Effect of water absorption on the properties of selective laser-sintered PA12 specimens

The purpose of this study is to characterize the mechanical properties of laser-sintered polyamide specimens subjected to water immersion for up to 28 days to facilitate the implementation and diffusion of this technology and material in components that are exposed to high-humidity or liquid-filled environments, as for biomedical, naval, and maritime sectors. In addition to conventional tensile tests, flat-top cylinder indentation tests were carried out to define a local dependence of the properties along the building direction. Water absorption reaches saturation after 2 days of immersion with a weight variation of around 10.49% and a resulting diffusion coefficient one order of magnitude greater than the value of the base material, due to the porosity of the samples. Mechanical properties deteriorate due to the reduction in crystallinity and degradation of molecular chains. After just 2 h of immersion, the elastic modulus decreases from ~ 1 to ~ 0.8 GPa, the yield stress experiences a drop from ~ 20 MPa down to ~ 14 MPa and the ultimate tensile strength undergoes a decrease of 5 MPa from ~ 30 MPa as built. While no significant variations were observed for the elongation at the break due to the concurrent effect of plasticization and molecular degradation. Finally, the indentation tests highlight a local dependence of the properties along the building direction in favour of the central part of the samples, as it exposes a smaller surface to the surrounding environment during immersion.