Enhancing the thermoplastic behavior and mechanical performance of recycled HDPE/CaCO3 composites using oxidized polyethylene

There is a growing interest in sustainable materials based on recycled or natural feedstocks for the circular economy. Ideally, thermoplastic materials are anticipated to show appropriate melt-flow behavior for thermo-mechanical recycling, good melt stability, and mechanical performance. Thermoplastic polyolefins such as polyethylenes are used as single-use packaging materials and generate environmental concerns. This article reports the melt-processing and characterization of composite materials based on recycled high-density polyethylene (rHDPE) and naturally abundant calcium carbonate (CaCO3) mineral at various mass ratios such as 70/30, 50/50, and 30/70. Oxidized polyethylene (OPE) is used as an additive, with 20 wt% replacement of rHDPE, to improve the materials' mechanical performance and thermoplastic behavior. Various characteristics such as tensile, viscoelastic, melt-flow, phase morphology, and thermomechanical recyclability of the materials are analyzed. It reveals that composites with high CaCO3 content compatibilized with OPE show improved tensile strength and modulus. For example, the composite based on 10/70/20 (wt%) of rHDPE/CaCO3/OPE shows an average tensile strength of 27.4 MPa and Young's modulus of 4.5 GPa, in contrast to the rHDPE sample, which shows an average tensile strength of 12.4 MPa and Young's modulus of 967 MPa. Notably, adding OPE decreases the melt-viscosity of the rHDPE/CaCO3 materials, thus improving the composites' melt-flow and thermoplastic behavior. This study indicates the possibility of developing natural CaCO3-rich polymer composites with thermoplastic behavior for real-life applications with superior mechanical and melt-flow properties suitable for thermomechanical recycling.