Irish scientists have revealed it is “the stress” applied in making everyday products such as plastic bottles and containers that causes them to shred minute particles that cause pollution and jeopardise food safety.
Researchers at the Amber Centre in Trinity College have discovered that the way many everyday plastics are manufactured builds unseen stress into the material – stress that later drives the release of tiny plastic particles into our food and the environment.
When factories mould plastics into water pipes, bottles, and household products for food preparation, they cool the molten plastic quickly, so it keeps its shape.
“As it cools, the plastic naturally shrinks, causing a pressure build-up that ultimately gets frozen in as an internal pressure or stress,” said lead researcher Prof John Boland of TCD School of Chemistry at Trinity College.
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Their study published in Nature Communications shows this frozen-in stress causes plastic surfaces to erupt into microscopic blisters. “When these blisters burst open, they shed minute fragments – micropollutants – into the surrounding environment,” he added.
Polyethylene and polypropylene – the two most widely used plastics – account for about 71 per cent of all plastic pollution found in the environment.
By tracing how stress arises during manufacturing, the team uncovered a previously overlooked source of pollutants released from these plastics.
In laboratory tests the scientists deformed flat sheets of polyethylene and polypropylene, mimicking the stress frozen into real products.
Tiny “nanoscale blisters” formed and grew in number and size as the stress level increased, he said, forcing polymer and chemical additives from inside the plastic sheet on to its surface, from where they were released as micropollutants into the environment.
The same type of blisters formed inside commercial polypropylene bottles, especially around the highly stressed neck and cap regions, generating the vast majority of the plastic pollutants detected in the contents of these bottles.
“This discovery shows that frozen-in stress is a critical vulnerability that catalyses plastic degradation and the release of micropollutants,” Prof Boland said.
Low-cost, high-speed manufacturing methods are major contributors to the levels of stress found in plastic products today, he said. Global plastic production now exceeds 400 million tonnes annually, of which 20 million tonnes leaks into the environment.
As a consequence scientists estimate 170 trillion plastic particles are floating in our oceans. Micro and nanoscale plastics have been detected throughout the human body, with significant accumulations in the brain, heart and lungs and in many mammals.
“From standpoint of current manufacturing practices, plastics are naturally prone to falling apart,” Prof Boland said.
“To protect food, water and the wider environment, manufacturers urgently need to develop smart processing technologies that minimise the levels of built-in stress in plastic products,” he said.
