Abstract
In this paper, the oxy-fluorination process and the influence of different concentrations of fluorine and oxygen in the gas phase on the physicochemical properties of polyacrylonitrile(PAN)-based carbon fibers are described. The properties of the treated carbon structures are determined by zeta potential and tensiometry measurements. In addition, changes in surface composition and morphology are investigated by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Adhesion properties are characterized by the single fiber pull-out (SFPO) test. Furthermore, changes in intrinsic properties are described by means of tensile and density measurements. After a primary desizing effect by oxy-fluorination, an increased number of oxygen-containing surface functional groups could be detected, which led to more debonding work in SFPOs with an epoxy-based matrix. It was also shown that the polar surface energy grows with rising fluorine concentration in the reaction gas mixture. In addition, a minor increase of ~10% in the maximum strength of PAN-based carbon fibers is detected by single fiber tensile measurements after oxy-fluorination with a fluorine content of 5% in the reaction mixture.
Highlights
IntroductionNone of the great advantages of carbon fibers as reinforcing material for different composite types, including their high specific stiffness or strength, can come into effect without surface functionalization
None of the great advantages of carbon fibers as reinforcing material for different composite types, including their high specific stiffness or strength, can come into effect without surface functionalization.the structural application potential of fiber-reinforced polymers is limited by component properties prior to their processing and service in the aerospace or automotive industries or external loading, such as impact or tensile stress [1]
The research described in this paper reveals the effects of different concentrations of fluorine and oxygen in the gas phase during the modification process of carbon fibers
Summary
None of the great advantages of carbon fibers as reinforcing material for different composite types, including their high specific stiffness or strength, can come into effect without surface functionalization. The structural application potential of fiber-reinforced polymers is limited by component properties prior to their processing and service in the aerospace or automotive industries or external loading, such as impact or tensile stress [1]. Various methods have been developed and implemented in order to achieve good adhesion properties between this highly inert material and sizings or matrix materials [2,3]. Wet-chemical and electrochemical methods of oxidizing the fiber surface prior to sizing are the state of the art in carbon fiber production. Several atmospheric plasma technologies based on various process gases are nowadays commonly used to produce functional groups on a carbon fiber surface. The gases range from non-reactive gases, such as nitrogen, argon, carbon dioxide, Materials 2019, 12, 565; doi:10.3390/ma12040565 www.mdpi.com/journal/materials
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