TAGS: Sustainability/Natural Solutions
Using recycled polymer to produce lower value items like trash bags is common, and better than nothing. Yet, it is missing the mark for a self-maintaining circular economy.
Should one use 100% recyclates, or blend it with virgin resin, degradation mechanisms will occur during processing and use of the plastic part. This is one key aspect to tackle to develop high performance materials.
Let’s assume you are well-versed with the stabilization of conventional resins (PE, PET, PVC, etc.). If not, you may wish to start with these in-depth guides on antioxidants and UV stabilizers.
The question we will look at today is whether you should adopt new stabilization strategies when working with recycled polymers. Before talking about additive solutions to delay those degradation mechanism, a major parameter is the recycled plastic itself!
Thermal and UV protection challenges as per recycling stream
The quality and challenges greatly vary depending on your recycling stream. From the easiest to work with to the most challenging:
- Leftovers and scraps from your own production processes: knowing the precise composition and thermal history of your resin makes it simple.
- Post-industrial waste: this is when you are using waste that was generated by another manufacturing process. This recycling stream offers a great quality source; however, you may not have a full view on its detailed composition and its thermal history.
- Pre-consumer waste: typically, packaging waste, like a plastic film around goods on a transport pallet. Here again, you may experience limited composition variability, but the product went through the full cycle of use.
- Post-consumer waste: a high-volume stream which avoids that plastics end up clogging in the landfill. Yet, this is, by far, the most challenging source to work with. Composition can greatly vary from batch to batch and you have absolutely no clue on the past use and thermal story of your resin.
Depending on your recylcing stream, the challenges in stabilizing your PE, PET, or any other plastic will be quite different.
Let’s now review how you can stabilize your “experienced” resin for its new life.
How to go through another processing cycle?
The recycled material has already experienced thermal stress in its previous life, which is often reduced by adding suitable antioxidants and heat stabilizers. Nowadays, additives are used at optimal concentration, hence, you can’t assume your resin contains enough antioxidants or heat stabilizers for your new thermal cycle.
As a starting point, you may consider adding stabilizers as you would do with a virgin material. Degradation in recycled polymer follows the same mechanisms as with their virgin courterpart. Hence, the same chemistries can be used to help your material withstand your manufacturing process.
Antioxidants and heat stabilizers prevent the deterioration of physical and mechanical properties. They bear all the thermal stresses themselves before it transfers to the internal structure of the plastic. So, stabilizers serve the same purpose in recycled plastics as they do in virgin resin.
Hold on, it is not as easy as it seems! The recyclate may have impurities and contaminants depending on the recycled material stream. As we saw before, post-consumer recycled plastics will be more prone to this problem. Such particles can act as a degradation promoter. If you are experiencing an accelerated degradation of your recycled plastic, it is probably what is happening in your system.
Using grades specifically made for recycled plastics, such as the new
IrgaCycle™ series by BASF, can prove beneficial. These PCR-suited grades usually assure their primary function as conventional grades, but they also neutralize possible contaminants and impurities. This would help boost the performance of your materials.
–Chat with our assistance team if you struggle with a premature degradation of your recycled compound.
UV protection for recycled plastics: What is needed?
If you target an outdoor application, you must ensure that your parts will not degrade when exposed to the sun. The same chemistries as you would use with a virgin material will protect your plastics from brittleness, yellowing, chalking, losing color, or gloss.
For more guidance, check out our in-depth guide and learn about the light stabilizers that you can use for the commonly recycled resins.
Grades specifically designed for recycled resin will bring extra protection against sun degradation by neutralizing degradation-promoting residues which could be contained in the recycled polymer.
The incertainty around the recyclate composition and its possible variability from batch to batch can lead to another problem.
You could end up adding stabilizers in excess in your final material, if there remain light stabilizers from former life of your recycled material. Beyond the solubility threshold, the additive could migrate to the surface and leach out during the molding or extrusion process.
On the positive side, parts made with recycled polymer are often dark color as it is difficult to eliminate pigments. Don’t forget that carbon black absorbs UV and will contribute to the overall UV resistance of your parts!
Do you struggle with your recycled plastics?
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