RECYCLING | ADDITIVES
Additives key to upcycling
Recycling plastics back into high value applications can present challenges but additive technologies are available to help fix processing, performance and odour issues, writes Jennifer Markarian
The plastics industry has long been reprocessing much of its process scrap and a good trade has developed in post-industrial recyclate, but the growing mandate to recycle more means taking on post-consumer recyclate (PCR). That presents a number of challenges – PCR is a high variability feedstream that is typically comprised of a mix of resin types and colours with varying rheologies. In addition, the levels of additives remaining in the polymer are unknown and that must be given serious consideration. And there is a high possibil- ity of bad odours and organic contaminants. It is a daunting prospect. Fortunately, additive suppliers already have a handle on these problems. Many are working to put forward new products targeted to the industry need to move beyond recycling to upcycling. Part of that process it to educate recyclers and recom- pounders, who – especially in the US where PCR recycling is less widely practiced than in Europe – may be new to the benefits additives provide. While demand for polymer additives is currently higher among European recyclers than those in the US, the US recycling industry is changing, says Robert Keller, Sustainability Manager at BASF Plastic Additives. “As public awareness and advocacy increases in the US, interest in increased recycling and re-use is gaining momentum, as evidenced by
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increased investments and acquisitions in the recycling industry and infrastructure,” he says. BASF researchers have developed additive
formulations to enable “ready for recycle” virgin HDPE that is sufficiently well stabilised to maintain its properties through multiple extrusion steps. The degradation pathway of the HDPE under investiga- tion was molecular weight increase and molecular weight distribution broadening and the researchers identified formulations that yield optimal molecular weight retention using a combination of a phos- phite, phenolic antioxidant, and Irganox E201 (Vitamin E). They also found that formulations that provided the best melt flow control tended to be slightly more discoloured, with a higher yellowness index and more gas fade discolouration. However, they point out that colour is not typically critical in many applications using recycled resin. Keller says that post-industrial plastics, with their
better quality and more consistent supply, are already more broadly recycled than post-consumer resins. However, these novel additive solutions for PCR “aim to address the address variability in material quality and the polymer degradation accumulated over their lifetime of light and heat exposure.” BASF’s researchers have investigated the antioxi- dant and light stabiliser combinations needed to
October 2019 | COMPOUNDING WORLD 31
Main image: Even the best mechanical technologies will struggle to create high value plastics from PCR without additive modification
PHOTO: SHUTTERSTOCK
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