Surfactant-modified carbon fiber–epoxy composites: Interfacial control of mechanical performance

Interfacial load-transfer inefficiency between carbon fibers and epoxy matrices limits the mechanical reliability of carbon fiber–reinforced polymer composites. This study treats Triton X-100 surfactant concentration as a controlled interfacial design variable and evaluates its effect on the mechanical behavior of short carbon fiber–epoxy composites. Fibers were surface-modified at 1, 2, and 3 wt.% Triton X-100 and incorporated into compression-molded epoxy composites at ∼40% fiber volume fraction. Tensile and compressive properties were measured per ASTM D3039 and D695; wettability, surfactant uptake, void fraction, and fracture morphology were characterized by contact angle goniometry, gravimetric analysis, Archimedes densitometry (ASTM D792), and scanning electron microscopy. The 1 wt.% composite exhibited tensile strength of 116.00 MPa (∼40.3% above untreated: 82.67 MPa) and a comparable compressive strength gain, while elastic modulus remained constant at ∼2.0 GPa across all conditions. Gravimetric analysis confirmed monolayer adsorption at 1 wt.% and excess deposition at 2 wt.%, consistent with the observed mechanical optimum. SEM revealed reduced fiber pull-out (64 ± 9 μm to 22 ± 4 μm) and suppressed debonding in the optimally treated composite. Controlled surfactant treatment provides a scalable, non-destructive route to enhance interfacial efficiency and mechanical performance in short carbon fiber–epoxy systems.