Investigation of thermal and mechanical properties of blends of recycled thermoplastic wastes with homopolymer polyethylene and polypropylene

The amount of waste of plastic, whose usage area and production is increasing, is also increasing day by day. Plastic pollution is one of the biggest environmental problems of our time and causes extensive damage to ecosystems and human health. In addition to plastic raw material and production costs, the transportation, storage and recycling costs of waste plastics; the decrease in fishery/aquaculture and tourism revenues caused by plastic pollution and the costs of cleaning activities indicate the need for the necessary studies for the plastic circular economy. In recent years, the world has focused on climate change, environmental pollution, water management, energy and resource efficiency, and sustainable development. In the Twelfth Development Plan published in Turkey in October 2023, it was emphasized that the need for the development and promotion of standards for recycling waste and recycled secondary products continues. Strict policies aimed at restricting plastic production and demand, when combined with policies aimed at increasing recycling rates, support the use of recycled plastics instead of primary production. The aim of this study is to investigate the thermal and mechanical properties of blends formed by recycled thermoplastic waste with homopolymer polyethylene and polypropylene. HDPE/r-PE, PP/r-PP and LDPE/r-PE samples were prepared by mixing homopolymer LDPE, HDPE and PP with post-consumer recycled plastics (r-PP and r-PE) by extruder, containing 0%, 10%, 20%, 30% and 100% recycled thermoplastic by weight. Thermal, mechanical and morphological properties of the samples were analyzed by Thermogravimetric Analysis (TGA), Differential Thermal Analysis (DTA), Differential Thermogravimetry (DTG), Differential Scanning Calorimetry (DSC), Dynamic Mechanical Analysis (DMA), Scanning Electron Microscopy (SEM) and Swelling Test. In TGA/DTA-DTG analyses, it was seen that all samples degraded in a single stage; as the recycled material ratio in the samples increased, the degradation onset temperature decreased and the thermal stability decreased. In DSC analyses, it was seen that as the recycled material ratio increased in HDPE/r-PE and PP/r-PP samples, the melting temperature (Tm) values did not change; the melting enthalpy (ΔHm) values and crystallinity degrees (Xc) decreased. In DMA analyses, it was seen that the storage modulus decreased as the temperature increased in all samples and the tan δ peak temperatures decreased as the recycled plastic ratio in the samples increased. In SEM images, it was seen that the samples exhibited a single phase morphology; It was observed that as the proportion of recycled material in the samples increased, voids and small pits began to form. It was observed that as the proportion of recycled plastic in the samples increased, the swelling values decreased.