PET Recycling Filtration: The Complete Guide to rPET Melt Filtration

PET (polyethylene terephthalate) presents a specific set of filtration challenges that distinguish it from polyolefin recycling. Three properties make rPET filtration technically demanding in ways that standard LDPE or PP recycling equipment is not designed to handle.

First, thermal sensitivity. PET degrades rapidly above its processing temperature window — typically 270–290°C for bottle-grade resin. Degradation produces acetaldehyde (AA), which is a taste and odour contaminant in food-contact applications with a very low detection threshold. Any filtration system that creates dead zones or residence time irregularities — including screen changers that generate melt stagnation during the change cycle — introduces thermal degradation risk that manual systems cannot avoid.

Second, contamination hardness. Post-consumer PET bottles carry glass fragments, metal closures, aluminium labels, silicone gaskets, and ceramic particles — all significantly harder than the polymer melt they travel in. These abrasive particles damage screen pack wire mesh faster than soft contaminants and accelerate breaker plate wear. Even at low concentrations by weight, these hard particles are highly abrasive to fine filtration elements.

Third, intrinsic viscosity (IV) sensitivity. Recycled PET undergoes IV degradation during reprocessing — each thermal cycle reduces molecular chain length and reduces IV from the typical bottle-grade specification of 0.72–0.78 dl/g. Pressure events during screen changes cause local overheating and accelerated IV degradation at the filter zone. Continuous filtration eliminates these pressure events, preserving IV closer to input specification throughout the extrusion run.

The contamination profile of post-consumer PET bottle flake — the primary feedstock for rPET extrusion — differs significantly from post-consumer polyolefin film. Food-grade rPET requires very low levels of metals, PVC and non-PET polymers in the feedstock. In practice, real-world flake streams from collection and sorting systems routinely exceed these targets before washing.

The particles that reach the melt filtration stage after washing, drying, and solid-state processing include: residual PVC cap liner fragments (which degrade at PET processing temperatures and release HCl), polyolefin caps incompletely separated in NIR sorting, adhesive residues from labels, fine glass fragments from broken bottles in the collection stream, and metal shards from aluminium closures. Food-contact rPET applications typically require fine filtration, below 100 μm, to protect the final product from contamination defects and analytical failure in migration testing; for these requirements, request a technical alignment.

Every screen change on a discontinuous system is a thermal degradation event in rPET processing. When melt flow is interrupted or reduced during a screen change — whether for 30 seconds on a hydraulic system or 30 minutes on a manual one — the polymer in the dead zones of the filter housing continues to experience thermal exposure without the cooling effect of melt flow. At PET processing temperatures of 270–290°C, every minute without flow adds IV degradation and acetaldehyde formation.

The practical consequence is that manual and hydraulic screen changers introduce a recurring quality risk that is invisible in standard process monitoring but detectable in downstream product testing. A food-contact rPET thermoforming sheet manufacturer running manual screen changers generates a thermal degradation event at every screen change — each one a potential source of elevated AA or colour deviation in a batch that may not be identifiable until it has already been converted and tested.

A continuous and self-cleaning screen changer, such as the ScrapeAway laser melt filter, cleans the filter while melt keeps flowing: there is no flow interruption, no pressure drop event and no stagnant melt zone during a screen change.

The effect is IV preserved closer to the input specification, which directly affects downstream processability in bottle preform injection and fiber spinning, where the IV floor leaves little margin.

The correct screen changer technology for rPET extrusion depends on three variables: the contamination level of the incoming flake, the end application quality requirements, and whether the line processes bottle-grade or lower-grade rPET streams. The selection logic is straightforward once these three variables are known.

For the full decision framework, see the guide to continuous vs discontinuous screen changers →

The EU Packaging and Packaging Waste Regulation imposes mandatory minimum recycled content requirements that are rewriting the economics of rPET processing. The 30% recycled content mandate for PET beverage bottles by 2030 — rising to 65% by 2040 — means that converters must process significantly more post-consumer rPET per tonne of output than today.

Lines that run moderate rPET content today will face much higher filtration loads as recycled content rises. The right moment to specify filtration that keeps the line running is when the line is planned for higher rPET content, not when downtime becomes unmanageable.

The economic case for continuous filtration in rPET processing has three components that are absent or minor in virgin polymer processing: direct downtime cost, quality scrap from thermal degradation events, and IV loss-related yield reduction.

Direct downtime follows the same arithmetic as other extrusion applications: screen changes per shift × minutes per stop × shifts × operating days ÷ 60 × throughput gives the output lost every year.

Quality scrap from thermal degradation is harder to quantify but real. Each screen change event generates a batch of material with elevated acetaldehyde or colour deviation that must either be downgraded (non-food-contact use) or scrapped entirely. On a food-contact production line where the entire batch between screen changes must meet migration testing specifications, a single degradation event can condemn hours of output.

For a complete calculation of the direct downtime component on your rPET line, use the Cofit calculator — it takes under two minutes with four input values.