Small model ships from the 3D printer

Make 3D printing more sustainable

forschung leben – the Magazine of the University of Stuttgart (Issue September 2021)

Recyclable base materials, ecologically degradable auxiliaries: scientists from the University of Stuttgart’s Institute of Polymer Technology (IKT) are working on sustainable additive manufacturing processes.
[Photo: University of Stuttgart/IKT]

A number of different production processes are covered by the term "additive manufacturing" but they all have one thing in common: unlike "subtractive manufacturing" or machining, in which a workpiece is created by removing material until the desired shape is achieved, a computer program uses a 3D model to build up plastics, metals, ceramics or synthetic resins layer by layer to form a three-dimensional workpiece. As Dr. Alexander Geyer, head of processing technology at the Institute of Polymer Technology (IKT) explains: "to the greatest extent possible, we only use as much material as we really need in 3D printing and we deposit it in exactly the right place."

Less warehousing and logistics

There are many benefits to additive manufacturing: most post-processing steps are eliminated; less scrap waste is created and material consumption is reduced, and it is possible to create almost any design and complex geometry. 3D printing is used to produce scale models, tools or even spares on demand, all of which are fabricated directly on site, which means that warehousing space and logistics operations can be reduced. The processes involved are still slow and not suitable for mass production, but they do open up new possibilities in industries such as medical engineering in which bespoke patient products are required, or the aerospace sector, which needs lightweight polymer-based components.

Biodegradable: a support structure made of salt and polymer

The 3D printers in the IKT lab’ operate almost silently. Products from the experiments being conducted there, which include everything from trainer insoles to car brake calipers to a model ship, line the shelves. What may appear frivolous at first glance is actually helping basic research. Geyer and his team are trying to find innovative technologies to make 3D printing more sustainable whereby they are focusing on two main processes among others, which are selective laser sintering (SLS) and fused deposition modeling (FDM). 

The SLS process uses a plastic powder that is finer than sand and the powder bed is melted in a construction space that is heated to high temperatures at the points specified by the 3D computer model before being lowered so that the next layer (which is just 100 micrometers thick) can be applied. The surrounding powder supports the structure and the end product can be easily extracted from it.

Recycle old powder

The problem is that around 70% of the most commonly used plastic powder is damaged by the high temperatures after which it is mixed with new powder so that it can be reused. As Dr. Sandra Weinmann, a research assistant at the IKT explains: "This results in material quality fluctuations. Regenerating the powder during the manufacturing process is more sustainable." The chemist wants to recycle the used powder by combining the powder particles with a modifier, which is designed to ensure that the material damage is repaired directly. Initial trials have been promising. One of the current tasks is to find the optimum recipe and to adapt the equipment accordingly.

Weinmann's Institute colleague, Silvia Lajewski, is working on optimizing the FDM process, which involves melting a strand of plastic in a heated nozzle before applying it to a construction platform at predefined points. The problematic parts include those structures that are supported by a second material during the manufacturing process to achieve complex geometries with such things as pronounced overhangs: these are usually dissolved in a water bath to remove them after solidification.

Water-soluble and biodegraded support material

But this pollutes wastewater with harmful microplastics. "Conventional wastewater treatment plants are unable to filter it out," says Lajewski. That is why she wants to develop a water-soluble support material that can also be biodegraded through bacterial metabolism. She is currently using a twin-component material made of polymer and a highly refined salt, the basic concept being that the salt from the finished structures dissolves in the water, which makes them so porous that they can be removed without leaving any residue. Lajewski is also working step-by-step towards finding the ideal combination between the components and to develop a usable formula.

Both projects are already attracting a great deal of interest within the industrial sector. Despite some initial successes, the researchers still have a lot of detailed work to do. For Geyer, her research is a good example of the "adjusting screws we can turn to answer key future questions in 3D printing, such as recycling and protecting resources and the environment."

Editor: Jutta Witte

Dr. Alexander Geyer, Institut für Kunststofftechnik, e-mail, phone: +49 711 685 62850

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