Influence of nitric acid treatment time on the mechanical and surface properties of high-strength carbon fibers

Abstract

High-strength carbon fibers were treated with nitric acid and periodically analyzed by several different methods to develop an understanding of overall property changes and how they relate to composite design. Fiber diameter, tensile strength, surface morphology, surface chemistry and surface energy were all evaluated as a function of treatment time and two distinct stages of change were identified; the first characterized by surface modification and the second by carbon material loss. Initially, the tensile strength, degree of surface oxidation and surface energy all increased. The surface oxidation consisted primarily of carbonyl and carboxylic acid types. Then in the second stage, both the tensile strength and surface oxidation reached stable levels and the fiber diameter began to rapidly decrease. The surface morphology and energy were the only properties that showed no obvious changes from one stage to the next. The surfaces were found to be smooth through all treatment times and the energy increased steadily throughout. It is believed that the variation of all of these properties is related to the fiber microstructure and how it varies through the cross-section of high-strength fibers. Specifically, high-strength carbon fibers are known to have better microstructural organization and alignment in the near-surface layer than within the interior.

Shear strength and fracture toughness of carbon fibre/epoxy interface: effect of surface treatment

“…Therefore, we conclude that the moderate acid treatment can improve shown in Figure 7. Overall, the Young's modulus decreased slightly after acid oxidation; the decline is due to acid etching that removes microvoids and the amorphous outer layer from the carbon fibre surface [15]. Some researchers mentioned also another potential mechanism of the modulus variation: a change in the orientation of crystallites in CFs [19].…”

“…On the one hand, these grooves and pits provide more bonding sites, increasing the interfacial adhesion. On the other hand, they introduce serious defects on the surface of carbon fibres, decreasing their tensile strength [15]. Post microbond test, samples were examined with FE-SEM to verify the location and mode of the failure.…”

“…Han et al [3] pointed out that the tensile strength of CF decreased extensively after two hours of surface treatment. Langston et al [15] stated that the best functionalization efficiency and highest oxygen concentration was obtained with the surface treatment of 80 min. Wang et al [16] found that 15 min was preferred to pursue best electrical conductivity of CFs.…”

The usability of recycled carbon fibres in short fibre thermoplastics: interfacial properties

“…Highly oriented graphitic planes are formed on the outer surface of carbon fibre by heat treatment during manufacture [53]. This highly aligned outer layer is typically 1.5 lm thick [53] and relatively weak [54,55], and removal of this layer can increase the tensile strength [56] and improve the interface strength in carbon fibre/epoxy systems [57]. It has also been suggested that the removal of the outer layer removes surface flaws, which are known to be a significant factor for tensile strength properties [56].…”

Quasistatic and dynamic mechanical characterization of a woven carbon fiber–zinc oxide nanowires–epoxy composite

“…The chemical treatment approach utilizes acidic reagents (e.g., chlorosulfonic acid, nitric acid, etc.) to attach functional groups such as carboxyl, ether or hydroxyl to the fiber to improve the load transfer and adhesion between the fiber and the matrix . It was demonstrated that the chemical treatment improves the wettability and the surface roughness of the fibers which, in return, increases the tensile strength and the interlaminar shear strength of the composite .…”