3D printing with PLA

Summary of Issue
PLA is the most common plastic used in 3D printing [1]. Unfortunately, 3D printing is prone to waste; through failed prints and surplus material discarded once printing is complete. PLA is at times subject to a degree of greenwashing, being touted as an environmentally friendly material. It is a bioplastic, and therefore could be described as carbon-neutral and compostable. However, the reality is more complicated.
Questions Raised
1.What is the environmental impact of PLA filament?
2.What practical measures can be taken to reduce the environmental impact of 3D-printing with PLA?
3.What PLA recycling options are available?
Information and recommendations (TL;DR)
While PLA is indeed a bioplastic, an industrial composter is required for it to biodegrade. It's challenging to recycle; therefore, PLA is a precious material that should be used with care.
1.Reduce the amount of PLA used by attending to print infill density and wall thickness settings.
2.Check mechanical tolerances with small parts before printing larger models.
3.Minimise the use of support structures.
4.Reduce print failure rate and improve print quality by storing your filament in a dry, dust-free environment.
5.Repurpose waste PLA (create plectrums, for example).
6.Buy and use recycled PLA filament.
7.Recycle waste PLA into new filament as a DIY project. An advanced but achievable project.
Notes
In addition to its ubiquitous use in 3D printing, PLA (Polylactic acid) is used in food packaging. Its a bioplastic, derived from renewable, plant-based materials such as corn starch. A common misconception is that as PLA is a bioplastic, it will naturally decompose; making it an environmentally-friendly choice of material. PLA is biodegradable but unfortunately, will break down exceptionally slowly without the intervention of industrial processes. The rate of decomposition is dependent on the environment the PLA is placed in. Analysts suggest that a PLA bottle could take anywhere from 100 to 1000 years to fully decompose in landfill. Conversely, when placed in an industrial composting facility (an anaerobic digestor), PLA can decompose within three months [2]. Filamentive estimated that globally, eight thousand tons of 3D printing material would enter landfill in 2019 [8].
Is it possible to send waste PLA, resulting from print errors, discarded support structures and old prototypes, to an industrial composting facility? Municipal waste collection programs are likely to vary geographically. In the UK, domestic compostable waste collection is commonplace, intended for food scraps. However, PLA would be seen as contamination if mixed with this. Furthermore, falling into the catch-all, Recycling Grade 7 (the higher the number, the harder to recycle) PLA cannot be recycled by municipal waste programs [3]. Placing large quantities of PLA into domestic recycling would contaminate the recycling stream [4].
So where does this leave us? By attending to the familiar three R's (Reduce, Reuse & Recycle), our environmental impact can be reduced in the use of PLA.
REDUCE
There are a few practical measures that can be taken to reduce the amount of PLA filament we use.
Infill density and wall thickness
A reasonably easy adjustment is to reduce the infill density and wall thickness of a 3D print. This will, however, affect the strength of the printed object, and therefore its ability to withstand an applied load. Where strength is integral to a design, it may still be feasible to reduce the infill and wall thickness on test prints (when checking tolerances, for example).
Tolerances
It may not be necessary to print an object in its entirety to check mechanical tolerances. For example, the tolerance of a screw hole can be scrutinised in isolation, using just a small amount of filament.
Support structures
Consider the orientation and design of models to reduce the number of support structures required. All3DP has an excellent article on this topic. As a general rule of thumb, models that overhang by 45 degrees or more will require support structures, albeit printer dependent. Reducing layer thickness can help improve your printers ability to print overhangs. While reorientating a model on the print bed may eliminate the need for specific support structures, other techniques such as chamfering can be employed to reduce overhang angles.
Dual extruder 3D printers can make use of water-soluble PVA filament for support structures. However, there are some concerns that the growing use of water-soluble polymers by consumers and by industry could have a detrimental environmental impact [5].
Storage
Waste can be reduced by ensuring your filament is stored in a clean, moisture-free environment. A dusty spool of PLA is likely to cause failed prints. Once PLA has absorbed moisture, it becomes brittle, and print quality decreases. All3DP suggest a range of storage solutions, including in-situ storage for loaded filament. Furthermore, filament dust can be removed using a clip-on filter.
Spools
Filament typically comes, loaded on a plastic spool intended to be discarded once the filament is spent. Consider buying filament on a more easily recycled metal/cardboard spool. In the UK, Filamentive is a good source of such filament:
REUSE/RECYCLE
There are ways (albeit somewhat experimental), in which makers can recycle and reuse waste PLA.
Reuse
Some creative approaches to repurposing waste filament can be found online. Of interest to guitarists might be these plectrums cut from PLA. Another example is the Plastic Smoothie. The filament is cut into small pieces using a food processor, melted into a sheet in a small oven then used as raw material for a laser cutter. Another interesting experiment was conducted during a study by Dew and Rosner [6]. Waste filament was reheated to use as a fixative for printed objects, and also moulded into new items.
Create New Filament
​Filabot manufactures a system for extruding (and re-spooling) waste filament. This began as an open-source project (the Filabot Wee). The current Filabot machines are sophisticated but costly, perhaps only within the means of larger maker spaces. Alternatively, open-source projects exist and DIY guides are available, explaining how to create extruding machines.
Buy Recycled Filament
It is possible to purchase filament made from recycled PLA. Again, Filamentive is a good source. However, bear in mind that, to retain strength, such filament is likely to be a mix of recycled PLA and virgin material. Filamentive PLA contains 55% recycled material.
External Links and References
[1] https://www.filamentive.com/how-sustainable-is-pla/
[2] https://www.scientificamerican.com/article/environmental-impact-of-corn-based-plastics/
[3] https://all3dp.com/2/3d-printer-recycled-plastic-tips-for-your-waste-plastic/
[4] https://www.theguardian.com/environment/2008/apr/26/waste.pollution
[5] https://www.sciencedirect.com/science/article/pii/S0301479718310016
[6] https://dl.acm.org/doi/10.1145/3322276.3322320
[7] https://all3dp.com/2/is-pla-recyclable/
[8] https://www.filamentive.com/the-3d-printing-waste-problem/​
Contributor
​Alex Lucas​
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Contents
Summary of Issue
Questions Raised
Information and recommendations (TL;DR)
Notes
REDUCE
REUSE/RECYCLE
External Links and References
Contributor