Carbon fibre oxidation, textural and surface changes

Abstract

This work reports on the variations in specific surface, porosity, surface functionality and dimension of commercial carbon fibre subjected to oxidative treatment with nitric acid. Scanning electron microscopy (SEM) observation did not reveal any topographic changes on the fibres, although crypton adsorption evidences increases in specific surface and microporosity.Oxidative treatment has an effect on fibre length, although it also slightly reduces the fibre diameter and the fibre strength, as measured in terms of the elastic modulus.Functional analysis by means of volumetric measurements and X-ray photoelectron spectroscopy (XPS) reveals an increase in the overall fibre surface acidity through carboxy group increase. Prolonged treatment gradually removes hydroxy groups from the fibre surface.

The Effect of Chemical and Thermal Treatment for Desizing on the Properties and Chemical Functional Groups of Carbon Fiber

“…In addition, Ibarra et al reported that micropores increased on a specific surface of CF in line with the nitric acid treatment time after treatment in a tetrahydrofuran (THF) solution for 24 h using the Soxhlet method. It was confirmed that the mechanical strength decreased [29]. On the other hand, in the case of thermal desizing, Ahmed et al, described that, when heat treatment was carried out in an oven at 380 • C for 1 h, the epoxy on the CF surface was removed and oxidized to CO 2 and water vapor [30], and Liu et al showed that CF/PEEK composites fabricated by resizing polyetherimide (PEI) to CF subjected to desizing in an oven for 30 min increased the ILSS value by 16.1% compared to composites without sizing treatment [31].…”

“…In the case of desizing with acetone, a change in the CF surface in terms of conformity with time and temperature could not be observed. On the other hand, when using thermal desizing in a nitrogen atmosphere, no surface defects appeared on the CF up to 500 • C, but it was confirmed that the surface of the fiber was harmed at 1000 • C. Ibarra et al confirmed that the desizing treatment using THF was smooth without significant changes on the CF surface and that there were almost no defects [29], and Kim et al found that CF reacts with oxygen in the atmosphere at above 500 • C when it is heat treated in an oxygen atmosphere. It was also reported that surface defects were generated and then partly disappeared, along with a decrease in the diameter of CF from above 600 • C [34].…”

“…Desizing treatment is a method that can improve wettability with fluids by exposing the surface of the CF and forming functional groups containing oxygen while removing the sizing agent. Moreover, it is carried out before the surface treatment, which generally involves chemical treatment methods [21][22][23][24][25][26][27][28][29] using organic solvents (e.g., acetone and ethanol) and thermal treatment [29][30][31][32] methods. In the case of using acetone as a chemical treatment method, the treatment temperature varies from room temperature to 70 • C, and the treatment time varies from 10 min to 24 h, depending on the researcher, so there is no consistency in the optimal treatment conditions [22][23][24][25][26].…”

Investigating the Effects of Nitric Acid Treatments on the Properties of Recycled Carbon Fiber

“…Changes in tensile strength between 25 °C and 100 °C were similar to changes at 25 °C within the margin of error. Ibarra et al showed that when surfaces were treated with nitric acid at 80 °C, tensile strength had no significant difference from untreated CF up to 7 h but that it decreased to 80% compared to untreated CF at 12 h [ 19 ]. Rong et al reported that when heat treatment was performed in an oxygen atmosphere, pitting occurred on the surface of the fiber, and the surface area increased without a change in tensile strength at 420 °C for up to 1 h, but after 2 h, the tensile strength decreased, the pitting agglomerated, and the surface area gradually decreased [ 29 ].…”

“…In general, surface treatment includes wetting methods (liquid oxidation) such as sulfuric acid and nitric acid [ 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 ], dry methods (dry gaseous oxidation) [ 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 ] such as high-temperature treatment in an atmosphere of oxidizing gas or inert gas, electric oxidation methods [ 3 , 30 , 31 , 32 ], the plasma method [ 33 , 34 , 35 , 36 , 37 , 38 , 39 ] of surface treatment using ionized gas, and exposure to strong energy such as ozone and ultraviolet rays (energetic ions oxidation) [ 40 , 41 , 42 ].…”