Eco-friendly surface modification of thermotropic liquid crystal polyarylate fibers via a polyethyleneimine/pyrogallol system for enhanced interfacial adhesion with rubber

Abstract ue to their outstanding mechanical properties and chemical resistance, thermotropic liquid-crystal polyarylate (TLCP) fibers are ideal for reinforcing rubber-based composites. However, their chemically inert surface results in weak interfacial adhesion with the rubber matrix. While the conventional resorcinol-formaldehyde-latex (RFL) system improves adhesion, it poses carcinogenic risks. This paper therefore proposes an innovative, environmentally friendly ‘activation-bonding’ dual-layer surface treatment strategy to address this issue. First, a surface activation layer is formed using a water-based epoxy resin (WEP) and a blocked isocyanate (BI) to introduce reactive epoxy groups. Secondly, a polyethyleneimine (PEI)-pyrogallol (PGA) interpenetrating network is formed as the bonding functional layer, replacing the RFL system. The results demonstrate that this modification strategy successfully creates an interfacial layer on the fiber surface through a combination of chemical bonding and physical encapsulation. At an optimal curing temperature of 180 °C, the H-pullout force between the modified TLCP fibers and natural rubber increased by 90.4 % (from 14.94 N to 28.45 N ) compared to the force between untreated fibers. Microstructural and energy-dispersive spectroscopy analyses confirmed that the interfacial failure mode shifted from adhesive to cohesive failure, with vulcanization occurring between the rubber matrix and the impregnation layer.