The tailoring of interfacial adhesion and its effects on material properties for carbon-fiber reinforced polymeric composites

Carbon fiber reinforced polymeric composites have long been of interest owing to their remarkable properties of high strength, toughness, and low weight. Part of their appeal comes from their customizability to fulfil a large number of applications. Controlling the degree of interfacial adhesion between fibers and polymeric matrix is one of the important ways of optimizing composite properties for desired applications. The present study examines a simple technique for modulating adhesion, its measurement using single-fiber fragmentation, and its effects on the tensile, flexural, and impact properties of the corresponding fiber tow composites. Adhesion was modified by coating untreated Hexcel IM7 fibers to various levels with room temperature 'vulcanizing' silicone dissolved in the mixed alkane solvent Isopar (TM) L. The matrix polymer was Epon862 with an Epikure curing agent W. Fiber tows consisted of 12k fibers, and were tensile, 3-point bend and 'charpy' impact tested to evaluate their mechanical properties. Interfacial adhesion was reduced from 101 MPa to near zero, while impact toughness was more than doubled. The tensile modulus decreased only up to 25%, while the flexural modulus decreased by approximately 50%. Ultimate flexural strength and flexural modulus decreased. Energy to failure had no meaningful changes.