Effects of humidity on mechanical properties and microstructure of 3D printed PLA filament

Hamezah, Fatima Hanim (2021) Effects of humidity on mechanical properties and microstructure of 3D printed PLA filament. Project Report. Universiti Teknikal Malaysia Melaka, Melaka, Malaysia. (Submitted)

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Abstract

Polylactic acid (PLA) filament is sensitive to humidity due to its hygroscopic properties, resulting in bubbles and poor printing quality of 3D printed parts. Even though it is significant to control the PLA filament's humidity and store it properly after use, many Fused Deposition Modelling (FDM) users ignore this factor. Many studies focus on the effect of process parameters on the 3D printed part; however, the influence of humidity on the printing quality is less explored. Moisture can influence the mechanical properties of 3D printed parts due to the water's existence, which could alter the polymer chain's bonding, resulting in a lower mechanical strength. The objectives of this study are to investigate the influence of humidity on the tensile strength, fracture strength, and the alteration of microstructure caused by moisture. In order to do so, three conditional settings were established; a new PLA roll acts as the reference, used PLA roll stored in the vacuum bag with desiccant, and used PLA roll stored in an open environment, exposed with the humidifier for 24 - 150 hours. These filaments are subsequently used to fabricate specimens that comply with ASTM D638 – Type IV (tensile specimen) and ASTM D790 (flexural specimen) to be tested in the Shimadzu AGS-X Universal Testing Machine (UTM) at the speed of 5mm/s, and 50 mm/s, respectively. The fractured tensile specimen is then sputtercoated and used in the Scanning Electron Microscope (SEM) machine to study its microstructure. The results show that the humidity decreases the tensile and flexural strength while increasing the fracture strain. The presence of moisture causes the polymer to plasticize, increasing its deformability and reducing its rigidity as the moisture alters its molecular structure. The SEM images show that humidity expands the interlayer gap, promoting enhancement in the fracture strain due to increased macromolecules deformation space. Nevertheless, we found that the used PLA filament stored in a vacuum bag with some desiccants shows an equivalent tensile strength with the reference specimen. To conclude, humidity influences the mechanical properties and should be controlled for a good printing quality of PLA parts. As a recommendation, all 3D printing users are advised to store their PLA filament in a vacuum bag with dehumidifying agents to substitute for the drying cabinet to control the humidity in their printing.

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