Structure–property relationships of FFF-printed PETG under UV radiation and water uptake

This study investigates the effects of accelerated aqueous and ultraviolet (UV) aging on the structural, thermal, and mechanical behavior of polyethylene terephthalate glycol (PETG) parts produced by fused filament fabrication (FFF). Printed PETG samples were exposed to distilled and saline water at 70 °C for ten weeks and to UV radiation for up to 1000 h. Water immersion resulted in low water uptake (below 1%), confirming the low hygroscopicity of PETG. Dynamic mechanical analysis revealed a reduction in storage modulus and a slight decrease in glass transition temperature, consistent with reversible water-induced plasticization. Tensile properties showed a modest increase, attributed to partial stress relaxation and interlayer cohesion enhanced by prolonged exposure near the glass transition temperature. Under UV radiation, PETG maintained an amorphous structure and exhibited only minor molecular-level changes, as indicated by subtle modifications in carbonyl and C–H vibrational bands. Thermal properties remained stable, with minimal variation in glass transition temperature. Mechanical performance also improved slightly at intermediate exposure times, likely due to thermally assisted rearrangement of printed layers. Overall, the results demonstrate that PETG retains its structural integrity under both moisture and UV exposure, supporting its suitability for outdoor and marine applications when printed under controlled processing conditions.