Experimental investigation and micromechanics modeling of ground tire rubber as a physical compatibilizer in kaolinite-reinforced HDPE composites

The recycling of waste tires, classified as hazardous solid waste, provides a sustainable way to reuse discarded materials while solving environmental issues and material performance limitations. This study offers a new approach to improve compatibility in kaolinite-reinforced high-density polyethylene (HDPE) composites by adding ground tire rubber (GTR) as a physical compatibilizer. Composites were created through melt compounding with different combinations of binary and hybrid fillers at various amounts (0, 5, 10, 15, 20 wt.% and hybrid mixes of 15:5, 10:10, and 5:15 wt.% kaolinite: GTR). GTR not only adds flexibility as a secondary reinforcing phase but also greatly enhances the dispersion of kaolinite particles, reduces agglomeration, and boosts interfacial adhesion with the HDPE matrix. A thorough testing process, including morphological (SEM), structural (FTIR), mechanical, rheological, and dynamic mechanical analyses, was carried out. The ternary hybrid composite containing 80/5/15 wt.% HDPE/kaolinite/GTR showed the best overall properties, with a tensile strength of 28.58 MPa, a Young’s modulus of 836.62 MPa, and a strain at yield of 21.06 mm/mm. Additionally, predictive modeling using Voigt, Reuss, Voigt–Reuss–Hill, and Tsai–Pagano micromechanical models indicated that the Tsai–Pagano model aligned most closely with the experimental results. These findings demonstrate GTR’s potential as a sustainable and functional compatibilizer in polymer–clay systems, supporting eco-friendly material development for advanced uses like durable and energy-efficient building materials coatings.