Thomas Kriewaldt – ME 514 Project Proposal
1. Summary
This project will assess how different nozzle temperatures, infill densities, and part orientations affect the properties of bottle-derived recycled PET material after extrusion through an FDM printer. Through a series of tensile tests on parts with distinctive combinations of these parameters, quantitative relationships will be established, advancing the reliability of every print using rPET and, most importantly, reducing PET plastic waste stemming from both failed parts and the general failure to recycle PET bottles.
2. Introduction & Background
Plastic waste is at the vanguard of the many environmental problems humanity faces today. Polyethylene Terephthalate (PET) is one of the most widely adopted polymers today; commonly, it is found in “disposable” bottles, containers, packaging, and films. The world produces over eighty million metric tons of virgin PET (vPET) each year [1]. While these PET-derived products can be recycled, only around 33% of PET bottles are actually recycled as of 2023 [2]. This leaves around 55 million metric tons of plastic left to rot in our landfills, oceans, and environment. This polymer is not easily biodegradable, so it can persist for decades, secreting microplastics which affect ecosystems and human health through accumulation up food chains. Expanding applications of recycling beyond current industrialized solutions could help individualize accountability for reusing PET bottles. A systemic shift like this could help boost recycling rates, reducing plastic waste further and by even more significant amounts than current projections.
In recent years, recycled PET (rPET) has increasingly been converted into filament for Fused Deposition Modeling (FDM) printing. This material is innately strong and also exhibits high UV and thermal stability. These features make it a viable alternative for people looking to reduce their environmental footprint. Commercial systems, such as the RePET accessory, help convert PET bottles into printable filament. The working principle of these systems is to shape strips of PET (trimmed from bottles) into hollow filaments, which are then extruded via the printer’s nozzle [3]. However, there remains a lack of characterization on how FDM settings and process variables influence the mechanical properties of rPET parts. Trial-and-error is often used to specify nozzle extrusion temperatures, layer heights, infill densities, or print orientations, which is suboptimal for maximizing fabrication efficiency. This project presents a reproducible study to determine these outcomes by varying key print parameters and quantifying their impact on output tensile properties. Establishing guidelines for FDM print settings with this material could increase the reliability of recycled prints, minimize additional waste from failed prints, and ultimately support a more practical adoption of rPET for future consumer and manufacturing applications.
3. Impact
If this project is successful, it could yield experimentally validated characterization of recycled materials for FDM printing, reducing reliance on iterative and arbitrary parameter selection. By varying the nozzle temperature, the raster orientation (angle) in the X-Y plane of the print bed, and the infill density, this study will establish key relationships between these settings and the resulting mechanical properties of the printed part. This data will lower the knowledge barrier for prospective users, making recycling into rPET 3D printing much more approachable, efficient, and practical. This will also reduce material waste stemming from constant iteration and failed prints when using the trial-and-error method to adjust specific parameters. On the more technical side, the mechanical outputs from the rPET test material will help quantify material properties, further standardizing this process as a dependable and renewable option. Such tests can demonstrate that bottle-derived filaments are a feasible option in PET recycling, and extend this existing framework to larger commercial applications or to a broader audience interested in reducing their plastic consumption.
4. Methods/Approach
This study seeks to quantify the relationship between FDM printing parameters and the resulting mechanical properties of rPET. Recycled plastic bottles will have their labels and any residual glue removed, then air compressed and heated to remove impurities. The bottle will then be cut to a fixed width based on its thickness and pulled through a bottle stripper to form strips. The RePET extrusion accessory will be mounted to a Bambu Labs A1 printer, and the strips will be shaped into filament, then extruded. Each iteration of the part will be varied slightly to experimentally evaluate three key parameters: nozzle temperature (nominal, -5°C, +5°C), raster orientation angle (0°, 30°, and 45° conformations on the X-Y plane), and the infill density (10%, 30%, and 50% using a standard grid infill). In total, 27 parts will be constructed for testing for each combination of these print variables, and labeled accordingly to ensure full traceability.
Tensile testing will be carried out on ASTM-style dogbone specimens using a calibrated force gauge with video recording to capture the maximum load at failure. This approach is novel, as it is one of the first studies to characterize the tensile strength of bottle-derived rPET rather than the more commonplace pellet-fed injection-molded recycled PET. It also isolates in-plane raster angle effects on part strength without introducing z-layer variability. We can use quantitative test data to improve the consistency of rPET part outcomes and minimize waste from failed prints, instead of constantly relying on guesswork. However, there are some risks associated with this project, including inconsistent filament diameter, which could lead to process failure. Poor layer adhesion, warping, and mechanical gauge inconsistencies could also derail portions of the project. However, these risks will be mitigated by continuous calibration and monitoring. Even if the data shows no meaningful trends between parameters, it will still be insightful to measure process variability for future bottle-derived rPET additive manufacturing applications.
5. Future Plan
The next phase of this work, if consistency in printing with bottle-derived rPET is established, will focus on compiling optimal print settings for this material based on testing. Developing a framework to connect parameters to the mechanical properties of the output part will enable more robust future guidelines for reproduction. Then, a practical object will be created using these optimized settings to demonstrate real-world applications of this workflow. This object should be something that frequently breaks under tensile loads, like a clothes hanger, which often breaks around the hook when excessive loads are applied. I plan to personally utilize this project and its findings to recycle PET bottles into rPET parts, reducing my plastic waste output. Additional future steps may include documenting and sharing the process and optimal print settings for this material to increase visibility into how to reduce plastic waste and instead recycle it into viable FDM-fabricated parts.
6. References
[1] A. Z. Werner et al., “Tandem chemical deconstruction and biological upcycling of poly(ethylene terephthalate) to ?-ketoadipic acid by Pseudomonas putida KT2440,” Metabolic Engineering, vol. 67, pp. 250–261, Sep. 2021, doi: 10.1016/j.ymben.2021.07.005.
[2] “2023 US PET Bottle Recycling Rate Reaches Highest Level in Decades; Recycled PET Content in US Bottles Reaches Highest Level Ever,” NAPCOR. Accessed: Mar. 04, 2026. [Online]. Available: https://napcor.com/news/2023-pet-bottle-recycling-reach-new-heights/
[3] “RePET,” ECODECAT3D. Accessed: Mar. 04, 2026. [Online]. Available: https://ecodecat.com/pages/repet