Autoclave Treatment of Sisal Fiber and Its Effect on Fiber Properties and on the Pull-out Behavior from Cementitious Matrix

Natural fibers as reinforcement of cementitious matrices have become a material with greater toughness, strength, and sustainability for the construction industry. However, their use can generate some inconveniences due to the high-water absorption of the natural fiber, which affects the production and durability of composites. In this work, the autoclave treatment of sisal fibers was carried out in order to determine time and pressure values that result in a lower water absorption of the fibers. The fibers were exposed to 1.0 or 1.5 atm of vapor pressure for 30, 60 and 90 min and their structures were evaluated by X-ray diffraction, differential scanning calorimetry and scanning electron microscope. The effect of treatment on fiber dimensional variation, fiber mechanical properties, and fiber-matrix bond was investigated. Composites reinforced with treated fibers were produced and subjected to bending tests. The results indicate that the autoclave treatment with 30 min and 1.5 atm reduced the water absorption from 134% to 90% and the dimensional variation from 63% to 18%. However, structural modification of the fibers reduced the fiber’s tensile strength and bond strength. Composites reinforced with treated fibers showed lower flexural strength and toughness than those reinforced with natural fibers.