As attention has focused on the problem of plastic pollution in the environment, governments and the private sector have taken steps to promote recycling and reduce plastic waste. These measures include phasing out certain single-use plastics and setting specific goals on plastics recycling.
Plastics remain a vital material for products however, from mobile phones to cars and washing machines. As we strive to move to a circular economy, how can we factor plastics into that equation?
According to the Ellen Macarthur Foundation, we need a systemic approach, which creates a system that works in practice without losing economic value, and without causing plastic waste or pollution. We need to rethink how we make, use and reuse plastics, redesigning the system in which the material is used.
Although this is an industry-wide issue, each company handles it differently. The choices are the same for each firm, however – to design and materialise upfront, to either use a substitute for plastic or pick a plastic that is recoverable and recyclable. When using plastic, ensure you use the least amount possible for form, fit, and function.
If you use plastic, you must design your product and commercial offerings to be more reliably recovered, which entails maintaining a commercial arrangement with a customer that incentivises them to return it. Modular design and disassembly instructions can ensure you have the means of recovery, whether it is to reuse the plastic assembly in a new product, or melted down or reprocessed into a secondary product.
Developing a circular approach
Circularity is still in its infancy, and much work is required until it becomes common practice. According to the Circularity Gap Report, only 8.6% of the world economy is circular.
For manufacturers, modular design helps significantly. It allows mass customisation, but more importantly it provides for a ‘bill of disassembly’, with disassembly instructions attached.
The name of the game in the circular economy is not necessarily to recover all the material and melt it back down and make it into something new – the objective is to use something as long as you can and then when you cannot, take off the most significant components possible and reuse them as much as possible at that large component level. If neither of those applies, then you recover to the material level, grind it up, melt it down, and remanufacture something else.
There is nothing perfect in industry, so circularity is more of a spectrum – from single-use throwaway products, up to the utopia of a fully circular product, which is probably unachievable for decades. But the idea is to move towards zero landfill incrementally, and whatever reprocessing you need to do, do so with zero carbon release. Of course, you will never get to zero waste or carbon, but you can get closer.
A new way of thinking
Working with designers on this new way of thinking can be a slow process. At present, their focus is not necessarily trying to eliminate plastic. If they do use it, the aim is often to do so in a way that it can be recovered. That is not a perfect situation, but it is where mainstream thinking is now.
There are several ways that designers can move in the right direction. The first is through requirements management, which can be regulatory or mandated by a particular company. Those requirements can be explicitly linked to the design and their test cases, and help ensure that the designers honour the design intent set in the requirements.
For the products you manufacture, there are also material databases, such as Ansys Granta or the Higg Material Database in retail. It is a highly invested and growing field of companies that provide service catalogues of materials, with curated data that allows designers to understand their recyclability, REACH and RoHS compliance, and the embodied carbon in their extraction and creation.
When the material is selected, these attributes can be pulled into the PLM systems, through CAD during the design stage. It can then be 'rolled up' in the assemblies and bills of materials in Windchill, so you can understand all the materials selected and the total or hazardous material footprint.
For purchased components, there are similar catalogues, such as SiliconExpert or Octopart, where you can select capacitors, bolts, screws, or other components with similar curated information about the recyclability of the material, what it is made of, how hazardous it is, its embodied carbon and supply chain risks at the component level.
All that material and component information in the attributes curated within those databases can be rolled up. The first customers are starting to do that within PLM, then exporting those for lifecycle analysis.
Designing for disassembly
The next step is the ability to recycle or reuse parts or assemblies at the end of life. As mentioned earlier, modular design can play a role in disassembling a product. But it starts to fall apart technologically when you have a part containing multiple materials, such as moulded plastic with some metal.
The question then is what you do with that. You can disassemble something, and the plastic is recoverable, but because it is formed within metal, it will almost certainly go straight to a landfill.
An umbrella is a perfect example of that. It has some aluminium in it, and it has a recyclable plastic moulded handle. But most regions are not set up to recycle umbrellas – they get thrown away and scrapped, even though they are all recyclable at the component level.
Unless you are making a disassembly bill of materials that can practically separate those recyclable materials through a disassembly procedure, it is a mess. That is where software needs to improve and perform better.
To overcome this challenge requires a design engineer to adopt a different mentality. There are a few techniques that we have seen work to achieve this. The first comes back to requirements that say you can only mix these materials if you can take them apart, which would be requirements tracing.
Generative design can also play a role, whereby you put constraints within a generative design model and then send your CAD model to it. Then it will rearrange the part within the constraints given to the generative design.
The limitation is that the generative design model is limited to one or just a few materials at a time. The generative models need to be enhanced to handle a mix of metal and plastic.
With optimisation simulations within PLM workflows, you can have ‘promotion validators’. With a promotion validator, before an engineer can release a design or set it up for review, it can enforce specific simulations or optimisations, with the results sent back so engineers cannot skip a step where it can remove excess material or suggest a way for better separation.
Some companies are also starting to ‘gamify’ the carbon roll-ups of their design, which they can do interactively and translate into something meaningful. For example, if an engine designer is trying to reduce weight out of an engine that might be used in a million trucks, changes that reduce the carbon footprint can be tracked and reported in real-life ways. We have seen analysis showing that type of feedback is highly motivating for engineers.
Although the journey to a circular economy for plastics will be slow, steps are already being taken. The pace will increase as more companies adopt modular and generative design technologies. But for now, every opportunity to reduce the harm from plastic should be taken, as each incremental improvement, however small, moves us closer to where we ultimately need to get to.
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Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.