Mechanical or chemical recycling? That is the wrong question

of Dr. Magdalena Laabs July 23, 2026

The industry does not need one winning technology. It needs the right process for the right waste stream, and an honest account of how much material actually returns to circulation.

The debate on plastics recycling is often presented as a contest between two technologies.

On one side, mechanical recycling is described as the only rational option because it uses less energy and preserves the value already embedded in the polymer. On the other, chemical recycling is presented as the technology that will finally solve the problem of mixed, multilayer and contaminated plastic waste.

Both claims contain an element of truth. Both become misleading when they are applied to every polymer and every waste stream.

There is no single technology that is equally suitable for PET, PE, PP, PA, PVC, PS, PUR, PMMA, composites and laminates. Nor is there one generic material called “plastic waste”.

There are waste streams with a defined composition, use history, level of degradation, additive content, moisture, contamination and foreign materials. Only after these variables have been examined can a recycling route be selected responsibly.

First, the terminology must be clear

Mechanical recycling does not intentionally break a polymer down into monomers. The material is sorted, shredded, washed, separated, dried, filtered, degassed, melted, homogenised and pelletised, or processed directly into a new product.

This does not mean that the polymer structure remains entirely unchanged.

During use, washing, drying and reprocessing, the material is exposed to heat, oxygen, moisture and shear. The following phenomena may occur:

polymer-chain scission,
oxidation,
branching,
crosslinking,
hydrolysis,
changes in the molecular-weight distribution,
depletion of stabilisers,
formation of volatile degradation products.

In PP, chain scission frequently increases the melt flow rate. In PE, oxidation may cause chain degradation as well as branching or gel formation. PET is particularly sensitive to moisture during melt processing because hydrolysis lowers its molecular weight and intrinsic viscosity.

For this reason, the statement that a material contains “100% recyclate” tells us nothing by itself about processing stability, batch-to-batch consistency or fitness for a particular application.

Where does mechanical recycling have the strongest advantage?

Mechanical recycling performs best with relatively clean, homogeneous thermoplastic streams whose composition can be controlled.

Examples include:

PET bottles from separate collection systems,
crates, pallets and transport containers circulating in controlled loop
PE film from homogeneous industrial streams,
PVC pipes and profiles collected through dedicated systems,
post-industrial waste with a known formulation,
selected HDPE and PP streams after effective sorting.

In these cases, most of the value already created in the polymer can be retained. There is no need to break the material down into smaller molecules, purify reaction products and polymerise them again.

A well-designed mechanical process may include optical sorting, metal separation, density separation, washing, drying, melt filtration, degassing, stabilisation, compatibilisation and controlled blending of batches.

It is therefore not simply a matter of “melting waste again”.

Modern mechanical recycling is a materials-engineering process whose effectiveness depends on an understanding of polymers, additives, rheology, degradation and the intended application of the recyclate.

Where do its limitations begin?

The main limitation of mechanical recycling can be summarised in one sentence:

The quality of a recyclate cannot exceed what the quality of the feedstock and the available purification methods allow.

Sorting by the main polymer type does not yet create a homogeneous material. Two packages labelled PP may contain different copolymers, fillers, stabilisers, pigments and coatings, and may have very different ageing histories.

Most polymers are also immiscible at the molecular level. Even an apparently similar PE and PP mixture can form an unstable phase morphology and show reduced impact strength, tensile performance and elongation.

Compatibilisers can improve adhesion between phases, but they cannot replace compositional control. A formulation that works for one blend may be ineffective in another.

Melt filters alone do not solve the problem either. A filter can retain paper, aluminium, wood, sand and other solid particles. It cannot remove a second molten polymer, dissolved additives, pigments, migrated substances or all compounds responsible for odour.

Particularly challenging streams include:

multilayer packaging,
heavily coloured plastics,
waste contaminated with food residues,
agricultural films containing soil, water and organic matter,
plastics containing flame retardants,
waste electrical and electronic equipment plastics
composites and crosslinked plastics,
materials with an unknown use history,
waste containing substances that restrict reuse in food-contact applications.

This does not mean that mechanical recycling inevitably leads to downcycling. Downcycling often results from poor separation, uncontrolled mixing or the use of a recyclate in an application whose requirements it cannot meet.

There is also no universal number of cycles after which a plastic “can no longer be recycled”. The answer depends on the polymer, its previous application, stabilisation, moisture, temperature, residence time in the melt-processing system, shear intensity and the properties required from the next product.

Chemical recycling is not one technology

The term chemical recycling covers processes with fundamentally different mechanisms.

Solvolysis

Solvolysis uses a reaction between the polymer and a suitable chemical medium. It may include glycolysis, methanolysis, hydrolysis or aminolysis.

It is best suited to polymers containing bonds that can be cleaved selectively, including PET, PA, PC and certain polyurethanes.

One potential advantage is the recovery of high-purity monomers or oligomers. This does not mean that any feedstock can be accepted. Solvolysis usually requires a well-characterised stream, while additives, metals, colourants and other polymers can complicate the reaction, product purification, and solvent or catalyst recovery.

