Workhorse additives historically used without issue
Most PP in a package 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 PP. 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
- Fillers – note that many fillers are dense, so particular attention should be paid to the overall blend density
- Impact modifiers
- Chemical blowing agents
Additive usage should be minimized to maintain the best performance of recycled PP for future uses.
EVOH is a common layer material used to increase the barrier properties of PP. It is not separable in the recycling process and therefore will become part of the recycled PP. Although EVOH blended with PP is not without issue (it may cause splay when extruded or molded and contribute to die lip build up) it is generally accepted. EVOH has performed successfully in previous critical guidance tests. Some recycled PP users have experienced molding problems at values approaching 3%. Its use should be minimized to maintain the best performance of recycled PP for future uses.
REQUIRES TEST RESULTS
Testing must show that layers and coatings will either separate and be removed from the PP in the recycling process or have no adverse effects on the recycled PP in future uses. When used, their content should be minimized to the greatest extent possible. Some layers and coatings have been found compatible with PP or are easily separated in conventional recycling systems. Companies that are considering such barrier materials and are unsure of their compatibility with recycling should ask their suppliers to provide APR test results.
Additive concentration causing the overall blend to sink in water
Many of the additives and fillers used with PP 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, the blend sinks in water rather than floats. 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 polypropylene reclaimer and any PP in the blend will be lost.
Degradable additives (photo, oxo, or bio)
Recycled PP 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 PP. Additives designed to degrade the polymer by definition diminish the life of the material in the primary use. If not removed in the recycling process, these additives also shorten the useful life of the product made from the recycled PP, possibly compromising quality and durability.
Degradable additives should not be used without testing to demonstrate that their inclusion will not materially impair the full-service life and properties of any product made from the recycled PP that includes the additive. Testing must show that these additives will either separate and be removed from the PP in the recycling process or have no adverse effects on the recycled PP in future uses. When used, their content should be minimized to the greatest extent possible.