The following is part of Sun Chemical’s SunSustain Green Paper Series.

Introduction: Hidden Barriers – or Enablers! – to Circularity

Flexible film packaging plays a critical role in modern supply chains by protecting products, reducing food waste, and enabling efficient logistics. Yet flexible films remain one of the most challenging packaging formats to recycle at scale. Public and regulatory discussions most often focus on substrate/polymer choice and package structure, particularly the shift toward mono-material polyethylene (PE) and polypropylene (PP) solutions. While these efforts are essential, they are only part of the solution.

Inks, coatings, and adhesives – present in relatively small quantities and often invisible to the end user – can ultimately determine whether a package successfully enters existing recycling streams or is rejected, downgraded, or discarded. These materials are typically designed for aesthetics, graphics and design, print quality, protection, and lamination performance, not for survival through washing, melting, and re-extrusion. As a result, improper selection of these items can unintentionally undermine otherwise well-designed recyclable film structures.

Building on earlier SunSustain green papers, including those addressing nitrocellulose binders and regulatory/legislative drivers, this paper explores the critical importance of inks, coatings, and adhesives on film packaging recyclability. It highlights known challenges, emerging solutions, and the importance of a system-level approach to enable real, scalable circularity.

The Recycling Reality for Flexible Films

Mechanical recycling remains the dominant end-of-life pathway for flexible polyolefin packaging. These processes rely on a series of steps – collection, sortation, washing, grinding, melting, and re-extrusion – to convert waste films into reusable resin. At each stage, non-polymeric components can introduce unwanted defects in the recyclate, such as discoloration, haze, odor, gel formation, and/or reduced mechanical properties.

Unlike rigid packaging, flexible films have a high surface-area-to-volume ratio. This means inks, coatings, and adhesives represent a proportionally larger share of the total package chemistry, even when applied at very low weights. When these materials are not designed or chosen with end-of-life processing in mind, for example – if they are thermally unstable, insoluble, or incompatible with the base polymer – they can degrade recyclate quality significantly. In practice, the result is downcycling, loss of economic value, and/or failure to meet recyclability guidelines and certifications.

Inks: From Decoration to Recycling Compatibility

The Nitrocellulose Challenge

Nitrocellulose (NC) has long been the workhorse binder for solvent-based flexographic inks, valued for its printability and film-forming properties. However, NC begins to decompose thermally at temperatures below those typically used in plastics reprocessing. During recycling, this degradation leads to generation of volatiles, odor, discoloration, and physical defects in recovered plastics, making NC an increasingly acknowledged barrier to flexible packaging recyclability.

The development of thermally stable NC alternatives represents an important step forward for the packaging market. These alternative binder systems demonstrate that high-quality printing and improved recyclability do not need to be mutually exclusive. However, focus on binder replacement alone is insufficient. Pigments, dispersants, waxes, and other additives must also be carefully selected to avoid carryover color, haze, or unwanted interactions during recycling.

Sun Chemical has developed a global NC-alternative ink platform, which exhibited excellent performance in third-party recyclability testing.

Washable and Deinkable Ink Systems

One potential pathway toward improved recyclability is ink removability. Washable (or deinkable) inks are designed to detach from the film surface during standard recycling caustic wash steps, allowing filterable ink particles to be separated from the polymer. When successful, this approach can significantly improve the appearance and value of recycled resin, since color and other formulation components are removed.

Deinking performance in plastic recycling depends on the complete print system and packaging structure. Laminations that encapsulate inks within multi-layer constructions are a primary barrier to effective ink removal, given that they prevent inks from being exposed to wash solutions and separated during recycling. Overprint varnishes and coatings can also prevent solutions from contacting the inks, while lamination adhesives that do not readily separate or break down during washing and processing can reinforce ink entrapment by maintaining layer integrity. Thus, inks should be chosen not as standalone products, but within the context of the full, integrated packaging design.

Coatings: Functional Performance in a Recycling Context’

Coatings play a critical role in flexible packaging by delivering a range of performance attributes. Protective coatings are commonly used to provide surface durability, abrasion resistance, slip control, and heat or scuff resistance, while barrier coatings are designed to impart oxygen, moisture, grease, or aroma resistance. These functions are often achieved through different coating chemistries and film‑forming mechanisms, which must be evaluated based on their intended role in the package.

