Production and investigation of the mechanical properties of nano CaCO3 and walnut shell filled polymer composites

ABSTRACT Sustainability is the balanced and long-term maintenance of natural resource use, environmental management, and social development. Today, the design, production, and importance of sustainable and environmentally friendly materials are increasingly significant. In this study, green hybrid composites were produced using high-density polyethylene (HDPE) as the matrix material, 20% walnut shell as the filler material, and 1%, 3%, and 5% nano calcite (CaCO3). All materials were first mixed through mechanical blending and then granulated using an extruder. Subsequently, test samples were produced from the prepared mixtures using the injection molding method according to relevant standards. The produced samples underwent tensile testing according to ISO 527-1, three-point bending testing according to ISO 178, Charpy impact testing according to ISO 180, and hardness measurements to characterize their mechanical properties. DSC and TGA tests were conducted to determine the thermal properties of the composites. FT-IR, water absorption tests, and gloss measurements according to ASTM D523 were performed to identify physical and chemical properties. The microstructures of the composites were examined using SEM. The tensile strength of the 20% walnut shell-filled sample was found to be close to that of pure HDPE. However, the addition of nano calcite slightly decreased the tensile strength regardless of the amount. The effect of the composites on the tensile modulus of elasticity was negligible, with similar values observed. The highest bending strength was measured as approximately 46 MPa in the 20% walnut shell-filled composite. While the addition of nano calcite negatively affected the bending strength, it significantly increased the impact strength. It was determined that the nano calcite and walnut shell filler influenced the mechanical and thermal properties of the composites, altered the water absorption capacity and microstructure, and affected the material's gloss. Considering the mechanical and thermal performance and the physical and chemical properties of the prepared composites, it was concluded that they could be used in various industrial applications. These composites provide sustainable alternatives, especially in the automotive, construction, and packaging sectors, where the demand for environmentally friendly materials is increasing. Keywords: Nano CaCO3, Walnut Shell, HDPE, Polymer composites, green composite