Adhesion of RFL-coated aramid fibres to sulphur- and peroxide-cured elastomers

The performance of fibre-reinforced composites is strongly dependent on the nature and the strength of the fibre–matrix interface. Good interfacial bonding is required to ensure load transfer from matrix to reinforcing fibres. For rubber-reinforced composites, resorcinol formaldehyde latex (RFL) is known as a fibre surface coating which is able to provide good adhesion between rubber and fibres. But the performance of this substance in many cases can be largely affected due to exposure of the coated fibres to air and light. Moreover, most data available in the literature concern sulphur-cured elastomers only. In the present study, aramid fibres are investigated, because of their significantly higher modulus and strength compared to other commercial fibres. The adhesion of these fibres in compounds based on sulphur-cured natural rubber and peroxide-cured ethylene propylene diene rubber is investigated after being coated with RFL which is the most common adhesive coating for various sort of fibres, including aramid. The effect of physical interaction between fibres and rubbers is shown to be minor, and the effect of ageing of RFL on its ability to bond with rubbers using peroxide and sulphur curing systems are shown. As a result of ageing, ozone is able to decrease the double bonds of the latex part of the RFL, which negatively affects the RFL–rubber adhesion in sulphur-cured systems, while it has almost no effect in peroxide-cured systems. It is also discussed that, unlike in sulphur vulcanization in which bonding happens just between the latex in the RFL and rubber, peroxide is able to generate bonds between elastomer and the resin structure of the RFL-coating.