Improving the Circular Economy of 3D Printing with Plastic Recycling

Researchers from France’s Université de Lorraine and Michigan Technological University explore a topic that many users are very concerned about, detailed in the recently published ‘Plastic recycling in additive manufacturing: A systematic literature review and opportunities for the circular economy.’

As 3D printing has skyrocketed into the mainstream in recent years, so has the production—and discarding—of enormous amounts of materials, far beyond the standard ABS and PLA. And while users around the world are concerned with trash piling up in landfills, there are new considerations for re-use and recycling of 3D printing materials.

Such activity has been well highlighted from the assessment of material to recycling and composting, to recruiting robots for recycling. In this latest study, the researchers investigate the further concept of a ‘circular economy’ with the use of distributed recycling via additive manufacturing (DRAM), including six stages for this research.

The wonders of plastic may abound for some applications; however, the amount of waste produced is undeniably disturbing, and threatens the environment on every level. The authors point out that while ‘recycling rates remain small,’ there is the hope that recycling in AM processes could lead the way for a more positive trend—especially as the market is predicted to expand substantially, with the authors citing a projected number of over $23 billion US by 2026.

Technical framework for quality assessment of recycled plastics. Adapted from (Karlsson, 2004;Vilaplana and Karlsson, 2008).

AM production, and consequent recycling efforts, could reasonably become centered around local facilities rather than global, offering more ease in recycling, along with beginning to do so earlier in growth of the technology overall. A circular economy could allow for the use of more local supply chains—resulting in-situ recycling. This could also mean less need for transportation of materials.

“Hence, AM can be seen as a recycling tool to reuse a thermoplastic waste material, and then influencing the structure of material supply to improve resource consumption efficiency. Indeed, using open source technology is an important driver to boost the local recycling process,” state the authors.

Typical polymers used in additive manufacturing include:

• Thermoplastics
• Thermosets
• Elastomers
• Hydrogels
• Functional polymers
• Polymer blends
• Composites
• Biological systems

“Considering the waste management, certainly the principle layer-by-layer improves the material yields (ratio of final product weight/input material weight). However, examples of waste include powdery materials that are no longer useable, waste generated by unexpected defects and/or supporting structures created in the printing process,” stated the researchers.

Overview of single-step AM processes that uses polymer materials. Adapted from (Gonzalez-Henríquez et al., 2019; Singh et al., 2017a,b,c).

The DRAM process consists of the following six steps:

1. Recovery
2. Preparation
3. Compounding
4. Feedstock
5. Printing
6. Quality

Closed-loop recycling framework for distributed recycling via additive manufacturing (DRAM) process.F.A. Cruz Sanchez et al. / Journal of Cleaner Production 264 (2020)

Noting that both recovery and preparation stages of the AM recycling process are ‘less studied,’ the researchers suggest greater efforts should be expended in pre-treating recycled materials. They also recommend better models for collection of waste, and both technology and methodology to evaluate waste material overall.

“ … it was observed that a big amount of work has already been done in the scientific community in order to validate the technical feasibility at compounding, feedstock and printing stages for numerous mono and composites—materials based on recycled assets. This is explained by the fact that the structural and feasibility of production assessment levels are well documented in the literature,” concluded the researchers. “Nevertheless, to maximize the potential of distributing recycling, attention should be focused on the willingness to use recycled 3D objects. Several driven applications of waste material were found including furniture, toys. The validation of DRAM needs to continue to show the usefulness of recycled printed parts. However, the research on the creation of minimal standards and legal framework are major elements to validate.

“Finally, we have proposed different future research paths at the micro, meso and macro level to better understand the connections between circular economy and distributing recycling to reach the full potential. The establishment of such links can aid in the development of technical, social and economic aspects fostering waste management policies to improve the closed and open loop recycling.”

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Global results of the literature review.F.A. Cruz Sanchez et al. / Journal of Cleaner Production 264 (2020)