How it Works

iGEM Guelph has developed a method of valorizing plastic lab waste in a way that minimizes environmental and financial burdens while also improving the efficiency and ergonomics of lab work. The lab-scale Polypropylene Extruder converts plastic lab waste into high-value 3D printer filament and the Parts Library provides a variety of low cost 3D-printable equipment accessories to make lab work more efficient and ergonomic.

The Polypropylene Extruder

The Polypropylene Extruder is small enough to fit on a lab bench, easy to assemble, and less expensive than commercially available equipment, making it a great tool for lab groups on a budget like iGEM teams.

The Engineering Cycle

In building our plastic extruder, we followed the iGEM engineering cycle, which involves the stages of Design, Build, Test, and Learn.

1. Design: We began by designing the extruder with a focus on processing polypropylene, considering its melting point and material properties. Key design elements included precise temperature control and an extrusion chamber tailored to handle the properties of polypropylene effectively.
2. Build: After finalizing the design, we proceeded to build the extruder. This involved assembling the heating elements, extrusion chamber, and motorized components. We utilized 3D-printed parts and off-the-shelf components to construct a functional prototype.
3. Test: Once built, we ran multiple tests to assess the extruder’s performance, focusing on extrusion consistency, temperature regulation, and the quality of the recycled plastic output. Initial tests revealed issues with temperature fluctuations and motor torque, which required further adjustments.
4. Learn: Through these tests, we learned that maintaining a stable extrusion temperature was critical for consistent performance. This insight led us to redesign certain components, such as the heating system, and improve motor control to enhance the machine’s reliability.

By iterating through this cycle, we were able to refine the extruder's performance, making it both efficient and adaptable for plastic recycling purposes.

The Construction Manual

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Section 1: Parts List

Part	Quantity	Total Price ($)
Extruder Barrel Screw Nozzle	1	200
Mica Band Heaters	2	23.11
8mm-14mm Shaft Coupler	1	24.85
Max6675 K-Type thermocouple	1	10.99
Cooling Fans	2	9.59
Mineral Wool Insulation	1	~10
Reversible High Torque DC Motor	1	22.59
Wood Frame (⅜”) Plywood (⅛”) Plywood	1 1	~18 ~8
Spool Supports	1	5.48
Batteries (9V)	4	9.98
Toggle Switches	4	20.33
Arduino Uno Kit Arduino Uno Relay Module Stepper Motor ULN 2003 Motor Driver Potentiometers (50KΩ) Resistor (220Ω) NPN Transistor Wires	1 1 1 1 1 2 1 1 ~20	53.92
Hardware Screws Nuts & Bolts Brackets	~20 ~10 6	~14
Total:		430.84

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Section 2: Extruder Assembly

Step 1: The Screw, Barrel & Nozzle Assembly

• Instructions: Slide the screw into the barrel and tighten the nozzle on the front. Place the barrel on the support to level.
• Function: The extruder screw has a unique design which forces plastic through the barrel as it’s heating while applying mechanical pressure which melts the plastic as it’s forced through the nozzle to create filament.

Step 2: The Heaters

• Instructions: Slide both band heaters onto the extruder barrel so they are on either side of the first thermocouple inserts, and tightly fasten them to the barrel.
• Function: The heaters are 35mm mica band heaters, designed to fit around our extruder barrel. They operate on 110V AC and deliver 380W.

Step 3: The Insulation

• Instructions: Place the semi-cylindrical pieces of mineral wool around the extruder barrel, and wrap in heat resistant aluminum insulation. Additionally, fasten the extruder barrel to the frame using the U-bolt.
• Function: The Insulation can withstand high temperatures and traps the heat from the band heaters for safety purposes and to retain heat and minimize energy consumption.

Step 4: The Coupler

• Instructions: Tightly fasten the coupler to the shaft of the screw.
• Function: The coupler connects the motor shaft to the screw allowing us to rotate the screw. It has a 14mm side to connect to the screw and an 8mm side to connect the motor. This is a flexible coupler which allows for minor misalignment between the two shafts.

Step 5: The Motor

• Instructions: Slide the motor shaft into the coupler and tighten. Attach the motor to the 3D printed support and brackets to secure it in place.
• Function: The motor in use is a reversible high torque gear reduced DC motor. The motor operates on 24V and rotates at 20-30 rpm.

Step 6: The Hopper

• Instructions: Screw the hopper assembly onto the opening in the extruder barrel.
• Function: The hopper funnels the plastic into the extruder.

Step 7: The Cooling Fans

• Instructions: Secure both cooling fans to the base with the use of brackets.
• Function: The cooling fans help to cool the filament as it exits the nozzle.

Step 8: The Stepper Motor

• Instructions: Attach the wooden supports to the base with the brackets. Attach the 3D printed stepper motor support to the wooden supports, and attach the Stepper motor to the 3D printed support.
• Function: The stepper motor allows for accurate control over the rotation speed of the spool. The stepper motor is a BY J-48.

Step 9: The Spool

• Instructions: Place the filament holder supports on the base, and place the spool on the filament holders supports. Insert the 3D printed motor spool coupler into the spool and attach to the stepper motor.
• Function: The spool controlled by the stepper motor stores and neatly winds the extruded filament as it’s produced.

Step 10: The toggle switches & potentiometers

• Instructions: Fasten the 4 switches and potentiometers to the control panel.
• Function: The toggle switches manage power to the heaters, fans, motor, and stepper motor, while the potentiometers adjust the speed of the motor and stepper motor. This allows for manual operation of the apparatus, ensuring both safety and control.

