FEICA Recycling Terminology and Definitions

Terminology and definitions to be used in the context of adhesives in packaging recycling

Various organizations publish guidelines on recycling, including requirements for adhesives in recycling. Different terminology is used in these guidance documents, and this terminology often differs from that used in the adhesive industry and by adhesive users. In this context, FEICA wants to help all stakeholders develop a common understanding of requirements important for adhesives and adhesive recycling. A common language and technically sound definitions will help foster better understanding among stakeholders and facilitate easier exchange of expertise.

Classification of adhesives used in packaging

Adhesives can be classified according to their chemistry and function. The following adhesive chemistries and functions may be found in packaging: Adhesive chemistries used in or on packaging Polyurethane Adhesives Polyurethane adhesives are based on reactive chemistry in which isocyanates react with polyols and/or water. The high thermal resistance of polyurethanes, including resistance to autoclaving processes, results from chemical cross-linking. This cross-linking is achieved either by using a two-component liquid polyurethane adhesive system or by moisture curing of a one-component reactive polyurethane adhesive. Where liquid adhesive systems are concerned, solvent may be added to one or both components to reduce their viscosity. One-component polyurethane adhesives can be liquid adhesives or (reactive) hot-melt adhesives.

(Non-reactive) Water-Based Adhesives

Water-based adhesives can be dispersions or solutions. Polymer dispersions are two-phase systems where polymer particles are dispersed in water. In solutions, polymers are dissolved in water and the system is single-phase (the product is a clear liquid). Water-based adhesives are applied as liquids at room temperature or slightly elevated temperatures and set through water evaporation and/or water absorption into the substrate (penetration).1

