Shane O Neill
PET is an abundant source of potentially recyclable material. Using a four stage process, we have managed to obtain 3D-printable filament from PET bottles. The bottle stripper, made of readily available materials found anywhere is the world, has the capability to turn most large plastic bottles into one long strip. This allows for further processing in order to create 3D printable filament from the recycled plastic. There is also a 3D printed version available for download.
The aim of med3DP is to use 3D printing to provide solutions to a variety of medical problems in areas of short supply. To support this aim, 3D printing equipment combined with a cheap, abundant supply of material is needed. By using one of the most ubiquitous items found all over the globe, plastic bottles, it is possible to create 3D printing material using the process given here.
By shredding the bottle into one long strip using a custom designed bottle shredder it is possible to greatly increase the speed of PET recycling. Following the remaining three steps of cutting, drying and extruding it has been demonstrated that recycled PET can be turned into 3D printable filament.
Originally, the stripper was constructed out of chip wood, copper tubing, screws, washers and a steel blade. The design progressed as to be almost entirely made out of 3D printed plastic; the steel blade is still required however. Both designs are based on the same principles: A tube is fixed perpendicularly to a rigid surface and a steel blade is mounted, parallel to the surface, at a distance measured using a plastic bottle (the bottle is placed through the pole, any area in which the edge of the bottle and the rigid surface meet is a good place for the blade to be mounted). This simple design allows for an entire bottle to be reduced to a single long strip less than 2mm thick in only 3 minutes.
Now, the bottles are ready for cutting. The bottom of a bottle is removed and the insides cleaned with Acetone to remove surface impurities. Next, the bottle in placed on the pole. The bottle is rotated into the blade, causing an almost horizontal cut in the bottle. A strip passes through the gap between the blade and the rigid surface. At this point the strip can be grasped and pulled. It is only necessary to pull in one direction while maintaining a pulling angle approximately perpendicular to the blade. Then, it possible to "unravel" the bottle as fast as you can pull.
Now that the strip has been obtained, it is arranged neatly and cut into precise small square sections using a stationary guillotine with two elastic bands attached at either end. The flakes are gathered on a tarp made of tinfoil placed on the ground. The flakes are similar to commercially available PET or PLA pellets in appearance. However, the composition of this PET will almost certainly be severely degraded.
The flakes are placed in a 60°C oven overnight to remove excess water. The average wet weight value of the material is approximately 23.6g with dry weight being 23.3g. The drying prevents the creation of steam during extrusion, and prevent degradation of the plastic which occurs by hydrolysis.
The dried plastic squares are placed in a hopper and extruded at a temperature of 240°C. The filament produced can then be printed at a nozzle temperature of 255°C and a printing bed temperature of 80°C. The filament was printed using an Ultimaker 2 primter with a nozzle dimater of 0.4mm.