Feature first published in the January–February 2021 issue of 3D ADEPT MAG. Interviews and research reflect that period, bringing together commercial materials, research projects and maker experiments at different stages of maturity.
Additive manufacturing materials can be surprising in their formulation, origin or processing. This feature explores five approaches, from polypropylene for water contact to concrete patterns inspired by nature.
These examples do not all have the same level of validation. Performance depends on the process, testing and application; an original idea alone does not establish industrial effectiveness.
1. Polypropylene for water contact
Producing parts in contact with water requires materials and processing compatible with the intended use.
For a drinking-water fitting, water quality, mechanical performance, watertightness and installation conditions are distinct requirements.
Ricoh presented its polypropylene powder for selective laser sintering (SLS), intended for industrial parts and applications involving water contact.
Ricoh’s 2021 documentation lists WRAS material approval. The manufacturer describes the water-quality tests as follows:
“ – it doesn’t affect the quality of water by changing its appearance, taste or odour;
- it doesn’t leach toxic compounds and heavy metals which may be harmful;
- and it doesn’t promote the microbial growth within piping removing therefore the risk for generating unsightly slime formation.”
“Combined with its chemical stability and water tightness, parts produced with our polypropylene material are an ideal solution for producing functional prototypes and serial components for applications in contact with water” Enrico Gallino, Senior Engineer – Material Specialist Additive Manufacturing at Ricoh UK comments.
Material approval does not approve every printed part or installation. Its scope and conditions are distinct from finished-product qualification, as WRAS explains; this historical reference does not confirm current approval status.
2. Space exploration
Made In Space developed the use of a polyetherimide/polycarbonate (PEI/PC) blend for manufacturing in orbit. Its March 2018 review lists the material among those used by the Additive Manufacturing Facility aboard the International Space Station.
The company described the properties sought for space applications as follows: “it is not going to emit particles in a vacuum, it’s resistant to the UV environment, it’s resistant to atomic oxygen, so it can perform actual uses in space.”
PEI-based formulations are not interchangeable. In particular, ULTEM 1010 is a PEI resin and should not be described as a PEI/PC blend alongside modified formulations. Performance, off-gassing and suitability for space applications need assessing for the specific material, process and part.
As MIS’ President & CEO said during the launch of this material: “Manufacturing in PEI/PC really expands the value of in-space manufacturing for human spaceflight. PEI/PC is a truly space-capable material. With it, extra-vehicular activity (EVA) tools and repairs, stronger and more capable intra-vehicular activity (IVA) tools, spares, and repairs, and even satellite structure can be created on site, on demand. That enables safer, less mass-intensive missions and scientific experiments.”
These possibilities described by the company do not replace mission-specific testing and qualification.
3. Turning human waste into a 3D printing material
The student project Astroplastic explores another route: producing a bioplastic from compounds found in human waste for potential use in space.
A team from the University of Calgary presented the project at iGEM in 2017. This was research, not a printing process already qualified for space missions.
The project Astroplastic: From Colon to Colony seeks to combine waste management with local material production to reduce the resources that need transporting.
For this January–February 2021 feature, project lead Alina Kunitskaya answered our questions about the results and limitations of the research.
Could you please explain the process of using human waste for creating a 3D printing material?
Our project called “Astroplastic” aims to address two major challenges with future human missions to Mars: sustainable waste management and the high cost of shipping materials to space. In our system, poly(3-hydroxybutyrate) bioplastic, or PHB for short, is produced by genetically engineered Escherichia coli bacteria that use volatile fatty acids found in solid human waste.
To describe the proposed process in more details, astronauts’ feces are first collected into a storage tank using a vacuum toilet. Feces are then transferred into another tank and left to ferment for 3 days with bacteria naturally found in human feces to increase the concentration of volatile fatty acids. Next, the liquid containing volatile fatty acids and other nutrients from human waste is separated from solid particles using centrifugation followed by filtration. The obtained volatile fatty acids are then added to a fermenter containing the engineered PHB-producing E. coli. Lastly, PHB produced by bacteria is extracted from the liquid harvest stream and dried, resulting in the powdered bioplastic material.
Did you actually go to the end of the experience to discover what kind of objects (flexible, solid, etc.) – and on which AM technology -one can print such type of materials?
We expect that the produced bioplastic can be used to print solid objects. In particular, we hope astronauts will be able to use it for printing tools and small items that may be used as spare parts for maintenance repairs or science experiments. Since the final product is a powdered plastic material, we considered using selective laser sintering as the most suitable AM technology. However, our experiments have been done on a small scale so we didn’t have enough material to test the use of produced material in selective laser sintering so far.
How different would this 3D printable material be from other materials we usually used for 3D printing?
Although PHB has been used in 3D printing before, it can be quite brittle. We would need to further investigate if there is a need for post-processing of the produced bioplastic to create a blend with suitable properties.
What is happening with the project “Astroplastic: From Colon to Colony” so far?
