Session: ASME Undergraduate Student Design Expo

Paper Number: 175632

Recycling Pet Water Bottles Into 3d Printer Filament: System Development and Filament Characterization 

Rising plastic production, especially in single-use polyethylene terephthalate (PET) water bottles, increases every year paints a sinister state of one of the largest environmental crises of the twenty-first century. While polyethylene terephthalate plastics may be recyclable, they are not recycled. A very small percentage of the total PET waste is recycled as most of it goes to landfills or oceans generating environmental challenges.. Currently, new efforts are being made to transfer the PET bottles into thin fibre that can be used as a filament in 3D printing. This research investigates methods to achieve this recycling process through a system that is designed and developed at San Jose State University. 

The proposed recycling system focuses on transforming discarded PET bottles into usable 3D printing filament, providing a cost-effective and eco-friendly alternative to conventional 3D printing filaments such as ABS or PLA. The system is designed for sustainability, affordability, and reliability, addressing previous limitations in cutting consistency, extrusion quality, and process automation. It is composed of four primary subsystems: cutting, extraction and alignment, extrusion, and spooling. These components work together to convert a 2-liter PET bottle into a neatly coiled roll of filament, ready for direct use in FDM 3D printing.

The cutting mechanism consists of a custom-built 3D-printed frame that holds a standard plastic water bottle in place and rotates it against a fixed X-Acto knife blade. This design ensures the bottle is sliced into even 8–9 mm wide strips, which were determined through experimentation to be the optimal width for smooth feeding and extrusion. To power this mechanism, an AC motor was selected over a stepper motor due to its higher torque (from 100 to 500 mNm), which is necessary to cut through PET consistently without jamming or loss of speed. 

This motor simultaneously drives the extraction system, pulling the strip through the cutter and maintaining tension across the feed path. The extraction system is supported by a series of alignment guides that keep the strip centered and flat as it progresses toward the extruder. Alignment guides were 3D printed using PLA  and ABS material (100% infill) to sustain the operating load. 

For the extrusion phase, the system utilizes a repurposed 3D printer heating block. This component was chosen for its compact design and compatibility with PET’s thermal properties. To ensure consistent melting, the temperature is regulated at 235°C using a K-type thermocouple in conjunction with a PID controller. Through extensive testing, this temperature was validated as the ideal melting point, producing clean, stable filament without degradation or blockage. The melted plastic is extruded through a nozzle to form a uniform filament strand, with an approximate target diameter of 1.75 mm.

Once the filament exits the heating block, it is immediately routed to the spooling mechanism. This unit employs a NEMA 17/NEMA 21 stepper motor to draw the filament through the extruder and wind it onto a spool in a clean, uniform pattern. Stepper motors were selected here for their precision and controllable speed, which is essential to prevent stretching or diameter inconsistencies while the filament is still soft. By carefully tuning the spooler speed to match the extrusion rate, the system produces neatly wound filament rolls with minimal variation.

Throughout development, design validation included strip-width testing, torque assessments for motor selection, thermal calibration for PET flow, and spooling consistency checks. The system operated successfully to provide enough PET fibre that is now being tested in the lab for the tensile strength that will be compared to that obtained for PLA and ABS fibres. Preliminary data is being collected and full discussion on the mechanical properties of the PET fibre will be included in the poster. Details of various parts and their operations will also be discussed in greater detail. 

Presenting Author: Suhaan Saeed IntelliScience Institute

Presenting Author Biography: I am currently conducting research as a research intern at the Department of Mechanical Engineering, San Jose State University. My research interest revolved around 3D and 4D printing. I am specially interested in environmental issues that can be solved by using current technologies including recycling of plastics. After my graduation, I intend to continue research in this field.

Authors:

Sohail Zaidi San Jose State University
Suhaan Saeed IntelliScience Institute