Performance of additively manufactured polylactic acid (PLA) in prolonged marine environments

Abstract

Additive manufacturing has seen rapid growth in a variety of sectors due to its advantages in cost and lead-time reductions. However, there is still skepticism regarding the ability for additively manufactured materials to withstand extreme conditions. In this report, AM polylactic acid (PLA) was submerged in seawater at several temperatures to deduce long-term effects of marine environments for these materials. An accelerated aging model was developed to predict life of PLA over years with only weeks or days of exposure. Samples were submerged in artificial seawater between one and ten weeks with temperatures ranging from 22 °C to 60 °C. Several mechanical tests were then conducted on the submerged samples, such as quasi-static tensile, nanoindentation, and direct impact Hopkinson pressure bar tests to deduce different mechanical properties after aging. For the seawater samples, diffusion data was collected to measure water absorbed by the specimens. An Arrhenius relationship was then studied, and a model for accelerated aging was developed with resulting acceleration factors. Results indicated clear aging in PLA over the timeframe studied, and it was deduced that the acceleration factors of aging between 22 °C and 40 °C, 22 °C and 50 °C, and 22 °C and 60 °C, were 1.91, 3.56, and 5.57, respectively. Results demonstrated a clear aging in PLA; it can be predicted that PLA will lose 0.5% ductility at around 5166 h (30.75 weeks) and will suffer a 10 MPa drop in yield strength at around 2084 h (12.4 weeks) while submerged in 17 °C seawater.