Functional plastics – designing for circularity

Few, if any, materials can compete with plastics in terms of adaptability and versatility – many different material properties can be derived from the same basic chemistry, meaning that complex product assemblies can be made with a single type of plastic. From a circularity point of view, this is extremely valuable, as it could make recycling much more straightforward. Products that consist of parts that are made with a combination of different materials typically need to be separated before recycling, a process that can be time-consuming and sometimes near-impossible, depending on the assembly methods used. Making complex assemblies from a single material greatly simplifies this process, and sometimes eliminating the need for separation altogether. 

Arguably, plastic materials are most often used for rigid moulded parts and flexible film applications. Adding ribs for strength, hooks for fastening and integrated hinges to rigid parts is well understood and widely used, but the versatile nature of plastics also allows for manipulating the material on the molecular level. By controlling the direction of the long strands of molecules that make up plastic materials it is possible to create thin and durable so-called biaxially oriented plastic film materials with excellent barrier properties, replacing metalized films and films that are made with a combination of plastic materials.

Products with soft grips and other features often use a rigid plastic material in combination with an elastomer, often based on completely different chemistries, making recycling difficult. But often it is possible to find an elastomer that is partially based on common rigid plastics, like polypropylene, PET and polyamide. Often these material combinations can be recycled without separation if certain guidelines are followed for the design of the product. Contact a recycler that is specialised in your industry’s waste stream to find out what options are available.

On the theme of softness, many plastics are available as expanded foam. Depending on the specific type of plastic, these may look very different in terms of structure, but they have in common that they can be used for cushioning, or combined with a rigid outer skin to create recyclable lightweight composite parts with excellent strength to weight ratio, to name just a few examples.

Textiles is another area where plastics have a lot to offer. Extruded plastic filament can be fine-tuned to fit a wide range of textile applications, from woven and knitted fabrics to felt and synthetic down. Polyester (PET), polyamide and polypropylene are some of the most common synthetic textiles that could be fixed to a rigid, structural frame made with the same material for product integration. For assemblies that require an adhesive, there are several copolyester- and polyamide-based alternatives that does not have a negative effect on the recyclability of the product.

Textiles are also a key component in composite materials, where they offer a level of strength and rigidity that moulded plastic parts on their own could never provide. Traditionally, composites are often made with a glass- or carbon fibre textile and thermoset resin matrix, making them difficult to recycle. But more recently so-called self-reinforced composites – meaning that the reinforcing fibre and resin matrix are based on the same material – are becoming increasingly common. Polypropylene-based self-reinforced composites are most common so far, but PET- and polyamide-based alternatives also exist.

By taking a moment to analyse a project brief and breaking it down into its key requirements, there is a good possibility that there is a plastic material out there with the flexibility to satisfy all needs. Think of the exhibitors at K 2022 as a unique overview of the plastics industry for making new connections and identifying circular plastic solutions.