The use of natural fibers as an additive in polymeric matrices has attracted interest of the automotive industries, for its low cost, mechanical properties, biodegradability and lightness. However, the hydrophilic nature of the fiber makes polymer compatibility difficult. Fiber surface treatments can be used to enhance the fiber/matrix interface. In the present work, polypropylene (PP) composites reinforced with fibers from macadamia nutshell were obtained and characterized. Macadamia nutshell fibers were treated by an alkaline treatment with sodium hydroxide (NaOH 4%) to improve adhesion between fibers and matrix. Fibers were characterized by techniques of Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD). The PP was mixed with the macadamia fibers (treated and untreated), in proportions of 5 and 10% (wt/wt) using a thermokinetic mixer. Furthermore tensile, flexural and impact specimens (Pure PP and composites) were prepared by an injection molding process and tested for evaluation of mechanical properties. The results showed that the insertion of treated fibers in the PP matrix increased the stiffness of the composites. However, the composites reinforced with untreated fibers presented higher impact energy absorption when compared to composites reinforced with treated fibers.

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