethylene

Disposal of used bicycle wheels poses a significant environmental challenge. This study explores a recycling approach by incorporating ground rubber particles from used tires with low-density polyethylene (LDPE). The present study investigates the effect of GTR on the physical and mechanical properties of LDPE with the addition of hollow glass microspheres (HGMS), as a hybrid composite. This composite has useful properties for engineering applications that combine the properties of the composite materials. The composites were formulated with GTR ratios (10%, 20%, and 30%) and HGMS ratios (0%, 1.5%, 3%, 4.5%, and 6%). The materials were processed using a single-screw extruder and an injection molding machine under specific mixing conditions, i.e., 130 °C, 0.6 MPa, and 160 °C. The composites were subjected to comprehensive tests to study their microstructure, physical, and mechanical properties on a large scale. The TGA test showed that the inclusion of varying amounts of GTR insignificantly affected the onset temperature of weight loss, and it had no effect on the final degree of loss and stability. In contrast, the addition of HGMs increased the onset temperature of failure to 300 °C. The addition of HGMs resulted in the highest percentage of residual material compared to the percentage of residual material at 0% HGM. The manufactured composites were analyzed using scanning electron microscopy (SEM), which revealed the microstructure of the composite. The examination particularly emphasized the weak bond between the base material and the additives. The investigation showed a consistent distribution of the additives throughout the base material, with specific clusters of empty glass spheres. A negative correlation was found between the density of the composite and the percentage of void content and water absorption. Mechanical tests showed that tensile and flexural strengths decreased with increasing GTR levels by about 27% for tensile strength and 29% for flexural strength at 20% and 30% GTR. However, the presence of additives significantly affected the hardness and impact strength values, with significant improvements at higher levels of HGMS by up to 15% for impact strength. The hybrid composite containing 10% GTR and 3% HGMS showed encouraging results.