Only skin deep? Depth-resolved photo-oxidation of 3D printed polymers PLA, ABS, PETG, HIPS and PC after 322 days of continuous UV exposure

This study investigates the effect of long-term UV radiation exposure on the mechanical and structural properties of selected polymeric materials - PLA, ABS, ABST, PETG, HIPS and PC - fabricated using 3D-print based Fused Filament Fabrication (FFF) method. Existing research in the field of polymers weathering has predominantly examined combined degradation factors (UV irradiation, humidity and thermal cycling) over the timescales rarely exceeding a few months, which prevents attribution of property changes to individual agents. To isolate the contribution of UV radiation specifically, samples were exposed up to 7744 consecutive hours (i.e. 322 days) of UV irradiation in an environmental cell with controlled humidity and temperature. The mechanical properties were characterized using nanoindentation, which allows for spatially resolved measurements of hardness and elastic modulus in the near-surface region, thereby enabling the detection of degradation gradients on the order of tens of micrometers. The lack of methodological consistency in the current literature hinders the cross-material comparison; this study addresses the gap by applying nanoindentation uniformly across wide range of selected materials prepared and tested under identical conditions, while studying these properties after a very long exposure to UV radiation.