Used cooking oil from McDonalds: a sustainable material for 3D printing

Most traditional 3D printers create a shape by excreting a synthetic resin layer by layer, which is then hardened using UV light. Thanks to the abundance of scientific activity in this field, we have a number of resins and 3D printing methods to choose from. However, These resins are very expensive – A typical high-resolution photo-curable resin used in SLA/DLP can cost upwards of $500 per litre.

Scientists from the University of Toronto have an innovative solution to this problem: Waste cooking oil from McDonald’s. The oils that we use today fall into two categories: saturated and unsaturated. The carbon chains in saturated oils are all connected using single bonds. All the other hands of carbons are tied to other functional groups particularly hydrogen.

The unsaturated cooking oil used in McDonald’s has a lot of double bonds which allows it to undergo a chemical process called ‘acrylization’. Essentially, this causes the cooking oil to change into a resin that is sensitive to light in the same way that commercial 3D printing resins are. Acrylization has previously been demonstrated for soybean oil. The researchers wondered if this could be extended to waste cooking oil (WCO) – a commodity produced in abundance thanks to our growing fast food habits.

McDonald’s alone produces 600 tons of WCO every day. Disposing of all of this using conventional techniques will lead to severely clogged drains. They are therefore sold off to biodiesel plants and soap manufacturers. While efficiently getting rid of the WCO, it is not very cost-effective as the end products are rather cheap.

The 3D printing resin technique, however, may prove to be highly viable economically.

The cooking oil is retrieved at the end of the day and subjected to filtration to remove the residual solids (think french fry particles). They are then chemically treated using acrylic acid and boron trifluoride etherate, among others. The resin is formed in a single step – which is an improvement over other acrylizaton techniques that require complex chemical setups.

The team has successfully demonstrated 3D printing of complex shapes using their novel resin.

Resolutions of up to 100 um have been attained making this on par with synthetic resins in terms of capability. The butterfly shown on the left was printed using the new resin while the one on the right was printed using a commercial resin. The results speak for themselves.

The difference is that the WCO resin only costs 50 cents per litre. Significantly, the new resin is environmentally compatible and degrades in the soil. None of the additives added are harmful in any way. The scientists who have developed this technique hope that it can be extended to all waste cooking oils from all brands.

The significant reduction in the price combined with the enormous benefit to the environment is likely to make this method mainstream in the near future.