Researchers in Brazil and Great Britain have found a way to turn recycled coffee beans into 3D printed conductive materials which can be used to create a caffeine detector. In doing so, they demonstrated one of the many possibilities of using 3D printing as part of the circular economy.

In a circular economy, products do not become waste, but are reused for other purposes. And since you’re a circle, you can start at any time. So let’s start with the part most people will be familiar with: the coffee beans.

Coffee machines that work with disposable pods are popular because they give people so many choices. Choose one flavor in the morning, another in the afternoon, and your guests can have their choice. But like many things that are quick and convenient, coffee pods produce a lot of waste. While small pods can be made from biodegradable materials or easily recycled aluminum, several brands still use plastic.

This inspired researchers to look for an easy way to reuse this plastic. Polylactic acid (PLA) from coffee beans can be adapted into 3D printing filaments. But with the right treatment, PLA can even become a conductive material so it can be used to 3D print sensors, for example.

Here is where the process becomes circular: in the production of coffee in pods, the coffee must be tested for quality. One of the steps is to measure the caffeine content. This can be done using sensors, so they close the loop, researchers in Brazil have tried make these sensors from reused coffee pods.

“Polymer base obtained from used pods can generate devices with high added value,” one of the researchers of the study, Bruno Campos Janegitz, he told the São Paulo Research Foundation (FAPESP).

By adding a compound called carbon black to recycled plastic, Janegitz and his colleagues were able to create a conductive filament that could be used to 3D print components to create a caffeine sensor. They tested the sensors to prove they work by measuring caffeine in a sample of coffee and tea and showed that the plastic can be recycled about three times before the plastic loses its quality.

The big picture

If you’re only thinking about this from the point of view of coffee pod recycling, this story might not make a whole lot of sense. After all, if coffee bean waste is a problem, why not focus on producing them from biodegradable materials or avoid them altogether? But don’t think of this as a way to get rid of coffee pods per se, but as a demonstration of how to achieve a circular economy. It doesn’t have to be coffee pods or caffeine sensors, but any other type of PLA waste can become any other device made from 3D printed conductive plastic. It might inspire someone working on a different manufacturing process to explore ways to manufacture sensors or ways to recycle their plastics that are perhaps less avoidable than coffee pods.

3D printing opens the way for creative solutions and this study shows that it can be used as part of a possible circular economy, and that it can be used to make electrochemical components.