UV light negatively affects PET bottles recovered for recycling

A new research study by Plastic Technologies Inc. (PTI), Holland, Ohio, a provider of preform and package design, package development, rapid prototyping, preproduction prototyping and material evaluation engineering for the plastic packaging industry, has found that exposing postconsumer bottles to ultraviolet (UV) light prior to recycling has a severe impact on the physical properties and visual attributes of bottles made from recycled PET (rPET). The PTI white paper can be downloaded from www.plastictechnologies.com/solve/white-papers-and-articles/how-light-impacts-rpet.aspx.

Intrinsic viscosity, yellowing and haze are some of the attributes that provide challenges when using rPET along with virgin material, PTI says. RPET producers have engineered elaborate processes to minimize those characteristics to create material that provides the desired environmental attributes along with key visual and processing properties, PTI says. (PTI’s family of companies includes Bowling Green, Ohio-based Phoenix Technologies, an rPET producer. Phoenix is profiled in the July 2015 issue of Recycling Today.)

The bottles used in this study were not densely packed into large bales. Sunlight easily could penetrate through the several layers of bottle sidewalls, even reaching the bottles located at the bottom of the open crate, the company says.

“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,” says Dr. Frank Schloss, vice president of PTI. “However, one should consider all the potential causes of yellowing that can that 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.”

PTI says storage conditions are just one more factor that can be added to the natural tendency of PET to yellow with each additional melting. This is because of adhesive label residues, trace amounts of residual label material, inks and coatings that can bleed from the label onto the PET flake, as well as additives that cannot be removed by the washing process, the company notes. 

“As an industry, we have focused on how package components affect next generation materials but haven’t really considered storage impact,” Schloss adds. “The more effort we make to remove all of the quality impediments, the greater the chance that our next generation materials will meet marketing, processing and environmental objectives.”