The bioplastic project is a sustainable design system that utilizes a unique liquid printing technique to create 3D products from biodegradable materials, start to finish. This is an independent research project.

Objective

Synthetic plastics dominate the product industry from the polyethylene in your plastic bags to the polyester in your favorite sweater. First, we wanted to find a biodegradable material that could replace the existing everyday applications of plastic. We settled on a collagen-based bioplastic as our material, with a formula unique from existing plant-based bioplastics, which currently dominate the bioplastic industry. Secondly, because bioplastic exists natively as a liquid, we needed to create a liquid printing system capable of producing 3D products with it.

Material Research

  • durable (solidifies into an unbreakable material)

  • malleable (creates different shapes/thicknesses)

  • cost-effective (more than halves the price of producing epoxy plastics)

  • lightweight

  • versatile (creates new properties when mixed with different materials)

We conducted many material studies in order to find the correct chemical recipe for our alternative material, a bioplastic made from three simple ingredients: gelatin, water, and glycerine. 

We chose collagen-based bioplastic not only because it is environmentally sustainable, but also for an array of material advantages. It is:

The difficulty of working with bioplastic is that it exists as a liquid, takes half an hour to become a semi-solid, and completely hardens after 72 hours of drying. We needed to create a printing system that would allow us to extrude the liquid bioplastic and suspend it in the desired 3D shape as it solidified, which traditional 3D printing methods cannot do

Aloe

  • durable (solidifies into an unbreakable material)

  • malleable (creates different shapes/thicknesses)

  • cost-effective (more than halves the price of producing epoxy plastics)

  • lightweight

  • versatile (creates new properties when mixed with different materials)

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Initial prototype for printing system. Bioplastic extruded through syringe into aloe gel.

In order to do this, we utilized an equal-density printing technique, where the density of the bioplastic material being extruded matched that of the gel it was being printed into. We conducted this small-scale experiment until we were confident in the both the material properties of bioplastic and aloe gel, and the interaction of the two in our process.

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Bioplastic removed from aloe gel shortly after extrusion.

Once familiar with these principles, we then proceeded to design our system on a larger scale utilizing the precision of a robot arm and digital fabrication.

Tool Design

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The tool for the printing system is a syringe that extrudes the bioplastic into a tank filled with the gel support. A motor coupled with the syringe controls the speed as well as the direction of the extrusion (emptying or refilling material). The robotic arm controls the pathway, or shape of the extrusion. 

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The robotic arm reads its directions from computer code we generated in order to create the shape pathways we rendered in Rhino 3D below.

Code and 3D visual rendering behind our printed forms

Implementation

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Final syringe tool implemented onto the robotic arm

After designing and assembling our tool, we conducted many test runs in the lab to evaluate the optimum parameters of printing such as the speed and angle of extrusion. We printed three 3-dimensional shapes in the liquid printing system (cylindrical, lemniscate, and hexagonal prism) in order to test which form best held its shape after completely curing. Below is a table summary of these digitally designed forms, resulting physical forms, materials used, and printing parameters.

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In order to test the angle of extrusion this system was capable of printing at, the first shape we printed (form 2 in the figure above) had a vertical offset of 3 millimeters, where each hexagonal cross section would be twisted 3 mm clockwise. Because this form was unsustainable, and collapsed in on itself once excavated from the aloe transmission gel, we determined that the extrusion angle has to be exactly at 90 degrees, and printed the consequent forms at this angle.

Analysis

Forms

Every form we printed experienced transfiguration after being removed from the printing tank and left to dry. Across all four shapes, the drying process caused a curling or buckling around the edges (pictured above).

  • Form 1, the cylindrical form, experienced the most rapid deformation from the period of time between excavation and drying. Water loss caused the cylinder to shrink from a height of 5 cm to its final flat disk-like shape.

  • Form 2, the offset hexagonal prism, collapsed at excavation and dried in this shape.

  • Form 3, the lemniscate, shrunk more dramatically at its base than at its top, creating an uneven prism that was not perfectly vertically stacked. It shrunk from a height of 8 cm to 4 cm, losing 50% of its height due to water loss.

  • Form 4, the hexagonal prism provided the more stable result overall, as its dried form most closely resembled its designed one. Although the integrity of the shape was well preserved, it was not precluded from shrinkage due to water loss. The hexagonal prism shrunk from 10 cm to 6 cm, losing 40% of its height. 

Printing Process

There were two main inefficiencies with the printing process itself that can be improved:

  • When the bioplastic material cooled, it would congest the syringe tip and inhibit further extrusion. We remedied this by manually reheating the tool, but would like to solve this issue mechanically in a redesign of the tool.

  • The force of the stepper motor was too much for the syringe made out of PLA material, so a redesign would entail using a stronger material in our tool such as ABS.

Future Research

While we made bounds in progress, this is just the beginning of our research. 

This liquid printing technique is a system from which we can create a 3-dimensional printed product using collagen-based bioplastic. Through digital means, we created much more control over the shape and height of the bioplastic forms than we had in our prototype, or that exists in any other printing system for collagen-bioplastic. However, the resulting forms are not stagnant; they are changing and display an agency of their own over time through the way they cure. Future research will be targeted at finding an application for this collagen-based bioplastic, and for determining whether or not we can leverage its mutability towards a use. While its drying creates variability between the designed form and the physical form, perhaps the use is in this process of drying itself, which can be used for 4-dimensional printing technologies. Or still, perhaps there is use in the resulting physical forms curling and lacing which create organic forms impossible to design digitally.

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