Chemical recycling vs. mechanical recycling: differences, opportunities and challenges

Recycling is a key building block of the circular economy. But not all plastic recycling is the same: alongside the widespread mechanical recycling, chemical recycling is becoming increasingly important – especially for hard-to-recover plastic waste from industry, commerce or households. The objective of both methods is identical – to keep plastics in the loop and save raw materials – but the approaches differ fundamentally.

In this article we compare the two processes in detail, explain which plastics are suitable for each, where the limits lie and what role these processes could play in the plastics industry in future. Particular attention is paid to engineering plastics, which are used in demanding applications and place high requirements on material quality and purity.

Criterion	Mechanical recycling	Chemical recycling
Process	Melting down	Breakdown into raw materials
Energy demand	low	higher
Costs	lower	higher
Purity of type	required	less critical
Quality	can decrease	often virgin-material level
Application	standard plastics	hard-to-recover plastics

What is mechanical recycling?

Mechanical recycling is a physical processing method. The plastic is not chemically altered, but mechanically converted into smaller components such as regranulate or ground material, which can then be used again in plastics processing – e.g. for injection moulding, extrusion or thermoforming processes.

Typical process steps are:

1. Sorting by plastic type (manual or automated, e.g. by near-infrared sensor technology)
2. Size reduction (e.g. shredding, grinding)
3. Cleaning (washing, separating foreign matter)
4. Drying
5. Extrusion into regranulate or direct use as ground material

A prerequisite for a high-quality result is an input stream that is as pure in type and clean as possible. Contaminated, mixed or heavily degraded plastics can only be mechanically recycled to a limited extent. With repeated recycling, material quality can also decrease due to thermal stress and chain degradation.

What is chemical recycling?

In contrast to the mechanical process, chemical recycling aims at a material recovery of the molecular structure. The polymers are broken down into their basic building blocks so that these can be used again as starting materials for new plastics or other chemical products. The result is a recyclate that can achieve virgin-material quality.

The most important processes are:

• Pyrolysis: Thermal decomposition of plastics at high temperatures in an oxygen-free atmosphere into oil or gas mixtures.
• Depolymerisation: Breakdown of polymers (e.g. PET, PA) into monomers by targeted chemical reaction.
• Solvolysis: Dissolution of certain polymers in solvents, usually with catalysts.
• Gasification: Production of synthesis gas from plastic waste for further use in the chemical industry.

The major advantage: even heavily contaminated, mixed or non-separable plastic fractions – such as multilayer films or end-of-life products containing fillers – can be processed. This means chemical recycling can be used in particular where the mechanical process reaches its limits.

Why is chemical recycling used for hard-to-recover plastics?

Many plastic waste streams can only be mechanically recycled to a limited extent. These include contaminated plastics, composite materials, multilayer packaging or mixed plastic fractions that are difficult to separate by type. With these materials, mechanical recycling often reaches technical and economic limits.

This is precisely where chemical recycling comes in. Through processes such as pyrolysis, depolymerisation or gasification, the plastics are broken down into their chemical basic components. This means that plastic waste that is unsuitable for classic recycling processes can also be recovered.

Particularly in the packaging industry, large quantities of complex materials are generated that consist of several plastic types or additional layers. Engineering plastics from mechanical engineering, the automotive industry or electronics also often contain material combinations that make separation by type more difficult. Chemical recycling opens up additional recovery options for these material streams.

A further advantage is that new plastics of high quality can be produced from the raw materials obtained. This allows valuable resources to be kept in the loop and reduces the amount of plastic waste that would otherwise have to be recovered for energy or disposed of.

For this reason, chemical recycling is regarded as an important complement to mechanical recycling and as a key building block for as closed a circular economy as possible for plastics.

