The performance of polyolefin composite materials reinforced with lignocellulosic fibers in terms of properties and mechanical behavior is strongly influenced by the strength of the interphase between the matrix and the reinforcements. The creation of a strong interface is hampered by the hydrophilicity and hydrophobicity of the reinforcing material and that of the matrix, respectively. Alkali treatment and the addition of compatibilizers have been a common solution to solve the interfacial problem. In this work, untreated short alfa fibers, treated with 3% sodium hydroxide (NaOH), polypropylene (PP), and compatibilizer (MAPP) were extruded and then injection molded to obtain tensile specimens. The alfa fiber length distributions in the composite were obtained by dissolving the matrix of the composite in a Soxhlet apparatus to extract the fiber. The results obtained for the composite at 30% by weight and with a combined treatment (NaOH + MAPP), showed a higher tensile strength compared to untreated composites. In addition, the morphology and the chemical composition of the fiber were analyzed to further discuss the results of micromechanical models. The interfacial shear strength (τ) and orientation factor (η0) of the alfa fibers in the polypropylene matrix were determined during the analysis of the modified Kelly and Tyson model. The results obtained from these models showed that the () of the combined treatment composites was higher compared to the untreated composites.
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