Designing for Circularity - A Guide to Sustainable Plastics




This post is presented by the K-Show, the world’s No.1 trade fair for the plastics and rubber industry. Visionary developments and groundbreaking innovations will again lead the industry into new dimensions at K 2022 in Düsseldorf, Germany.

The K Show comes around every three years in Dusseldorf and is the worlds biggest event for plastics. It is an event I have been attending for the last 15 years and since that first visit I realized what a gem it was for designers. Even one day -although in reality you need at least three- gives you more information than you would find from six months of desk research. These are a series of articles on plastics and interviews with designers in 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 maximizing the chances of recovery and recycling at the end of life of plastics products.

Starting with the origin of the raw materials that go into plastics production, the vast majority of plastics today are petrochemical-based virgin materials, but increasingly plastic suppliers are exploring alternative raw materials such as bio-based feedstocks or recycled materials. Typically suppliers offer plastics that are made with a combination of petrochemical- and bio-based raw materials, or virgin and recycled material. Always ask suppliers to confirm the ratio of specific raw materials and relevant certificates such as ISCC Plus or SCS Recycled Content.

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

The specific type of plastic material will have a massive impact on the durability, functionality and user experience of plastic products. Generally speaking, commodity plastics such as polypropylene, polyethylene and PET will have a lower environmental impact than high-performance engineering polymers like ABS, polycarbonate and polyamide. Understanding the expected life-span and likely usage scenarios of a product is crucial for selecting the right material – the larger environmental footprint of an engineering polymer will be balanced if it is put to good use in a product with a long-life span.

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

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

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

While black and dark greys are fine for many applications, there are several recyclers that specialize in color separation for bright and light color recycled plastics, as well as recyclers that are able to provide transparent recycled plastics. These materials require careful sorting and cleaning for good results, which means that they typically have a larger environmental footprint compared with black and dark grey recycled plastics that are less complex to recycle. In this context, selecting the right recycled plastic for the right application is crucial. This and other aspects of circular plastics are discussed in the ‘Climate protection and plastics – do they go together?‘ K Talk, available to watch here. Also be sure to take a look at the theme days programme at the Plastics Shape the Future space at K 2022, which covers many of the topics outlined above.

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 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.

NaturePlast oystershell and seashell plastic (photo credit: Gianni Diliberto)

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 metallic 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 specialized 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 do 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 analyze 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.

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