Recent discussions about increasing the use of recycled PET (rPET) in packaging inevitably must discuss the greater collection and recovery of PET in thermoforms, such as clamshell packaging. However, both the quality and quantity of recycled bale material determines how much rPET ends up being used in new packaging products, and the recycling of PET thermoforms introduces certain challenges.
In one example of addressing the quantity issue, Canadian grocery chains have called for their suppliers to supply clamshells only made from PET, resulting in a healthier stream of mainly-PET material in the recycling loop. But it's the quality requirements for this recovered material that standard recycled PET thermoforms don't support.
The most obvious problem is that most PET clamshells and salad trays use different kinds of labels than PET bottles use – and these labels can be difficult or impossible to remove with conventional washing processes in recycling facilities. The Canadian grocers’ initiative has reportedly attacked this problem by requiring that only certain adhesives be used with thermoforms, and some adhesives suppliers have quickly complied.
The Association of Postconsumer Plastic Recyclers is aiding the PET thermoform effort by providing testing, standards and guidance in its PET Thermoform Label and Adhesive Evaluation Program. The trade association has even established a protocol “for Evaluating PET Thermoform Labels and Adhesives for Compatibility with PET Recycling”.
Besides describing a detailed test procedure, this document refers to another key obstacle to PET thermoform recycling: thermoforming- and bottle-grade PET resins are different. “[T]he intrinsic viscosity [IV] of thermoform PET is generally lower than the intrinsic viscosity of carbonated soft drink bottle PET, but can be nearly the same as for water bottle PET.” This issue with IV deserves more discussion in future editions of this blog.
Mike Tolinski is the author of Plastics and Sustainability, published in Oct. 2011 by Wiley-Scrivener, and he is Contributing Editor for Plastics Engineering magazine of the Society of Plastics Engineers in the USA. His views have been shaped by his engineering, university, and journalism experience in the plastics and manufacturing industries over the past 21 years.