Recycling food packaging into material suitable for new food packaging presents a significant challenge. New materials must meet strict food safety standards, yet the recycling process often introduces contaminants. Researchers at Wageningen University & Research (WUR) have investigated this issue, mapping the journey of a common high-density polyethylene (HDPE) milk bottle from production to recycling. Their findings reveal critical points of contamination, offering valuable insights for improving recycling processes and material design.

The Journey of a Milk Bottle
Plastic milk bottles experience multiple stages in their lifecycle. After production and use, they are discarded into household recycling (PMD) waste streams. These bottles are then collected, transported to sorting facilities, and eventually processed into compressed bales for recycling. However, WUR researchers identified unexpected contamination at two critical points: when bottles enter the sorting facility and after being compressed into bales. The research uncovered that incoming bottles sometimes carry small quantities of chemicals originating from their caps and labels. More surprisingly, bottles exiting the sorting process exhibited diverse and significant contamination levels. This contamination stemmed from interactions within the compression bales, where residues from different types of plastic packaging mixed, compromising the quality of the recycled material.

The Problem of Bale Contamination
At the heart of the issue lies the baling process. Different types of polyethylene (PE) plastics, including detergent bottles, shampoo containers, and cleaning product packaging, are pressed together into dense bales. During this process, residual chemicals from less clean packaging migrate, contaminating even relatively clean items like milk bottles. This cross-contamination not only reduces the quality of recycled material but also raises food safety concerns.

Designing for Circularity and Safer Recycling
Armed with this knowledge, the researchers propose several design and process improvements to enhance recycling safety. Packaging design must prevent the transfer of chemicals from caps and labels to bottles. This could involve using alternative inks or adhesives and reformulating cap materials to minimise leaching. Separating food-grade plastics from non-food-grade packaging before baling would reduce contamination. Creating distinct bales for different plastic types could preserve material quality. Aligning packaging design across manufacturers to use consistent materials and components can simplify recycling and improve outcomes. For instance, standardising the type of PE used could reduce variability in the recycled material. Establishing stricter sorting standards and separate streams for food-grade plastics can help produce recycled materials that meet stringent food safety requirements.

Towards a Circular Economy
The findings underscore the importance of addressing contamination early in the recycling process to enable high-quality material recovery. Solutions like standardised packaging and improved sorting technologies not only enhance recyclability but also support the transition to a circular economy. By tackling these challenges, the industry can reduce waste and create safer, more sustainable materials for food packaging.

Source: Wageningen Food & Biobased Research
Photo: Wageningen Food & Biobased Research