Abstract
This study focuses on the preparation of carbon fiber precursors from solutions of cellulose in N-methylmorpholine-N-oxide with the addition of bis(trimethylsilyl)acetylene, studying their structural features and evaluating thermal behavior. The introduction of a silicon-containing additive into cellulose leads to an increase in the carbon yield during carbonization of composite precursors. The type of the observed peaks on the differential scanning calorimetry (DSC) curves cardinally changes from endo peaks intrinsic for cellulose fibers to the combination of endo and exo peaks for composite fibers. For the first time, coefficient of thermal expansion (CTE) values were obtained for Lyocell fibers and composite fibers with bis(trimethylsilyl)acetylene (BTMSA). The study of the dependence of linear dimensions of the heat treatment fibers on temperature made it possible to determine the relation between thermal expansion coefficients of carbonized fibers and thermogravimetric curves, as well as to reveal the relationship between fiber shrinkage and BTMSA bis(trimethylsilyl)acetylene content. Carbon fibers from composite precursors are obtained at a processing temperature of 1200 °C. A study of the structure of carbon fibers by X-ray diffraction, Raman spectroscopy, and transmission electron microscopy made it possible to determine the amorphous structure of the fibers obtained.
Highlights
Carbon fibers (CFs), as an important class of heat-resistant fibers [1], have been intensively studied due to their excellent properties, such as high strength, heat resistance, low density, and chemical stability [2,3,4]
The relevance of the problem lies in obtaining CFs with the required mechanical characteristics, and with a necessary coefficient of thermal expansion (CTE), which is known to be closely related to the structure of such fibers [9]
We prepared composite precursors based on cellulose and BTMSA, studied their structure and properties, and received carbon fibers from them
Summary
Carbon fibers (CFs), as an important class of heat-resistant fibers [1], have been intensively studied due to their excellent properties, such as high strength, heat resistance, low density, and chemical stability [2,3,4]. Using the direct solvent NMMO with water content of about 8% makes it possible to obtain Lyocell fibers from concentrated cellulose solutions (up to 18%) [18]. An accumulated experience of processing cellulosic precursors into carbon fibers has shown that it is impossible to obtain high-quality CFs and increase carbon yield without the flame retardants and pyrolysis catalysts, which are able to influence the course of the thermal reaction used [24,25,26,27]. The task of this work was to obtain composite precursors based on cellulose and bis(trimethylsilyl)acetylene through solid-phase solutions in NMMO, and to study their structure and thermal behavior, as well as to determine the chemical composition and structure of the resulting carbon fibers
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