IMPROVING S-2 GLASS/EPOXY INTERFACES BY A VAPOR DEPOSITED AMINO-SILANE

Fiber type, reinforcement architecture, and resin dictate the properties of fiber-reinforced composites. However, often overlooked, the fiber/matrix interphase plays a critical role in composite performance. Critical flaws in the fiber cause breakage when a part is stressed. The ability to effectively redistribute load through the matrix and interphase into the neighboring fibers becomes vital. This reloading efficiency dictates whether the failing interphase finds the critical flaws in the adjacent fibers, causing the process to continue uncontrollably till the component fails. Fiber manufacturers use sizing packages, a proprietary mixture of film formers, coupling agents, lubricants, and solvents. These coatings are applied using a liquid bath approach, leading to poor control over the interphase morphology. This study explores the effectiveness of 3-aminopropyl trimethoxysilane (APS) as an adhesion promotor between S-2 glass fiber and epoxy by applying APS using a novel room-temperature vapor deposition method to create a thin and uniform silane coating directly onto the glass surface. This covalent network will allow for a direct covalent network to form between the fiber surface and the epoxy with less concern for thick silane layers building up and crosslinking. These crosslinked silane networks are detrimental to the interphase, preventing epoxy from effective diffusion into the interphase. Dynamic contact angle analysis showed strong evidence of a thin silane coating on the fiber. In addition, the fiber pullout technique tested interphase properties between S-2 glass and Dow DER353 cured with Amicure PACM. The APS coated fibers showed a 25-36% increase in interfacial shear strength over the unsized and performed similarly to the commercial sizing package. Further optimization of the coating design can potentially lead to further improvements in interphase performance.