RECYCLING | ADDITIVES


residence time in the extruder; a longer residence time introduced some branches onto the polymer backbone, which improves melt strength and is beneficial for processability. They concluded that the additive would allow “tunable” processability. For PET, a key measure is intrinsic viscosity.


Polypropylene degrades during reprocessing, and the average molecular weight (MW) typically decreases with each processing cycle. As illustrated in this graph, Nexam’s additive was introduced during the ninth processing cycle to simulate addition to post-consumer recyclate. The additive was able to rebuild the MW of PP. Source: Nexam


has recently submitted requests for food-contact approval from other major global regulatory bodies. Nexam Chemical said that its Reactive Recy- cling additive masterbatches for rPP can tune flow characteristics and enhance processability and quality. The technology elevates the utility of rPP so it doesn’t need to be “downcycled,” the company claims. Nexamite R201 builds molecular weight (ie,


decreases melt flow ratio [MFR]) of PP. Nexamite R203 is an enhanced version that also builds molecular weight of rPP. Nexamite R202, on the other hand, is a vis-breaking additive that increases MFR and reduces molecular weight, if needed to match the process.


Tuning flow A study published in March by researchers from the Department of Applied Science and Technology at Politecnico di Torino, Italy, investigated the impact of thermomechanical degradation on PP micro- structure during multiple extrusion cycles. PP degrades structurally through chain scission that reduces molecular weight, but a reactive extrusion process with Nexam’s additive was able to rebuild the chains. The experiments showed that Nexamite additive is able to prevent breakdown when added to PP and to restore the molecular weight when added to a simulated post-consumer rPP (as shown in the graph). The researchers also found that the additive acted differently depending on the


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Nexam Chemical said its IV-enhancing additives for rPET are seeing expanded use in multiple regions where rPET use is growing. For example, in the US, IV enhancers are being used in PET foamed sheets, that are used for replacing polystyrene in food packaging. In Pakistan’s growing packaging market, locally produced rPET sheets and other types of rPET applications are using the IV enhancers, the company reported in a July press release. Nexam said it is seeing growth also in Australia, Mexico, and South America. Techmer PM’s HiTerra rPET Revive is an additive


concentrate that counteracts the degradation expe- rienced during reprocessing of PET. The additive works by rebuilding the polymer chains to increase viscosity and reduce yellowness. “RPET Revive can allow for a higher regrind/


recycle rate and improve productivity,” said Steve Smith, Techmer PM’s Market Manager for Rigid Packaging, in a release. “We selected the active ingredient to be compatible with PET resins used in fibre and moulding applications. Converters can use it in the production of thermoformed sheets, and the product is showing good potential for use in bottles, as well.” The additive is suitable for food-contact applications. StabiPlus REMAP 00485 from additive supplier


Repi is a liquid additive that is added during PET recycling to maintain the brightness (ie, L-value) of rPET, said Karsten Fritsch, Business Development Manager Thermoplastics at Repi. While anti-yellow- ing additives successfully mask the yellowness that comes from discoloration due to degradation by correcting the b-value, this new functional additive prevents the drop in L-value that is typically seen in rPET. Fritsch explains that the additive can be adjusted depending on the application. The suggested minimum addition rate is 0.134%. The additive does not affect intrinsic viscosity, and it has EU and FDA food contact certifications.


Compatibilisers Compatibilisers are particularly helpful in recycled plastics streams that may contain multiple polymers or small amounts of one polymer as a contaminant of the primary material. (A range of compatibilisers and coupling agents were described in Compound- ing World May 2024 issue.) Most recently, European masterbatch provider Gabriel-Chemie has intro-


October 2024 | PLASTICS RECYCLING WORLD 19


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