# Recycling of Multilayer Polymeric Barrier Films: an Overview of Recent Pioneering Works and Main Challenges

Hissein Bechibo Adam, Mohamed Yousfi, Abderrahim Maazouz, Khalid Lamnawar

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Hissein Bechibo Adam, Mohamed Yousfi, Abderrahim Maazouz, Khalid Lamnawar. Recycling of Multilayer Polymeric Barrier Films: an Overview of Recent Pioneering Works and Main Challenges. Macromolecular Materials and Engineering, 2025, 10.1002/mame.202400414. hal-05041105

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# Recycling of Multilayer Polymeric Barrier Films: an Overview of Recent Pioneering Works and Main Challenges

Hissein Bechibo Adam, Mohamed Yousfi, Abderrahim Maazouz, and Khalid Lamnawar*

Multilayer barrier flexible polymer films are gaining attention for their lightness and versatility, representing over 17% of global plastic packaging production, primarily in the food sector. However, their complex chemical composition and strong interlayer adhesion—due to the presence of tie layers pose significant recycling challenges. This review explores waste management technologies for these complex films, including physical recycling (mechanical recycling, delamination, and selective dissolution-precipitation) and chemical recycling (pyrolysis, gasification, and depolymerization). Among them, mechanical recycling is the least energy-intensive and most environmentally friendly but is hindered by polymer degradation. Delamination, the least impactful solvent-based method, offers advantages, while selective dissolution-precipitation achieves high polymer purity but has a substantial environmental footprint due to excessive solvent use. Chemical recycling, though highly energy-intensive, produces derivatives with purity comparable to virgin materials. Therefore, the recent insights into each recycling process and their main scientific and technological challenges are summarized and discussed. Furthermore, life cycle assessment (LCA) studies on multilayer film waste management are reviewed. One proposed eco-design strategy involves transitioning from multi-material to mono-material multilayer films, offering a promising path toward sustainable management.

## 1. Introduction

Since their discovery in the 1950s, plastics have become an integral part of daily life, enjoying growing popularity across various application sectors.[1] According to Plastics Europe,[2] global plastic production reached 400.3 million tonnes in 2021, with a further increase of 3% recorded in 2023.[3] Additionally, Plastics Europe[2] reports that plastic packaging constitutes 44% of global plastic use, making it the most significant application sector (Figure 1).

Among these diverse applications, flexible films (26% of global plastic packaging) have gained widespread popularity due to their remarkable properties, such as versatility, lightness, resilience, and printability.[4] These films are utilized across various industries and are categorized into two main groups: packaging and nonpackaging applications.[5] Packaging can be further divided into primary packaging, secondary, and tertiary packaging.[6] Primary packaging, which is in direct contact with the product, serves the purpose of protecting it, while secondary and tertiary packaging combines primary packages to ensure safe and efficient

transportation.[7,8] Based on their structure, flexible films can be classified into single-layer and multilayer films. Single-layer films are typically used for secondary and tertiary packaging, whereas multilayer films, composed of multiple layers of polymeric and nonpolymeric materials, are utilized for primary packaging requiring complex properties. These multilayer films, produced through processes such as co-extrusion, can comprise between 2 and over 20 layers.[4,9] They account for 17% of global flexible packaging production, with their primary application being food packaging.[7] On the other hand, nonpackaging applications include garbage bags, labels, as well as films used in agriculture and construction.[10] Regarding plastics, polyethylene (PE) is the most widely used material, whether in the field of packaging or in sectors other than packaging. In the primary sector, low-density polyethylene (LDPE) and high-density polyethylene (HDPE) are predominant, followed by polypropylene (PP) and polyethylene terephthalate (PET). For agricultural applications as well as in the secondary and tertiary sectors, low-density polyethylene remains the most commonly used material.[7]

The introduction of technologies like co-extrusion has significantly reduced the thickness of multilayer films, leading to

H. B. Adam, M. Yousfi, A. Maazouz, K. Lamnawar
Université de Lyon
CNRS, UMR 5223
Ingénierie des Matériaux Polymères
Université Claude Bernard Lyon 1
INSA Lyon
Université Jean Monnet
Villeurbanne, Cedex F-69621, France
E-mail: Khalid.lamnawar@insa-lyon.fr

A. Maazouz
Hassan II Academy of Science and Technology
Rabat, Morocco

The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/mame.202400414

© 2025 The Author(s). Macromolecular Materials and Engineering published by Wiley-VCH GmbH. This is an open access article under the terms of the [Creative Commons Attribution License](https://creativecommons.org/licenses/by/4.0/), which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

DOI: 10.1002/mame.202400414
<figure><img src="image_3.png" /><figcaption>**Figure 1.** Distribution of the global plastic applications.[2]</figcaption></figure>

lower material consumption and production costs.[11] However, the production and accumulation of multilayer packaging increase yearly due to the growing consumer reliance on packaged goods, causing a significant recycling challenge. Currently, multilayer films cannot be recycled as efficiently as single-layer films (e.g., PET beverage bottles or HDPE milk bottles) due to limitations in conventional recycling technologies.[12] These films are often deemed non-recyclable, with post-consumer management options largely limited to energy recovery or landfilling.[13,14] According to a study conducted in Europe by Plastics Europe et al., in 2020, 46% of postconsumer plastic packaging waste was recycled, 37% was used for energy recovery, and 17% was landfilled.[2] Due to their structural complexity, it is highly likely that a significant proportion of non-recyclable packaging originates from multilayer films.[14] Consequently, manufacturers are exploring mono-material approaches.[15] However, multilayer films combine multiple layers into a single structure, creating a synergy of properties that are challenging to replicate with mono-materials, complicating their phase-out. Despite these challenges, the European Commission has set an ambitious goal to make all multilayer packaging reusable or recyclable by 2030.[15] It is therefore crucial to develop effective strategies for managing waste derived from multilayer packaging.

The primary objective of the present article is to review the various recycling methods for multilayer barrier flexible polymer films. To achieve this, the main characteristics of multilayer films were first examined, followed by a discussion on the main recycling techniques, including mechanical recycling, delamination, selective dissolution precipitation, and chemical recycling. Finally, the life cycle analysis studies on the recycling of multilayer film waste were examined and an approach focused on eco-design was proposed, aiming to transform multi-material multilayer films into mono-material ones.

## 2. Structure of Multilayer Plastic Film

Multilayer films are a combination of several flexible or semi-rigid layers, typically produced by lamination or coextrusion. These films can include polymer layers as well as inorganic layers, such as aluminum or SiOx coatings. Each layer serves a specific function within the overall structure of the film.[13] The functionalities of each layer are detailed in Table 1.

The sealing layer (1), which is in direct contact with the products, plays a crucial role in limiting migration and ensuring optimal interaction, particularly through the use of an inner polyolefin layer.[16] To maintain the freshness of the products, it is often essential to prevent any exchange of gases or liquids or to adjust the packaging material's permeability to certain specific substances. To control permeability or prevent gaseous exchanges, it may be important to increase the layer's thickness or use specific barrier layers (2). These layers are critical in preventing oxidation, microbial spoilage, and moisture variations, and preserving flavors and aromas while blocking unwanted external odors.[13] Oxygen barrier layers prevent oxygen infiltration into the packaging, thus reducing the oxidation of fatty foods and the degradation of oxygen-sensitive products. Additionally, they inhibit the proliferation of aerobic microorganisms. Other layers also complement this function, such as light barrier layers, typically made of aluminum or polymer enriched with TiO₂, which help maintain freshness.[17] Migration barrier layers play a significant role in multilayer films. Within the multilayer structure, they prevent undesirable substance exchanges between the material's layers or between the packaging and the product. These layers ensure food safety and quality, meeting strict food industry standards.[13] Tie layers (3) are intermediate layers that provide a strong bond between the different layers of multilayer materials that may have physical or chemical incompatibilities. These layers are made of polymers grafted with acids or anhydrides and ensure the structural integrity of the material. They maintain cohesion and enhance the mechanical properties of the material.[6] To provide robustness and mechanical stability, it may be necessary either to increase the thickness of certain layers or to integrate a structural layer (4). This layer optimizes the thickness of other layers without compromising the overall performance of the material.[6,13] The outer layer (5), on the other hand, protects multilayer films from external aggressions such as humidity, scratches, and temperature variations while offering strong thermomechanical resistance. This layer is used to meet specific requirements, such as printability or functionalization, and also contributes to the packaging's visual appeal.[13] The prints and aesthetic or functional elements contained in the outer layer are generally protected by a coating (6).[13,16]

**Figure 2** highlights the structure of a five-layer film as described above. This multilayer configuration is designed to opti-
<table><caption>**Table 1.** Layers, functions, and commonly used materials for multilayer food packaging, inspired by.[6,13,16,17]</caption><thead><tr><th>Layer</th><th>Function</th><th>Material</th></tr></thead><tbody><tr><td>(1) Seal layer (Innermost layer)</td><td>Heat temperature (low melting temperature),<br>inert against filling goods</td><td>LLDPE, LDPE, EVA, ionomers, OPP, OPA, OPET</td></tr><tr><td>(2) Barrier layer</td><td>Resistance against:<br>Moisture</td><td>LDPE, LLDPE, HDPE, OPP, EVA, ionomers, PVDC, PET</td></tr><tr><td></td><td>Oil/grease</td><td>PET, HDPE, PA, Ionomers, EVOH, PVDC</td></tr><tr><td></td><td>Water vapor</td><td>PP, HDPE, LDPE, PVDC</td></tr><tr><td></td><td>Aroma/flavour</td><td>PET, PA, EVOH, PVDC</td></tr><tr><td></td><td>Oxygen</td><td>EVOH (standard), PA or PET (below standard), Aluminum (Exceeding<br>standard), PVDC (biaxially oriented), PA, Oriented PET, SiOx, or Al2O3</td></tr><tr><td></td><td>Light</td><td>Coatings aluminium, TiO2-filled polymers</td></tr><tr><td>(3) Tie layer</td><td>Combines two chemically incompatible materials</td><td>polyurethanes, acid/anhydride grafted polyolefins</td></tr><tr><td>(4) Structural layer</td><td>Provides:<br>Toughness</td><td>PE, PET</td></tr><tr><td></td><td>Puncture resistance</td><td>HDPE, PA</td></tr><tr><td></td><td>Stiffness</td><td>PP, PET, HDPE, LDPE, PA, EVA, Ionomers, EVOH</td></tr><tr><td></td><td>Stability</td><td>PP, PET, PA, EVA, Ionomers, EVOH</td></tr><tr><td>(5) Outer layer</td><td>Provides printing surface and mechanical<br>performance</td><td>PE or PET</td></tr><tr><td>(6) Coating (outermost layer<br>facing environment)</td><td>Optional thin film to protect the printed material</td><td>Any specialized polymer</td></tr></tbody></table>

Abbreviations used: LLD (linear low-density), LD (low-density), HD (high-density), PE (polyethylene), EVA (ethylene-vinyl acetate), OPP (oriented polypropylene), OPA (oriented polyamide), OPET (oriented polyethylene terephthalate), PVDC (polyvinylidene chloride), EVOH (ethylene-vinyl alcohol).

mize properties such as barrier protection, mechanical strength, and flexibility, ensuring the film meets the technical requirements for its intended application.

