As a first line of defence against the spread of COVID-19 the facemask, a simple covering worn to reduce the spread of infectious agents, has affected the lives of billions across the globe. An estimated 129 billion facemasks are used every month, of which, most are designed for single use. Naturally, this presents a challenge of immense scale to mitigate the impact of disused Personal Protective Equipment (PPE) on our environment.
After realising that the all too familiar facemask is not ‘some sort of paper’ but often a polymer with a high percentage of Polypropylene (PP), the idea of recycling these masks into new, and somewhat useful products became a subject of interest. Could PPE waste be turned into something useful for society? (3D Printing / Injection Moulding).
Filament extrusion kit
Ender 3 Max
Elegoo Mars and High Temp Resin
SLA 3D Printer and TR300 Resin by Phrozen
Processing Facemasks into granules for filament extrusion
Through early experimentation it was realised that the fibrous composition of masks posed a challenge to any conventional methods of plastic recycling, the cause of many a ‘clogged machine’. To overcome this issue a step prior to grinding the masks is introduced, where the masks are heated and pressed to form a hard sheet. This takes the material to its glass transition point where the Polypropylene fibers fuse together to create something with more rigidity. In this example, a simple iron and non-stick baking paper are used.
The rigid sheets are then broken-up into smaller parts to put through the blender (300W Breville Blend Active), achieving the fine granules of facemask blue PP pictured on the right. For comparison, the sample ABS material supplied by Filastruder is also shown. This process of increasing rigidity improves results from extrusion by reducing pressure instability in the barrel of the filament extruder. Further, this prevents the issue of fibres jamming the machine barrel. The blue granules are fed into the extruder to produce filament.
To address concerns around contamination of the material produced, it should be noted that the masks are heated throughout the process of extrusion to a temperature far beyond that which SARS-CoV-2 has been shown to survive.
Another issue to consider is the pre-processing of masks i.e. removing ear loops and metal nose straps. These are fairly easy to remove manually, although could present difficulties in automating the sorting/preparation process. It might be that in the future users are prompted to separate these parts before recycling.
This image shows the most recent set-up of the filament extrusion kit in action. You can see a video of this on the project blog post (link).
The Filastruder is vertically mounted using a 3rd party non-standard vertical hopper found on thingiverse.
Nozzle temp: 170 C
Voltage: 11V (turned down to reduce speed)
Amps: 1.6 (current limited)
Nozzle hole diameter: 1.75mm
Filawinder: Automatic speed
This set up produced good results, however there are still issues with achieving a consistent filament diameter.
Nevertheless, 7 meters of ‘useable‘ filament was spooled with an average diameter of 1.5 mm (-0.25 mm below the standard of 1.75 mm). These initial results suggest that with further refinement it will be possible to achieve the desired diameter within a reasonable tolerance. At the time of writing this post, the standard nozzle has already been drilled from 1.75 mm to 1.9 mm, and parts for a motor driven vertical feed are being 3D printed. Improving these aspects of the system should get the filament closer to the ideal 1.75 mm diameter.
This first batch of filament was used to run some early stage tests on an ender 3 desktop 3D printer.
Printing with Facemasks
Polypropylene (PP) is notoriously difficult to 3D print as it doesn’t bond well to common printer build platforms. However, it does bond well to itself, PP. A trick is therefore to print on normal clear tape as this is often also PP. Using this method it was surprisingly straightforward to 3D print with our rudimentary stock of filament on a low-cost, run-of-the-mill machine. This highlights that issues currently reside in producing the filament and not in 3D printing with it, or other applications.
Printer: Creality Ender 3 Max
Nozzle temp: 235 C
Bed temp: 100 C
Print speed: 40 mm/s (slow)
Fan speed: 100>#/li###
Retraction: 4mm (Bowden)
Retraction speed: 30 mm/s
Flowrate: 350% (account for thinner filament)
These settings worked well considering the inconsistency in diameter of filament. The flowrate took some playing with.
Whilst not very widely used as a material in 3D printing, some properties of PP make it an alternative worth exploring. These include the materials durability, and resistance to chemicals and fatigue. Polypropylene is also both food and microwave-safe.
In addition to the points above, PP is one of the most common polymers in use. From an environmental standpoint the use of recycled Polypropylene, and polymers in general, poses an opportunity to reduce the consumption of virgin material in rapid prototyping processes such as 3D printing and Injection Moulding.