Abstract
The aim of this work is to review a possible correlation of composition, thermal processing, and recent alternative stabilization technologies to the mechanical properties. The chemical microstructure of polyacrylonitrile (PAN) is discussed in detail to understand the influence in thermomechanical properties during stabilization by observing transformation from thermoplastic to ladder polymer. In addition, relevant literature data are used to understand the comonomer composition effect on mechanical properties. Technologies of direct fiber heating by irradiation have been recently involved and hold promise to enhance performance, reduce processing time and energy consumption. Carbon fiber manufacturing can provide benefits by using higher comonomer ratios, similar to textile grade or melt-spun PAN, in order to cut costs derived from an acrylonitrile precursor, without suffering in regard to mechanical properties. Energy intensive processes of stabilization and carbonization remain a challenging field of research in order to reduce both environmental impact and cost of the wide commercialization of carbon fibers (CFs) to enable their broad application.
Highlights
It is not surprising that the carbon fibers (CFs) market has an annual growth of about 10%, mainly in the form of composites, and this trend is expected to continue in the forthcoming years [6,7]
The manufactured CFs had a higher density than 1.75 g/cm3, smaller interlayer spacing, lower porosity, and better preferred orientation, which led to a considerable increase in tensile strength and Young’s modulus [75,98]
Structure on the stabilization is reviewed, and attention is mainly paid to the effect
Summary
Carbon fibers (CFs) are widely used as reinforcement in advanced composite materials, in aircraft construction, rocket engineering, automotive, wastewater treatment, structural supercapacitor units, smart textiles, and sports. Thermal oxidative treatment (or stabilization) is frequently regarded as the most crucial step in CF production in order to obtain high strength CFs [15,19]. It corresponds to 75%–80% of the total manufacturing duration of CFs [13]. The attack of oxygen radicals on already cyclized structures leads to high thermal stability, infusibility of heat treated PAN fibers, and carbon yield is maximized [23]. A promoting effect is evidenced on intramolecular crosslinking reactions during carbonization related to the extent of oxidation, and has an impact on forming high strength CFs. Aromatization or stabilization index of PAN fibers is often monitored through FTIR, DSC, and XRD. Concerning the relative importance of each treatment, oxidative stabilization is considered as the most significant step as proved by a multitude of review papers either on CF manufacturing [2,4,5,42,43], or stabilization [1,10,35,44]
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