Additive manufacturing with biopolymers and biobased materials

Increasing the diversity of materials is one of the central challenges for the comparatively young production technology of additive manufacturing. This is because a larger range of materials specifically optimized for additive manufacturing also increases the number of possible fields of application for the technology. In this field of tension of new processes as well as the new design freedom in component design made possible by additive manufacturing, there is now an opportunity to increasingly examine the use of bio-based materials and biopolymers. This is one of several aspects in the sustainability consideration of additive manufacturing.

The term biobased materials is broad and is not limited to Biopolymere . It also includes materials that contain natural fibers or natural-based granules and powder materials. The term biopolymers is used in the following to refer to applications for polymers based on natural raw materials, but the property of biodegradability is not the primary consideration. For these biopolymers, monomers are produced from renewable raw materials, for example by fermentation, and subsequent polymerization produces the corresponding biopolymers. In order not to compete with the production of food, one often relies on residual materials from agriculture , but also forestry.

For use in additive manufacturing , the bio-based materials must be available either as powder, filament, or photopolymerizable resin, depending on the additive manufacturing process used.

Use of bio-based materials in additive manufacturing processes - an overview

The fused deposition modeling (FDM) process is based on melting polymers in filament form. The use of the biopolymer polylactic acid (PLA) in the FDM process is an established material-process combination and is being tested or used in various industries, such as the packaging industry or medical technology .

Polyhydroxyalkanoates (PHA) can also be used as FDM filament. These biopolymers, unlike PLA, are made by using special bacteria that produce the biopolymer in their cells. Filaments based on a blend, i.e. a mixture of PLA and PHA, are also available. This can improve the biodegradability of PLA.

In the field of the FDM process, the processing of fiber-filled filaments and of continuous fibers is also developing steadily. This offers the opportunity to use natural fibers, such as cellulose or hemp fibers.

Farther, polyamide 11 powder (PA 11) can be produced using castor bean as a biopolymer. These polyamide powders can be used in the selective laser sintering (SLS) process, in which a laser fuses the plastic particles together layer by layer.

Also under development is the use of ground miscanthus, also known as Chinese reed, in powder form for use in the additive manufacturing process of binder jetting. In binder jetting, the base material is in powder form. A binder is applied via an ink-jet system, similar to a commercial office printer, which bonds the particles together layer by layer.

New biobased formulations are also being developed for the additive process group of photopolymerization, which is based on the use of photocrosslinkable resins. For example, there are developments on the use of itaconic acid as a UV-curing component based on biotechnological production from sugar production by-products. Furthermore, there are developments based on vegetable oil in the form of soybean oil.

3D printing with crab shells

Side streams of animal origin, such as crab shells or insect carapaces, are also being investigated for their usability in additive manufacturing. They are made of chitin, the second most abundant biopolymer in the world. Dr. Kristin Protte from the Fraunhofer Institute for Manufacturing Engineering and Automation in Stuttgart is conducting research on this topic. She is working on further developing functionalized chitin particles into a printable material via an enzymatic crosslinking reaction. The material is to be produced in such a way that its properties allow it to be used for plastic components with a two-year service life. The aim is to optimize the flow properties for the printing process, for which Protte is using gelatin. Kristin Protte is a speaker at the Online Forum "Biopolymers" of Bayern Innovativ , where she will report on her developments.

The examples, which are at different stages of development or application, show the numerous possibilities for the use of bio-based materials in additive manufacturing.

The use of single-use plastic will be banned in EU member states from July 2021, and many people are also increasingly critical of environmental pollution caused by microplastics, which is driving the development of biopolymers and concepts towards a circular economy. However, there are many challenges to be solved here in terms of suitable raw material sources, reproducible material properties, recycling and biodegradability. Since the development of new material systems is always strongly tied to manufacturing processes, numerous opportunities arise in the interplay of these two rapidly developing segments.

Sustainability - a trend in additive manufacturing

The fact that sustainability plays an important role in additive manufacturing is also demonstrated by the forecast of the Belgian 3D printing service provider Materialise, which cites sustainability as one of the five trends in additive manufacturing for 2020 . However, the described use of bio-based materials is only one aspect when considering sustainability. This is because the layer-by-layer structure that is characteristic of additive manufacturing means that materials are used in a way that conserves resources.

Furthermore, additive manufacturing enables new, more intelligent designs that allow reduced material use and, consequently, reduced component weight or increased efficiency in gas turbines thanks to optimized burner tips. This highlights the potential of additive manufacturing as a component of sustainable production.

As key technology against the backdrop of Industry 4.0 , an increased increase in decentralized production would also be conceivable, reducing transport distances as well as only demand-driven manufacturing through on-demand production.