| Summary: | In this work, a comprehensive shrinkage and tensile strength characterization of unsaturated polyester (UPE-8340) and vinyl ester (VE-922) epoxy matrices and composites reinforced with multiwall carbon nanotubes (MWCNTs) was conducted. The aspect ratio of UPE and VE with methyl ethyl ketone peroxide (MEKP) was kept at 1:16.6; however, the weight of the MWCNTs was varied from 0.03 to 0.3 gm for the doping of the reinforced nanocomposites. Using a dumbbell-shaped mold, samples of the epoxy matrix without MWCNTs and with reinforced UPE/MWCNT and VE/MWCNT nanocomposites were made. The samples were then cured in a typical ambient chamber with air and an inner gas (carbon dioxide). The effect of the MWCNTs on UPE- and VE-reinforced composites was studied by observing the curing kinetics, shrinkage, and tensile properties, as well as the surface free energy of each reinforced sample in confined saline water. The CO<sub>2</sub> curing results reveal that the absence of O<sub>2</sub> shows a significantly lower shrinkage rate and higher tensile strength and flexural modulus of UPE- and VE-reinforced nanocomposite samples compared with air-cured reinforced nanocomposites. The construction that was air- and CO<sub>2</sub>-cured produced results in the shape of a dumbbell, and a flawless surface was seen. The results also show that smaller quantities of MWCNTs made the UPET- and VE-reinforced nanocomposites more stable when they were absorbed and adsorbed in concentrated salt water. Perhaps, compared to air-cured nanocomposites, CO<sub>2</sub>-cured UPE and VE nanocomposites were better at reducing shrinkage, having important mechanical properties, absorbing water, and being resistant to seawater.
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