چكيده به لاتين
Epoxy resin is one of the most important and widely used thermoset polymers in the engineering industry. This polymer deforms under loading conditions even at room temperature. Besides, epoxy resins are often exposed to a humid environment that has destructive effects on their properties. This study aimed to increase the mechanical properties of epoxy resin and reduce the moisture penetration and its destructive effects by functionalized multi-walled carbon nanotubes (FMWCNT). In actual service conditions, it is less probable that polymers are exposed to a constant environmental condition during the whole life, while usually varying environmental conditions are applied. Therefore, in this research, the mechanical properties in cyclic environmental conditions are also investigated. Neat epoxy and FMWCNT nanocomposites with the weight percentages of 0.1, 0.3, and 0.5 are fabricated and subjected to tensile and creep tests. Also, the residual strength and stiffness of the specimens are investigated after creep loading. The fracture surfaces of the specimens, the dispersion, and the reinforcement mechanisms of FMWCNT are investigated by scanning electron microscopy. The cyclic hygrothermal aging used in this study comprised three stages of moisture absorption, desorption, and reabsorption under a temperature of 50oC. The nanocomposite with 0.3 wt% of FMWCNT retained 9.37% and 9.52% less moisture in absorption and reabsorption than pure epoxy, respectively. Moisture diffusion coefficients increased after each step compared to the previous step and the nanocomposite sample had a lower diffusion coefficient than pure epoxy in the all steps. The highest improvement in elastic strain, creep strain and steady-state rate of the creep test was observed by nanocomposite (0.3 wt%) with 31.48%, 69.1%, and 74.07% improvement, respectively. Nanocomposite specimens had a strength improvement of 35.89%, 22.56%, 41.66%, and 32.98% and also had a residual strength improvement of 41.27%, 30.01%, 44.28%, and 39.18% compared to pure epoxy in the before aging, absorption, desorption and reabsorption steps, respectively.
