Unlocking the Potential of Mechanical Recycling for Polyethylene Films

Polyethylene films are everywhere—stretch wraps in warehouses, grocery bags in homes, and countless flexible packaging materials. Yet, despite their ubiquity, these films often end up as waste, posing significant environmental challenges. Mechanical recycling offers a promising route to reclaim these materials, but ensuring consistent quality from heterogeneous post-consumer waste streams is a complex task. Our research explores how pre-treatment and melt filtration strategies can improve both efficiency and material quality, providing insights that are directly relevant to the plastics recycling industry.

The study focuses on industrially relevant waste streams, including linear low-density PE (LLDPE) from stretch films, low-density PE (LDPE), and mixed post-consumer films collected through yellow sack systems. By systematically varying washing parameters—temperature, duration, and the use of alkaline treatments—and examining their interaction with melt filtration steps, the researchers were able to identify processing conditions that optimize the mechanical and chemical properties of recycled PE.

Understanding the Challenges of PE Film Recycling

Polyethylene films differ widely in polymer type, thickness, additives, and contamination levels. These variations can dramatically influence processing behavior and final material properties. The CHASE study found that washing temperature and chemical treatment directly impacted melt flow index (MFI), thermal stability, and the removal of surface contaminants. For example, alkaline washing increased the removal of residual inks and adhesives, resulting in cleaner pellets, but excessive alkalinity or prolonged washing could degrade polymer chains, reducing mechanical performance.

The heterogeneity of waste streams remains the most significant challenge. Linear low-density PE from industrial stretch films responded differently to washing than mixed post-consumer films. Mixed streams exhibited greater variability in melt flow and higher residual contaminants, highlighting the need for tailored process parameters rather than a one-size-fits-all approach.

The Role of Melt Filtration in Material Quality

Melt filtration was shown to be crucial for improving optical clarity and reducing volatile organic compounds (VOCs), which are critical for downstream applications such as extrusion or film manufacturing. The study demonstrated that a two-stage filtration could significantly reduce visible impurities and improve homogeneity without compromising thermal properties. This step ensures that recycled PE meets the quality standards required for industrial reuse, particularly in applications sensitive to appearance and odor.

Quantitatively, the researchers observed that optimized washing and melt filtration could improve MFI consistency by up to 20%, thermal degradation onset temperature by 10–15 °C, and reduce VOC emissions by nearly 30% compared to minimally processed streams. These improvements make the recycled material more predictable and reliable for industrial processes.

Industrial Implications

For the plastics industry, these findings are highly relevant. Mechanical recycling of PE films is a key pathway to meet EU recycling targets, but industrial adoption has been hindered by inconsistent material quality. By implementing process optimization—carefully adjusted washing and multi-stage melt filtration—recyclers can produce higher-quality rPE that performs closer to virgin materials. This not only expands the potential applications for recycled PE but also reduces waste sent to landfills and decreases the environmental footprint of plastic packaging.

Moreover, understanding the relationship between waste stream composition and processing conditions allows recycling facilities to design more efficient, cost-effective workflows, avoiding unnecessary degradation while maximizing throughput. In practice, this means that industrial recyclers can achieve both economic and environmental benefits simultaneously.

Project partners

The work was carried out by Competence Center CHASE GmbH ↗ in collaboration with Johannes Kepler University Linz, Institute of Polymeric Materials and Testing ↗ and LIT Factory, Johannes Kepler University Linz ↗.

The paper was published in Journal of Applied Polymer Science 2025 (e57463), the authors are Johanna Langwieser, Sandra Czaker, Jörg Fischer: Investigation of Pretreatment and Mel Filtration in Mechanical Recycling of Polyethylene Film Waste Streams - CHASE PDF ↗