Long-term mechanical performance of 3D printed thermoplastics in seawater environments

Abstract

This study investigates the effects of 3D-printed thermoplastics' long-term exposure to ocean water. The work focuses on seawater diffusivity rates and mechanical performance to discuss material candidates for long-term undersea structures. Several commonly available thermoplastics were printed using Fused Deposition Modeling and then submerged in an ocean water solution for a prolonged period at elevated temperatures. The thermoplastics studied included Nylon, ABS, PLA, PCTG, PETG, and ASA. The different temperatures corresponded with distinct accelerated rates of water mass diffusion. The solution's water level, temperature, and salinity were monitored and maintained during the accelerated weathering process. The total mass of each specimen and its elastic modulus were recorded daily using a precision scale and a Dynamic Mechanical Analyzer machine. The change in mass was used to calculate the activation energy of each material system by defining the degradation to have an Arrhenius behavior and using a new polynomial fit-based technique. The new polynomial fit-based method was robust compared to a one-dimensional system that uses Fick's law of diffusion. Results also showed that the 3D printed structures, regardless of their composition, are susceptible to extremely high diffusivity rates compared to their bulk material behavior. Lastly, mechanical properties decreased for all polymers, and the stiffness of the aged specimens was proportionally affected by the change in mass.