Mechanical recycling contamination risks the circular plastics economy, say Manchester researchers, but quality control analytics can help.

A study from The University of Manchester into the effects of the cross-contamination of polymers on the outcome of mechanically recycling plastics has found that the presence of contaminants radically alters degradation mechanisms. However, poor sorting can lead to mixing polyolefins together, changing the way that the plastic degrades during the recycling process. While well understood for polyethylene, the study, published in ChemCircularity, 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.