Experimental characterization of the thermoviscoelastic response of PA 6 under UV exposure

In engineering applications, the mechanical performance of polymers can be significantly influenced by environmental factors such as heat, moisture, and ultraviolet (UV) radiation. Although UV exposure is generally associated with material degradation, some studies report non-monotonic changes in mechanical properties during early stages of aging. In this work, moisture-equilibrated polyamide 6 (PA 6) is subjected to controlled short-term and long-term UV exposure and characterized by gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). The combined experimental approach provides complementary information on molecular, thermal, and thermoviscoelastic material changes induced by UV exposure. Short-term UV exposure results in a pronounced increase in storage modulus, while spatially unresolved GPC analysis of material spanning the entire sample thickness reveals only minor changes in number- and weight-average molar mass. DSC likewise indicates only minor changes in crystallinity. With increasing exposure time, spatially unresolved GPC analysis reveals a progressive reduction in molar mass, accompanied by a decrease in stiffness and changes in the thermoviscoelastic response. ... mehrTemperature-frequency sweeps and master curve construction based on extended time–temperature superposition indicate that UV exposure affects the effective relaxation behavior within the investigated temperature-frequency range. The findings provide experimental insight into the evolution of UV-induced aging effects in PA 6 and may support future efforts in modeling long-term thermoviscoelastic material behavior.