Enhancing sustainability in extrusion blow molding: effect of recycled and re-recycled low-density polyethylene on the physical, flow behaviour, mechanical, structural and thermal properties

Extrusion blow molding (EBM) is widely used for manufacturing plastic products, with low-density polyethylene (LDPE) being a key material due to its flexibility and processability. However, its high consumption contributes significantly to plastic waste accumulation and the depletion of non-renewable resources. Recycling LDPE is a promising approach to reducing plastic waste, but multiple reprocessing cycles and blending can alter the properties, potentially affecting product quality and performance. Grasping the degradation mechanisms and property retention of LDPE blends is essential for upholding product quality while advancing sustainability.This research investigates the impacts of recycled LDPE (rLDPE) and re-recycled LDPE (rrLDPE) on LDPE blends, focusing on physical, flow behavior, mechanical, structural, and thermal properties. The findings indicate that moisture content and density increased with higher recycled content due to oxidation, while melt flow index (MFI) increased, which implies a reduced in molecular weight. Both tensile and impact strength diminished, especially in rrLDPE blends, underscoring ongoing polymer degradation. Fourier transform infrared spectroscopy (FTIR) analysis verified oxidative alterations through increased hydroxyl (-OH) and carbonyl (C=O) functional groups, while differential scanning calorimetry (DSC) results indicated a reduction in crystallinity from 49.17% (vLDPE) to 34.23% (rrLDPE), confirming structural degradation. Blends with ≤30 wt% rLDPE maintained acceptable performance, while rrLDPE content exceeding 10 wt.% led to significant deterioration. These findings provide insights into optimizing sustainable LDPE formulations, balancing environmental benefits with material integrity.