Espresso cups, flower pots and even decorative objects can be made from the waste from coffee preparation, researchers report. They have developed a 3D printer paste that consists of old coffee grounds, water and two other sustainable ingredients. The experiments show that it can be used in conventional 3D printers to produce various objects with just a few modifications. These objects are stable, biodegradable and can be easily recycled, say the scientists.
Instead of casting, molding or milling, printing is done: techniques for producing three-dimensional objects through the additive application of substances have already found their way into many areas of application. The processes are being further refined and new materials are being developed for special 3D printing systems. In addition to many different plastics, building materials can also be used for special processes. Concepts for the use of biodegradable substances such as cellulose have also already been developed. The team led by Michael Rivera from the University of Colorado in Boulder is also working on such approaches. The researchers are exploring the extent to which less processed basic substances could be suitable for producing a sustainable 3D printer paste.
Basic substance with symbolic character
As Rivera reports, he came up with the idea for coffee grounds through a conversation with the owner of a coffee shop during the Covid-19 pandemic. Normally, the large quantities of used coffee grounds were regularly picked up and taken to a composting facility. But during the pandemic, this no longer worked reliably and enormous amounts of coffee grounds accumulated. When he looked at the mountains of waste, the scientist came up with the idea that the material might be suitable for use in 3D printing. As Rivera explains, the currently most widely used 3D printers use so-called thermoplastics as the printing material. Polylactic acids (PLA) are already in use, but they are only biodegradable under certain conditions in special composting plants. “In a landfill, where most PLA ends up, it takes up to 1,000 years to decompose,” says Rivera. The idea is that the use of purely plant-based coffee grounds could be advantageous and also make a widespread waste product usable.
So Rivera and his colleagues began to explore the extent to which the substance could be turned into a practical printer paste. For this purpose, the laboratory became a test kitchen in which the researchers added various test substances to the starting material. As it turned out, the optimal recipe is surprisingly not complicated and can actually be “cooked” at home by anyone interested. Therefore, only two easily available powder substances need to be added to the dried and finely ground coffee grounds, which lead to gelling and subsequent hardening: cellulose gum and xanthan gum. Both are biodegradable substances that are often used in food.
Successful recipe
Water is then added to the mixture to form a thick paste. “It’s about the consistency of peanut butter,” says Rivera. The material can then be used in a conventional 3D printer with the help of a few additional tubes and a syringe. Depending on the design program, different structures can be created, which are then air-dried. In doing so, they develop considerable strength, which corresponds to that of certain concrete substances, say the researchers.
To illustrate the potential of the concept, they created various example objects from the coffee grounds printer paste: For example, biodegradable planters were created in which seedlings can be grown. In keeping with the topic, the researchers also printed coffee cups that are easy to drink thanks to a thin additional coating. To illustrate the purpose of the approach, they also created a jewelry pendant that bears a symbol of sustainability.
The scientists have now presented their results at the Association for Computing Machinery conference in Pittsburgh. Additionally, they have already made the recipe and their process freely available on the Internet. As Rivera concludes, he sees the approach as having symbolic and groundbreaking significance in addition to its actual potential for use: The project is intended to raise awareness of the issue of sustainability and could encourage other researchers to develop other types of sustainable printing materials, says the researcher.
Source: University of Colorado Boulder, publication of the proceedings: DIS ’23: Proceedings of the 2023 ACM Designing Interactive Systems Conference, doi: 10.1145/3563657.3595983