Effects Of Ammonia Plasma Modification On Surface Properties Of Aramid Fibers And Interface Properties Of Aramid/Epoxy Composites

Aramid fibers reinforced composites have excellent heat-resistance and mechanical properties,which have been widely used in many important fields such as aerospace,national defense and military industry.However,surface of aramid fiber is smooth and chemically inert due to the high orientation and crystallization of their molecular chains,which led to poor interfacial adhesion of aramid fibers reinforced composite.Therefore,surface modification of aramid fiber is necessary,in order to enhance the interfacial adhesion of fibers and matrix and improve the whole performance of their composites.Aramid fibers were surface modified by ammonia plasma treatment in this paper and Interfacial adhesion of the aramid fibers reinforced epoxy composite was studied.The effects of ammonia plasma treatment time,plasma power on surface chemical composition,surface morphologies,surface roughness and surface energy of aramid fibers were investigated by X-ray photoelectron spectroscopy(XPS),scanning electron microscopy(SEM),atomic force microscopy(AFM)and dynamic contact angle analysis(DCA),respectively.Meanwhile,interfacial shear strength(IFSS)of the aramid fibers reinforced epoxy composites were studied by micro-debonding test.Ammonia plasma treatment affected significantly the surface properties of aramid fiber.The results indicated the ammonia plasma treatment introduced some nitrogenous polar groups to aramid fiber surfaced,enhanced surface roughness and changed surface morphology of aramid fibers by plasma treatment etching.Both the chemical and physical changes result in the noticeable enhancement of fiber wettability with surface free energy increasing.However,plasma treatment condition should be suitable during surface modification of aramid fibers by Ammonia plasma.Excessive plasma treatment time and high plasma power would decrease the incorporated polar groups and damage the fiber surface,impairing the bulk properties of aramid fiber.The effects of ammonia plasma treatment time and power on interfacial adhesion of aramid fiber/epoxy composite were studied by interface shear strength(IFSS)test.The results showed that extending treatment time and increasing discharge power(without damage fiber strength)could both enhance interfacial adhesion of aramid fiber/epoxy composites.Meanwhile,optimal treatment condition was obtained:plasma power was 100 W,treatment time was 15 min and discharge pressure was 30 Pa.