A study on the effects of electrochemical oxidation and silane modification applied to fibers in short carbon fiber-reinforced structural adhesives and adhesive joints

Abstract

In this study, electrochemical surface treatment and various silane modifications were applied to fiber structures incorporated into adhesives to enhance the performance of bonded systems. Initially, electrochemical oxidation was performed on the fibers added to the adhesive, increasing the active oxygen groups on their surfaces. Subsequently, silanization was carried out using 3-aminopropyltriethoxysilane (APTES) and glycidoxypropyltrimethoxysilane (GPTMS) as silane agents, improving the surface energy of the fibers. The structural adhesive used in the study was a two-component epoxy adhesive. Composite adhesives were prepared by incorporating carbon fibers treated with electrochemical oxidation and silane modification at weight fractions of 1 %, 2 %, 3 %, and 4 %, and adhesive joints were fabricated using these modified adhesives. According to the results of surface wettability experiments, carbon fibers cleaned with acetone exhibited highly hydrophobic behavior, while fibers subjected to electrochemical oxidation displayed highly hydrophilic behavior. However, subsequent silanization treatments following electrochemical oxidation transformed the surface wettability of the fibers to hydrophilic behavior. Furthermore, the application of electrochemical oxidation to the fibers increased the adhesive's nominal maximum stress value by approximately 126 %, while subsequent silanization treatments following electrochemical oxidation enhanced the nominal maximum stress value by approximately 177 %. These improvements are also supported by the results obtained from shear tests, with the degree of enhancement varying depending on the fiber content added to the adhesive. Changes in the surface functional groups and surface morphologies of the samples were analyzed using X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) imaging.