Heat-Based Fabrication Techniques for Upcycling HDPE Plastic Bags
Himani Deshpande, Akash Talyan, Noah Posner, Hyunjoo Oh
Alongside the environmental impact, upcycling discarded plastic bags exhibits interesting, unique material characteristics that attract our attention. For instance, compared to paper, a plastic sheet is water resistant and more durable; compared to wood, it is softer and more foldable; and compared to leather, it provides a more rigid texture. These traits enable a wide range of creative possibilities for makers. In order to support exploring such unique materiality of plastic bags, we developed a set of fabrication techniques based on two categories: additive fabrication and subtractive fabrication.

We propose the fabrication pipeline combining both additive and subtractive processes as below:
Prep: Cut discarded plastic bags and stack them in layers
Additive process - Global fusion: Apply heat and pressure to fuse the plastic layers into one seamless sheet
Subtractive process - Cut and score the fused sheet using a laser cutter to obtain the shape required
Additive process - Local fusion: Fold along the scores and join using a soldering iron to generate the final object

1) Global Fusion
Global fusion is a way to completely and uniformly fuse layers of plastic throughout. We used four different machines (clothing iron, toaster oven, hand-held heat press and table-top heat press), which are commonly available in maker spaces, and tested each machine’s capacity in terms of global fusion.
Clothing iron : Difficult to get smooth fusion over 30 layers of plastic due to inability to apply uniform heat and pressure
Oven : Cumbersome setup and long wait time
Hand-held heat press : Human pressure, higher time needed
Table-top heat press: Mechanical pressure, low time, lower temperatures

It is important to understand the safe zone in terms of temperature used to fuse the HDPE plastic bags. The temperature needs to be in a range around the melting point of HDPE. This range of temperatures will fuse the plastic layers but will not burn them. This reduces the chances of the release of toxic fumes significantly. Our intent during the whole process is to keep the fusion temperature as low as possible for the given number of sheets.
2) Cutting and Scoring
In order to be able to fold the fused plastic sheets into objects, the sheets need to be cut into the desired shape and scored where the folds are supposed to occur. For the purposes of our experiments, we have used a laser cutter to cut and score the fused sheets. The laser cutter settings required for through cuts and score cuts have been mapped to the number of the sheets through our experiments. 
Different kinds of score patterns are possible to obtain variance in flexibility. Increasing the depth of the score-pattern-cut increases the capacity of the sheet for bending. 
3) Local Fusion
Once the layers of plastic bags are globally fused, and cut and/or scored, we use the resultant sheets to make 3D objects. After the desired shapes have been cut, local fusion techniques can be used to join the different shapes together to create an object. 
Variable Thickness Generation
This technique can be used when a seamless sheet of fused plastic with variable thickness is desired. This technique is intended to be used before using the soldering iron technique (discussed later). Global fusion is not able to accurately produce sheets of variable thickness and if said variable thickness is desired, separately fused sheets need to be locally fused.
Soldering Iron technique
This technique is used for joining two pieces of fused plastic sheets quickly and without the use of a heat press. For the purposes of our testing, we have used a soldering iron with temperature control and some pieces of aluminum foil to shield the iron from plastic melting and sticking to it. This technique is for the assembly processes where we use the fused sheets and connect them to create 3D objects. 
To demonstrate the expressive possibilities that our fabrication techniques provide, we developed three application prototypes.

Sling Bag



future work
We see this project as an early stage of our long terms study towards upcycling plastic bags. 
1) Investigate ways to reduce the labor and speed-up the process of cutting and stacking plastic bags
2) Develop a software library that can provide guidance based on intended sheet designs
3) Diversify the scope of resulting sheets by combining layers of plastic bags with other materials including conductive materials and thin electronics to synthesize different behaviors resulting in a broad spectrum of expressive and computational materials.
The core motivation of our project is to reuse discarded plastic bags. Throughout this project, we needed to collect a huge number of discarded plastic bags from people around us, which include our friends, colleagues and at times, even strangers. While doing so, we discovered that people frequently store one-time used plastic bags in a drawer or under the sink in hopes that those bags will be of some use later.  And when asked for plastic bag donations, they happily gave away these bags as they were getting used again for a purpose. This makes us think that the maker community of upcycling abandoned materials can be potentially bigger than we perceive now. That is, if we develop tools and techniques using machines widely accessible around us and show compelling examples, maybe we could invite more people to this hands-on, creative tangible learning activity.