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Cycles of wetting and drying can change the microstructure of vegetable fibers through a mechanism known as hornification, which modifies the polymeric structure of the fiber-cells resulting in a higher dimensional stability. In the present work the influence of hornification on the sisal fiber-matrix bond adhesion as well as in the sisal fiber dimensional stability and mechanical behaviour under direct tension was evaluated. Furthermore, cementitious composites reinforced with randomly dispersed hornified sisal fibers were developed and characterized under bending loads. The results show that the tensile strength and strain at failure of the hornified sisal fibers were increased by about 5% and 39%, respectively, whereas the modulus of elasticity was reduced by 9%. The fibers also presented higher dimensional stability with the hornification process. The fiber-matrix bonding was improved and the pull-out resistance of the fibers submitted to ten cycles of wetting and drying was increased by about 40% to 50%. The higher fiber-matrix bond strength contributed to an increase in the ductility and post-cracking behaviour of the composite. The fracture process was characterized by the formation of multiple cracks with the hornified sisal fibers presenting a higher ability to bridge and arrest the cracks.

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The objective of this work was to investigate the effects of mercerization on chemical, morphological and thermal properties of Amazon Piassava Fibers. The effect of this treatment was studied using XRF, SEM, XRD and TGA. The fibers have been treated in 5% and 10% NaOH for 60 min. The XRF results for treated and untreated fibers showed that there is a decrease in the amount of SiO 2 by increasing the NaOH concentration. It has been possible to observe through SEM in untreated fiber that the surface presents a well arranged pattern of silicon rich star-like protrusions. For the two concentrations, SEM allowed to notice that the removal of deleterious surface impurities and fiber roughness was enhanced. The removal of organic material after treatment can be observed in the TGA analysis. XRD analysis indicate an increase in the crystallinity index, 0.19 to 0.31 after the treatment for 10% concentration solutions.