However, it is important to note that not all multilayer films require each of the layers mentioned above. While the outer and inner layers are often essential for most applications requiring multilayer films. The other layers can be optional. Increasing the number of layers makes the recycling process more difficult.

### 3. Sorting

The sorting of collected waste plays a fundamental role in the efficiency of recycling processes and the valorization of materials. It ensures the production of high-quality recycled materials. Mixed waste collected is generally sorted in material recovery facilities (MRFs). The technologies and equipment used in sorting centers vary depending on the incoming waste stream. Facilities can generally be categorized into two types, although each sorting

<figure><img src="image_4.png" /><figcaption>**Figure 2.** Example of structure of multilayer film with five layers.</figcaption></figure>
center has unique characteristics due to differences in collection strategies.[7]

### 3.1. Mixed Solid Waste (MSW) Collection System

In Europe, facilities processing mixed household waste employ Mechanical-Biological Treatment (MBT). The incoming waste stream consists of organic kitchen waste and recyclable materials. Several sorting stages are implemented. For instance, a trommel is used for size-based separation, while eddy current systems and magnets extract ferrous metals and aluminum. These facilities typically recover metals, beverage cartons, and certain plastics such as LDPE, HDPE, and PET for recycling.[18] However, in this type of facility, flexible films are considered contaminants and are sent to landfill.[7]

Although Mechanical-Biological Treatment (MBT) is commonly used in Europe for the management of mixed municipal solid waste (MSW), approaches vary by region. In the United States, for example, the majority of such mixed household waste is landfilled, while a portion is incinerated for energy production. In China, this waste is either incinerated for energy recovery or processed through Mechanical-Biological Treatment, a technology that is rapidly expanding in the country.

### 3.2. Separate Collection System

This collection method aims to limit contamination of material streams and optimize the recycling of sorted materials. The sorting of recyclables from a separate collection system takes place in either single-stream or clean MRFs. The incoming waste stream consists of mixed recyclables, such as paper/cardboard, plastic, and glass. The sorting process occurs in several stages. The first step involves removing plastic bags from the waste stream. The most common method remains manual sorting, carried out by highly trained and experienced operators. Currently, suction systems are installed to collect and transport manually picked materials, while bag separators are used to open and empty plastic bags. The next stage focuses on separating flexible films, which are 2D in nature, from rigid and heavy objects, which are 3D. This is achieved through ballistic separation: this technology directs heavy 3D materials downward on an inclined screen, while lighter 2D elements move toward the upper end of the separator. Another employed technique is air classification, where lighter materials are carried by an air stream while heavier materials remain on the conveyor. However, both of these processes— ballistic and air separation—share a common limitation: they do not differentiate between various lightweight materials, such as paper and plastic film. To address this challenge, a third technology is employed: near-infrared (NIR) spectroscopy analysis. This process is based on analyzing the reflectance spectrum within the near-infrared range. It utilizes the wavelengths reflected by a material after being exposed to a near-infrared light source.[7,19]

Studies have demonstrated the effectiveness of this technology. For example, McKinlay and Morrish in 2016,[20] reported that NIR can identify PP, PE, and mixed polyolefins. Additionally, multilayer multimaterial structures such as PET/PE and PP/PE were successfully detected.[7] Nevertheless, this technology also

has limitations: thin coatings, such as polyvinylidene dichloride (PVdC), and black-colored materials are not detectable by current equipment. Moreover, NIR does not distinguish between surface-printed and reverse-printed materials.[7,21,22]

In 2020, Chen et al.[22] investigated the feasibility of detecting and sorting multilayer flexible plastic packaging using NIR spectroscopy. Their laboratory-based results indicate that it is possible to separate and classify monolayer, bilayer, and trilayer samples. They also observed that, for glossy samples, printed surfaces influence the spectra. Furthermore, increasing material thickness alters spectral characteristics, making classification easier. Koinig et al.,[23] conducted a study aimed at improving the separation of monolayer and multilayer films through transreflection measurements and the application of machine learning approaches. Their findings indicate that the success of near-infrared sorting depends on the availability of high-quality spectral information. They also demonstrated that the introduction of reflective backgrounds enables transfection measurements, thereby facilitating the differentiation between monolayer and multilayer materials. This approach increased detection rates from 46% to 74% with an aluminum reflector and up to 78% with a copper reflector. In addition to improving detection rates, the introduction of reflective backgrounds enhanced the individual recognition of different materials.

## 4. Recycling Methods of Multilayer Films

The recyclability of multilayer films is complex due to their heterogeneous compositions. Multilayer films typically consist of a mix of materials so their varying physico-chemical properties, coupled with their thermal immiscibility, make conventional recycling processes challenging. Separating the layers is both technically and economically difficult.[24,25] To enhance their recyclability and reduce the amount of waste sent to landfills, several methods have been developed and documented in the literature, as illustrated in Figure 3. These methods include physical recycling, which encompasses mechanical recycling, delamination, and selective dissolution-precipitation, as well as chemical recycling, which involves pyrolysis, gasification, and depolymerization.

### 4.1. Mechanical Recycling

Mechanical recycling is a process that treats plastic waste to decontaminate it and produce clean polymer products. The recycled materials must retain adequate mechanical properties and functional performance, allowing them to be reused in both downcycling and upcycling applications. This method is widely adopted thanks to its technical and economic viability and can be implemented in either a closed-loop or open-loop system. In a closed-loop recycling system, the input waste generally contains fewer impurities. The process involves transforming the waste through extrusion, which includes heating, degassing, melting, and regranulating the material. In contrast, open-loop recycling involves several stages: shredding, washing, drying, and regranulation. The input waste may consist of a single type of material or a mix of compatible plastics. However, open-loop recycling can
<figure><img src="image_5.png" /><figcaption>**Figure 3.** Classification of Recycling Processes for Multilayer Plastic Waste.</figcaption></figure>

be complicated by contamination from incompatible adhesives, plastic additives, inks, or polymer residues, which can affect the mechanical properties of the recycled products. Consequently, this process is typically suited for less demanding applications, such as bin liners, pipelines, or agricultural products.[7]

Mechanical recycling may involve the following steps[26,27]:

* **Baling:** If the plastic is not processed immediately at the sorting site, it is often baled for transport.

* **Separation and Sorting:** Based on shape, density, size, color, or chemical composition.

* **Shredding and Grinding:** Reducing the size of the sorted plastic into flakes.

* **Washing and Drying:** Removal of contaminants.

* **Compounding and Granulation:** Optionally reprocessing the flakes into granules, which are easier for processors to handle.

The steps of mechanical recycling for multilayer films are those detailed above. However, flexible films present particular challenges during recycling. Their light weight and multilayer nature make sorting complex. They are also difficult to grind due to their tendency to wrap around the blades. During washing, more intense processes are necessary if the removal of inks and adhesives is desired. Drying is also essential due to their ability to absorb moisture. Extrusion is more complex because of the low bulk density of the films and feeding difficulties. In contrast, rigid films are easier to sort, grinding is more effective due to their rigidity, they contain fewer contaminants, and extrusion is more homogeneous and less challenging. In conclusion, recycling flexible films is more demanding than recycling rigid films due to their low density, tendency to agglomerate, and the contaminants they contain. Innovative technologies are needed to improve their recyclability.[7,26]

Despite these challenges, understanding the composition and behavior of multilayer films is essential to improving their recyclability. In particular, multilayer flexible films are designed

with specific configurations that influence their performance and degradation during recycling.

The common configurations of multilayer films for food packaging consist of two outer layers made of polyolefins, mainly PP or PE, and a central layer used as a barrier, such as EVOH or PA. Adhesive layers are used to combine these layers and create a structure comprising at least five layers.[28] When mechanically recycled, these types of films become blends in which the constituent polymers degrade over recycling cycles due to exposure to intensified thermomechanical conditions (temperature, pressure, and shear). Several studies have been conducted in this regard, notably the one led by Zhan et al.,[28] on the thermomechanical reprocessing of multilayer films for food packaging. Similarly, Saikrishnan et al.,[29] studied the thermomechanical degradation of a polymer blend based on PP and LDPE (PP/LDPE), subjected to five consecutive twin-screw extrusion cycles. The effects of this reprocessing on rheological, thermal, and mechanical properties were analyzed. This thermomechanical process induced β-scission in the PP chains, resulting in a decrease in viscosity, disruption of the crystalline structure, and a slight reduction in mechanical properties. LDPE was also subjected to 100 extrusion cycles to study the impact of recycling cycles on its properties.[30] The melting and crystallinity temperatures of LDPE remained unaffected during recycling. However, extensive extrusion led to thermal degradation and gelation of LDPE, resulting in simultaneous chain scission and crosslinking of its chains. The results also indicate that the processability and durability of LDPE were significantly affected only after the fortieth extrusion cycle. Other studies[31–33] further enrich this research on polymer degradation using different reprocessing techniques, emphasizing the structural evolution of polymers over recycling cycles.

In 2023, Turriziani et al.[34] examined the mechanical recycling of two types of post-industrial multilayer barrier films designed for meat packaging: PE/PE/Additive/PA/Additive/PE/PE (Film A) and PE/Additive/PA/EVOH/PA/Additive/PE (Film B). These films, containing varying concentrations of compatibiliz-
ing additives based on polyolefins grafted with maleic anhydride (MA) (0%, 5%, and 7%), were recycled through extrusion. The results of this study reveal that films incorporating a compatibilizer exhibited a significant improvement in their mechanical properties, particularly in elongation at break, compared to films without this additive. A similar study was conducted recently by Zhan et al.[28] These researchers investigated the effect of multiple thermomechanical recycling cycles on the properties of multilayer barrier films to evaluate the recycling limit of the blend. The three materials used were LDPE (70 wt.%), LLDPE-g-MA (20 wt.%), and EVOH (10 wt.%). The authors thermally mixed these three materials (200 °C, 5 min, and 60 rpm) before subjecting them to thermomechanical reprocessing, which included thermal compounding, grinding, and injection molding over six cycles. In their study, the mechanical, morphological, thermal, and rheological properties of the blend were analyzed throughout the different recycling cycles. The results revealed that, in terms of mechanical properties, the tensile strength and modulus of the blend remained unchanged during the cycles. However, a decrease in elongation at break was observed after four recycling cycles. The authors attributed this degradation in properties primarily to the gelation of EVOH in the recycled blend, as evidenced by the observation of larger EVOH agglomerates in the LDPE matrix. Furthermore, results from differential scanning calorimetry revealed that the crystallinity ratio of EVOH decreased with increasing the number of recycling cycles, suggesting degradation of this material. From a rheological perspective, the results indicated increased interaction between LDPE and EVOH, attributed to the crosslinking of LLDPE-g-MA and EVOH. However, after four recycling cycles, rheological properties, particularly the storage and loss moduli, decreased. This reduction suggests the possibility of phase separation caused by EVOH gelation. In conclusion, the authors stated that using polymer blending to reclaim EVOH-based multilayers with LDPE is promising for up to four recycling cycles.

