An integrated approach to sorting

We all know the issues created by plastic waste. Now more than ever, emphasis is being placed on handling this resource in a responsible, sustainable manner to ensure plastics can be recycled. Plus, with new regulations being introduced regarding recycled content used in plastic bottles in particular, a new approach to recycling is imperative.

For this to happen, though, we must implement efficient recycling processes so the plastics are handled correctly and the highest possible purity can be achieved.

Plant operators are opting for high-efficiency solutions, which today can include fully integrated presorting and flake-sorting lines from a single manufacturer rather than a mix-and-match lineup from different suppliers.

The strain on recycling plants

The rate of plastic production continues to rise on a global scale. The latest figures suggest more than 396 million tons of plastics were produced for the global marketplace in 2018, a 3.2 percent increase compared with the previous year, according to Statista.

But most of this plastic does not have a long-term future. In Europe alone, almost 40 percent of plastics produced are used for food and product packaging, according to the PlasticsEurope trade association, which is typically single-use plastic. Most of these products are being incinerated or disposed of in landfills. This means more pressure is being placed on plastics producers and retailers than ever before.

With this rise in production comes the need for efficient recycling systems to ensure plastics are handled correctly and brought back into the loop.

Higher purity is needed to ensure material is of a sufficient quality to meet regulations, too. Recycled-content laws introduced in October 2018 in the European Union mean that packaging producers must now ensure plastic bottles have a minimum of 25 percent recycled content by 2025. Reprocessing plant operators must employ systems that can increase the purity and yield of their recycled plastics to a level that is suitable for use in food packaging.

Using the efficiencies of flake sorting

Flake sorting could help reprocessors improve the purity and yield of their recycled plastics.

Currently, polyolefins are in high demand, but recycling levels for some of the thermoplastics within this polymer family are still very low. Polyolefins include polypropylene (PP) and polyethylene (PE) and its variations, such as high-density polyethylene and low-density polyethylene. Although the market for high-quality recycled plastics traditionally has been more focused on polyethylene terephthalate (PET), demand for recycled polyolefins signals their importance to the market and the need to recycle these materials efficiently.

To further accelerate recycling rates and output quality, plant operators could rely on flake sorting—a technique that already is used in PET recycling plants and can be the difference between downcycling and upgrading plastics.

The flake sorting process for PET bottles involves a series of steps: After a first step of presorting by color and material type and a subsequent washing process, the bottles are put into a grinder or shredder and turned into flakes. Once the bottles have been reduced in size, the resulting flakes can contain PP and PE (which come mostly from the bottle caps), pieces of metal, polyvinyl chloride from remaining labels and small quantities of other contaminants. The flakes then go through a vigorous cleaning process that involves different combinations of metal separators, sieves and air separators—called wind-sifters—and multiple steps of floatation, hot and cold washing, rinsing and drying. These steps further reduce contamination.

Even though the above process is very effective, small amounts of contaminants can remain in the recycled PET flake because of their size, density or magnetic characteristics. These small impurities and color deviations can negatively affect the recycled pellets, which are typically used to make another PET beverage bottle. Sorting out all the impurities to generate recycled PET pellets that have the same quality as virgin plastics should be the goal. A high-technology, sensor-based solution could purify the flakes up to the required standards and remove any remaining contaminants.

A different approach

Implementing a flake sorting machine alone might not help to improve the overall yield and purity of the recycled plastics unless it is part of a carefully integrated solution.

To achieve the highest purities, operators could benefit from a system that integrates presorting and flake sorting, ideally using technology manufactured by the same company. Presorting separates plastic bottles from other types of plastic but also sorts them by color. A precise presorting process is important because it reduces the bulk of color and material contamination. When the resulting bottles are shredded and turned into flake, the amount of remaining contamination is managed more easily by the sensors of the flake sorter, which are designed to detect and remove the small contaminants that are generated during the shredding process.

Using optical sorting systems from the same manufacturer to presort the plastics prior to the flake sorting step can enable the fine-tuning of both sorting operations according to the input material and level of contamination. This is crucial to improving the final product and to reaching new levels of purity while increasing the overall efficiency and yield of the process.

Plant operator benefits

By using an integrated approach to optical sorting, plant operators can realize numerous improvements operationally and financially. An efficient presorting process prior to flake sorting can help reduce the need for manual sorting, which supports decreased operational costs (or means human resources can be used elsewhere within the recycling plant).

In addition, by using one supplier for the presorting and flake sorting machines, higher levels of accuracy could be achieved because the solutions are built to work in unison. Maintenance also can be streamlined, which could mean less downtime and increased overall capacity.

For companies to meet recycled-content mandates and pledges, a new approach to recycling could be beneficial. Modern, highly integrated presorting and flake sorting solutions can contribute to the future of plastics recycling.

Tom Eng is senior vice president and head of Tomra Sorting Recycling.