Image description: Plastic items littered on a beach with waves in the background.

Researchers at the Amber Centre in Trinity College have revealed “the stress” applied in making everyday products such as plastic bottles and containers that causes them to shred micro-plastic particles, ending up in the environment and bodies.

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. This frozen-in stress causes plastic surfaces to erupt into microscopic blisters, which shed minute fragments when they burst open, that ultimately pollute food and the environment.

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. Polyethylene and polypropylene are two of the most widely used plastics and 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. “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.