Short-term seawater performance of FDM-printed polylactic acid (PLA): Effects of printing speed on morphological, thermal, surface, and microhardness characteristics

In this study, the short-term behavior of polylactic acid (PLA) specimens produced by fused deposition modelling (FDM) at different printing speeds in a seawater environment was investigated. PLA specimens were produced at printing speeds of 40, 60, 80, and 100 mm/s and immersed for 30 days in natural seawater obtained from the Çanakkale Strait, Türkiye. The morphological, elemental, thermal, surface microhardness, and surface/pore characteristics of the specimens before and after seawater exposure were evaluated using optical microscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDS), melting point analysis, Vickers microhardness testing, and Brunauer-Emmett-Teller (BET) surface area analysis. Vickers microhardness was used as an indentation-based near-surface indicator and was not interpreted as a substitute for tensile, flexural, or impact performance. Optical microscopy and SEM analyses showed that no pronounced cracking, delamination, or macroscopic structural deformation occurred in the specimens after 30 days of seawater exposure. However, particulate deposits and local morphological heterogeneities were observed on the specimen surfaces. The detection of Ca, Na, and Mg elements on the specimen surfaces after seawater exposure indicated the accumulation of seawater-derived inorganic species on the PLA surface. The preservation of the melting temperature at approximately 175.5°C in all specimens, together with similar thermal behavior, indicated that short-term seawater exposure had no pronounced effect on the bulk thermal behavior of PLA. The microhardness results showed an increase in near-surface hardness, particularly in specimens produced at printing speeds of 60 and 80 mm/s. BET analyses revealed printing-speed-dependent changes in surface area and pore characteristics. Overall, the findings indicate that short-term seawater exposure causes changes in the surface properties of PLA rather than pronounced bulk degradation. The results also demonstrate that printing-speed-dependent microstructural differences affect the interaction behavior between PLA and seawater. This study provides experimental data on the effect of FDM printing parameters on the behavior of PLA in marine environments and contributes to the understanding of the environmental performance of biodegradable polymers.