I’m responsible for 3D printing related operations within the School of Biomedical Engineering & Imaging Sciences. I manage a range of 3D printers that start from your typical desktop or consumer-based plastic printers – known as Fused Deposition Modelling (FDM) printers – to Stereolithography (SLA) Resin based printers, which use a UV curing resin and a directed UV light to cure and build models. We also have our two latest printers waiting to be installed, a Selective Laser Sintering (SLS) printer and a Direct Metal Laser Melting (DMLM) printer. The former prints from a Nylon powder, and the latter prints from a Titanium metal powder. A precisely directed 250-watt laser is used in a process called Powder Bed Fusion (PBF) to ‘weld’ the titanium powder together.
My specialty is additive manufacturing, and it’s the process by which most components and prototypes are developed within our Biomedical Engineering workshops. Additive manufacturing is a way of building components through adding material together to produce a model. Subtractive, which is the other form of manufacturing, requires specialised tools to ‘chip’ away at a material stock, such as aluminum. Subtractive manufacturing is generally a more wasteful process than additive manufacturing.
Plant-based plastics: Why do we use them?
The material we use most commonly is PLA, which stands for Polylactic Acid. PLA is a bioplastic derived from fermented plant starch, and is internationally used in single use cups and takeaway containers for its eco-friendly and near carbon neutral footprint. Being a plant-based plastic, its production is better for the environment as it requires a CO2 feedstock to grow the plantations. It is also a low melt plastic, requiring less energy to produce, and during use the plastic doesn’t off-gas and release any toxic fumes. It even offers the potential for a carbon negative industry, if other renewable sources of energy were used in its production.
There are a lot of advantages to using this material, but there is another side of this material that may not be so sustainable that I am trying to tackle.
The issue with this material is the belief it is readily biodegradable, and easily recycled. PLA cannot be recycled with other plastics; it is a ‘CODE 7’ plastic, which is “OTHER”, and it shares the same code with Nylon, and Polyester, which get sent to landfill. It is, however, both biodegradable and easily recycled, but it’s often not done properly and for that reason PLA usually ends up in landfill, especially from 3D printing Waste. For PLA to be broken down by biodegradation, it requires Industrial Composting, which is essentially a heated and pressurised form of composting. If this were the process by which waste PLA was treated, after 90 days, you would get Lactic Acid. I guess it would make more sense to put PLA plastics in with food waste then…
The practical side: waste generated by 3D printing
3D printing Filament comes on a spool, about 1.75mm in diameter, and it is this that is fed into the 3D printers to produce our models and prototypes. There is no way to identify what material is being fed into the 3D Printers other than what is written on the spools, so there is no way this plastic post-3D printing would ever be recycled or can even be identified.
An inventory count on the amount of filament we have just in our school estimated around 300kg. Just one of our workshops uses around 50kg a year with a 5% waste, and our teaching workshops have been estimated to use around the same amount of material but with a 30% estimate on waste. Waste in this context refers to failed prints, scrapped prototypes, and the support material required to print parts with overhangs (otherwise they would print in midair). So, we are producing a fair amount of waste just within this school, and with the rapidly growing 3D printing industry the UK alone is estimated to produce 379,000 kg of PLA waste every year, out of an estimated 1,148,400kg of filament used. That’s an average of 33% waste.
3D printing produces a finite amount of microplastic. We use sophisticated AI driven 3D Printers, and part of the calibration process is for the printer to produce a strip of material around the build plate which is then assessed by a Micro Lidar to calculate the flow rate of the material, before it also ‘poops’ a controlled amount of material out of the nozzle to purge any remaining material that may contaminate printing.
Looking to the future: How King’s is reducing waste in 3D printing
We now have a solution to this problem, and we now have the machinery to recycle our 3D print waste and give the plastic a second life. We’ve purchased a motorised plastic shredder from Felfil, and a filament maker. With this set-up we also have the capability to recycle plastic bottle caps and bottles as they are made from PET, which is a widely used 3D printer filament.
Having this recycling programme within King’s will make it one of the very few worldwide with this application.