Effects of nano SiO₂-NaOH-silane coupling agent surface treatment on behavior of ramie fiber/vinyl ester resin composite

In order to improve the mechanical performance and water resistance of ramie fiber/vinyl ester resin composite, a joint surface treatment method of nano SiO₂-NaOH-silane coupling agent KH570 was proposed, and the chemical structure, surface morphology, crystallinity of the ramie fiber after surface treatment and the mechanical properties and water absorption behavior of the surface treatmented ramie fiber/vinyl ester resin composite were investigated. The results show that the fibroglia on the ramie fiber surfaces is dissolved by alkali liquid which loosens the fibers and improves the fiber/resin interface binding. The crystalline order index of the ramie fiber increases first and then decreases as the alkali concentration increases. The reaction between ramie and silane coupling agent increases fiber water contact angle and hydrophobicity, and the interface binding is furtherly improved. With the combined treatment of nano SiO₂-NaOH-silane coupling agent KH570, the crystalline order index of the ramie fiber decreases while the static water contact angle increases, resulting in enhancement of the mechanical properties of the ramie fiber/vinyl ester resin composite. The water absorption of the ramie fiber/vinyl ester resin composite also decreases with the incorporation of nano SiO₂.