SURFACE TREATMENT OF CARBON FIBERS BY ULTRAVIOLET LIGHT+OZONE: ITS EFFECT ON FIBER SURFACE AREA AND TOPOGRAPHY

摘要

Carbon fibers require surface treatment in order to establish suitable adhesion to polymeric matrices. In general, the surface treatments are oxidative processes and can be carried out in either liquid phase or gas phase. Three major methods are currently practiced by carbon fiber manufactures: 1. anodic oxidation, a wet process where solution concentration and amperage must be maintained; 2. exposure to ozone gas at elevated temperature; and 3. treatment in caustic solutions such as nitric acid. Surface treatments result in improved fiber-matrix shear properties through a two part mechanism. First, a weak, defect-laden outer layer is removed from the surface of the fiber which generates a stronger surface to sustain shear loading. The second contribution of surface treatments is the deposition of chemical functionalities, most notably oxygen containing moieties that improve wetting and bonding between the fiber and matrix [1]. This work describes the use of ultraviolet (UV) light in the presence of ozone (UVO) as a method for treating graphitic surfaces, a technique which has been successfully applied for the surface treatment of many polymer materials (2-5). UVO treatment involves several complimentary processes to potentially oxidize a surface. First, photons with wavelengths of less than 300 nm have sufficient energy to break many chemical bonds forming radicals on the surface which are then available to react with oxygen (see Table 1). Second, UV photons with wavelengths of 254 nm have sufficient energy to disassociate ozone into atomic oxygen, a highly reactive species, which can oxidize the surface. Additionally, UV photons with wavelengths of 185 nm can disassociate oxygen to form atomic oxygen which is a very reactive species capable of oxidizing many materials.