Introduction
Coating is a strategic enabling technology in both flexible and rigid packaging, for plastic polymers as well as cellulosic substrates, as it can provide barrier properties against moisture, oxygen, grease, and aromas without compromising packaging recyclability or lightweighting. In the context of the new Regulation (EU) 2025/40 (PPWR), coating design is becoming a key factor in achieving the A–C recyclability performance grades required from 2030 onwards and in complying with the limits on non-recyclable content.
In plastic polymers, functional coatings – such as thin barrier layers based on metal oxides, nanocomposites, or biopolymers – can reduce film thickness, optimize performance, and enable the incorporation of increasing percentages of post-consumer recycled content, as required by the PPWR for each packaging component. Proper coating engineering also helps prevent contamination of recycling streams and supports the technical documentation required to demonstrate compliance with design-for-recycling criteria.
In cellulosic materials, coatings based on cellulose derivatives, biopolymers, or hybrid organic/inorganic systems improve mechanical strength and water-vapour barrier properties – by up to 70% in some studies – making paper competitive with plastic in applications involving moisture or food contact, while maintaining compatibility with cellulose-fibre recycling processes. From a PPWR perspective, selecting coatings that are compatible with recycling processes and minimizing the non-cellulosic fraction are key strategies for maximizing recyclability performance.
In-depth analysis
Coating formulation and application are becoming critical factors in preventing packaging from being downgraded to recyclability performance grades D or E and consequently excluded from the EU market from 2030 onwards.
For plastic polymers, high-performance barrier coatings – such as nanocellulose, metal oxides or inorganic materials deposited under vacuum, and biopolymers – make it possible to replace complex multilayer structures with mono-material solutions (PE, PP, PET) compatible with existing recycling streams. At the same time, they reduce the risk of contamination and facilitate the demonstration of compliance with RecyClass/CEFLEX recyclability criteria.
Water-based and PFAS-free solutions, for example, demonstrate that it is possible to achieve an OTR below 1 cc/m²·day and a WVTR below 1 g/m²·day with a coating weight of approximately 1 g/m², while maintaining recyclability and supporting the use of post-consumer recycled content, a requirement applying across all plastic components of packaging.
For cellulosic substrates, the challenge lies in balancing barrier performance – against water, oil, and oxygen – with disintegrability in paper recycling processes. Coatings based on cellulose derivatives, nanofibrils, and lignin improve performance without exceeding the critical threshold of 5% by mass of non-cellulosic components, a necessary condition for the recyclability of fibre-based packaging.
The ability to demonstrate, through independent testing, that the coating does not hinder fibre release and does not adversely affect the quality of the recycled pulp is now a prerequisite for achieving recyclability performance grades A–B.
From this perspective, coating is not merely a technical additive, but an integral element of circular design that directly affects market access, economic competitiveness, and the regulatory compliance of packaging within the new PPWR framework.
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Recyclable-by-design mono-material flexible packaging with high barrier properties realized through graphene hybrid coatings
Due to the large production of plastic packaging, packaging mismanagement represents a significant problem for the environment and the related economic/social contexts. A new route towards sustainable recycling has been identified in the design of the plastic products together with their end-of-life recycling options. Following this approach, in this work, new recyclable-by-design mono-material flexible films with high barrier properties to gases and UV radiation have been developed by applying graphene oxide (GO) and graphene oxide/montmorillonite (GO/MMT) hybrid coatings on polyolefin substrates. The coatings induce a remarkable reduction of the UV transmittance (40–60%) and of the oxygen (94–99%) and water vapour (68–73%) permeability of the films, with very good stability after prolonged water immersion. Reprocessing tests demonstrate the easy recyclability of the coated films, whose commercial analogues are currently considered as non-recyclable. By extrusion and compression moulding, recycled films are obtained in which the nanostructured phases result well embedded in the polymer matrices. The mechanical properties of the samples obtained by reprocessing coated polyethylene and polypropylene films are comparable to those of the reprocessed pristine films. Moreover, no significant release of GO by water immersion for 24 h at room temperature is detected from the recycled samples. Overall, the results indicate that the application of thin GO/MMT coatings to realize mono-material barrier films for packaging applications is an effective strategy to realize high performance products able to be easily recycled. These mono-material flexible films represent a new sustainable end-of-life option with respect to current commercial multi-layer products.
