Adhesion of Short and Continuous RFL-Treated Aramid Fibers to Sulfur and Peroxide Cured Rubbers

The performance of composites reinforced with short fibers and continuous cords is strongly dependent on the nature and the strength of the fiber-matrix interface. Good interfacial bonding is required to ensure load transfer from matrix to reinforcing fibers. For rubber reinforced composites, Resorcinol Formaldehyde Latex (RFL) is known as a fiber surface coating which is able to provide good adhesion  between rubber and fibers. The performance of this substance can be largely affected by exposure of the coated fibers to air and light. Most data available in literature concern sulfur-cured elastomers only.

     In the present study aramid fibers are investigated, because of their significantly higher modulus and strength, compared to other commercial fibers. Their adhesion after being coated with RFL in compounds based on sulfur-cured NR and peroxide-cured EPDM is investigated. The effect of physical interaction between fibers and rubbers is shown to be minor, and the effect of aging of RFL on its ability to bond with rubbers using peroxide and sulfur curing systems is shown. As a result of aging, ozone is able to decrease the double bonds of the latex part of the RFL, which negatively affects the RFL-rubber adhesion in sulfur-cured systems, while it has almost no effect in peroxide-cured systems. It is also argued that, unlike in sulfur vulcanization in which bonding happens between the latex in the RFL and rubber, peroxide is able to generate bonds between elastomer and the resin structure of the RFL-coating.