Abstract
This research examines the possibilities of regulating the structure of cellulose precursor fibers spun from solutions in N-methylmorpholine-N-oxide when replacing aqueous coagulation baths with thermodynamically softer alcohol baths at different temperatures. The fibers were spun by the dry jet–wet method in isobutanol coagulation baths with a temperature of 25 °C and 70 °C. The study of the phase state of the solvent–coagulant system using viscometry and point cloud methods revealed the temperature-concentration regions of the single-phase and two-phase states of the system. Using elemental analysis, DSC (differential scanning calorimetry) and XRD (X-ray diffraction) methods, it was shown that just spun fibers, due to the presence of a residual amount of solvent and coagulant in them, regardless of the temperature of the precipitator, have an amorphous structure. Additional washing with water completely washed away the solvent and coagulant as well, however, the structure of cellulose changes slightly, turning into a defective amorphous-crystalline one. A relationship was found between the phase composition, structure, and properties of just spun fibers and precursors washed with water. Thus, the loss of structural ordering of both just spun and washed cellulose fibers leads to a decrease in strength characteristics and an increase in deformation. The thermal behavior of the fibers is determined by their phase composition. Fibers just spun into hot alcohol containing a coagulant and traces of solvent acquire thermal stability up to 330 °C. During the pyrolysis of the obtained precursors up to 1000 °C, the value of the carbon yield doubles. The amorphized structure of the obtained fibers allows us to consider it as a model when analyzing the transformation of the structure of precursors during thermolysis.
Highlights
The estimated total annual production capacity of all carbon fibers (CF) in the world in 2014 is104,600 t
Changes in the composition and temperature of the precipitation bath allow to vary the structure of the resulting fibers
Precipitation into alcohol without additional washing with water of the samples does not exclude the residual amount of solvent and precipitant in the fibers, which leads to an amorphous structure of the samples
Summary
The estimated total annual production capacity of all carbon fibers (CF) in the world in 2014 is104,600 t (in 2017 136,500 t). The estimated total annual production capacity of all carbon fibers (CF) in the world in 2014 is. Growing demand for CF stimulated an active growth in their production and an annual increase in capacity by 10% until 2020 [1]. The main advantages of carbon fibers are high flexibility, tensile strength and stiffness, adsorption, thermal stability, low coefficient of thermal expansion (CTE), etc. Due to these properties, CF and composites based on them are widely used in various industrial sectors. CF are not interchangeable in the construction of reactors, as insulation, where the key properties are resistant to high temperatures and pressure and radioactive radiation [2,3,4]
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