Eliminating Aluminum Impurities from Waste HDPE Containers through Two-Stage Melt Filtration for Sustainable Enhanced Regeneration

Eliminating aluminum impurities from waste high-density polyethylene (HDPE) containers represents a pivotal challenge in achieving sustainable regeneration of plastic materials. Aluminum contaminants pose significant obstacles to the purity and performance of recycled HDPE. Herein, this study systematically investigates the purification, processing optimization, and mechanical enhancement of recycled HDPE. First, a two-stage melt filtration method is proposed to effectively remove aluminum foil impurities, achieving a removal rate of 99.5% under filter pressures below 18 MPa. Pressure change analysis further determines optimal filter replacement intervals: 15-20 min for the primary filter and 60 min for the secondary filter, ensuring filtration efficiency. Granulation temperature effects are evaluated, revealing that within 220-250 °C, the melt flow index decreases from 0.30 to 0.20 g/10 min, while elongation at break declines from 120% to 70% with rising temperature. Comparative analysis of cooling methods demonstrates that rapid cooling in 25 °C water for 10 min (vs natural cooling in 25 °C air for 16 h) enhances melt flow index by 0.1 g/10 min, impact strength by 5-10 MPa, and elongation at break by 5-20%, albeit reducing flexural strength and modulus by 1-2 MPa and 20-60 MPa, respectively, while tensile strength remains unaffected. These findings provide actionable insights for optimizing industrial production parameters and provide a predictive basis and foster efficiency. Finally, blending 3-5 wt % polyolefin elastomer with recycled HDPE is validated as an effective strategy to significantly improve toughness. Collectively, this work establishes a comprehensive framework for refining recycled HDPE processing and performance, offering practical solutions to enhance sustainability and efficiency in polymer recycling applications.