Comparison: chemical vs. mechanical recycling

Criterion	Mechanical recycling	Chemical recycling
Technology	Physical processing	Molecular or chemical breakdown
Suitability for	Pure-in-type, clean plastics	Material streams with contaminants, composites, residues
Quality of the recyclate	Limited, mostly for lower-grade products	Close to virgin-material quality (depending on process)
Energy input	Relatively low	Significantly higher, depending on the process
CO₂ balance	Good to very good	Varies, depending on energy sources
Scalability	High – established plants	Still being built up, few large-scale plants
Costs	Lower	Higher (currently)
Regulation / recognition	Established, legally clear	Partly still legally unclear (e.g. EU targets)

Advantages of mechanical recycling

Low costs and energy consumption

Mechanical processes are established, efficient and associated with comparatively low energy input.

High recycling rates for pure-in-type plastics

Particularly suitable for polyethylene (PE), polypropylene (PP) or polyethylene terephthalate (PET).

Simple implementation in existing infrastructure

Many recycling companies have established mechanical processes.

Advantages of chemical recycling

Recovery of hard-to-recycle plastics

Multilayer composite films or contaminated industrial waste can also be recovered.

Recyclates with virgin-material quality

Ideal for applications with high requirements – e.g. in the automotive industry or medical technology.

Contribution to a genuine circular economy

Because chemical recycling also covers plastic types that were previously considered non-recyclable.

Mechanical recycling of plastics – process and advantages

Mechanical recycling of plastics is the most frequently used recycling process. The aim is to process plastic waste and feed it back into the production cycle as recyclate. The chemical structure of the plastic is retained in the process.

The process begins with the collection and sorting of plastic waste. The materials are then size-reduced, cleaned and separated by plastic type. After washing and drying, the material is melted down. Granulates or ground materials are produced from the melt, which can be used to manufacture new plastic products.

Mechanical recycling is particularly suitable for pure-in-type plastics such as polyethylene (PE), polypropylene (PP) or polyethylene terephthalate (PET). The cleaner and more homogeneous the starting material, the higher the quality of the recycled plastic.

The most important advantages of mechanical recycling include the comparatively low energy demand, established processes and the economical processing of large quantities of material. As a result, the process helps to reduce the consumption of fossil raw materials and to put plastic waste to sensible further use.

The limits of mechanical recycling become apparent above all with heavily contaminated, mixed or multilayer plastic waste. In such cases the process reaches technical and economic limits, which is why chemical recycling processes are used as a complement.

Chemical recycling of plastics – process and areas of application

Chemical recycling of plastics is becoming increasingly important because many plastic waste streams are only suitable for mechanical recycling to a limited extent. The aim of the process is to break plastics down into their chemical basic components or recoverable raw materials. These can then be used again to manufacture plastics or other products.

In contrast to mechanical recycling, the material structure is not retained in chemical recycling. Instead, the plastics are broken down by thermal, chemical or catalytic processes. The best-known processes include pyrolysis, depolymerisation and gasification. These produce, for example, oils, gases or monomers that serve as starting materials for new production processes.

Chemical recycling is particularly suitable for mixed, contaminated or multilayer plastic waste. This includes composite packaging, engineering plastics or materials that are difficult to collect separately by type. For such material streams, the process offers additional recovery options and complements existing recycling concepts.

The most important areas of application include the packaging industry, the automotive industry, the chemical sector and the processing of engineering plastics. Companies are increasingly using chemical recycling to return hard-to-recover plastic waste to the raw materials cycle and to reduce dependence on fossil resources.

On the other hand, there is a higher energy demand as well as higher investment and operating costs compared with mechanical recycling. Nevertheless, chemical recycling is regarded as an important building block of a future circular economy, especially for plastic waste that can barely be processed with classic recycling processes.

Mechanical vs. chemical recycling of plastics in comparison

Mechanical and chemical recycling pursue the same goal: to keep plastic waste in the materials cycle for as long as possible. However, the two processes differ significantly in terms of their processes, areas of application and requirements for the starting material.

In mechanical recycling, plastics are sorted, size-reduced, cleaned and melted down again. The chemical structure of the material is retained. This process is particularly suitable for pure-in-type and clean plastic waste. It is energy-efficient, economically established and enables the processing of large quantities of standard plastics.