Huang et al.,[35] studied the properties of an LDPE/EVOH blend (85%/15% by weight) by incorporating LDPE-g-MA as a compatibilizing agent. The results revealed an improved dispersion of the EVOH phase within the LDPE matrix. The blend exhibited stable thermal properties of melting and crystallization, despite variations in the amount of compatibilizer. The mechanical properties, particularly tensile strength and tear resistance, were significantly enhanced by optimizing the quantity of LLDPE-g-MA used. In a similar study, Lee et al.,[36] investigated the effect of the compatibilizer on the crystallization, rheological, and mechanical properties of LDPE/EVOH blends (70%/30% by weight). This research demonstrated that the addition of LLDPE-g-MA promotes a more homogeneous and finer dispersion of the EVOH phase within the LDPE matrix. The crystallization of EVOH was delayed, primarily due to the formation of LLDPE-g-EVOH and the reduction in the size of EVOH domains. Furthermore, the results highlighted a significant improvement in rheological properties, including increased melt viscosity and enhanced storage modulus. Likewise, mechanical properties, such as tensile strength, were improved due to better interfacial adhesion facilitated by the addition of LLDPE-g-MA. A more recent study on the effect of compatibilization was conducted by Cabrera et al.[37] This research focuses on a model blend composed of LLDPE, EVOH, and LLDPE-g-MA, inspired by the composi-

tion of multilayer food packaging. The results of this study show that the presence of the compatibilizer improved the interfacial adhesion between LLDPE and EVOH, due to a chemical reaction between LLDPE-g-MA and EVOH.

Although mechanical recycling is a promising approach to address the issues of multilayer plastic waste, as mentioned in the studies above, this approach generally leads to irreversible modifications of the physicochemical properties of the polymers present in multilayer films. These changes, attributed to high temperature, pressure, and shear force conditions,[38–41] result in the degradation of the polymers. Furthermore, the exposure of these recycled polymers to oxygen, moisture, and residual contaminants leads to thermo-oxidative degradation.[42–44]

Barrier layers, such as EVOH and PA, which we will use as examples, also undergo structural evolution when subjected to different extrusion cycles. As reported by Zhan et al., EVOH exhibits gelation after several recycling cycles. To avoid overcomplicating this study, we propose discussing the reaction mechanisms that generally govern the structural evolution of EVOH under thermomechanical reprocessing over multiple cycles. Onishi et al.[45] identified two reaction mechanisms for the crosslinking of EVOH, the first involving the oxidation of hydroxyl groups on the EVOH chains. **Figure 4**, illustrates this mechanism on a segment of polyvinyl alcohol.

EVOH undergoes cross-linking in the presence of oxygen. During this process, the alcohol groups in the polymer backbone are oxidized to form carbonyl groups, releasing water. When exposed to heat, radicals are generated and combined with each other, resulting in the cross-linking of EVOH.

The second mechanism of EVOH cross-linking involves intermolecular dehydration between EVOH chains. **Figure 5**, illustrates this process, demonstrating how EVOH chains become cross-linked through intermolecular dehydration.

Regarding PA, Researchers from the University of Rouen[48] have developed new high-barrier multilayer composite films based on polyethylene and polyamide. They studied the structure and barrier properties of these films. PA6 is sensitive to water, which acts as a plasticizer due to its polar nature, thereby increasing free volume (swelling effect) and enhancing the diffusion of water molecules during permeation. This variation in free volume is influenced by the extrusion process, during which residual water and extrusion constraints (temperature, duration, and shear) may induce the formation of hydrogen bonds between PA6 chains. Another study, conducted by Mistretta et al.,[49] focused on the thermomechanical degradation and reprocessing behavior of LDPE/PA6/Cloisite 15A systems. Several extrusion cycles were performed to assess the recycling limits of the blend. The results of this study reveal that after four extrusion cycles, the system's viscosity decreases, indicating complex thermomechanical degradation. This degradation includes, in particular, the breakdown of the clay's organic modifier, leading to the formation of radical species. These radicals interact with polymer macromolecules, causing chain scission phenomena. Furthermore, the LDPE/PA6 blend also undergoes degradation, resulting in branching and crosslinking phenomena. A similar study, conducted by Goitisolo et al.,[50] focused on PA6-based nanocomposites subjected to five injection molding cycles at 230 °C. The results showed that the PA6 remained stable and only underwent slight degradation after reprocessing at 270 °C. The study
<figure><img src="image_6.png" /><figcaption>**Figure 4.** EVOH cross-linking mechanism by oxidation according to Onishi et al.[45–47]</figcaption></figure>

reveals that during reprocessing at 270 °C, viscosity decreases, indicating a reduction in molecular weight. In the work of Dong et Gijsman,[51] it is reported that the thermo-oxidative degradation mechanism of polyamides can be described according to the general oxidation mechanism. These mechanisms are presented in **Figure 6**. The carbon-hydrogen bonds of the methylene groups adjacent to the nitrogen are the weakest bonds in aliphatic polyamides, which means that most oxidation reactions occur at these carbon atoms. However, some reactions can also take place in the methylene groups adjacent to the carbonyl groups of the amide groups. This thesis is supported by several other studies.[52–56]

According to Dong et Gijsman, the oxidation of PA6 is a complex process that leads to the formation of hydroperoxides. These can decompose into alkoxy radicals (Figure 6), which can extract hydrogen and lead to the formation of unstable alcohols. These alcohols can then decompose into amides and primary aldehydes, or induce β-scission (Figure 7). These processes result in a decrease in molecular weight and a reduction in mechanical properties.

While mechanical recycling represents a promising approach for processing multilayer film waste, its effectiveness is often constrained by the inherent heterogeneity of the polymer layers that compose them, leading to the degradation of the mechanical properties of the recycled materials. To overcome this limitation, the use of compatibilizers has emerged as a key strategy. The following section explores the mechanisms, methods, and benefits of compatibilization in the context of multilayer film recycling.

The issue of immiscibility in polymeric materials can be addressed in several ways. Two polymers are considered immiscible when they have different chemical structures and rheologi-

cal properties. A preferred strategy for reducing immiscibility is to introduce compatibilizers. According to Koning et al.,[57] compatibilizers are macromolecular species with interfacial activities allowing homogeneous polymer blends. They generally have a block structure in their chains, where one constituent block is miscible with one component of the blend and another block is miscible with the other component.

There are two approaches to compatibilization: physical and chemical. Physical compatibilization involves incorporating copolymers prepared beforehand into the blend of immiscible polymers. Chemical compatibilization, on the other hand, refers to an in-situ reaction that occurs when the polymer blends are being processed. The latter approach is also known as reactive compatibilization and requires mutual reactivity between the two components of the blend.

The mechanism of compatibilization must meet the following conditions[58]:

* Lower interfacial tension, resulting in finer dispersion.

* Stabilization of the resulting morphology against the effects of shear and temperature during processing.

* Improved adhesion between the different phases in the solid state.

Compatibilizers can be grouped into three categories based on the interactions between the compatibilizers and the mixture[26]:

* **Block or graft copolymers:** These compatibilizers are constructed from different polymer segments, where one segment is more compatible with the matrix phase and the other with

<figure><img src="image_7.png" /><figcaption>**Figure 5.** EVOH cross-linking by intermolecular dehydration according to Onishi et al.[45–47]</figcaption></figure>
<figure><img src="image_8.png" /><figcaption>**Figure 6.** Oxidation mechanism for aliphatic polyamide. Adapted with permission[51] Copyright 2010, Elsevier.</figcaption></figure>

the dispersed phase. The compatibilizer migrates to the interface, reducing interfacial tension. An example of this is a PE/PP block copolymer, used in PE/PP blends.

*   **Non-reactive polymers containing polar groups:** Interfacial tension is reduced by secondary intermolecular interactions between these polymers. The non-reactive polymer will be compatible with the matrix, and compatibilization will be influenced by the type of secondary interaction (e.g., dipole < Van der Waals < hydrogen bonding). Examples include poly-methyl methacrylate (PMMA) and polycaprolactam (PCL).

*   **Reactive functionalized polymers:** The reactive group covalently bonds to the dispersed phase, while the polymer backbone is compatible with the matrix. Adhesion between the phases is highest with these types of compatibilizers. Examples include polypropylene grafted with maleic anhydride (PP-g-MA) or polypropylene grafted with glycidyl methacrylate (PP-g-GMA).

A significant amount of research has been conducted to identify the most appropriate compatibilizers for specific polymer systems. **Table 2** shows the compatibilizers commonly used for various polymer systems.

Multilayer polymer materials consist of several layers, often heterogeneous, which complicates their recyclability. The compatibilization process employs chemical substances to facilitate mixing and improve the mechanical stability of multilayer films, allowing for the recycling of all layers in a single stream without the need for separation.[11] These methods enhance miscibility by introducing an additional component into the structures. Compatibilizers are typically block copolymers, selected based on the polymer blend and, therefore, directly dependent on the packaging components.[26]

In 2000, Wyser et al.[84] investigated the recycling of multilayer packaging material systems, based on polypropylene and silicon oxide-coated poly(ethylene terephthalate). In particular, the effect of maleic anhydride-grafted polypropylene, used as a compatibilizer, on the mechanical properties of the recycled material was studied. According to the author, without a compatibilizer, and at low compatibilizer concentrations, the blend exhibits a coarse

morphology and is brittle due to a lack of adhesion between the two polymer phases, PP and PET. The addition of PP-g-MA compatibilizer, at concentrations between 5% and 10% by weight, induces a fine morphology, and the blend demonstrates excellent ductility, thanks to efficient interfacial stress transfer, as revealed by strain-induced crystallization in the PET domains. Beyond 10% by weight of PP-g-MAH, a brittle interphase forms between the PP and PET, leading to a corresponding decrease in the blend's ductility.

## 4.2. Delamination

The lamination of multilayer films generally requires the use of adhesives. These adhesives create a chemical bond between the different layers of the film. However, to delaminate a multilayer film, it is essential to break down or dissolve the adhesive. The delamination of multilayer films is promising, as it enables the recovery of layers without any degradation. The delamination rate largely depends on the interaction between temperature and solvent diffusion through the film.[85] Another crucial factor affecting this rate is the solvent's access to the target. To improve solvent/target access, multilayer films are cut into small pieces (1×1 cm, 2×1,5 cm, or 3×3 cm), as reported by several researchers in the literature.[14,86-90]

In 2023, Šleiniūtė et al.[86] studied the delamination of aluminum-containing multilayer food packaging using nitric acid. The role of nitric acid was to dissolve the aluminum layer and separate the different layers of the packaging. In this study, the authors focused on four parameters: nitric acid, temperature, agitation, and ultrasound, to achieve layer separation. The results of their experiments showed that all the studied parameters were essential for achieving an optimal outcome. Although the process is effective without ultrasound, it proved to be the most critical factor for obtaining faster results.

