Shaping through folding and self-healing
We present a completely new shaping method to develop 3D polygon structures starting from synthesized SH-polymers sheets, which utilizes the SH-properties of these polymers. This shaping process is termed, "shaping through folding and self-healing". In this process, a 3D polygon structure is developed by folding a 2D SH-polymer sheet, similar to making an origami structure. The sides of 3D polygon structure are made air tight using a SH-procedure at relative low temperatures, not higher than 90°C.
The construction of the cubic SPC entails three SH-procedures. The temperature profiles (T-profile) of these procedures differ: the temperature and the duration of the isothermal step depend on the required viscosity for sealing the 3D structure. For these three only the T-profiles will be given in, we will not discuss in detail the behavior of the polymer network during these procedures.
Construction of the SPC
First, a plus shape was cut out of the synthesized DPBM-FGE-J4000 sheet. This plus sign was folded and placed into the Teflon Mold. Teflon is used because of its chemical inertness and because it prevents the polymer from sticking to the mold, which would happen when glass or metal molds are used. To seal the sides of the open cube, the SH-property of the material was used.
The mold was placed in a furnace, at a temperature of 3 °C below the gel transition temperature (Tgel = 81.0 °C). At this elevated temperature the polymer chains have enough mobility to close the gaps between the vertical planes of the cube in a few hours. The temperature cannot exceed the Tgel, because the sheets inserted in the mold would start deforming. The SH-process used to form the DPBM-FGE-J4000 (open) cube, was done in a furnace at 78 °C for 4 hours. After this the part was cooled down with a gradient of ± 0.5 C ◦ min −1. Hereafter, the cubic part remained for 24 hours in the mold at 25 °C such that the conversion could converge to the equilibrium conversion. The cubic part was gently removed from the cubic mold.
Next, a stiffer sheet is connected to the open side of the cubic part. This bottom part consists of a -J4000 sheet that was placed directly on the cubic part and a stiffer bottom -J2000 sheet. The additional -J4000 sheet placed between the cubic part and the -J2000 sheet was used to create a better connection. The Tgel of the -J2000 series (98.5 °C) is higher than the one of -J4000 (81.0 °C). The -J4000 sheet was placed on top of the J2000 sheet, and this was placed in a furnace at 90 °C. After 15 min at this high temperature, the top -J4000 sheet turned into a gel-like structure, while the -J2000 sheet remained solid. At that time, the sheets were taken out of the furnace and the cold -J4000 cubic part was immediately pushed on top of the gel-like -J4000 sheet, which sealed the cubic part. The furnace was brought to 60 °C before the whole part was reinserted. The furnace was held at this temperature for 6 hours after which it was cooled down to room temperature at 0.5 °C min −1. Before the shaping process continued the part was left untouched for 24 hours, to reach equilibrium conversion.
Finally a small metal tube had to be inserted in the bottom plate of the SPC, through which the compressed air will be injected in the cell. A hole (D = 2 mm) was made in the bottom sheet of the cubic part. Two small pieces (5 × 5 mm) were cut out of the -J4000 sheet and placed over the metal tube. Next this metal piece was placed in a furnace at 90 °C. Again after 15 min, the -J4000 polymer pieces had attained a gel-like behavior and the metal piece was taken out of the furnace. The hot metal tube was pressed through the hole in the cubic bottom part and the gel-like -J4000 pieces sealed the connection. The furnace was cooled down to 60 °C, after which the assembly was reinserted, held at this temperature for 4 hours, and finally cooled down naturally in the furnace to room temperature.
The SPC-prototype resulting from the manufacturing was constructed out of 2D DA-polymer sheets, using three SH-procedures. For this manufacturing technique, which relies on shaping through folding and self-healing, only relatively low temperatures are required (Tmax = 90 °C).