Coir fibers have gained the interest of composite material reinforcement mainly because of their excellent mechanical properties in combination with their lightweight structure. Pure carbon nanotubes (CNTs) have hydrophobic surface and limited dispersion stability. CNTs may lack chemical affinities to these matrices and thus dispersion of CNTs into matrices poses the biggest practical challenge. The addition of a surfactant (sodium deoxycholate, NaDC) to a CNT improves its solubility in water, leading to anionic and cationic functional groups on the nanotubes surface. Epoxy resin acts as excellent component in binding CNTs to the coir fiber. After being treated with sulfuric acid and nitric acid in the ratio (3:1 v/v), multi-walled carbon nanotubes (MWCNTs) were functionalized with sodium deoxycholic acid to obtain functionalized-CNTs (f-CNTs). NaDC/CNT composites with different CNT loadings (i.e., 0.05, 0.1, 0.15, and 0.2 wt.%) are produced by initially dispersing the f-CNTs and sonicated. The main aim of this work was to investigate the impact of functionalizing MWCNTs as a coating material on coir fibers along the length of the beam of size 20 x 20 x 80 mm beam. The chemical interaction between the f-CNTs and coir fibers is established by Fourier transform infrared (FTIR) spectroscopy analysis. Scanning electron microscope (SEM) microstructural investigation demonstrates an improvement in the mechanical and fracture toughness of epoxy composites with 0.1 wt.%, owing to the proper MWCNT dispersion (with surfactant NaDC). Energy dispersive X-ray spectroscopy (EDX) studies were carried out to validate the elemental composition of the sample. Consequently, it can be concluded that the CNT-coating proved effective in performing as a molecular coupling agent to make the composite structure compatible. Microscopic studies demonstrated coating of epoxy/f-CNTs and epoxy/non-functionalized-CNTs (n-CNTs) onto the fibers increased the contact through interlocking between the coir fiber, CNTs, and cement matrix.

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