Evaluation of carbon fiber surface treated by chemical and cold plasma processes

Abstract

Sized PAN-based carbon fibers were treated with hydrochloric and nitric acids, as well as argon and oxygen cold plasmas, and the changes on their surfaces evaluated. The physicochemical properties and morphological changes were investigated by atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), tensile strength tests and Raman spectroscopy. The nitric acid treatment was found to cause the most significant chemical changes on the carbon fiber surface, introducing the largest number of chemical groups and augmenting the roughness. The oxygen plasma treatments caused ablation of the carbon fiber surface, removing carbon atoms such as CO and CO 2 molecules. In addition, the argon plasma treatment eliminated defects on the fiber surface, reducing the size of critical flaws and thus increasing the fiber's tensile strength.

Processing of Carbon Fiber/PEI Composites Based on Aqueous Polymeric Suspension of Polyimide

“…The exposition time was chosen based on studies of Nohara et al (Burakowski, 2001;Nohara et al, 2005) who concluded that the fibers treated superficially with nitric acid shown an increase roughness (measured by Atomic force microscopy and SEM) and a small decrease in tensile strength of single filaments of the carbon fiber (2143  471MPa to 1924  658MPa) -ASTM D-3379, due to removal of surface layers weakly attached to the fiber surface and the reduction of critical failures, that act as stress concentration. Analysis by XPS (X-ray photoelectron spectroscopy) it was also used and found the introduction of polar groups such as C-OH, C=O and COOH at the fiber surface treated with nitric acid (Burakowski, 2001;Nohara, et al, 2005).…”

“…For applications that require high performance, the most commonly used thermoplastic are PEI (polyether imide), PPS (polyphenylene sulfide) and PEEK (polyether ether ketone) (Kong, 1996;Nohara, 2005;Nohara et al, 2005). Thermoplastic can be classified by their molecular structure as either amorphous or semicrystalline polymer.…”

“…These functionalities www.intechopen.com can be obtained by coating the reinforcement or treating its surface with an interfacial bonding agent or coupling agent (Gao, Kim, 2001;Nohara et al, 2005).…”

“…The interfacial bond between the carbon filaments and the resin matrix can be enhanced by enlarging the surface area, which provides more points of contact/anchorage between the fiber and the matrix, or by enhancing the physicochemical interaction between the components (Burakowski, 2001;Nohara et al, 2005;Zielke, et al, 1996;Pittman Jr. et al, 1997).…”

“…All these methods contribute to improve the stress transfer from the relatively weak and compliant matrix to the strong and stiff reinforcing fibers (Burakowski, 2001;Nohara et al, 2005;Zielke, et al, 1996;Pittman Jr. et al, 1997;Yue et al, 1999;Lee, Kang, 1997).…”