Chemical recycling, by contrast, relies on breaking plastics down into their chemical basic components. This means that mixed, contaminated or hard-to-recover plastic waste can also be processed. The raw materials obtained can then be used to manufacture new plastics or other chemical products.

While mechanical recycling currently accounts for the largest share of plastics recovery, chemical recycling is regarded as an important complement for material streams that can only be recycled to a limited extent with classic processes. The two technologies are therefore not in competition, but complement each other within a modern circular economy.

Criterion	Mechanical recycling	Chemical recycling
Process	Size reduction and melting down	Chemical breakdown
Material structure	Retained	Dissolved
Energy demand	Lower	Higher
Costs	Lower	Higher
Suitable for	Pure-in-type plastics	Mixed and complex plastic waste
Raw material quality	Can decrease with every cycle	Often comparable with virgin material
Industrial prevalence	Very high	Still being expanded

Both processes will be needed in future for a sustainable plastics economy. Mechanical recycling remains the preferred solution for high-quality and pure-in-type plastic waste, while chemical recycling creates additional possibilities for hard-to-recover materials.

Challenges of chemical recycling

• High investment costs for plants
• Not yet established across the board
• Regulatory uncertainties, e.g. regarding the recognition of recyclates
• Life cycle assessment varies greatly depending on the energy source and process control

When is which process suitable?

The choice of the suitable recycling process depends on numerous factors – above all the input material, the desired quality level of the end product and the economic framework conditions.

• Mechanical recycling is eminently suitable for homogeneous, pure-in-type, non-contaminated plastics, such as those arising as production waste in industry. This process is also established and cost-effective for packaging waste with high collection quality.
• Chemical recycling is used above all when the material mixture is too complex for mechanical separation – for example with multilayer composites, plastic-metal bonds or heavily contaminated waste from the post-consumer sector. Molecular breakdown is also sensible for engineering plastics that have been used in safety applications.

In future, a differentiated recovery depending on the material stream is likely to become established. Mechanical recycling remains the preferred method wherever it is technically possible and ecologically sensible. Chemical recycling complements this system as a bridge to the complete circulation of complex plastic waste.

Conclusion

Chemical recycling is not a replacement, but a complement to mechanical recycling. Both processes have their justification – depending on the type of material, degree of purity and desired product quality. While mechanical recycling is very efficient economically and ecologically, the chemical process offers new possibilities for previously non-recyclable plastics.

For industry, this results in an expanded toolbox: only those who find the right strategy for the right material stream can operate sustainably, efficiently and in compliance with the law in the long term.

Frequently asked questions about mechanical and chemical recycling

What is mechanical recycling?

Mechanical recycling is the processing of plastic waste by sorting, size reduction, cleaning and melting down again. The chemical structure of the plastic is retained in the process.

What is chemical recycling?

In chemical recycling, plastics are broken down into their chemical basic components or recoverable raw materials. These can then be used again to manufacture plastics or other products.

What advantages does mechanical recycling offer?

Mechanical recycling requires comparatively little energy, is economically established and is particularly suitable for pure-in-type plastic waste. This means large quantities of plastics can be recycled efficiently.

What disadvantages does mechanical recycling have?

The quality of the material can decrease with every recycling cycle. In addition, the process is mainly suitable for clean and pure-in-type plastic waste.

When is chemical recycling used?

Chemical recycling is used above all for mixed, contaminated or hard-to-recover plastic waste. This includes, for example, composite packaging or engineering plastics with a complex structure.

Is chemical recycling better than mechanical recycling?

Both processes have different areas of application. Mechanical recycling is usually the more efficient solution for pure-in-type plastics. Chemical recycling complements this process for plastic waste that is difficult to recover mechanically.

Which plastics are suitable for mechanical recycling?

Thermoplastics such as PE, PP and PET are particularly suitable. These materials can be processed several times and processed again.

What role does recycling play for the circular economy?

Recycling reduces the consumption of fossil raw materials and helps to keep plastic waste in the economic cycle as valuable materials. Mechanical and chemical recycling together contribute to a more sustainable use of plastics.