Team:Stanford-Brown/Plastic
Plastic Folding
Testing and Applications
Figure 1 Using infrared light, we can make the plastic polystyrene joint
in between the cardboard substrate to contract and fold
Why plastics?
Plastic is an extremely versatile material that can be used in a multitude of applications such as in medical devices, construction, prototyping, and much more. Currently, many common plastics require the use of petrochemicals to manufacture. To utilize the benefits and versatility of plastics in long term space travel and space colonies would require the importation of petrochemicals into space. With the limited volume and mass payloads of space travel, our team wanted to try to find an alternative to manufacturing plastics in space.
Our team looked to synthetic biology to find a solution to the manufacture of plastics in space to minimize the use of petrochemicals. This summer we wanted to engineer the bacterium Escherichia coli to produce two kinds of plastic: Polystyrene and P(3HB). The prospect of being able to send a sample of bacteria into a space station or colony and having that bacteria manufacture plastic is an exciting prospect for our team.
How does plastic fold?
Most plastics are long organic polymers with a high molecular weight. When these long chains of monomers are pre-stretched in their manufacturing they have a relatively high level of organization. When heated to their glass transition temperature, these pre-stretched plastics will contract in the dimension that they were pre-stretched. With the use of pigments, (and in our case, biopigments) we can select where and how the pre-stretched plastic contracts. By drawing these pigments on the plastic and using infrared light from the sun, we can make the plastic fold. This is because in a flat sheet of pre-stretched plastic, drawing a dark line on the plastic will allow that section of the plastic to heat up and contract faster than the rest of the plastic. Having the dark line only on one side of the plastic will cause the plastic to fold toward that side as seen in figure 1.
By having plastics fold, we can quickly prototype new designs of self-folding by simply printing on biopigments onto plastic sheets and applying infrared light to the plastic. These designs can range from simple cups and containers to complex solar sails and arrays.
Figure 2 Polystyrene joints adhered to a cardboard substrate
Figure 3 After heating joints with infrared lamp the plastic folded
Figures 2 and 3 on the right show the before and after folding photos from figure 1. Figures 4 and 5 demonstrate the folding mechanism of using pigment on polystyrene sheets. Figures 6 and 7 below show the before and after photos of testing the degree of contraction in a two dimensionally prestretched polystyrene sheet. We find that they contract to roughly 11% of its original area. Figures 9 and 10 demonstrate the same folding mechanism as figure 1 with a different box design. Figures 11 and 12 is one of our many attempts to make a pigmented design to fold into a water tight container. Figure 13 shows some of the designs that was folded using sunlight. Figure 14 and 15 shows the microbial biopigments we grew to pigment our plastics.
Figure 4 Polystyrene sheet cut into a box pattern with black pigment on inner edges
Figure 5 Self-folded box after applying heat from infrared lamp
Figure 6 Before heating the plastics: Polystyrene (PS) and Polylactic Acid (PLA)
Figure 7 After heating the plastics evenly the plastics contracted in two dimensions to 11% its original area
Figure 8 Printing pigment on sanded plastic sheets
Figure 9 Before heating polystyrene joints adhered to cardboard substrate
Figure 10 Heating causes the plastic to shrink and fold the cardboard
Figure 11 Simple pigment pattern on polystyrene sheet
Figure 12 Plastic sheet folding up to a more cup-like container
Figure 13 Using sunlight to heat and bend polystyrene
Figure 13 Growing biopigment producing E. coli to use to print on plastic
Figure 13 Biopigment produced by our transformed E. coli on strips of plastic