RSM optimisation of the mechanical properties of novel waste LLDPE plastic composites reinforced with waste glass and shea nut shells

Recycling remains a major way to efficiently manage the abundant waste plastic causing environmental and ecological threats. Repurposing waste plastic and other waste materials such as Waste glass and Shea Nut Shells (SNS) as construction materials could reduce the carbon footprints of the construction industry. This study focused on optimising the mechanical properties of hybrid Linear Low-Density Polyethylene (LLDPE) composites containing waste LLDPE plastic, waste glass and Shea Nut Shell (SNS) using response surface methodology. Composite specimens were produced via extrusion at 80–100 °C with varying proportions of constituent materials (LLDPE: 30–70%, waste glass: 10–30% and SNS: 20–40%). The density, compressive strength, flexural strength, dimensional stability, thermal behaviour, morphology and water absorption of the composite mixes were evaluated to assess their viability as sustainable construction materials. Results show that composites with higher glass content exhibited enhanced mechanical properties with a compressive strength of 19.84 N/mm2, while a balanced combination of all three constituents achieved an optimal flexural strength of 17.39 N/mm2. Notably, the optimised composites satisfied requirements for structural lightweight concrete (ACI 318-19), concrete roofing tiles (BS EN 490:2011 + A1:2017) and ceramic tiles (BS EN 14411), demonstrating the potential of these waste-derived materials for sustainable construction applications.