https://www.sciencedirect.com/science/article/abs/pii/S0921344921007345
Effect of coating weight on barrier performance and recyclability of solvent based PLA coated paper
A recyclable water barrier coating for paper was developed using a biobased poly(lactic acid) (PLA) dissolved in ethyl acetate, a safe solvent for food contact applications. Citric acid (CA) was added as a plasticizing additive. Coatings prepared at 5, 10, 15, and 20 wt% solids were applied onto 50 g m−2kraft paper, to achieve coat weights of 2.00 ± 0.50, 4.50 ± 1.10, 6.68 ± 0.72, and 9.98 ± 2.26 g m−2. An optimal coating weight 6.68 ± 0.72 g m−2 reduced water vapor transmission rate (WVTR) from 222.37 ± 6.22 to 83.97 ± 0.62 g m−2·day−1, whereas a higher coat weight 9.98 ± 2.26 g m−2 increased WVTR to 133.11 ± 6.84 g m−2·day−1, indicating that barrier performance is governed by coating uniformity rather than thickness alone. Cobb values decreased from 20 ± 0.82 to 3 ± 0.47 g m−2 (1 min) and from 36 ± 2.05 to 27 ± 1.25 g m−2 (1440 min), while grease resistance reached kit 11.2 ± 0.40, exceeding commercial food-wrap benchmarks. ATR-FTIR confirmed increasingly carbonyl intensity (∼1750 cm−1) with coat weight, indicating improved surface coverage, consistent with surface film formation and cross-sectional SEM evidence of a largely confined layer with limited penetration. Repulpability criteria met across all coat weights, with recyclability handsheets properties satisfying guideline thresholds up to 6.68 ± 0.72 g m−2, while slightly higher stickies were observed at 9.98 ± 2.26 g m−2. These findings establish that low-add-on, uniform PLA coating can simultaneously deliver barrier performance and recycling compatibility, offering a pathway toward circular barrier coated paper and paper products.
https://www.sciencedirect.com/science/article/abs/pii/S0300944026004935
Bio-based furan polyester/cellulose composites with enhanced barrier properties and closed-loop recyclability for sustainable food packaging
To solve the problem of insufficient barrier properties caused by the hydrophilicity and porous structure of traditional cellulose materials, the use of polymers to modify cellulose has attracted attention. However, traditional modification methods can affect the recoverability of cellulose materials. This study developed a bio-based furan polyester/cellulose composite (PBPF-paper) through molecular design to solve the problem. The inherent rigidity of furan rings in PBPF grants exceptional gas barrier properties, while cleavable ester bonds enable closed-loop chemical recycling. Crucially, the multiple hydrogen bonds between these esters and cellulose create a robust interface, integrating high strength, barrier properties, and recyclability into a single material which is a challenge rarely achieved in prior studies. PBPF50-paper achieved a 386 % increase in tensile strength compared to Raw paper, and ultralow water vapor and oxygen transmission rates are 4.33 g/(m2·24h) and 0.14 barrer, respectively. The composite maintained stable water/oil resistance even under extreme conditions (90 °C) and enabled closed-loop recycling via alkaline hydrolysis. Practical strawberry preservation tests with only 17.74 % weight loss after 7 days verified its effectiveness over conventional packaging. This work provides a novel strategy for designing recyclable cellulose-based composites with integrated strength, barrier properties, and sustainability, advancing eco-friendly solutions for food packaging applications.
https://www.sciencedirect.com/science/article/abs/pii/S1385894725117294
Development of fluorine-free, all-water-based bilayer-coated paper with superhydrophobicity, oil resistance, and anti-bacterial adhesion properties for high-performance food packaging
Food spoilage causes massive waste and safety risks, demanding eco-friendly packaging. Conventional paper coatings use nondegradable plastics/hazardous solvents, whereas biobased coatings lack water resistance and have high bacterial adhesion. To solve this problem, an all-water-based, fluorine-free bilayer coating was developed for superhydrophobic, oil-resistant paper (SS-ABC): sodium alginate (SA)/soy protein isolate (SPI) base layer for oil repellency, and alkyl ketene dimer (AKD)/bamboo powder (BP)/carboxycellulose nanofiber (C-CNF) top layer for superhydrophobicity. SS-ABC showed superhydrophobicity (water contact angle: 156.80 ± 0.44°; Cobb60: 14.89 ± 0.70 g/m2), water sliding angle (16.48 ± 0.68°), and oil resistance (Kit rating: 10/12; oil contact angle: 100.25 ± 0.72°), meeting GB/T 44834-2024. It reduced E. coli/S. aureus adhesion by 83.78 %/84.90 % compared with uncoated paper, maintained stability under 95 °C hot water/oil and 80 abrasion cycles, and complied with GB 31604.1–2023 (migration ≤10 mg/dm2). Mechanistically, SA/SPI interactions and Ca2+crosslinking enhanced the oil barrier performance; AKD recrystallized into platelets (with C-CNF/BP acting as supports) for dual-scale roughness, with AKD alkyl chains lowering the surface energy. This strategy enables biodegradable and recyclable paper, offering a green food packaging solution to reduce waste and improve industry sustainability.
https://www.sciencedirect.com/science/article/abs/pii/S2212429225023776
