Highly Interfacial Adhesion and Mechanism of Nylon-66/Rubber Composites by Designing Low-Toxic RF-like Dipping Systems

Fiber-reinforced rubber composites (FRRC) are widely used as load-carrying and anti-pressure products. Resorcinol–formaldehyde–latex (RFL) dipping is widely used to improve interfacial adhesion between fiber and rubber in industry. Unfortunately, high volatility and toxicity of RFL do great harm to humans and the environment during the open dipping process. In this work, a phloroglucinol–terephthalaldehyde–latex (PTL) dipping system based on a low-toxic and low-volatile resin was developed to achieve equivalent interfacial adhesion instead of RFL ones. The reaction mechanism, chemical structure, and wettability changes on the Nylon-66 (PA66) fiber surface were characterized. The effect of the phloroglucinol/terephthalaldehyde (P/T) ratio on the dip pick-up, morphology of the fiber surface, and interfacial structure of FRRC was investigated to expound the interfacial adhesion mechanism. At the optimum P/T ratio (1/2.2), a dipping layer with uniform and suitable dip pick-up is achieved on the fiber surface, which ensures the formation of an appropriate graded interfacial layer with enough crosslinking density and modulus, under the synergistic effect of co-vulcanization with rubber, and accordingly strengthens interfacial adhesion. The dipped fiber possesses excellent interfacial adhesion, dynamic fatigue life, and storage stability at the RFL level. This new dipping system is environmentally friendly and easy to scale up without making any change in the process and equipment.