We were able to successfully engineer E. coli to produce PHB bioplastic, which was tested using a simulant of solid human waste. Since bacteria naturally produces PHB granules internally, we also engineered bacteria to secrete the produced PHB for easier extraction. In parallel to these biological experiments, we also developed a concept for a start-to-finish PHB production process on Mars based on feedback from experts, determined optimal operating conditions for several steps, and tested several steps in the lab. This project was presented at the International Genetically Engineered Machine (iGEM) competition, receiving a gold medal and a nomination for Best Manufacturing Project.
Following the iGEM competition, we also investigated how to adapt the proposed process to the microgravity environment (as the initial process was developed for the Martian gravity environment). In particular, we tested the plastic extraction step of the process in microgravity aboard a parabolic flight.
Is there a general method for determining whether a feedstock can produce consistent filament?
As a student group, we had limited resources and expertise to test the use of our product. At this stage of the project, we relied on existing literature involving our product or similar type of products (powdered plastic material) to determine the feasibility of using this material and to identify suitable AM technologies.
4. Turning VHS magnetic tape into filament
If you are part of generation X or Y, then you are certainly familiar with VHS, which stands for Video Home System, a standard for consumer-level analog video recording on tape cassettes. With all the streaming platforms that are available today, these tape cassettes have become quite obsolete.
Russian maker Andrew, known as Brother, experiments with filaments derived from plastic waste. His YouTube channel includes experiments using VHS cassette tape.
“I want to save the planet from garbage, at least a little. I think that if many people repeat my experiments, the planet will become cleaner. Passing by the landfill, I saw over 100 VHS cassettes. At first, I thought I would use cassette casings, but I finally decided to try melting the tape”, he told 3D ADEPT Media.
Brother retrieves the magnetic tape from inside the cassettes and prepares it to form filament.
He describes using a purpose-built device to combine tape from several cassettes into a strand of approximately 3 mm, with repeated trials to adjust consistency.
“The tape filament needs to be heated higher than a standard 3D printer filament so he prints at a much slower rate, but the resulting product is indistinguishable from a normal print except for the color,” Bryan Cockfield stated in the Hackaday post. “It has some other interesting properties as well, such as retaining its magnetism from the magnetic tape, and being a little more brittle than PET plastic although it seems to be a little stronger.”
After several tests on his Omni 3D printer, the maker noted that filament is quite strong and delivers prints with a smooth texture. However, when asked how different is this 3D printable material from other materials he usually used for 3D printing, he said:
“I usually print with unusual materials which are recycled plastics. Therefore, I cannot compare such materials with 3D printing materials used in factories. The VHS filament is interesting in that it has electrical conductivity, albeit with high resistance, and magnetization. Post-processing is unnecessary for this material. The printed objects have a very nice structure. There are not many tapes left in the world. And of course, such a filament production technology cannot be introduced into mass production, but you can peep the composition of the tape and create a factory filament on its basis.”
These observations concern a maker experiment. The interview provides neither standardised filament characterisation nor a life-cycle assessment demonstrating an environmental benefit.
5. Concrete toolpaths inspired by lobster shells
While construction 3D printing provides a wide range of benefits for the building industry, one of the most important challenges builders face is with materials. Researchers keep exploring the materials possibilities for this specific segment and have already come out with some unexpected ideas to print structures in the construction industry. One of them includes fly ash – a residue from burnt coal.
However, if we write these lines, it’s to address one of the challenges raised by one of the most used materials in construction 3D printing: concrete. Except that this time, we’ll talk about lobsters and concrete.
In research presented on 19 January 2021, an RMIT University team investigated printing patterns inspired by the internal structure of lobster shells.
The inspiration lies in the helicoidal organisation of that structure. The aim is to orient printed concrete’s mechanical properties to the loads it must carry, without equating measured strength with long-term durability.
The researchers combined these paths with a steel-fibre-reinforced mix. Results concern the formulations and specimens tested; they do not establish superiority over every conventional concrete.
Speaking of the benefits of bio-inspired approach in 3D concrete printing, lead researcher Dr Jonathan Tran said: “We know that natural materials like lobster exoskeletons have evolved into high-performance structures over millions of years, so by mimicking their key advantages we can follow where nature has already innovated.”
The team tested the impact of printing the concrete in helicoidal patterns (inspired by the internal structure of lobster shells), cross-ply and quasi-isotropic patterns (similar to those used for laminated composite structures and layer-by-layer deposited composites) and standard unidirectional patterns.
The results showed strength improvement from each of the patterns, compared with unidirectional printing, but Tran said the spiral patterns hold the most promise for supporting complex 3D printed concrete structures.
“As lobster shells are naturally strong and naturally curved, we know this could help us deliver stronger concrete shapes like arches and flowing or twisted structures,” Tran said.
“This work is in early stages so we need further research to test how the concrete performs on a wider range of parameters, but our initial experimental results show we are on the right track.”
RMIT reported in January 2021 that further studies could use a newly acquired large-scale mobile concrete printer.
This selection illustrates the range of approaches explored. Moving from an idea, an experiment or a commercial material to an application depends on demonstrated properties and intended-use requirements.
This feature was first published in the January–February 2021 issue of 3D ADEPT MAG.
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