Workhorse additives historically used without issue
Most PE film contains some form of additives. The “workhorse" additives commonly used have not been shown to cause significant issues with the recycling process or further uses of the recycled PE. Commonly acceptable workhorse additives include:
- Thermal stabilizers - These additives typically enhance the further processing of the polymer and are therefore preferred for recycling.
- UV stabilizers – These additives typically enhance the further processing of the polymer and are therefore preferred for recycling
- Nucleating agents
- Antistatic agents
- Antifog agents
- Lubricants and processing aids
- Slip and anti-blocking agents
- Fillers – note that many fillers are dense, so particular attention should be paid to the overall blend density
- Chemical blowing agents
Additive usage should be minimized to maintain the best performance of recycled material for future uses.
SiOx and AlOx barrier coatings
Vacuum-deposited coatings like SiOx and AlOx are accepted as Preferred only when applied directly to PE films without the use of additional wet coatings or primers. These materials are completely inert, non-detectable by any metal detection method used in the recycling industry and deposited as nanometric thin layers on film surfaces, with negligible effect on film density. These layers represent a lower percent in weight when compared to additives normally present in PE films like SiO2 or similar antiblocking agents, listed as Preferred above.
PVDC degrades at low temperatures rendering large portions of the recycled PE unusable.
Additive concentration where density is greater than 1.0
Many of the additives and fillers used with PE are very dense and when blended with the polymer increase the overall density of the blend. When their weight percentage reaches the point that the blend density is greater than 1.00 g/cc, the blend sinks in water rather than floats. Density is an important property and float-sink tanks are critical separation tools used by film reclaimers. Therefore, a sinking material will be considered waste by a film reclaimer and any PE in the blend will be lost.
REQUIRES TEST RESULTS
Metalized layers are extremely thin coatings of metal deposited on the film as a vapor. They should not be confused with actual metal layers addressed as “foil” in this document. Metalized layers are not removed in the recycling process and are melted and blended with the PE. This may cause material discoloring. In some cases, a metalized film will be detected early in the recycling process by metal detectors designed to protect machinery from catastrophic damage. Metal detectors may not be able to differentiate between a metalized film and a solid metal part, so the entire package may be discarded rather than accept the risk.
Vapor deposited metal layers are frequently applied to oriented polypropylene (OPP) or polyester (OPET) films for flexible packaging laminations that may end up in the PE recycling stream. Since PP and PET have higher melting points than PE, negative effects of these metallized laminates may occur in the extrusion and melt filtration processes. However, when deposited into recyclable substrates like PE, oriented or not, mono (OPE) or biax (BOPE), the layer of aluminum metal is at the nanometric level, which should not present any significant risk to recyclers on the melt filtration step.
Test methods (in order):
Additive concentration where density approaches 0.996
Many of the additives and fillers used with PE film are very dense and when blended with the polymer increase the overall density of the film. When their weight percentage reaches the point that the film density approaches 0.996 g/cc, the film may sink in water rather than float and it should be tested. Density is an important property and float-sink tanks are critical separation tools used by reclaimers. Therefore, a sinking material will be considered waste by a film reclaimer and any PE in the blend will be lost.
Degradable additives (photo, oxo, or bio)
Recycled film is intended to be reused into new products. The new products are engineered to meet particular quality and durability standards given properties of typical recycled film. Additives designed to degrade the polymer and diminish the life of the material in the primary use may also shorten the useful life of the product made from the recycled film, possibly compromising quality and durability, if not removed during the recycling process.
Other additives and coatings
A growing number of innovative materials are being used as additives and coatings in PE film packaging. These materials must be tested to determine their impact on PE film recycling processes and the PCR produced: unconventional additives, layers, plasma coatings, liquid PVOH, EVOH, curable barrier coatings (chemically, EBeam or UV), and other barrier coatings not listed .
Vacuum-deposited coatings like AlOx and SiOx including additional layers of primers or other wet coatings need to be tested for recyclability.