Application scientists are continuously seeking novel, outside the box solutions for water treatment applications. This investigation embraces void spaces inherent to additive manufacturing (AM) while other researchers seek to reduce voids toward the goal of fully dense parts. Here, we investigate novel methods enabled by Material Extrusion (MatEx) 3D printing (3DP) of polymer-zeolite composites to both isolate and enhance ammonia adsorption kinetics through print parameter selection. We compounded natural zeolite into polylactic acid (PLA) using a twin screw extruder to immobilize the zeolite; this enables on-demand customization by 3DP high surface area, deployable, and retrievable structures inspired by natural stratified monoliths. Results demonstrated that incorporating different zeolite loadings (8-32% w/w) in printed, submersible structures improved ammonia removal, with 32% zeolite structures reducing ammonia below toxic levels. To determine the most important print parameters for increasing the porosity of both neat PLA and the PLA-zeolite composite, a Taguchi design of experiments using a L8 orthogonal array with 5 factors (extrusion temperature, nozzle size, layer height, deposition speed, print direction) and 2 levels was executed. Generally, layer height, nozzle size and temperature were significant factors for increasing porosity. Lower temperature resulted in higher viscosity, greater flow instability across the nozzle and greater porosity. Faster deposition speed significantly increased porosity of the PLA-zeolite composite only (not neat PLA) due to turbulent hydrodynamic flow; faster speed was not important for neat PLA due to lower viscosity and less flow instability at higher shear rates. For the PLA-zeolite composite, printing faster at lower temperatures through larger nozzles resulted in lower density and greater porosity, leading to faster water absorption and greater ammonia adsorption kinetics. This investigation provides an avenue for further research into novel environmental applications of AM by leveraging void spaces inherent to 3D printing that is an often studied shortcoming of the technology for structural applications. This research finding and novel application of AM is likely applicable to adsorption of other chemical classes by integration of different adsorbent powders into the printable polymer.

Tuning material extrusion 3D print parameters to increase porosity to enhance adsorption

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