Surface modification of Kevlar fiber by nanoSiO2 deposition in supercritical fluid

In this work, we modified Kevlar fiber first by depositing nano SiO2 on its surface from sol-gel reaction of tetraethylorthosilicate (TEOS) and formic acid using supercritical carbon dioxide (scCO(2)) as the solvent. The results showed that the Kevlar fiber surface can be successfully deposited with nano SiO2 in this manner while its properties were hardly affected by the supercritical carbon dioxide environment. However, special attention needs to be given to an optimal scCO(2) pressure for the purpose of enhancing the interfacial adhesion and shear strength between Kevlar fiber and epoxy resin as too low or too high pressures result in certain morphologies of deposited nano SiO2 particles that give rise to insufficient penetration of the resin into the fiber surface. Plasma treatment was found to provide a significant surface etching effect that is more effective than nano SiO2 deposition alone. Moreover, it has such a synergistic effect with nano SiO2 deposition that when they were employed sequentially, the interface between the Kevlar fiber and the epoxy resin has the strongest adhesion and shear strength, which are 83.6% higher than those in the original composite with no surface treatment.