Significantly more plastics are to be recycled in the European Union in the future. This is the target set by the European Commission in its second action plan for the circular economy. Currently, only around a third of plastic waste in the EU is recycled. The global recycling rate is not even 10 per cent. To change this in the future, technology is needed to optimise the dosing, transport and processing of waste. It must become faster, more accurate and more cost-effective. There is potential in chemical recycling in particular.
What role does plastics recycling play in the circular economy?
Plastics are light and sturdy. Nevertheless, they have fallen into disrepute in recent years. Photos of plastic bags and bottles in the world's oceans have characterised the negative image of the material. More than 20 percent of the world's plastic waste still ends up in the environment. Yet this waste is ideal for resource-saving recycling. Thanks to modern technology, the raw materials can now be recycled several times and kept in the circular economy for a long time. Environmentally harmful landfilling is no longer necessary. A ban on this form of disposal has been under discussion in EU bodies for some time.
In its "Green Deal", the European Union has formulated the goal of achieving a circular economy by 2050. An increase in the recycling rate of plastic packaging should contribute to this. This is to rise to 60 percent in the member states by 2030. In order to achieve this, the industry also needs to make several adjustments.
Options for recycling plastic waste
Plastic waste can be turned into new plastic products. This reduces CO2 emissions and promotes a sustainable circular economy. A distinction is made between mechanical and chemical recycling methods. The third option is incineration as alternative fuel.
Mechanical recycling
In mechanical recycling the plastic waste is first thoroughly sorted, washed and shredded. The preconditioned flakes are then melted, filtered and granulated after the addition of additives and, if necessary, fillers. The resulting plastic granulate can be processed into new products as recyclate. Mechanical plastics recycling is the preferred form of recycling according to politics and legislation. The energy requirement for mechanical recycling is significantly lower than for chemical recycling. However, it is only suitable for unmixed plastic waste such as industrial packaging or plastic bottles. Such products make up a large proportion of the world's plastic waste. However, there are also numerous other articles in which plastics are processed and for which recycling is more difficult.
Chemical recycling
If plastic waste cannot be sufficiently sorted or cleaned, it can be recycled as a feedstock. In chemical recycling, the polymers are broken down using thermal energy. Common processes include pyrolysis and gasification. This produces synthetic oils and gases, which can be used instead of fossil feedstock for the production of virgin plastics. These in turn are suitable for the manufacture of products with high hygiene requirements, such as food packaging or items used in medical applications. The higher energy requirement for chemical recycling has long hindered its commercial utilisation. Recently has progress been made, with the result that feedstock recycling is now considered an alternative to incineration. More efficient processes, the increasing use of renewable energy in processing and an overall rise in demand for recycled products have improved the framework conditions for chemical recycling. Rising CO2 prices are also increasing the financial attractiveness of recycling, as incineration is becoming more expensive.
Utilisation as fuel
If it is not possible to separate waste sufficiently, for example because plastic is mixed with organic waste, the last option is incineration. In the interests of a sustainable circular economy, this should be avoided wherever possible. It is used in the cement industry, for example. Waste is used there as an alternative fuel that helps to reduce the use of fossil fuels.
Challenges when dosing waste
In recycling processes, the consistent dosing of bulk materials with highly fluctuating properties is a challenge. Precise and continuous feeding and reliable operation are crucial to ensure efficient processing. When handling shredded plastics and mixed waste, a number of special features need to be taken into account.
Fluctuating composition and quality
When it comes to plastics recycling, most people first think of plastic bottles and shopping bags. However, polymers have numerous other uses, for example as a building material, in vehicle production or in household appliances. In such cases, the plastic is already mixed with other raw materials during production. The materials can no longer be easily separated later on. Particularly problematic in recycling are foreign bodies (e.g. stones), which can damage machines, and toxic substances, which must not enter the circular economy. For this reason, inadequately separated waste or waste from hospitals, for example, are not suitable for mechanical recycling.
Poor flow properties
The low bulk density of plastic waste makes dosing and transporting the material difficult. Backlogs or blockages can occur when feeding to machines (reactors, extruders or ovens). In some cases, bridges form in the product, preventing free discharge. Compared to other bulk materials, the light and poorly flowing material is more difficult to handle. The flow properties of mixed plastic waste in particular can vary greatly. Reliable and accurate dosing is essential for a continuous process
High volume and low density
The low weight of plastics is a disadvantage when it comes to recycling. The material has a high volume and low density, which makes transporting and processing the waste challenging.
How to overcome the challenges
Chemical recycling is still in the development stage in most countries. However, the dosing of poorly or barely sorted waste has already been tried and tested in other industries. The cement industry is a good example. More and more plants there are using alternative fuels to fire their clinker kilns. Waste of various origins and in varying mixing ratios is used for this purpose. Manufacturers such as Qlar have test centres in which the flow properties of the fuels are examined in order to select the appropriate machine components. The knowledge from the cement industry can be used as transfer knowledge to optimise the processes in chemical recycling. The company also has many years of experience in mechanical recycling and can also contribute this expertise in a profitable way. In the course of the "Green Deal", this networked knowledge is becoming even more important.
Conclusion: These are the future requirements
Plastics recycling is becoming increasingly important as an environmental protection measure. In order to achieve circular economy, more waste should be recycled. Manufacturing processes must become faster without sacrificing accuracy.
Mechanical engineering needs solutions for the increased requirements. Software also plays an important role here. Modern dosing solutions already have complex control systems that record a large number of process parameters and therefore offer great potential for digital and intelligent solutions. Ideally, smart machines will be able to react independently to changes in flow properties and adjust settings using artificial intelligence (AI) based on this collected data. In other industries, such as cement production, problematic waste is already being processed. Manufacturers with the relevant experience can utilise this transfer knowledge for plastics recycling.
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