PLA filaments filled with PTFE/FEP fluoropolymers: effects on surface wettability, roughness, mechanical performance, and dimensional accuracy

Fused filament fabrication (FFF) enables low-cost and flexible production of PLA parts; however, achieving highly water-repellent surfaces without post-processing remains challenging due to the inherent process-induced texture and the sensitivity to formulation and printing conditions. This work evaluates whether incorporating fluoropolymers (PTFE or FEP) as fillers in PLA filaments can enhance repellency while maintaining printability and overall performance. Composite filaments (PTFE 1–40 wt%; FEP 1–50 wt%) were extruded and printed under constant parameters; wettability, roughness, water absorption, geometric stability, and tensile behavior were characterized, and a two-factor ANOVA was applied. On the bottom face, the water contact angle increased from 66.2° (PLA) to > 120° (40 wt% FEP) and 116.5° (40 wt% PTFE), while the sliding angle (50 µL) decreased from 19.7° to 12.9° (40 wt% PTFE) and 13.8° (40 wt% FEP). Roughness decreased (Ra 33 to 6–8 μm; Rz 150 to < 40 μm) and water uptake at 120 h dropped from 7.2% to 1.8% (40 wt% PTFE) and 3.6% (50 wt% FEP). FEP maintained flatness (≤ 0.045 mm), whereas PTFE increased warpage (~ 0.25 mm at 40 wt%). ANOVA confirmed a significant effect of filler content on wettability and strength (p ≤ 0.002) and of fluoropolymer type on dimensional deviation (p = 0.026), with adjusted R² ≈ 80–97%. Overall, PTFE maximizes barrier/hydrophobicity at the expense of dimensional accuracy, whereas FEP better preserves geometric stability while still achieving high hydrophobicity.