This is how plastic packaging is sorted for recycling

Plastics dominate the packaging market today and have largely replaced other, traditional packaging materials. Different plastics are used in production, depending on the area of application for which the respective packaging is intended.

This raises the problem of how the different types can be separated and sorted from each other as quickly, cost-effectively and accurately as possible before recycling, because perfect pre-separation on the consumer side cannot be realized at present. The following article describes diverse plastics as well as recycling processes and shows methods of sorting.

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What are the plastics for packaging?

The consumption of plastics in Europe for various applications amounts to around 57 million t per year as of 2021, 15 million t of which are in Germany.

The material is used for short-life packaging, for example, for food, but also for long-life products for the automotive industry, the construction industry, household goods and electrical appliances. The most common types are polymers, namely:

• Polypropylene (PP)
• Polyethylene (PE); mainly as PE-LD (LD = Low Density) and PE-HD (High Density).
• Polyethylene terephthalate (PET)
• Polystyrene (PS)
• Polyvinyl chloride (PVC)
• Polyurethane (PUR).

What role does recycling play in plastics?

Similar to waste paper, electrical appliances or construction waste, the recycling of plastics is a central issue in everyday life and at the same time a global problem. With a worldwide annual production of 391 million tons, you can easily imagine how much waste this creates.

Since most plastics are not biodegradable and have a decay time of between 20 and 1,000 years, it quickly becomes clear how important recycling is for this material.

Plastic waste is not only a challenging environmental problem, for example when you consider the pollution of the oceans and seas with plastic particles.

The huge production volumes consume equally huge amounts of natural resources, which will soon no longer be available without efficient recycling.

In addition, many toxic gases are released when plastic waste simply goes into an incinerator.

So the main advantages of plastic recycling are:

• Resource consumption of crude oil and natural gas is reduced.
• Plastic does not end up in nature or in the oceans, or at least in smaller quantities.
• Recycling instead of incineration reduces greenhouse gas emissions.
• Products and packaging made from recycled plastic have the same qualities as virgin material.

Recycling techniques for plastics

The technical standard in Germany makes it possible to sort plastic waste in state-of-the-art facilities. The various types, such as PE, PET, PS, etc., are separated by type and then compressed into large bales before being delivered to the manufacturing companies.

Because of the wide range of plastic types, the recycling industry uses four different methods:

• mechanical recycling
• thermal recycling
• chemical recycling
• biological recycling

Of the just over six million tons of recycled plastic waste in 2019, 46.6 percent (2.93 million tons) was recycled for materials and raw materials. 52.8 percent (3.31 million t) went to thermal recovery and was incinerated to generate electricity and heat. The remaining 0.6 percent or 40,000 t ended up in landfills.

Mechanical recycling

Mechanical or mechanical recycling turns plastic waste into so-called secondary materials. To do this, the plastics are first shredded, then washed and dried. The small parts are melted down in an extruder and then processed into granules with a uniform grain size.

The chemical structures are retained in the process. Mechanically recycled plastics are used to make new products such as packaging, components for vehicles and electrical appliances, or even furniture.

Thermal recycling

The basic idea behind thermal recycling is to utilize the heat potential of different plastics by incinerating them. During incineration, it does not matter if the waste is not sorted by type or if it is contaminated.

The energy yield is then used to generate electricity, steam or district heating. In this way, certain amounts of primary fuels such as oil, gas and coal can be saved.

Chemical recycling

Chemical recycling often comes into play when plastic waste cannot be properly recycled to the required standards using mechanical processes for environmental or economic reasons.

The original building blocks such as polymers, monomers and atoms are broken down so that the chemical structure of the waste is changed. The building blocks can then be used to produce either new plastics, but also fuels and chemicals. One disadvantage of this method is that it requires a lot of energy.

Four processes are available for the chemical recycling of plastic waste:

• Solvolysis (reaction with solvents)
• Depolymerization (thermal)
• Pyrolysis (decomposition of hydrocarbons)
• Gasification.

