Plasma etching and plasma polymerization coating of carbon fibers. Part 2. Characterization of plasma polymer coated carbon fibers

Unsized AS-4 carbon fibers were subjected to RF plasma etching and/or plasma polymerization coating in order to enhance their adhesion to vinyl ester resin. Ar, N-2 and O-2 were utilized for plasma etching, and acetylene, butadiene and acrylonitrile were used for plasma polymerization coating. Etching and coating conditions were optimized in terms of plasma power, treatment time, and gas (or monomer) pressure by measuring the interfacial adhesion strength. Interfacial adhesion was evaluated using micro-droplet specimens prepared with vinyl ester resin and plasma etched and/or plasma polymer coated carbon fibers. Sur-face modified fibers were characterized by SEM, XPS, FT-IR, alpha-Step, dynamic contact angle analyzer (DCA) and tensile strength measurements. Interfacial adhesion between plasma etched and/or plasma polymer coated carbon fibers and vinyl ester resin was reported previously (Part 1), and characterization results are discussed is this paper (Part 2). Gas plasma etching resulted in preferential etching of the fiber surface along the draw direction and decreased the tensile strength, while plasma polymer coatings altered neither the surface topography of fibers nor the tensile strength. Water contact angle decreased with plasma etching, as well as with acrylonitrile and acetylene plasma polymer coatings, but did not change with butadiene plasma polymer coating. FT-IR and XPS analyses revealed the presence of functional groups in plasma polymer coatings.