Nuclear techniques to recycle plastics and promote the circular economy

Plastic pollution is one of today's biggest environmental problems and nuclear technology can help to convert plastic waste into raw materials, thereby promoting a more sustainable and raw material-efficient circular economy.

Traditional plastics recycling

Plastic recycling operations generally do not use radiation and, while very useful, are only suitable for products with less demanding technical requirements, such as school chairs.

Plastic waste is usually mixed plastics, mostly household waste such as single-use packaging. As a mixture of various types of plastics with different properties, they are very difficult to recycle.

To recycle mixed plastics, they are first cleaned and shredded and then mixed in different proportions (soft and hard plastics) together with an aluminium base to control the density of the final product. This mixture is fed into an extruder, where it is melted and homogenised at a temperature of 150-200 degrees Celsius (high enough to melt the plastic, but not so high as to degrade it). This limits the release of toxic gases.

But the properties of this final product are limited and it is only suitable for creating commodity products.

Recycling of mixed plastics with radiation

If recycled plastic had better thermo-mechanical properties, i.e. more plasticity, the possibilities would be much greater. It would open up a demand and a market for recycled plastic by radiation at the industrial level, which in turn would reduce the demand for virgin plastics.

Radiation can increase the thermo-mechanical properties of mixed recycled plastics. This creates a much wider and more versatile range of plastic reuse possibilities.

At the Philippine Nuclear Research Institute (PNRI) in Davao, in the south of the country, and with the help of the International Atomic Energy Agency (IAEA), a special programme for recycling plastics using nuclear radiation techniques has been launched.

First, small plastic pellets are placed in a container. The container is placed in a small, self-protected irradiation device (larger devices will be needed on an industrial scale).

The plastic pellets are irradiated until they receive a predetermined optimal dose. During irradiation, the polymers in the plastic become more reactive, which means that when the plastic is melted, structural changes in the polymers will occur, and it will also be easier to mix the different components found in the waste.

These irradiated pellets are mixed with the shredded mixed plastic, and then the same plastic extrusion and melting steps are performed, only this time with the addition of radiation-modified natural fibres.

Once homogenised and melted, the plastic is placed in cold water to cool it and then fed into a machine that cuts it into very small pieces. The result is a much stronger plastic that retains its original rigidity and hardness.

These plastic chips are ready for a wide variety of uses, including high-value-added products such as building materials and mechanical parts.

Once this technology has been adapted on an industrial scale, it will be of great help in promoting a circular economy and maintaining beaches and oceans.

In the future, the technique can be deployed in many other places to help protect the environment and reduce plastic pollution.