Oil palm fibers were first ground, washed several times with a
cationic detergent, and dried at room temperature. Then, the oil
palm fibers were immersed in a 1.6 mol/L sodium hydroxide aqueous solution (El Mechtali et al. 2015) for 48 h and treated with
an acetic acid solution (5%) to neutralize the remaining hydroxide.
These fibers were finally air-dried for 24 h and used as reinforcement inside the hybrid composites. The alkali treatment was applied to remove lignins, waxes, and oils covering the external surface of the fibers which could limit the adhesion with the polymer
matrix (El Mechtali et al. 2015).