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Section 3: Control and Automation

Step 1: The Heaters

• Circuit Diagram & Code:
• Function: The heating circuit utilizes an arduino to mimic a conventional PID temperature controller. The thermocouple is the key sensing element, which detects the temperature in the extruder barrel, and relays this information to the arduino. The arduino controls the input to a single channel relay module, which acts as a switch turning on and off the connection of the two heaters in parallel and the AC power source. The relay module turns off once the temperature set-point is exceeded, to maintain a constant temperature. In the case of polypropylene we are using a set-point of 170°C to exceed the melting point of 160°C.

Step 2: The Motor

• Circuit Diagram:
• Function: This circuit controls the speed of the motor to allow for fine tuning of the extrusion rate, and filament diameter with the use of a potentiometer and a NPN transistor. The potentiometer outputs a variable voltage to the base of the NPN transistor, which varies the current supplied to the motor.

Step 3: The Stepper Motor

• Circuit Diagram & Code:
• Function: This circuit controls the speed of the stepper motor to achieve consistent winding of filament around the spool. The output of the potentiometer is connected to an analog input pin on the arduino. The arduino correlates the input voltage from the potentiometer to a rotation speed of the stepper motor.

Step 4: The Fans

• Circuit Diagram:
• Function: This circuit controls the speed of the motor to allow for fine tuning of the extrusion rate, and filament diameter with the use of a potentiometer and a NPN transistor. The potentiometer outputs a variable voltage to the base of the NPN transistor, which varies the current supplied to the motor.

Why Polypropylene?

Polypropylene is one of the most common plastics used in biology labs because it is autoclavable, non-polar, and resistant to aqueous solutions of salts, acids, and bases, making it ideal for sterile applications in molecular biology work⁶. Centrifuge and sample tubes, pipette tips, and trays are some of the common consumables made from polypropylene⁶. Polypropylene is a desirable material for 3D printer filament because it is durable, flexible, and lightweight compared to other plastics⁷. With a price point ranging from $60 to $120 per kg, polypropylene is a high-value 3D printer filament that costs more than most other varieties⁷.

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Next Steps

In future works, the thermal and mechanical properties of the polypropylene filament should be characterized and the optimization of its printability should be investigated.

Properties of the filament including strength, stiffness, melting temperature, and deformation and flow behaviour are important for assessing its quality and applications. The strength and flexibility of polymers is tested via impact, tensile, and flexural testing in which a standardized sample of the polymer is subjected to hitting, pulling, and bending forces, respectively. The polymer’s response to heat is measured via differential scanning calorimetry and deformation and flow behaviour is measured via rheometry⁸. This testing should be completed on the recycled polypropylene filament to assess its performance in comparison to new polypropylene filament and identify areas for improvement. Future works could involve the modification of the recycled polypropylene filament using chemical or physical additives to enhance its properties and therefore increase its value.

Due to the high rate of warpage and lack of bed adhesion that polypropylene exhibits, there are several steps that should be done in future work to improve the printability of the filament acquired from the extruder⁹. The use of scrubbed ultra-high-molecular-weight-polyethylene (UHMWPE) as a printing bed has been shown to provide significant bed adhesion for polypropylene¹⁰. The UHMWPE has a similar chemical structure to that of the polypropylene, allowing for significant adhesion¹⁰. Furthermore, scrubbing the UHMWPE increases the surface area, allowing for further adhesion between polypropylene and the bed¹⁰. Therefore, labs making use of this recycled polypropylene filament should invest in such a printing bed for their printers. Additionally, the printer settings at which the material is printed will affect the final quality of the print⁸. As such, the use of a design of experiments (DOE) such as the Taguchi method, could aid in optimizing the printer settings to minimize warpage and maximize bed adhesion⁸.

The Parts Library

The Parts Library is a digital collection of 3D printable parts created to improve the usability and functionality of common lab equipment while reducing costs associated with upgrades. The parts are designed to facilitate and streamline lab activities by improving workflow and retrofitting equipment to make it more ergonomic.

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Accessibility and Applicability

All parts are simple and adjustable to satisfy user needs and accommodate a variety of equipment models while being easy to print and use with limited 3D printing experience. Both .SLDPRT and .STL files are provided to make the parts accessible to users with or without the SOLIDWORKS software. .STL files are ready to print and compatible with all 3D printers. .SOLIDWORKS files allow users to modify the parts and see how they are made.

3D printers are becoming increasingly more common in biology labs and are often found in school campuses and community spaces such as libraries, making them easily accessible to small-scale research groups like iGEM teams. Thus, the Parts Library is a valuable tool for research groups regardless of if they own a 3D printer.

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User Testing

The parts were designed to solve issues identified by iGEM Guelph’s Wet Lab team and external lab groups, who were consulted via the Accessibility in the Laboratory survey created by the Human Practices team. Throughout multiple iterations of designing and testing, the parts were tested in-lab by iGEM Guelph’s Wet Lab team and improved based on user feedback. Many have been used in iGEM Guelph’s lab with great success throughout this year’s project!

Microcentrifuge Tube Decapper Thumbpiece Analytical Balance Tube Holder Cell Phone Microscope Holder Salad Spinner Centrifuge Attachment Multi-Microcentrifuge Tube Decapper Vortex Tube Holder Single Pipette Holder Incubator Plate Holder Gel Electrophoresis Comb Test Tube Holder