Mechanical recycling contamination risks the circular plastics economy, but quality control analytics can help
A study from the University of Manchester into the effects of polymer cross-contamination on the outcome of mechanically recycling plastics has found that the presence of contaminants radically alters ...
A study from the University of Manchester into the effects of polymer cross-contamination on the outcome of mechanically recycling plastics has found that the presence of contaminants radically alters degradation mechanisms.
When it is done well—in other words, when yogurt containers (polypropylene, PP) are sorted from milk jugs (high-density polyethylene)—mechanical recycling is the most environmentally beneficial way to turn plastic waste into new products in a circular plastics economy, turning containers into containers and jugs into jugs.
However, poor sorting can lead to mixing polyolefins, changing the way plastic degrades during the recycling process.
While well understood for polyethylene, the study, published in Chem Circularity, focuses on what happens when PP is mixed with HDPE. Researchers found that contaminants act as stress aggregators and that the phase separation caused by contamination weakens the material. While HDPE can tolerate a few percent contamination, even 1% of HDPE in PP alters the degradation mechanism.
The result of this contamination, even at this small scale, is a recyclate with radically altered physical properties, a change that affects structure-property relationships and reduces the material's overall performance, especially in the context of industrial reuse.
Researchers argue that while efforts have been made to normalize polymers based on processing history and end-use application, approaches like these consider only a limited number of material grades and do not represent the broad range of polyolefin grades and blends.
They suggest that cross-contamination needs better analytical tools that can serve as quality control in industrial processes, demonstrating the need for better sorting in household and industrial recycling.
"A circular plastics economy is essential to developing a sustainable relationship with plastic waste. Developing the quality controls necessary to assess contamination in recycled products is an essential step toward that future," said Professor Michael Shaver.
More information
Arpan D. Patel et al, Measuring the impact of cross-contamination on quality in polyolefin blends, Chem Circularity (2026). DOI: 10.1016/j.checir.2026.100112 linkinghub.elsevier.com/retrie … ii/S3051294826001088
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Citation: Mechanical recycling contamination risks the circular plastics economy, but quality control analytics can help (2026, August 3) retrieved 3 August 2026 from https://phys.org/news/2026-08-mechanical-recycling-contamination-circular-plastics.html
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