What a 200 kg Reject Taught Us About PET 1 Plastic, Plastic Bags, and Recycling Labels

It was a Thursday in early Q1 2024 when the pallet showed up. Two hundred kilograms of rejected food packaging lids, wrapped in film, with a note taped to the shrink wrap: 'yellow streaking, please evaluate.' I remember thinking: here we go.

I handle quality and brand compliance reviews at Avient. In practice that means I check material before it reaches customers—roughly 200 unique jobs a year. In 2023 I rejected about 6% of first-run deliveries for reasons from off-spec tint strength to missing paperwork. When a pallet of returns arrives, I try not to jump to conclusions. I investigate.

This particular customer molds food packaging from recycled PET. They bought the same Avient masterbatch formulation from us for two years without drama. That was the first red flag. Most color issues show up after a formula change, a new lot, or a supplier switch. When a product runs fine for two years and suddenly streaks, the problem usually lives in the process, not in the colorant.

Masterbatch, if you are not deep in the plastics world, is basically a concentrated pellet of pigments and additives carried in a polymer. It is how a molder colors a batch of otherwise clear or natural resin. The carrier has to be compatible with the base plastic. The pigment has to survive the melt temperature. We spend a lot of energy in our lab getting that right. But no amount of pigment engineering can compensate for a base material that is falling apart.

First look in the lab

Under the lab lights, the lids had the same defect pattern: yellowish streaks in the direction of melt flow, plus glossy black specks scattered across the surfaces. We looked at the specks under the microscope first, then ran them on the FTIR. The spectrum was consistent with oxidized LDPE, not with PET. That was the moment I started asking different questions.

We checked their drying logs. Fine. We checked our batch records for the Avient masterbatch. Also fine. Then I called the plant manager, and that is when he mentioned the bags.

They had started a sustainability push in January 2024. Part of it involved collecting plastic grocery bags from the breakroom and feeding them into the same reclaim bin as their PET bottle scrap. He had read that plastic bags are recyclable. He assumed recyclable meant compatible. It is not.

Why PET 1 plastic and film bags do not mix

PET 1 plastic—the resin code #1 inside the chasing arrows triangle—is polyethylene terephthalate. It is what clear water bottles and most rigid food trays are made of, and it processes hot, around 260°C or higher. Plastic grocery bags are usually LDPE, resin code #4 on the same triangle. LDPE is a different polymer. It softens around 105–115°C. At PET processing temperatures, it does not blend in. It burns, breaks down, and leaves yellow streaks and dark specks. That was exactly what we saw.

If you have asked yourself 'can you recycle plastic bags,' the honest answer is yes but not through the curbside cart. Retail drop-off bins accept clean film and send it to a film recycler. That is its own stream, with its own markets. It was never designed to be mixed into PET bottles or PET food packaging.

I do not have hard data on how many contamination problems like this happen across the industry. But based on the returns I review every year, my sense is that 10–15% of color complaints trace back to someone mixing incompatible recycled films into a rigid process. The colorant was never the issue.

What the Teflon logo taught me

During the visit, we found something else in the reclaim bin: a nonstick baking sheet with the well-known Teflon logo on it. Everyone recognizes that mark on cookware. It signals a fluoropolymer coating, not a resin type. Putting that sheet into a PET reclaim stream is like throwing a laminated mailer into office paper recycling—it contaminates the whole batch.

This became the clearest example I have of why markings matter. A resin ID code tells you what polymer you are holding. A brand logo like the Teflon logo tells you that a coating or treatment was applied. People mix these up all the time, and that confusion costs real money.

A sorting problem, not a colorant problem

We ran a quick comparison in our lab: parts with clean rPET and our standard Avient masterbatch, and parts with 2% of the customer's bin scrap added. The contaminated samples looked exactly like the rejected lids. The Delta E between the two sets was above 4.5. For background, brand-critical color tolerances usually sit below Delta E 2, per Pantone color matching guidelines. Above 4, the color shift is obvious to almost anyone. There is no pigment package that can fix degraded polymer.

The full reject was about 900 kilograms of lids. The redo cost them roughly $22,000 when you include material, freight, and lost production time. It could have been caught in ten minutes with a basic incoming-material check.

I wish I could say our side had asked about their reclaim stream earlier. We had not. One of our standing rules for suppliers is 'verify incoming material.' I had written that rule into every contract we signed with vendors, but I had never applied it to our customers' reclaim streams. It took a $22,000 rework and a 900 kg reject to make me see that the rule applies both ways.

How we fixed it

The fix was not glamorous. We added a receiving checklist: verify the resin code, check the certificate of analysis, look for visible film or coated items before anything gets added to the regrind bin. We also put a separate bin beside their press with a sign that said 'film bags go to store drop-off.' Simple signage fixed what chemistry cannot.

Avient's application team reformulated the masterbatch slightly to tolerate normal variation in post-consumer PET reclaim. But we told them plainly: no colorant is a substitute for a clean feed stream. As of our last check in May 2024, they had not had a rejected lot since the new protocol went in. Their first full production run after the fix measured Delta E 1.1 against the agreed standard. That is a good result.

What I keep telling customers

Every material has an identity. Sometimes it is printed as a resin code, sometimes as a brand mark, and sometimes there is no label at all. The Teflon logo on nonstick bakeware and the #1 inside the chasing arrows on a water bottle are not the same kind of information. One describes a coating. The other describes the plastic itself. Learning to tell them apart is not an environmental slogan—it is a production skill.

Recycling is a good goal, and so is using recycled content. But polymer compatibility does not care about intentions. PET 1 plastic is recyclable. Plastic bags are recyclable. They are just not recyclable together. Knowing that difference earlier would have saved a customer 900 kilograms of rejected lids and a very uncomfortable phone call.

I still review every lot that leaves our plant, and now I also ask what is coming into theirs.