Comparison between alternative chemical treatments on coir fibers for application in cementitious materials

Abstract

Agricultural production generates several residues, for example, oilseed residues (cotton, soy, sunflower, and palm oil) and fruit residues (coconut, pineapple, and cashew). Research shows several agents for the surface treatment of natural fibers, such as using alkalis in different proportions and exposure times. The chemical treatment removes surface impurities like wax, oils, fats, and insoluble compounds. However, few studies investigate the effect of chemical treatment type on coir fibers' physical-mechanical and microstructural properties. In this context, the present work aims to evaluate the impact of three chemical treatments: sodium hydroxide, oxalic acid with a concentration of 5 (wt. %) (1 and 2 h), and sodium bicarbonate 10 (wt. %) (120 and 168 h) in coir fibers. This study investigated the contents of extractives, lignin, hemicellulose and cellulose contents, mechanical properties, Fourier transform infrared spectroscopy, contact angle test, atomic force microscopy, scanning electron microscopy, X-ray diffraction, and thermogravimetric analysis. Besides, the FTIR test showed the removal partial of the amorphous constituents. The best results obtained by the treatment content of oxalic acid for 1 h promote a removal partial of extractives, lignin, and hemicellulose content. In addition, tensile strength increased by 22.9% compared to the untreated fibers. The increase in fiber roughness due to the chemical treatments promote better interaction with the cement paste and can reinforce cementitious materials.