The impact of sorting quality on the properties of recycled flexible plastic packaging

Abstract

Sorting is crucial for the recyclability of plastic packaging waste, yet flexible packaging poses challenges due to factors like low film mass, color variations, and multi-layer structures. This study assessed the impact of sorting quality on recyclate properties by analyzing four sorting grades. Grade 1 was compiled based on the composition of commercial wastes in Upper Austria. Composition analysis showed that Grades 2 and 3 had high polyethylene (PE) film content (87.1% and 84.0%, respectively), while Grade 4 had significantly less (59.6%) and higher contamination levels (23.2% vs. 7.0% in Grade 2). Mechanical recycling and characterization revealed that better sorting improved recyclate properties. Oxidation onset temperature (OOT) remained stable across Grades 1 to 4. Density decreased from Grade 1 to Grade 4. Transparency declined with increasing contamination, with Grade 4 exhibiting 3,510 inclusions/m2 compared to 250 inclusions/m2 in Grade 1. Mechanical properties, such as strain and stress, also decreased from Grade 1 to Grade 4, as larger inclusions (300–599 µm) in poorly sorted grades disrupted the polymer matrix and reduced tensile strength. Comparisons with three commercial recyclates highlighted the superior quality of well-sorted materials. This study demonstrates that improved sorting enhances recyclate quality, emphasizing the need for advancements in sorting technologies, optimized waste collection systems, and increased market demand for recyclates to support a circular economy.