The problem of accumulating plastic waste represents not only an environmental pollution issue but also a social, technical, and economic problem. High-density polyethylene (HDPE) is one of the commonly used polymer materials because it is easy to process, has good strength, and toughness. As part of the master's thesis, we investigated whether the mechanical, thermal, and surface properties of HDPE, obtained from recycled bottle caps from various sources, which has already been recycled 10 times, change with further recycling. Tensile testing was used to assess tensile strength, the differential scanning calorimetry (DSC) method was employed to measure melting temperature, crystallization temperature, changes in enthalpy during melting and crystallization, and nanoindentation procedures were used to examine surface properties such as elastic modulus, hardness, energy storage modulus, energy loss modulus, and surface profile during indentation. We found that the mentioned properties in the observed material, which we measured, remain unchanged up to and including the 25th recycling cycle, with changes of no more than 10% compared to the original recycled material.
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