Apart from organic acids, other organic solvents have also been studied for the delamination process. Fávaro et al.[87] conducted a study on the depolymerization of multilayer packaging consisting of a layer of aluminum-coated PET and a layer of a 70/30
<figure><img src="image_9.png" /><figcaption>**Figure 7.** Possible reactions of oxidation formed alkoxy radicals. Adapted with permission[51] Copyright 2010, Elsevier.</figcaption></figure>

mixture of LLDPE and LDPE. The packaging was laminated using a polyurethane adhesive. The delamination of the film was performed using acetone at 50 °C under agitation for 4 h. The PET was depolymerized using ethanol under supercritical con-

<table><caption>**Table 2.** Compatibilities commonly used for a variety of polymer systems (inspired by[26]). Abbreviations used: PA (polyamide), PS (Polystyrene), Acrylonitrile butadiene styrene (ABS), PC (Polycarbonate).</caption><thead><tr><th>Polymer system</th><th>Compatibilizers commonly used</th><th>References</th></tr></thead><tbody><tr><td>PE-PET</td><td>PE-g-AA, PE-g-IA, PE-g-GMA, SEBS, SEBS-g-GMA, SEBS-g-MA</td><td>[57, 59–61]</td></tr><tr><td>PP-PET</td><td>PP-g-AA, PP-g-MA, SEBS, SEBS-g-MA, SEBS-g-GMA, EVA, EVA-g-MA</td><td>[57, 62–67]</td></tr><tr><td>PP-PE</td><td>EVA, EPDM, SEBS</td><td>[57, 68–70]</td></tr><tr><td>PP-PA</td><td>PP-g-GMA, PP-g-MA, SEBS-g-MA</td><td>[57, 71, 72]</td></tr><tr><td>PE-PA</td><td>PE-g-MA, PE-g-GMA</td><td>[73–76]</td></tr><tr><td>PP-PS</td><td>SBS, SEBS, EVA</td><td>[77, 78]</td></tr><tr><td>ABS-PC</td><td>ABS-g-MA, PP-g-MA, epoxy resins, PMMA</td><td>[79–81]</td></tr><tr><td>PC-PS</td><td>PC-g-PS, PS-Par, SEBS-g-PC</td><td>[82, 83]</td></tr><tr><td>PE/PA/EVOH</td><td>Polyolefin-g-MA</td><td>[34]</td></tr><tr><td>LDPE/EVOH</td><td>LLDPE-g-MA, LDPE-g-MA</td><td>[28, 35]</td></tr></tbody></table>

ditions, resulting in two derived products: diethyl terephthalate and ethylene glycol. Additionally, metallic aluminum was recovered through the PET depolymerization process. The polyethylene obtained during the delamination process could be easily recycled through extrusion. The method can be considered environmentally friendly, as the solvents are recovered by distillation.

In 2016, Cinelli et al.[91] studied a multilayer structure composed of PET, PE, and whey protein as a central adhesion layer. Several configurations were tested to determine the most suitable composition. The results showed that when the whey protein in the dry film samples reached 17% of the total weight, the performance was suitable for practical applications. The whey protein layer, used as a barrier against oxygen and moisture, replaces non-recyclable petrochemical materials and can be removed by washing with enzymatic detergents containing protease enzymes, allowing PET and PE to be separated.

Another delamination method is described by Vagnoni et al. 2023,[92] who investigated recycling multilayer packaging waste using switchable anionic surfactants (SAS). The multilayer waste, consisting of LDPE and aluminum, was loaded into a flask containing 100 mL of aqueous solutions with capric (C10) or lauric (C12) SAS. The system was heated to 90 °C for 2 h. At the end of the process, the delaminated LDPE layers were manually recovered, and the precipitated aluminum was filtered off.
<table><caption>**Table 3.** A summary of solvents used in the delamination process.</caption><thead><tr><th>Film structure</th><th>Type of adhesive</th><th>Solvent</th><th>Process condition (delamination temperature and time)</th><th>References</th></tr></thead><tbody><tr><td>PE/Acrylics or Polyurethane (PU)/ Aluminum</td><td>Acrylics and Polyurethane</td><td>Nitric acid</td><td>3 scenarios studied: 55 °C for 120 min, 65 °C for 210 °C and 75 °C for 240 °C</td><td>[86]</td></tr><tr><td>Multilayer flexible plastic film (e.g., PP/PU/Aluminum/PU/PET)</td><td>Polyurethane</td><td>Formic acid</td><td>75 °C for less than 34 min</td><td>[85]</td></tr><tr><td>PE/Aluminum/PET</td><td>Polyurethane</td><td>Acetone</td><td>50 °C under stirring for 4 h</td><td>[87]</td></tr><tr><td>Polyamide/PU/polyolefin (PP or PE)</td><td>Polyurethane</td><td>Diethylene glycol</td><td>150 °C for 3 h</td><td>[88]</td></tr><tr><td>PE/PE adhesive layer/Aluminum/PE adhesive layer/Printed paper/PE</td><td>PE adhesive layer</td><td>Benzene, ethanol and water</td><td>5 min at 60 °C and 100 rpm stirring speed</td><td>[89]</td></tr><tr><td>LDPE/Aluminum</td><td>No adhesive or glue was detected between the LDPE and aluminum.</td><td>C12-TEA (lauric acid-triethanolamine)</td><td>90 °C for 2 h</td><td>[92]</td></tr></tbody></table>

In 2020, Nieminen et al.[90] studied the recovery of aluminum and plastic from pharmaceutical blister packaging waste using a deep eutectic solvent (DES, lactic acid – choline chloride) as well as pure lactic acid, both considered green solvents. In this context, the author examines the effects of temperature, solvent concentration, agitation, and the solid-liquid ratio on the delamination of multilayer packaging. The results indicate that, among the four parameters studied, temperature proved to be the most significant factor in the separation time, with higher temperatures leading to faster separation. The results also reveal that the aluminum fraction loses mass when treated with lactic acid, while treatment with DES causes aluminum corrosion. Finally, this study demonstrates that, as bio-sourced and environmentally friendly solvents, lactic acid and DES can be considered viable new alternatives for the chemical separation of plastic and aluminum.

Researchers at the University of Alicante are developing a combined delamination and de-inking process. In food contact applications, ink is sometimes deposited between film layers. Therefore, delamination must be performed before deinking to facilitate access to the ink trapped between layers. Additionally, another study from the same university complemented this work. Berkane et al.[25] investigated the improvement of delamination through microperforation of multilayer waste. Microperforation allows the etching solution to diffuse more effectively and facilitates the removal of adhesives, inks, and metals present at the interfaces of multilayer waste. This process involves creating small holes in plastic films, which can be achieved using lasers, punches, pins, or needles. The authors studied a multilayer composed of PET sprayed with aluminum powder (PET/Al) and used a 10% sodium hydroxide (NaOH) solution as a dissolving agent. Cationic or nonionic surfactants were added to the solution to enhance the process. The results indicated that microperforation improved delamination by reducing the treatment time. The diffusion coefficient was five times higher with maximum microperforation. The study concluded that microperforation is a promising pre-treatment for industrial mechanical recycling, potentially used after the separation, sorting, and pre-washing of plastic waste to improve the permeability of multilayer packaging before delamination.

In order to facilitate packaging delamination, other efforts have also been made in the design of multilayer structures, including the switchable solvents (switchable hydrophilicity solvent (SHS), N,N-dimethylcyclohexylamine (DMCHA))[93] reversible cross-linking adhesives,[32,33] water-based adhesives,[94] switchable anionic surfactants,[92] etc.

A summary of solvents used in the delamination process is shown in Table 3.

### 4.3. Selective Dissolution-Precipitation

Selective dissolution-precipitation is a recycling method that uses a solvent system to dissolve and separate heterogenous polymers by isolating them one by one. The isolation of target polymers is normally achieved by precipitation using antisolvents, or by solvent evaporation.[95] A variety of investigations have demonstrated that a separation step, such as using the difference in density of the material, is necessary after the polymer has been dissolved.[96] According to Zhao, Lv, and Ni, the dissolution process is influenced by factors such as polymer and solvent types, polymer size, polymer molecular weight, dissolution temperature, dissolution time, and concentration.[97]

In 2021, Georgiopoulou et al.[98] conducted a study on recycling post-consumer multilayer Tetra Pak packaging using the dissolution-selective precipitation process. Tetra Pak packaging, initially made from waxed paper, now comprises laminated rigid paper (75% by weight), LDPE (20% by weight), and aluminum foil (5% by weight). The packaging consists of five layers:

* LDPE (low-density polyethylene): protects printed information and packaging from moisture and external impacts.

* Paper/Cardboard: ensures rigidity and contributes to the packaging's stability and durability. The packaging is printed on this layer.

* LDPE: is the adhesion layer between the cardboard and aluminum foil.

* Aluminum: constitutes a barrier to ultraviolet rays, oxygen, odors, and bacteria.

* LDPE: Layer in contact with the liquid, acting as a sealing layer for the liquid content.

Two processes are used to separate Tetra Pak packaging: hydropulping and dissolution-precipitation. In the hydropulping
<table><caption>**Table 4.** A summary of the solvent and antisolvent system, along with other dissolution parameters (inspired by[14,99]).</caption><thead><tr><th>Polymer</th><th>Solvent</th><th>Antisolvent</th><th>Dissolution temperature</th><th>References</th></tr></thead><tbody><tr><td>LDPE and HDPE</td><td>Xylene</td><td>n-hexane</td><td>100 °C</td><td>[96]</td></tr><tr><td>PP</td><td>Xylene</td><td>n-hexane</td><td>140 °C</td><td>[96]</td></tr><tr><td>PS</td><td>D-limonene</td><td>—</td><td>25 °C</td><td>[14]</td></tr><tr><td>PET</td><td>benzyl alcohol</td><td>methanol</td><td>180 °C</td><td>[14]</td></tr><tr><td>PVC</td><td>Dichloromethane</td><td>methanol</td><td>40 °C</td><td>[14]</td></tr></tbody></table>

process, demineralized tap water is used as a solvent to separate paper from others. The packaging is ground and mixed with water, then stirred at 400 rpm for 2 h at room temperature to swell the paper and split the packaging into outer LDPE/paper and inner LDPE/aluminum/paper layers. Agitation is continued for an additional 3 h at 700 rpm to further separate the LDPE from the aluminum using centrifugal forces. After the hydrophilic process, the mixture is filtered to separate the paper from the aluminum-PE laminate and the LDPE layer. A second hydrophilic cycle is performed to recover any remaining paper. The aluminum-PE laminate is then isolated through selective dissolution via a precipitation process, where xylene dissolves the LDPE, and isopropanol acts as an antisolvent to precipitate it.[95]

Another dissolution-precipitation method has been described by Achilias et al.,[99] who conducted a study on the use of the dissolution-precipitation technique for recycling various polymers derived from packaging waste, specifically those used in food, detergent, and pharmaceutical applications. The polymers investigated included polyethylene (LDPE and HDPE), PP, PS, PET, and poly(vinyl chloride) (PVC). A tailored system of solvents and antisolvents was employed to effectively dissolve and precipitate these materials. The authors reported that this approach yielded excellent material recovery rates. A detailed summary of the solvent-antisolvent system and other dissolution parameters is presented in Table 4.

In 2020, Walker et al.[100] investigated the recycling of complex polymeric multilayer materials (with three or more layers) into their constituent resins using a method called Solvent Targeted Recovery and Precipitation (STRAP). The study employed a post-industrial multilayer film composed of PE, EVOH, and PET. The STRAP process selectively dissolves one layer of the multilayer material using a solvent in which the targeted polymer is soluble, while the other polymers remain unaffected. The dissolved layer is then separated from the remaining material through mechanical filtration and precipitated by either adjusting the temperature or adding a cosolvent (antisolvent), which causes the dissolved polymer to become insoluble. This process is repeated for each layer, producing separate recyclable streams. The solvents and antisolvents are distilled and reused, and the recovered layers are obtained as dry, pure solids. The STRAP process for separating a mixture of PE, EVOH, and PET into pure resins is divided into three stages[100]:

* **Selectively dissolving the PE in toluene at 110 °C**, then separating the solubilized fraction from the EVOH and PET by mechanical filtration.

