ABSTRACT The viscoelastic behavior of Luffa cylindrica (LC)–reinforced epoxy composites under dry and moisture‐saturated conditions was investigated using the time–temperature superposition (TTS) principle to enable extrapolated long‐term mechanical prediction. Four systems were examined: neat RENLAM epoxy, LC–RENLAM, LC–6 wt% linseed‐oil‐modified (LSO) RENLAM, and a dual‐matrix (encapsulated) composite comprising an LSO‐modified inner submatrix encapsulated by an unmodified epoxy shell. Dynamic mechanical analysis over broad temperature–frequency ranges (30°C–120°C, 1–100 Hz) provided storage‐modulus spectra for master‐curve construction and shift‐factor analysis, enabling extrapolation over multiple decades of reduced time. Moisture exposure reduced the apparent Arrhenius activation energy governing time–temperature sensitivity in single‐matrix systems to ≈30 kJ mol −1 , consistent with plasticization effects. In contrast, the dual‐matrix architecture preserved coincident dry and wet master curves and exhibited an increase in apparent activation energy from ≈25 to ≈39 kJ mol −1 , indicating enhanced resistance of the viscoelastic time scale to temperature under moist conditions. These results demonstrate that spatial control of matrix architecture can preserve thermorheological simplicity in humid environments, enabling stable viscoelastic response over multiple decades of reduced time within the validated TTS window in natural‐fiber/epoxy composites.
Anastasiou et al. (Tue,) studied this question.