Page 55 - MSAM-3-3

Materials Science in Additive Manufacturing MEX optimization printing of rHPDE from milk jugs

4.4. Printing on print beds with different surface
roughness
The results of prints on the smooth and roughened
surfaces are presented in Tables 2 and 3, respectively. The
correlations between PT, PBT, and print bed adhesion
were further investigated. Parts that met the criteria for
good adhesion to the print bed and easy removal after
printing were printed at lower temperatures (both PT
and PBT). For example, parts printed at a PT of 210°C
were easily removable (Table 3). Conversely, parts
printed at a PT of 240°C and PBT of 24°C required a more
challenging removal process, which could potentially
damage both the part and the print bed. Parts printed
at a PT of 240°C and PBT of 50°C were impossible to
remove by hand.
In addition, it was observed that printing at lower
temperatures (both PBTs and PTs) resulted in increased
warping, which is not desirable. Figure 4. Predicted adhesion in relation to print temperature and
measured print bed temperature
4.5. Printing with different print beds and PTs
content, resulting in different polymer compositions and
We quantitatively assessed the effects of varying PTs and properties. Therefore, further work may be necessary to
PBTs, determined the shear strength of the print bed investigate the use of other rHDPE sources, such as bottle
adhesion, and evaluated the ease of part removal from the caps, different milk jugs, or a combination of sources,
print bed.
considering that HDPE is a commonly used packaging
The aluminum print bed improves the heat transfer plastic found in numerous products.
from the heater plate to the print surface, ensuring that
the print surface matches the temperature set for the print. Furthermore, it is important to conduct further
Furthermore, using an enclosure during printing mitigates investigation to evaluate and improve the interlayer
the impact of unpredictable external air movements, adhesion of the printed parts, as weak adhesion may lead
maintaining a more stable environment for printing. This is to interlayer delamination (cracking) during printing or
important as such air movements can lead to inconsistent part removal.
cooling due to convection. 17 Warpage may still occur even within the temperature

The adhesion strengths between the printed parts range recommended in Section 4.5. Exploring the use
and the print bed were examined using a shear test by of brims or raft options during printing might further
tension loading (Figure 3). The shear strength values are improve print bed adhesion and should be considered.
summarized in Table 6. From the table, a linear regression Finally, only cursory measurements on surface
model was plotted, resulting in a predictive function finishing and mechanical characteristics of the extruded
(Equation II) that relates print bed adhesion, PBT, and PT.
A surface plot demonstrating this relationship is depicted rHDPE filament and printed samples have been carried
in Figure 4. The recommended PBT range is between 30°C out, as these readings are similar to those reported in
8,19-21
and 45°C and PT between 220°C and 235°C according to previous studies. Thus, no further characterization of
the relationship shown in Figure 4. the materials or substrates was followed up, as these are
already reported in the literature.
Predicted adhesion = 37.7 + (0.18 × PBT) + (0.15 × PT) (II)
In summary, the purpose of this study was to explore
4.6. Limitations and recommendations the recycling methodology of HDPE from used milk jugs
The milk jugs from Meiji Co. used in this project were into printable filaments. While the results are promising,
assumed to be from the same source and to have the same further investigation and streamlining of the protocol are
chemical composition. However, it should be noted that warranted, and the current potential application for this
the results obtained from this study may not apply to other work would be in education to promote the concepts of
sources of rHDPE due to potential variations in additive sustainability and waste reduction.

Volume 3 Issue 3 (2024) 12 doi: 10.36922/msam.4084