A team from Iowa State University’s Polymer and Food Protection Consortium published results in Advances in Materials Science and Engineering about cleaning recyclable plastic. The study focuses on polypropylene (No. 5) flakes from dairy tubs and other food packaging and tests typical industrial washing practices.
Scientists compared physical agitation, agitation with sodium hydroxide, ultrasonic vibration, and sodium hydroxide with an industrial detergent. No detectable phthalates or bisphenols appeared after physical agitation alone or agitation plus sodium hydroxide. However, ultrasonic vibration and the sodium hydroxide plus detergent method released two phthalates into the wash water: di(2-ethylhexyl) phthalate (DEHP) and di-cyclohexyl phthalate (DCHP).
The team also simulated how wash water is reused. Using the sodium hydroxide plus detergent method with the same water for 15 cycles, they measured rising DEHP levels: 10 times the drinking-water limit after the first wash and 25 times after 15 cycles. At the same time, detergent concentration fell, suggesting the flakes absorbed some cleaner. The authors, Greg Curtzwiler and Keith Vorst, say the findings reveal gaps in knowledge about cleaning and wash-water management and point to health concerns linked to phthalates.
Possible treatments under study include foam fractionation, electro-oxidation, and a bio-based treatment using carbon nano-onions. Reducing water use by better sorting or low-water cleaning could help, but changes must be economically viable. Funding came in part from the Institute for the Advancement of Food and Nutrition Sciences.
Difficult words
- phthalate — chemical in plastics that can harm healthphthalates
- polypropylene — a common plastic used for food containers
- sodium hydroxide — a strong chemical often used for cleaning
- ultrasonic — very fast sound waves used to cleanultrasonic vibration
- detergent — a chemical soap used to remove dirt
- absorb — to take in a liquid or substanceabsorbed
- viable — possible to do and economically acceptable
Tip: hover, focus or tap highlighted words in the article to see quick definitions while you read or listen.
Discussion questions
- Do you think reusing wash water for recycling is acceptable if it reduces water use? Why or why not?
- What practical changes could recycling centres make to reduce chemical risks from cleaning?
- How could better sorting before washing help reduce water use or contamination?
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