Fuente: Journal of applied polymer Lugar: RESEARCH ARTICLE A blocked waterborne polyurethane/latex (WPU/L) impregnation system replaces toxic resorcinol and formaldehyde in polyester fiber/rubber composites. Optimized formulation achieves RFL-comparable adhesion (peel force 5.47 N/strand) with < 2% fiber strength loss. Mechanistic studies reveal three synergistic factors: increased surface polarity, covalent urethane linkages, and sulfur-mediated co-vulcanization at the interface.

ABSTRACT
The performance of fiber-reinforced rubber composites is highly dependent on the interfacial adhesion between the fiber and the rubber matrix. Conventional resorcinol-formaldehyde-latex (RFL) dipping systems, although effective, pose significant health and environmental risks due to the toxicity of resorcinol and formaldehyde. In this study, a formaldehyde-free and resorcinol-free blocked waterborne polyurethane/latex (WPU/L) dipping system was developed. Key synthesis parameters, including blocking agent ratio, DMBA content, initial R-value, final R-value, and WPU/L mass ratio, were systematically optimized to improve emulsion stability, thermomechanical properties of the adhesive film, and interfacial bonding performance. Under the optimal conditions (5% DMBA, initial R-value of 2.7, final R-value of 1.2, and WPU/L mass ratio of 17/100), the treated polyester fiber/rubber composites exhibited a peel force of 5.47 N/strand and an H-pullout force of 61 N, substantially outperforming untreated fibers (~1 N/strand) while retaining > 98% of fiber tensile strength. XPS and SEM analyses revealed that the enhanced adhesion originates from increased polarity, hydrogen bonding, and co-vulcanization at the interface. This work presents a candidate reduced-toxicity dipping system to replace conventional RFL and establishes a structure-performance framework for designing sustainable interfaces in polymer composites. Direct comparative validation with RFL under identical conditions remains an important direction for future work.