Molecular grafting of nanoparticles onto sisal fibers - adhesion to cementitious matrices and novel functionalities

•Cement materials have good compression resistance, but poor tensile strength.•Vegetable fibers can be used as reinforcement to improve tensile resistance.•Vegetable fibers have not good adhesion on cement due to swelling / drying cycles.•Chemical surface treatment can improve adhesion of vegetables fibers on cement.•MnO2 grafted nanoparticles have improve adhesion of sisal fibers on the cement. Cement materials have good compression strength, but poor tensile resistence. Aiming to improve this property, natural fibers can be applied as reinforcement. However, natural fibers have low adhesion with cement, and surface treatments are needed. In this work, sisal fibers were submitted to a cationization process followed by the grafting of two kinds of nanoparticles, Fe2O3 and MnO2. It is a usual treatment to dye fibers to the fabrics. The fibers microstructural characteristics were evaluated, before and after treatment, by using FTIR, XRD, TGA, DSC, SEM, water absorption, and tensile strength tests. The effect of the nanoparticles on the sisal fiber-cement matrix adhesion was evaluated by single fiber pull-out tests. The results show the cationization process removes part of lignin, increasing the fiber crystallinity, while the grafting of nanoparticles reduces the fiber crystalline degree, which indicates that nanoparticles grafting in the lignin spaces. The nanoparticles grafting acts as a catalyst of cellulose formation during the thermal degradation changing the initial fiber degradation profile. All treatments have caused a reduction in the absorbed water amount, become the fibers more stable dimensionally. They have improved the fiber adhesion on the cementitious matrix, being the sisal fiber grafting with MnO2 the best result. [Display omitted]