Designing for Circularity – A Guide to Sustainable Plastics

This post is presented by K-Show, the world’s # 1 trade show for the plastics and rubber industry. Visionary developments and groundbreaking innovations will once again take the industry to new dimensions at K 2022 in Düsseldorf, Germany.

The K Show is held every three years in Dusseldorf and is the world’s largest plastics event. It is an event that I have been participating in for 15 years and from that first visit I realized how much a jewel it was for designers. Even one day, even if you actually need at least three, gives you more information than you would find from six months of desk research. This is a series of articles on plastics and interviews with designers from global brands that discuss the current status quo of plastics.


As a designer, plastics and sustainability can be difficult to navigate. There are so many parameters to consider: from the origin and environmental footprint of raw materials, to the durability and quality of specific materials, and to maximizing the possibilities for end-of-life recovery and recycling of plastic products.

Starting from the origin of the raw materials that go into the production of plastics, the vast majority of plastics today are virgin materials of petrochemical origin, but more and more plastics suppliers are exploring alternative raw materials such as bio-based raw materials or recycled materials. Suppliers typically offer plastics made from a combination of petrochemical and biological raw materials or virgin and recycled material. Always ask suppliers to confirm the relationship between specific raw materials and relevant certificates such as ISCC Plus or SCS Recycled Content.

The development of bio-based renewable chemistry for plastics production is already well underway, with many plastic suppliers offering materials derived from a wide variety of plants, from agri-food crops to forestry by-products and more plants. associated with the textile industry. A small but growing number of plastic suppliers have also launched carbon capture and utilization products, CCUs. Both topics are explored in the “Industry Climate Neutrality: Wish – Reality – Future” K Talk roundtable, available for viewing here.

The specific type of plastic material will have a huge impact on the durability, functionality and user experience of plastic products. In general, basic plastics such as polypropylene, polyethylene and PET will have a lower environmental impact than high-performance engineering polymers such as ABS, polycarbonate and polyamide. Understanding the expected lifespan and likely usage scenarios of a product is critical to selecting the right material: a technopolymer’s increased environmental footprint will be balanced if it is best used in a long-lasting product.

The use of additives to improve certain properties and aesthetics of plastics is another element to consider in this context. Several suppliers and compounders offer non-halogenated flame retardants, antimicrobial additives that do not contain heavy metals, and non-toxic mineral dyes, just to name a few. Additives also have an impact on the recyclability of plastics, so it’s always worth confirming the impact of specific additives with a recycler who specializes in the type of plastic you are considering using.

Designing for circularity with plastic is a big topic in itself, but selecting the right kind of recycled plastic is also a complex task that deserves a closer look. The vast majority of the recycled plastics offered by suppliers will only be available in black or shades of dark gray. This is a result of the specific way most plastics are recycled today, so-called mechanical recycling. This process takes the plastic waste, separates it by type, grinds it and melts it into flakes or pellets that can be molded into new plastic products. Most recyclers do not separate plastic waste by color, which means the resulting material will be an unattractive brownish-gray mix of all colors of plastic waste. Most recyclers get around this by adding black or dark gray pigments to the recycled material to give it color consistency.

Covestro: Makrolon RE made with recycled cooking oil (photo credit: Gianni Diliberto)

While dark blacks and grays are fine for many applications, there are several recyclers who specialize in color separation for light and light colored recycled plastics, as well as recyclers that can supply clear recycled plastics. These materials require careful selection and cleaning to achieve good results, which means they typically have a greater environmental impact than black and dark gray recycled plastics which are less complex to recycle. In this context, it is crucial to select the right recycled plastic for the right application. This and other aspects of circular plastics are discussed in the section “Climate protection and plastics: do they go together?” K Talk, available for viewing here. Also be sure to check out the themed day schedule at the Plastics Shape the Future space at K 2022, which covers many of the topics outlined above.

Very few materials can compete with plastics in terms of adaptability and versatility: many different material properties can derive from the same basic chemistry, which means that it is possible to make assemblies of complex products with a single type of plastic. From a circularity standpoint, this is extremely valuable, as it could make recycling a lot easier. Products that consist of parts made from a combination of different materials typically need to be separated before recycling, a process that can be time-consuming and sometimes nearly impossible, depending on the assembly methods used. Making complex assemblies from a single material greatly simplifies this process and sometimes eliminates the need for separation altogether.

NaturePlast plastic shell and shell (photo credit: Gianni Diliberto)

Arguably, plastics are most often used for rigid molded parts and flexible film applications. The addition of ribs for strength, hooks for attachment and integrated hinges to rigid parts is well known and widely used, but the versatile nature of the plastic also allows the material to be manipulated on a 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 films with excellent barrier properties, replacing metal films and films that are made from a combination of plastic materials.

Products with soft handles and other features often use a rigid plastic material in combination with an elastomer, often based on completely different chemicals, making recycling difficult. But it is often possible to find an elastomer that is partly based on common rigid plastics, such as polypropylene, PET and polyamide. Often these material combinations can be recycled without separation if certain product design guidelines are followed. Contact a specialist waste stream recycler in your industry to find out what options are available.

On the subject of softness, many plastics are available as expanded foam. Depending on the specific type of plastic, these can 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 an excellent strength-to-weight ratio. , to cite just a few examples.

Textile is another area where plastics have a lot to offer. The extruded plastic filament can be fine-tuned to suit 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 fabrics that can be attached to a rigid, structural frame made of the same material for product integration. For assemblies that require an adhesive, there are several copolyester and polyamide based alternatives that do not have a negative effect on the recyclability of the product.

Fabrics are also a key component in composite materials, where they offer a level of strength and stiffness that printed plastic parts alone could never provide. Traditionally, composites are often made with a glass or carbon fiber fabric and a thermoset resin matrix, making them difficult to recycle. But more recently so-called self-reinforced composites are becoming more common, which means that the reinforcing fiber and the resin matrix are based on the same material. Self-reinforced polypropylene-based composites are the most common so far, but alternatives based on PET and polyamide also exist.

By taking a moment to analyze a project brief and break it down into its key requirements, there’s a good chance there is a plastic material with the flexibility to meet all needs. Think of the K 2022 exhibitors as a unique overview of the plastics industry to create new connections and identify circular plastic solutions.

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