PSI - Issue 56

Dan Ioan Stoia et al. / Procedia Structural Integrity 56 (2024) 90–96 Author name / Structural Integrity Procedia 00 (2019) 000–000

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Table 1. Mechanical properties of the samples. Sample type

Maximum Tensile Strength [MPa] Elongation at break [%]

Raw filament Air extruded

41.18 ±1.86 40.06 ± 4.97 36.35 ± 1.35 33.18 ±10.46 31.88 ± 10.64

54.71 ± 12.44 51.94 ± 32.80 24.88 ± 6.49

Fourteen deposited traces

Two deposited traces One deposited trace

6.05 ± 3.86 2.72 ± 1.60

The thermal reprocessing of the polymer may lead to different degree of crystallinity. This phenomenon was evidenced by the DSC analysis of the raw and extruded filament (figure 7). The two polymers exhibit similar glass transition temperatures and cold crystallization peaks and slightly different melting peaks. The melting area instead are significant different, which lead us to the conclusion that the reprocessed polymer has a lower crystallinity and therefore a higher amorphous structure. The curves in the figure 7 were shifted in order to be more visible. In conclusion, the crystallinity of the raw filament is higher (the area of the melting peek is 12.67 J/g) than the extrude PLA (which has a melting area of 8.646 J/g), the last one having an increased percentage of amorphous structure. The DSC analysis is sustaining from the structural point of view the mechanical properties determined by tensile testing.

Fig. 7. DSC curves for raw and extruded PLA filament

4. Conclusions The paper presents an experimental study on the mechanical behavior of the PLA in tensile testing in different conditions of obtaining the samples: raw filament; air extruded filament, one trace deposited on the platform, two consecutive traces deposited on the platform and fourteen consecutive traces deposited on the platform. The material printed on the build platform has lower mechanical properties compared to the raw filament and respectively to air-printed one, the best results (41.18 ±1.86 MPa tensile strength and 54.71 ± 12.44 % elongation at break) being obtained for raw material (the filament extracted directly from the roll). The higher standard deviation for one and two deposition traces indicates a low process stability when it comes to only one or two printed traces. The very low elongation at break in this case indicate a rapid cooling of this samples.