Sequential Covalent Grafting of PEI and TEPA Onto Oxidized Carbon Fibers: Surface Regulation and Interfacial Performance

Abstract

Abstract

ABSTRACT A facile two‐step modification combining nitric acid oxidation and sequential PEI–TEPA (polyethylenimine–tetraethylenepentamine) grafting was proposed to eliminate the intrinsic surface inertness of T700 carbon fiber. Acid oxidation strips surface sizing and introduces plentiful oxygen‐containing groups to activate the fiber surface, yet it simultaneously generates extra structural defects, which is confirmed by Raman spectra. Subsequent covalent grafting of PEI–TEPA consumes surface carboxyl groups via amidation and enriches surface amino and amide groups, as verified by XPS results. SEM observation and quantitative AFM characterization demonstrate that acid etching increases fiber surface roughness, while the grafted PEI–TEPA coating constructs a uniform and compact polymer layer and optimizes the surface micro‐morphology. Contact angle measurement indicated oxidized fibers become more hydrophobic, whereas PEI–TEPA grafting greatly improves the intrinsic surface hydrophilicity of carbon fiber itself. Although acid etching causes slight degradation of fiber mechanical performance, the grafted polymer coating repairs oxidation‐induced surface defects and effectively recovers single‐fiber tensile properties. Furthermore, micro‐droplet IFSS tests confirm that the constructed amine‐rich interlayer significantly enhances the fiber–matrix interfacial bonding and load‐transfer efficiency by providing sufficient chemical interaction sites. This mild modification strategy effectively tunes the surface roughness, wettability, surface chemical composition and interfacial performance of carbon fibers and provides a facile and reliable route to fabricate amino‐enriched functionalized carbon fiber substrates for high‐performance composite interfaces.