Investigation of moisture absorption and long-term properties of carbon nanotube-reinforced vinyl-ester composites

Vinyl-ester resin (VE) is a polymer matrix frequently used in several civil applications, but its long-term properties in humid and harsh environments can be a concern. Carbon nanotubes (CNTs) have remarkable mechanical, physical, and thermal properties. Adding them to the resin is a promising solution and makes it possible to manufacture cost-effective products with enhanced engineering properties. Our study investigated the chemical functionalization of multi-wall carbon nanotubes (MWCNTs) through acid oxidation to evaluate the durability-related properties of vinyl-ester-based nanocomposites. Samples containing 0.1 wt% of as-received CNTs and functionalized CNTs were characterized by scanning electron microscopy (SEM), elemental analysis, and X-ray photoelectron spectroscopy (XPS). A small amount of two dispersing agents (BYK 104S and BYK 9076) was added to the mixtures to produce high particle stability in the nanocomposites. Barrier properties and moisture diffusivity were determined by immersing samples in a water bath at 50°C. Aging was conducted by fully immersing samples in NaOH solution at 50°C. Matrix degradation was assessed with tensile tests, dynamic mechanical analysis (DMA), and differential scanning calorimetry (DSC) before and after conditioning. The results indicate that the addition of oxidized CNTs significantly improved the mechanical, physical, and durability properties of the composites. Additionally, unlike nanoclay-based nanocomposites, oxidized CNTs do not increase water absorption at saturation.