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Materials Science in Additive Manufacturing 3D printing of anti-microbial parts

Figure 1. Arrangement of test specimens (tensile bars and disks for anti-microbial testing) in the build chamber. The tensile bars were printed with a
Z-direction orientation. High-speed sintering allowed both shapes and all the parts to be fabricated in a single build. The Z-direction is normal to the plane
of the powder bed surface

Table 1. Process parameters for the manufacturing of DSM micro-extruder (co-rotating conical twin screws,
polyamide 12 disks and bars using high‑speed sintering DSM, Netherlands) at a processing temperature of 200°C
and a speed of 10 revolutions/min for 2 mins. To create the
Parameters Specifications melt for molding the test disks. Mg(OH) was incorporated
Machine voxeljet AG PA12 Type B into PA 12 at a loading of 5 wt.%. 2
Powder weight ratio (used: virgin) 70:30 The DSM micro-extruder system has a DSM mini
Process temperature (°C) 173 injection molder as a separate unit. The micro-extruder
Sintering lamp power (SLP; %) 100 had an attachment (a heated vessel) that allowed the melt
Sintering lamp traverse speed (m/s) 0.15 from the DSM micro-extruder to be transferred to it. The
Greyscale (GS) 3≙18 pL/voxel heated vessel holding the melt was then attached to the
Build box wall temperature (°C) 140 DSM mini injection molder. With this system, there was
Build box floor plate temperature (°C) 175 no need for pelletization of the compounded melt and
Powder recoater temperature (°C) 130 re-melting for IM.
Layer thickness (mm) 0.08 After melt compounding, disks (diameter: 25 mm;
thickness: 1.55 mm; i.e., same dimensions as the HSS
disks) containing the biocidal additive were injection-
After completion of the build job, the test specimens molded using the DSM mini injection-molding unit with a
in the PA 12 powder cake were cooled in the machine 3.5 cm injection mold. The mold temperature was fixed at
3
for 7 h and then taken out. To remove any remaining 60°C. Pure PA 12 powder was also melted at 200°C using
adhering powder, the parts were blasted with glass beads the DSM micro-extruder and injection-molded to form a
at 3 bars in a Normfinish DI 12 injector blasting cabinet control disk for anti-microbial evaluation.
(KALO, Netherlands). The test specimens (disks and bars)
were each de-powdered for about 20 s at a distance of 2.5. Preparation of Mg(OH) suspension for
2
approximately 20 cm. dip-coating of PA 12 disks and bars
2.4. Melt-compounding and injection molding of A concentrated aqueous suspension (7 wt.% Mg(OH) 2
Mg(OH) and PA 12 powder and 93 wt.% of water) was also provided by Aqua Inc.
(USA). This aqueous dispersion of Mg(OH) was diluted
2
2
The Mg(OH) nanocrystals and PA 12 powder were as previously described (Figure 2). The concentration of
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2
physically mixed and melt-compounded using a 15 cc Mg(OH) after dilution was 10000 ppm.
2
Volume 3 Issue 4 (2024) 4 doi: 10.36922/msam.4970