The effect of alkali treatment on mechanical, morphological and thermal properties of date palm fibers (DPFs): Study of the interface of DPF-Polyurethane composite

This paper focuses on investigating the effect of alkali treatments on the bond characteristics of date palm fibers (DPFs) in a polyurethane (PU) matrix, including the bond strength, pullout energy. This kind of fiber treatment is generally used to improve the mechanical behavior of composites. Raw DPFs underwent a surface modification method by alkali treatment with different percentages of NaOH: 0 wt%, 2 wt%, 5 wt% and 10 wt%. All treatments were carried out under mild conditions without heating for 1 h. The Fourier transform infrared spectroscopy (FTIR), tensile properties, surface morphology and thermal gravimetry analysis (TGA) of treated DPFs were investigated. The experimental results showed that the alkali treatment can effectively remove non cellulosic materials and enhance the tensile strength of DPFs. In order to investigate on DPF-PU adhesion, the fiber pullout test was also carried out. It was found that the DPF-PU interfacial properties increased after the alkali treatment, especially fiber pullout energy. Indeed the optimal alkali concentration was reported at 5 wt% in terms of the bond characteristics, and, this is mainly due to the reduction of the amorphous parts of the fibers.