Effect of humidity on the degradation of fused deposition modelling fabricated PLA parts

Abstract

Additive manufacturing technologies are becoming increasing popular due to its ability to fabricate complex geometries parts from a wide variety of materials. Fused deposition modelling (FDM) is a popular additive manufacturing method used to process thermoplastic materials due to its low-cost and ease of operation. Polylactic acid (PLA), is a bio-degradable material widely used in numerous applications and can be processed using FDM. However, the durability and reliability of parts fabricated with PLA material reduces over time and when exposed to certain conditions. This paper cover findings related to the degradation of PLA over time, and when exposed to different humidity conditions. The specimens were exposed to two different moisture conditions with relative humidity of 56.5% and 27% and the tensile strength of the specimens were measured every week over a period of 4 weeks. Tensile test specimens were fabricated according to ASTM D638-14 and tensile strength was used to quantify the degradation of the PLA material. The objective of the experiment was to determine degrading strength of PLA with respect to time and moisture. A reduction in tensile strength was observed for specimens stored in both ambient and moisture-controlled environment suggesting the degradation of PLA material over time. However, the degradation in strength of PLA is much more significant for specimens stored in ambient conditions with higher relative humidity. The results can be associated with possible hydrolytic degradation as moisture from surrounding is absorbed by the PLA material over time.