Effect of hornification on the structure, tensile behavior and fiber matrix bond of sisal, jute and curauá fiber cement based composite systems

Several fiber treatments are used to mitigate the high water absorption of vegetable fibers. Wetting and drying cycles are usually performed in the industry of paper and cellulose to reduce the volume variation of these fibers. This procedure stiffens the polymeric structure of the fiber-cells (this process is known as hornification) resulting in a higher dimensional stability. The aim of this study is to determine the effect of the hornification on the chemical and mechanical behavior of natural fibers and how these properties influence the fiber matrix bond. For this purpose, 5 and 10 cycles of wet and drying were applied to curauá, jute and sisal fibers. Fiber pull-out tests were performed in the embedment length of 25 mm. Direct tensile tests were performed in natural and hornified fibers. Furthermore, X-ray diffraction, thermogravimetry analysis, infra red spectroscopy and nuclear magnetic resonance were used to investigate the influence of the hornification on the chemical properties of the studied fibers. Modifications on the fiber morphology were observed with a scanning electron microscope. The results indicate changes on the tensile strength and strain capacity of the studied fibers, showing that morphology, physical aspects and chemical composition play an important role on the efficiency rate of hornification. Significant improvement in the fiber-matrix interface was observed through the pullout tests. It was concluded that 5 cycles promotes a better performance to curauá and sisal fibers. Only the sisal fibers show improvement on its bond mechanisms after 10 cycles.