Feature first published in the March–April 2020 issue of 3D ADEPT MAG, then posted online in July 2021. Interviews describe work and expectations from that period; technical clarifications prevent overgeneralising their findings.
The 2017 study by Geyer, Jambeck and Law estimated cumulative global virgin-plastic production at 8.3 billion metric tonnes through 2015. Around 9% of the 6.3 billion tonnes of waste generated had been recycled. 3D printing can use selected recycled feedstocks, but environmental benefit depends on process, energy, losses and product lifespan.
What is special about recycled materials for 3D printing? What are the differences between recycled and non-recycled materials for 3D printing? Speaking of plastic materials, can all types of plastic be recycled for 3D printing? Or is there a specific type of plastic that can be recycled? Can the recycled and printed filament be recycled again? What about the quality and characteristics of these filaments compared to non-recycled filaments? Do recyclable materials present any advantages for mass production in AM?
The aim is to identify what to check before integrating these materials into repeatable production: waste origin, formulation, filament consistency and part properties.
For this 2020 feature, Mogens Hinge, associate professor at Aarhus University in Denmark, discusses characterising recycled plastics for AM.
Recycled VS Non-recycled materials for 3D Printing
According to Hinge, in terms of usage, apart from the fact that the material is recycled, there is not a great difference between recycled and non-recycled materials for 3D printing. However, doubts remain regarding the properties they are supposed to deliver.
Recycling guarantees neither identical properties to virgin material nor an automatic quality loss. Sorting, contamination, thermal history, formulation and extrusion need control. Cost comparisons must also include equipment, energy, labour and rejected material; an 80% saving cannot be generalised without an identified protocol.
When asked about the quality and characteristics of recycled materials for 3D printing and non-recycled materials, the Associate Professor at Aarhus University (Denmark) explains: “there is so much (maybe even all) undocumented, good and bad filament on the market today. In most cases, you only know the material type (e.g. PLA, ABS, PETG) and the thickness (1.75 or 3 mm Ø). In some few cases, there is also a printing and bed temperatures (often generic). Thus, no quality or characteristics are supplied for 3D printing filament today, why should this be different for recycled materials? It is a common mindset we face all the time that now that it is recycled then we need documentation. Most consumers have never looked at the documentation for virgin material and most cases do not have it at all. Thus, what will the knowledge of, e.g. Tg and melt-flow-index for a recycled 3D printing material be compared to [non-recycled materials]? If you ask, does it print – Yes to a very high quality, good bridging, minimal stringing, low oozing, good bed adhesion, etc.”
This assessment concerns filaments the interviewee encountered at the time; it does not mean that no manufacturer supplied technical data.
Manufacturers may use different preparation and formulation methods. A proprietary method is not necessarily patented and does not itself guarantee each batch’s properties.
Reflow supplies recycled filaments. MEAN’s 2019 Deciduous pavilion provides an example: it combines PETG elements printed with Reflow filament, a printed concrete base and a milled plywood floor. The plywood was not 3D printed. This project does not document chemical monomer recycling at Reflow.
What type of material can be recycled for 3D printing?
“In theory, all plastics can be recycled, but there are plastic types (e.g. PVC) that degrade heavily during processing and thus would be less suitable for recycling. It is clear that some types of plastic will not make sense to recycle as 3D printing filament, as not all plastics are suitable for 3D printing”, said Hinge.
Recovering value from waste differs from turning it back into filament. Thermosets do not remelt like thermoplastics, and mixed or contaminated waste does not automatically become printable.
PLA recycling for 3D printing was studied before 2020. Biodegradability under certain conditions does not rule it out, although moisture, chain degradation and thermal cycles can change properties and printability.
The 2017 EcoPrinting study also converted fully recycled ABS into filament and printed test specimens. Properties and processing settings changed after recycling. ABS is not inherently flame-retardant; that performance requires an appropriate formulation and qualification.
To avoid plastic waste, researchers and companies have been studying what kind of materials can be recycled for 3D printing. The goal is to avoid plastic waste while developing a filament that can enable many 3D printing applications.
The project announced by Aarhus University on 13 January 2020, with Aage Vestergaard Larsen A/S, specifically targeted recycled filament with consistent, documented quality.
Speaking of the situation in Denmark, Gitte Buk Larsen, business developer and marketing manager at Aage Vestergaard Larsen A/S, said three reasons explain the raison d’être of this project: “firstly, it hasn’t yet been possible to produce filament from 100% recycled plastic. Secondly, no one has cracked the code for producing filament based on a data sheet in order to ensure uniform quality. And thirdly, there are currently no filament producers in Denmark.”
This statement expresses the project’s industrial ambition in its January 2020 context. It should not be read as a global absence of fully recycled filament; recycled ABS experiments had already been published in 2017.
PETG is another option, illustrated by Deciduous. Its properties should be assessed from the supplier’s formulation and material data rather than assumed identical to PLA or ABS.
Bio-based PEF comes from separate work: Kucherov and coauthors reported printing and repeated recycling experiments in 2017. This study does not establish that Reflow was developing the material. Bio-based describes feedstock origin; it demonstrates neither greater biodegradability than PLA nor a zero carbon footprint for every application.
Can the recycled and printed filament be recycled again?
In the case that the original printed filament was not a recycled material in the first place, this question would have had a twofold answer: Yes & No. Indeed, according to Trinota, a medical 3D printing company, to know if a material is recyclable, one should ask “if there will be an end user of the recycled material?”. If there is somebody willing to buy the end product, then the material is recyclable – generally any material is recyclable, as long as there is somebody willing to pay for it.”
A buyer provides an economic condition, not proof of technical feasibility or environmental benefit. Collection, sorting and property control remain necessary.
In the case where the recycled filament is already used, the question becomes difficult to answer. “We do not know. It is known that all plastics degrade (to different degree) during processing (recycling normally includes shredding, extrusion, and sometimes compounding). Thus, plastic recycling (when implemented) will face the challenge of 4th, 5th, 6th etc. generation material that would be somehow degraded. In some cases, unrealistic to reach 4th gen. and in other cases no problem at all. This is strongly depending on plastic type and added stabilizers (additives). This needs to be investigated further”, stated Hinge.
Any specific advantages for mass production?
From the very beginning of this article, the goal has been clearly defined: exploring if recycled 3D printing materials can be a viable option in the use of 3D printing as a mass production tool.
The interviews principally highlight the need for comparable data: composition, recycled content, filament diameter, flow behaviour and the mechanical performance of printed parts.
Series production depends on batch-to-batch repeatability, traceability and application requirements. These 2020 examples show avenues for development; they cannot establish a single maturity or performance level for every recycled material.
This exclusive feature has originally been published in the 2020 March/April issue of 3D ADEPT Mag.
THE 3D ADEPT WEEKLY NEWSLETTER
The industry moves fast. Stay ahead.
Every week, the latest additive manufacturing news, in-depth features and real-world applications, straight to your inbox. Plus, be the first to know when a new issue of 3D ADEPT Mag is out.
Free · One email a week · Unsubscribe anytime
Clicking loads our email provider’s sign-up form, including its analytics and Google’s anti-bot protection. You’re only subscribed if you complete the sign-up. Read our privacy policy.