Graphene, a carbon allotrope, became a significant area of research with its superior electrical, mechanical, optical properties, etc. There are several methods to obtain graphene oxide from graphite, one of which is the Hummers method. In this study, several modifications and pre-treatments preceding the Hummers method have been employed. Three different graphene oxide fibers have been produced by three different procedures, i.e. fibers obtained by Hummers method with pre-oxidation step, modified Hummers method and modified Hummers method with pre-oxidation step. It has been observed that pre-oxidation has a significant effect on graphene oxide fiber properties produced by wet spinning process (coagulation). Modified Hummers method without pre-oxidation leads to the highest breaking strength and breaking elongation. Reduced fiber linear density, breaking strength and breaking elongation together with increased crimp were observed in graphene fiber due to the addition of pre-oxidation step.
Continuous graphene oxide fiber focused for the last seven years have a very large application area such as electronic textiles, photovoltaics, batteries, fuel cells, sensors, filters. This study reports the effect of processing parameters such as time, temperature of the exfoliation together with dispersion preparation methods of graphene oxide on the properties of continuous graphene oxide fibers produced by coagulation bath. Relationship between changing parameters and structural properties of graphene oxide fiber, fiber morphology, roughness, crystalline structure have been discussed. It has been shown that crystalline structures and responses to changing parameters are different when it is an exfoliated state, dispersion state, and fiber state. For example, crystalline sizes and number of layers of GO fiber were higher than those of GO dispersion, while the crystallinity degrees and d-spaces at the GO fiber were always less than that of GO dispersion. Higher exfoliation time leads to an increase of Tex count of fiber, while longer ultrasonic time resulted in lower value compared to both shorter ultrasound time and mechanical homogenization. Shorter ultrasonic treatment and shorter exfoliation time leads to higher electrical conductivity compared to mechanical homogenization. Shorter ultrasonic treatment results in vaguely tendency of an increase of breaking strength.
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