Biological recycling

Biological recycling by composting plastic waste is possible if the starting product was made from renewable raw materials. However, the degradation takes several years and therefore proceeds quite slowly.

The proportion of biobased and thus also biodegradable plastics worldwide has so far been negligible, at around three million metric tons compared with the 391 million metric tons of conventional plastics mentioned above.

Sorting techniques for plastics

Sorting plastic waste is an essential prerequisite for a successful recycling process. Clean and unmixed recyclables achieve the best results in the subsequent recycling steps and therefore have great value-added potential.

The extensive production of plastics in Germany and the masses of plastic waste require high-quality, state-of-the-art sorting facilities in order to build and maintain a sustainable infrastructure.

The first step of sorting is in the hands of the consumer. The more plastic waste is already separated and properly disposed of in the household, the easier it will be later to separate it by machine in recycling plants to obtain sorted material.

Here, so-called near-infrared scanners are primarily used to detect and distinguish between all materials that are processed for packaging.

The sorting by near infrared spectroscopy (NIRS)

The NIRS process is a spectroscopic technology that provides a fast and easy-to-trace measurement method to detect all packaging materials. Here, a near-infrared sensor measures the reflected light of the valuable material.

The signal coming back then allows a clear classification of each individual plastic. Of course, it would be ideal if only monomaterials were used for packaging, as these are the easiest to recycle. This is where the producers in the packaging industry are called upon.

Near-infrared spectroscopy is the dominant technique for sorting plastic waste in the recycling process for a number of reasons. First, it is very fast and can provide results within milliseconds. Mobile NIR scanners take slightly longer at two to three seconds.

Secondly, it works non-destructively, so that the analyzed plastic can be recycled without further ado. And thirdly - this is very important - NIRS can identify a wide range of different plastics, which makes recycling much more efficient.

In the recycling of plastic waste, NIR spectroscopy is mainly used in two ways. First, it helps to classify the plastic waste into different categories by detecting the absorption bands and using the corresponding information for separation.

Secondly, NIRS makes it possible to determine the degree of purity of plastics. Here, the absorption of infrared radiation is measured at different wavelengths and then compared with a standard model.

Which substances must be separated from each other?

When recycling plastic waste, the main thing is to separate the different types of plastic. However, there is also packaging and components that contain other materials besides plastic, for example paper and cardboard or various metals, possibly also glass and wood. Here, too, separation must take place in order to obtain flawless granulate after recycling.

Challenges in sorting and recycling - and how can they be overcome?

The first challenge is the large amount of plastic waste. In order to recycle them all, an appropriate infrastructure of suitable plants must be available or created.

In addition, packaging manufacturers can take care to simplify the recycling process as early as the design and manufacture of their products by avoiding mixing different plastics or combining them with other materials.

High-tech facilities are required for sorting, which - globally speaking - has so far only been possible in a few countries that have the relevant know-how and the necessary capital to build such facilities.

Conclusion

Techniques are now available for sorting and recycling plastic waste that enable it to be recycled efficiently and quickly. However, there is still a lot of room for improvement here, because so far only around 55 percent of waste in Germany is used for new purposes. In less industrialized countries, the proportion is significantly lower. A rethink among producers, but also among consumers, is urgently recommended for the future.

FAQ

1. How much plastic waste is produced in Germany every year and how is it recycled?

   In 2019, around 6.5 million tons of plastic waste was generated in this country. Of this, 46.6 percent was recycled for materials and raw materials and 52.8 percent was thermally recycled. The remaining 0.6 percent was disposed of in landfills.

2. Which process is particularly suitable for sorting plastic waste?

   Near-infrared spectroscopy is particularly well suited for fast and uncomplicated sorting. Infrared sensors are used to analyze the reflected light of the plastics, which allows clear classification.

 

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