Mechanical recycling is one of the most effective and widely used approaches to solving the problem of plastic waste. From an engineering perspective, challenges in polymer recycling include the difficulty in achieving uniform material properties due to the variability in source quality and recovery process applied. In this research, waste recycled packaging material was repeatedly extruded to investigate the effects of thermomechanical stress on its structure and thermal stability. The measurement was carried out using Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA). FT-IR spectra of the analyzed samples show that after the third extrusion cycle, significant changes in the structure can be observed, which indicate oxidation and degradation processes. The TGA results also indicate a significant deterioration of the thermal stability of the material after the third extrusion. It can be concluded by the decomposition of recyclate in two degradation steps, where the onsent degradation temperature of the first step is lower compared to the initial recyclate. Additionally, the structure and thermal properties of mixtures of virgin PE-HD and recyclate from the fifth extrusion cycle in mass ratios of 30/70 and 50/50 were investigated. It was found that the addition of virgin PE-HD reduces the concentration of polymer degradation products and affects the reduction of mass loss of the first degradation step. The obtained positive effect of mixing the original and recycled polymer on the properties of the material indicates the potential of the recycled material for further use.