ANTIOXIDANTS & STABILISERS | ADDITIVES
Whether for a few days or a few decades, ensuring plastics maintain their performance throughout their intended lifetime means using effective antioxidant systems. Peter Mapleston reviews the latest developments
Bringing stability to plastics
Plastics have earned a reputation for durability but that is not by chance. Whether for long-life applica- tions such as automotive parts, products intended for just a few years in the field – literally – such as agricultural films, or single-use packaging that is destined – hopefully – for near immediate recycling, plastics need chemical additives to provide sufficient stability to survive processing and intended use. Polyolefins are key beneficiaries of such additives: antioxidants, UV absorbers, and hindered amine light (HALS), and heat stabilisers. Additive suppliers continue to make progress in developing products for this sector that are better performing, more cost-effective, and safer. Plastics deteriorate over time as a result of the polymer chains reacting with oxygen via autocata- lytic reactions. Antioxidants, added at a sufficient concentration, slow down these oxidation reactions. “With an increased focus on recycling polymers it has become important to reconsider what consti- tutes ‘sufficient stabilisation’ for even single-use short service-life applications,” says Dr Niall Marshall, Technical Manager with Everspring Middle East (part of Taiwanese producer Everspring Chemical). “As the volume of polymer to be recycled
increases –the European Commission’s Strategy for Plastics in a Circular Economy envisages that all
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plastic packaging will be recyclable by 2030 – the quality of the recyclate will become more important as it finds uses in more demanding applications. The stabilisation system will be required to protect the polymer during processing, use and reprocessing.” Marshall notes that in applications with short service lives such as packaging, the stabilisation requirements for processing are more demanding than those for the service life. For such cases, Everspring offers customised combinations of well-proven stabilisers such as its Evernox range of hindered phenolic antioxidants and Everfos phosphites, together with what he says are highly effective boosters such as Everstab FS042, a dialkyl hydroxylamine which acts as a catalytic chain- breaking radical scavenger. Recent work carried out by Everspring as part of a study with a plastics recycler has shown that while the same families of stabilisers, with their proven performance and broad regulatory approvals, are able to meet future requirements of stabilising the polymer sufficiently to allow for successful post-use recycling, there are some additional factors which need to be taken into account. “Even virgin polymer which appears to have the same levels of stabiliser performance after five extrusions is found to have a significantly different
Main image: Surface crazing is one of the most immedi- ately visible signs of inadequate polymer stabilisation
September 2018 | COMPOUNDING WORLD 39
PHOTO: SHUTTERSTOCK
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