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Mechanical recycling is a mechanism that aims to recover plastic waste using mechanical processes, including granulation, washing, drying, and compounding. The goal of such processing is to create a closed-loop economy in which plastic waste can be transformed into the same or similar product to be used again. This project is focused on the mechanical recycling of PLA (polylactic acid), a thermoplastic aliphatic polyester derived from renewable resources, such as corn starch, tapioca roots, chips or starch, or sugarcane, which is a commonly used plastic in 3D Printing. This polymer has a glass transition temperature between 50-60 degrees Celsius and a melting temperature of around 180 degrees Celsius. 

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The steps of our current proposed mechanical recycling system are:

1. Granulation: pulverization of failed 3D prints into small pellets

2. Dehydration: removal of moisture in the plastic pellets

3. Extrusion: mixing pellets with virgin PLA in a formulaic manner, which are melted and extruded into filament thread

4. Cooling and Spooling: cooling of hot filament thread and collection for 3D printing. 

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We have separated the project into three major stages: research, implementation, and expansion. We are currently at the research stage, which focuses on refining our recycling process. In order to refine our current process, we are focusing on extruding our filament with consistent diameter and identifying the optimal ratio of virgin to recycled PLA  to create recycled filament that can be printed in the same way as 100% virgin filament. Our preliminary literature review revealed that there is no research that specifically addresses the mechanical and printing properties of PLA filament as it undergoes multiple rounds of recycling and printing, thus this will be the main focus of our research. In the implementation stage, we aim to scale up this system into an economically viable alternative by further developing the recycling workflow and PLA collection system. In the future expansion stage, we hope to also include recycling of other 3D printing plastic such as ABS. 

 

Find the Standard Operating Procedures​ for Granulation, Extrusion, and 3D Printing here.

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