The addition of stabilizers is essential for maintaining the value and properties of plastics after they are recycled. However, the kind and quantity of stabilizers that are needed can vary according to the resin involved and the purpose for which it will be used.
“The reason for stabilizers is, of course, they interrupt the natural degradation process for plastics through oxidation,” says Rudolf Pfaendner, division director for plastics at the Fraunhofer Institute for Structural Durability and System Reliability, based in Darmstadt, Germany. “By doing this, you get a material which can be processed thermally at high temperatures and which will last for many years.”
Processing stabilizers, long-term heat stabilizers and UV and light stabilizers are the most commonly added. While stabilizers sometimes are added when virgin plastic is produced and compounded, recyclers cannot assume the protection still is effective because it degrades over time, especially when plastics are reprocessed. The resulting plastic would exhibit inferior properties. For example, plastic that is used outdoors without the additional protection of a stabilizer can develop cracks and fade.
“That’s the risk you face if you don’t add the right amount of stabilizers for the applications you are going for,” says Pfaendner.
He says another challenge is that in most cases, recyclers don’t know
“The reason for stabilizers is, of course, they interrupt the natural degradation process for plastics through oxidation. By doing this, you get a material which can be processed thermally at high temperatures and which will last for many years.” -- Rudolf Pfaendner, Fraunhofer Institute
Songwon, a Korea-based plastic additives company with U.S. operations headquartered in Friendswood, Texas, cites a case in which a polymer that was used in a packaging application with a short lifetime requirement is recycled and returned to the processing stream for automotive applications. In that case, Songwon says, it would recommend a customer add its Songnox 3001-2, a long-term stabilizer.
Preserving molecular weight
Repeated recycling also can damage polymers through molecular weight degradation. Certain stabilizers can help preserve molecular weight, which is essential for mechanical characteristics. For example, Songwon says its Songnox 21B stabilizer protects the molecular weight of polymers, including polypropylene (PP) and polyethylene (PE), during processing.
In partnership with chemicals manufacturer Sabo SpA,
Within the past couple of years, Pfaendner says he has seen an increase in the availability of new stabilizers designed specifically for recyclers.
“There are more and more companies like Baerlocher, PolyAd Services [headquartered in Bensheim, Germany] and Mitsui [Chemicals] [headquartered in Tokyo] that offer products specially designed for recycled materials,” Pfaendner says. The companies put together specific stabilizer combinations that typically are needed for recycling, making it easier for recyclers than buying stabilizers separately. The prepackaged combinations also are designed to ensure proper dosing.
Baerlocher, with global headquarters in Unterschleissheim, Germany, and U.S. locations in Cincinnati and Dover, Ohio, offers custom
While stabilizers sometimes are added when virgin plastic is produced and compounded, recyclers cannot assume the protection still is effective because it degrades over time, especially when plastics are reprocessed.
Baerlocher says its
Some recyclers are reluctant to add stabilizers because of cost, but Pfaendner says it isn’t always necessary to add a lot of them.
“In any case, whenever you recycle and process, the addition of
For more information: Baerlocher USA, 513-482-6300, www.baerlocherusa.com; Fraunhofer Institute for Structural Durability and System Reliability LBF, 49-6151-705-0, www.lbf.fraunhofer.de/en.html; Songwon, 281-648-1585, www.songwon.com