Characterization of the thermal, water absorption, and viscoelastic behavior of short date palm fiber reinforced epoxy

Two epoxy resins (flexible and rigid) with new formulations that are more respectful of the environment are used to make five blends of epoxy resins in different proportions reinforced by 30% date palm fibers (DPF). The purpose is to determine how the blend’s composition and the addition of DPF affect the material’s thermal, water absorption, and viscoelastic properties. It was found that water absorption increases with the increase of flexible epoxy content. The incorporation of DPF multiplies the water absorption by about 6. Thermogravimetric analysis (TGA) revealed that the maximum degradation temperature (T_max) increases with increasing flexible epoxy content. The incorporation of DPF causes a slight decrease in T_max. Dynamic mechanical analysis (DMA) showed that raising the amount of flexible epoxy reduces the storage modulus (E’) while expanding the size of the transition zone. Conversely, the incorporation of DPF increases E’ over the studied temperature range. Similarly, increasing the percentage of flexible resin decreases the glass transition temperature (Tg) from 65.15 °C (100% rigid) to 29.75 °C (100% flexible). On the other hand, the incorporation of DPF improves the Tg. Isochronous stress-strain curves revealed that, at room temperature, the R50S50 epoxy (50% flexible + 50% rigid) and the R50S50R composite (R50S50 + 30% DPF) have linear viscoelastic behavior for tensile stress of 0.5 MPa and nonlinear one for higher stresses. The Schapery model was successfully used to model the nonlinear viscoelastic behavior of R50S50 epoxy and R50S50R composite.