Date of Award


Document Type


Degree Name

Master of Science (MS)


Mechanical Engineering

Committee Chair/Advisor

Cameron J. Turner

Committee Member

Garrett J. Pataky

Committee Member

Gregory M. Mocko


Polylactic acid (PLA) is a biopolymer made from renewable resources such as sugar and corn. PLA filament is a popular material used in Fused Deposition Modeling (FDM) 3D-printing. While this material has many advantages, all the failed parts, support structures, rafts, nozzle tests, and the many prototype iterations during the 3D-printing process contribute to the plastic pollution and release of greenhouse gases. Although PLA is biodegradable, it can take years to degrade in landfills. Instead of throwing away PLA waste and buying new filaments, PLA can be recycled. Amongst the different recycling technologies, mechanical recycling is the most environmentally friendly. In this project, PLA filaments were mechanically recycled. One of the goals in this study was to identify the barriers to recycling and to introduce a more detailed recycling process. To achieve this goal, three different recycling extruders were tested to find the most user-friendly, which was the Noztek Pro Desktop extruder. Moreover, a new and more detailed material preparation process was introduced. In this method, PLA was first shredded. Then liquid nitrogen was added to make the material more brittle and easier to crush, and finally, it was ground. Additionally, the most effective process parameters for extrusion were presented. These parameters included temperature of 200 ºC, a pulley speed of 1.5 m/min, and using fans to cool the extruded filament before winding. The next goal was to evaluate the process with the added details and find the impacts of successive mechanical recycling on the properties of PLA. Therefore, a comprehensive testing was done including thermal (TGA and DSC), chemical (FTIR), and mechanical tests (tensile). Filaments could be recycled for three generations however after the third recycling, the filament no longer printed reliably. The test results demonstrated degradation of PLA. The UTS decreased from 44.7 MPa to 40.5 MPa, strain at break decreased from 10.4% to 7.5%, and the modulus, E, decreased from 1.603 GPa to 1.055 GPa. The FTIR results suggested that all samples had the same chemical structure of PLA. However, decreased intensity peaks around 920/cm show a decrease in crystallinity. In addition, a decrease in the absorbance band in the carbonyl region around 1750/cm, an intensity change from 700/cm to 2000/cm regions, and an intensity decrease around the 1180/cm-1240/cm were also observed. The DSC analysis showed that the Tg values were between 61.97 ℃ and 62.95 ℃, the cold crystallization temperatures had a range from 117.87 ºC to 128.81 ºC, and the melting temperatures ranged from 158.48 ºC to 161.28 ºC. Moreover, The TGA results showed that the decomposition temperatures were between 311.33 and 337.5 ºC.

The recycling process was initially successful, however, after the third generation the filament became unprintable. This was due to decrease in crystallinity and molecular weight which caused brittleness, lower strength, and nozzle clogging. This research provided important design data regarding performance and limitations of recycled PLA.



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