When is PET not PET? When it is PETG.
To the typical consumer, the difference between PET and glycol-modified PET is simply a letter.
But to a polymer scientist worth her molecular weight, there's a huge difference. Especially when it comes to recycling.
And that's why the Association of Plastic Recyclers worked for years to clarify that difference in California, culminating in the recent passage of a new law that defines exactly what constitutes PET.
A workhorse of the container business, PET is the most recycled resin, especially in bottle bill states like California, where there is a financial incentive to recapture the material.
The resin identification code for years has labeled PET as a No. 1. But some PETG-container makers also have been putting a No. 1 code on their products.
And that's a problem because PET and PETG perform differently during the recycling process, explained APR Technical Director John Standish.
“It's distinctly different,” he said. “It might sound silly, but people go, ‘It's polyester, and all polyesters are the same.' And no, they are not.”
PETG flakes, when recycled, end up glomming on to PET flake to create clumps that disrupt processes and equipment.
“PETG is a copolymer. So it's a polyester. But it's a different composition than the PET that's used to make injection stretch blow molded bottles, which are what a Coke bottle, a Pepsi bottle, a single-serve water bottle [are made from],” Standish said.
The introduction of glycol to create PETG from PET creates a distinct material, one that performs differently during processing as well as recycling.
PETG, in the thermoformed container market, is used in food packaging. It's also frequently used to package medical devices and electronics.
It's typically a shade of blue in thermoformed medical applications, and not typically found in the recycling stream, Standish explained.
“All we really did in California, we introduced a piece of legislation that really clarified their existing law,” APR Executive Director Steve Alexander said. “All we did was just reinforce the definition of what PET was for the purposes of the resin identification code in California.”
California emerged as an important market to make the distinction due to the state's Rigid Plastic Packaging Container Law, which assesses fees to container- makers based on the resin used, Alexander explained.
“There's a huge financial incentive to label your product anything but a [No.] 7, if you will, so that's certainly a part of it. But there's also, I guess you would say, the negative connotation of a 7 being less than optimally recyclable,” Alexander said.
PETG, he said, “wasn't a 1, that's all we were saying, and the legislature agreed with us.”
“We've probably been complaining about it for six or seven years. We struggled to come up with a solution,” the executive director said.
Earlier work involved trying to create change through the ASTM industry standards process, but that didn't go anywhere.
“We just decided to take a shot legislatively, and we were able to be successful. It's been a recognized problem for quite a long time,” Alexander said.
“We created legislation that simply was the definition of what PET is. It doesn't even mention PETG. There could be other potential contaminants we eliminated as well, but PETG was the primary one we were focusing on,” he said.
It's no surprise that polymer chemistry can get confusing to the layman, so here's the language from the new law, AB 906:
“Polyethylene terephthalate is generally referred to as PET; it is also known as PETE, which is used in California statute. PET is widely used in water and soft drink bottles and is used for a variety of other products. PET is recyclable; PET flakes and pellets are commonly recycled into other types of packaging and fiber (e.g., carpet and microfiber).
“Polyethylene terephthalate glycol-modified (PETG) refers to PET plastic resin with the addition of glycol. PETG eliminates hazing that can occur when manufacturing PET containers and is less brittle than PET. PETG also produces a softer and more pliable exterior surface, which is viewed by some as more comfortable to hold for consumers. Unlike PET, PETG does not have a consistent melting point and becomes molten when heated.
“Because both PET and PETG are comprised of polyethylene terephthalate, they are both required to be labeled with the ‘1' resin code. However, PET has a much higher processing temperature than PETG. This creates significant challenges for recycling. When processed together, PETG melts and becomes sticky while PET remains solid. This results in PETG sticking to PET chips, forming large clumps that cannot be processed. This bill revises the definition of polyethylene terephthalate to exclude PETG so that the materials can be effectively sorted prior to recycling,” the analysis states.
The new law, which becomes effective Oct. 1, defines PET through certain characteristics, including its “melting peak temperature.”