Investigating the effects of liquid-plasma treatment on tensile strength of coir fibers and interfacial fiber-matrix adhesion of composites

The liquid-plasma treatment based on microwave plasma in the liquid was used to treat coir fiber in this study. The effects of such treatment on tensile properties of coir fiber and its compatibility with the epoxy matrix were investigated. Water and sodium bicarbonate (NaHCO3) solution was used as a medium in this treatment. Tensile properties and interfacial shear strength (IFSS) between coir fiber and epoxy resin were determined with single fiber tensile and pull-out tests respectively. Fourier transform infrared spectroscopy, scanning electron microscope and X-ray diffraction were used to characterize the alteration of treated coir fibers. The results show that tensile strength of coir fibers slightly reduce after liquid-plasma treatment with both water and sodium bicarbonate medium except on 12 wt% sodium bicarbonate solution medium for 5 min exposure time. Meanwhile, the interfacial shear strength of coir fiber-epoxy matrix is obtained improvement after water and sodium bicarbonate medium treatment due to good interfacial adhesion between fiber and matrix which could be influenced by micropores on fiber surfaces leading to interlocking adhesion.