In cementitious composite the vegetable fibers may suffer various degrees of degradation when exposed to alkaline medium. The alkaline degradation of macromolecular components of fibers mainly by lignin solubilization and cellulose defibrillation, compromising the physical and mechanical properties. The resistance of plant fiber to alkali attack can be improved by chemical surface treatments such as acetylation that can reduce the hygroscopic nature of lignocellulosic introducing hydrophobic functional groups in its chemical structure. Thus, the aim of this study was the application of the acetylation treatment at different levels to improve the durability of the fibers.The acetylation treatment in curauá fiber was applied at different temperatures and reaction times, and its efficiency, considering the reduction of hydrophilicity and maintenance of the physical-mechanical performance of fibers was evaluated by water absorption, mechanical resistance, infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis and diffraction of x-rays. When acetylated curauá fibers absorbed up to 55% less water than untreated fibers. In strength, losses were up 52%. The acetylation treatment introduced hydrophobic chemical groups in the composition and changed crystalline character of fibers.
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