Pyrolysis

Pyrolysis decomposes polymers at high temperature under oxygen-limited conditions. It produces a mixture of oil, gas, waxes, solid fractions and other products.

It is considered particularly for PE and PP mixtures that cannot be recycled effectively through a mechanical route.

It is nevertheless incorrect to say that pyrolysis “turns every plastic back into oil”.

PE and PP undergo largely random chain scission, producing a complex hydrocarbon mixture. Polymers such as PS and PMMA can depolymerise more selectively, giving a higher proportion of styrene or methyl methacrylate.

PVC, PET, PA and polyurethanes introduce chlorine, oxygen, nitrogen and other heteroatoms. These can contribute to corrosion, coke formation, oil contamination, equipment fouling and catalyst deactivation.

Pyrolysis oil intended for a steam cracker often requires purification, dechlorination, hydrotreatment and metal removal. It may also have to be blended with a much larger quantity of fossil feedstock because it cannot be used directly as a drop-in replacement for petrochemical naphtha.

Pyrolysis therefore also needs sorting, feedstock preparation and a defined input specification.

Gasification

Gasification breaks the material down much further, producing synthesis gas composed mainly of carbon monoxide and hydrogen.

The technology may tolerate more diverse streams than selective depolymerisation, but it requires very high temperatures, large installations and advanced gas cleaning.

If the syngas is combusted, the result is energy recovery rather than a closed material loop. Only its conversion into new chemicals and polymers can form part of material recycling.

Solvent-based dissolution

Dissolution processes are sometimes grouped under chemical recycling for marketing purposes, but it is more precise to distinguish them as solvent-based physical recycling.

The polymer is dissolved, separated from some additives and other components, and then precipitated. Its chemical structure does not necessarily have to be broken down.

The method may be useful for selected laminates and contaminated polymers, but it requires efficient solvent recovery, emission control and a rigorous energy balance.

The central question: what is the actual recycling product?

In chemical recycling, three very different values are easily confused

the liquid or gas yield directly after conversion,
the quantity of product delivered to a petrochemical installation,
the amount of material ultimately used to manufacture a new polymer.

These figures are not interchangeable.

If one tonne of waste produces oil, gas, wax, solids and residues, the entire output cannot be described as new feedstock for plastics production. Some gas may be used to heat the process. Some oil may enter the fuel pool. Some carbon remains in residues, coke or by-products.

From a circular-economy perspective, the decisive value is not merely the yield of an intermediate product. It is the proportion of waste-derived carbon that ultimately becomes part of a new material.

The EU Waste Framework Directive explicitly excludes energy recovery and reprocessing into fuels from the definition of recycling. This distinction is fundamental.

Mass-balance accounting is necessary, but it cannot replace a material balance

In large petrochemical installations, chemically recycled feedstock is usually mixed with fossil feedstock. It is then impossible to identify which individual molecules in a finished package came from waste.

Mass-balance accounting is therefore used as a controlled method for attributing a defined share of production to recycled feedstock.

In June 2026, the European Commission adopted Decision 2026/1425 on calculating recycled plastic content in single-use beverage bottles. The rules allow mass-balance accounting for additional recycling methods, but introduce important safeguards:

fuels and losses receive an allocation factor of zero,
material may only be attributed where a technically feasible chemical route exists,
accounting is performed at individual-facility level,
the accounting period may not exceed three months,
a negative material balance is not permitted
the data and accounting system are subject to verification.

This is an important development, but the scope of the Decision must be described accurately. It concerns the calculation of recycled content in single-use beverage bottles. It is not an automatic approval of every chemical-recycling claim.

Mass balance is a chain-of-custody method for controlling flows and allocating shares. It does not prove that every molecule in a particular product physically originated from waste.

Which technology has the lower environmental impact?

Mechanical recycling generally uses less energy because it preserves the polymer structure and requires fewer conversion stages.

This conclusion must not, however, be applied automatically to every case.

A JRC report comparing real recycling scenarios illustrates how strongly the result depends on the waste stream and the application of the recovered product.

For one tonne of sorted PET packaging waste, the modelled net climate savings were approximately:

1,933 kg CO₂e for mechanical recycling,
1,711 kg CO₂e for partial glycolysis,
while energy recovery generated a net burden of approximately 1,241 kg CO₂e.

These figures are not universal factors for every PET installation. Results depend on yield, energy consumption, chemical inputs, residue treatment, and the type and proportion of virgin material displaced by the recycled output.

The ranking may change for other polymers. For PS, selective styrene recovery may outperform the production of a mechanically recycled material with a limited ability to displace virgin PS. For mixed polyolefin films, the apparent advantage of pyrolysis may disappear once high energy consumption, oil upgrading and the share of output entering fuels are included.

Any credible comparison should therefore establish:

whether the technologies process the same waste strea
whether the system boundaries are equivalent,
whether sorting and feedstock preparation are included,
the actual material yield,
the share of output that replaces virgin feedstock,
the fate of gas, wax, solids and rejects,
the consumption of energy, hydrogen, solvents and catalysts,
whether product quality is included,
whether the functional unit is one tonne of waste, one tonne of product or a defined material function.

