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The interaction properties between natural fiber and matrix play an important role in the mechanical performance of composite materials. The adhesion properties and the mechanical interaction between an Ichu fiber (Stipa obtusa) treated with sodium hydroxide and a cementitious matrix were studied by conducting experimental, numerical, and analytical pull-out tests. Through the experimental tests, the force-displacement curve for a fiber length embedded 5 mm deep in the cementitious matrix, maximum force, cohesive parameters, and the type of interface failure were determined. The results were used to calibrate the numerical and analytical models for different lengths of fiber (3, 5, 7, 9, and 11 mm) embedded in the cementitious matrix. The numerical model was implemented in the finite element software Abaqus CAE, and the analytical formulation considered the fiber embedded in a half-space continuous medium. From the experimental test, the force-displacement curve, interfacial shear strength of 0.124 MPa, and the softening type slip were obtained, despite obtaining the hardeningtype slip in certain tests. The numerical and analytical results of the load-displacement curve closely approximate the experimental results. This study provides a numerical and analytical model to simulate the alkali-treated Ichu fiber-cementitous matrix interface. [ABSTRACT FROM AUTHOR]

Since natural fibers is a combination of different materials, this are classified as a composite material, where the cellulose microfibers are the reinforcement and the lignin and the hemicellulose are the matrix, which hold the microfibers. Raw fibers, generally present a low density and with this, low cellulose content; however, after the alkali treatment, cellulose proportion increase and the other constituents were reduced as expected, except the ashes. Since the true density of the cellulose, hemicellulose, lignin, extractives and ashes are different; true density measurement can be an alternative to determine the composition of the fibers (cellulose, lignin and extractives), as long as, fibers belong to the same family (species). Since the density of cellulose is higher than the other constituents, alkali treated fiber will have a higher density than raw fibers. [Extracted from the article]

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Natural fibers are a renewable resource that has become an economic alternative to replace synthetic fibers as reinforcement in composite materials. In this study, the aim was to characterize physical and thermal properties of the Andean Stipa obtusa and Jarava ichu leaves (grasses known as ichu) before and after the alkaline treatment. Energy dispersive spectrum identified external phytoliths on the surface of nontreated raw leaves. With the alkaline treatment, improvement on the thermal stability and increment in the crystalline index and size was observed. Additionally, raw leaves present a hydrophobic behavior; however, with the treatment this hydrophobicity was lost for Stipa obtusasignificantly but not for the Jaravaichu. Furthermore, low surface energy was observed for the nontreated raw leaves and increasing consistently for the treated fibers. According with these results, these grasses are quite interesting materials from which fibers can be extracted for engineering applications such as composite materials. [ABSTRACT FROM AUTHOR]