Improvement of Tensile and Bending Properties by Hot Alkali Surface Treatment for Structural Flax Composites

Recently, economic and ecological pressures have prompted the composites community to intensively pursue environmentally friendly materials. Their applications are usually limited to non-structural parts. Since the fiber reinforced composites have a weak bond at the interface between the matrix and fiber, treating the natural fiber by alkali treatment can increase the bonding strength. At present, there have been many studies on the alkali treatment of flax fiber composites. However, there are not many studies on the alkali treatment of flax fiber at different temperatures, so the main purpose of this research is to explore the effect of low concentration alkali treatment at different temperatures on the mechanical properties of flax fiber composites. The results showed that the flexural strength increased by 10–15%, but the tensile strength decreased when the alkali treatment started from room temperature to 120°C. Finally, it is noticed that in the 160°C NaOH solution, the bending strength increased 28.8% and tensile strength increased 8.6%.