A stack of printed PLA discs isn't the obvious way to clean water. Researchers at the University of Waterloo report that, with two chemical modifications, it works surprisingly well. According to 3D Printing Industry's report on the work, a 20-layer stack of the modified discs removed 90% of polystyrene microplastics from test water. The authors, named as Crawford and Mekonnen, published the study in the journal Separation and Purification Technology. Most of the gain comes from material treatments, not printer resolution, which makes this a materials story first and a printing story second. One caveat on sourcing: FilamentFeed could not read the journal paper itself. Everything below comes from two secondary accounts, and we note where they disagree.
The Problem With Printing a Filter
Filters work by having openings smaller than whatever they are meant to catch. Microplastics are far smaller than anything an extrusion nozzle can lay down. Hackaday's write-up, by Maya Posch, puts it plainly: FDM alone cannot print pores fine enough. So the Waterloo team used the printer only for the coarse structure and relied on chemistry for the fine work.
The coarse structure is simple. Each disc is 39 mm across and perforated with an offset grid of 1 x 1 mm holes. The discs are stacked with their hole patterns alternating, so water can't run straight through. It has to zigzag between layers, which raises the chance that a particle touches a surface. Contact matters here more than sieving. Each layer is less a strainer than a place where particles can get stuck.
As a baseline, the team stacked eight plain PLA discs and ran water containing polystyrene microplastics at 100 ppm through them. That stack captured 16% of the particles. It is a respectable number for a mesh of millimetre-scale holes, but nowhere near a useful filter.
Step One: Print It, Then Dissolve Part of It
The first modification uses a sacrificial additive. The researchers blended low-molecular-weight polyethylene glycol (PEG) into the PLA at 10 parts per hundred resin. After printing, they dissolved the PEG back out with hot water. The PEG's former spaces become pores in the PLA, ranging from about 100 nanometres to 10 micrometres, with surface irregularities up to roughly 50 micrometres. Hackaday says the PEG formed spheres within the material and that the PLA-PEG10 formulation gave the best porous structure of the samples tested.
The two outlets disagree on the etching conditions. 3D Printing Industry says boiling water. Hackaday gives 80 °C. The paper would settle it, but we couldn't read it, so treat the exact temperature as unconfirmed. Either way, the idea is the one behind dissolvable support filaments: one component is designed to wash away and leave a shape behind. The difference is scale. Here the "support" is spread through the part as microscopic inclusions instead of printed as a separate structure.
The added surface roughness helped. Eight etched discs captured 37% of the microplastics, more than double the plain-PLA result.
Step Two: Make It Sticky
The second modification is a coating. The team applied poly(2-ethylhexyl acrylate), an acrylic pressure-sensitive adhesive with a glass transition temperature of about -50 °C. At room temperature it sits well above that point, so it stays soft and tacky instead of glassy. Particles that touch it tend to stay put. 3D Printing Industry also notes that the polymer can be synthesized from waste diapers, a small sustainability bonus for a device meant to clean up plastic pollution.
With the acrylic coating, eight layers reached 51% removal. The researchers also tried polydopamine, a competing coating, which reached 46% at the same layer count. The acrylic adhesive won, though not by much.
Scaling the Stack
The headline number comes from adding layers. Going from eight to 20 coated, porous discs raised removal from about 51% to 90%. The same change barely helped plain PLA, which gained only six percentage points. That contrast is the main finding. Extra layers only help when each layer can actually hold particles. Stacking more smooth, uncoated discs mostly gives the water a longer path past surfaces that don't grab anything.
According to 3D Printing Industry's summary, the filter works by gravity, with no pump required. That keeps the concept simple, but the coverage gives no flow rates or throughput figures, so how much water a stack can handle, and how fast, remains open.
The Limits
3D Printing Industry calls the work a proof of concept, and the caveats are real. Removal was less effective on particles smaller than 10 micrometres: after filtration, 80% of the particles that got through were under 10 micrometres, while nearly all particles larger than 50 micrometres were captured. Hackaday notes that the authors list further system improvements and reusability as open questions. Reusability matters for a sticky filter in particular. An adhesive surface that has captured particles has, by definition, used up some of its capacity, and the coverage doesn't say whether a loaded stack can be cleaned, recoated or only thrown away.
The tests also used one particle type, polystyrene beads, at a fixed concentration of 100 ppm, in surfactant-stabilized water rather than real-world wastewater. 3D Printing Industry notes that fibrous microplastics from laundry effluent were not tested, and that the surfactant itself may have affected adhesion. Real-world water carries a mix of polymers, shapes and sizes, along with organic matter that could foul an adhesive coating. None of that has been tested yet, according to the available reporting.
What It Means for Makers
This project is unusually accessible. The base geometry is a 39 mm disc with a grid of 1 mm holes, which any working FDM printer can make, and the base material is PLA. Most of the hard work is materials processing done after printing, not anything the printer itself needs to do better. That is a useful reminder of how much a printed part's performance can depend on what is mixed into the filament and what happens to the part afterward.
It is not a weekend build, though. A 10 phr PEG-PLA blend is not an off-the-shelf filament, and a synthesized acrylate adhesive is not a hardware-store coating. More importantly, nothing here has been shown to make water safe to drink. A 90% capture rate for one plastic in a lab test is a research result, not a certification. Makers looking for drinking-water treatment should use filters rated for that purpose.
Two ideas carry over directly to other printed parts. First, sacrificial additives let you create porosity at scales far below nozzle resolution. Second, surface chemistry can matter more than geometry: in these tests, going from etched to adhesive-coated discs raised eight-layer removal from 37% to 51%, while taking uncoated PLA from eight to 20 layers added only six percentage points. Both techniques could matter well beyond water filters as printed parts move into functional, chemistry-dependent applications. For now, the Waterloo stack is a good demonstration that an ordinary print plus the right post-processing can do far more than the bare part.
