Effect of electrochemical treatment on pull-out properties of 73/27 HBA/HNA copolyester fibers in thermosetting matrix

The surface of high-strength 73/27 HBA/HNA fibers was electrochemically modified in aqueous sodium hydroxide solution (10 wt %) with the change of the applied current to improve the interfacial shear strength (IFSS) of the fiber in the thermosetting matrix. A sodium component was identified on the surface of the treated fibers by scanning electron microscopy (SEM). The detection of sodium is best interpreted as the existence of a negative charged functional group ( - COO^-Na⁺) on the surface of the treated fibers. A pull-out test was used to measure the IFSS of the HBA/HNA fibers and epoxy/amine cure system. According to the calculating value from Greszczuk's geometrical model, the IFSS increased with the applied current in the range of 50-450 mA. However, no further increase in the IFSS was observed for strong treatment (1500 mA). There was an optimum by applied current to obtain maximum IFSS. The electrochemical treatment of the 73/27 HBA/HNA copolyester fibers was effective in altering their surface chemistry and improving the interfacial adhesion at the moderate treating conditions.