From a recyclability perspective, both protective and barrier coatings can introduce challenges when their chemistries are not compatible with mechanical recycling processes. Highly crosslinked coatings, coatings with high softening or melting temperatures, and those that persist as insoluble residues through washing and extrusion can remain embedded in plastic flakes or be carried into the melt. In addition, nitrocellulose‑based coatings are problematic for the same reasons as nitrocellulose-based inks, described previously.

Innovations in functional coatings, on the other hand, offer pathways to mitigate flexible packaging recyclability challenges. Certain barrier and protective coatings can replace entire film or metallization layers, reducing structural complexity and overall material usage. When designed with appropriate thermal behavior, solubility, and controlled interaction with inks, functional coatings can enable downgauging, support mono‑material and mono-web constructions, and improve ink wash‑off or fragmentation behavior during recycling. In this way, coatings can shift from being a recyclability constraint to becoming a key enabler of circular plastic packaging design – provided they are engineered as part of an integrated system rather than as standalone solutions.

Adhesives: Structural Integrity Without Negative Impact

Lamination adhesives play a critical, though often under‑recognized, role in packaging recyclability. While adhesives are essential for structural integrity, barrier performance, and durability, they can also have a disproportionate influence on recycling outcomes when they are not designed with end‑of‑life considerations in mind.

Incompatible adhesive systems may contribute to phase separation, gel formation, or incomplete melt homogenization, and in multi‑layer or printed structures they can encapsulate inks or pigments between layers, limiting both effective deinking and clean reprocessing. These effects can negatively impact recyclate quality even when the primary polymer itself is fully recyclable.

Significant progress has been made in addressing these challenges through solvent‑free and recycling‑compatible lamination adhesive technologies, particularly those based on Ultra‑Low Monomer (ULM) polyurethane chemistries. ULM technology is specifically designed to minimize residual reactive species, reduce the risk of unwanted side reactions during reprocessing, and improve stability during melt filtration and extrusion. These characteristics support improved polymer integrity and reduce the likelihood of gel formation or contamination in recycled streams.

Importantly, these advances are not theoretical. Sun Chemical has invested in structured recyclability testing, including formal evaluation programs conducted in alignment with European recycling (RecyClass) protocols. These programs assess adhesive behavior under defined recycling conditions, providing data on melt behavior, filtration performance, and compatibility within existing recycling streams. Such testing enables objective validation that functional adhesive performance can coexist with recyclability requirements, and several Sun Chemical lamination adhesive products are formally approved through this process.

As with inks and coatings, early material selection and validation are essential. Adhesives should be evaluated as an integral part of the packaging system rather than as an afterthought. When selected and qualified using recognized recyclability frameworks, modern adhesive technologies can deliver the required structural and functional performance without introducing negative impacts at end of life, supporting both packaging performance and circularity objectives.

System Design for Recyclability

True recyclability cannot be achieved by optimizing individual components in isolation. Recycling processes evaluate the package as a complete system, and unexpected interactions between inks, coatings, adhesives, and substrates can lead to failure – even when each component appears compliant on its own.

A system-based design approach includes early collaboration across the value chain, alignment with recyclability guidelines, validation under realistic recycling conditions, and transparency around formulation choices. Experience has shown that small changes in low-level components like pigments, inks, coatings, and adhesives can have outsized effects on recycling performance.

Looking Forward: Beyond Compliance

Regulatory pressure – including Extended Producer Responsibility (EPR) schemes, recyclability mandates, and emerging toxics‑in‑packaging requirements – is accelerating change in flexible packaging design. However, the opportunity extends well beyond meeting minimum compliance thresholds. Higher‑quality recyclate supports stronger recycling economics, improves material circularity, and helps close material loops at scale.

In this context, Sun Chemical’s Beyond Compliance program reflects a proactive approach that goes beyond recyclability alone by addressing substances of concern that are increasingly within regulatory scope under EPR frameworks. By integrating chemical stewardship, recyclability performance, and forward‑looking regulatory assessment, this approach helps reduce brand owner reputational risk and future compliance risk while supporting safer, more sustainable packaging systems.

Innovation across ink binders, washable ink systems, functional coatings, and recycling‑compatible adhesive technologies demonstrates that packaging can deliver performance, differentiation, and circularity simultaneously. When designed and validated holistically, these components enable cleaner recycling outcomes while aligning with evolving regulatory and societal expectations. In this framework, inks, coatings, and adhesives are not secondary considerations – they are foundational enablers of a truly circular economy for film packaging.