Recycling Plastics in Fabrication & Design: 3D Printing Raw Materials from Plastic Waste

Alaeddine Oussai, Zoltán Bártfai, László Kátai, and István Szalkai explore ways to improve recycling in 3D printing, releasing the details of their recent study in ‘Development of 3D Printing Raw Materials from Plastic Waste.’

Using plastic and dealing with the trash it produces has become normal around the world—leaving many to look back on the years when we enjoyed products in reusable glass containers—like milk, for example. The authors point out that while plastic waste, regarding type and quality, varies around the world, many types are suitable for re-use. For 3D printing, however, recycling processes are still being heavily explored:

“The current applications for using recycled plastics in fabrication and design are fairly limited, on a small scale, plastics (such as ABS, HDPE, or PET) are shredded and formed into pellets, and then either extruded into lament to be used in existing 3D printers, or injection molded into small parts and pieces of larger components.

“At a large scale, recycled HDPE is melted into sheets and either used directly as sheets in construction, or then heat formed from a sheet into components for construction. These methods of fabrication using recycled plastics are the norm because of their affordability and straightforward processes, yet each method leaves some complexity to be desired.”

For this study, the researchers focused on both polyethylene terephthalate (PET), often referred to as polyester, and polylactic acid (PLA). While it is true that recycling can be both complicated and confusing for consumers everywhere, there are four basic exercises associated with the process:

• Mechanical reprocessing into equivalent products
• Secondary processing into products with ‘lower properties’
• Chemical constituent recovery
• Quaternary energy recovery

PET recycling circle

Known as a #1 recycling plastic, PET is made of monomer ethylene terephthalate. This is a material often used to make plastic bottles, as well as thin films and solar cells, offering high mechanical strength and temperature resistance.

End markets for PET recirculates in Europe and in the USA (Petcore, 2011; Napcor, 2011).

PLA is one of the most common types of 3D printing filament, known for its plant-based nature and resulting biodegradability. And while its true nature in terms of degrading are still being explored, this material is used widely by users and researchers too, featured in studies exploring the potential for a more circular economy, development of biodegradable blends, direct waste printing with pellets, and much more.

“Although PLA is a biodegradable material, which would significantly reduce environmental pollution associated with its waste, the knowledge behind this material recycling and changes in the properties of PLA upon its multiple processing is a very important subject of discussion,” state the authors.

Other materials like polyvinyl chloride (PVC) can break down in only several days. PVC is also affordable and offers the potential for making high-performance parts. Polyethylene’s PE’s are also commonly used, offering density, toughness, and flexibility.

Today, overall recycling efforts, and within 3D printing also, are geared toward less use of energy, less sorting during the process, and the eventual inclusion of what are now non-recyclables. Currently only poly (ethylene terephthalate) (PET) and polyethylene (as 9 and 37% of the annual plastic produced) are being mechanically processed.

The researchers mention a previous research solution as they developed a ‘crusher,’ for re-using plastic. The device consists of a crusher and extruder, along with 12 blades.

overview of the complete design of the crusher

Overview of the complete design of the extruder

Other recycling methods include chemical technology; however, the researchers point out that right it is considered to be too expensive due to the amount of energy it consumes. They point out that incineration is an option too.

“In the current scenario there is growing demand and interest towards chemical recycling methods with low energy demand along with compatibility of mixed plastic waste to overcome the need for sorting and expanding the recycling technologies to traditional non-recyclable polymers,” concluded the researchers.

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