Water Durability of 3D-Printed PEEK and PEEK Carbon Fiber Composites

This study investigates the water absorption behavior of 3D-printed amorphous PEEK and short carbon fiber-reinforced PEEK (PEEK-CF) produced via fused deposition modeling. Water uptake was measured in distilled and seawater over extended exposure (~1125 h). PEEK-CF samples in seawater exhibited the highest absorption by mass (~6% increase), while PEEK and PEEK-CF in distilled water reached ~4% increase by mass, and PEEK in seawater reached ~4% increase by mass. The elevated water uptake observed in PEEK-CF compared with unreinforced PEEK is attributed to osmotic pressure and voids at the fiber-matrix interface. Diffusion behavior of the amorphous PEEK and PEEK-CF deviated from Fickian kinetics and followed the Vas-power model (modified Lucas-Washburn equation) more closely. Moisture exposure had a notable impact on mechanical properties: PEEK-CF showed up to a 32% reduction in tensile modulus, whereas the mechanical properties of unreinforced amorphous PEEK remained largely unaffected by water absorption. A modified rule of mixtures incorporating knockdown factors for water uptake, fiber length, and orientation accurately predicted the observed mechanical degradation. These findings underscore the need to consider moisture effects when designing with 3D-printed PEEK-CF composites.