Turn Trash Bags Into Interactive Inflatables Using a 3D Printer!

This project, which I named as "Therms-Up!", introduces a DIY method of creating fun inflatables and prototyping interactive materials from wasted thermoplastic bags that easily found at home. Here, I will explain how to use Fused Filament Fabrication (FFF) 3D printer like Ender 3, Prusa, etc. to heat-seal different types of wasted thermoplastic bags and create crease patterns for origami structures.

You can find some examples I've made using the introduced method from the video on top. Also, details can be found from this research paper

MOTIVATION

I had been working on this project during the COVID-19 lockdown (2020 Summer) when I had a limited access to any fancy fabrication tools at the lab and had to stay at home all day.

While I were locked down at home and doing a remote work, as an active maker and crafter, I was interested in utilizing household wastes and repurposing them to turn into interactive inflatable materials at home. And when I was eating a bag of chip, got a fun idea 😏

So I collected thermoplastic bags consumed at home over 3 weeks as you can see from the attached photos like from shipping bag, shopping bag, delivery bag, chip and snacks etc. 

Next, I categorized them to work with this DIY method using a 3D printer. I have been producing these interactive inflatables and having so much fun at home. Let me share how I did it. 

Hardware

• Any wasted thermoplastic bags (PP: polypropylene, PE: polyethylene)
• e.g. See the attached photo above: Ziploc (a), Bubble wrap(g), plastic shipping envelope (c, d), retort food package (h), chip bag (f), plastic shopping bag (b, e), cereal bag (f)
• If you are not sure of the material, try to find if the wasted material has any recycling code printed on.
• Piece of cardboard (size of your buildplate). I just cut something like a Amazon delivery box
• Aluminum foil for grill purpose (thickness: 0.3 μm ~) < this foil is only needed for Ziploc, HDPE plastic bag, Bubble wrap (please find details from the below characterization table)
• FFF 3D Printer. I used Ender 3 with a 0.4mm nozzle. *You don't need any filament!*
• For alternative: Clothing iron or soldering iron
• Straw: straw needs to be inserted in between the heat-sealed bag to work as a air-channel
• Glue gun or tape: this is for sealing the straw insertion area so that prevents air from leaking out

Software

• Inkscape to create heat-sealing pattern: https://inkscape.org/
• J-Tech Laser tool Plug-in for Inkscape (to generate G-CODE): https://jtechphotonics.com/?page_id=2012
• AxiDraw to use Hatch Fill pattern: https://github.com/evil-mad/axidraw

The basic idea of this method is using the heat from the 3D printer's extruder to heat-seal the thermoplastic bags. Depending on how you setup the extruder temperature and the extruder's height from the buildplatform, you can play with creating different patterns, engraving, and heat-sealing. As you can find from the table below in Step 2, each thermoplastic has a different melting point. When they melt, it tends to stick together so that can be used with heat-sealing process for making a container for chips or cereal for example.

* Although the listed thermoplastics (PP, PE) does not contain toxic material like di(2-ethylhexyl)phthalate and are approved by FDA for food packaging, I'd recommend to use our method in a well ventilated open space/room.

The characterization table shown above summarizes different setup required for the different types of thermoplastics. Photos on the side shows several examples representing each material.

The most parameters of the 3D printer you need to work with are: printer head height (Z), travel speed, extruder temperature. I also marked whether I'd recommend to put a cardboard piece underneath the thermoplastic bag or put the aluminum foil on top.

You can refer those values from the table. You might need to tune a bit depending on which 3D printer you're using with.

Create the Heat-sealing Pattern and Convert it into a G-code

I used Inkscape to create traces and patterns (for hand drawing, I used Adobe Illustrator and exported it to SVG to open it on the Inkscape for generating the G-code).

I used the ’Gcode tools’ in the Inkscape extensions to generate G-code. Using a G-code plug-in like J Tech Photonic Laser Tool is also helpful for generating the code quickly.

To create a hatch fill patterns, I used the AxiDraw extension. Before opening the generated G-code in any slicer software, I edited the header of the G-code to have it the temperature of the extruder and printing bed based on the setup table I attached.

In order to control the temperature of the 3D printer extruder via G-code that generated from the Inkscape, you need to add the following command on the head of the G-code, and the footer at the end of it. G-code can be edited by any notepad software or IDE You can find detailed information for the each command from here https://reprap.org/wiki/G-code

Header:

G1 Z5.5 F1200; Linear move of Z height to be 5.5mm, with speed 1200mm/min
M104 S160 ; set up the extruder temperature by changing the number next to the 'S'
M105
M109 S160 ; set up the extruder temperature by changing the number next to the 'S', and WAIT
M204 P500.00 R1000.00 T500.00 ;Setup Print/Retract/Travel acceleration
M205 X8.00 Y8.00 Z0.40 E5.00 ;Setup Jerk
G28 ; Move to origin(Home)
G90 E0 ; Set to Absolute Positioning
G0 Z20 ; Rapid move of Z height to be 20mm from the bed
G21  ;Set unit to [mm]

Footer

G0 Z20
G28 X0 Y0
M18
M106 S0 ;Turn-off fan
M104 S0 ;Turn-off hotend
M140 S0 ;Turn-off bed

You can find G-codes for the several examples and *.SVG files.

• *.svg files (Inkscape)
• G-codes : I've put the G-code examples in different folders depending on the plastic material you want to use.

This one requires a bit more patience and might need some iterations to find your best printer setup to work with Ziploc.

Only when using the Ziploc, putting a cardboard underneath causes defects so that fixing the Ziploc directly on the printing bed works best.

Also, to avoid any slips between the foil and Ziploc during the extruder travel, I sprayed water on the Ziploc sruface and placed the foil on top to make the foil and Ziploc sticking together via surface tension without leaving any sticking traces on the Ziploc.

Before running the printer, it is important to fix the materials on the printing bed with or without cardboard using a clip or tape and make sure that the plastic film is stretched to have a tension for minimizing wrinkles

I used a aluminum layer of multilayered plastic bags, such as a retort food package, to fabricate a touch/pressure sensor.

I created a capacitive based sensors. The advantage of using the thermoplastic material is that we can stick the sensor trace to any other plastic materials by applying heat.

To demonstrate this idea, I cut a walnut package in two identical square shapes and pasted them on a HDPE shopping bag using a iron (see the attached photo).

I created a simple inflatable with the sensor patch on each side, which detects its shape-deformation by capacitive variance due to the distance variance of the HDPE layers. Also, by using a zipper attached on the walnut package, the pressure sensor’s stiffness can be adjusted by adding a sponge inside. 

Reference to use the capacitive sensor using the Arduino

1. Prepare a bag of chips that you just finished :)
2. Cut the seam to unfold the bag, and clean the inside by soap and water. Let it dry.
3. Draw origami patterns (origami patterns will be given or patrons can come up with their own ideas) on the unfolded sheet of the bag and cut.
4. Heat up mini iron (or soldering iron)
5. Fold the sheet of the bag following the origami pattern you just drew and seal it by the heated-up iron with tube/straw inserted on the edge.
6. Hot glue/or tape around the tube/straw so that air cannot leak.
7. Blow through the straw and have fun with the shape-changing robots!

Here (Github) I also uploaded several example files and templates that you can follow folding

If you want to know more about this project, you can find more technical details from our published paper here

Thank you and hope you enjoying crafting!