Chemicals with unknown toxicity form when polypropylene plastic is heated.

Chemicals with unknown toxicity form when polypropylene plastic is heated.

Jun 25, 2010

Reingruber, E, M Himmelsbach, C Sauer and W Buchberger. 2010. Identification of degradation products of antioxidants in polyolefins by liquid chromatography combined with atmospheric pressure photoionisation mass spectrometry. Polymer Degradation and Stability 95:740-745.

Synopsis by Evan Beach
New chemicals – with unknown toxic properties – are present after heating commercial polypropylene plastics during manufacturing.

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The chemical composition of an everyday plastic could be more complicated than what a list of raw ingredients would suggest, report a group of Austrian chemists.

Their discovery concerns chemicals that manufacturers add to stabilize polypropylene (PP) plastics. The synthetic antioxidant additives break down when exposed to high temperatures typical of the manufacturing process, especially when they are combined with a common mineral filler called talc.

The results of this study add to the body of knowledge about chemicals found in everyday plastics. The findings could be used to more thoroughly assess the implications for environmental and human health.

Antioxidants are added to protect the structure of the plastic.  They are designed to react quickly with oxygen, sacrificing themselves to protect the PP chemical chain.

The discovery of the new chemicals is of concern since they may occur in commercial products where they could migrate out of the plastic and potentially into humans.  Talc-filled PP plastic is typically found in car parts, household appliances, and building materials.

The researchers did not measure the toxicity of the newly discovered chemicals, but their molecular similarity to the controversial product additives BHT and BHA suggests that they merit further study. While still widely used, the synthetic chemicals BHT and BHA have known health effects. They are used as antioxidants in many products, including food, cosmetics, pharmaceuticals, plastics and some petroleum-based greases and lubricants. BHT has been shown to cause mutations, tumors and endocrine effects in test animals. It has been responsible for allergic responses in people. BHA can also mimic the female hormone estrogen.

The researchers tested six commercial antioxidant additives, four of which had structures similar to BHT. In the presence of heat and talc, the additives lost parts of their chemical structures in predictable ways. This predictability means that chemists might be able to anticipate what will happen when new additives are exposed to heat and design for safer breakdown processes.

The chemists showed that although most of the pure additives were stable at 239 degrees Fahrenheit, all of them broke down when talc was present. Some also broke down when blended with the PP.  PP generally melts above 266 F. If the additives were blended into melted plastic, the high temperature would lead to their degradation, and thus, the new low-molecular-weight chemicals.

The observed decrease in molecular weight could lead to faster migration out of the plastic.  This question and the issue of toxicity could be resolved by further study.

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