* **Selectively dissolving the EVOH fraction in dimethyl sulfoxide (DMSO) at 95 °C**, then separating the solubilized fraction from the remaining PET by mechanical filtration.

* **Recovering the solubilized PE and EVOH fractions by lowering the temperature of the corresponding solutions to 25 °C** and adding acetone or water, respectively, to precipitate the polymer resins into solid form. The recovered materials, particularly PE and EVOH, are then separated from the toluene-acetone or DMSO-water mixtures by filtration. The solvents used in this process are isolated by distillation and can be reused.

To demonstrate the STRAP process described above, the authors first attempted to separate a physical mixture of resin pellets composed of PET, EVOH, and PE in a 7:2:2 ratio. They illustrated the separation process in Figure 8. The yields obtained for recovering the original polymers were quantitative: 98.5% by weight for PE, 95.7% for EVOH, and 100.7% for PET. The authors then sought to apply this technique to a rigid post-industrial multilayer film manufactured by Amcor Flexibles, one of their partners in this project. This multilayer film is primarily composed of PET, PE, and EVOH. The film was cut into small rectangular strips (1 × 1 cm) and dissolved successively, first in toluene at 110 °C, and then in a solvent composed of DMSO at 95 °C. Each dissolution step was performed with a solid-to-liquid ratio of 1:4 by mass. Following a vacuum filtration process, the filtered solutions were mixed with antisolvents at room temperature. These antisolvents consisted of four masses of acetone or water with respect to toluene or DMSO. Once cooled, the mixtures were filtered, and the residues were dried in a vacuum oven overnight at 85 °C to remove residual solvents.[100]

In 2021, Sánchez-Rivera et al.[101] studied the recovery of heterogeneous multilayer materials using the STRAP process, controlling temperature and reducing the amount of antisolvent. They compared two types of the STRAP process (STRAP-A and STRAP-B) for separating a multilayer film composed of PE, EVOH, PET, and EVA. With the STRAP-A process, PE and EVOH were dissolved respectively in toluene and DMSO, then precipitated in acetone and water, used as the respective antisolvents. This process does not allow the separation of PE from EVA. In the STRAP-B process, PE and EVOH were dissolved respectively in toluene and a mixture of 60% DMSO and 40% water (v/v). PE was precipitated by cooling the solution from 110 to 35 °C, and EVOH from 95 to 35 °C. According to the authors, one of the main differences between the STRAP processes was the yield of PE obtained. The yield of PE was higher with STRAP-A. This difference in yield is attributed to the presence of EVA in the PE. EVA is soluble in toluene and can also precipitate when acetone is added, along with PE. To remove EVA from PE, the authors used the STRAP-B process and performed a separation by lowering the temperature of the toluene to precipitate PE, while EVA remained in the solvent. EVA was then precipitated by adding acetone as an antisolvent. In the same paper, the authors attempted to separate a multilayer film composed of polyethylene terephthalate glycol (PETG), PE, EVOH, PET, and EVA. The dissolution of PETG was carried out at 87 °C for 4 h using a mixture of 60% dimethylformamide (DMF) and 40% tetrahydrofuran (THF) (v/v), followed by precipitation with n-propanol, prior to processing the other components. The same authors published a study in 2023[102]
<figure><img src="image_10.png" /><figcaption>**Figure 8.** STRAP process used to separate PP and EVOH32. A) Process schematic for deconstructing an Amcor Evolution multilayer film into its constituent resins using the STRAP process. B) Photographs of the Evolution film and the recovered resin using the STRAP process in (A). C) Photographs of comingled plastic resin beads consisting of 7:2:2 PE, EVOH, and PET and the recovered resins using the same procedure in (A). Adapted with permission.[100] Copyright 2020, from American Association for the Advancement of Science.</figcaption></figure>

on a printed multilayer film composed of PE, EVOH, PET, and polyurethane-based inks. Once PE and EVOH were separated, the ink was dissociated from PET using gamma-valerolactone (GVL).

To further the studies presented earlier, this section focuses on the dissolution of multilayer materials using green solvents. Cavalcante et al.,[103] explored the deconstruction of facial mask waste into separate components by employing green solvents. The dissolution method used by the authors in this study enables either the recovery of polypropylene (PP) or the production of nanofiltration membranes. For the recovery of polypropylene (PP), the layers of surgical masks were dissolved in p-cymene at a concentration of 15% by weight, at 140 °C, under stirring at 300 rpm. Subsequently, 25 mL of an antisolvent (ethanol, ethylene sulfite, γ-valerolactone, or terpineol) was added. The mixture was then stirred at room temperature overnight, thereby enabling the recovery of recycled PP microbeads with various mor-

phologies (powder, flakes, or grains). Regarding the production of nanofiltration membranes, the mask layers were dissolved at a concentration of 15% by weight in p-cymene at 140 °C for 20 min. The PP/green solvent systems were then cast onto a glass plate heated to 100 °C using an Elcometer 4340 film applicator (application speed: 6 cm s⁻¹; blade gap: 200, 250, or 300 µm). The resulting film was immersed in a 10 L ethanol bath maintained at a temperature of 20, 40, or 60 °C, before being cooled to room temperature. Another similar study, conducted by Ramírez-Martínez et al.,[104] focused on the use of green solvents for the dissolution of polyolefins (PP or LDPE) and membrane fabrication. The polyolefins were completely dissolved in solvents such as D-limonene or α-pinene. The polyolefin/green solvent system was then cast and immersed in an ethanol bath to extract the residual solvents and produce membranes.

The solvents used in dissolution-precipitation processes are grouped in the **Table 5**.
<table><caption>**Table 5.** Summary of Solvents used in selective dissolution-precipitation processes (inspired by¹⁴⁾).</caption><thead><tr><th>Target polymer</th><th>Solvent</th><th>Antisolvent</th><th>Dissolution temperature [°C]</th><th>Dissolution time</th><th>References</th></tr></thead><tbody><tr><td rowspan="3">LDPE</td><td>Xylene</td><td>Isopropanol</td><td>85</td><td>2 h</td><td>[95, 98]</td></tr><tr><td>biodiesel</td><td>ethanol</td><td>150</td><td>10 min to 1.5 h</td><td>[105]</td></tr><tr><td>Xylene</td><td>n-hexane</td><td>100</td><td>30 min</td><td>[99]</td></tr><tr><td>PE</td><td>toluene</td><td>acetone</td><td>110</td><td>4 h</td><td>[100, 101]</td></tr><tr><td rowspan="2">HDPE</td><td>Xylene</td><td>isopropanol</td><td>100</td><td>1 h</td><td>[95]</td></tr><tr><td>Xylene</td><td>n-hexane</td><td>100</td><td>30 min</td><td>[99]</td></tr><tr><td rowspan="4">PP</td><td>Xylene</td><td>isopropanol</td><td>135</td><td>1 h</td><td>[95]</td></tr><tr><td>Xylene</td><td>n-hexane</td><td>140</td><td>30 min</td><td>[99]</td></tr><tr><td>p-cymene</td><td>ethanol, ethylene sulfite, γ-valerolactone, or terpineol</td><td>140</td><td>—</td><td>[103]</td></tr><tr><td>benzyl alcohol</td><td>methanol</td><td>180</td><td>30 min</td><td>[99]</td></tr><tr><td rowspan="2">PVC</td><td>GVL (remove PU ink)</td><td>—</td><td>125</td><td>1 h (2x)</td><td>[102]</td></tr><tr><td>dichloromethane</td><td>methanol</td><td>40</td><td>30 min</td><td>[99]</td></tr><tr><td rowspan="2">EVOH</td><td>DMSO</td><td>water</td><td>95</td><td>30 min</td><td>[100, 101]</td></tr><tr><td>DMSO (60%)-water (40%)</td><td>Cooling from 95 to 35 °C</td><td>95</td><td>1 h</td><td>[100, 101]</td></tr><tr><td>PETG</td><td>DMF (60%)-THF (40%)</td><td>n-propanol</td><td>87</td><td>4 h</td><td>[101]</td></tr></tbody></table>

According to walker et al,¹⁰⁰ The two technologies currently marketed on an industrial scale for recycling multi-layer materials and similar to STRAP are APK's Newcycling process and the Creasolv process developed by Unilever and the Fraunhofer Institute. The Newcycling process, developed by APK, and recently acquired by LyondellBasell, enables the separation of multilayer polymers containing aluminum foil through preferential dissolution using solvents such as alkanes, isooctanes, or cyclooctanes. Since 2018, APK AG has been operating an 8000-ton-per-year plant in Germany based on this process, and it suggests that polyethylene, PET, polystyrene, polylactic acid, and aluminum could also be recovered using this method.

APK AG has patented an innovative process designed to remove at least one polymer component from plastic film waste. In this patent, several scenarios have been considered. The first scenario involves the extraction of PE from plastic film waste containing this polymer. After a mechanical pretreatment that includes washing with water at ambient temperature, the PE-based plastic film waste is dissolved in an n-heptane bath at 90 °C for 60 min, enabling the recovery of PE. The second scenario concerns plastic waste composed of 98% by weight of transparent sheets, 2% by weight of colored sheets, 4% by weight of HDPE sheets, and less than 0.2% by weight of metal and wood (based on the total weight of the solid content). The transparent and colored sheets are primarily composed of LDPE. The material is perforated and then immersed in an n-heptane-based solvent at a temperature between 85 and 90 °C for 60 min, allowing for the dissolution of LDPE. The undissolved components are subsequently removed via solid-liquid mechanical separation using a centrifuge. The third scenario focuses on solvent-based recycling of a multilayer film composed of PE/PA from a post-industrial source. These multilayer films are dissolved in an n-heptane bath at 90 °C to solubilize the PE. Subsequently, an antisolvent, specifically ethyl acetate, is added to extract the PE. The

recovered materials, namely PE and PA, are then extruded and regranulated. Another example, similar to the previous one, involves the extraction of PE from PE/PA multilayer films. A PE/PA film is immersed in a methylcyclohexane bath at 95 °C under agitation for 30 min. The PE dissolves, while the non-solubilized material is removed. The solvent is then evaporated under reduced pressure to obtain the extracted material. Finally, the last scenario involves a multilayer PE/PET film. The extraction of PE was carried out using a method analogous to the previous scenario, employing methylcyclohexane at 9 °C under agitation for 30 min.¹⁰⁶

The Fraunhofer Institute, in collaboration with CreaCycle GmbH, has developed a dissolution-precipitation process called Creasolv. This process, licensed to other companies, relies on the selective dissolution of polyolefins using a solvent from a group of aliphatic hydrocarbons. An antisolvent, such as 1-propanol or 1,3-propanediol, is then used to precipitate the polyolefin from the mixture. They have also worked on separating polystyrene.¹⁰⁰,¹⁰⁷

