In an article published on July 27, 2015 by the news provider Plastics News, reporter Jim Johnson informs about a new study investigating the impact of UV light exposure on polyethylene terephthalate (PET) containers before reprocessing. Researchers Francis M. Schloss and Julie Brown of Plastic Technologies, Inc., U.S., exposed post-consumer virgin material PET bottles to sunlight on a rooftop for a year. Other PET bottles were stored inside and irradiated with fluorescent light. A third control set of PET bottles was stored without light exposure. The researchers found that UV light does not alter the appearance of the exposed PET bottles. However, when the exposed PET bottles are recycled into resin pellets which are in turn used to create recycled PET bottles, yellowing occurs. Every melting cycle of PET adds more yellowness to the recycled product, but exposure of PET to UV light prior to recycling is one of several factors that significantly enhances the yellowing effect. Schloss and Brown recommend that recyclers and reclaimers do not store post-consumer PET bottles in open sunlight areas in order to ensure that the visual attributes of recycled PET bottles are equal to virgin PET bottles. Schloss notes that it is yet unclear how much of an impact other factors such as additives and residuals have on PET yellowing.
Yellowing in PET is attributed to a break down or ageing of the polymer. The present study did not investigate chemical migration changes in PET bottles due to UV light exposure.
Jim Johnson (July 27, 2015). “Research shows how UV light degrades recycled PET.” Plastics News
Plastic Technologies, Inc. (2015). “How light impacts rPET.”
Schloss, F. M. & Brown, J. (2015). “How light impacts recycled polyethylene terephthalate (rPET) characteristics.” Plastic Technologies, Inc. (pdf)