Abstrakt

Fiber-reinforced polymers are essential in modern engineering for their strength and stiffness, yet their inherent brittleness often leads to failure through delamination. To address this, thermoplastic hot-melt adhesives (HMAs) are increasingly utilized as toughening interleaves; however, achieving optimal performance requires a fundamental understanding of how these molten polymers spread across fabrics. Six carbon fabrics with different architectures, weights, and manufacturers were characterized by morphology, sizing, roughness, and chemical composition, and studied alongside six commercial HMAs with varying melting temperatures and viscosities. Spreading behavior was evaluated by measuring the contact angle of molten adhesive droplets on the fabric surface using a high-temperature contact angle measurement system. The results showed generally good contact angle behavior of carbon fabrics by the thermoplastic adhesives, with most contact angles below 90°, indicating favorable spreading of the molten polymers on the fiber surfaces. However, fabrics differed noticeably: Satin showed the highest contact angles, while several twill fabrics showed improved spreading. It was determined that surface chemistry is the decisive factor in the spreading process, far outweighing physical parameters such as surface roughness or fabric areal weight. Specifically, the presence of nitrogen- and oxygen-containing functional groups on the fiber surface significantly enhances interfacial affinity through hydrogen bonding and dipole–dipole interactions with the polar amide and ester groups of the adhesives. Fabrics lacking these specific chemical species showed limited spreading, as their interaction was dominated by weaker dispersive forces. While adhesive viscosity also influences spreading dynamics, chemical compatibility remains the primary requirement for effective impregnation.