CreaCycle and the Fraunhofer IVV Institute have jointly developed the CreaSolv process, based on a standard treatment technology patented by the Fraunhofer Institute. One of the innovations derived from this process focuses on the recycling of at least one target polymer from plastic waste containing one or more contaminants. This invention presents several examples of material recovery. The first example concerns the recovery of expanded polystyrene (EPS) from insulating materials containing hexabromocyclododecane (HBCD). In this process, expanded polystyrene is dissolved in CreaSolv FR5 (10%, i.e., 10% polystyrene and 90% CreaSolv FR5) at a temperature ranging from ambient to 80 °C. To achieve this, 60 g of EPS is introduced into a 1-L container. The beaker containing 540 g of CreaSolv FR5 is then stirred for 60 min to facilitate dissolution. Spraying the EPS pieces with a portion of the solvent accelerates
ates dissolution, thereby halving the required processing time. Subsequently, 60 g of water is added as a precipitating agent to the dissolved polystyrene while maintaining stirring until visible precipitation occurs. After precipitation and gel formation, the liquid supernatant is removed. The viscous gel mass (153 g) is retained using a spatula, while the liquid supernatant is either decanted or poured off. Additionally, the supernatant, consisting of 487 g of solvent and 19 g of free aqueous phase, is separated into two liquid phases using a separating funnel. The HBCD-containing solvent is then subjected to a vacuum distillation process to gently separate the solvent from HBCD while avoiding excessive thermal stress, which could otherwise lead to the formation of undesirable polybrominated reaction products. The purified solvent distillate (465 g) can then be reused for the next batch (re-dissolving EPS) or for further extraction stages (re-dissolving the precipitated EPS gel). The water separated using the separating funnel can also be reused for precipitation. This process can be repeated until the desired concentration of HBCD in the polystyrene is achieved. Another example involves the recovery of ABS containing brominated flame retardants. ABS is dissolved in a dibasic ester or propylene carbonate (10%, i.e., 10% ABS and 90% solvent) at 80 °C. Water is used as an antisolvent to precipitate the dissolved polymer into a gel. The solution, composed of solvent and water, is separated from the gel, and the individual phases (water and solvent) are then isolated using a separating funnel. The solvent, purified of flame retardants through a distillation process, can be reused for subsequent polymer dissolution cycles. The separated water can also be reused for precipitation. These steps can be repeated until the desired amount of flame retardants has been removed. Finally, additional examples involving various other polymers have also been reported in this invention.[108]

Germany's Saperatec and Australia's PVC Separation have developed processes for separating multilayer materials using solvents, but without requiring complete dissolution of the polymers. Saperatec uses a process to separate multi-layer materials by reducing the interfacial tensions between PET, PE, and aluminum in an 18 000-ton-per-year plant that was expected to come online in 2021. The Australian company has developed a method for delaminating multilayer films using a solvent with a low boiling point. By exposing the films to hot water, the solvent is expelled, and the desired polymers are released and can be separated by density differences in a sieve.[107]

SAPERATEC GMBH has patented a process for separating a metal layer from a polymer in a multi-layer packaging material, where the polymer layer rests on the metal layer. This invention involves placing the packaging material in a bath containing a separation fluid, which is a mixture of water, at least one carboxylic acid, and at least one co-surfactant or hydrotrope. This separation fluid allows for a high degree of delamination within a given treatment time (e.g., 30 min). It affects the aluminum in the metal layer only to a very limited extent and has a flash point above 100 °C. The process then allows for the removal of the separated polymer layer and metal layer from the bath.[109]

PureCycle is another example of a company implementing multilayer recycling technology. It commercializes a patented purification recycling technology initially developed by The Procter & Gamble Company ("P&G"). PureCycle has established a facility capable of processing 54 000 tons per year to recover polypropy-

lene from post-industrial and postconsumer waste, producing a resin with near-virgin characteristics, known as ultra-pure recycled ("UPR") resin. The PureCycle process consists of two key steps: Feed Pre-Processing ("Feed PreP") and the dissolution principle. The Feed PreP stage involves collecting, sorting, and preparing polypropylene waste. The second stage entails dissolving multilayer waste in a proprietary solvent under high temperature and pressure to extract purified polypropylene. This process leverages supercritical fluids to extract and filter contaminants without altering the chemical structure of the polymer. Unlike other processes, PureCycle's technology can handle large volumes of plastic waste from diverse sources, but it recovers only a single recycled polymer component.[106,110]

One of Procter & Gamble's innovations concerns the purification process of recycled polypropylene. This invention explores several scenarios for PP recovery. One such scenario focuses on recovering mixed-color recycled PP flakes derived from post-consumer waste originating from the United States and Canada. To extract the PP, the flakes are placed in an autoclave equipped with a mechanical overhead agitator. The autoclave is then completely filled with n-butane and maintained at an internal fluid temperature of 140 °C under a pressure of 900 psig (6.21 MPa). The system is agitated for 10 min under these conditions, followed by an additional 10-minute stabilization period. A volume of n-butane is then evacuated from the autoclave into a sample collection flask, still at 140 °C and 900 psig (6.21 MPa). This extraction procedure is repeated four more times. The residual material in the autoclave after extraction is then dissolved in n-butane. The system pressure is adjusted to 12.41 MPa, and agitation is maintained for 10 min at 140 °C. The agitation is then stopped, and the solution is left to settle for 30 min at 140 °C under 6.21 MPa. After decantation, the solution is evacuated from the autoclave by displacement with pressurized nitrogen, preequilibrated at 140 °C and 1800 psig. The solution exits the autoclave through a dip tube and passes through two columns filled with thermally traceable solid media. The first column contains ≈21 g of Fuller's Earth (8–16 mesh), pre-mixed in a beaker with 21 g of Fuller's Earth (30–60 mesh). The second column consists of 21 g of silica gel (Siliccycle Ultra-Pure Silica Gels, SiliaFlash GE60) mixed with 21 g of aluminum oxide (Activated Alumina, Selexsorb CDX, 7×14). The fluid exiting the bottom of the second pressurized container is depressurized through a pressure regulator into a side-arm Erlenmeyer flask. After depressurization, the solvent vapor is vented through the side-arm outlet, while the liquid and solid fractions are collected in vials. The extracted solids are initially white and, after molding, become colorless and translucent, similar to virgin polypropylene. The opacity significantly decreases from 100% to ≈10%. Heavy metal contamination is greatly reduced: sodium concentration drops from 136 000 ppb to 4100 ppb, and other elements are reduced by 77% to 100%. The ash content also decreases, from 1.2117% to 0.3874%. The odor intensity improves significantly, reaching a rating of 0.5/5 compared to 3.75/5 for untreated post-consumer polypropylene, although a slight "plastic" smell remains. Finally, the polyethylene content decreases from 5.5% to 1.1%, indicating increased material purity. Other recovery scenarios have also been explored as part of this invention.[111]

To address the issues related to the recycling of multilayer films, there are several promising industrial approaches and pro-
<table><caption>**Table 6.** Methods for the treatment of multilayers and their degrees of maturity (inspired by[13]).</caption><thead><tr><th>Procedure/company</th><th>Raw material/recovery</th><th>Capacity</th><th><sup>a)</sup>TRL</th><th>Current status</th></tr></thead><tbody><tr><td></td><td colspan="4">Solvent-Based Recycling Processes</td></tr><tr><td>Creasolv (Fraunhofer IVV) [108, 112, 113]</td><td>PE from post-consumer multilayer pouches</td><td>1000 t/a</td><td>7</td><td>Pilot plant (2019) for recycling post-consumer multilayer pouches in Indonesia</td></tr><tr><td></td><td>PE and PP from, e.g.; multilayer (post-consumer) consisting of PE/PA, PP/PET, and aluminum content</td><td>Truckload per day (≈5 m³ per day)</td><td>5</td><td>Construction of an industrial-scale pilot plant (2020) in Germany as part of the "circular Packaging" project.</td></tr><tr><td>Newcycling (APK AG) (bought by LyondellBasell) [13, 107]</td><td>- Post-industrial (PE/PA and aluminium from multilayer films, separation of PE from PP)<br/>- Post-consumer</td><td>8000 t/a</td><td>7</td><td>Operation of a pilot plant (2018) in Germany and recently bought by LyondellBasell.</td></tr><tr><td>Saperatec GmbH [13, 109]</td><td>PET, PE, and aluminum from each other, Paper, plastic, and aluminum (liquid cartons)</td><td>18 000 t/a</td><td>5-6</td><td>Pilot plant (completion 2023).</td></tr><tr><td>Purecycle (Procter & Gamble) [13, 106, 110]</td><td>- Post-industrial (PP recovery)<br/>- Post-consumer (PP from, e.g., food and liquid packaging)</td><td>54 000 t/a</td><td>6</td><td>The plant is expected to be fully operational later in 2024.</td></tr><tr><td>Solvent-targeted recovery and precipitation (Chemical Upcycling Waste Plastics (CUWP)) [100]</td><td>PE, EVOH, and PET from each other</td><td>/</td><td>1</td><td>- STRAP originated in the University of Wisconsin and its development is based/funded on a U.S. Department of Energy project/consortium called CUWP<br/>- Release (solvent) of the target polymer from the composite system with subsequent precipitation and repetition for the next target polymer.</td></tr><tr><td>Recycling of post-consumer multilayer Tetra Pak packaging with the selective dissolution-precipitation process [98]</td><td>LDPE from aluminium (Tetra Pak cartons)</td><td>/</td><td>1</td><td>Separation through selective dissolution-precipitation process</td></tr></tbody></table>

cesses for their recycling at various degrees of maturity (TRL). These are summarized in Table 6.

## 4.4. Chemical Recycling

Chemical recycling offers an alternative to mechanical recycling by breaking down the macromolecular chains of polymer structures to obtain original monomers or other valuable chemical products.[96] The products resulting from the chemical decomposition of polymers can be used as raw materials for manufacturing new products. This method overcomes the limitations of mechanical recycling by directly processing heterogeneous polymers.

