From the 3D printer to the dishwasher: researchers develop biodegradable support material

In the world of additive manufacturing, innovations are constantly revolutionising the possibilities. Despite the progress, there is one major challenge: the need for support structures. They prevent material layers from sagging – but removing them after printing can have environmentally damaging consequences. In the AquaLoes project, the Institute for Polymer Technology at the University of Stuttgart is tackling this challenge.

In an interview with K-MAG, Lars Schmohl and Frederik Gutbrod talk about the newly developed water-soluble and fully biodegradable support material, the process of their research and what a dishwasher has to do with it all.

You have developed a support material for 3D printing. What inspired you to do this and what is special about it?

Lars Schmohl and Frederik Gutbrod: Additive manufacturing enjoys great popularity in industry and home applications due to its almost infinite freedom in design possibilities and simple production of components. In the strand delivery process, also known as fused filament fabrication (FFF), support structures are required when printing complex structures (undercuts and overhangs, etc.) so that subsequent material layers are secured against sagging.

Since these support structures have to be removed again after printing, the use of soluble materials has now become established for this purpose. By dissolving them with an appropriate solvent, e.g. water, after printing, a high-quality surface finish of the 3D component can be achieved. Of course, the material of the component does not correspond to the material of the support structures. However, these support structures dissolved in water then often end up as individual dissolved polymer chains in the waste water and thus inevitably in the environment. Therefore, our goal was to develop a plastic that is both water-soluble and completely biodegradable in water.

What is the composition of the material? What was the development process and the challenges in selecting the appropriate compound?

Schmohl and Gutbrod: The support structure material is currently made up of a mixture of three components. A polyhydroxybutyrate-co-valerate (PHBV) was used as the base polymer. PHBV is a bio-based polymer and is also fully biodegradable in environments with low bacterial activity such as seawater. Due to its low elongation capacity, a short-chain polyethylene glycol (PEG) was additionally compounded in as a plasticiser, which can also be biodegraded. In order to achieve a rapid release of the support structure from the component, a very fine table salt was also used.

More than 30 different formulations were developed for the pressure and dissolution tests. The aim was to achieve a high salt content in order to achieve the fastest possible dissolution process. However, with the increase in salt content, the stretchability and thus the processability of the filament also suffers. So it was always necessary to weigh up these two points in order to achieve a suitable mixture. Furthermore, strong crystallisation occurs with the base polymer PHBV, which can lead to warping of the component even during printing.

What is the detachment process like for the developed material? What options have you tested here?

Schmohl and Gutbrod: The detachment process is somewhat different from other conventional water-soluble support structures (such as PVA). In our case, the entire support structure material does not dissolve, but only the salt, which fragments the support structures in a first step. When the 3D-printed component is removed from the water bath, any remaining residue can be removed without leaving any residue by light mechanical action.

The removal process for the developed material takes longer than for conventional materials. How do you plan to tackle this challenge in the future?

Schmohl and Gutbrod: In our tests, the printed component was placed in demineralised water in each case. As expected, with an increase in temperature, the time after which the support structures could be removed without residue dropped from 24 to 4 hours. The use of a commercially available dishwasher was also successfully tested.

To close this gap, one approach would be to test higher dissolving temperatures depending on the material pairings (component material to support structure material) or the use of a type of washing line. Furthermore, it could be possible that a higher elongation capacity of the compound allows a higher salt content and thus a faster dissolving process.

The issue of microplastics plays a major role when it comes to the contact of plastics with water. How do you solve this problem in your development?

Schmohl and Gutbrod: This issue also plays a major role for us in this project. The components were chosen in such a way that there is no permanent entry of microplastics into the environment. The PHBV and the PEG are completely biodegradable even in seawater.

You are currently looking for industrial partners. What do you hope to gain from such a partnership and what kind of companies or experts are you looking for?

Schmohl and Gutbrod: We would like to develop the material mixture, which is not yet ready for the market, into a product suitable for industrial use. Here, companies from the most diverse directions can contribute to the commercialisation of the product. Both material suppliers and filament manufacturers might be interested in working with us.

You have applied for a patent for the 3D printing support material. What are the next steps to bring this product to market?

Schmohl and Gutbrod: The next important steps will deal with increasing the stretchability and scaling up the support structure production, both in terms of other 3D printing processes and in terms of the achievable component size. These issues will be crucial for a market launch.