High-performance polyacrylonitrile-based pre-oxidized fibers fabricated through strategy with chemical pretreatment, layer-by-layer assembly, and stabilization techniques

Novel high-performance polyacrylonitrile (PAN)-based pre-oxidized fibers (i.e. OPFHA-MEA-L) with improved thermal stability and flame-retardant and mechanical properties were designed and made from the pristine PAN fibers through chemical pretreatment with hydroxylamine hydrochloride (HA) and monoethanolamine (MEA) aqueous solutions, then coated with chitosan (CS) and sodium tripolyphosphate (STPP) via layer-by-layer (LbL) assembly, and finally followed by stabilization in the air. The morphological structure, flammability, and thermal and mechanical properties of fabricated OPFs were systemically investigated. The results indicated that the PAN fibers after chemical pretreatment with HA and MEA had a large amount of hydrophilic groups. It would facilitate the increase of pre-oxidation degree for PAN fibers during stabilization and the deposition of positively and negatively charged CS-STPP flame-retardant coating. The fabricated OPFs (i.e. OPFHA-MEA-10) demonstrated superior comprehensive properties with charred residue of about 68.2%, breaking strength of about 295.1 N, breaking elongation of 12.6%, and limiting oxygen index value of about 41.5%, respectively, contributing to the improved thermal stability and flame-retardant and mechanical properties. It is envisioned that this innovative type of high-performance OPFs could be utilized for potential applications as flame retardant and in high temperature filtration.

Impact of Alternative Stabilization Strategies for the Production of PAN-Based Carbon Fibers with High Performance

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.

Structure–property relationship of carbon fibers derived from polyimide/polyacrylonitrile blends

A series of polyimide/polyacrylonitrile (PI/PAN) blend fibers with different PAN weight ratios were prepared through a two-step wet-spinning method and stabilization process and then were carbonized at 1500°C under high-purity nitrogen atmosphere, yielding in PI/PAN-derived carbon fibers. The effects of PAN content on the structures of the PI/PAN blend fibers were systematically investigated. The elemental composition, aggregation structure, carbon yields, and electrical properties of the PI/PAN-derived carbon fibers were also analyzed. The imidization degree and molecular orientation of the PI/PAN blend fibers increased first and then decreased with increasing PAN content, which directly affect the aggregation structures and properties of the corresponding PI/PAN-derived carbon fibers. As a consequence, the carbon fibers derived from PI/PAN-35% exhibited perfect graphite structure with a planar spacing d002 of 0.349 nm, high carbon content of 97.14%, and low electrical resistivity of 1.89 × 10−5 Ω·m, attributing to the high degree of orientation along the fiber axis and low value of φa/ φc in the PI/PAN blend fibers.