Effect Of γ Ray Irradiation On The Kidney Sectional Carbon Fiber And Composite Interface

A study on the surface characteristics of kidney sectional carbon fiber (CF), interfacial properties of kidney CF/epoxy composites and distribution of kidney CF in composites was carried out. Besides, the highly efficient, energy-saving and convenientγ-ray irradiation technique was employed to activate kidney section CF surface, improve the interface adhesion of composites and optimize the structure of CF.The surface physicochemical properties of kidney and circular section CF were investigated by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and surface energy analysis. The results indicated that the kidney section CF outperformed the circular section CF in surface energy and its non-polar component. The two kinds of fibers had the same element composition, but the different cross-section shape. The Brunauer-Emmett-Teller (BET) adsorption tests showed that the kidney sectional CF had a larger specific surface area than the circular CF. Thus the former had the slightly better wettability with epoxy and phenolic resin. It was found that the graphitization degree of kidney CF was the same as that of circular CF by X-ray diffraction (XRD) analysis.According to the interlaminar shear strength (ILSS) and interface shear strength (IFSS) tests, the interfacial properties of composites were evaluated. The interfacial adhesion of kidney CF/epoxy was better than that of circular CF/epoxy and the IFSS of kidney CF/epoxy was 33% greater than that of circular CF/epoxy. The kidney CF/epoxy composites perform shortly better than circular CF/epoxy composites in tensile, flexural and compressive strength. The fracture topography of composites showed that the concave of kidney CF had a good adhesive interface with matrix and the adhesive joint looks like the mechanical anchor. The concave and convex of kidney CF mutually embraces with each other in composites, which results in the firm interface between fiber and matrix. Besides the concave of kidney CF can also embrace with each other in composites, which did harm to the interface adhesion of composites because of weak wetting with resin. It was shown that the kidney CF distributed more non-uniformly than the circular CF in composites via metallographic microscope.The irradiation dose of 300kGy and irradiation dose rate of 6kGy/h of kidney CF were determined by the optimizing experiments. Epoxy/acetone solution mutual irradiation, chloroepoxy mutual irradiation and acrylic acid pre-irradiation were selected as the representatives. Furthermore, the mutual irradiation of kidney CF in rare earth solution was found to be efficient. By the SEM and atomic force microscopy (AFM) characterization, it was found that the grooves of the irradiated fiber surface became wider and deeper compared with the original CF and more pieces of tiny fragments stuck to the fiber surface. Both the O/C rate and the amount of carboxyl and carbonyl groups were increased. The grafted layer was not formed on the fiber surface. The surface energy of kidney CF was increased after irradiation. Thermogravimetric analysis (TGA) was used to investigate the adsorption of kidney CF in resin. The results showed that the irradiation by the other methods improved the adsorption ability of kidney CF in epoxy resin, except irradiation in air.ILSS of CF/epoxy composites was selected as the evaluation criterion of various modification methods. It was shown that pre-irradiation treatment had the advantage of mutual irradiation for acrylic acid, mutual irradiation exceeded marginally pre-irradiation for chloroepoxy and ILSS value of epoxy mutual irradiated CF/epoxy reacheed the maximum with 20.2% improvement. Gamma ray irradiation grafting achieves the same effectiveness as plasma treatment and moreover performs better than coating and ultrasonic treatments. It was observed that the more resin stuck on the fiber surface in fracture surface of composites after irradiation treatment of CF and the"mechanical anchor"existed between matrix and irradiated fiber by SEM images. The results of electron spin resonance (ESR) showed that CF may graft with irradiation media by free radical mechanisms. The mechanisms of composite interface improvement were explored after irradiation grafting.To study the change of different structures in CF, Raman spectra was used to investigate the irradiated CF and XRD was employed to analyze CF, turbulent carbon and graphite. It was found that the interlayer space (d002) of CF decreases and the graphite degree of CF increases with the irradiation dose. The interlayer space of kidney section CF decreased with the maximum of 0.066nm after irradiation at 2000kGy. The size (La) of graphite microcrystallite was increased at low dose and decreased at high dose. For the graphite, the interlayer space (d002) was reduced and the graphite degree was improved after irradiation. However, the structure of turbulent carbon was not influenced byγ-ray irradiation.The density of kidney sectional CF was determined by the sink-float method. The density of CF was enhanced at the low dose and trend to stabilize at the high dose. The bundle and filament tests of CF and Weibull distribution function were applied to evaluate the mechanical performance. It was indicated that CF tensile strength was enhanced in the range of 0~300kGy and reduced with the increasing absorbed dose when the dose exceeded 300kGy. The Young's modulus was increased and the cracking specific elongation was decreased as the dose increases at the range of 0~2000kGy. The uniformity and reliability of kidney CF was improved by irradiation treatment. The degradation experiments showed that the degradation of surface modification was decided by the storage conditions of CF and there was not the degradation of mechanical performance of kidney CF as the time flies.