Natural Polymer-Based Water-Based Adhesives

Adhesives based on natural polymers are derived from animal or plant materials. Where animal sources are concerned, polymeric substances are typically proteins such as casein. Where plant sources are concerned, these are typically carbohydrates such as starch. Adhesives may also include mixtures of animal and plant-based polymers combined with synthetic polymers. Since natural polymers are typically hydrophilic, they are usually dissolved in the form known as colloidal solutions in water. A special case is natural rubber latex, which is non-hydrophilic and forms a dispersion in water. Hardening of the adhesive occurs in both cases through water evaporation. Synthetic Polymer-Based Water-Based Adhesives Polyvinyl acetate (PVA) dispersions have useful application and performance characteristics for a wide range of applications on paper for both paper-to-paper and paper-to-plastic bonding. Dispersions based on acrylic resins (polymers) offer high initial bond strength. The softness of acrylic dispersions is widely adjustable, thus enabling the production of both pressure-sensitive and non-pressure-sensitive adhesives. Acrylic polymers can be produced both in dispersion form and as water-based solutions. Polyolefin / EVA-Based Hot-Melt Adhesives Polyolefins and also ethylene vinyl acetate copolymers (EVA) are thermoplastic polymers used in (non-reactive) hot-melt adhesives. (Non-reactive) Hot-Melt Adhesives Non-reactive hot-melt adhesives belong to the group of physically setting adhesives, where hardening occurs without any chemical modification of the polymer. Before application, the adhesive is heated and generally begins to melt at temperatures above 100°C. The adhesive is then applied to the substrate in liquid (molten) form. During cooling, physical setting occurs where the hot melt transforms into a crystalline or amorphous solid. Non-reactive Solvent-Based Adhesives A number of non-reactive, non-cross-linked polymers are completely soluble in organic solvents. These solutions can be used to coat paper and more typically plastic substrates with a coating stage followed by a drying phase. These coatings can function as adhesives under certain conditions. Rubber-Based Pressure-Sensitive Hot-Melt Adhesives Rubber-based hot melts typically rely on styrene block copolymer rubbers combined with a suitable adhesive to form pressure-sensitive (non-reactive) hot melts. The applied adhesive remains in a permanently tacky state. Reactive Adhesives Reactive adhesives do not rely solely on a physical bonding process. Adhesives contain reactive groups that in some cases participate in chemical reactions with the substrate surface as well, resulting in very resistant final adhesive applications. After hardening, reactive adhesives are usually insoluble in water or do not significantly soften with increasing temperatures. UV-Cured Acrylic Adhesives UV-cured adhesives are typically acrylic polymers and are widely used for pressure-sensitive applications. Unlike water-based acrylic dispersions, UV-curable acrylics typically do not contain water. They can be directly applied liquid adhesives or hot melts applied in the molten state. In both cases, the applied adhesive is cured by exposure to UV light. Reactive Acrylic Dispersion Adhesives Acrylic dispersions can be cross-linked with isocyanates to increase their thermal and chemical resistance. Functions of adhesives in or on packaging Labeling (non-pressure-sensitive) Most rigid packaging uses labels to present marketing and legal information related to the product. Labeling offers many advantages over direct printing, such as greater production flexibility and the ability to more easily reuse or recycle the container after label removal. A wide variety of adhesives are used for labeling. For paper labels, water-based adhesives such as acrylic dispersions or more traditionally natural polymer-based adhesives are used. For bonding non-absorptive label materials, typically plastic labels, non-reactive hot-melt adhesives are used. Pressure-Sensitive Applications Pressure-sensitive applications are used in the production of self-adhesive labels. The adhesion may be permanent or the label may be designed to be easily removed by hand. Pressure-sensitive applications are also used for resealable food packages and resealable closures. Generally, acrylic dispersions are used to produce pressure-sensitive adhesives. In some cases, non-reactive hot-melt chemistry and UV-cured acrylic adhesives may also be used. lamination. Most flexible packaging consists of two or more layers, each serving a specific function such as sealability, product protection, and resistance to tearing or perforation. These layers must be bonded to each other with adhesives. The most common technology in use is polyurethane lamination adhesives because they show excellent resistance to fillers and thermal stress, and have low migration potential due to their reactive structure. Acrylic dispersions can also be used to produce multilayer lamination for flexible packaging. Cold Seal Applications Cold adhesive bonding applications are used to seal the edges of packaging made from a wide range of different substrates such as paper and polypropylene (PP) or polyethylene (PE) films. In pressure-activated systems, heating is not required to achieve sealing; the two cold-sealed sides are pressed together. Cold seals are typically sealed in the temperature range of 15 to 25°C, and the absence of heat makes them ideal for packaging temperature-sensitive foods such as frozen products, chocolate, or cookies. Cold seals typically contain a mixture of natural rubber latex and acrylic dispersions. Heat Sealing Applications Heat sealing refers to the bonding of two substrates through heat and pressure. This process is mainly used in lid applications where paper, aluminum, or plastic lids are bonded to paper or plastic food containers; for example, in the packaging of dairy products; plastic trays for ready meals and meat and ready noodle bowls. Heat seals are also used for sealing medical packaging. Heat-sealed adhesives are in most cases non-reactive solvent-based or acrylic dispersion-based products that are applied and dried on one or both substrates to be bonded together. In some cases, non-reactive hot melts may also be used for heat sealing. Adhesive Applications in Fiber-Based Packaging Production Unlike plastic packaging, which can be shaped by injection molding, blow molding, or thermoforming, most fiber-based packaging is shaped by adhesive applications. Most often, a single sheet of paper or board is folded or shaped and then self-adheres. For most fiber-based packaging applications such as corrugated cardboard, box manufacturing, side seaming,4 and cross and bottom bonding of sacks, non-reactive water-based adhesives are used. Polyolefin / EVA-based hot-melt adhesives are very commonly used for closing cardboard boxes on production lines (end-of-line application). Relevant Properties of Adhesives in the Recycling Process Regardless of chemistry or application method, adhesive applications in recyclable packaging (whether used in the packaging itself or on the label) must have certain properties to ensure they do not impede the recycling process in question. Many stakeholders have published guidance documents that help packaging manufacturers make the correct basic choices. Each adhesive class has its own behavior, and adhesive manufacturers should be involved in the development and updating of guidelines and in the evaluation of recycling options. Terminology related to adhesive behavior may differ among value chain actors and may cause misunderstandings. FEICA wishes to contribute to the establishment of a common language and common understanding and thereby facilitate communication between different actors. Therefore, FEICA proposes the following definitions for adhesive behavior during recycling: Water-Soluble / Alkali-Soluble Adhesive Application Any applied adhesive that is soluble in water or alkali during the recycling process. The dissolved adhesive is transferred to the process water and remains in solution until the wash liquid enters a recovery or cleaning phase. Releasable Adhesive Application Any applied adhesive that can be released on at least one side of the bond under specified conditions during the recycling process. After release, the adhesive remains on one or both substrates. The process water does not accumulate adhesive (recycling of the wash solution is not recommended). • Water-releasable: Any applied adhesive that can be released on at least one side of the bond in water under specified conditions during the recycling process. • Alkali-releasable: Any applied adhesive that can be released on at least one side of the bond in alkali under specified conditions during the recycling process. [caption id="attachment_136345" align="aligncenter"] Table 1: Correlation between adhesive chemistry and function.[/caption] Table 1 summarizes typical uses of adhesives for packaging by relating function to chemistry. It cannot be assumed that a fully dried water-based adhesive layer will automatically be re-soluble or dispersible in water. 2 A mixture having particles with diameters ranging from 1 to 1000 nanometers but still remaining uniformly dispersed throughout the solution. 3 The 'setting' process of reactive adhesives is called 'curing.' For non-reactive adhesives, the term 'setting' is used. 4 Side seaming is used to form paper bags, pouches, and sacks from flat paper/paper rolls by overlapping the paper and applying adhesive to the seam areas.  

Source:

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