Difficulties sorting black plastics are prevalent for recyclers due to their ‘invisible’ properties when passing through current analytical sorting systems.
But a new technology has been developed by researchers in Germany which can detect black plastics, making sorting large quantities cheaper and easier - and it’s soon to be available as an effective and affordable solution.
With an approximate 4% rise every year in global plastic production since 2011, and plastic production reaching 311 million tonnes in 2014, the demand to manage plastic waste is increasing and becoming even more of a concern. Many EU countries for example still use the landfill option over recycling and regeneration - which resulted in 8 million tonnes of plastic being sent to European landfill in 2014.
For a while, plastic recyclers have been struggling to sort black plastics into material type compared to other coloured plastics. Black plastics, often used in large items such as car instrument panels, motorcycle exteriors and in construction (as they have the best UV resistance), contain soot which gives it it’s dark colour.
This carbon black pigment absorbs the light used by optical sorting systems, resulting in little or no light being reflected back to the detector - making them essentially invisible. Because of this the computer is unable to identify where it is on the conveyor belt, let alone what type of plastic it is made from.
On top of the problems of increasing plastic production and the continual use of landfill, there is an additional demand for black plastic recycling due to an increase in automotive recycling programs and legislation across the EU.
An affordable plastic sorting system
A team from the Fraunhofer Institute has developed a new system in which black plastic can be detected and therefore sorted. The added bonuses are that it is cheaper, is able to work with large quantities, and is much more affordable than the machines currently being used with high frequency cameras.
“For the first time, we have developed an affordable sorting system that detects every plastic colour, including black, both in real time and in large quantities.”
Professor Thomas Längle, Head of department at Fraunhofer IOSB
Currently, electromagnetic waves near the infrared range are used but this new method uses lower frequency radiation (terahertz), between microwaves and radio waves. This new process is colour independent, allowing black plastics to be sensed.
The different types of plastic shreds can be distinguished within milliseconds whilst travelling at a speed of around 2-3 m/s along a conveyor belt. When a non-recyclable material is discovered, the intelligent computer algorithm signals the use of a blast of air, along with a colour camera for more precision, knocking them off the belt.
Good news for recyclers
In terms of precision, it is less accurate than the high frequency cameras but they are often too expensive for recyclers, costing in the region of€1,000,000. Despite this, the new system works at 98-99% accuracy, and is self-learning so this increases over time. With the added ability to sort black plastic in to material types in large quantities and at an affordable price - between 0.1% and 1% of the price of a high frequency camera currently used - this new technology is likely to be very popular.
An additional benefit is that this new technology isn’t only limited to recycling applications and fighting plastic waste. With slight adjustments it can be applied to processes that use conveyor belts and require categorisation, like the food production industry for example. The Fraunhofer researchers are hoping that this technology will be available in 2017, with it ready for general market release by the end of that year.
Good news for producers
Lowering the cost of sorting systems should lead to major improvements in the plastic recycling industry. Traditionally when the price of PRNs rise, recyclers will try to increase their output to maximise the revenue they can obtain at this higher price. This in turn leads to more supply of PRNs onto the market, causing the price to fall. Usually, within the plastic market, the period from price rise to price fall is around 3-4 quarters. This has an impact on producer’s yearly compliance costs. This new technology should help reduce this time period.
In the past, when prices started to rise, recyclers would not be able to consider major capital investment in machinery, due to the prohibitive costs (€1,000,000). With an investment cost of 1% of this, investing in machinery to fulfil demand and increase output should be far more viable. This could see the impact of higher prices last a much shorter time period.
Finally, the reduction in the costs of machinery will reduce the costs of recycled plastic as a material. This could help it to compete with the low virgin plastic prices the sector is experiencing and help to remove the sectors dependence on PRN revenues in times of perceived crisis.
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