Today, plastic waste represents a valuable resource for producing chemicals and fuels. The focus is not only on energy recovery or mechanical recycling but also on generating valuable products such as monomers and petrochemical feedstocks.[114] As mentioned in section 3, there are three categories of chemical recycling: pyrolysis, gasification, and depolymerization. Catalytic pyrolysis is a widely used process for recycling polyolefins and other addition polymers. The products of pyrolysis include liquids and gases containing the desired substances. However, the costs of separation operations are generally high, so recycled products are often used as fuels.[115]

### 4.4.1. Pyrolysis

Mixed plastic waste, such as PE+PP, PET+PE, PET+PP, and PE+PVC combinations, as well as multilayer packaging, fiber-reinforced composites, and polyurethane from construction and demolition, remains particularly difficult to recycle. These types of waste are generally incinerated. However, pyrolysis emerges as a promising alternative for the treatment of these plastics. This thermal process, operating at temperatures ranging from 300 to 800 °C in the absence of oxygen, breaks down plastic materials into three main fractions: gases, liquids (also known as pyrolysis oils), and solid residues (called char).[116]

Undri et al.,[117] studied the recycling of a multilayer film (Paper/PE/Aluminum) via microwave-assisted pyrolysis. Microwaves were applied at a frequency of 2.45 GHz and a power of 3 kW, using various absorbers (shredded tires, carbon, and iron powder) and equipment configurations. The results revealed that the paper was pyrolyzed into a bio-oil containing water, alcohols, aldehydes, acids, and anhydrosugars. The PE was transformed into a highly viscous liquid and a solid at room temperature. The aluminum was recovered as intact, unaltered samples. Another similar study, conducted by Sivagami et al.,[118] focused on the catalytic pyrolysis of polyolefin-based waste and multilayer packaging in the presence of commercial zeolite-based catalysts. The multilayer packaging mainly consisted of biaxially oriented

<footnote><sup>a)</sup> Technology Readiness Level[107]: TRL 1-3 represents proof of concept/research; TRL 4-6 represents development; and TRL 7-9 represents deployment.</footnote>
polypropylene (BOPP), metalized BOPP layers (MET/BOPP), PET, metalized PET (MET/PET), PE/PET, and mixed polyolefin plastics. Pyrolysis, carried out at temperatures ranging from 450 to 500 °C, enabled the thermocatalytic depolymerization of the various plastics. The waste, pre-shredded into fragments of 2 to 5 cm, was mixed with a commercial zeolite catalyst (in the form of rods 3 mm in diameter and 8 mm in length) before being introduced into a pyrolyzer for heating. The products obtained — oil, gas, and char — showed that BOPP-based plastic waste had higher oil yields and calorific values (65 to 75%, 45.14 kJ g⁻¹) compared to PET-based multilayers (17.8%, 30 kJ g⁻¹) or metalized laminated plastics (13%, 37 kJ g⁻¹). The study also revealed that combining polyolefin-based waste with PET-based multilayers and BOPP/MET doubled the liquid yield and significantly altered the physicochemical characteristics of the resulting pyrolysis oil. This series of studies is complemented by the work of Veksha et al.,[¹¹⁹] on the conversion of flexible plastic packaging waste containing 12% and 28% by weight of PET (PET-12 and PET-28, respectively) into oil and multi-walled carbon nanotubes. The mixtures were pyrolyzed, and the volatile components produced were treated with catalysts (9% by weight of Fe₂O₃) supported on a ZSM-5 zeolite at 400 °C to remove oxygenated hydrocarbons that could degrade the oil quality. This process yielded oil samples containing fractions similar to gasoline, diesel, and heavy oils or waxes. The non-condensable gases were converted into multi-walled carbon nanotubes. The results show that the nature of the plastic packaging influences PET yields (PET-12: 2.4% by weight; PET-28: 1.5% by weight) as well as the properties of the resulting carbon nanotubes, due to differences in gas composition. Moreover, these carbon nanotubes have the potential to replace conventional electrode materials.

Although the pyrolysis of multilayer films represents an interesting solution, it is not fully suitable for recycling these materials due to their heterogeneity and architectural complexity. The presence of inorganic layers used as barriers, metals such as aluminum, and adhesives complicates the process and can generate undesirable by-products requiring additional treatments. Furthermore, pyrolysis can produce harmful compounds, such as hydrogen chloride (from PVC) or polycyclic aromatic hydrocarbons (PAHs). It should be noted, however, that multilayer films are generally composed of polyolefins rather than PVC, although post-consumer multilayer films may be contaminated with the latter. Finally, the heterogeneity of the layers in these films requires high temperatures (ranging from 400 to 800 °C), which significantly increases energy costs.

### 4.4.2. Gasification

Gasification is a chemical process that involves converting a solid feedstock, whether pretreated or not.[26] This process is based on partial oxidation,[120–122] enabling the conversion of almost all organic matter,[123] into a gaseous mixture containing CO₂, CO, H₂, CH₄, and other light hydrocarbons. This process requires an oxidizing agent, which can be a mixture of steam and pure oxygen or simply air.[124]

In 2013, Wilk et al. Hofbauer,[125] investigated the conversion of mixed plastic waste in a steam and dual fluidized-bed gasifier. Various plastic types were analyzed, including PE, PP, and the

blends PE/PS, PE/PET, and PE/PP. The results showed that the gas produced from PE was rich in CH₄ and C₂H₄ and had a lower heating value (LHV) of 25 MJ Nm⁻³. The proportion of PE converted into C₂H₄ was 22%. The study also demonstrated that blending PE with other polymers led to an increase in CH₄ and C₂H₄ concentrations as the PE proportion increased. Furthermore, gas from pure PP contained more CH₄ and less C₂H₄ compared to gas derived from PE. The study emphasized that polymer blends behaved differently from pure polymers. The PE/PP and PE/PS blends generated higher amounts of H₂ and CO, suggesting that the decomposition products of the polymers in the blend strongly interacted, significantly influencing the gasification process. During this process, more water was converted, improving both gas production and reforming reactions, leading to an increase in H₂ and CO yields at the expense of CH₄ and C₂H₄. The PE/PET blend differed from the others due to the high oxygen content of PET, which resulted in an increase in CO₂ emissions, reaching 28%. Conversely, when oxygen-free polymers were gasified, and CO₂ was only produced from reactions with steam, its level was reduced to ≈8%.

Another study, conducted by Li et al.,[126] explored the synergistic effects of co-processing (co-pyrolysis and co-gasification) of mixed plastic waste composed of PP and PS to optimize syngas production and energy recovery. This co-processing was carried out using a fixed-bed reactor at a temperature of 1173 K. The study found that the reforming reaction involving CO₂ was enhanced, leading to higher yields of H₂ and light hydrocarbons (HC). The co-processing of the PP/PS blend, with a higher PS content, resulted in stronger synergistic effects and increased syngas yields. In contrast, the co-gasification of the PP/PS blend with 40% PP content (2P3S) exhibited maximum synergistic effects on H₂, CO, and total syngas, with increased yields of 88.8%, 77.7%, and 74.2%, respectively. The study further revealed that each gram of 2P3S feedstock consumed ≈1.80 g of CO₂, leading to the highest recovered energy (27.49 kJ g⁻¹) and a maximum overall energy efficiency of 43.2%. The findings also indicated that thermal cracking and CO₂ reforming reactions, as well as the enhanced reactivity of carbon black, were the main contributors to increased yields of H₂, HC, CO, and total syngas during co-gasification.

Finally, Kannan et al.,[127] conducted a study on energy recovery through the c-gasification of PE waste and PET-containing blends. The results showed that the PE/PET blend had a positive effect on syngas yield and LHV. In the absence of external oxidizing agents, the primary and secondary oxidizing agents within the feedstock contributed to achieving a high syngas LHV (≈9 MJ Nm³), effectively eliminating the issue of nitrogen dilution. This study also highlighted that the energy efficiency of the PET-containing blend was significantly higher than that of PE gasification alone.

### 4.4.3. Chemical Depolymerization

The depolymerization of multilayer films is a promising method, as it recovers the various polymer layers in their original monomeric or oligomeric forms. These recovered materials can be reused in the production of new materials. One example of this promising approach is the study conducted by Ügdüler et al.,[128]
<table><caption>**Table 7.** Comparison of life cycle analysis of different multilayer film recycling methods.</caption><thead><tr><th>Technology</th><th>Configuration of Multilayer Films</th><th>Solvent</th><th>System Boundary</th><th>Energy used [MJ/kg]</th><th>Reference Greenhouse Gas [GHG] Emissions [Kg CO<sub>2</sub> eq./Kg]</th><th>GHG Emissions Reduction [%]</th><th>References</th></tr></thead><tbody><tr><td>Mechanical recycling</td><td>Multilayer films based on PE/PP, PA/PP and PET/PA</td><td>-</td><td>Collection, Sorting</td><td>-</td><td>2902</td><td>90</td><td>[133]</td></tr><tr><td>Mechanical recycling</td><td>Post-consumer flexible multilayer films based on LDPE</td><td>-</td><td>Washing, Sorting</td><td>Washing is the section that consumes the most energy.</td><td>0.46655</td><td>-</td><td>[134]</td></tr><tr><td>Mechanical recycling</td><td>PA/PE, PE/EVOH, PA/PE, PE/polyvinylidene dichloride (PVDC) and PA/EVOH/PE.</td><td>-</td><td>Energy consumption</td><td>-</td><td>-</td><td>-</td><td>[135]</td></tr><tr><td>Delamination</td><td>PA/PU/PO</td><td>Diethylene glycol</td><td>Difficult to recover the solvent</td><td>-</td><td>2.5</td><td>63</td><td>[88]</td></tr><tr><td>Delamination</td><td>Multilayer film waste based on PET and LDPE</td><td>Green organic solvents (ethyl acetate, biodiesel, 2-methyl tetrahydrofuran, and cyclopentyl methyl ether) and CO2 switchable solvents/additives comprising tertiary amines as switchable hydrophilicity solvents (SHSs), and switchable anionic surfactants (SASs) in aqueous solutions</td><td>Collection, Sorting</td><td>-</td><td>-<br>Tray PET:0.12596<br>- PET Film:0.43164<br>- POT LDPE: 0.04059<br>- LDPE Film: 0.46655</td><td>3%<br>-0.3%<br>-1.3%<br>-0.6%</td><td>[136]</td></tr><tr><td>Dissolution precipitation process</td><td>Post-consumer PET waste</td><td>GVL, water (antisolvent)</td><td>The process is energy-intensive.</td><td>17.86–56.22</td><td>1.08–3.55</td><td>50</td><td>[137]</td></tr><tr><td>Dissolution precipitation process</td><td>PE/EVOH/Ink/PET</td><td>dodecane (PE), DMSO/Water (EVOH)</td><td>The limitation of STRAP is that the process only produces small quantities of final material, less than 0.11 kilograms per week</td><td>100.8 (STRAP-A)<br>32 (STRAP-C)<br>19 (STRAP-B)</td><td>6.73 (STRAP-A)<br>1.48 (STRAP-C)<br>1.18 (STRAP-B)</td><td>-124<br>51<br>61</td><td>[101, 102, 138, 139]</td></tr><tr><td>Dissolution precipitation process</td><td>LDPE/EVA/TiO<sub>2</sub></td><td>limonene</td><td>The process is energy-intensive.</td><td>Heat (21.14), electricity (14.96), water (278.15)</td><td>2.37</td><td>60</td><td>[140]</td></tr><tr><td>Dissolution precipitation process</td><td>PA/PE</td><td>Mono ethylene glycol</td><td>High energy consumption</td><td>-</td><td>-</td><td>-</td><td>[141]</td></tr><tr><td>Pyrolysis</td><td>Metallised food packaging plastics waste (MFPW)</td><td>-</td><td>High energy consumption</td><td>-</td><td>-</td><td>-</td><td>[142]</td></tr><tr><td>Pyrolysis</td><td>Flexible packaging plastic waste based on PET</td><td>-</td><td>Sorting, Type and weight of catalyst</td><td>-</td><td>-</td><td>-</td><td>[143]</td></tr><tr><td>Chemical depolymerization</td><td>Multilayer film waste based on PET</td><td>-</td><td>Collection, Sorting</td><td>-</td><td>0.13105</td><td>23</td><td>[136]</td></tr></tbody></table>
<table><caption>**Table 8.** A brief comparison of multilayer material recycling methods.</caption><thead><tr><th>Criteria</th><th>Mechanical recycling</th><th>Delamination</th><th>Dissolution-precipitation</th><th>Pyrolysis</th><th>Depolymerization</th></tr></thead><tbody><tr><td>Film Complexity</td><td>++</td><td>+</td><td>-</td><td>-</td><td>-</td></tr><tr><td>Product Quality</td><td>-</td><td>+</td><td>++</td><td>±</td><td>++</td></tr><tr><td>GHG Emissions</td><td>++</td><td>±</td><td>±</td><td>-</td><td>±</td></tr><tr><td>Cost</td><td>++</td><td>+</td><td>-</td><td>-</td><td>-</td></tr><tr><td>Environmental Impact</td><td>+</td><td>±</td><td>±</td><td>-</td><td>±</td></tr></tbody></table>

Legend: ++: Highly favorable; +: Favorable; ±: Moderate or condition-dependent; -: Unfavorable; -: Highly unfavorable.

