Aramid fiber surface treatments to improve adhesion to epoxy matrices: Thermal and chemical treatments

The objective of this research is to develop a fundamental. understanding of adhesion of the Technora aramid fiber to an epoxy matrix. For aramid fibers in tire rubber applications, an epoxy containing coating is placed on the aramid fiber bundle and given a high temperature treatment prior to incorporation into tire rubber. It appears that a minimum temperature is required for this coating to be effective suggesting that chemical bonding is taking place, The role of chemical interactions between the aramid fiber surface and the epoxy molecule was determined in this study by conducting epoxy treatments at high temperature on the aramid fiber, Technora. Samples were immersed in liquid epoxy DGEBA or-other epoxy functional resin and treated at temperatures up to 240degreesC. Excess non chemisorbed material was removed from the surface by soxhlet extraction. Surface analysis of the fibers after exposure to multifunctional and monofunctional epoxy was completed using Xray Photoelectron Spectroscopy (XPS). Aramid fiber structure or tensile strength is not affected by the elevated temperature epoxy treatment. Adhesion measurements indicate that a significant increase in the fiber-matrix interfacial shear strength of up to similar to60% between the fiber and an amine cured epoxy matrix resulted from these treatments. The effect of the epoxy oligomer chain length was investigated by repeating the high temperature treatment with various difunctional epoxies with longer length as well as with multifunctionality. While the amount of chemisorbed epoxy remained the same in each case, increasing oligomer length did not increase the adhesion but using multifunctional epoxy did increase the adhesion. Chemisorption of epoxy molecules to the aramid fiber surface has been shown to be responsible for this increase.