PSI - Issue 83

Manuel A.R.V. Esteves et al. / Procedia Structural Integrity 83 (2026) 146–153

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Fig. 1. Nominal geometry and dimensions of Charpy specimens.

For impact characterization, twenty Charpy specimens were produced. The larger sample size for this test was selected to enable a statistically meaningful assessment of the influence of testing temperature on the absorbed impact energy. A detailed overview of the experimental variables and the number of specimens is provided in Table 3. Five specimens were tested for each Charpy configuration.

Table 3. Test plan for fracture characterization.

Test

Extrusion temperature [°C]

Material conditions Virgin PLA and recycled PLA

Testing temperature [°C]

Number of specimens

Charpy

220, 237 and 255

24.1 and -30.9

40

Following fabrication, all specimens were dimensionally inspected using a digital calliper with a resolution of 0.01 mm. These measurements were used in the subsequent calculations of stress and energy absorption to ensure that the evaluated mechanical properties accurately reflected the actual specimen dimensions. 2.3. Specimen fabrication All specimens were manufactured using a FDM 3D printer, namely the Bambu Lab X1-Carbon. This system features a build volume of 256×256×256 mm³ and represents a modern generation of desktop FDM equipment. A key characteristic of this printer is its fully enclosed architecture, which enables improved control of the thermal environment surrounding the printed parts. By promoting more gradual and uniform cooling, this configuration reduces thermal gradients, limits warping, and enhances dimensional accuracy. The printer operates with 1.75 mm diameter filament and was equipped with a standard 0.4 mm nozzle for all tests, although alternative nozzle diameters are available. A textured polyetherimide build plate was used to ensure reliable first-layer adhesion. This platform consists of a thin PEI coating applied to both sides of a stainless-steel sheet, facilitating strong adhesion during printing while allowing easy part removal after cooling. According to the manufacturer, the PEI surface remains stable at temperatures up to 180 °C, a limit supported by previous studies reporting negligible physical aging below approximately 175 °C, even after prolonged thermal exposure. The primary objective of this investigation is to compare virgin and recycled PLA in terms of both mechanical performance and processability in FDM. Particular attention was given to extrusion stability, deposition consistency, and the occurrence of manufacturing defects such as nozzle clogging. Among all printing parameters, extrusion temperature was identified as the most critical variable, due to its direct influence on melt flow behavior, interlayer bonding, and final mechanical properties. For virgin PLA, recommended processing temperatures typically range from 190 to 220 °C. In contrast, recycled PLA generally requires higher extrusion temperatures to compensate for polymer chain scission and the associated reduction in melt viscosity resulting from previous processing cycles. It has been suggested that an increase of approximately 20% relative to the temperature used for virgin PLA is necessary to ensure stable extrusion of recycled material (Wei and Bähr 2024). Based on these considerations, three nozzle temperatures were selected for this study: 220 °C, applied to both virgin and recycled PLA, and 237 °C and 255 °C, applied exclusively to recycled PLA. All remaining printing parameters were kept constant. A detailed summary of these parameters is provided in Table 4.