However, the use of multiple solvents cannot be ruled out. Compared to other methods, delaminated products generally require good sorting. In the case of printed multilayer films, a de-inking step is required.

The selective dissolution-precipitation method attracts particular attention in the recycling of multilayer films due to the selective separation of the different layers via precipitation or cooling. This process could be adapted to different combinations of multilayer films. The recycled layers generally retain their chemical structure and are essentially of high purity. However, the use of solvents, anti-solvents, and precipitation processes leads to a significant increase in the energy used and the cost of the process. Furthermore, the use of anti-solvents significantly increases GHG emissions, as reported in the LCA section (in the case of STRAP-A). Instead of anti-solvents, a cooling or evaporation system is generally implemented to precipitate the dissolved products. Consequently, this alternative also helps to reduce GHG emissions.

Regarding pyrolysis, it is a method that converts multilayer films into derived products such as oils, gases, and solid residues. This process is capable of treating complex mixtures or contaminated films. However, compared to other methods, it has a significant environmental impact. Due to the use of high temperatures, this process results in high energy costs.

The use of depolymerization allows for the chemical transformation of multilayer films into their base monomers or oligomers. However, this method appears to be the most energy-intensive, similar to pyrolysis. This process generally requires the use of solvents or catalysts, which increases its relative cost. For example, glycolysis often requires excessive use of solvents, which supports the previous point. The advantage of this method lies in its ability to produce monomers or oligomers of high purity, close to that of virgin materials.

The choice of method will depend on the environmental, and economic goals and the specific nature of the multilayer films to be treated.

## 7. Eco-Design Through Recycling: Replacing Multimaterial Multilayers by Mono-Material Multilayer-Based Configurations

In this section, we will address the concept of eco-design through the recycling of multilayer films. The notions of multi-material and mono-material will be introduced and explored. A multimaterial multilayer plastic film refers to packaging composed of several layers of polymers of different natures. Conversely, a

mono-material multilayer film consists of layers made from polymers of the same nature. This latter type of film is gaining popularity due to its ease of recycling and compatibility with existing recycling streams.

For instance, a coextruded PE/PE or PP/PP film perfectly exemplifies a mono-material multilayer film. These films exhibit high mechanical properties and barrier performance, particularly against moisture.[116] The barrier properties can be compensated by the addition of organo-modified clay,[48] nanocellulose,[144] and graphene hybrid coatings.[145]

In 2022, Guerritore et al.,[145] developed new flexible mono-material films, designed to be recyclable, with high gas and UV barrier properties. This enhancement was achieved by applying hybrid coatings based on graphene oxide and graphene oxide/montmorillonite onto polyethylene (PE) and polypropylene (PP) substrates. The study focused on cast films of PE and PP, as well as the aqueous dispersion of graphene oxide (GO) and Cloisite Na⁺ (MMT). The application of GO and GO-MMT coatings on PE and PP films was carried out using a “K Hand Coater” (Royston, UK). The coating thickness ranged from 140 to 200 nm, corresponding to volume fractions of 0.2%–0.3% for PE-based systems and 0.3%–0.4% for PP-based systems. The results of this study reveal that these coatings provide remarkable UV barrier properties, as evidenced by a 40%–60% reduction in transmittance at a wavelength of 400 nm. Additionally, oxygen permeability was reduced by 97.5%–98.5% for PE and 94%–96.5% for PP. Water vapor transmission was also decreased by 68%–72.5% for PE and 70.4%–78.8% for PP. The recyclability of these films was demonstrated through laboratory-scale reprocessing by extrusion. After extrusion and compression molding of the films, homogeneously distributed 2D nanostructures were observed in the effective section of the recycled samples. These structures result from the fragmentation of the original coatings and the dispersion of stacked platelets within the polymer matrices. The study shows that these platelets were well aligned along the film direction. Furthermore, in the case of PE films, polymer phase mixing within the platelets was also observed. Finally, the results indicate that the presence of nanofillers in the recycled samples did not significantly affect the mechanical properties of the polymers compared to virgin recycled films. In conclusion, this study demonstrates that applying graphene-based coatings to produce monomaterial gas-barrier films for packaging applications is a promising strategy. It enables the design of high-performance products while ensuring their recyclability.

According to European Directive 94/62/EC, as amended by Directive (EU) 2018/852, multilayer packaging may be considered monomaterial packaging under certain conditions. This directive
<figure><img src="image_11.png" /><figcaption>**Figure 9.** Eco-design by recycling: from multi-material multilayer to mono-material multilayer.</figcaption></figure>

defines multilayer packaging as packaging composed of several distinct materials. Thus, a multilayer package can be classified as “monomaterial” if the proportion of different materials, including impurities, does not exceed the 10% threshold.[146]

The proposed European PPWR regulation (2022), which aims to enhance the recyclability of packaging in Europe, sets out specific rules for multilayer packaging. It introduces strict recyclability criteria: a multilayer package containing less than 10% impurities may be exempt from certain recycling obligations for composite materials, provided that it is primarily composed of a single recyclable material.[147]

These two legislative texts are part of an effort to facilitate the recycling of multilayer packaging and reduce its environmental impact.

With the aim of complying with the two legislative texts detailed above, new multilayer film configurations have been developed to reduce both the proportion and the number of components in these films, thereby facilitating their recyclability. Figure 9, perfectly illustrates these new configurations of multi-micro-nano-layer films, characterized by a reduced number of components and produced using a process called coextrusion. This process relies on the use of multiple extruders—three in this case—each fed with different materials: Material B (MatB, polyolefin-based material: PE, PP, etc.) in extruder B, Material C (MatC, barrier material: EVOH, PA6, PVDC, etc.) in extruder C, and Material A (MatA, binder) in extruder A.

The materials are then melted and directed to the feed block, whose function is to confine them. This coextrusion process enables the production of a five-layer film at the feed block outlet when all three extruders operate simultaneously. Additionally, multiplier elements installed on this feed block allow for an increase in the number of layers. The total number of layers obtained is given by the formula $2^{n+2}+1$, where n represents the number of multipliers.

The objective is to reduce the number of components while preserving the film's barrier, mechanical, and physicochemical properties. This involves eliminating the binder and reducing the proportion of the barrier material to below 10%. Subsequently, the forced assembly process, combined with the multiplier elements, enables the creation of micro-nanolayer films composed primarily of polyolefins, with a barrier material content of less than 10%, in compliance with the European directive.

Studies have already been conducted on the eco-design approach through recycling.[4,145] Further research is currently underway as part of the PEPR project (Priority Research Programs and Equipment).

## 8. Conclusion and Perspective

The production of plastic waste represents a global challenge that requires appropriate solutions. Flexible plastic films, increasingly prevalent in the industrial sector, particularly in packaging, present specific challenges for recycling. These films are generally composed of multiple layers with different chemical properties, which complicates their recyclability. In this work, various treatment methods are proposed, including physical recycling, which encompasses mechanical recycling, delamination, and selective dissolution-precipitation, and chemical recycling, which includes pyrolysis, gasification, and depolymerization.

However, most of these methods have limitations when multilayer films come from post-consumer waste, as the latter are often composed of mixtures of different types of polymers with unknown compositions. Conversely, when multilayer films come from post-industrial waste, they are generally clean and of known
composition, making them compatible with most of the methods mentioned above.

Among all these methods, mechanical recycling is the least energy-intensive and has the lowest environmental impact, followed by delamination. Life Cycle Assessment (LCA) studies reveal that the selective dissolution-precipitation method has a significant environmental impact due to the intensive use of solvents, anti-solvents, and energy required for the process. Chemical recycling, on the other hand, is the most energy-intensive method and has the highest environmental impact. However, its main advantage lies in the high purity of the resulting products, comparable to virgin materials.

One of the solutions proposed in this study for recycling multilayer films involves adopting an eco-design approach aimed at replacing multi-material multilayer films with mono-material multilayer films. However, this method requires thorough and rigorous study to ensure its feasibility and effectiveness.

## Acknowledgements

The authors are grateful for the financial support from PIA France 2030 and the French National Research Agency (ANR) through the PEPR program Plastics 22-PERE-0002.

## Conflict of Interest

The authors declare no conflict of interest.

## Keywords

eco-design, life cycle assessment, multilayer barrier flexible polymer films, recycling

Received: November 7, 2024

Revised: February 25, 2025

Published online:

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<figure><img src="image_12.png" /></figure>

Hissein Bechibo Adam obtained his mechanical engineering degree from INSA Lyon in 2021, followed by a specialized master's in polymer processes from IFP School in 2022. He then worked for two years at Michelin as a business and sustainable development engineer in thermoplastics and elastomers. Since 2023, he has been a Ph.D. student at the Polymer Materials Engineering (IMP) laboratory at INSA Lyon, focusing on multilayer polymer barrier films. His research investigates their elaboration, rheology, and recyclability to enhance their integration into the circular economy.
<figure><img src="image_13.png" /></figure>

**Mohamed Yousfi** obtained his Ph.D. from Grenoble INP in 2010. After postdoctoral research on self-reinforced multiphase polymer systems for sustainable and high-performance applications, he joined the Polymer Materials Engineering (IMP) laboratory at INSA Lyon in 2017 as an associate professor. His research activities are focused specifically in the area of interfacial rheology, polymer processing, and related fields. Currently, he is involved in different collaborative research projects including additive manufacturing applications, plastics recycling as well as the processing of thermoplastic polymer foams. Since 2023, he has been an Editorial Board Member of Applied Rheology (De Gruyter).

<figure><img src="image_14.png" /></figure>

**Abderrahim Maazouz** is a full professor of Polymer Engineering and Science in the Laboratory of Polymer Materials Engineering (IMP) at the National Institute of Applied Science (INSA Lyon, University of Lyon), France. Prof. Maazouz's research interests cover wide domains, including i) Structure/processing/property relationships of polymers; ii) Rheology and process engineering of polymer materials, biopolymers, and their composites; iii) Interfacial phenomena in the polymer and composites processing; iv) Monitoring and optimization of polymer processes.

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**Khalid Lamnawar** obtained his Ph.D. degree in 2007. Since then and beyond some Post-doctoral positions, he rose to become associate in 2010 and full professor in 2021 at INSA Lyon-France. His research is focused on rheology, processing & recycling of polymers and their multiphase systems (including biopolymers, and composites). He is/has been actively involved as Principal Investigator (PI) of numerous scientific projects. He is the organizer/chair of many national and international conferences. Owing to his accomplishments, he has given more than a dozen invited lectures and seminars to industrial and academic organizations and he has been recognized with numerous awards. Leader of Rheology and Polymer Processing group in his Lab and editorial member of many journals, he is Organizer and the general chair of YRD 2021 and the AERC 14-17 April 2025 to be held in Lyon. Since 2022, he is PI of France 2030 PEPR Recycling of Plastics.