br Acknowledgement br Introduction In

Acknowledgement
Introduction In the past few decades, research and engineering interest has been focused toward lignocellulosic fibers such as flax, hemp, sisal and date palm due to their several economical, technical and environmental advantages (Mwaikambo and Ansell, 2002; Bernard et al., 2011). They are an interesting, environmentally friendly alternative to the use of glass fibers as reinforcement in engineering composites (Barreto et al., 2010; Al-Oqla et al., 2014). Indeed, lignocellulosic fibers are renewable and nonabrasive. Moreover, they exhibit excellent mechanical properties. The use of lignocellulosic fibers in the polymer materials tends to grow due to the fact that natural fibers are less costly and have low specific weight and comparable strength and stiffness with glass fiber (Mwaikambo and Ansell, 2002; Qatu, 2011; Al-Oqla and Sapuan, 2014). The properties of composites reinforced lignocellulosic fibers are obviously related to individual properties of their components, but also to the fiber-matrix interface (Riccieri et al., 1999; Barreto et al., 2010). In general, mechanical failures of these composites are mostly due to fiber pullout, fiber debonding, and fiber breakage. Indeed, the role of the matrix in a fiber reinforced composite is to transfer the load to the stiff fibers through shear stresses at the interface. This process requires a good bond between the polymeric matrix and the fibers. Poor adhesion at the interface means that the full capabilities of the composite cannot be exploited and leaves it vulnerable to environmental attacks that may weaken it, thus reducing its life span. Insufficient adhesion between hydrophobic polymers and tolterodine tartrate fibers result in poor mechanical properties of the natural fiber reinforced polymer composites. Lately many studies (Valadez-Gonzalez et al., 1999; Ray et al., 2002; Herrera-Franco and Valadez-Gonzalez, 2005; Wong et al., 2010) have reported about chemical modifications of lignocellulosic fibers that improve their interaction with polymeric matrices. One of the most studied chemical treatments is named “Alkalization” which consists on treating lignocellulosic fibers in an alkaline solution in order to remove lignin, pectin, waxy substances, and natural oils covering the external surface of the fiber cell wall (Mwaikambo and Ansell, 2002). Gassan and Bledzki (1999) improved the tensile, flexural strength and stiffness of jute-epoxy composites by using an NaOH treatment process with different alkali concentrations. Alawar et al. (2009) found that alkali treatment improved the tensile and thermal degradation proprieties of date palm fibers. Besides, Mishra et al. studied the effect of soda concentration on tensile strength of the sisal-glass hybrid polyester composites, sisal fibers were treated with 5 and 10 wt% NaOH solutions and found that treated fibers improved the tensile strength of the composites compared with the untreated one. However, 5 wt% NaOH was found to promote better mechanical properties than 10 wt% NaOH (Mishra et al., 2003). Wong et al. (2010) reported that alkali treatment increases the strain at break and ductility of treated bamboo-polyester composites compared to untreated ones. They also noticed that the interfacial shear stress (IFSS) increases with the increase of alkali concentration. However, as the concentration of NaOH increases, the percentage of improvement decreases. Therefore, the aim of this study is to evaluate the interfacial adhesion properties between untreated date palm fiber and alkali treated date palm fiber impregnated in a thermoplastic matrix (polyurethane).
Materials and methods
Results and discussion
Conclusion In this research, alkali treatment was performed in order to improve the interfacial properties of date palm fiber and polyurethane. The following points were concluded:
Acknowledgment The authors are grateful for the financial support of the IRESEN institute (Institut de Recherche en Energies Solaire et Energies Nouvelles) (Inno PV-2013) located in Rabat, Morocco.