Without this information, a claim that one technology is “greener” is primarily a marketing statement.

How can mechanical and chemical recycling work together?

The most rational system is a cascading one.

1. Homogeneous streams should be directed to mechanical recycling

If a material can be cleaned and reused while maintaining the required properties, breaking it down into monomers or hydrocarbons would unnecessarily destroy value that has already been created.

2. Mechanical recycling must continue to develop

We need better sorting, compositional traceability, stabilisation, degassing, odour removal, compatibilisation, purification and quality control.

Digital product passports and more accurate information about polymers, adhesives, barrier layers, pigments and additives will also become increasingly important.

3. Selective dissolution can purify selected materials without destroying the polymer

This is an intermediate route for streams that cannot be cleaned sufficiently by mechanical methods but do not need to be broken down into monomers.

4. Depolymerisation should be used where the chemistry of the polymer supports it

PET, PA, PC, PMMA, PS and selected polyurethanes should not be treated in the same way as PE and PP. Each polymer family requires a separate assessment of reaction chemistry, selectivity, purification and recovery economics.

5. Pyrolysis should process selected residual fractions, not compete for the best feedstock

Its justification is strongest when it processes waste that cannot be used effectively in mechanical recycling, particularly properly prepared mixed-polyolefin streams.

If a pyrolysis plant starts consuming clean, homogeneous PE or PP that could have been returned through mechanical recycling, it no longer complements the system. It begins to compete for its most valuable feedstock.

6. Rejects also require quality control

A reject from sorting or mechanical recycling is not automatically a suitable feedstock for chemical recycling. It may contain excessive PVC, PET, PA, metals, moisture, paper, glass, fillers and organic residues.

A chemical-recycling plant also needs an input specification.

Seven questions to ask any recycling-technology supplier

What exact composition and contamination level can the feedstock have?
What is the yield of product suitable for new polymer production, rather than the total yield of liquid, gas or pellets?
What proportion ends as fuel, process gas, residue, wastewater or reject?
Which feedstock-preparation stages have been omitted from the presented cost and emissions balance?
How much energy, water, hydrogen, solvent, catalyst and other chemicals does the process consume per tonne of waste?
Which virgin feedstock can the process output actually replace, and at what substitution ratio?
Do the results come from a continuously operating industrial installation, or from a laboratory or demonstration process?

Only after these questions have been answered can we determine whether we are looking at an industrial technology or merely an attractive process diagram.

We do not need a technology war

According to the JRC model for 2022, the average end-of-life recycling rate for plastics in the EU was only 19.6%. Mechanical recycling dominated, while the contribution from chemical recycling remained negligible.

This shows that mechanical recycling alone has not closed the loop. It does not prove that it should be replaced by chemical recycling.

Mechanical recycling should remain the first choice where it preserves the material and produces an output of the required quality. Chemical recycling should extend the range of waste that can be recovered, rather than diverting clean streams simply because they are easier to process.

The European Commission expressed this principle clearly in its 2026 Decision: chemical recycling should complement mechanical recycling, which is generally environmentally preferable where it delivers recycled outputs of sufficient quality and technical performance.

The correct question is therefore not: mechanical or chemical recycling?

How can we preserve the greatest possible share of material value, use the least possible energy, and direct the smallest possible share of carbon into fuels, emissions and waste?

Only then are we discussing a genuinely circular plastics economy.

References

European Commission, Joint Research Centre, Amadei A., Venturelli S., Manfredi S., Plastics materials flows in the EU-27 and their environmental impacts. Unveiling the European plastic value chain, 2025.
Garcia-Gutierrez P. et al., Joint Research Centre, Environmental and economic assessment of plastic waste recycling, 2023.
European Commission, Implementing Decision (EU) 2026/1425 on calculating recycled plastic content in single-use beverage bottles, 30 June 2026.
European Union, Directive 2008/98/EC on waste, consolidated text.
European Union, Regulation (EU) 2025/40 on packaging and packaging waste.
Schyns Z.O.G., Shaver M.P., Mechanical Recycling of Packaging Plastics: A Review, 2021.
Uekert T. et al., Technical, Economic, and Environmental Comparison of Closed-Loop Recycling Technologies for Common Plastics, 2023.
Jeswani H.K. et al., Life cycle environmental impacts of chemical recycling via pyrolysis of mixed plastic waste, 2021.
Klotz M. et al., The role of chemical and solvent-based recycling within a sustainable circular plastics economy, 2024.
Schade A. et al., Plastic Waste Recycling: A Chemical Recycling Perspective, 2024.

The English version is the original version of this article. All other language versions were generated using automated translation. In case of any discrepancy, please refer to the original English text.

Plastics recycling, mechanical recycling, chemical recycling, polymer recycling, circular economy, plastic waste, recycling technologies, pyrolysis, depolymerisation, solvolysis, mass balance, plastics processing,