UV-induced transformations and mechanical performance of 3D-printed thermoplastic CFRP, GFRP, and AFRP composites

This study evaluates the effects of UV radiation on the residual flexural properties of 3D-printed continuous carbon (CFRP), glass (GFRP), and aramid (AFRP) fibre-reinforced polymer composites. Flexural properties were assessed after accelerated UV irradiation for 720, 1440, and 2160 h, approximately equivalent to 1, 2, and 3 years of cumulative UV dose in Melbourne, thereby isolating UV‐specific degradation from other weathering factors (moisture, thermal cycling, wind or rain). Scanning Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR) were used to characterise microstructural and chemical changes. For CFRP and GFRP composites with Onyx® matrix, UV exposure triggered both photodegradation and cross-linking, with the latter dominating and enhancing mechanical strength. Retention values were highest for GFRP composites (up to 147 %), followed by CFRP composites (up to 142 %). In contrast, AFRP composites initially showed improved strength retention at 1440 h of UV exposure (103 %), but overall strength declined after prolonged exposure (94 % at 2160 h). SEM confirmed surface microcracking and embrittlement, while FTIR revealed oxidation and chemical transformation beyond the surface. These results highlight fibre-specific UV degradation responses and offer insights into the long-term performance of 3D-printed thermoplastic composites for outdoor structural applications.