What rPET Means for Seaming
rPET — recycled polyethylene terephthalate — is PET film that contains post-consumer or post-industrial recycled content. From a polymer chemistry standpoint, rPET is still PET: a semicrystalline polyester with the same fundamental structure as virgin material. The same Class 4 solvents are required, and the same solvent-welding mechanism applies.
What changes is consistency. Virgin PET comes from a controlled polymerization process with tight specifications. rPET comes from a recycling stream — collected bottles, washed, flaked, reprocessed into film. Every step in that chain introduces variability that virgin material does not have.
Sources of Variability
Crystallinity differences. The thermal history of recycled PET — how it was originally processed, how it was collected and stored, and how it was reprocessed into film — affects its crystallinity. rPET may have higher or lower crystallinity than virgin PET of the same nominal grade, and that crystallinity can shift between batches as the recycling feedstock changes.
Crystallinity directly affects seaming. Higher crystallinity means more resistance to solvent penetration — the seaming window shifts toward the “not enough solvent” end. Lower crystallinity makes the film more receptive — the window shifts toward the “too much” end. Neither is necessarily a problem if you know which direction it has shifted, but batch-to-batch variation means the window moves unpredictably.
Contaminant levels. Recycled PET may contain trace levels of other polymers (PVC, PETG, polyolefins), adhesive residues, colorants, or degradation products from prior use and reprocessing. Most film manufacturers remove these to very low levels, but “very low” is not “zero.”
For seaming, contaminants matter because they can affect surface energy, solvent absorption rate, and the clarity of the bond zone. A contaminant that concentrates at the film surface — even at trace levels — can interfere with the initial solvent wetting step or create weak points in the interdiffused bond.
Molecular weight distribution. Each reprocessing cycle degrades PET’s molecular weight to some degree. Lower molecular weight means shorter chains, which affects both the mechanical strength of the film and the dynamics of chain interdiffusion during seaming. In practical terms, this typically manifests as slightly different optimal dwell times for the solvent. [INFERRED]
Intrinsic viscosity (IV). IV is the standard measure of PET molecular weight and is tracked by film manufacturers. rPET generally has lower IV than virgin PET. Films with higher rPET content may have lower IV, which changes how the polymer responds to solvent. Film suppliers publish IV specifications, and these are worth tracking if seaming consistency is a concern.
Practical Impact on Seaming
The variability in rPET does not mean that it cannot be seamed well — it means that the process cannot be set once and forgotten.
A setup validated on virgin PET may need adjustment. If you develop your seaming parameters on virgin PET film and then switch to rPET (or increase the recycled content percentage), the seam may be weaker or stronger than expected. Neither direction is guaranteed — it depends on the specific rPET batch.
The seaming window may be different. On virgin PET, the acceptable dosing range is already narrower than PETG (see PET film). On rPET, that window may shift or narrow further. A dosing level that was comfortably within spec on virgin PET might be marginal on an rPET batch with higher crystallinity.
Lot-to-lot consistency is not guaranteed. Two deliveries of the same rPET film grade from the same supplier may behave differently at the seaming station because the recycling feedstock changed between production runs. This is fundamentally different from virgin PET, where lot-to-lot variation is tightly controlled.
Quality Control Recommendations
The response to rPET variability is more frequent testing, not a fundamentally different process:
Seam peel testing on every new lot. On virgin PET, you might validate once per film grade and run with confidence. On rPET, test each incoming lot. If the seam strength or failure mode changes, adjust dosing before running production.
Track film IV and crystallinity data. If your film supplier provides these values on certificates of analysis, record them and correlate with your seaming performance. Over time, this builds a map of which material properties predict seaming adjustments.
Narrow your internal dosing specification. If your acceptable dosing range on virgin PET was, say, the full width of the Class 4 manufacturer’s recommended range, consider tightening your internal target for rPET. Running closer to the center of the window gives you more margin when the window shifts.
Retain samples from each lot. When a lot seams well, keep film samples. When a lot is problematic, compare the two. Surface energy measurements (contact angle, dyne testing) can sometimes reveal differences that explain the seaming behaviour.
Regulatory and Sustainability Drivers
Brand owners are increasing recycled content in packaging across all components, including sleeves. Regulatory frameworks — particularly in Europe and parts of North America — are setting minimum recycled content targets. Some brand owners specify a minimum percentage of recycled content in their sleeve films.
This means rPET is not an option converters can avoid. The percentage of recycled content in sleeve films is increasing, and the supply chain is building toward higher rPET content as a default rather than a specialty offering.
The Tension
This is the core reality of rPET in shrink sleeve seaming: sustainability demands recycled content, but seaming demands consistency. The two pull in opposite directions.
Recycling infrastructure is improving, and film manufacturers are investing in better sorting, washing, and reprocessing to tighten rPET quality. IV control, contaminant removal, and crystallinity management are all getting better. But the feedstock is inherently variable — it comes from waste streams, not reactors — and some degree of variability is structural to the material.
Converters who seam rPET successfully are the ones who accept the variability as a given and build their quality control around it, rather than treating rPET as interchangeable with virgin material. The solvent, the equipment, and the fundamental process are the same. The diligence required is higher.
For the Class 4 solvent requirements that apply to both virgin PET and rPET, see PET seaming. For comparison with the amorphous alternative, see PETG vs. PET.