The storage conditions of post-consumer polyethylene terephthalate (PET) bottles could affect further recycled PET bottles, according to a recent Plastic Technologies, Inc. research study. The study found that exposing PET bottles to ultraviolet (UV) light prior to recycling has a severe impact on next-generation rPET bottles’ physical properties and visual attributes, including yellowing and haziness.
Typically, rPET producers have engineered processes to minimize the natural tendency of PET to yellow with each additional melting due to adhesive label residues and additives. “As an industry, we have focused on how package components affect next-generation materials, but haven’t really considered storage impact,” says Dr. Frank Schloss, vice president of PTI. “The more effort we make to remove all the quality impediments, the greater the chance our next-generation materials will meet marketing, processing and environmental objectives.”
According to PTI, the bottles used in the study were not densely packed into large bales. Instead, the researchers created conditions where sunlight could easily penetrate through the several layers of bottle sidewalls, even reaching the bottles at the bottom of the open crate.
“What the average effect might be on an entire bale of bottles compared to what was seen in this study is a matter of debate,” explains Schloss. “However, one should consider all the potential causes of yellowing that can limit the percentage of recycled PET that can be used. Exposure to UV radiation, whether it is from outside bale storage or possibly even exposure to fluorescent lighting in retail stores, should be considered as another contributor to rPET quality degradation.”